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UBC Theses and Dissertations

The extraction and analysis of dissolved trace metals from seawater using on-line flow injection inductively… Nicolidakis, Helen 1995

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THE EXTRACTION AND ANALYSIS OF DISSOLVEDTRACE METALS FROM SEAWATER USING ON-LINEFLOW INJECTION INDUCTIVELY COUPLEDMASS SPECTROMETRYbyHELEN NICOLIDAKISB.Sc. (Hons), The University of British Columbia, 1989.A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THEREQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(DEPARTMENT OF CHEMISTRY)We accept this thesis as conformingto t e required standardTHE UNIVERSITY OF BRITISH COLUMBIAMAY 1995© Helen Nicolidakis, 1995In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of STR’/The University of British ColumbiaVancouver, CanadaDateDE-6 (2/88)IIAbstractA method utilizing flow injection (Fl) for on-line preconcentration withinductively coupled plasma mass spectrometry (ICP-MS) detection has beendeveloped for analyzing dissolved zinc, cadmium, nickel, copper, lead,manganese, gallium and niobium in seawater. This method was used toinvestigate the distributions of these trace metals in the western, central andsub-Arctic North Pacific Ocean.Using on-line Fl methods to replace conventionalpreconcentration/separation techniques results in significant decreases insample and reagent volumes and sample work up and analysis time. Thismethod used a column filled with 8-hydroxyquinoline on silica resin topreconcentrate up to 18 millilitres of seawater for a minimum sample throughputof six per hour. Concentrations of these elements ranged between 0.01 and 12nmol/kg, with analytical precision being better than 12 % for all elements exceptCu, and detection limits in the low picomolar range (1 - 90 pmol/kg). Theaccuracy of the technique was verified by analysis of standard referencematerial from the National Research Council of Canada for Zn, Cd, Ni, Cu, Pband Mn.This Fl method was also incorporated into the design of a prototypesampler with multi-sampling capabilities which was developed to preconcentratetrace metals from seawater remotely. The sampler was submerged in-house fora period of one week, and operated successfully. Before collectingcontaminant-free seawater samples, a second generation sampler is required.The results obtained for Zn, Cd, Ni, Cu, Pb and Mn using the on-lineFl-ICP-MS method developed here showed the expected distributions, agreeingwell with profiles previously determined using the same samples and withprofiles measured by other labs in the same region of the North Pacific.IIIThe first set of dissolved Ga data from the western North Pacific arepresented here. When coupled with published data from the sub-Arctic NorthPacific Current and from the central gyre, the new information yields a betterunderstanding of the controls of dissolved Ga behaviour in the North Pacific. Atall stations, Ga shows high surface concentrations, a minimum at — 1000 m andincreases at greater depth. Sub-surface maxima at — 500 m are observed in thecentral gyre and in the sub-arctic North Pacific Current, but not in the westernNorth Pacific. Dissolved Ga in surface waters is highest in the central gyre (14to 19 pmol/kg), an area with low dust input from the Asian continent and lowproductivity. In the western Pacific, where dust input and productivity are bothhigh, surface water Ga values are lower (9 to 12 pmol/kg). This indicates thatthe high levels of Ga in the central gyre and the presence of the sub-surfacemaximum in this region are not due to advection from the western North Pacific.The lowest surface concentrations (4 to 10 pmol/kg) are found in the sub-ArcticNorth Pacific Current, an area with low dust input and high productivity.The first full depth profiles of niobium in the ocean are reported in thisdissertation. The Nb distributions in the North Pacific show low surfaceconcentrations and sub-surface and mid-depth maxima coincidental with theboundaries of the°2 minimum. Nb concentrations range between 10 and 80pmol/kg in surface waters, 40 and 100 pmol/kg in the upper boundary of the°2minimum zone, 40 and 200 pmol/kg in the lower boundary of the°2 minimumzone and 10 and 100 pmol/kg in deep waters. The concentrations decrease withdistance from the Asian continent, and increase in the North Equatorial Current,suggesting horizontal advection of high Nb waters from both the western andeastern Pacific boundaries. The distribution of Nb may also be affected by Mnand nutrient cycling and pH changes in the°2 minimum zone, though the extentof these cannot be ascertained at present.ivTable of ContentsAbstract.iiTable of Contents ivList of Tables ixList of Figures xGlossary xivAcknowledgments XviiCHAPTER 1. INTRODUCTION I1.1 Background I1.2 Distributions of Trace Metals of Interest in Seawater 31.2.1 General Overview 31.2.2 Zinc, Cadmium and Nickel Zinc Cadmium Nickel 101.2.3 Copper 101.2.4 Lead 111.2.5 Manganese 111.2.6 Gallium 121.2.7 Niobium 131.3 FlowinjectionAnalysis 131.3.1 Introduction and History 151.3.2 Channel Geometry in FIA 161.3.3 On-Line Matrix Separation and Preconcentration 181.3.4 FIA and Seawater 19V1.4 Inductively Coupled Plasma Mass Spectrometry 201.4.1 History of the ICP-MS 201.4.2 Instrumentation Overview 211.4.3 Advantages and Limitations of the ICP-MS 231.4.4 Sample Introduction Methods Fl-ICP-MS On-Line Preconcentrationand Matrix Separation with Fl-ICP-MS 261.5 Ship board and In Situ analysis 261.5.1 Ship board Determinations 261.5.2 In Situ Measurements and Sampling 27CHAPTER 2. DEVELOPING AN IN SITU SAMPLER 302.1 Designing the Prototype sampler 302.2 Components of the Prototype sampler 312.2.1 Computer Board 332.2.2 Interface Circuitry 352.2.3 Pump Head and Motor 362.2.3.1 Pump Shaft 372.2.4 Flow Meter Design 382.2.5 Valves and Column Design 392.2.6 Battery Pack 412.2.7 Casing 422.2.8 Electronics Hardware 432.2.9 Filter 442.3 Operation of the Prototype Sampler 442.2.1 General operation 44vi2.3.2 Pump Control .442.3.3 Valve Control 452.3.4 Flow Meter Control 452.4 Flow Meter Calibration 462.5 Prototype Sampler Testing 492.5.1 Preliminary Testing at Sea 492.5.2 Submersion Testing 502.5.3 Contamination Control 512.6 Conclusions 52CHAPTER 3. EXPERIMENTAL AND TECHNIQUE DEVELOPMENT 533.1 Materials and Reagents 533.1.1 Reagents 533.1.2 Bottles 543.1.3 Seawater Standards 543.1.4 Resins 543.2 Sample Collection 553.2.1 Seawater Samples 553.3 On-Line Fl-ICP-MS Instrumentation 563.3.1 Apparatus for Flow Injection Manifold 563.3.1.1 Valves 563.3.1.2 Peristaltic Pump 573.3.1.3 Design of the Extraction Column and Fl Fittings 573.3.2 On-Line FI-ICP-MS Manifold used for Preconcentration 583.3.3 Automation of the Fl manifold and Data Collection 603.3.3.1 Pump Calibration 603.3.3.2 Automation and Manifold Control 61vi’ Data Collection .613.3.4 ICP-MS 613.3.4.1 Operating Conditions 623.3.4.2 PlasmaQuad Control and Software 643.4 Method Development 663.4.1 Chelating Resins Studied 663.4.1.1 Chelex-100 673.4.1.2 8-HQ on TSK 673.4.1.3 8-HQ onXE-305 683.4.1.4 8-HQ on silica 683.4.1.5 Comparing 8-HQ on XE-305 and Silica Backbones 683.4.2 Silica based 8-HQ pH Studies and Recovery Tests 703.4.2.1 On-Line Studies 703.4.3 Flow Rate 733.4.4 Interelement Interferences 763.4.5 System Blanks and Detection Limits 773.4.6 Precision and Accuracy 783.5 Sample Preparation 81CHAPTER 4. OCEANOGRAPHIC RESULTS AND DISCUSSION 834.1 Characteristics of the Ocean Stations Sampled 834.2 Dissolved Zn, Cd, Ni, Pb, Cu, Mn, Co and Cr in the North Pacific Ocean . . .854.2.1 Nutrient-type Elements (Zn, Cd and Ni) 854.2.1.1 Dissolved Zn in the North Pacific 854.2.1.2 Dissolved Cd in the North Pacific 904.2.1.3 Dissolved Ni in the North Pacific 944.2.2 Nutrient Type with Scavenging Element (Cu) 98VIII4.2.3 Scavenged Type Element with an External Source (Pb) 1024.2.4 Oxidative Scavenging Type Elements (Mn) 1064.3 Dissolved Ga in the North Pacific Ocean 1124.3.1 Ga Distribution in Surface and Intermediate Waters 1154.3.2 Ga Distribution in Intermediate Waters 1174.3.3 Dissolved Ga Distribution in Deep Waters 1214.3.4 Vertical-Advection Diffusion Model 1224.3.4.1 Application of this model to Ga 1234.3.5 Comparison with Al 1284.3.6 Conclusions 1314.4 Dissolved Nb in Seawater 1334.4.1 Depth Profiles 1334.4.1.1 Dissolved Nb in the Surface Waters 1364.4.1.2 Dissolved Nb in the Intermediate and Deep Waters 1374.4.2 Comparison with Dissolved and Mn 1384.4.3 North Pacific Intermediate Waters 1434.4.4 Comparison with V 1454.4.5 Comparisons with Zr and Mo 1464.4.6 Conclusions 148CHAPTER 5. CONCLUSIONS 149CHAPTER 6. FUTURE WORKS 152BIBLIOGRAPHY 153APPENDIX A THE INFILTREX II SAMPLER 166APPENDIX B SOFTWARE ROUTINES 170APPENDIX C CIRCUIT SCHEMATICS 173APPENDIX D SIM MODE SCAN OF ELEMENTS 176APPENDIX E OCEANOGRAPHICAL DATA 178ixLIST OF TABLESTable 2.1 Physical components of the prototype sampler 33Table 2.2 The average flow meter response at different flow ratesat the 95% confidence limit 48Table 3.1 ICP-MS Operation Conditions 63Table 3.2 Recovery of the 6 metals from 6 mIs of a 0.5 ppb spikedseawater sample adjusted to pH 8 69Table 3.3 Concentration of metals in the mixed standard solutionused for standard additions 72Table 3.4 Results of the on-line pH studies 73Table 3.5 Time needed for each preconcentration cycle using 6 mIsof seawater and 2 mIs of DDI before and after sample loadingusing the on-line system 74Table 3.6 Potential interferents of the 12 isotopes. From reference [111] .77Table 3.7 The average of five system blanks and detection limits (3a)for 6 mIs of seawater in nmol/kg 78Table 3.8 The determination of dissolved Mn, Ni, Cu, Zn, Cd, Pb, Ga and Nbin NASS-3 seawater reference material 80Table 4.1 Results obtained from the vertical-advection diffusion model fordissolved Ga in the deep waters of the North Pacific 126Table 4.2 Enrichment factors of Ga with respect to Al [20, 112] fromstations 10, 15 and 16 130xLIST OF FIGURESFigure 1.1 The three major distribution types:(A) Conservative. (B) Nutrient Type. (C) Scavenged 5Figure 1.2 Types of FIA manifolds:A. Single line. B. Two line with single confluence point.C. Solvent extraction. D. As (B.) with a packed reactor 15Figure 1.3 Schematics of the most commonly used microreactorgeometries found in FIA applications 17Figure 1.4 A schematic of the VG PlasmaQuad ICP-MS 22Figure 2.1 A schematic of the prototype sampler (a) Front view.(b) Rear view 32Figure 2.2 A representation of the Ziatech computer board andconnections to the sampler component controllers onthe electronic circuit board 36Figure 2.3 Cross section of top endplate to show a schematic ofpump head to pump motor connection 37Figure 2.4 Interior of the flow meter hardware 39Figure 2.5 A schematic of the flow manifold used to preconcentratemetals from seawater using the new sampler 41Figure 2.6 Schematic of the battery pack:(A) view from the side(B) view from the top and bottom of battery pack 42Figure 2.7 Plots of the 50 data point sets of the flow meter responseover a range of flow rates between 0.8 to 8.0 mI/mm 47Figure 2.8 Flow meter response vs. Flow rate 49xiFigure 3.1Figure 3.2Figure 3.3Figure 3.4Figure 3.5Figure 4.1Figure 4.2Figure 4.3Figure 4.4Figure 4.5Figure 4.6Figure 4.7Figure 4.8Figure 4.9Figure 4.10Figure 4.11Figure 4.12Figure 4.13Figure 4.14Figure 4.15Figure 4.16Figure 4.17Figure 4.18Figure 4.19On-line Fl-ICP-MS preconcentration manifold used for:(A) Loading (B) Elution 59A two minute SIM mode scan of 114Cd 65Plots of pH vs. % response for 8 elements studied on-line 71Metal response vs. flow rate for the 8 elements 75Dissolved Ga at station P26. A. Data from reference [53].B. Results from this work 81North Pacific study area 84Dissolved Zn in the western North Pacific 87Dissolved Zn in the central North Pacific 88Dissolved Zn in the eastern North Pacific in the sub-Arctic gyre. . .89Dissolved Zn vs. the nutrient silicate 89Dissolved Cd in the western North Pacific 91Dissolved Cd in the central North Pacific 92Dissolved Cd in the eastern North Pacific in the sub-Arctic gyre. .93Dissolved Cd vs. the nutrient phosphate 94Dissolved Ni in the western North Pacific 95Dissolved Ni in the central North Pacific 96Dissolved Ni in the eastern North Pacific in the sub-Arctic gyre. . .97Ni versus phosphate (A, C) and silicate (B, D).A and B: At all depths. C: Upper 800 m. D: Below 800 m 98Dissolved Cu in the western North Pacific 99Dissolved Cu in the central North Pacific 100Dissolved Cu in the eastern North Pacific in the sub-Arctic gyre.101Dissolved Pb in the western North Pacific 103Dissolved Pb in the central North Pacific 104Dissolved Pb in the eastern North Pacific in the sub-Arctic gyre.105xl’Figure 4.20 Dissolved Mn in the western North Pacific 107Figure 4.21 Dissolved Mn in the central North Pacific 108Figure 4.22 Dissolved Mn in the eastern North Pacific in the sub-Arctic gyre.109Figure 4.23 Dissolved Mn and °2 versus depth atstations 1,5, 10,15, l6andP26 110Figure 4.24 Dissolved Ga in the western North Pacific 113Figure 4.25 Dissolved Ga in the central North Pacific 114Figure 4.26 Dissolved Ga in the sub-Arctic eastern North Pacific 115Figure 4.27 Global fluxes of mineral aerosol to the oceans in mg m2 yr1 117Figure 4.28 Contours generated by combining data from this studywith those from previous work [53] 120Figure 4.29 Element versus salinity plots in deep waters showingnet release, conservative mixing and removal byparticle scavenging distributions 122Figure 4.30 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 700 m at station 10 124Figure 4.31 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 700 m at station 16 124Figure 4.32 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 750 m at station P 26 125Figure 4.33 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 600 m at station 15 125Figure 4.34 Potential temperature- salinity relationship below l000mat station I 126Figure 4.35 Depth profiles of dissolved Al at stations 15 and 16 [112] 128Figure 4.36 Depth profiles of dissolved Ga/Al ratios at stations 15 and 16.Al data from reference [112] 130XIIIFigure 4.37 Dissolved Nb profiles from the Western North Pacific 134Figure 4.38 Dissolved Nb in the central North Pacific 135Figure 4.39 Dissolved Nb in the sub-Arctic eastern North Pacific (P26) 136Figure 4.40 Dissolved Nb and°2 in the North Pacific with respect to depth .139Figure 4.41 Dissolved Nb and Mn against depth in the North Pacific 141Figure 4.42 Plots of potential temperature versus salinity to determinethe North Pacific Intermediate waters at the six stations 144Figure 4.43 Profiles of dissolved V, PC4 and in the North Pacific 146Figure 4.44 Dissolved Zr and Mo in the North Pacific Ocean [90, 126] 147xivGLOSSARY8-HQ 8-hydroxyquinoline8-HQ-si I ica 8-hydroxyquinol me bonded to silica8-HQ-TSK 8-hydroxyquinoline bonded to a vinyl polymer agglomerate8-HQ-XE-305 8-hydroxyquinoline bonded to a macroreticularstyrene-divinylbenzeneA amperesND analog to digitalAV research vessel “Aleksander Vinogradov”ASCFA air segmented continuous flow analysisCFA continuous flow analysisDACA board data acquisition and control adapter boarddc direct currentDCP-MS direct current plasma mass spectrometrydigital I/O digital input/output lines on a computer used forcommunicationsDPASV differential pulse anodic stripping voltametryDPCSV differential pulse cathodic stripping voltametryECD-GC electron capture detection gas chromatographyFl flow injectionFl-ICP-MS flow injection inductively coupled plasma mass spectrometryxvGC gas chromatographyGFAAS graphite furnace atomic absorption spectormeterHEPA high efficiency particle air (filter)HS hydrographical stationICP-AES inductively coupled plasma atomic emission spectroscopyICP-MS inductively coupled plasma mass spectrometrykHz kilo HertzmA milliamperesmM millimolarmlz mass to charge ratioNAA neutron activation analysisN.C. normally closednM nanomolarnmol/kg nanomole per kilogramNO. normally openPC personal computer (386SX)pM picomolarpmol/kg picomole per kilogramppb part per billionppm part per millionxviPQ PlasmaQuadpsi pounds per square inchRAM random access memoryREE rare earth elementROM read only memoryrpm revolutions per minuteRSD relative standard deviationSBSR single bead string reactors sample standard deviationsalinity grams of dissolved salts in one kilogram of seawaterSIM single ion monitoringV voltsxviiAcknowledgementsThis research could not have come to fruition without the input andassistance of many people. Comments, suggestions and insults from the manygroup members, both past and present have been very helpful (!), especiallythose from Dr. Larry Bowman, Dr. Oliver Lee, Dr. Brad McKelvey, Adrian Cook,Robert Mugo, Lucila Lares, Remy Chretien and Lu Chen.To Dr. Adrian Wade, I appreciate your effort and guidance during thisproject inspite of your circumstances these last four years. To Dr. Kristin Orians,your enthusiasm, drive and attitude throughout these last six years have beeninstrumental in keeping me going and helped put things into perspective. A bigthanks goes to Dr. Tom Pederson, whose comments during the writing of thisdissertation were superb. Much of the technical side of things could not havebeen started without the work of the Mech. Shop, especially Des Lovrity, BrinPowell and Brian Snapkauskas and Electronics, especially Mike Hatton. Youroptimism and solutions to problems, both great and small, were amazing.I appreciated and miss the many coffee breaks I shared with Dr. DonYapp and Christopher Alexander during those dark times. I also thank mylongtime university comrades from waaaayyyyy back: Reka Vasarhelyi,Donnaree Nygard, and Karen Long, all members of Hell’s Chemists, and DebraArmitage and her volumes of fun (and in this day and age, safe) farm facts.Without the moral support of my family, my path in life would have beenmuch different. A simple thank you cannot even begin to convey the gratitudeand respect I have for my parents, Tony and Vasso Nicolidakis. Finally, deepestthanks and gratitude to my husband, Kevin Soulsbury, whose knowledge,understanding and patience can never be over-emphasized nor surpassed.ICHAPTER 1. INTRODUCTION1.1 BackgroundA trace metal is one whose concentration in seawater is less than a fewparts per billion (ppb). Analysis of such elements is very important forunderstanding environmental systems as these metals are involved inbiogeochemical cycles, can be indicators of the effects of human impacts on thenatural environment and can act as water mass tracers (i.e. follow the movementof bodies of water) in the study of ocean circulation [I].Few analytical techniques are capable of the precise and accuratemeasurements needed for determination of these metals in the nanomolar (nM)and picomolar (pM) ranges in the complex seawater media. Atomicspectroscopy techniques are most popular since they generally have the lowestdetection limits, typically ranging between sub-part per million (ppm) to low ppblevels [2]. Inductively coupled plasma atomic emission spectroscopy (ICP-AES),which is a multi-element technique, is used moderately for trace metal analysisbut suffers from overlapping emission line interferences and from matrix effects.The most commonly used technique in the oceanographic community is graphitefurnace atomic absorption spectroscopy (GFAAS). GFAAS has much lowerdetection limits than ICP-AES for most metals, but GFAAS has a much sloweranalytical throughput as it is a single element technique and each measurementtakes several minutes due to the length of time needed for sample drying andashing. The recent analytical technique based on mass spectrometry known asinductively coupled plasma mass spectrometry (ICP-MS) is also widelybecoming accepted throughout the analytical community, though it is not yet ascommon as GFAAS. IC P-MS is a multi-element technique which provides rapidsample throughput, detection limits similar to those of GFAAS, a large working2range, and the ability to make isotope measurements [2]. Even with GFAAS orICP-MS detection, a separation/preconcentration is still needed for seawatersamples.Conventional separation/preconcentration steps for seawater samplesinvolve both a large volume of sample and a long processing time. For example,a method for gallium uses a 4 litre sample of seawater which is processed over a24 hour period in a class 100 clean room [3]. Methods which minimize either orboth sample volumes and processing time are gaining popularity. Of these, flowinjection (Fl) methods are finding favour for seawater processing. Samplehandling, processing time and sample volumes can be greatly minimized byincorporating concepts and principles of Fl to seawater analysis.With Fl methods, samples are enclosed in Teflon tubing, minimizing thecontact between the sample and the laboratory environment. Minimal contact ofthe sample with environmental contaminants during processing is vital. Potentialsources of contamination in the field and laboratory include bacteria, dust and/orrust present in the air and on clothes of laboratory personnel.Adapting existing methods to Fl involves extensive miniaturization. Thesample volume is greatly minimized such that only millilitres are needed.Because the sample is continuously moving, Fl methods can be used on-line toseparate/preconcentrate trace metals with a variety of detectors.It would be ideal for trace metal analysis if all processing and detectioncould take place in situ and yield real time multi-elemental results. Samplersexist which measure single elements in real time, but have no facility forpreconcentration. Shipboard methods exist which permit preconcentration, butthese typically have single elemental detection.This thesis will detail the development of a prototype in situ sampler formultiple sampling of a variety of elements from seawater per sampler3deployment, and the development of an on-line Fl-ICP-MS system used topreconcentrate and analyze Mn, Ni, Cu, Zn, Ga, Nb, Cd and Pb in storedseawater samples.Chapter 1 contains an introduction to trace metal behaviour in seawaterand a detailed description of the aforementioned trace metals. This chapter alsodetails the evolution of Fl methods for seawater, the use of the ICP-MS, andgives examples of present day on-board trace metal measurements and in situanalyzers. Chapter 2 presents a detailed description of the development of anew in situ sampler for extracting trace metals from seawater. Chapter 3describes the development of the on-line Fl-ICP-MS system used to analyze themetals which was designed and constructed in-house. The results obtainedfrom the analysis of stored seawater using the Fl-ICP-MS system will bediscussed in Chapter 4. Finally, conclusions resulting from the whole body ofwork, and potential future experiments will be detailed in Chapters 5 and 6.1.2 Distributions of Trace Metals of Interest in Seawater1.2.1 General OverviewThe behaviour of metals in seawater is complex with dissolved saltscomprising between 2.8 to 3.8 % by weight of seawater [1]. The oceanicdistributions and biogeochemical behaviour of dissolved metals are controlled bythe complex interactions between inputs, internal cycling and removalprocesses, coupled with physical transport and mixing within the oceans.Elements enter the oceans through a variety of sources at theboundaries. For example, rivers are a major source of Cl, Ba and Ca,, but arenot a significant source for Fe [4-5]. The sources for some elements can alsoact as sinks (i.e. removal) of other elements. The atmosphere is a source ofgases, including CC2, °2 and N2 [6,7]. The atmosphere is also a source of4trace metals (e.g. Al and Pb) as winds carry continental dust to the sea [6-9].The atmosphere also acts as a sink for Na due to salt spray being transported toland. Hydrothermal vents in the ocean floors are a source of Li, Rb, Mn and Febut a sink for Mg, F, and S [10, 11]. Sediments and pore waters, which arecontained within the sediments, are a sink for many elements. Elements canalso undergo biological and physical interactions within the ocean.Some elements are utilized by phytoplankton and grazing zooplankton[12]. The subsequent sinking and decomposition of dead phytoplankton and theproduction of fecal pellets by grazing zooplankton are sources of particles, whichare also important in controlling the distribution of some trace metals. Particlesmay also adsorb many trace metals as they sink. Eventually, the particles eitherredissolve at depth, freeing bound metals back into the ocean or are buriedwithin the sediments, thereby acting as a sink [13-15].These interactions also control the average length of time an elementresides within the oceans before it is removed. Oceanographers estimate thisresidence time by assuming that the ocean is a uniformly mixed reservoir atsteady state [16]. The residence time of an element (t) is defined as the totalamount of that element in the ocean divided by either the rate of its supply to thesea or its rate of removal , i.e.,r= (eq. 1.1)dt)sorrWhere A is the amount of the element dissolved in the ocean and (dAldt) iss or rthe amount introduced or removed each year. Elements which are reactive cannot be assumed to be fully mixed within the ocean. Therefore residence times5which are calculated to be less than the ocean’s mixing time (Ca. 1000 years)indicate element reactivity.To elucidate the interactions of an element and to discern its behaviour inthe oceans, it is useful to look at variations in concentration as a function ofdepth at a given location (i.e., a depth profile). Generally, depth profiles can bedescribed as one of (or in some cases a combination of) three distribution types:conservative, nutrient-type and scavenged (Figure 1.1).(A) [X] (B) LXI (C) LX]atmosphericDepth Depth Depth inputdeep watersourceFigure 1.1 The three major distribution types:(A) Conservative. (B) Nutrient-type. (C) Scavenged.Conservative elements have concentrations that vary only with salinity.These metals are present in higher concentrations in the oceans relative to theircrustal abundance, are removed slowly from the oceans and thus have longresidence times. While almost all the major elements which exist in millimolarrange (e.g. Na, K, Mg and Cl) behave in this manner, only a few trace elementshave conservative distributions, e.g., U and Cs.Some trace metals, such as Cd, Ni and Zn, exhibit nutrient-type behaviourin that they show a strong correlation with macronutrient distributions (i.e.,phosphate, nitrate and silicate). Vertical distributions of these elements show asurface depletion due to biological uptake, and an increase to a mid-depth6maximum which may then decrease slightly with depth. The maximum is due tothe decomposition of sinking organic matter and fecal pellets which releasenutrients and associated metals at depth. There are two general types ofnutrient distribution based on whether an element correlates with either hard orsoft part macronutrients (shell formation or metabolism, respectively).Scavenged elements, such as Al and Pb, are rapidly removed from thewater column, primarily by adsorption onto sinking particles. Metals with thistype of distribution strongly reflect their external sources with theirconcentrations rapidly decreasing with distance from that source. These metalshave short oceanic residence times (i.e. less than 1,000 years), differ inconcentration in different ocean regions and have low concentrations relative totheir crustal abundance. Scavenged metals are valuable as tracers forelucidating the transport and mixing mechanisms in the oceans.The ability to measure trace metals accurately in seawater, over the last20 years, is a result of the realization of contamination controls during allseawater handling stages and the advent of analytical instrumentation withsufficient sensitivity and selectivity for measuring these elements. Trace metalanalysis requires careful planning for sample collection, storage,preconcentration/matrix separation processes to extract trace constituents frommajor ions, and determination. Minimizing contamination risks is of utmostimportance for reliable trace metal data. Many trace metals are present interrestrial sources, i.e., dust, and in the ship’s environment ( e.g., rust) in levelsmuch higher than seawater. Reasonable avoidance of contamination was notfully realized until the late 1970’s with the development of a clean method forsampling lead by Schaule and Patterson [9]. By 1979, Bruland eta!. [17]developed clean seawater sampling utilizing Teflon-coated Go-Flo bottlesattached to Kevlar line, and clean seawater handling by filtering seawater at sea7in a special clean area on board ship. Further processing is then carried out inshore based laboratories in Class 100 clean rooms requiring acid cleanedbottles, specially designed equipment and ultra pure reagents.The most common analytical methods used in trace metal analysis involvepreconcentration and matrix separation steps, such as ion-exchange or chelatingresins, solvent extraction or co-precipitation, with detection by GFAAS orICP-AES [1,18-30] or more recently, ICP-MS (which is discussed in detail insection 1.4). Even with preconcentration, detection of most trace metals can stillprove difficult. Other methods used for trace metal preconcentration anddetection are differential pulse anodic stripping voltammetry (DPASV) anddifferential pulse cathodic stripping voltammetry (DPCSV) [31-33].Bruland [18] used dithiocarbamate extractions and Chelex-1 00ion-exchange for determining Cd, Zn, Ni and Cu in the North Pacific usingGFAAS detection. Dithiocarbamate extraction with GFAAS detection has alsobeen used to preconcentrate Cd, Cu, Fe, Ni and Zn in samples from theNorth-east Atlantic and Al, Cd, Co, Cu and Ni from waters collected near theBritish Isles [19, 20]. Extractions using 8-hydroxyquinoline (8-HQ) have beenused for Al and Mn in samples from the Pacific [21, 22]. Chelex-1 00 has alsobeen used for Pb, Cd, Co, Cu, Mn, Ni, Fe and Zn in different seawater samples[23-25]. Ion-exchange methods using 8-HQ bonded onto different backboneshave also been used, including 8-HQ-TSK ( a vinyl polymer agglomerate resingel) to extract Al, Mn, Fe, Co, Cu, Cd and Cd from seawater [26] and 8-HQbonded to silica (8-HQ-silica) and other polymer supports to preconcentrate Cd,Pb, Zn, Cu, Fe, Mn, Ni and Co [27, 28]. Co-precipitation has also been used forCu and rare earth elements (REEs) [29, 30]. DPASV has been used to measureCd, Cu, Pb and Zn in seawater, and DPCSV has been used for Cu and Zn[31 -33].8With the difficulty involved in taking replicate samples at each samplinglocation, an alternative criterion for accepting the validity of trace elementmeasurements is commonly used. This criterion is the concept ofoceanographic consistency [34]. Oceanographically consistent data showsmooth variations that are related to known physical, chemical and biologicalprocesses. Thus, the concept requires that trace metal concentrations changesmoothly with depth in the open ocean due to the long mixing time of seawaterand the long distances between strong trace element sources at the oceans’margin and interior.1.2.2 Zinc, Cadmium and NickelCadmium, nickel and zinc are discussed together as they all exhibitnutrient-type distributions in seawater and their concentrations in seawater arecontrolled by internal cycling. Though some of these elements do play activeroles in biological systems, their distribution in the oceans may be controlledprimarily by other indirect mechanisms. Zn is a biologically important tracemetal, and next to iron perhaps the second most important essential traceelement. It is present in many enzymes involved in carbohydrate, lipid andprotein metabolism [12,35]. Directly below Zn in the periodic table is Cd. WhileCd has a similar distribution type as Zn, it is not known to be biologicallyessential [18, 36]. Nickel, a first row transition element, is biologically essentialand is found in some proteins [12].While these three metals have similar distribution types in seawater, theyhave different ocean chemistries. In general, the vertical profiles of these threemetals show a surface depletion, increasing concentrations with depth, reachinga maximum coherent with the nutrient maxima. Below this maximum, theconcentrations of these dissolved metals decrease slightly in the deep sea, due9to deep ocean circulation patterns and the intensity of respiration. A moredetailed background will now be given on each of these elements. ZincZinc is a first row transition metal which exists as a divalent ion inseawater, primarily as a mixture of its free ion, hydroxy-, carbonato- and chiorocomplexes. Its concentration ranges from Ca. 0.05 to 9 nmol/kg (0.003 -0.6 ppb). The first contamination free and oceanographically consistent data forZn were reported in 1978 by Bruland et a!. [35] using two different concentrationtechniques - a dithiocarbamate organic solvent extraction technique and aChelex-100 resin ion-exchange resin, and analyzed using GFAAS. Thedistribution of Zn is highly correlated with that of silicate, a major nutrient in theoceans [35, 37, 38]. Silicate is found in opal, which is used by some organismsto construct protective hard shells. Silicate and Zn are involved in a deepregeneration cycle (e.g., have concentration maxima deeper in the water columnthan “soft part” nutrients, such as phosphate and nitrate), as it takes a longertime for the shells to dissolve as they sink towards the ocean floor. This is alittle surprising since Zn is important in soft part processes. Clearly Zninvolvement in hard part cycles is the dominant control. CadmiumCadmium is a second row transition metal, directly below Zn in theperiodic table. It is divalent in seawater and primarily exists as chlorocomplexes in the oceans and is a non-essential element, though it exhibits anutrient-type distribution. One explanation is that Cd may be taken up byphytoplankton in their quest for Zn in low Zn regimes [39, 40]. The oceanicconcentrations of Cd range between I pmol/kg and I nmol/kg (0.0001 - 0.1 ppb).Its oceanic distribution is dominated by its involvement in a shallow regeneration10cycle similar to the soft part nutrients, P043and N03, thus its maximumconcentration is correlated to that of these nutrients. The distribution of Cd inthe Pacific was first determined in 1976 [411 using a method based on theco-precipitation of Cd with dithiocarbamate followed by GFAAS determination. NickelNickel is a first row transition metal and is divalent in the oceans, existingprimarily as the free hydrated ion and chloro- and carbonato- complexes. Theconcentration of Ni in seawater ranges between 2 and 12 nmol/kg(0.1 - 0.7 ppb). The first oceanographically consistent profiles for Ni wereobtained in 1976 [42] using a co-precipitation method with GFAAS detection.The vertical profile for Ni obtained was found to be similar to those of themicronutrients indicating involvement in the biogeochemical cycle, with Ni beingregenerated both at shallow depths, like NO3and P043,and in the deep waters,like silicate [1 8,37,38].1.2.3 CopperCopper is a first row transition metal and in seawater is a divalent ionprimarily existing as the carbonato- and hydroxy- complexes, as the freehydrated ion and in organic complexes. Copper concentrations in seawaterrange from 0.5 to 6 nmol/kg (0.03 - 0.4 ppb). While it is a required micro-nutrientin seawater, its distribution in seawater is unique, exhibiting nutrient typebehaviour in the surface waters, removal in intermediate and deep waters, and abottom water source [18, 43]. The first consistent results for Cu in seawaterwere reported in 1977 [44] using co-precipitation and GFAAS detection.Vertical profiles of dissolved Cu are controlled by internal cycles, showinga surface depletion with a linear increase in concentration towards the bottom.The apparent deviation from a typical nutrient type profile is due to in situ11scavenging in the deep waters. With this type of distribution, a simpleadvection-diffusion model can be used to estimate the (first order) scavengingremoval rate in deep waters [29]. The residence time of Cu in the deep watershas been reported to be roughly 1000 years [18, 29, 43].1.2.4 LeadLead is a heavy metal and is a divalent ion in seawater, existing as thechloro- and carbonato- complexes. The concentration of Pb in the open oceanranges between 5 and 175 pmol/kg (0.001 - 0.04 ppb). It is a non-essential andpotentially toxic metal. Its distribution in seawater is driven by scavengingremoval processes and external inputs primarily due to anthropogenic sources,specifically atmospheric inputs of alkyl leaded gasoline [9, 45, 46]. The firstreliable data for Pb distributions in seawater were obtained in 1976 [9] usingisotope dilution mass spectrometry detection.Once introduced into the ocean, Pb is rapidly removed via scavengingwhich results in decreased concentrations the deep sea. With the declining useof leaded gasoline over the last 20 years, Pb surface concentrations have beendecreasing, resulting in a subsurface maximum in most regions [9]. The extentof anthropogenic perturbation of Pb is unique among trace element distributionsknown to date, but does have an analogue in the distributions of nuclearbomb-produced radionuclides(137Cs and 3H).1.2.5 ManganeseManganese exists in seawater primarily as the free hydrated Mn2 ionand as its chloro- complexes. The sources of Mn into the ocean are riverine,atmospheric and submarine hydrothermal inputs [22, 47-50]. Dissolved Mnconcentrations range from 0.2 to 3 nmol!kg (0.01 - 0.2 ppb). Manganeseparticipates in a wide range of biogeochemical processes, including being12released from aeolian particles in surface waters [22, 47] and adsorbed ontosinking particles [49]. It is also a required micro-nutrient and involved in internalcycling [47, 49]. The first geochemically consistent study of Mn in seawater wasreported in 1977 [50] using neutron activation analysis (NAA) and GFAAS.Manganese can exist in a variety of oxidation states under differentenvironmental conditions. In sub-oxic or anoxic water (water withconcentrations 10 pmol), it exists as dissolved Mn (II). Although Mn (II) isthermodynamically unstable in oxic waters, it is kinetically inert and thus isslowly oxidized to insoluble Mn (Ill, IV) oxyhydroxides. The oceanic distributionof Mn is dominated by external sources, resulting in maxima in the surfacewaters and in the deep ocean near hydrothermal regions. Internal cycles whichproduce an oxygen-minimum zone also results in dissolved Mn maxima [51].1.2.6 GalliumGallium is a multi-isotopic metal, which lies below Al in the periodic table.In seawater it is a trivalent ion which exists as hydroxides, i.e., Ga(OH)3andGa(OH)4. The first set of Ga data, published in 1958, which used aco-precipitation method with spectrophotometric detection, indicated that theelement concentration in seawater was Ca. 0.4 nmol/kg [52]. With the advent oftrace metal clean sampling and handling techniques and the availability ofadvanced instrumentation, recent results using GFAAS and ICP-MS detectionafter preconcentration using 8-HQ on TSK showed that Ga actually exists inseawater at low picomolar concentrations (10 to 50 pmol/kg) [3, 53, 54].The primary source of Ga to the open ocean may be atmospheric inputsof crustal dust to the surface water and diffusion out of the sediments and/or asediment surface remineralization source to the deep water [3, 54]. Verticaldistributions of the element in these more recent studies show a sub-surface13maximum, low concentration in the intermediate waters and increasing levelswith depth into the deep water. The sub-surface maximum may be caused byeither horizontal advection and/or a vertical process involving exchange withsinking particles. These profiles of dissolved Ga suggest complex controlsincluding multiple sources, reversible exchange and scavenging processes allcontributing to the distribution of dissolved Ga in the ocean.1.2.7 NiobiumNiobium sits directly below vanadium in the periodic table, It is thought toexist in seawater in the +5 oxidation state, primarily as Nb(OH)6. The onlyknown data on Nb in seawater are from 1958 where Carlisle and Hummerstoneanalyzed two filtered samples from the English Channel and found values 0.5nmol/kg [55]. Naturally occurring Nb and radioactive 95Nb, an important fissionproduct in fallout, have been found to bioaccumulate in terrestrial plants, marineplants, molluscs and fish [56,57]. In fish, 95Nb was apparently found to bebound organically in viscera [57].1.3 Flow Injection AnalysisMost manual methods of analysis undertaken in research laboratoriesinvolve the handling and processing samples in the form of liquids. Many ofthese methods involve repeated steps for each sample before an analysis canbe made. Some methods involve the use of potentially hazardous chemicals orenvironmentally sensitive compounds. Over the last 20 years, many manualmethods involving repetitious steps and/or the handling of sensitive orhazardous chemicals have been successfully automated with the developmentof flow injection analysis.Flow injection analysis (FIA) has been demonstrated as an ideal tool forhandling and processing samples prior to their determination [58]. Sample14handling using FIA may be as simple as transporting the analyte to the detectoror as complex as a solvent extraction, a reaction and a back extraction of theanalyte prior to detection.Simple FIA consists of pump(s), tubing, an injection valve and a flowthrough detector. The most common means of propulsion in FIA is the peristalticpump. Examples of FIA manifolds are shown in Figure 1.2.FIA is based on a combination of three principles: sample injection,controlled dispersion of the injected sample zone and reproducible timing of itsmovement from the injection point toward and into the detector. Applying FIA toautomated chemical analysis results in a versatile system which yields fast,precise and accurate results. Systems using FIA have improved repeatability,lowered reagent and/or sample consumption and shortened analysis times [58,59] when compared with batch sample handling.Using FIA systems, reproducible timing is possible for repeated injectionsof sample(s), stream switching, reaction and detection operations. Each samplein a FIA system is under identical conditions at identical points in the system.Therefore, the sample can be measured at one point even if the reaction has notgone to completion or if the analyte is unstable. Separation techniques such asliquid-liquid or liquid-solid extractions which may have less than 100% samplerecovery can still give highly reproducible and quantitative results.A FIA system also provides a means of carrying out an analysis in aclosed system. This allows the use of materials which are toxic or unstable in airas they are not exposed to the user or the environment. This also enables theanalysis of samples such as trace metals in seawater which can be easilycontaminated in an open laboratory environment.15A.pumpR — — IDetect0.injection if,valveB.J\rtecto1,pumpa:AW(organicW(aqueous)SD.Figure 1.2 Types of FIA manifolds:A. Single line. B. Two line with single confluence point.C. Solvent extraction. D. As (B.) but incorporating a packedreactor.1.3.1 Introduction and HistoryThe term flow injection analysis (FIA) was first used by Ruzicka andHansen in 1974 [60]. FIA can be considered a branch of continuous flowanalysis (CFA). An older and more established form of CFA is air segmentedcontinuous flow analysis (ASCFA). In ASCFA samples are separated by eitherair bubbles or inert fluid when first sampled. This breaks the stream into manysmaller, nominally identical segments. Appropriate reagents are added and thew16product is detected typically by a colorimeter once a “steady state” is reachedbetween the sample and reagents. Since the air bubbles are compressible,highly reflective and electrically non-conductive, they can severely distort theanalytical signal. This distortion can be removed by using a cell volume lessthan the sample volume, removing the bubbles prior to measuring the sample ordigitally discriminating the bubbles and sample using either the difference inreflectivity or conductivity and reproducible system timing. While the presenceof air bubbles does have drawbacks, positive effects are also found. Thepresence of air bubbles in the stream limits sample dispersion, promotes mixingof the sample and reagents by generating turbulent flow and also scrubs theinner walls of the analytical conduits.In FIA, individual samples are injected into a moving, non-segmentedcontinuous stream. Nagy was the first to use sample injection intonon-segmented flow streams in electrolyte experiments in 1970 [611. In 1974,Ruzicka and Hansen [60] and Stewart et al. [62] independently demonstrated theadvantage of flow-induced sample dispersion as the sample carrier stream ispumped through narrow bore tubing. This affected the controlled mixing of thesample with the stream resulting in a transient response. They proved that CFAwithout air segmentation is possible and that the “steady state” assumptioninherent to ASCFA is unnecessary. Since its inception, over 3000 papers onFIA have now appeared in the literature, the majority concerned with replacingconventional manual procedures with FIA systems.1.3.2 Channel Geometry in FIAThe analyte signal in FIA is normally in the form of a peak, its height,width or area related to concentration. The FIA peak is a result of two kineticprocesses which occur simultaneously when the sample is injected into a17reagent stream. The first is the physical process of zone dispersion which iswell reproduced for each individual injection cycle. This results in aconcentration gradient of sample within the sample stream. The second is thechemical process(es) which result from reactions between sample and reagentspecies.Different geometric forms of the FIA microreactor have been used toincrease the intensity of radial mixing. This reduces the parabolic velocity profilein the axial direction and results in the reagent becoming more readily mixedwith the sample. The different geometries are straight, coiled, knitted and singlebead string reactor. These are illustrated in Figure 1.3.ABJAJW__Detector- IFigure 1.3 Schematics of the most commonly used microreactor geometriesfound in FIA applications:A. Straight open tube. B. Coiled tube. C. Knitted reactor.D. Single bead string reactor.If a straight channel (Figure 1.3 A) is used the laminar flow is undisturbedand the radial diffusion is not sufficient to affect the axial dispersion formedduring sample injection. This results in an asymmetrical peak. The coiledgeometry (Figure 1.3 B) is the most common and when used causes secondaryflow within the coiled tube which promotes mixing in the radial direction andyields a more symmetrical peak [63]. The “knitted” reactor (Figure 1.3 C) is aresult of tightly and irregularly knotting an appropriate length of tubing [64]. Thistubing configuration causes the carrier stream to move in a chaotic manner18which effectively promotes radial dispersion. All these reactors have the samesurface to liquid ratio.The single bead string reactor (SBSR) (Figure 1.3 D) is the most effectivedevice for promoting radial mixing in a tubular reactor [58]. It was originally usedin post column derivatization [65] and was introduced to FIA by Reijn et al. [66].The SBSR consists of packed glass beads in a piece of FIA tubing. It allowssymmetrical peaks to be obtained within the time domain and channel length of atypical FIA experiment and prevents peak broadening. Due to the presence ofthe beads, the surface to liquid ratio is very high. This is beneficial ifliquid-surface interaction is desirable, as when using immobilized reagents,enzymes or packed reactors.1.3.3 On-Line Matrix Separation and PreconcentrationPacked reactors subject an injected sample to appropriate on-linepretreatment in order to facilitate the detection of the analyte [67]. Differentmaterials have been used in these packed reactors or columns. Ion-exchangeresins have been used to preconcentrate an analyte or remove any backgroundmatrix components which could interfere with the analysis.In FIA preconcentrations, the dispersion of the injected sample is reducedby first introducing a relatively large volume of sample solution from which theanalyte is retained on an incorporated miniaturized packed reactor (e.g., amicrocolumn), and then released, normally in a much smaller volume, andpassed through a detector. This was originally proposed to enhance thesensitivity of the measurement of trace cationic elements in very dilute aqueoussamples in flame atomic absorption spectroscopy (AAS). The system involved asingle-line, two valve FIA system with a packed reactor downstream from bothvalves but before the detector [68].19Many methods have been published using a variety of resins and morecomplicated manifolds, [e.g. 69-71], including a two directional operation of amicrocolumn when loading sample to prevent matrix material from entering theflow through detector [72]. Other refinements include the use of time-basedinjections for sample, where the sample is loaded onto a microcolumn for a setperiod of time [69]. Multi-elemental determinations where also made usingICP-AES detection [72].1.3.4 FIA and SeawaterFIA is suited to the analysis of metals in seawater since the sample isentrained in narrow bore poly fluorocarbon tubing (i.e., Teflon), protecting it fromany surrounding contamination sources and minimizing sample volume. Teflonis an inert fluoro-polymer which, once cleaned, is free from contamination. FIAhas been used in combination with many detection methods for determining anumber of trace elements from seawater. It has been employed for on-linesample processing, particularly sample preconcentration and matrix separationby incorporating an ion-exchange or chelating resin in the manifold.A number of methods using FIA for on-line preconcentration and matrixseparation have been developed with a number of detectors for single elementmeasurements from seawater. Chemiluminescence has been used with FIA tomeasure Co, Fe and Mn [73-75]. Manganese has also been measured using aspectrophotometric method after on-line preconcentration using FIA [76]. Thesedetectors can also be used for ship board work since they are robust. The useof FIA for on-line preconcentration reduces exposure of the sample to potentialcontamination from the ship. Together they provide the scientist tools to analyzemetals from seawater soon after sample collection.20On-line preconcentration methods using FIA have been coupled withatomic absorption spectrometry (AAS) and ICP-AES detection for themulti-elemental determination of some first row transition and heavy metals.Fang etal., measured Cu, Zn, Pb and Cd using Chelex-100 forpreconcentration, resulting in up to a 105 fold concentration and a samplingfrequency of 60 samples per hour using a dual column FIA manifold with flameAAS detection [71]. Another method used ICP-AES detection to measure Cu,Cc, Cd, Pb and Zn in seawater after on-line preconcentration using 8-HQimmobilized on porous glass [69]. More recently, FIA has been used for on-linepreconcentration and matrix separation of trace metals from seawater withICP-MS detection [77,78]. More details are given in section Inductively Coupled Plasma Mass Spectrometry1.4.1 History of the ICP-MSThe concept of combining a plasma as a source of ions with massspectrometry detection for trace metal analysis was developed by A.L. Gray in1970 [79]. Initially, this was developed as a tool for geologists who found thatinductively coupled plasma atomic emission spectroscopy (ICP-AES) gave poorresults for many elements of geological importance (e.g., the rare earthelements). ICP-AES is plagued by complex spectra and poor detection limits formany elements. Matrix interferences from line-rich elements such as calciumand aluminum and easily ionizable elements such as sodium and potassium arealso a problem. Gray demonstrated a direct current plasma-mass spectrometry(DCP-MS) technique for determination of trace metals in solution. WhileDC P-MS gave low backgrounds and simple spectra, it was evident that the DCPwas a far from ideal source. It suffered from poor sample volatilization,dissociation and ionization.21Inductively coupled plasma mass spectrometry (ICP-MS) was firstproposed in 1975. In 1977 the Ames Laboratory in the US collaborated with theBritish Geological Survey to develop the technique. In 1980, Houk eta!. [80]produced the first spectra of Ark, H and 0 from the ICR Later, spectra ofanalyte ions (i.e., Mg, Cr) were produced. The first commercial instrumentwas introduced by SCIEX at the 1983 Pittcon analytical conference, withVG instruments introducing theirs shortly after.1.4.2 Instrumentation OverviewAn overall schematic of the ICP-MS system is shown in Figure 1.4. Theliquid sample is pumped by a peristaltic pump into the nebulizer where anaerosol is formed. The aerosol droplets from the nebulizer are separatedaccording to size in the spray chamber. Small droplets are not condensed orimpacted on the double-pass spray chamber walls but are transported to the ICPby the argon carrier gas. The larger droplets are prevented from reaching theplasma since they may not completely desolvate in the plasma and thuscontribute to water loading. Typically only Ca. I % of the sample solution actuallyreaches the ICP for most basic set-ups.22Figure 1.4 A schematic of the VG PlasmaQuad ICP-MS.In the ICP, the aerosol droplets are desolvated, vapourized, atomized andthen ionized, mainly as a result of the high temperatures within the plasma.Some of the ions are then extracted into a high vacuum region in two steps.First the ions from the central channel of the ICP are extracted by the aperture ofthe sampling cone. Behind the sampling cone, the gas pressures are reduced toabout 5 mbar by a rotary pump. The gas expanding into the lower pressureregion causes the temperature to drop rapidly preventing further reactions whichcould change the gas composition. Part the of gas jet formed is extracted intothe aperture of the skimmer cone. Beyond this point the gas (containing ionizedsample) enters an even lower pressure region ( <3 x I 6 mbar).23The ions pass through a series of electrodes, or lenses, which focus theions into the mass spectrometer. The quadrupole mass analyzer operates as atunable variable bandpass mass filter where ions are resolved (0.5 to 1.0 amuresolution) on a basis of mass-to-charge (mlz) ratio. A full scan of the massrange is accomplished in under a second. Only ions with the selected m/z ratioare transmitted through the quadrupole mass analyzer to subsequent detectionby a channel electron multiplier. The channel electron multiplier can operate ineither of two modes, pulse counting or analog counting mode. In pulse counting,pulses from individual ions above a set discriminator level are counted. Thisgives the highest possible sensitivity and is used for samples of sub-ppmconcentrations. In analog mode, the electrons are collected by the normalcollector electrode and the current is then amplified by a linear amplifier with theapplied voltage set at -1500 V. This gives a faster response and is used forsamples with ppm or greater concentrations.The pulses from the detection system are fed to a microprocessor-controlled multichannel scalar data acquisition unit. A second microprocessorlooks after the overall instrument operation. The overall system is controlled bya personal computer.1.4.3 Advantages and Limitations of the ICP-MSSince the ICP-MS became commercially available, it has been acceptedfor oceanographic analyses [34]. The advantages of the ICP-MS for trace metaldetection over other detection systems are many. It is highly sensitive withdetection limits on a par with GEMS for most elements. It measures multipleelements and isotopes facilitating elemental determinations by isotope dilution.The mass spectra of the analytes are simple with any overlap interferences byother species predictable. It has a working range covering six orders of24magnitude and less than 1 second is required per isotope determination, It alsoenables one to easily measure refractory elements [34, 81].Unfortunately, there are also disadvantages to the ICP-MS. It is anexpensive instrument to purchase (at present, Ca. $250 k) and expensive to run.Overlap interferences due to plasma and solvent ions can give extremely highbackgrounds. These interferences can be from isobaric ions, oxide formationand doubly charged ions. To minimize the formation of oxides and doublecharged ions, gas flow rate, RF power and ions lens settings have to beoptimized. Matrix interferences are also a potential source of high backgroundsor signal suppression. This results in not being able to directly nebulizeseawater due to its high salt content (ca. 3%), thus requiring a separation step.While these problems can be severe, generally, the advantages of the ICP-MSoutweigh its disadvantages.I 4.4 Sample Introduction MethodsSample introduction into the ICP-MS by nebulization has been the weaklink in the whole system. Solution nebulization introduces large amounts of 0,N, S and Cl from water or acid matrix into the plasma. Tan and Horlick studiedthe effects of various acid matrices on metals [82]. Nebulizing sampling systemsalso cannot tolerate high salt matrices which can clog some nebulizers or uponionization of the matrices within the plasma, cause clogging of the cone orifice[83,84]. While continuous nebulization of concentrated acid ( > 5%) into theICP-MS does not generally affect the nebulizer, it does accelerate conedeterioration [83].Memory effects can also be a problem if large volumes of samples, orsamples with high concentrations of certain analytes are nebulized through thesystem. Memory effects occur when an element “sticks” to surfaces in the25analyte pathway and slowly comes off over time. This can result in highbackgrounds of that analyte until the analyte is completely removed by rinsingthe system with concentrated acid for a period of time [85]. Coupling thenebulizer with different sample introduction methods can minimize some of theseproblems. FI-ICP-MSThe first work using a simple flow injection loop to introduce smaller anddiscrete samples into the ICP-MS instead of continuous nebulization was carriedout by Houk and Thompson in 1983 [86]. Volumes of 50 to 200 pL of a I %HNO3 solution with Mg and Ni were injected into the ICP-MS. Detection limits of2 to 50 mg/L, with a precision of I to 3 %, were found. Injection of 100 or 200 pLvolumes of a 40 mg/L Mg standard 50 times did not plug the sample orifice. Itwas also possible to inject urine and serum directly into the ICP-MS with only afive fold dilution.The use of an Fl loop to introduce samples minimizes cone clogging anddeterioration and memory effects [83-86]. It is also necessary if only a smallvolume of sample is present. For example, a method for determining Zr fromseawater results in a final analyte volume of less than two mIs [87]. The analyteis drawn into a 300 pL Fl loop by a pump allowing for a second measurement tobe made. Even after injecting this small volume into the ICP-MS, the systemneeds to be rinsed with 2 N HNO3 for several minutes to bring the backgroundto acceptable levels and minimize any memory effects before anothermeasurement can be made. Gold was also determined using Fl-ICP-MS byincorporating an Fl loop after the pump with the sample being drawn into theloop by suction to minimize contamination from the pump tubing [88]. On-Line Preconcentration and Matrix Separation with Fl-ICP-MSThe use of FIA for on-line preconcentration and seawater matrixseparation has also been coupled with ICP-MS detection [77, 78]. Beaucheminand Berman adapted the off-line immobilized 8-HQ-silica method of the NationalResearch Council of Canada (NRC) group [89] for on-line preconcentration bypassing up to 10 ml of seawater through a 80 mg resin column to measure Mn,Cu, Co, Mo, Cd, Pb and U. McLaren et a!. [78], have modified a commerciallyavailable chelation concentration system for on-line preconcentration to permitthe simultaneous determination of Fe, Mn, Cc, Ni, Cu, Zn, Cd and Pb in 5 mlseawater samples in under 10 minutes by ICP-MS. Columns used in this systemcontained MetPac CC-i resin, which came with the system, and 8-HQ-silicaresin. Accurate determinations for all elements except for Fe and Co were foundfor both NASS-1 and CASS-3 certified standard seawaters.1.5 Shipboard and in situ analysis1.5.1 Shipboard DeterminationsThere are many advantages for performing analyses while at sea. Theseinclude checking for sample contamination, providing immediate results whichmay aid in choosing sampling locations and obtaining data on metal speciationwhich can change during sample storage [34, 90]. A reliable seagoing methodshould either physically contain the sample or alter the chemistry of theanalyte(s) in the sample to reduce the potential of shipboard contamination. Asship time is expensive [91], minimizing the sample processing and analysis timeis desirable. The simplest way to maximize sample throughput is to minimize thevolume of seawater needed to preconcentrate the metal(s) for detection. Finally,the seagoing detector must have low detection limits and function well underrough conditions.27Measures and Edmond [92,93] developed a seagoing method based onelectron-capture detection gas chromatography (ECD-GC) to analyze Be, Al, Asand Se as volatile metal-chelates. This method is also multi-elemental as theGC separates the metal-chelates before they reach the ECD. The same methodwas adapted by Mugo and Orians to measure Cr (Ill) and total Cr [90]. Seagoingtechniques using DPASV and DPCSV for the speciation of Zn, Cd, Cu, Pb, Co,Ni and Fe have also been developed [31-33, 94].Flow injection methods using suitable detectors are being accepted asseagoing methods for the same reasons as Fl is suited for seawater processingand analysis. Sample and reagent volumes are minimized and the Teflon tubingcommon to Fl manifolds encloses sample and minimizes contact between thesample and the ship environment. Seagoing methods using on-line columnpreconcentration using flow injection with 8-hydroxyquinoline resin has beenused with chemiluminescence detection to measure Co and Mn [73,75] and withspectrophotometry to measure Mn [76].1.5.2 In situ Measurements and SamplingLong-term monitoring is essential to discern processes which lead to thenatural variability in the oceans and to assess the anthropogenic impact ongeochemical cycles. Temporal changes in the oceans, including spring blooms,other seasonal activities, etc., require a ship to be present for sampling. Thelack of long-term oceanographic studies at most locations severely limitsunderstanding of ocean processes. With the prohibitive costs of operating amodern research vessel [91], and the decreasing availability of ship time, it isbecoming necessary to develop remote in situ sensing and measurementdevices.28In situ measurement systems, which can be moored and operateunattended for long time periods, such as up to one year, are now beingdeveloped in order to overcome the lack of long-term monitoring of the ocean.Automated chemical analyzers have met with limited success since they aresubject to sensor drift and biofouling, though some progress has been made[95]. Another approach for long-term sensing is the use of chemical sensors[34].Sensor systems, which use electrodes, fiber-optics or chemical field-effecttransistors, are mechanically simple [96]. Currently, the most common chemicalsensors use oxygen and pH electrodes [97]. These systems are not used widelyfor other analytes, because very few chemistries are known which are reversible,have quick response times and have the sensitivity and selectivity to detectanalytes at low to sub micromolar concentrations.Short-term, in situ determinations of a series of elements have been doneusing unsegmented, continuous-flow analyzers, using colourimetric detectors,known as scanners (submersible chemical analyzers) [98]. Nitrateconcentrations have been measured in situ, to a depth of 2000 m by a scannertethered to a vessel [99]. Redox species such as sulfide, Mn and Fe have beenmeasured in hydrothermal vents at depths of 2500m by mounting scanners onmanned submersibles or towed from a research vessel [100].Speciation measurements on Zn have also been made in situ usingthin-film gels. An ion-exchange resin with an ion-permeable gel membranebarrier of known thickness is suspended in natural waters. Quantitative data onconcentration and speciation are then obtained over time periods between1 hour to one week [101].One limiting factor of these in situ analyzers and sensors is that they donot provide simultaneous multi-elemental results. An in situ sampler can be29optimized to collect multi-element samples but the collected samples need to beanalyzed at a shore based laboratory. Commercially available in situ samplersinclude Axys Instrument LtcVs INFILTREX II [102]. Another sampler(non-commercial) uses a fluidized bed of complexing agent and has beenoptimized for seven elements (Cd, Cu, Fe, Ni, Mn, Pb and Zn); no results basedon this method have been published as yet [103].Generally, the area of in situ samplers for trace metals is a young field.Samplers that do exist are either in prototype stages or are adaptations ofexisting samplers used for the collection of organics. Rarely do these samplerscollect both multi-elemental and multiple samples.30CHAPTER 2: DEVELOPING AN IN SITU SAMPLERThis chapter describes the development and evaluation of a newprototype sampler with the capability of multiple sampling for in situpreconcentration of trace metals in natural waters. This prototype was modeledon a commercially available apparatus, the INFILTREX II which is manufacturedby Axys Environmental Ltd. (Sidney, BC) and was designed in conjunction withDr. L.E. Bowman of the Chemistry Department, UBC. Initially, the intent was tomodify the INFILTREX II for our purposes [104], but it became apparent that anew sampler had to be designed. Detailed descriptions of the INFILTREX IIsampler, its operation, limitations and attempted modifications are found inAppendix A.2.1 Designing the Prototype samplerThe prototype sampler was initially designed to operate at flow rates lessthan 10 mI/mm and have miniature columns for multiple samples, incorporate abuffer or standard solution stream, monitor the flow rate over the course of asample preconcentration and withstand pressure to seawater depths of 3000 m.The sampler was to be controlled by an on-board computer which could beaccessed using another PC, and operate remotely at preprogrammed timeintervals.It was important for the sampler to operate at slow flow rates (e.g. lessthan 15 mI/mm) since in most ion-exchange extractions, including the use of8-HQ resins, the binding kinetics between the free metal ions in seawater andthe chelating resin could result in less than total recoveries at higher flow-ratesdue to insufficient contact time between the seawater and the resin. Typical flowrates are between 0.5 and 5 mL/min [27, 105 -106]. At faster flow rates,31depending on resin used, the possibility of incomplete metal extraction fromseawater may result in artificially low concentration measurements.The sampler was designed to hold up to six separate columns. Thismultiple sampling capability would reduce the need to redeploy the samplerwhen gathering replicate samples, full depth profiles or undertaking temporalvariability studies. The columns were miniaturized to decrease the amounts ofresin and reagents needed, as well as decrease column blanks.To preconcentrate trace elements which are not readily extracted atambient seawater pH, a separate channel was incorporated to allow the additionof a buffer to the seawater stream before it passed through the resin columns.This increases the versatility of the sampler. To determine the volume ofseawater through each column without having to physically collect the seawater,the flow rate was monitored during each preconcentration cycle.2.2 Components of the Prototype samplerThe overall design of the new in situ sampler, front and back, is shown inFigure 2.1. Table 2.1 lists the physical components of the prototype sampler,together with a brief description of each component. The circuitry and softwarenecessary for controlling the sampler are described later in this chapter.32computer plugendLhydrowire brackets with pump motor, electronicscomputer board and battery packsampler spine which containsflow meter,valves and manifold6-pin6 resin columnsflow meterwatef’outflow6 solenoid hex valvewires to 8-pin cable(b)Figure 2.1 A schematic of the prototype sampler(a) Front view. (b) Rear view.In (b) the Teflon tubing manifold has been removed for clarity.handle water in-flowfiltersandwich(a)valves and flow meterpump headhousingspineendoutlet of sandwich filter2-way switching valveone end of 8-pin cablecolumn union for resin columnswires to 6-pin cable33Component DescriptionComputer Board On-board timer and enough digital I/O to controlsampler. Programmed through another PC.Pump Peristaltic pump head driven by a gear motorValves (a) One six solenoid normally closed hex-valve(b) One two-way switching valveFlow meter Time-of-flight design, using three thermistorsColumns Mini-columns with resin, also used for on-line workCasing Aluminum pressure housing with spinePie-filter 142 mm filter sandwich with 0.45 pm filterBattery pack 45 “D Cells” batteries, 9 sets of 5 in seriesTable 2.1 Physical components of the prototype sampler.2.2.1 Computer BoardA computer board to control the operation of the sampler was sought touse in the prototype sampler. The following criteria were assessed whenchoosing the computer board:Communication between the computer board and a personal computermust be possible to permit the programming of the computer board priorto deployment. The RS-232 mode of communication was preferred for theprototype system.2. The computer board must control a number of valves as well as the pumpand the flow meter. To accomplish this, the computer board must have atleast eight digital input/output lines (digital I/O’s).343. The computer board must contain a timer/counter as this would berequired when using the flow meter.4. The computer board must contain sufficient memory to run the controlsoftware and to store any data collected. A minimum of 64 K of randomaccess memory (RAM) was envisaged.The computer board chosen to control the prototype sampler was aZiatech ZT88CTOI computer board (Ziatech Corp., San Luis Obispo, CA). Briefdetails are given below regarding the operation of the computer board. Thereader is referred to the manufacturer’s instruction manuals for moredetails [107, 108].The Ziatech computer board required a power supply of 7 V dc with 0.8 Acurrent, On initialization, the computer board is set with three drives; two(assigned P: and Q:) which are read only memory (ROM) drives and the third(assigned R:) which is a RAM drive and comes with a total of 128 K RAM. TheROM drives contain the operating system. To change any program contained inthe operating system (e.g., AUTOEXEC.BAT), that program must be copied tothe R: drive and then altered. When the Ziatech board is powered, the R: driveis checked for any altered operating system programs and then any operatingsystem programs not found on the R: drive are run from the ROM drives.The Ziatech computer board comes with Microsoft DOS 3.3 (MicrosoftInc., Mississauga, ON) in the EPROM, 48 programmable digital I/O lines, a realtime clock and a counter/timer. It is accessed by another PC by using anRS-232 serial cable. Once connected to the PC, the Ziatech board installs theC: and A: drives of the PC as remote drives (U: and T: respectively). To test anddebug programs using the Ziatech computer board with the PC still connected,an executable version of the program is run from either of the remote drives. Ifthe program is to be tested using the Ziatech computer board only, i.e., the PC is35disconnected, then a different procedure is utilized. Prior to the installation ofthe program on the Ziatech computer board, a second RAM drive (assigned S:)must be formatted and assigned up to 64 K of the available RAM. Theexecutable version of the program is then copied to this drive. Changes arethen made to the operating system programs so that the required program is runon power-up. The interface between the Ziatech computer board and the PC didnot function correctly when the operating system installed on the PC wasMicrosoft DOS version 6 and upwards. Problems were experienced whenaccessing the remote drive U:, i.e., drive C: on the PC. In any event, the Ziatechboard still can read remote drive T: (drive A: on the PC).All the software written during the development of the prototype sampler,was coded in Microsoft BASIC 7.0 (Microsoft Inc., Mississauga, ON).22.2 Interface CircuitryConnections between the Ziatech computer board and the electricalcomponents of the prototype sampler are shown in Fig. 2.2. The status of thevalves, the pump motor and the length of the heating pulse for the flow meterwere controlled via the digital I/O port (connector J7). The signal from the flowmeter was monitored using the counter/timer (connector J2). Thecommunications port (connector J6) was used when accessing the computerboard by a PC.The digital I/O lines on the Ziatech computer board defaulted to a HI state(+5 V) on initialization. This was problematic as the valves and pump werepowered by this operation. As a result, a program was included in the operatingsystem of the computer board to set the digital I/O’s to a LO state prior tooperation of the sampler. The source code for this program (HIGHLO.EXE) is36Column Valve ControllersI through 6Figure 2.2 A representation of the Ziatech computer board and connections tothe sampler component controllers on the electronic circuit board.2.2.3 Pump Head and MotorThe pump design was based on the in situ analyzer, the SCANNER,developed by Johnson et al. [98] at Moss Landing, CA. This analyzer has beenused to study manganese in hydrothermal vents at depths greater than 2500 m.In the prototype design, a MASTERFLEX® size 13 peristaltic pump head(Cole-Parmer Instrument Co., Chicago, IL) was affixed to the outside of the topendplate. The pump head sat on a pump shaft which protruded through theendplate. The pump shaft was rotated by a 24 V brushless gear motor (Pittman,Harleysville, PA), with a 19.7:1 gear reduction, situated inside the pressurehousing. A schematic of the pump interface shown in Figure 2.3. Thisarrangement ensured that the flow manifold was kept at ambient seawaterpressure during deployment of the sampler. In this way, the seawater isgiven in Appendix B., together with the source code of the program(SAMPLER. EXE) used to run the sampler.Triggers Flow Meter CircuitTo send Heat Pulseto Flow MeterSwitching Valve ControllerPump Motor ControllerGroundGroundCounts Signal fromFlow Meter CircuitTo COM port of host PCorConnect Computer toPower for Sampler Deployment37preconcentrated at its own pressure and flow problems due to pressuredifferences in the flow manifold are removed.1. pump head2. pump head mount3. exterior of endplate4. interior of endplate3. 3. 5. pump shaft interface6. pump motor mount7. pump motor8. power connection9. interior spine(for boards and battery pack)Figure 2.3 Cross section of top endplate to show a schematic ofpump head to pump motor connection.Parts not associated with the pump interface have beenomitted for the sake of clarity. Pump ShaftThe pump shaft was designed and constructed after much consultationwith members of the UBC Dept. of Chemistry mechanical shop. The pump shaftlinked the pump head, in seawater, to the pump motor inside the pressurehousing. In the oceans, the pressure increases from atmospheric at the surfaceto atmospheric plus one atmosphere for every 10 m of depth. The pressureinside the pressure housing was at atmospheric. Due to the potential pressuredifferential between seawater and the inside of the housing, it was necessary todesign a special housing for the pump shaft which kept seawater from leakinginto the pressure housing, while allowing the pump shaft to turn easily.1.38Several pump shafts were built using special bearings. These were alltested for several days by placing the water-filled housing under a pressure of2700 psi, using compressed N2. The special bearings seal when they are underpressure. Before the pump shaft was used, the bearings were sealed bytightening a series of screws on the top plate of the pump shaft assembly,wherein the bearings are contained. This ensured that the seal was sufficient toprevent the leakage of seawater at shallow depths when the seawater pressureis close to atmospheric. To check the seal, the pump shaft was connected to themotor which was powered by a 15 V power supply. The bearings provided someresistance to shaft rotation, which was quantified by monitoring the currentdrawn from the 15 V power supply. Experience showed that a proper seal wasformed when the current drawn by the motor was between 300 and 400 mA.2.2.4 Flow Meter DesignThe flow meter incorporated into the prototype sampler was based on athermal-pulsed time-of-flight liquid flow meter developed at Dow Chemical Ltd.for use in liquid chromatography [1091. The flow meter (Fig. 2.4) is essentiallythree glass-tipped thermistors (Fenwal Electronics, Milford, MA), placed inseries. The flow meter was placed downstream of the extraction columns toprevent any contamination of sample due to the glass coating. The heatingthermistor (model #121 -4O2EAJ-Q01) was pulsed with 100 mW of power for400 milliseconds. The sensing thermistor (model #123-8O2EAJ-P01), placeddownstream, sensed the heat pulse. An identical thermistor was added to theflow meter upstream of the other two to monitor the ambient seawatertemperature.391. Seawater temperaturesensing thermistor2. Heating thermistor63. Heat pulse sensing thermistor4. Teflon tee-piecesFlow 1.6 mm Id.direction 5. Teflon connectors6. Teflon spacerFigure 2.4 Interior of the flow meter hardware.Each of the three thermistors was imbedded in commercially availableTeflon® tee-pieces (i.d. 0.8 mm, Omnifit, Rodchester, NY) using clear marinesilicone sealant. Before sealing, the thermistors were placed so their tips werein the centre of the tee-piece junction. Teflon® connectors were constructed toconnect the tee pieces in series. The reference and heating thermistors wereseparated by 3cm, i.e., the lengths of the arms of the tee pieces. The distancebetween the heating and the sensing thermistor was 4.5 cm.The wires from each thermistor were connected to one end of the 6-pinunderwater pluggable cable ensemble. The other end connected the thermistorsto the flow meter circuitry situated inside the pressure housing. As the flowmeter was in contact with seawater and the wires of each thermistor were fragile,it was necessary to minimize corrosion and breakage by covering all exposedwiring with thin plastic and a silicone sealant.2.2.5 Valves and Column DesignThe choice of switching valves was very critical when designing theprototype sampler. The valves needed to function underwater and underpressure. In addition, the valves had to be compact and self-contained due tospace considerations. This precluded the use of pneumatic valves and led to3cm 4.5cm9the appropriate solenoid valves being sought. Finally, to prevent contamination,40all wetted areas of the valves had to be made of an inert material. A six-solenoidnormally closed (N.C.) hex valve and a two-way normally open (N.O.)I N.C.switching valve were purchased from NResearch (NResearch Ltd., Northboro,MA). All wetted areas of these valves were Teflon® and the valves operatedwith 12 V power and 0.4 mA. These valves were not specifically designed forunderwater applications, but consultation with the NResearch technicianssuggested that the valves would function adequately if the individual solenoidswere coated to prevent water leakage. Therefore, all exterior surfaces and wireswere coated with a silicone sealant.The flow manifold incorporated five mini-columns designed and builtin-house. These columns were filled with 8-HQ on silica. The resin wassynthesized in house by L. Yang (Department of Chemistry, UBC), using themethod detailed by Marshall and Mottola [106]. The components of the manifoldwere connected with Teflon® narrow bore tubing (i.d. 0.8 mm, Cole-Parmer,Chicago, IL). The pump tubing used on the peristaltic pump head wasMASTERFLEX® C-Flex tubing (size 13, Cole-Parmer, Chicago, IL).A schematic of the flow manifold is shown in Figure 2.5. The out-flowfrom the filter sandwich was connected to the N.O. port of the two-way switchingvalve and a buffer or standard (if required) was connected to the valve’s N.C.port. The switching valve’s common port was connected to the common port ofthe six solenoid hex-valve. Five of the six N.C ports of the hex valve wereconnected to mini columns, the sixth one used to flush the system once in thewater before sampling commenced. All the six ports were attached to a commonTeflon® eight port connector (Omnifit, Rochester, NY). Of the two remainingports on this connector, one was plugged and the other was connected to theflow meter. The out-flow from the flow meter returned to the environment.41Buffer/standardSeawater fromfilter sandwichColumnsBack toseawaterFigure 2.5 A schematic of the flow manifold used to preconcentrate metalsfrom seawater using the new sampler.Each solenoid had two wires, one for connecting to power and the otherfor connecting to ground. All wires from each solenoid that were designatedground were connected to the ground pin of one end of the 8 pin underwatercable ensemble. Each of the remaining solenoid wires were connected to theindividual pins. This connected the valves to their control circuits in the interiorof the casing found at the other end of the cable.22.6 Battery PackThe battery pack (Fig. 2.6) was constructed out of a Nylon polymer. Ithoused 45 “D-celI” batteries (each 1.5 V) in nine sets of five in series. Six ofthese sets of five provided the 15 V to power the motor and valves. The threeremaining sets powered the computer board and the electronic circuit board.This battery configuration was necessary as the power drain of the prototypesampler was considerably more than that of the INFILTREX II sampler due to theaddition of valves, the pump design and the computer board. The batteryhousing was attached to the top endplate by two metal supports. The computervalvePumpFlow meter6-port solenoid 8-portvalve connectorboard and electronic circuit board were also attached to these supports.42A 1. Pump head1 2. Top endplate3. Pump motor4. Computer and circuit boardsB. Support spines6. Nylon battery pack7. Power supplies8. Oneofninesetsof five batteries in seriesFigure 2.6 Schematic of the battery pack:(A) view from the side(B) view from the top and bottom of battery pack.2.2.7 CasingThe aluminum casing was built in the UBC Dept. of Chemistry mechanicalshop out of a 71.12 cm long, 1.27 cm thick piece of aluminum tube with an i.d. of15.24 cm. This accommodated the computer and circuitry boards and batterypack. Calculations made by staff at the mechanical shop indicated that analuminum tube of these dimensions would withstand the pressure at depths upto 3000 m.The casing was attached to a 106.68 cm long, 0.635 cm thick aluminumspine, which was also built in the UBC Dept. of Chemistry mechanical shop. Thevalves, flow meter and underwater connector plugs were attached on theunderside of the spine (Fig. 2.1 B). These components were protected with apiece of sheet aluminum during transport. During deployment, the sampler wasattached to the hydrowire by the two hydrowire brackets present.The endplates which sealed the aluminum tube casing were also made ofaluminum. Each endplate had double silicone 0-rings to ensure a water tight7243seal. The bottom endplate, once attached to the sampler, closed the circuit ofthe battery pack. The top endplate had the pump motor and pump shaft screwedinto it. When the top endplate was removed, the whole interior was alsoremoved.On the exterior side of the top endplate were the pump head and threefemale underwater pluggable cable connectors (Impulse Enterprises, San Diego,CA). Two of the connectors were six pin with ground (model # BH-6-FS), theother was an eight pin with ground (model # BH-8-FS). The first six pinconnector was used to access the computer board. Prior to deployment, thisconnector linked the computer board to the PC. When the sampler was to bedeployed, a closed plug was attached to this connector, linking the computerboard to the battery pack, and thus commencing sampler operation.The second female six pin and the eight pin connector in the top endplatewere linked to two other female underwater pluggable cable connectors(model #s BH-6-FS-SS and BH-8-FS-SS) via a 6 pin two-way male connectingcable and a 8 pin two-way connecting cable, respectively (model #s lL6-MP and1L8-MP). These other cable connectors were wired to the flow meter (using the6 pin) and to the valves (using the 8 pin). This six pin connector ensemblelinked the three thermistors in the flow meter to the flow meter circuitry. Theeight pin connector ensemble linked the seven valves to the valve controlcircuitry.2.2.8 Electronics HardwareAll electronic components used in the circuit boards were obtained fromActive Components Ltd. (Vancouver, BC) unless otherwise specified. All theelectronic circuitry incorporated into the prototype sampler was built on to asingle board by the UBC Dept. of Chemistry electronics shop (see Appendix C).442.2.9 FilterThe 0.45 pm filter sandwich was the only part or the original INFILTREX IIsampler to be used in the prototype sampler. Anything passing through the filterwas considered to be dissolved (this is the standard definition of dissolved,although colloidal material may be present). The filter sandwich was attached tothe sampler bracket by two metal plates which also sealed the sandwich andprevented water leakage from its sides. The original in-flow tube to the filtersandwich was unchanged, but an adapter had to be built to connect the out-flowfrom the filter sandwich to the two-way switching valve.2.3 Operation of the Prototype Sampler2.3.1 General operationThe prototype sampler was programmed to pump for a specified length oftime through each port of the six-way solenoid valve. While each separate valveis open, the two-way valve switches between the seawater stream and thebuffer/standard stream every few seconds (typically 10 seconds in the seawaterstream position and I second in the buffer/standard position). The flow meterrecorded one measurement every 12 to 14 seconds during the total operationtime of the sampler. These flow rate measurements were stored in six separatefiles, one for each port ( and therefore column) of the six-way solenoid valve.2.3.2 Pump ControlThe computer board turned the pump on or off by sending a HI or LOsignal to the pump controller on the circuit board. When the signal was HI, thepump controller connected the pump motor to +15 V dc, causing the pump motorto rotate. The pump speed changed only by fluctuations in this input voltage.Thus, the pump speed slowed as the batteries in the battery pack were drained.45Since flow rate measurements were taken regularly, this was not a problem. Inaddition, the operating time of the pump was less than ten minutes per columnand repeated operations (greater than 10 times) did not cause a drop in the flowrate.2.3.3 Valve ControlThe seven solenoid valves, i.e., six on the hex-valve and one on the2-way switching valve, are controlled using the identical relays used forcontrolling the pump motor. When the computer triggers a particular relay HI,that relay connects the its valve to the 15 V dc supply. This opens the valveallowing water to flow through it.2.3.4 Flow Meter ControlThe flow meter operated as follows: A heat pulse was sent through theheating thermistor for 400 milliseconds and the timer was started. When theheat pulse was sensed, the timer was stopped. A 3.5 second wait was built intothe circuit in the event that if a pulse was not sensed, the timer would still stopand another pulse would be sent out at preset time intervals. The signal wascoupled with a 10 kHz frequency generator. The Ziatech computer board thencounted the number of oscillations at 10 kHz for each measurement. Therefore,this measurement was the number of oscillations of the 10 kHz signal during thetime the heat pulse was first pulsed to when it was detected. These values werestored in separate files in the Ziatech computer board’s memory for eachcolumn. The flow rate was inversely proportional to the counts. Afterdeployment of the prototype sampler, the flow rate files were down loaded to aPC. The series of measurements by the flow meter were then averaged andusing the calibration file, described below, the volume of seawater through eachcolumn was determined.462.4 Flow Meter CalibrationTo calculate the actual flow rate, the flow meter was calibrated bycollecting Ca. 50 measurements at 5 to 10 different flow rates over the workingrange (between 0.8 to 7 mI/mm) and averaging the results. An Alitea peristalticpump (Alitea USA, Medina, WA) was used to obtain the range of flow ratesneeded for the calibration. Typical calibration results are shown in Figure 2.7.The calibration plots in this figure indicate that the flow meter response becomesunstable at flow rates greater than — 7.0 mI/mm and flow rates less than—1.0 mI/mm.Generally, the pulsing of the peristaltic pump is noticeable over the 50points measured at each flow rate. Though it should be noted that it is mostpronounced at the slowest of the stable flow rates. Visual inspection of the plotsin Figure 2.6 indicated that the effects of pulsing decrease with increasing flowrate. Upon examination of Table 2.2 , which shows the average of each of thedata sets at each flow rate at the 95% confidence level, it is apparent that thefluctuations in the flow meter response is similar between the flow rates of 1.5 to6.3 mI/mm.47U)a)C)NC9-0a)U)C00U)a)a)4-,a)0LLFigure 2.7 Plots of the 50 data point sets of the flow meter response over arange of flow rates between 0.8 to 8.0 mI/mm:A. Working range of flow meter.B. Borderline to non-working flow meter range.N.B. The number of 10 kHz oscillations are inversely proportionalto the flow rate.25000Plots of Flow Meter Response at Various Flow Rates60000500004000030000200001000000 5 10 15 20 25 30 35 40 45 50Data Point Number48Flow Rate Averaged FlowMeter Response0.81 30181 ± 19911.58 10188±772.36 8193±893.13 7417±993.91 7085±1045.50 6182±906.29 5653 ±717.09 5264 ±7947.99 9935 ±3280Table 2.2 The average flow meter response at different flow ratesat the 95% confidence limit.A plot of the flow meter response as a function of the flow rate is shown inFigure 2.8. Excluding the two extremes, the flow meter had a linear responsebetween flow rates of 2.3 to 7.1 mI/mm (regression coefficient, R2= 0.991). Thisrelationship deviated when the lowest stable flow rate of 1.58 was included(regression coefficient, R2= 0.901). The linear response between flow rates of2.3 to 7.1 mI/mm greatly simplifies the conversion between the number of countsfrom the flow meter to flow rate.The pump system on the sampler had a maximum flow rate of ca.8 mI/mm when an external power supply of 15 V was used. With columns inplace, the flow rate lowers to Ca. 6 mI/mm using the same voltage, which is wellbetween the linear working range of the flow meter.4930000a)Cl)__1500012500Z510000Cl) 0 7500a)5000Flow rate (mi/mm)Figure 2.8 Flow meter response vs. Flow rate.2.5 Prototype Sampler Testing2.5.1 Preliminary Testing at SeaThe first testing of the prototype sampler involved taking the casing to seaduring a “line P” cruise to station P 26 (50°N 145°W) in March 1993. At thisstage of the sampler development, the valves and pump head were alreadyattached to the casing’s exterior, and the computer electronic circuit boards werein place and wired to the exterior attachments. Prior to the cruise, a prototypecomputer program was written to ensure the valves and pump motor worked inthe correct manner. The exposed surfaces of the valves were coated withsilicone sealant for protection.The casing (particularly the pumphead interface) was tested for leakagedue to pressure changes by sending the sampler to depths of 500 and 1000 m.Prior to testing, the computer and electronic boards were removed to prevent10438X - 773, r2 = 0.901 (with 1.58 mI/mm)= 9451X - 598, r2 = 0.991*0 1 2 3 4 5 6 7 8 9 1050their damage if leakage did occur. Once the sampler was retrieved from depth,its interior was checked for leakage. Less than 25 mIs of seawater was found atthe bottom of the casing. The water was removed, but the exposed metalsurfaces, i.e. contacts on battery pack and bottom endplate, still corroded. Theleakage occurred at the pump interface, but the seal was not broken when testedlater. The seal, which works when pressure is applied, was not tight when firsttested. The outcome was slight leakage of seawater until the pressuredifferential between the casing and the seawater was high enough to retightenthe seal. This was remedied in later tests by tightening the seal beforedeployment. This was accomplished by running the motor and adjusting thecurrent to between 0.3 and 0.4 A by tightening the metal plates which hold theseal in place.After deployment the valves were inspected and checked by applying15 V to each valve separately. The solenoids within each valve appeared to beworking since the typical switching sound was heard. Later it was discoveredthat seawater had seeped into the interior of the solenoids, freezing the valvesinto the N.O. position. The valves were removed, disassembled and cleaned.One of six valves in the hex-valve sustained damage. A replacement solenoidvalve could not be purchased and another hex-valve was not available. Insteadthe port of the bad valve was plugged and the sampler control program wasrewritten to account for the changes in operation.2.5.2 Submersion TestingOnce the sampler was recleaned, the flow meter was connected andtested successfully, it was subjected to a week long submersion test in house.This involved placing the sampler into a Plexiglas tank filled with tap water forfive days. The on-board computer was linked to another PC in order to run the51control program and to collected the data from the flow meter. Each day thesampler operation was monitored, checking that the pump worked, the valvesopened and closed properly, the flow meter operated and that the relevant flowrate data was collected by the computer. No problems were encountered,though some rust formation occurred on some of the valves.The sampler was then removed from the tank and opened up to check itsinterior for any leakage. Only slight condensation was observed, which wasremedied by adding a drying agent to the interior (e.g. CaO). The valves had tobe disassembled and cleaned, with only the switching valve becominginoperable.2.5.3 Contamination ControlThe seawater manifold of the sampler, without the columns, was cleanedwith 2 N nitric acid for several days. High blanks were found for the elements Ni,Mn, Pb and Zn and were attributed to the flow meter. When blanks werecollected from the manifold before the flow meter, they were found to be muchlower. In real operations contamination of samples by the flow meter would notoccur since the metals are extracted onto columns before the seawater passesthrough the flow meter. During blank collection, one of the thermistors in theflow meter was severely damaged and replaced with a partially repairedthermistor. The flow meter worked intermittently and hence not reliably with thereplacement thermistor.The columns which were to be used with the sampler were also tested.Each column was cleaned with acid until blank levels were low. They were thenrinsed with DDI water and left for one week. The blank levels of the columnswere found to be extremely high for Mn, Ni, Cu, Zn and Pb. Off-line tests wereconducted on the 8-HQ on silica resin to determine its stability in 2 N nitric acid52and in DDI water over a one week period. Higher blanks were observed for theresin stored in DDI than for the resin stored in 2 N nitric acid. Though both hadhigher blank levels than that of the newly cleaned resin. Thus, the resin wouldhave to be freshly cleaned before used with the sampler.The column, without resin was also tested since some metal is present inthe flangeless fitting used for the columns. High blanks were observed afterstoring the column for one week after cleaning. It was concluded that a newsturdy, metal free miniature column would need to be designed, or replace the Flfittings with metal free ones.26 ConclusionsAfter consultation with the Department of Chemistry mechanical shop, itwas decided that using the existing sampler to collect uncontaminated tracemetal samples would not be possible after the extensive testing involved.Instead, a second generation sampler, based on the prototype, with all seawaterwetted sampling components replaced, be built before contaminant-free tracemetal samples could be collected in natural waters.53CHAPTER 3: EXPERIMENTAL AND TECHNIQUE DEVELOPMENTThis chapter details the development of an on-linepreconcentration/matrix separation FI-ICP-MS manifold using a chelating resinof 8-hydroxyquinoline on silica to determine multiple elements from seawaterunder one set of conditions. The elements successfully analyzed using thissystem were Zn, Cd, Ni, Cu, Pb, Mn, Ga and Nb from seawater adjusted to pH 8.Other elements tested were Cr and Co. Chromium suffered from high variablesystem blanks due to the resin. Cobalt had low system blanks but suffered frominterferences attributed to residual matrix effects caused by preconcentratingseawater.The Fl manifold was designed and built in-house. It could be operatedeither manually or via computer. The chelating resin column was incorporated inthe sample loop in such a manner that the directions of flow of the seawatersample and eluent were opposite. This reduced column packing, preventedseawater from entering the ICP-MS, and altered the elution patterns of the tracemetals such that they were all eluted simultaneously. Up to 13 isotopes weresimultaneously determined using the peak jump mode of the ICP-MS. This wasan improvement on other on-line Fl-ICP-MS methods using “multiple elements”software of their ICP-MS which could typically measure up to 4 isotopessimultaneously [77,78].3.1 Materials and Reagents3.1.1 ReagentsAll reagents were prepared using distilled deionized (DDI) water (18 Mc2,Nanopure, Barnstead/Thermolyne Corp., Dubuque, IA and Millipore WatersAssociates, Mississauga, ON). A stock mixed metal solution was prepared byserial dilution of 1000 ppm atomic absorption standards ( Johnson Matthey Inc.,54Seabrook, NH, and J.T. Baker Chemical Co., Phillipsburg, NJ) in 0.1% (v/v) nitricacid (double subboiling-distilled in quartz, Seastar Chemicals Inc., Sidney, BC)and used for standard additions. In the rest of this dissertation the prefix “Q-”will denote ultra clean acids and bases. Samples were pH adjusted usingQ-ammonium and Q-acetic acid (Seastar Chemicals Inc.). Q-nitric acid was alsoused to make 2.0 N Q-HNO3for column elution and cleaning.3.1.2 BottlesAll new polyethylene (PE) bottles used for trace metal work were firstrinsed with acetone to remove any organic residue. The bottles were thenrinsed with DDI water, filled with 4 N HCI (reagent grade, BDH mc, Toronto, ON)and heated overnight at 65°C. The bottles were not completely filled to allow forany expansion of the acid during the heating. The next day, the bottles wereremoved from the oven, inverted and left overnight to cool. The bottles werethen rinsed with DDI water and stored in 0.1% Q-nitric acid until use. Bottleswhich previously contained seawater were rinsed well with DDI water and storedin 0.1 to I % Q-nitric acid prior to reuse.3.1.3 Seawater StandardsNASS-3 Open Ocean Seawater Reference Material (National ResearchCouncil of Canada, Ottawa, ON), a seawater standard, was used to assess theaccuracy and precision of the on-line method developed for trace metal analysisin seawater.3.1.4 Resins8-hydroxyquinoline (8-HQ) on silica resin was synthesized in-house byL. Yang (Department of Chemistry, UBC), using the methods published byMarshall and Mottola [106]. The 8-HQ on Fractogel (TSK) was synthesized55previously by Dr. K.J. Orians using the method published by Landing et a!. [26].The 8-HQ on XE-305 resin was purchased from Seastar Chemicals. Chelex-100was purchased from Bio-Rad Laboratories (Richmond, VA).3.2 Sample Collection3.2.1 Seawater SamplesSamples were collected by the author and/or K.J. Orians, B.A. McKelvey,R.K. Mugo and H.R.C. MacLean ( Departments of Chemistry and Oceanography,UBC). Trace-metal clean methods developed by Bruland et al. [17] were used.Acid cleaned Teflon®lined “Go-Flo” bottles (30 L, General Oceanic, FL) weresuspended on Kevlar line. The bottles were closed prior to being lowered intothe ocean to avoid potential contaminants present in the ocean’s surfacemicro-layer. The bottles were opened once they had reached a depth of 5 to10 m, and then lowered to the desired depths. At the depth of sampling, thebottles were allowed to flush for several minutes before they were closed,triggered by a Teflon® messenger (Department of Chemistry mechanical shop,UBC).Once the bottles were brought back on board ship, they were securednext to a clean area in preparation for filtering the samples. This clean room hadwalls, ceiling, and all exposed surfaces covered with polyethylene sheets andduct tape. Placed inside this makeshift clean room was a high efficiency particleair (HEPA) filter which was used to create a slight positive pressure inside theroom. Equipment used for filtering, collecting and acidifying samples was alsoinside the clean room. Samples were filtered at sea in this clean room through0.45 polycarbonate membrane filters using a 10 psi N2 over-pressure andthe filtrates were collected in acid leached PE bottles. The samples were thenacidified to pH 2 with 2 mIs 6N Q-HCI per litre of seawater prior to storage.56Further processing and analysis was carried out in a shore-based cleanlaboratory.3.3 On-Line Fl-ICP-MS Instrumentation3.3.1 Apparatus for Flow Injection ManifoldThe Fl manifold used for this work incorporates the chelating column inthe sample loop. In this configuration, the column can be considered as aspecial form of a sample loop [58]. The analyte is concentrated on the columnwhich is analogous to the filling of the sample loop in conventional FIA. Theanalyte is then stripped from the column and analyzed which is analogous to theinjection of the sample into the carrier stream. ValvesTwo valves were used in the manifold. A 2-way switching valve ( BiovalveCorp), consisting of two normally closed ( N/C) solenoids, was used to switchbetween the column rinse solution and the seawater sample. This valve waselectronically controlled through a relay allowing one to switch the valvemanually, or by a computer through an IBM data acquisition and control adapter(DACA) board (Mendelson Electronics, Dayton, OH) using one digital I/O line.For the sake of clarity, this valve will be referred to as the “switching valve” forthe remainder of this work.A second valve, a 6-port injection valve with pneumatic actuator(Rheodyne Inc., Cotati, CA), which needed a pressure of 80 psi to operate, wasused to switch the column between sample preconcentration (load position) andelution (inject position). Electronics designed in-house [110] were used tocontrol the pneumatic actuator either manually or through the connected57computer. For the sake of clarity, this valve will be referred to as the “injectionvalve” for the remainder of this work. Peristaltic PumpA six channel Alitea peristaltic pump (Alitea USA, Medina, WA) was usedto transport seawater or rinse solution through the column. The pump wascontrolled by the computer through an analog to digital (AID) channel on the IBMDACA board. Clear Tygon pump tubing (Cole-Parmer, Chicago, IL) was usedwith the pump. When incorporated into the flow manifold, the pump operated atflow rates between 0 and 5 mI/mm. Design of the Extraction Column and Flow Injection FittingsThe extraction column was designed in-house. The body of the columnconsisted of a 5 cm length piece of 1.6 mm i.d. Teflon® tubing with flangelessfittings (Omnifit) at both ends. These were screwed into a Teflon® coupling,consisting of a plug with a 0.8 mm hole drilled into its middle. A 74 pmfluorocarbon-weave filter frit (Spectrum, Los Angeles, CA), placed between theplug and the column body, was used to keep the resin inside the column: Thefilter frit was cut into a small circle to fit inside of a lip machined into the plug ofthe coupling. The chelating resin column was incorporated into the manifoldwith standard flow injection fittings. The rest of the manifold was constructed outof 0.8 mm i.d. Teflon tubing using standard FIA fittings (Omnifit, Cole-Parmer,Chicago, IL) and was acid cleaned for several days prior to being used foron-line work.Prior to assembly of the columns, the Teflon couplings and frits were acidcleaned using the procedure previously described for cleaning the PE bottles.To load the resin into a column, one end of the column body was connected toone fritlcoupling ensemble and a syringe loaded with ca. 300 p1 of resin58suspended in DDI water was attached to the other end. Once the resin wasloaded into the column, the syringe was replaced with the other frit/couplingensemble and the column was sealed with Teflon plugs (Omnifit). Prior to useon-line, the column was incorporated into the on-line Fl-ICP-MS manifold andmetal background levels were monitored while acid was run through themanifold. During this process, the column was rinsed at a flow rate of 0.75mI/mm with 2 N Q-nitric acid until the background levels matched those of theacid.3.3.2 On-Line FI-ICP-MS Manifold used for PreconcentrationA schematic of the manifold used for on-line preconcentration and matrixseparation is shown in Figure 3.1. The 2-way switching valve was placedupstream of the pump, thus either the seawater or rinse streams would be drawninto the pump. The injection valve, with the chelating resin column in the sampleloop, was placed downstream from the pump. In the sample load position eitherrinse or seawater passes through the column and to waste.A second peristaltic pump (Gilson), forming part of the VG PlasmaQuadsample introduction system, continuously pumped I % nitric acid rinse into theICP-MS. The injection valve was connected to the PlasmaQuad between thissecond pump and the ICP-MS. To flush the Fl system, the acid rinse solutionwas replaced with 2 N Q-nitric acid prior to switching the injection valve to theelute position. The eluent was not continuously run through the ICP-MS toconserve the eluent and to minimize any deterioration of the sample cone andother parts of the ICP-MS. Since only one switching valve was available,switching between the I % nitric acid rinse and the eluent (2N Q-HNO3)wascarried out manually.59(A)O.75m1/min(B)rinseseawater2N nitric acidrinseseawaterto ICP-MSto waste6-port injection valvewith chelating columnto ICP-MSto wasteFigure 3.1 On-line Fl-ICP-MS preconcentration manifold used for:(A) Loading: The injection valve is in the sample load position, the2-way valve is in the seawater position. 1 % nitric acid wash isgoing to the ICP-MS.(B) Elution: After the column is rinsed to remove any seawater,the injection valve is switched to the elute position and now 2 N Qnitric acid enters through the column in the opposite direction towhich the sample was loaded. During elution, the Alitea pump isoff, and the 2-way switching valve is left in the rinse position, readyfor the next sample.A typical operation is described in detail: The 2-way switching valve isset to the rinse position, the pump turns on and the rinse solution is pumpedthrough the column for a pre-determined time interval. The 2-way switchingvalve then switches to the seawater position to pump the seawater through thecolumn. Finally, the switching valve returns to the rinse position to remove any1% acid washpumptraces of seawater. After rinsing, the manifold pump stops and the injection60valve switches to the elute position, allowing the eluent to enter the column inthe opposite direction to the loading of sample. The eluent, now containing thetrace metals stripped from the resin, enters the ICP-MS for metal determination.During the sample detection, the eluent continues flowing through the column,cleaning it and readying the column for another sample.3.3.3 Automation of the Fl manifold and Data CollectionThe Fl manifold was controlled using a 386 SX computer via an IBMDACA board. The computer controlled the operation of the 2-way switchingvalve, the injection valve and the Alitea pump. The original program FlArun,written in BASIC 7.0 (Microsoft) by Dr. 0. Lee as a more complex version of theflow injection development and optimization (FIDO) system software [110], wasmodified for this task. Pump CalibrationThe Alitea pump was calibrated using a subprogram within the controlprogram before use. Before running the calibration subprogram, the manifoldwas configured with the 2-way valve in the seawater stream position and theinjection valve in the sample load position with the chelating resin column inplace. The pump was manually set to its maximum speed. The pump speedwas controlled by adjusting the voltage to the pump via the computer through theAID channel.The calibration subprogram required the input of liquid density, length oftime to run the calibration, the pump speed setting (between 0 and 4095) andthe initial weight of the flask which the water is collected in. The program thenruns the pump at the speed chosen for the appropriate time and then asks forthe final weight of the flask. The subprogram then extrapolated a working flowrate range in mllmin for the on-line system from the data entered. These results61were then saved to a file which was accessed each time the manifold controlprogram was initiated. This calibration was repeated whenever modificationswere made to the system (i.e., replacing column, pump or Teflon tubing). Automation and Manifold ControlThe Fl manifold was computer controlled when used on-line with theICP-MS. The system was first incorporated into the ICP-MS sample introductionsystem and the subprogram which controlled the manifold was selected from themenu of the control program FlArun. The correct calibration file was chosen andthe flow rate (usually 3 mI/mm) was selected.Variables for each preconcentration/elution cycle were the length of timeneeded to rinse the column (at the preset flow rate) and the volume of sample tobe loaded. Data CollectionThe computer of the Fl manifold was not interlaced to the ICP-MS, thusdata were collected by the computer and software which controlled the ICP-MS(section The sample acquisition time was manually set such that.datawas collected during the time the eluted metal concentrations were highest. Thiswas determined by monitoring a mass of one of the metals during elution usingsingle ion monitoring mode (SIM). More detail about SIM and general ICP-MSoperations are given in the following paragraphs.3.3.4 ICP-MSA VG “PQ2 Turbo Plus” ICP-MS was used for both on-line and off-linework. A schematic of this instrument was shown previously in Chapter 1 asFigure 1.4. The system was equipped with a VG ICP torch and extractionsystem, an SX 300 quadrupole mass analyzer, and a channel electron multiplier62(Galileo Electro-Optics Corp). Data were collected with a Dell 486 computerequipped with 01S2 and PQ Vision 4.1.1 software. Pure (99.998 %) argon gas(Medigas, Vancouver, BC, Canada) was used as both plasma and carrier gas. Operating ConditionsThe IC P-MS was ignited and allowed to warm up for a minimum of 30minutes before optimizing the operating parameters. The mass analyzer wasmanually tuned to either m/z 115 or 238 to monitor either In or U in a 10 ppbtune solution containing these two elements, Ba, Co, Pb and Bi. The tunesolution was run through the ICP-MS and the signal to the mass analyzer wasoptimized by adjusting the argon gas flow rate(s), the distance between thesampling cone and the load coil, the torch position and the lens settings. Table3.1 shows the typical parameter ranges used for the quantitative work. Onceoptimized, the short term stability of the ICP-MS was checked using thescanning mode to measure the response of all elements in the tune solution fora 60 second acquisition time, repeated 10 times. The full mass range wasscanned continuously except for masses affected by the plasma (e.g. 40Ar,40Ar16Oand 40Ar2). The smoothness of the peak shapes were ascertained byvisually inspecting one of the full scans. Peak resolutions were checked byexamining the extent of separation between the and 11B isotopes and the206Pb, 207Pb and 208Pb isotopes. To achieve a good separation of the isotopesand still maintain the best possible sensitivity, the resolution (R) dial and thepeak shape (tIM) dial (which adjusts the peak width at 5 % peak height) wereused.63Parameter Typical Value(s)RF power (W) 1350Argon gas flow rate (L/min):Cooling gas 13.72 to 13.85Auxiliary gas 0.494 to 0.505Nebulizer gas 0.800 to 1.000Sampling position (mm above load coil) 13Sampler cone (nickel) orifice (mm) 1.0Skimmer cone (nickel) diameter (mm) 0.7Ion lens settings (V):Extraction lens -160 to -210Collector lens -2.0 to 0Li -2.5 toOL2 -60 to -30L3 Oto+5L4 -50 to -42Pole Bias -3to-4Operating pressure (mbar):Interface running pressure <0.1x104Expansion pressure 2.2 to 2.9Analyzer pressure (2.2 to 2.8)x106Table 3.1 ICP-MS Operation Conditions64In the work presented here, the instrument was used in multichannel peakjump mode. In peak jump mode, the quadrupole jumps from selected mass tomass, and stays at each mass for a set dwell time. This mode was used with a10.24 millisecond dwell time, one point per peak and a 20 second acquisitiontime. PlasmaQuad Control and SoftwareThe computer control of the in-house automated Fl manifold was notinterfaced to the PlasmaQuad (PQ) system due to the incompatibility of the twosystems. The VG system had a very complex interface which was not intendedto be altered. A RS-232 connection exists on the VG instrument for theinterfacing of the commercial Fl system that VG markets, but it was not suitablefor any other systems, including the Fl system developed for this work.The PQ program was manually controlled to make the desiredmeasurements across the eluent peak area. As soon as the injection valveswitched to the elute position, the program was triggered, and measurementswere made after a preset interval which allowed the eluent peak time to enter themass spectrometer. The time interval between triggering the PQ and taking themeasurement had been predetermined using the single ion monitoring mode ofits program.In the single ion monitoring mode (SIM), a single mass is continuouslymonitored over time, with the resulting measurement in the form of a peak.Thus, the elution peak can be observed and from this, the time the peak takes toreach the ICP-MS and the width of the peak can be determined. Once the timebetween elution and detection was determined, the SIM mode was used todetect any changes only when either the ICP-MS sample introductory system orthe Fl manifold had been altered, e.g. pump tubing replaced.65In this work the Cd signal was monitored in SIM mode to determine thelength of time between the switching of the injection valve to the elution positionand peak maximum reaching the ICP-MS mass analyzer. A typical response isshown in Figure 3.2. SIM scans of other elements are shown in APPENDIX D.From this, the PQ was triggered to wait for 25 seconds before collecting data for20 seconds (over the peak maximum). A longer collection acquisition resulted inlower total counts per second (cps), while shorter times resulted in largervariations in the responses of replicate analyses.14001200R 1000awfeco$ 6004002000.0012015 losFigure 3.2 A two minute SIM mode scan of 114Cd.663.4 Method DevelopmentThe work presented in this section was performed to optimize theoperation of the on-line Fl-ICP-MS system.3.4.1 Chelating ResinsSeveral resins were studied to determine their potential for on-linemulti-elemental preconcentration using the Fl manifold with ICP-MS detection.This on-line work was also necessary to find the ideal resin to use in the in situsampler discussed in Chapter 2. The chelating resin of choice would:1. Preconcentrate many metals over a broad pH range.2. Extract metals from seawater at flow rates between 2 and 5 mI/mm.3. Not suffer any back-pressure effects at these flow rates.4. Not change size with a change in pH.5. Have no or minimal degradation of the functional group over time.6. Have a high metal complexing capacity to minimize resin volume andrisk of column break through.7. Have quick exchange kinetics with the metals in seawater.8. Be easy to synthesize, or be relatively inexpensive if availablecommercially.The four resins chosen for study were 8-hydroxyquinoline (8-HQ) onsilica, 8-HQ on XE-305, 8-HQ on TSK and Chelex-1 00. Studies were carried outon-line using unspiked and spiked seawater samples, divided into subsampleswith each subsample adjusted to a different pH between 3 and 8. Half of theseawater samples were spiked with 0.5 ppb of Cd, Cu, Pb, Mn, Ni and Zn.Approximately 350 .tl of each resin was loaded into the individual columns. As aresult of these studies, 8-HQ on silica was used for all further work.Explanations for this choice are given below.673.4.1.1 Chelex-1 00Chelex-100 is known to shrink and swell with changing pH, being largestin its ammonium form and smallest in its hydrogen form. Chelex-1 00 consists ofa polystyrene matrix with iminodiacetic acid functional groups. It has slowexchange kinetics with trace metals, which may result in less than completerecoveries when used at flow rates greater than 0.5 mI/mm [105]. This resin wasloaded in a column in its ammonium form to ensure that the Chelex-lOC wouldnot exceed the column volume with changing pH. During the preconcentrationthere was no leakage of the column nor any problems with back pressure.When eluting the column with the acid, the resin compacted into one corner ofthe column causing enormous back pressure on the system, and attempts toredistribute the resin by agitation of the column and by passing a higher pHsolution through the resin did not work. 8-HQ on TSKThis resin was considered since its use with on-line FIA systems for tracemetals has been widely reported [73, 75, 76]. In the current work, severeproblems with the back pressure, experienced when using flow rates greaterthan 2 mI/mm, curtailed further study. This was attributed to the age andprevious usage of the resin, resulting in the resin backbone breaking up intofiner particles. Attempts to synthesize the resin in-house resulted in break-up ofthe polymer backbone during synthesis. Other reasons were attributed to thecolumn design and volume used. In other work published [73, 75, 76], resinvolumes used were approximately 100 p1 (cf. 350 p1 used here). The resin wasloaded into columns made of Tygon pump tubing held in place by glass wool ateach end. Glass wool was not used here since it could be a potentialcontamination source for metals such as Zn and Pb.683.4.1.3 8-HQ on XE-305This resin was studied since it is marketed by the Axys Group for tracemetal work and for use with the INFILTREX II sampler. Chemically, this resinhas the 8-HQ coupled to a styrene-divinylbenzene backbone [28]. The 8-HQ onXE-305 has a much larger bead size than the other resins used here (1 mmdiameter vs. <200 pm) which results in fewer chelating sites per unit volume.This resin did not change size with pH, nor did it suffer frombackpressure. However, using this resin in the on-line system resulted in lowsignal response for of the most trace metals studied, compared to 8-HQ on silica(section 8-HQ on silicaThis resin has been successfully used to extract Cr, Mn, Co, Ni Cu, Zn,Cd and Pb at pH between 6 to 8 in the NASS-3 and CASS-2 seawater referencematerials and it has been used for on-line work with both ICP-AES and ICP-MS[27, 77, 78, 81]. Furthermore, this resin is simple to synthesize in comparison to8-HQ on XE-305 [28,106]. However, potential problems with the resin includedthe possibility of metals being leached from the silica and the likelihood thatextended exposure of the resin to pH of 7 and higher could cause the chelate tohydrolyze off. Comparing 8-HQ on XE-305 and Silica BackbonesA comparison was made between the 8-HQ on XE-305 and silicabackbones with respect to their suitability for on-line work. Both resins, inidentical on-line configurations were used to measure seawater adjusted to pH 8and spiked with 0.5 ppb of Mn, Ni, Cu, Cd and Pb, using Ga as an internalstandard. A flow rate of 3 mI/mm was used, though in further studies the 8-HQon XE-305 resin was also evaluated at a flow rate of 1.5 mI/mm. The results69shown in Table 3.2 were corrected with the internal standard and blanksubtracted.At 3 mI/mm, the use of the silica based 8-HQ resin resulted in highersignals for all the elements measured. When the responses of the XE-305 resinat 3 mI/mm and at 1.5 mI/mm were compared, a marked increase for five of thesix elements is apparent (not Cd) at the slower flow rate. The results shown inTable 3.2 were used only to decide on the suitability of each resin for furtherwork on-line and for use with the in situ sampler. As a result of these studies,the remainder of the on-line work proceeded using the 8-HQ on silica resin.Isotope Silica resin XE-305 resin XE-305 resin3ml/min 3m1/min 1.5ml/minMn55 2770 1907 2767Ni58 2088 155* 1116Cu65 6958 2681 3621Zn66 4193 1671 2414Cd 114 2387 1440 973Pb 208 8589 6288 7266Table 3.2 Response of the 6 metals from 6 mIs of a 0.5 ppb spiked seawatersample adjusted to pH 8. The average of two trials are shown forall results using 3 mI/mm flow rate except where denoted by an *(one bad result for that element). All results are in integratedcounts per second (CPS).The drawbacks to the 8-HQ on silica resin, i.e., leaching of metals fromthe silica backbone and hydrolysis of the 8-HQ functional group, were not foundto be a problem. The resin was cleaned before analysis, and column blanksmeasured throughout the day showed no increase. The same column was used70for up to 4 months at a time with no visible signs of resin and performancedegradation.3.4.2 Silica based 8-HQ pH Studies and Recovery TestsOn-line experiments using the Fl manifold were used to determine theoptimum pH for the metals of interest and to determine the best pH to use formulti-elemental analyses. On-Line StudiesSeven 100 ml aliquots of seawater were adjusted to pH values between 2and 8. Each pH adjusted sample was divided into two subsamples, one leftunspiked and the other spiked with 1000 p1 of the mixed metal stock solutionlisted in Table 3.3. For each subsample, three 6 ml seawater volumes werepreconcentrated and eluted on-line for each sample using the general on-lineFl-ICP-MS procedures described earlier in section 3.3.2. The eluent contained0.5 ppb Rh as an internal standard. The results, shown in Figure 3.3, arenormalized to the highest value as the absolute recoveries cannot bedetermined with this type of system. Since this system incorporated FIA with itsbenefits including reproducible timing, 100% recoveries were not necessary aslong as the metal-resin interactions stayed constant throughout a set ofexperiments (i.e., under identical pH and flow rates).ci) Cl) 0 Cl) a)________________________________________________ci N (0 E 0 2Figure3.3PlotsofthepHdependencyoftheelementsusingtheon-linesystem.PointsaretheaverageofthreemeasurementsanderrorbarsrepresentIs.Responseswerenormalizedtothemaximumsignalofeachelement(inCPS).TwoisotopesofNiandCuareshown.•IIIGa--.-•.—IIIII123456789Zn-..—IIIIIII-Ni-B 6 —IIIIINb •....:Cu-Ei—IIIIIIICd0-..IIIIII123456789ITIIIII23456789pH123456789—.172Metal Concentration (ppb)Cd 10Cu 100Ga IMn 20Nb 10Ni 100Pb 2Zn 100Table 3.3 Concentration of metals in the mixed standard solutionused for standard additions.All elements showed smooth responses with pH except for Nb. The Nbresponse at pH 4 and 8 seem suspect since there was no gradual increase insignal response with changing pH, possibly indicating contaminated bottles forthe spiked samples at these two pH. If these points are ignored, it can be seenthat the recovery of Nb at pH 3, 5, 6 and 7 are similar, indicating a broad workingpH range for Nb, suggesting that the response of Nb at pH 4 should be similar tothat of the working range. At pH 8, the on-line results of Nb in the seawatersamples indicated that all the samples analyzed, spiked and unspiked, gaveconsistent results with good calibration curves. The pH chosen for subsequentstudies was pH 8, since all elements had optimal or near optimal responses atthis pH, except Cu.Absolute responses at optimum pH and at pH 8 for the added spikedmetals after preconcentrating 6 mIs are shown in Table 3.4. All responses were73greater than I 0 cps, even for the elements Mn, Cd, Pb, Ga and Nb, which werepresent in sub ppb concentrations.Spiked Optimum Response at ResponseIsotope seawater pH optimum pH at H 8(ppb) (x i03 CPS) (x 10 CPS)Mn55 0.4 8 109± 12 109± 12Ni58 2.0 5-8 499±23 497 ±27Ni60 2.0 5-8 260.±11 217± 12Cu63 2.0 3-6 472 ±37 137 ±29Cu65 2.0 3-6 292 ±21 71 ±2Zn 66 2.0 5-8 308 ±56 259 ±24Ga71 0.02 7-8 12.4±1.0 12.4±1.0Nb 93 0.2 3-7 5.2 ± 0.4 16.1 ± 1 .8Cd 114 0.2 8 80.6 ± 5.6 80.6 ± 5.6Pb 208 0.04 7-8 58.3 ± 6.6 57.4 ± 2.0Table 3.4 Results of the on-line pH studies. The response at optimum pHand pH 8 for each element is the average of the three analyses ±I s. All measurements were corrected for instrument drift using Rhas the internal standard. NB. **Samples believed to be bad.3.4.3 Flow RateThe extraction efficiency of a resin is dependent on the flow rate used topreconcentrate the sample onto a resin column. Slowing the rate of flow of asample can increase the extraction efficiency of a resin, but the length of timerequired to perform this extraction may make the use of this flow rate impractical.In on-line Fl manifolds used for the preconcentration of sample onto a resin, use74of the optimal flow rate is not necessary to obtain good results, as long as theflow rate stays constant throughout the entire experiment. When using an Flmanifold on-line with an instrument such as an ICP-MS, the time taken for eachanalysis is an important consideration since the ICP-MS is operating during thepreconcentration cycle of the Fl manifold. A lengthy preconcentration time,where no analyses are being made, not only reduces sample throughput butalso increases operating costs, defeating the purpose of an on-line system.The maximum flow rate of the preconcentration manifold was 5 mI/mm,however flow rates between I and 4 mI/mm were examined using 6 mIs of spikedseawater adjusted to pH 8 for sample loading and 2 mIs of DDI to rinse thecolumn between sample loading and eluting. The time needed for eachpreconcentration cycle at each of these flow rates are shown in Table 3.5. Theresults are displayed in Figure 3.4. For all elements, the best extractionefficiency was achieved at I mI/mm, with the extraction efficiency leveling to60% of the optimum response between flow rates of 2 and 4 mI/mm.Flow rate (mI/mm) Preconcentration cycleI 10mm2 5mm3 3min20sec4 2min30secTable 3.5 Time per preconcentration cycle using 6 mIs of seawater andrinsing with 2 mIs of DDI before and after sample loading.N.B. Add 2 minutes for elution to obtain time of I analysis.1.41.2-1.0-ci 00.8-C o0.6-00.4-D0.2-ci N CU____________________________________________________E1.4o1.2-1.0-0.8-0.6-0.4-0.2-0.0Flowrate(mi/mm)Figure3.4Metalresponsevs.flowrateforthe10elements.1,3,2and2measurementsweremadeforflowratesof 1,2,3and4mI/mm, respectively.Responseswerenormalizedtothemaximumsignalofeachelement.TwoisotopesofNiandCuareshown.Mn.. •0.IICu-Zn.-.•s•—IIINi—IIII-Nb•1.1—III012345Ga.. a•.0.—IIII-Cd.I.:IIII012345-Pb- :0III1234510II2345—.1 (7’76For the work presented in this dissertation, the maximum time peranalysis using the on-line Fl-ICP-MS method was chosen to be 10 minutes,resulting in a minimum throughput of 6 analyses per hour. From Table 3.5,using a I mi/mm flow rate would result in less that the six analyses per hour, for6 mIs of sample. For depth profiles, volumes of samples preconcentrated werebetween 12 and 18 mIs for each analysis. Therefore a flow rate of 3 mi/mm waschosen since the time per analysis was decreased and it was the middle of theflow rate range of the manifold.3.4.4 Interelement InterferencesThe ICP-MS does not suffer from line interferences as does the ICP-AES,but it does suffer from overlapping mass to charge ratio (mlz) for some elementsas a result of isobaric interference, doubly charged ions, and formation of oxide-and hydroxide- species [111]. Potential interferences are listed in Table 3.6.Of the possible interfering species listed in Table 3.6, Ca oxides andhydroxides would appear to be the most serious potential interferent since Ca ispresent in mM levels in seawater. During the preconcentration step, the majorseawater ions, including Na, Mg and Ca are almost totally not extracted fromseawater and are in effect separated from the trace elements. The effect of TiOon either Cu or Zn would not be noticeable since Ti is present in the pM rangewhile Cu and Zn are present in the nM range. Chromium and V have isotopesthat as oxides, can interfere with 66Zn. The effects of their oxides should beminimal since V is not significantly retained on the resin and total dissolve Cr ispresent in seawater at concentrations similar to than total dissolved Zn.Furthermore, the natural abundances of 50Cr and 50V are much lower than for66Zn (4.35%,0.24 % and 27.81 %, respectively), and even assuming that 50% ofCr and V existed as oxides in the plasma, their effects would be less than 10% of77the 66Zn signal. On-line work has shown that neither Sn nor Mo are significantlyextracted by the resin column during seawater preconcentration (< 10% of theCd signal), hence their effects, if any, are minimal with respect to Cd. Finally,the effect of doubly charged ions can be minimized by tuning the ICP-MS todecrease their formation in the plasma.Isotope Potential Interferents55Mn58Ni 58Fe, 42Ca16O60Ni 44Ca16O63CU 47Ti16O65Cu 49Ti16O, 130Ba266Zn 50Ti16O, 50V160, 50Cr16O, 132Ba271Ga 141Pr2 142Ce2, 142Nd2, 143Nd293Nb114Cd 114Sn, 98Mo16O208PbTable 3.6 Potential interferents of the 10 isotopes. From reference [111].34.5 System Blanks and Detection LimitsThe system blank was determined by subjecting I ml of pH 8 adjustedDDI to the same seawater loading and eluting procedure five separate times andaveraging the result. The detection limit of the system was determined as threetimes the standard deviation (3s) of the five system blanks. A calibration curveusing 12 mIs of unspiked and spiked seawater adjusted to pH 8 was used to78convert these results to nmol/kg. The system blanks and detection limits of theisotopes are shown in Table 3.7. For some elements, the lowest concentrationin seawater is less than three times the system blank, e.g. Cd. To measurethese elements, a larger volume of seawater would have to be preconcentrated.Isotope System Blank Detection Limit Seawater Range(nmol/kg) (nmol/kg) (nmol/kg)Mn 55 0.169 0.017 0.1-3Ni 58 0.298 0.047 2-12Ni60 0.212 0.040 see Ni 58Cu 63 0.105 0.016 0.5-4.5Cu 65 0.109 0.020 see Cu 63Zn 66 0.191 0.095 0.1-8.2Ga71 0.006 0.001 0.012-.030Nb 93 0.075 0.008 0.01 0-0.200Cd 114 0.007 0.002 0.001-1Pb 208 0.024 0.001 0.003-0.150Table 3.7 The average of five system blanks and detection limits (3s)for 6 mIs of seawater in nmol/kg. Quoted concentration range ofmetals in seawater are from reference [94], except for Nb whichwas determined in this work.3.4.6 Precision and AccuracyIt was particularly important to evaluate the precision of this method sincethe peak jump mode was used to measure the eluent peak maximum. OtherICP-MS instruments were able to monitor up to six individual mass settings inSIM mode simultaneously. The VG PlasmaQuad did not have this capability. In79the majority of off-line preconcentration studies, enough eluent was collected topermit the continuous aspiration of the solution into the ICP-MS. On-linemethods allowed only one measurement per elution, thus multiplemeasurements required multiple processing per sample.The accuracy and precision of this technique was assessed by theanalyses of dissolved Mn, Ni, Cu, Zn, Cd and Pb in seawater referencestandards from the National Research Council of Canada. The referenceseawater sample used was the Open Seawater Reference material (NASS-3). A300 ml portion of this water was adjusted to pH 8 and then subdivided into fourunequal aliquots: a 150 ml sample left unspiked and three separate 50 mlsamples, spiked with 50, 100 and 250 pis of the mixed metal stock solution(Table 3.3). Sample volumes of 12 ml were used for each analysis with 10measurements made on the unspiked subsample and three measurementsmade on each spiked subsample, all using the on-line Fl-ICP-MS method..The results from this study are shown in Table 3.8. Using Student’s t-test,the data show no significant differences between the found and certified resultsfor these metals at the 95 % confidence limit.The precision of this on-line method for Mn, Ni, Cu, Zn, Cd and Pb wasevaluated by examining the relative standard deviations (RSD5) determined for10 replicate analyses on the NASS-3 seawater standard. The RSDs werebetween 5 and 12 % for all elements, except for Cu ,which was higher. Theprecision of this method for dissolved Ga and Nb was also determined, but theaccuracy could not be ascertained in the same manner for the other elements,since no certified values of these two elements exist in seawater standards.80Element NASS3ceiiified NASS3found RSDs(ngIl) (ngII) (%)Mn 31±12 25±1 5Ni 263±63 247±11 6Cu 93±9 88±17 25Zn 218±30 190±12 9Cd 22±4 29±1 5Pb 31±10 32±3 12Ga -- 1.54±0.01 5Nb -- 37±3 5Table 3.8 The determination of dissolved Mn, Ni, Cu, Zn, Cd, Pb, Ga and Nbin NASS-3 seawater reference material.To evaluate the accuracy of the Ga response of this on-line Fl-ICP-MSmethod, a profile of dissolved Ga at station P26 previously reported [3] iscompared with the Ga profile obtained in this study (Figure 3.5). The dissolvedGa distributions obtained with the method developed here is similar to thatobserved previously at station P26, except that the sub-surface maximum isdeeper and more pronounced. Scatter exists in the profile using the on-linemethod, but the method was not optimized when these samples were analyzed.Therefore, the new Ga results are in reasonable agreement with the previouslypublished data.The only seawater data published for Nb comprise two surface watersamples from the English Channel in 1958. These results may not be accuratesince they predate the advent of contamination controls for seawater samplingand handling. Therefore, they cannot be compared to the results obtained in the81North Pacific. Generally, standard addition methods for mono-isotopic elementssuch as Nb are the most accurate.Dissolved Ga (pmol/kg)o 510152025303540 0 510152025303540— I I I I I I — I I I I I I500 A. B.FH1000 • a..g15002000.ü25003000350040001•145005000- -________________Figure 3.5 Dissolved Ga at station P26.A. Data from reference [3]. B. Results from this work,error bars represent the range of duplicate analyses.3.5 Sample PreparationOnce the parameters were optimized, the procedure for all samples andstandard additions analyzed by the on-line Fl-ICP-MS work involved taking 50 to250 ml subsamples from acidified seawater samples. The 50 ml subsamples ofseawater were placed in acid cleaned PE bottles (60 ml), and adjusted to pH 8using Q-ammonia and Q-acetic acid. Calibration curves were run using themethod of standard addition every 3 to 5 samples. For each standard additioncalibration, a 250 ml subsample of seawater was first pH adjusted, and thensubdivided into four acid cleaned DE bottles (60 ml). Three of the bottles werespiked with 50 to 1000 pi of a mixed standard solution (Table 3.3) while the82fourth was left unspiked. All the pH-adjusted bottles, both spiked and unspikedsamples, were then left for 24 hours to allow equilibration.The eluent used to strip the metals off the resin (2 N Q-nitric acid) wasspiked with 0.5 ppb of Rh which acted as an internal standard. This internalstandard was used to correct for any drift in the instrument response during thecourse of the day.Calibration curves for all elements were linear and gave correlationcoefficients, R2, between 0.950 to 0.999 (n= 6 to 12).83CHAPTER 4: OCEANOGRAPHIC RESULTS AND DISCUSSION4.1 Characteristics of the Ocean Stations SampledThe stations sampled in the North Pacific study area are shown in Figure4.1. The surface waters of these stations span five distinct water masses whichare characterized by their temperature and salinity values. The Oyashio Current(Station 1) is characterized by low temperature (T) and low salinity (S) as itcarries water from the Bering Sea and Sea of Okhotsk in the north to theJapanese Islands in the south. The Kuroshio Current (Station 5) flows fromsouth to north along the Asian coast from the equatorial Pacific and ischaracterized by high T and S. Station 10 is in the southern part of the centralgyre and is higher in both T and S as it is located at a lower latitude than theprevious two stations. The North Equatorial Current (Stations 15 and 16) bringshigh T and low S water from North America west across the Pacific Ocean.Station P26 lies at the convergence of the Alaskan Gyre and the North PacificCurrent and has low T and S water. As the North Pacific Current approachesthe North American coast, it begins to flow south creating the California Current.5545N 35 25 15140ENorthPacificstudyarea.•:Stationswhereverticalprofileswerecollected.x:Stationsfrompreviouswork[3]usedforcomparisonsinthisdissertation.A.VERTEXIV.B.VERTEXVA.C.VERTEXVC.Figure4.14150160170180170160150140W854.2 Dissolved Zn, Cd, Ni, Pb, Cu and Mn in the North Pacific OceanProfiles of Zn, Cd, Ni, Pb, Cu and Mn at Stations 1,5,10, 15 and 16 havebeen previously determined by off-line preconcentration with ICP-MS detectionand have been discussed in detail elsewhere [112]. These six elements at thesame stations were analyzed using the on-line Fl-ICP-MS method described inChapter 3 with good results, indicating that this method can be used topreconcentrate and analyze full depth profiles of these elements in one daycompared with up to 2 weeks with conventional processing.4.2.1 Nutrient-type Elements (Zn, Cd and Ni)Nutrient-type elements can have one of three distribution types. One typeresults in deep water regeneration with a deep water maximum similar to that ofSi, which is used by organisms in skeletal structures (e.g. Zn). A second typeshows a shallow regeneration leading to a mid-depth maximum, similar to thatfound for phosphate and nitrate, which are labile soft tissue nutrients (e.g. Cd).The third type results from a combination of shallow and deep regeneration (e.g.Ni). Dissolved Zn in the North PacificDepth profiles of dissolved Zn at Stations 1,5,10, 15, 16 and P26 areshown in Figures 4.2, 4.3 and 4.4. The profiles at these stations agree well withprevious Zn profiles in the North Pacific [35, 112]. Generally, the profiles(Figures 4.2, 4.3 and 4.4) follow those of the “hard-part” nutrient silicate,showing depleted Zn concentrations in surface waters which slowly increasewith depth to broad maxima between 1000 and 1500 m. This is a result of Znbeing removed from surface waters by phytoplankton and incorporated intoskeletal structures (e.g. diatoms), which then sink and are regenerated in deepwaters.86At Station 1, surface water levels of Zn are higher than at the other fivestations (2.5 nmol/kg versus 0.4 -0.6 nmol/kg at Stations 5, 10, 15 and P26 and0.9 nmollkg at Station 16). A deep water maximum at the same site is shallower(9 nmol/kg at 1000 m) compared to the other stations (7 - 9 nmol/kg at 1500 to2000 m). Below this depth the profiles are similar. There is considerable scatterin the Zn data at Station P26 due to the non-optimized procedure used for theanalysis. Allowing for the scatter in the data, the profile agree fairly well withprevious work at this location which showed a deep water maximum between1400 and 1800 m[113].The correlation between dissolved Zn and silicate is estimated by plottingdissolved Zn versus silicate from Stations 1, 5, 10, 15 and 16 (Figure 4.5). Alinear relationship is observed with a slope of 0.0523 Zn/Si (nmol kg1 tM1)and a regression coefficient, R2 of 0.947. The Zn/Si ratio obtained here is notsignificantly different to ratios observed previously at these stations (i.e.,0.0544) [112] and reported for east Pacific Ocean sites (i.e., 0.0535) [18].DissolvedZnconcentration(nmol/kg)0246810120246810120246810120-IIIIII-IIIII..1000-..•2000-.3000-4000-HS-1HS-5HS-10••5000-____“I,,______6000-___________________-___________________1’Figure4.2DissolvedZninthewesternNorthPacific.Eachpointistheaverageoftwoanalyses.Theerrorbarsindicatetherange.Thesymbol“representstheseafloorbottomsatallstations.88Dissolved Zn concentration (nmol/kg)0 2 4 6 8 10 12I I I I I..1000-2000 -3000-4000 -5000 - HS-156000 -________________________0 2 4 6 8 10 12%I I I I..1000- ••2000- :3000- II•I4000 -HS-165000 -6000 -Figure 4.3 Dissolved Zn in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.89Dissolved Zn concentration (nmol/kg)0 2 4 6 8 10 120- I I I.I ••I1000- • ..I•I2000- I I.c3000-4000-F,’,,5000 -P266000 -__________________________Figure 4.4 Dissolved Zn in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.12 -10- •:•o 30 60 90 120 150 180Dissolved S104 (jtM)Figure 4.5 Dissolved Zn vs. the nutrient silicate. Silicate data provided by lOS(Institute of Ocean Science, Sidney, BC)904.2.1.2 Dissolved Cd in the North PacificProfiles of dissolved Cd at Stations 1,5 and 10, 15, 16 and P26 are shownin Figures 4.6, 4.7 and 4.8. The dissolved Cd distributions at all these stationsagree well with previous Cd profiles in the North Pacific [18, 39, 41, 112, 113].Generally, Cd concentrations follow the “soft-part” nutrients, phosphate andnitrate, showing depleted Cd levels in surface waters which rapidly increase withdepth to broad maxima between 600 and 1000 m. The surface waters show highdissolved Cd at Station 1 (0.25 nmol/kg) which decreases to much lower levelsin the Kuroshio Current (HS 5) and central gyre (HS 10) stations (0.03 and 0.01nmol/kg, respectively). Cadmium values in the North Equatorial Pacific surfacewaters (Stations 15 and 16) are also lower than at Station 1(0.01 and 0.015nmol/kg, respectively) and are intermediate (0.15 nmol/kg) in the sub-Arctic gyre(P26). The elevated nutrient levels which occur at Stations 1 and P26 may bedue to isopycnal mixing and outcropping isopycnal surfaces at these sites. Thisresult may be enhanced at Station I due to a higher aeolian (wind-borne dust)input of Cd at this site [6, 113].As for Zn, the mid-depth maximum at Station I occurs at a shallowerdepth (—1.0 nmol/kg between 500 and 100Cm) than at Stations 5, 10, 15 and 16(—0.9 nmol/kg between 800 and 1500 m). At Station P26, the mid-depthmaximum of —0.9 nmol/kg is shallowest, occurring between 200 and 1500 m,also indicating isopycnal mixing with deeper waters further south which havehigher Cd levels. Below 1000 m all profiles are similar, showing slightdecreases in Cd below 1500 m. These observations agree well with previousstudies in these areas.DissolvedCdconcentration(nmol/kg)•I2000-I•I•.3000-4000-••5000-HS-1-“iiHS-5HS-10“I______“I’,6000--______________-_____________Figure4.6DissolvedCdinthewesternNorthPacific.Eachpoint istheaverageoftwoanalyses.Theerrorbarsindicatetherange.CD92Dissolved Cd concentration (nmol/kg)0.0 0.2 0.4 0.6 0.8 1.0 1.20-II I I1000-•. f/I,,2000 -3000 -4000 -5000 - HS-156000 -________________________0.0 0.2 0.4 0.6 0.8 1.0 1.20— I I..1000 -.2000-3000 -4000 -HS-165000 -____6000 -__ ___Figure 4.7 Dissolved Cd in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.Dissolved Cd concentration (nmol/kg)0.0 0.2 0.4 0.6 0.8 1.0 1.20-• HH1000-.2000-E •__-a 3000- 11a)4000-“F,,5000 -P266000 -________________________Figure 4.8 Dissolved Cd in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.The correlations between dissolved Cd and nitrate and phosphate havebeen observed previously [18, 39, 411. A plot of dissolved Cd versus phosphatefrom Stations 1, 5, 10, 15 and 16 is shown in Figure 4.9. The relationship islinear with a slope of 0.302 Cd/P (nmol kg1 jtM1)and a regression coefficient,R2 of 0.943. The slope determined here is lower than that observed at thesestations in previous work (0.325 Cd/P) [112] and to those reported in the eastPacific Ocean (i.e., 0.33 - 0.37) [17, 38].94Figure 4.9 Dissolved Cd vs. the nutrient phosphate. Phosphate dataprovided by lOSc,)0EC.C.)0ci>0C,,Co.1.21 . 0.5 1 .0 1.5 2.0 2.5 3.0 3.5Dissolved P043 (tM) Dissolved Ni in the North PacificProfiles of dissolved Ni at Stations 1,5, 10, 15, 16 and P26 are shown inFigures 4.10 4.11 and 4.12 and agree well with previous observations of Nidistributions in the North Pacific [1 8, 42, 112]. Generally, Ni in seawater has abiointermediate nutrient-type distribution with partial depletion in surface waters,a rapid increase in concentration in mid-depth waters similar to “soft-part”nutrients, phosphate and nitrate, and a broad maximum in deeper waters similarto “hard-part” nutrient, silicate.At Station 1, the surface concentration of Ni is slightly higher than atStations 5, 10 and P26 (3.5 versus 3 nmol/kg) and considerably higher than atStations 15 and 16 (—1.5 nmol/kg). The Ni concentration increases rapidly to—8 nmol/kg at 700 m, and then slowly to a broad maximum of 9-11 nmol/kgbetween 1500 and 3500 m, except at Station 1, which occurs between 1000 mand 2500 m and thus is shallower. This shallowing of the maximum, as for Znand Cd, indicates isopycnal outcropping of high nutrient waters at this station.DissolvedNiconcentration(nmol/kg)0246810121402468101214024681012140-II-IIII-IIII1000-..‘—2000--c-a3000-4000-HS-1HS-5HS-10.5000-____‘I’,,I,,,,6000--_____________-_____________Figure4.10DissolvedNiinthewesternNorthPacific.Eachpointistheaverageoftwoanalyses.Theerrorbarsindicatetherange.Co (7’96Dissolved Ni concentration (nmol/kg)0 2 4 6 8 10 12 140- I I I...1000-2000 -3000 -4000 -5000 - HS-156000 -_________________________0- . I I I I.•.1000- ••.2000-.3000-4000-HS-165000 -___“I6000 -_________Figure 4.11 Dissolved Ni in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.97Dissolved Ni concentration (nmol/kg)0 2 4 6 8 10 12 140- I I I1000- I I2000-3000-4000-•‘‘7/,,5000- P266000 -________________________Figure 4.12 Dissolved Ni in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.Dissolved Ni versus phosphate and silicate at Stations 1, 5, 10, 15 and 16are shown in Figure 4.13. The correlation between Ni and phosphate(regression coefficient, R2 = 0.804, Figure 4.13A) visually looks better than thatbetween Ni and silicate (R2 = 0.855, Figure 4.13B). The Ni-phosphaterelationship in the upper 800 m (Figure 4.13C) is stronger (R2 = 0.845) than thatof Ni-phosphate at all depths and the relationship between Ni and silicate below800 m (Figure 4.13D) is much worse. The improvement in the Ni-phosphaterelationship in the upper 800 m agrees with Bruland’s observations [18], thoughhe also observed that the Ni-silicate relationship improved below 800 m, which isclearly not the case in this work.9814 -____________________- -. S14-S12- C D10- y 1.96x + 1.930.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 30 60 90 120 150 180Dissolved P043 (pM) Dissolved Si04 (.tM)Figure 4.13 Ni versus phosphate (A, C) and silicate (B, D).A and B: At all depths. C: Upper 800 m. D: Below 800 m.4.2.2 Nutrient Type with Scavenging Element (Cu)Profiles of dissolved Cu at Stations 1,5 10, 15, 16 and P26 are shown inFigures 4.14, 4.15 and 4.16 and agree reasonably well with Cu distributionspreviously observed in the North Pacific [18, 29, 43, 112, 113]. There is morescatter in these plots, possibly as a result of the poor precision for obtained forCu with the manifold due to the pH used, which was not optimal for Cu extractionfrom seawater (section 3.4.6). Generally, the distribution of Cu is unique, withlow levels in surface waters as it is a required biointermediate nutrient andDissolvedCuconcentration(nmol/kg)52000-...3000-4000-HS-1HS-5HS-105000-771//—“I6000-____________________-____________________—____________________Figure4.14DissolvedCuinthewesternNorthPacific.Eachpointistheaverageoftwoanalyses.Theerrorbarsindicatetherange.(0 (0100Dissolved Cu concentration (nmol/kg)0 1 2 3 4 50-.1I I1000- 1.E 2000-3000-4000 -5000 - HS-156000 -_________________________0 1 2 3 4 50- I I I1000- •..2000-.3000-4000-HS-165000 -6000 -Figure 4.15 Dissolved Cu in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.101Dissolved Cu concentration (nmol/kg)0 1 2 3 4 50- I.1000- .2000-3000- 1•14000-“I5000 -P266000 -_________________________Figure 4.16 Dissolved Cu in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.gradual increase with depth as a result of removal in intermediate and deepwaters and a bottom source [18, 29].Copper levels in the surface waters at all stations are similar, withdissolved Cu at Stations I and 5 (—‘1 nmol/kg) being slightly higher than atStations 10, 15, 16 and P26 (—0.7-0.8 nmollkg). Values increase with depth tolevels between 3.5 and 4.5 nmol/kg at Stations 1, 10, 16 and P26 (the bottomwater value at Station 10 was bad for this element). Station 15 is only 1550 mdeep and the concentration in bottom water is 1.7 nmol/kg; samples below 3500m at Station 5 were not collected. A first order vertical advection diffusion modelhas been previously used to calculate Cu residence times in the deep water(below 1000 m) at these stations. These estimates ranged from 830 to 1100102years [1121, similar to previous studies [18, 29]. An explanation of the model isgiven in section Scavenged Type Element with an External Source (Pb)Profiles of dissolved Pb from Stations 1, 5, 10, 15, 16 and P26 are shownin Figures 4.17, 4.18 and 4.19 and agree well with those observed previously forPb in the North Pacific [45, 46, 112, 113]. Generally, Pb distributions have highsurface values and decreasing concentrations with depth, though some exhibit asub-surface maximum between 300 and 500 m. These profiles verify that thedistribution of Pb in seawater is driven by scavenging removal processes andexternal inputs via aeolian transport.Surface levels of Pb are highest at Station I (— 60 pmol/kg) and decreasewith distance from the Asian coast (30 and 40 pmol/kg at Stations 5 and 10,respectively). Surface Pb levels are low at Stations 15 and 16 (10 and 15pmol/kg, respectively) and intermediate at Station P26 (30 pmol/kg). At StationsI and 5 the Pb concentrations decrease with depth to less than 20 pmol/kg, andno sub-surface maximum is observed. Stations 10, 15 and 16 all show subsurface maxima. Stations 10 and 16 have sub-surface maxima of 40 pmol/kgbetween 200 and 500 m, while at Station 15, a sub-surface maximum of 25pmol/kg at 300 m is observed. The scatter in the Pb data at Station P26 hasobscured the profile, though even with scatter a suggestion of a sub-surfacemaximum is evident. Previous Pb from Station P26 has suggested a sub-surfacemaximum occurring between 300 and 500 m [113]. Below 500m at all stations,the Pb profiles become indistinguishable with Pb levels around 10 to 15 pmol/kgin deep waters.01000.2000•-3000040005000____6000Figure4.17DissolvedPbinthewesternNorthPacific.Eachpointistheaverageoftwoanalyses.Theerrorbarsindicatetherange.0 ()DissolvedPbconcentration(pmol/kg)01020304050600102030405060-II. .••r..HS-5“IHS-1.“I0102030405060IIøiI.—....HS-10.“I,’104Dissolved Pb concentration (pmol/kg)0 10 20 30 40 50 600- •• f-•-••1000- ••“I2000 -3000-U4000 -HS-155000 -6000 -_________________________0 10 20 30 40 50 600- .1,1 I••1000- •••‘ 2000-•3000-U•4000-• HS-165000 -“I6000 -Figure 4.18 Dissolved Pb in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.105Dissolved Pb concentration (pmol/kg)0 10 20 30 40 50 600- ‘__1000- I.2000- F•.3000- •.4000- :“I,5000 -P266000 -___________ ____________Figure 4.19 Dissolved Pb in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.Explanations have been proposed to explain the sub-surface maximaobserved at Stations 10, 15 and 16. The most commonly accepted is that theaeolian Pb input decreased due to reduced consumption of leaded gasolinesince 1974 which may have induced a sub-surface maximum in most regions [9].The data presented here supports this, since the mid-depth maxima of Pb aremuch greater in concentration than surface levels of Pb. Other possibilities havebeen argued for the mid-depth maxima [45], and if they are a factor, their rolewould be minor. One is that the Pb that is released from falling particles isgreater than the scavenging flux at the depth of the mid-depth maximum,resulting in the accumulation of Pb in the water column until the scavenging fluxequals or exceeds the decomposition flux as in deeper waters. Another is that106physical transport might supply Pb to the areas by isopycnal ventilation (i.e.movement of water of the same density from different locations).4.2.4 Oxidative Scavenging Type Elements (Mn)Profiles of dissolved Mn from Stations 1, 5, 10, 15, 16 and P26 are shownin Figures 4.20, 4.21 and 4.22 and agree well with previously observed Mndistributions in the North Pacific [47, 112, 113]. Generally, Stations 5, 10, 15and 16 have high surface values between 0.8 and I nmol/kg, decreasing to asub-surface minimum of 0.15 to 0.7 nmol/kg between 300 and 500 m,coincidental to the zone where dissolved °2 is decreasing, and then increasingto a mid-depth maximum of 0.3 to 1.2 nmol/kg between 1000 and 1500 m in the°2 minimum zone. Stations I and P26 have similar surface and sub-surfaceminima and mid-depth maxima values though the sub-surface minima and mid-depth maxima signals were shallower, occurring between 100 and 300 m andbetween 500 and 1000 m, respectively. Below 1500 m, all stations show Mndecreasing with depth.Previous work has shown that the sources of Mn into the ocean areriverine, either directly or via reducing shelf sediments, atmospheric andsubmarine hydrothermal [48-50]. Manganese participates in a wide range ofbiogeochemical processes, including release from aeolian particles in surfacewaters and adsorbed onto particles. It is also a required micro-nutrient.The Mn sub-surface minimum and mid-depth maximum has been found tobe due to a combination of horizontal advection of waters from reducing shelfsediments and the cycling of dissolved Mn(Il) and particulate Mn(IlI, IV)oxyhydroxides cycling in °2 minimum zone [51]. Profiles of °2 in seawater showhigh surface values, decreasing with depth due to its utilization duringrespiration and then increasing gradually due to upwelling of younger watersDissolvedMnconcentration(nmol/kg)•2000--c.G)3000-04000-HS-1HS-5HS-10•5000-‘I,,,“I’6000-__________________-___________________-___________________Figure4.20DissolvedMninthewesternNorthPacific.Eachpointis theaverageoftwoanalyses.Theerrorbarsindicatetherange.0108Dissolved Mn concentration (nmol/kg)0.0 0.3 0.6 0.9 1.2 1.50--H1 .1.1000- •.___2000 -3000-4000 -HS-155000 -6000 -______ _________________0.0 0.5 1.0 1.5 2.0 2.5 3.00- I I••1000- •..2000- •.3000- •.4000-• HS-165000 -“I6000 -__ _______Figure 4.21 Dissolved Mn in the central North Pacific. Each point is theaverage of two analyses. Error bars indicate the range.N.B. The change in scale of the abscissa.109Dissolved Mn concentration (n mol/kg)0.0 0.3 0.6 0.9 1.2 1.50- I..1000-2000-3000-.4000-“I,5000 -P266000 -__________________________Figure 4.22 Dissolved Mn in the eastern North Pacific in the sub-Arctic gyre.Each point is the average of two analyses. Error bars indicatethe range.higher in 02 originating in the North Atlantic and Antarctic regions. In sub-oxicwaters, particulate Mn(lll, IV) oxyhydroxides are reduced to Mn(ll) giving rise toa dissolved Mn maximum at the 02 minimum [49]. In waters with higher 02concentrations, dissolved Mn is oxidatively scavenged in its particulate form.Plots of dissolved Mn and dissolved °2 are at Stations 1,5,10, 15,16 and P26are shown in Figure 4.23.The data shown in Figure 4.23 agree with previous results [47-50, 112,113]. In surface waters, dissolved Mn is thought to be high due to desorptionfrom aeolian detritus. Beneath the surface, but before the 02 concentrationbegins to decrease, a sub-surface minimum in the Mn signal is observed whichprobable reflects a combination of oxidative scavenging and horizontal110• Dissolved Mn (nmol/kg) 0 Dissolved °2 (uM)• 0.0 0.3 0.6 0.9 1.2 1.5 0.0 0.3 0.6 0.9 1.2 1.5I I I I I I I I I I Io 0 60 120 180 240 300 0 60 120 180 240 300010002000-HS13000 04000 - o 005000 -0-__EHS 152000- 0 H1000 - -ci) 003000 004000- 005000 -0- I___cI2000- 04000- 000- 261000-THS1603000- 05000 -Figure 4.23 Dissolved Mn and °2 versus depth at Stations I, 5, 10, 15, 16 andP26.111advection of waters low in dissolved Mn. At the °2 minimum, a mid-depthmaximum in the Mn signal is observed. This has been attributed to acombination of in situ reduction of particulate Mn (Ill, IV) to dissolved Mn (II) andhorizontal transport of water which has been in contact with reducing slopesediments and is consequently depleted in °2 and enriched in Mn. As 02 levelsincrease slowly with depth, the dissolved Mn concentration decreases, againdue to oxidative scavenging. In deeper waters, between 2500 and 3500 m therelative increase may be attributed to waters enriched in Mn (II) from a nearbyhydrothermal vent if present.1124.3 Dissolved Ga in the North Pacific OceanPast studies in the eastern North Pacific and North Atlantic oceans haveshown that general distributions of dissolved Ga in seawater comprises a subsurface maximum, low concentration in intermediate waters and levels thatincrease with depth in deeper waters [3, 53, 54]. The sub-surface maximum maybe caused by either horizontal advection and/or a vertical process involvingexchange with sinking particles. These studies suggest complex controlsincluding multiple sources, reversible exchange and scavenging processes all ofwhich contribute to the distribution of dissolved Ga in the ocean. The primarysources of Ga to the open ocean may be atmospheric inputs of crustal dust tothe surface waters and diffusion out of the sediments and/or a sediment-surfaceremineralization to the deep water. Asian continental dust source may be amajor atmospheric source of Ga to the North Pacific.Depth profiles of dissolved Ga measured for this study from Stations 1,5and 10, Stations 15 and 16 and Station P26 are presented in Figures 4.24, 4.25and 4.26, respectively. Dissolved Ga concentrations are found to range from 3to 30 pmol/kg in the North Pacific Ocean. The values are low in the surface (4 to14 pmol/kg), and the profiles often show a sub-surface maximum between 300and 500 m, (ranging between 10 and 18 pmol/kg where present), a definite mid-depth minimum between 500 to 1000 m (3 to 9 pmol/kg) and increasingconcentrations with depth (13 to 30 pmol/kg). Generally, these results are inagreement with previously published dissolved Ga data in the North PacificOcean [3].The work presented in the following sections indicates two sources of Gato the oceans. Surface distributions indicate aeolian input from the Asiancontinent, which is known to be a major dust source to the surface waters of theDissolvedGaconcentration(pmol/kg)051015202530051015202530051015202530II—III—Ihl•V_.II:.1000-•..2000-.3000-4000-HS-1HS-5HS-10.5000-____“F,,“I,6000-____________________-____________________-“Figure4.24DissolvedGainthewesternNorthPacific.Eachpointistheaverageoftwoanalyses.Theerrorbarsindicatetherange.C)114Dissolved Ga concentration (pmol/kg)0 5 10 15 20 25 300- I1000-I.,,,,- 2000-3000-04000 -5000 - HS-156000 -_________________________0 5 10 15 20 25 300- ‘‘.FI-1 I I1000 - F..2000- I-.3000-O.4000-HS-165000 -f//Il6000 -_____________________Figure 4.25 Dissolved Ga in the central North Pacific. Each point is theaverage of two analyses. The error bars indicate the range.115Dissolved Ga concentration (pmol/kg)0 10 20 30 40 50 60I I I1000 - a.2000 -•I.3000 -4000-F-HF,,,,5000 -P266000 -________________________Figure 4.26 Dissolved Ga in the sub-Arctic station in the eastern North Pacific.Each point is the average of two analyses. Error bars indicaterange. N.B. Note change in scale on the abscissa.North Pacific. Deep waters indicate bottom water sources such as diffusion fromsediments and/or surface-sediment remineralization. A sub surface maximum isnot always observed in these profiles, but when present may be attributed tovertical exchange processes and/or isopycnal mixing. However, isopycnalmixing cannot explain the high Ga results observed at Station 10, relative to theother stations. Removal by scavenging is indicated throughout the watercolumn.4.3.1 Ga Distribution in Surface WatersThe Ga concentration in surface waters increases from the westernPacific into the central gyre and then decreases again at high latitude. The116surface concentration in the Oyashio Current (Station 1) is 9 - 10 pmol/kg; in theKuroshio Current (Station 5), — 12 pmol/kg; in the central gyre (Station 10), — 14pmol/kg; in Equatorial Current (Stations 15 and 16) 10 and 14 pmol/kgrespectively; and in the sub-Arctic North Pacific (Station P26), — 4 pmol/kg.The Ga distribution in the surface waters resembles the distribution of210Pb, which has an aeolian source. Concentrations of 210Pb were found to behighest in the central gyre surface waters [114]. While there are no Al data fromthe western North Pacific, this metal also has an aeolian source, and like Ga and210Pb exhibits high concentrations in the central gyre that decrease to the east,away from the Asian continent [8, 114]. This is contrary to what is observed inthe dissolved anthropogenic Pb distribution at these stations (section 4.2.3),which shows increasing levels of Pb closer to Asia, consistent with the east-westand north-south gradient in the North Pacific of the dust input from the Asiancontinent.Figure 4.27 shows the global fluxes of mineral aerosol to the ocean [6].Together with Figure 4.1, these data indicate that the dust input at Station 10 isless than that at Stations I and 5. Therefore, it appears that the higher dustinput to Stations I and 5 may be countered by the increased productivity andparticle scavenging in the eutrophic coastal Oyashio and Kuroshio Currentwaters. This would lead to the low dissolved Ga values in the surface watersobserved at Stations I and 5 relative to the levels in the central gyre.The concentrations determined in surface waters from Station 15, atopKarin Ridge in the North Equatorial Current, is similar to those observed in theOyashio and Kuroshio Current (Stations I and 5). Station 16, near Karin Ridgebut also in the Equatorial Current, exhibits a higher Ga concentration in surfacewaters, similar to that found in the central gyre (Station 10). The differencebetween Stations 15 and 16 may be due to patchiness in the upper ocean.117Results obtained for Zn, Cd, Ni, Pb and Mn also show higher concentrations insurface waters at Station 16. The lowest Ga valves are in the high latitudeeastern North Pacific surface waters (P26), due to a combination of lower dustinput in this area (Figure 4.27) and an increase in particle interactions withdissolved Ga due to the known high productivity at this station [113].60E 120’E 180 120W 60W 0_1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I:::::::___ooD___iiiii I 1111111 11111111 I I clii ciFigure 4.27 Global fluxes of mineral aerosol to the oceans in mg m2y(1[6].4.3.2 Ga Distribution in Intermediate WatersNo dissolved Ga sub-surface maxima are found at Stations I and 5.Instead, at Station 1, dissolved Ga steadily decreases from 9 - 10 pmol/kg at thesurface to — 5 pmol/kg between 750 to 1000 m and at Station 5, the surfacemaximum extends down to 500 m and then decreases to a minimum of 5pmol/kg at 100Cm. These profiles differ from vertical distributions in the easternNorth Pacific and North Atlantic Oceans where sub-surface maxima areobserved at depths between 300 and 500 m [3,54]. In the central gyre (Station11810), dissolved Ga shows a sub-surface maximum of —18 pmollkg between 100and 500 m, which then decreases to a mid-depth minimum of 9 pmol/kg at 1000m. This is similar to vertical profiles previously determined in the eastern part ofthe central gyre, but Station 10 exhibits a broader sub-surface maximum [3].At Stations 15 and 16, the Ga concentration decreases to a mid-depthminimum (—9 pmol/kg between 700 and 1000 m and —7 pmol/kg between 500and 700 m at Stations 15 and 16, respectively). The Ga distribution at Station16 is similar to that at Stations I and 5, but with higher concentrations at themid-depth minima. The Ga concentrations in intermediate waters at Stations 15and 16 are lower than at Station 10, suggesting that the former may beintermediate between the high productivity regime at Stations I and 5 and thelow productivity at Station 10. In addition, the dust input to Stations 15 and 16 isexpected to be lower since these sites are more distal from the Asian continent(Figures 4.1 and 4.27).In the high latitude eastern North Pacific (P26), dissolved Ga increasesto a sub-surface maximum of 13 pmol/kg between 300 and 500 m, and thendecreases to a minimum of 3 pmol/kg at 1000 m, presumably due to acombination of less dust input into these waters (Figure 4.27) and an increase inparticle interactions with dissolved Ga due to the extent of biological productivityat this station. These results generally agree with the data obtained from thisstation by Orians and Bruland [3], except that the sub-surface maximum is morepronounced in this study. The higher concentration in bottom water observed inthis work is due to the greater sampling depth (4200 m vs. 3900 m).The mid-depth minima observed in all the dissolved Ga profiles (Figures4.24, 4.25 and 4.26) and the sub-surface maxima observed in the central gyreand the eastern North Pacific could be advective features or the result ofreversible exchange processes with sinking particles. Dissolved Ga could be119associated with solid particles which undergo shallow regeneration, and thereleased Ga could then be adsorbed onto particle surfaces resulting in a mid-depth minimum. This has been argued for Al which has a mid-depth minimum[8] but not a mid-depth maximum. The sub-surface maxima observed atStations 10 and P26, could be due to a combination of increased regeneration atthis depth and reduced Ga reactivity allowing dissolved Ga to reach appreciablelevels before being re-scavenged.Advective origins of mid-depth water features have been suggested fortrace elements including Mn [51] and Pb [45]. Bismuth and 239, 240Pu have subsurface maxima which show no correlation with density and salinity features,implying more complex controls. Advective transport of water with high levels ofdissolved Ga from the ocean boundaries cannot produce the high the subsurface dissolved Ga maximum observed in the central gyre since dissolved Gaconcentrations are lower in coastal waters. Therefore vertical exchangeprocesses seem more probable.To visualize the possible horizontal and vertical processes in the upper1500 m of water in the North Pacific, a contour plot was generated (SURFER,Golden Software, Golden CC), compiled from the data presented here andprevious results [3] (Figure 4.28). This plot indicates that the Ga concentrationsin surface waters increase from the Asian coast (Stations I and 5) to a maximumin the western edge of the central gyre (Stations 10) and that the Ga sub-surfacemaximum does not occur in the western Pacific. Surface water Ga levels alsodecrease in equatorial waters and increase in the eastern part of the centralgyre (VERTEX IV), which shows the presence of the sub-surface maximum.Eastward of the central gyre, surface concentrations of Ga decrease and thesub-surface maximum becomes less pronounced (VERTEX VA and VC). The 12120pmol/kg contour line in this figure does shallow considerably at Station 16,indicating a north-south effect since it is the most southerly station shown.The Ga distribution shown in Figure 4.28 suggests that the increasing Gaconcentrations and broadening surface maxima between Stations I and 5 andthe eventual formation of a sub-surface maximum of greater concentration atStation 10 is likely due to the extent of reversible exchange with sinking particlesat each station and not to horizontal advection from elsewhere. Station P26 isnot included in the plot since it is at least 20° north of the other stations. Notethat the low dissolved Ga concentrations observed in the high latitude easternNorth Pacific indicate that lateral advection from this area is not the source ofthe sub-surface maximum in the central gyre.1 5 10 16 IV VA VC0250500- 750a)0100012501500Longitude120Figure 4.28 Contours generated by combining data from this study with thosefrom previous work [3]. Values are in pmol/kg. Please refer toFigure 4.1 for the latitudes of these stations.140E 160E 180E 160W 140W1214.3.3 Dissolved Ga Distribution in Deep WatersThe vertical profiles of Ga below 1000 m at all stations show increasingconcentrations with depth. Elements which such distributions havegeochemistries dominated by: in situ dissolution and oxidation of organic matterwhich releases trace constituents in the deep waters and at the sedimentinterface (e.g. Si and Zn); a flux from the sediments and subsequent mixing withupper waters by eddy diffusion and gradual upwelling (e.g. Ra); or a flux fromthe sediments which is advected upwards and subsequently removed by particlescavenging (e.g. Cu, Al).The behaviour of an element which shows increasing concentrations withdepth in the deep waters can be determined by plotting the concentration of thatelement against salinity, 5, (Figure 4.29), provided that a plot the twoconservative tracers, S and potential temperature, 0, (the surface temperature ofa small volume of water at depth adiabatically raised to the surface), yields alinear relationship. A non-linear S-O diagram may indicate the influence ofhorizontal advection, which would affect the element-salinity plot. Elementsalinity plots which show convex relationships indicate net release of anelement, linear relationships indicate conservative mixing, and concaverelationships indicate net removal of an element which has a bottom watersource. These relationships are shown in Figure 4.29.122Element concentrationO=KI[C1’W1’+Jo2z) Loz)ReeaSalinityIFigure 4.29 Element versus salinity plots in deep waters showing net release,conservative mixing and removal by particle scavenging.4.3.4 Vertical-Advection Diffusion ModelA simple vertical advection-diffusion model may be used to estimate thedeep water scavenging times for scavenged elements which have a bottomsource. The model may be expressed as [29,117]:(Eq. 4.1)where K is the vertical eddy diffusivity, W is the vertical advection velocity(positive downwards), [C] is the concentration of the element of interest, z is thedepth in kilometres and J is the term that accounts for scavenging removal. Thesolution to this equation can be arranged as:[C] = a. + (-j) z÷ [3S (Eq. 4.2)123where ci and f3 are constants and S is the salinity. Multiple linear regression of[C], S and z from equation 4.2 can be used to determine J/W, ci and f3. Thevalue of J, the scavenging term, can be determined assuming an upwelling rate(W) of 3.5 rn/yr (estimated from radioisotope distributions [117]).The scavenging residence times are calculated using the followingequation:1n2 (Eq.4.3)I Ww)I [ci\. ave4.3.4.1 Application of this model to GaThe model was used to determine the scavenging residence times of Gain the deep waters at Stations 10, 16 and P26. These three stations are found tohave linear S-O diagrams and the required convex [Ga]-S relationships (Figures4.30, 4.31, 4.32). The advection diffusion model was not applied to Station 5since seawater samples below 3000 m were not collected (hence, no bottomwater data). Station 15 has a linear S-O diagram and the required convex [Ga]-Srelationship, but the depth of the site was only 1550 m (Figure 4.33). Station Iwas found to have a non-linear S-O diagram (Figure 4.34) and therefore the Gadata from this site was not modeled.124Potential Temperature (°C) Dissolved Ga (pmol/kg)6 5 4 3 2 1 0 5 10 15 20 2533.8- I I - I I I700m A. 700m B.34.8 Station 10 4600m - 4600m35.0- -________________Figure 4.30 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 700 m at Station 10 in the westernNorth Pacific Ocean.Potential Temperature (°C) Dissolved Ga (pmol/kg)76543210 05101520253034.40- I I I I - I I I- 700m A. 700m B.U6- Station 16 4500m 4500m34.80 -_____________________-___ __ __ __ __Figure 4.31 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 700 m at Station 16 in the centralNorth Pacific Ocean.125Potential Temperature (°C) Dissolved Ga (pmol/kg)4 3 2 1 0 0 510152025303534.2— I — I I I I I I750m A. 750m B.34.3- . -\34.4- \ -(0345 -34.6Station P2634.7 4200m4200m34.8- -_______________Figure 4.32 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 750 m at Station P 26 in the eastern NorthPacific Ocean.Potential Temperature (°C) Dissolved Ga (pmollkg)7 6 5 4 3 2 1 8 10 12 14 1634.40- I I I - IA. 600m B.600m34.45 ->..C34.50 -C/)34.55 -—34.60 -Station 15 1500m 1500m34.65 -_____________________-_ _ __ _ __ __ _Figure 4.33 The A) Potential temperature-salinity and B) dissolved Ga-salinityrelationships below 600 m at Station 15 in the centralNorth Pacific Ocean.126Potential Temperature (°C)4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.034.40- I I I I I Il000m34.50 -34.55 -4600m34.75 -34.80 -___________________________Figure 4.34 Potential temperature - salinity relationship below 100Cm at StationI in the western North Pacific Ocean.Parameter Stn. 10 Stn. 16 Stn. P26c (pmollkg) 119 361 1300f3 (pmol/kg) -3.33 10.4 -38.0JIW (pmolkg1yfm) 4.61 5.58 10.7W (kmlyr) -0.0035 -0.0035 -0.0035[Ga]avg (pmol/kg) 16 15 1 1scavenging t% (yr) 700 530 200Table 4.1 Results obtained from the vertical-advection diffusion model fordissolved Ga in the deep waters of the North Pacific.The results obtained and the parameters used are shown in Table 4.1. Itshould be noted that there is an increase of only 20-30 years in residence timesif the shallowest deep water depth of 1000 m is used instead of 700 m. The127scavenging residence times for Ga ranged from 700 years in the central gyre(HS 10) to 200 years at the edge of the sub-Arctic gyre (P26). Longer residencetimes in the central gyre as compared to Station P 26 have been previouslyobserved for Ga and Al, with residence times for Ga determined to be 750 yearsin the central gyre and 100 years in the sub-Arctic North Pacific Current [3]. Theresults presented here are very similar. The difference between Stations 10 andP26 is attributed to lower biological production in the surface waters in thecentral gyre, resulting in fewer particles sinking to the sediments. The residencetime of Ga determined in the North Equatorial Current (Station 16) is found to be530 years, which is slightly less than that of Station 10.A flux from the sediments is required to maintain concentrations in bottomwaters since removal by scavenging is occurring. The Ga flux from thesediments at these stations can be estimated using the method of Munk [118]:FluxB -w [C] B + K (dZ)B (Eq. 4.4)where W is the vertical advective velocity, K is the vertical eddy diffusioncoefficient, [C] is the concentration of the element of interest, z is the depth. Thesubscript B refers to the change of concentration with depth at the seafloor.Using an estimate of 3.2 x I 7 cm2y(1 for K [119] and integrating from theseafloor to the penultimate bottom-water point available to calculate (dCldz), thefluxes needed to support the bottom and deep water distribution of Ga atStations 10, 16 and P26 are 8.3, 9.7 and 23 pmol cm2y(1 , respectively. Thecalculated fluxes at Stations 10 and 16 are similar, while that at Station P26 ismuch higher since a higher flux out of the sediments is needed to sustain theconcentration of Ga in the bottom-waters in this region of high scavenging. Atpresent, the source of the bottom water supply of Ga cannot be distinguishedbetween a flux from sub-surface pore waters and sediment-surface128remineralization, both of which have been suggested to account for thedistribution of Al [8]. In the North Atlantic, advection has also been argued forAl, but not in the North Pacific and hence advection is not considered to be abottom water source of Ga [120, 121].43.5 Comparison with AlTo understand the behaviour of Ga further, it is useful to compare it to Al,another hydrolysis-dominated element that sits just above Ga in the periodictable. Al is the most abundant metal in the earth’s crust and has been shown tohave a high atmospheric input to the surface oceans and to be very reactive.Aluminum data exist for Stations 15 and 16 (Figure 4.25) [112] and a detailedcomparison of Ga and Al at Station P26 already exists [3]. Dissolved Al in theNorth Pacific is rapidly removed from the surface waters with a mid-depthminimum at 1000 m [3, 8]. Slightly higher Al concentrations in the deep waterssuggest the possibility of a bottom source. Profiles of dissolved Al at Stations 15and 16 are shown in Figure 4.35.Dissolved Al (nmol/kg)0 2 4 6 8 10 0 2 4 6 8 100- ‘b ‘ -_____________. .1000- -E 2000--.3000--4000--5000- HSI5 - HSI6“F,6000- -__ __ _ __ __Figure 4.35 Depth profiles of dissolved Al at Stations 15 and 16 [112].129Comparing the crustal abundance ratio of Ga/Al to that of surfaceseawater (<500 m) and deep seawater (>1500 m at Stations 10 and 16; >1000 mat Station 15) should reveal any fractionation between Ga and Al in the oceans.From previous studies, it has been found that Ga/Al ratios are enriched 50 to100 times in surface waters with respect to those in average crust [3, 54].Explanations offered for the additional Ga present in surface waters includepreferential scavenging of Al in surface water, an additional but unknown Gasource, a greater abundance of Ga in the atmosphere source relative to thecrust and/or enhanced dissolution of Ga from dust inputs. Since no Al data areavailable from Station 10, Al values from another station, VERTEX IV,approximately 30° east of Station 10 were used in calculating Ga/Al ratios sincedissolved Al levels have been found to be relatively uniform in the central Pacificgyre [8]. A detailed comparison of Ga with Al was previously made at Station 10using Al data from VERTEX IV [1221. Therefore, the Ga/Al ratios at Station 10,determined by combining dissolved Ga data obtained here with dissolved Aldata from Station VERTEX IV, are included here for comparison only. A plot ofGa/Al ratios at Stations 15 and 16 are shown in Figure 4.36.The ratio data show that the enrichment factor of Ga with respect to Al inthe surface waters is higher than that in the average crust and increases furtherwith depth (Table 4.2). Thus, the geochemistries of Ga and Al must be differentin seawater. Sources of Al and Ga to the surface waters are believed to besimilar since dissolved Ga and Al concentrations have been correlated over arange of environments [54] and Al has a known aeolian source to the NorthPacific [123]. The most likely explanation for the high dissolved Ga/Al ratios isthat they result from a combination of enhanced scavenging of Al throughout thewater column and preferential dissolution of solid phase Ga. At Stations 15 and13016 the surface enrichment factors are similar if slightly lower than the 50 to 100fold range reported previously [3, 21].Dissolved Ga/Al concentration ratios (x 1000)0-2 4 6 8 10 O\24 6 8 101000- -I,,,,..2000- --3000- -o .4000--5000- HSI5 - HSI6“I6000- -__________________Figure 4.36 Depth profiles of dissolved Ga/Al ratios at Stations 15 and 16.Al data from reference [112]. The arrows indicate the crustalGa/Al ratios.Expected Ratio Surface Deep waterStation (mmol/mol) Enrichment EnrichmentHS 10 0.0705 120 340HS 15 0.0705 31 95HS 16 0.0705 38 163Table 4.2 Enrichment factors of Ga with respect to Al from Stations 10, 15and 16. [All at Stations 15 and 16 from reference [112]. [Al] usedto compare Station 10 are from Station VERTEX IV also in thecentral gyre [21]The extent of dissolution of Al from aerosols in surface waters is between5 and 10 % due to the refractory nature of the alumino-silicate component [124].Gallium has a larger ionic radius than Al (0.062 nm and 0.050 nm, respectively)131[125] and may be more associated with the readily leachable fractions of marineaerosols. This is the case for Cd, Zn and Pb [126] and Mn [127] which allundergo greater than 30% dissolution from marine aerosols in seawater. Atpresent, the exact source of Ga/Al enrichment is not known, though it appearsthat the supply of Ga is greater than the supply of Al to the surface waters.Preferential scavenging of Al over Ga in deep waters might be due toenhanced scavenging of neutral species over anionic species onto anionicparticle surfaces. The majority of Ga in seawater exists as Ga(OH)4 while Alexists mainly as the neutral Al(OH)3 [53, 54, 128]. Indeed, the scavengingresidence time for Al at Station 16 is calculated to be 430 years which is lessthan that estimated for Ga at this station (see Table 4.1). Previous work alsohave shown that the scavenging residence time for Al is shorter than that for Gaat P26 and at VERTEX IV [3]. This supports the notion that Al is more reactivethan Ga in seawater.4.3.6 ConclusionsDissolved Ga concentrations in the upper waters have been found to bethe highest in the central gyre, an area with low dust input from the Asiancontinent and with low productivity resulting in fewer sinking particles. A mid-depth maximum was also observed at this site. Stations I and 5, which areareas with high dust inputs and high productivity, had Ga values which werelower with no mid-depth maxima. This indicates that the high levels of Ga in thecentral gyre and the presence of the sub-surface maximum in this region is notdue to advection of water from the western North Pacific, but instead reflects theimportance of productivity and scavenging in dissolved Ga distributions. Galliumdistributions in the North Equatorial Current were similar to those in the coastalstations and is an area with lower dust inputs and higher productivity than in the132central gyre. The lowest near-surface Ga levels were found in the sub-ArcticNorth Pacific Current (Station P26) which is an area with high productivity andthe lowest dust input of all sites, reflecting the added effect of lowered aeolianinput into this region.In deep waters, the calculated scavenging residence times at Stations 10,16 and P26 are 700, 530 and 200 years, respectively, indicating increasedparticle scavenging at P26.Ratios of Ga/Al at Stations 15 and 16 indicate enrichment of Ga withrespect to Al in surface and deep waters. The extent of enrichment was similarto that found at other Stations [3, 21]. Previous work in the North Pacific foundsurface Al values which were low in the sub-Arctic North Current (P26) [3] andvalues ten times higher at sites bordering and in the North Equatorial Current[21]. Aluminum data at Stations 15 and 16 show similar high surface valuesfound in the North Equatorial Current. Scavenging residence times of Al atStation 16 show reactivity higher than that of Ga. Therefore, the high Ga/Alratios in seawater with respect to average crust are apparently due primarily toenhanced scavenging of Al. In addition, it is possible that the supply ofdissolved Ga to surface waters is greater than that expected by the crustal Ga/Alratio.1334.4 Dissolved Nb in SeawaterVery little is known about the behaviour of Nb in seawater. The onlypreviously published results were analyses of two surface samples taken fromthe English Channel made to aid a study of the accumulation of Nb by ascidians[55]. Unfiltered surface samples in that work were found to contain Nbconcentrations between 0.01 to 0.1 pg/I (0.1 to I nmol/kg). Niobium is predictedto exist in its i-V oxidation state and to be fully hydrolyzed in natural waters. Thepredicted speciation at pH of 8.2 is 88% as Nb(OH)6and 12% as Nb(OH)5[128]. In this section, the first profiles of dissolved Nb in seawater are presentedand possible mechanisms which control dissolved Nb in the North Pacific arediscussed.4.4.1 Depth ProfilesThe dissolved Nb profiles were determined at six sites in the North Pacific(Stations 1, 5, 10, 15, 16 and P 26) and are shown in Figures 4.37, 4.38 and4.39. The profiles show similar distributions: near-surface concentrationsranging from 10 to 80 pmol/kg; slight sub-surface maxima in the upper 500 mwith concentrations between 40 and 100 pmol/kg; and mid-depth minima below500 m (between 10 and 40 pmol/kg). Between 1000 and 1500 m, larger maximabetween 40 and 200 pmol/kg are observed. Concentrations decrease at greaterdepths to levels between 10 and 100 pmol/kg. The trio of Nb profiles at Stations1, 5 and 10 (Figure 4.37), show an overall decrease of dissolved Nb withdistance from the Asian coast, with Nb concentrations at Stations 16 and P26being similar to Stations I and 5.DissolvedNbconcentration(pmol/kg)040801201602000408012016020004080120160200cJ—.___.__•III—IIIIII..1000-.•2000--c...30004000-HS-1HS-5HS-10••5000-‘F,,’_______1,/I’_______6000-___________________-___________________-“Figure4.37DissolvedNbprofilesfromtheWesternNorthPacific.EachpointistheaverageoftwoanalysesTheerrorbarsindicatetherange.c)135Dissolved Nb concentration (pmol/kg)0 40 80 120 160 2000- iiI I1000 - I—“I2000 -3000 -4000 -HS-155000 -6000 -_________________________0 40 80 120 160 2000- ••‘.1I1000 -2000 --3000- •04000-• HS-165000 -f/f’,6000 -Figure 4.38 Dissolved Nb in the central North Pacific. Each point is theaverage of two analyses. The error bars indicate the range.136Dissolved Nb concentration (pmol/kg)0 40 80 120 160 200o-•. I I.1000 -2000- ••.3000- I I4000-“I,,5000 -P266000 -_________________________Figure 4.39 Dissolved Nb in the sub-Arctic North Pacific (P26). Each point isthe average of two analyses. Error bars indicate range.Although the depth resolution of the samples collected at these stations isnot sufficient to see smooth transitions in mid waters and the data show somescatter, the fact that the sub-surface and mid-depth maxima occur in everyprofile suggests that these features are real. Hypotheses to account for themwill be explored in the following sections. Dissolved Nb in the Surface WatersThe surface concentrations of dissolved Nb at Stations 1, 5 and 10 showdecreasing levels with distance from the coast. At Stations 16 and P26, theconcentrations are similar to those at Stations I and 5. The sources of Nb to theoceans are unknown, though the decreasing surface concentrations withdistance from the Asian coast observed at Stations 1, 5 and 10 are similar to thePb and Mn distributions described earlier (sections 4.2.3 and 4.2.4), which137reflect atmospheric sources and in the case of Mn, riverine sources to surfacewaters [5, 22, 127]. Therefore, there does appear to be a source of Nb to thesurface waters of the oceans, though its extent is unknown.At Stations 1, 5 and P26, dissolved Nb concentrations decrease in thesub-surface waters to 100 m and then increase with depth resulting in subsurface maxima at 500 m for Stations I and 5 and 750 m at Station P26.Stations 10 and 16 show low values in the surface waters, with Nb increasingwith depth to sub-surface maxima at 500 m at Station 10 and 300 m at Station 16(the surface values at Station 15 were lost). At all stations dissolved Nbimmediately decreases below these maxima to concentrations equivalent to orless than the surface dissolved Nb concentrations. This suggests that Nb, likeother hydrolyzed elements such as Al, Ga, Bi and Th, may be scavenged inseawater [3, 8, 115, 129]. The sub-surface maxima and minima observed atthese stations may be the result of advective features and/or due to reversibleexchange processes involving sinking particles. The declining Nb content withdistance from the Asian coast observed at Stations 1, 5 and 10 may suggest alateral advective source. Niobium may be incorporated into solid phases whichundergo shallow regeneration such as biological soft tissue and then may berescavenged onto particles present throughout the water column. This has beenpostulated for Ga [3, 53] and Co [130]. In 1958, Carlisle had shown that Nb isorganically bound in ascidians [131], thus it is possible that Nb could be found insoft tissue of plankton. Dissolved Nb in the Intermediate and Deep WatersIn intermediate waters (below 1000 m), the mid-depth minima increase tolarge sharp mid-depth maxima at all stations, which occurs at 1500 m at Stations1, 5, 10 and P26, and at 2500 m at Station 16. Below these depths, dissolved138Nb rapidly decreases to levels similar to or slightly higher than the mid-depthminima and surface concentrations. At Station P26, dissolved Nb shows agradual increase with depth. The narrow zone of the mid-depth maximumsuggests that Nb is rapidly scavenged throughout the water column as are otherparticle reactive elements. The source of this mid-depth maximum is unknown,though it may be a result of lateral advection of waters with high concentrationsof Nb, possibly from the continent boundaries, reversible exchange with sinkingparticles or cycling between a reactive and less reactive form of Nb.4.4.2 Comparison with Dissolved 02 and ManganeseA comparison between Nb and dissolved °2 distributions indicates anapparent relationship: in four out of five profiles (Figure 4.40), the Nb maximaoccur at low 02 levels. However, neither of the two Nb maxima in each profileoccur exactly at the°2 minimum. Instead, stations in the western North Pacific(HSI, 5 and 10) show a small sub-surface maximum which coincides with the topof the 02 minimum and a higher mid depth maximum which coincides with thebottom of the°2 depleted zone. At Station HS 16, the sub-surface Nb maximumoccurs at the top of the 02 boundary, but the mid-depth maximum which occursat the bottom of the°2 minimum is much lower in depth than at the other deepstations (2500 m compared to 1500 m for the rest).Since Nb is not predicted to undergo redox chemistry in seawater, itsdistribution in seawater may be influenced by an element that does undergoredox chemistry in seawater. Manganese is known to be redox sensitive and beassociated with the oxygen minimum in seawater, resulting in a large mid-depthmaximum attributed to a combination of lateral advection and cycling betweenparticulate Mn(lll,lV) and dissolved Mn(Il) forms in the°2 minimum zones [15,22, 47-51].05001000150020002500300035004000450050005500050010001500.c 200025000 30003500400045005000550005001000150020002500300035004000450050005500o Dissolved °2 (uM)50 100 150 200 250 300c.00 H85; 00-HSI5Figure 4.40 Dissolved Nb and °2 in the North Pacific with respect to depth.For Nb: Each point is the average of two analyses.For 02: Data obtained from lOS; uncertainties within the symbols.• Dissolved Nb (pmol/kg)0 50 100 150 200 250 300 0I I L139: bo-- 000:810:7THsiHS 16140Plots of superimposed Mn and Nb profiles, shown in Figure 4.41, illustratedifferences in their distributions since the maximum dissolved Mn concentrationoccurs at the 02 minimum. No particulate Mn data are available for thesestations, but other studies have found that particulate Mn is high in surfacewaters, decreases in the 02 minimum zone and then increases again with depthand increasing 02 concentrations [51]. The Mn signal in the °2 minimum zonehas been attributed to a combination of reversible dissolution/precipitationbetween particulate Mn (Ill, IV) oxyhydroxides and dissolved Mn (II) andhorizontal advection of water with high dissolved Mn concentrations fromcontinental boundaries.If one examines only the Nb levels at the surface, in the 02 minimum andat depth (ignoring the 02 minimum boundaries), it appears that the distribution ofNb may be controlled by scavenging onto sinking particles. At the upper °2minimum boundary, the constant cycling between dissolved and particulate Mnmay contribute to the small sub-surface maximum observed in the dissolved Nbconcentrations. Cobalt, which has a Mn type distribution, has been found tohave a broader and shallower mid-depth maximum in the central North Pacific.This is attributed to complex controls including cycling between reduction andoxidation of Mn(lll,IV) oxyhydroxides at the upper boundary of the 02 minimumand nutrient cycling since Co is biologically important [112, 132]. The subsurface maxima observed in the dissolved Nb distributions may be controlled bya combination of nutrient and Mn cycling.At the lower end of the 02 minimum boundary, once the dissolved Mn isoxidatively scavenged, it is not cycled back into the °2 minimum zone. Themore pronounced dissolved Nb mid-depth maximum may be influenced by thedissolution of Mn oxides in the upper end of the 02 minimum zone, which results0-500 -1000 -:: 1500 -. 2000 -2500 -0 3000 -3500 -4000 -4500 -5000 -55000500 -1000 -1500 -2000 -2500 -3000 -3500 -4000 -4500 -5000 -5500 -o Dissolved Mn (nmollkg)0.00 0.25 0.50 0.75 1.00 1.25 1.50I I I I I I I0 50 100 150 200 250 300Figure 4.41 Dissolved Nb and Mn against depth in the North Pacific.Points are the averages of two analyses.• Dissolved Nb (pmol/kg)Mn o.oo 0.25 0.50 0.75 1.00 1.25 1.50I I I I I141Nb050010001500200025003000350040004500500055000 50 100 150 200 250 300rHS1O-HS16HS 15142in a dissolved Mn mid-depth maximum. However the differences between theNb and Mn maxima indicate that additional processes must be involved.The offset between the dissolved Mn and Nb maxima suggests that thecontrols of dissolved Nb are much more complex, since if Mn cycling was asignificant control, the dissolved Nb mid-depth maximum should occur at thesame depth as that for Mn. The only published data of Nb in ferromanganesenodules (from a lake in the Malawi Rift, Central Africa) shows a 2.5 foldenrichment of Nb relative to crustal abundance, and a ratio of Nb/Al 16 timeshigher that the average crustal ratio shows, indicating an association betweenNb and oxide phases [133]. Another control of the Mn mid-depth maximum islateral advection from reducing shelf sediments [51]; thus lateral advection maybe a possible control for dissolved Nb.A further complication may be the effect of changing pH on dissolved Nbin seawater. The pH of seawater follows the 02 distribution and the hydrolysisof Nb(OH)5to Nb(OH)6 occurs at pH —7.5 in natural waters, resulting in —12%of dissolved Nb existing in the Nb(OH)5form at pH 8.2 [128,134]. The averageseawater pH is —8, though this can decrease to <7.6 at the 02 minimum [135].At pH 7.6, — 35% of dissolved Nb would be in the Nb(QH)5form, which may bemore reactive in seawater. As°2 and pH increase, the equilibrium betweenNb(OH)5and Nb(OH)6 would shift back again to Nb(OH)6. Element reactivityas a function of its hydroxide form has been previously suggested to explain theenrichment of dissolved Ga with respect to dissolved Al in seawater since Gaexists predominantly in the less reactive Ga(OH)4 form while Al existspredominantly as Al(OH)3 [3, 54]. It is possible that Nb scavenging is enhancedin the pH minimum which could partially explain the minimum observed between500 and 1500 m.1434.4.3 North Pacific Intermediate WatersThe entrainment of low salinity North Pacific Intermediate water mayinfluence the observed Nb distributions. Plots of potential temperature (0)versus S are shown in Figure 4.42. The North Pacific Intermediate waters areshallowest at Station P26 (15Cm), deeper at Stations 1, 15 and 16(300 rn), anddeepest at Stations 5 and 10 (700 m). It appears that this water mass is notinfluencing the maxima observed at these stations. The smaller sub-surfacemaxima occur at 500 m (Stations 1, 5 and 10), 300 and 750 m (Stations 16 andP26, respectively). Neither does it appear that the North Pacific Intermediatewaters influence the much larger mid-depth maxima occurring at these stations.This does not eliminate the possibility that horizontal advection of highconcentrations of Nb waters are a control on the distribution of Nb.144Potential Temperature14 12 10 8 6 4 2 0 20 16 12 8 4 033.50 - I I I I 34.0 - I IHS-1 270 m HS-5• 34.2 - •700 i• .34.00- • ••3425 Om•. .‘p S 34.6-34.50- 0m I348 •34.75- 5070m 4100m35.00 - 35.0 -_______________________25 20 15 10 5 0 30 25 20 15 10 5 033.50 - 34.00 - I I IHS-15 300 m33.75 - HSIO 550 -680 m 34.25 - 0 mp 34.00- •• •• 34.50-34.25 -• ••34.75- •34.50 -34.75 -35.00 0m’1500m4600 m 35.00 - • •••35.25- 23 m35.25-35.50 - 35.50 -302520151050 1412108642034.00— I I I 31- I IHS-16 300m P2634.25- Om 32- 150m2m34.50- • •%IIb4b 3334.75 - •4500m 34-lb..35.00- ••• 35-35.25-21 m 4200 m35.50 - 36 -___ ___Figure 4.42 Plots of potential temperature versus salinity to determine wherethe North Pacific Intermediate waters are present at all stations.1454.4.4 Comparison with VAs an aid to understanding the distribution of a particular metal inseawater, it is sometimes beneficial to compare its distribution to the knowndistribution of another element in the same column of the periodic table.Similarities or differences between elements in the same column of the periodictable may help in determining which oceanic processes may or may not be acontrol in the biogeochemical behaviour of a particular metal in seawater.Vanadium is located directly above Nb in the periodic table and its behaviour inseawater is very different from that for Nb.In seawater, V is predicted to exist in the (V) oxidation state as themetavanadate anion, H2V04 [1281. A typical depth profile shows a slightsurface depletion (10 % of average concentration) and then relatively uniformconcentration with depth. It is generally considered to be unreactive, though thesurface depletion may be explained by a biochemical uptake associated withphosphate. Early measurements indicated no fractionation of V between thePacific and Atlantic basins [136], though more recent studies indicate anincrease of 5 to 15 nmol/kg between the Atlantic Ocean deep waters and thedeep waters of the Pacific Ocean [137]. A typical profile of V is shown in Figure4.43.Vanadium also exhibits redox chemistry, and can exist in the (IV)oxidation state under acidic and/or reducing conditions in natural waters. It isalso enriched in organic rich sediments in anoxic or sub-oxic basins [138].There is no known nor predicted redox chemistry for Nb in natural waters.146• Dissolved V (nmol/L)‘ Dissolved PC4 (jiM)‘- 0 1 2 3 4 5I I I I• 20 25 30 35 40 45 50050010001500. 20002500300035004000450050000 50 100 150 200 2500 Dissolved°2 (jiM)Figure 4.43 Profiles of dissolved V, PC4 and 02 in the North Pacific Ocean[136].The V profile in the North Pacific shows that V has a nutrient-typedistribution, correlated with phosphate, except at the surface. There is noindication of scavenging, nor any association with Mn cycling in the depleted°2zone. This is in direct contrast with the Nb distributions observed in the NorthPacific, which show scavenging and a large mid-depth source coincident to thelower 02 minimum boundary in the western Pacific Ocean. Clearly, Nb is not ananalogue for V in seawater, indicating that the sources and reactivities of theseelements are different.4.4.5 Comparisons with Zr and MoNiobium is bracketed in the periodic table by Zr and Mo. These elementshave extremely different distributions in seawater. Zirconium is predicted toexist mainly as the hydrolyzed Zr(OH)4and Zr(OH)5 and has been found to147have a distribution very similar to those shown by the rare earth elements(REEs): a surface minimum with a gradual increase in concentration with depth[90, 139]. Molybdenum behaves conservatively and is present in seawater asMo042[140]. Molybdenum can also undergo redox reactions under reducingconditions in seawater [138]. Typical profiles of Zr and Mo in the North Pacificare shown in Figure 4.44.Dissolved Zr (pmol/kg) Dissolved Mo (nmol/kg)0 50 100 150 200 250 300 350 0 25 50 75 100 125 1500— I I I I500 -1000 -21500 -.c2000 --25O0 -U3000 -3500 -4000 -4500 -5000 -5500 -____________________________Figure 4.44 Dissolved Zr and Mo in the North Pacific Ocean [90, 140].Both these elements have very different distributions in seawatercompared to dissolved Nb. Niobium does not show a large increase with depthas does Zr (except at Station P26) and does not resemble the REEs, eventhough both Zr and Nb are expected to exist fully hydrolyzed in seawater. Thedistribution of dissolved Zr in the North Pacific is a result of removal by particlescavenging throughout the water column and an input from the sediments [139].Niobium does not show evidence of a strong bottom source at all locations,though both elements do show scavenging throughout the water column. Thisshows that different processes must be controlling these two elements.•.....148Molybdenum exists as an oxyanion in seawater and has a conservativedistribution, thus the processes controlling its distribution are different fromthose controlling Nb.44.6 ConclusionsThese full-depth North Pacific profiles of dissolved Nb are the firstreported for this element. The element generally shows a sub-surfaceconcentration maximum at the top of the °2 minimum and a much larger mid-depth maximum at the bottom boundary of the °2 minimum. Concentrations ofNb decrease from the Asian coast (Station 1) to the central gyre (Station 10),though the sub-surface and mid-depth maxima occur at the same depths for allthree stations. The concentrations of Nb in the North Equatorial Current(Stations 15 and 16) are similar to those observed near Asia, except that atStation 16, the sub-surface maximum is much larger that at the other stationsand the mid-depth maximum is deeper. In the sub-Arctic North Pacific Current(P26), the Nb profile is similar except for elevated concentrations in the deepwaters. Decreasing concentrations with distance from the continents indicatethe possibility of horizontal advection of deep waters with high concentrations ofNb originating from both sides of the Pacific Ocean. The distribution of Nb mayalso be affected by Mn and nutrient cycling and pH changes in the 02 minimumzone, although the relative influences of these phenomena cannot beascertained at present.To understand the distribution of Nb in the North Pacific better, and howthis distribution is affected by the°2 minimum zone, Mn cycling, pH changesand horizontal advection, more profiles need to be analyzed in other parts of theocean, with emphasis on high resolution sampling through the°2 minimum,preferentially in the eastern tropical Pacific.149CHAPTER 5. CONCLUSIONSAn on-line method using Fl-ICP-MS to preconcentrate and analyze Zn,Cd, Ni, Cu, Pb, Mn, Ga and Nb was developed. The accuracy of this methodwas determined by analyzing Mn, Ni, Cu, Zn, Cd and Pb in a NASS-3 openocean seawater standard. The results obtained with this method agreed with thecertified values. The accuracy of this method for the elements Ga and Nb couldnot be determined since there are no seawater standards with certified valuesfor these two elements. The precision of the on-line method was evaluated byexamining the RSDs determined for 10 replicate analyses on the NASS-3seawater standard. The RSDs were between 5 and 12 % for all elements,except for Cu which had an RSD of 25 %.A prototype sampler with multi-sampling capabilities was developed topreconcentrate trace metals from seawater remotely. The sampler wassubmerged for a period of one week in-house, and operated successfully.Repeated testing over time indicated that though the sampler functioned, thedeterioration of various components and structural degradation with use in acorrosive medium such as seawater, obviated the deployment of this instrumentfor the collection of uncontaminated trace metal samples. Significantredesigning of the sampler is needed; because the chemical aspects have beensatisfactorily explored as described elsewhere in this thesis, future developmentshould be directed by an engineer rather than a chemist.This Fl-ICP-MS method was used to determine six depth profiles of Mn,Ni, Cu, Zn, Cd, Pb, Ga and Nb from samples obtained in the western, centraland north-eastern North Pacific Ocean. The results obtained for Zn, Cd, Ni, Cu,Pb and Mn using this novel technique agree well with profiles previouslydetermined using the same samples but by other methods, as well as withprofiles measured in the general area.150The distributions of Mn showed high surface values ranging from0.8-1 nmol/kg, sub-surface minima of 0.15 and 0.7 nmol/kg at 100 to 500 m,mid-depth maxima of 0.3 to 1.2 nmol/kg at depths between 500 and 1500 m, anddecreasing concentrations with depth. The profiles for Zn, Cd and Ni showedthe expected nutrient distributions with low surface water concentrationsincreasing with depth to broad maxima coherent with the nutrient maxima anddecreasing slightly below this depth. Surface values for Zn, Cd and Ni were0.4- 2.5 nmol/kg, 0.01 - 0.25 nmol/kg and 1.5 - 3.5 nmol/kg, respectively, andincreased to mid-depth maxima of 7 - 9 nmol/kg between 1000 and 1500 m,0.9 -1 nmol/kg between 500 and 1500 m, and 9 - 11 nmol/kg between 800 and2500 m, respectively. The Cu distributions showed low surface values of0.7 - I nmol/kg and increased linearly with depth to values of 3.5 - 4.5 in deepwaters. The profiles of Pb showed high surface values of 10 -60 pmol/kg,sub-surface maxima of 25 -40 pmol/kg between 200 and 500 m at all stationsexcluding Stations I and 5, and decreased with depth to values of10- 15 pmol/kg in deep waters at all stations.The first set of dissolved Ga data from the western North Pacific havebeen presented here, and together with published data from the sub-Arctic NorthPacific Current and from the central gyre, result in a better understanding of thecontrols of dissolved Ga in the North Pacific. The Ga profiles had low surfaceconcentrations of 4 - 14 pmollkg, mid-depth minima of 3 - 9 pmol/kg andincreasing concentrations with depth to 13 - 30 pmol/kg in deep waters. In thecentral gyre and the sub-Arctic North Pacific sub-surface maxima of10 - 18 pmol/kg between 300 and 500 m were observed, a feature not seen inthe western North Pacific. Dissolved Ga was found to be highest in the centralgyre, an area with low dust input from the Asian continent and with lowproductivity resulting in fewer sinking particles. In the Kuroshio and Oyashio151Current, areas with high dust input and high productivity, Ga values were lower.This indicates that the high levels of Ga in the central gyre and the presence ofthe sub-surface maximum in this region is not advected from the western NorthPacific, where sub-surface maxima were not observed. The lowest Gaconcentrations in surface waters were found in the sub-Arctic North PacificCurrent, an area with low dust input and high productivity. This indicates thatparticle scavenging may provide the dominant control of the dissolved Gacontent in seawater, although dust inputs also play a role. In the deep waters,scavenging residence times were estimated for stations 10, 16 and P26 to be700, 530 and 200 years, respectively,The first full depth profiles of Nb in the oceans are reported in thisdissertation. The Nb distributions in the North Pacific show low surfaceconcentrations (10 - 80 pmol/kg), slight sub-surface maxima in the upper 500 mof the water column (40 - 100 pmol/kg), mid-depth minima similar to surfaceconcentrations between 500 and 1000 m, large mid-depth maxima of 50 to200 pmol/kg between 1000 and 2500 m, and lower deep waters concentrations(10 - 100 pmollkg). Both maxima were found to occur at the 02 minimum zoneboundary, with the larger maxima just beneath the oxygen minimum. The Nbdistributions decreased with distance from the Asian continent, and increased inthe North Equatorial Current, indicating horizontal advection of high Nb watersfrom both the western and eastern Pacific boundaries. The distribution of Nbmay also be affected by nutrient cycling in upper waters, Mn cycling in the 02minimum zone and decreased pH in the 02 minimum zone, though the extentcannot be ascertained at present.152CHAPTER 6. FUTURE WORKMany areas of this research could be extended further. The suite ofmetals currently being measured by the on-line Fl-ICP-MS method could beexpanded and the precision of the Cu determination improved. The on-linemethod should be further automated, by incorporating a second switching valveinto the manifold to switch between the I % nitric acid rinse solution and theeluent streams entering the ICP-MS. A major improvement to the on-linemanifold would be to trigger the PlasmaQuad’s data acquisition programautomatically upon the elution of the preconcentrated sample off the column.This would improve the precision between analyses and eliminate human error.The sampling rate of this system could be increased, either by using a pumpwith a faster flow rate, or by minimizing the system blanks further to decreasethe volume of seawater needed.The manifold should be used to determine other profiles of Mn, Ni, Cu,Zn, Cd and Pb in different parts of the ocean. Further profiles of Ga in thewestern North Pacific, including a north-south transect, should be analyzed tostudy further the influences of productivity and eolian input in its distributions.To obtain a better understanding of the behaviour of Nb in seawater, moreprofiles with high resolution sampling in the oxygen minimum zone in differentareas need to be collected and analyzed. 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INFILTREX II IN SITU SAMPLERA.1 The INFILTREX II samplerAxys Environmental Ltd. (Sidney, BC), manufactures an in situ watersampler, the INFILTREX II [102]. This unit is lowered from a ship or a buoy andsuspended at a known depth for sampling. As the sample is collected andconcentrated in its own environment, the chance of contamination during samplecollection is minimized.A.1.1 Physical AppearanceA schematic of the INFILTREX II sampler is shown in Figure A.1. Thespine of the sampler is approximately 75 cm long with hydrowire bracketsattached at the top and bottom of one side. In addition, the pressure housing, asingle extraction column and a filter sandwich are attached to the spine. Thepressure housing is 55 cm in length, and its inner diameter is approximate 10cm. This housing contains the electronics, the gear pump, the flow meter and abattery pack consisting of two 6 V lantern size batteries.The extraction column has an inner diameter of 2.5 cm and a length of37 cm. The resin supplied with the INFILTREX II system is an8-hydroxyquinoline functional group on a polystyrene divinylbenzene backbone(8-HQ-XE-305). To prevent contamination, all the tubing and column parts aremade of Teflon®. To remove particulate matter, the seawater is passed througha 0.45 pm pre-filter. The polycarbonate filter, which has a diameter of 142 mm,is contained within a filter sandwich. The filter sandwich is made of two piecesof a plastic fitted with a Teflon® coated silicone 0-ring.167a _.. d(‘ a. seawater inflow/ N e b. power plugc. casingb d. spinee. filter disk/ f. bracketsc g. seawater oufflowh. extraction columni. to pump and flow meter(interior of casing)Figure A.1 Front and back view of the INFILTREX IIA.1.2 OperationOperation of the INFILTREX II sampler is controlled using an single boardmicrocomputer. Software, supplied with the sampler, permits timed operation ofthe unit and the storage of key information such as battery voltage. Variablessuch as the pump speed and the total volume of seawater to be pumped may beset prior to deployment with the aid of a RS-232 serial interlace between thesampler computer board and a personal computer. An in-built clock allows forthe sampler to be programmed days in advance of its actual operation.When the sampler is operating, the seawater is drawn into the filtersandwich. After filtering, the seawater passes through the extraction columnwhere dissolved metals chelate to the active sites on the resin. The filtrate isthen drawn into the pressure housing through stainless steel tubing. Here, theflow rate is measured prior to the filtrate being drawn through the pump and backinto the environment.168A.1.3 Limitations of the INFILTREX II samplerAlthough the INFILTREX II sampler has been used for several years tosample trace metals in the seawater, a number of limitations exist:Flow rate: The sampler was originally designed for extracting traceorganics from seawater, and due to pump limitation, only operates between 50and 500 L/min. The flow rates available using the INFILTREX II sampler werenot considered suitable for the extraction of trace metals from seawater.Column Design: The single column configuration of the INFILTREX IIsampler allows for only one sample per deployment. The used column must bereplaced with a fresh column before the sampler can be redeployed. Thesampler must be deployed many times to gather replicate samples, a completedepth profile or to undertake temporal variability studies. This is time consumingand can become costly since many columns must be at hand if multiple samplingis performed.In the INFILTREX II sampler, a large column is employed in order towithstand the force of the high flow rates used and to increase the contact timebetween the resin and the seawater. The column has a volume of Ca. 725 mland a large volume of resin is required. Even when using a large volume ofresin, there would be no guarantee that a complete extraction of the trace metalsfrom the seawater would be achieved when such high flow rates are used. Tocompletely elute the metals from the column, the elution volume should be atleast three times that of the resin. Therefore a high volume of seawater isneeded since the eluent volume required will reduce the concentration factor. Inaddition, using a large volume of resin results in high column blanks, i.e., thebackground level of metals from the resin. Cost becomes a major considerationas the resin, the special columns and the eluent become expensive.169A.1 .4 Attempted Modification of the INFILTREX II SamplerTo make the INFILTREX II sampler more versatile and more attractive topotential users for trace metals, several modifications were proposed. Theaddition of more columns would allow multiple samples to be taken perdeployment. As discussed above, slower flow rates were required for tracemetal extraction. Lowering the flow rates would permit the use of smallerextraction columns, requiring less resin and eluent, which in turn would decreasethe column blanks and lower the cost.As a result of initial discussions with the scientists at Axys EnvironmentalLtd., it was concluded that the main limiting factor preventing the use of theINFILTREX II sampler at slow flow rates was the operating range of its flowmeter. The original intent was to replace the existing flow meter andsubsequently lower the pump speed [106]. The INFILTREX Il’s pump speed isadjusted by varying the voltage supplied to the pump motor. Higher voltagesresult in faster pump speeds and a quicker drain of the power supply. The Axysscientists suggested that it would be a simple operation to divide the voltage tothe pump motor in order to obtain the slower flow rates.A number of minor changes to the sampler were also required to enablethe multiple column design to function. For example, minor electronics forcontrolling the valves for the multiple column design would have to be added. Inaddition, the column manifold was to be adapted for flow injection type fittings.After the INFILTREX II sampler had been delivered, it was soon realizedthat the pump speed could not be slowed, nor could the necessary electronicsbe incorporated. The only course of action was to design and construct a newsampler incorporating the required modifications.170APPENDIX B. SOFTWARE ROUTINESOUT &HFAOI, &HFFOUT &HFAO2, &HFFOUT &HFAO3, &HFFOUT &HFAO4, &HFFOUT &HFAO5, &HFFENDLISTING OF PROGRAM “HIGHLO.BAS”set port I bits LO (false HI)set port 2 bits LOset port 3 bits LOset port 4 bits LOset port 5 bits LOLISTING OF PROGRAM “SAMPLER.BAS”DECLARE SUB BUFFER (col%Q, i%, buf%)DECLARE SUB FLOW (TMD%, CT2ADD%, Count&O, j%)DECLARE SUB BUFFER (col%Q, i%, buf%)pts% = 50DIM Count&(1 TO pts%)DIM col%(5)ctbase% &H40TMD% = ctbase% + 3CT2ADD% = ctbase% +2col%(1) = &HFEcol%(2) = &HFDcol%(3) = &HF7col%(4) = &HEFcol%(5) = &HDFcol%(6) = &HDFpumpon% = &HFEpumpoff% = &HFFbuf% = &H80‘looks like base is TULA‘(TCT2, LB-H B, mode 0, binary)‘sets pin 28(i/o24, bitO) high for valve I on 6-way valve‘sets pin 29(i/o25, biti) high for valve 2 on 6-way valve‘sets pin 30(1/026, bit2) high for valve 3 on 6-way valve‘sets pin 31 (i1o27, bit3) high for valve 4 on 6-way valve‘sets pin 32(i/o28, bit4) high for valve 5 on 6-way valve‘sets pin 33(1/029, bit5) high for valve 6 on 6-way valve‘sets pin 37(i/o32,bit0) high and turns on pump‘used to set pin 37 low and turn off pumpOUT &HFFFO, &H10 ‘clock and prescale select171OUT TMD%, &HBO ‘general mode register mitOUT &HFAOI, 0 ‘set port 1 bits LO= TIMER: DO: ti = TIMER: LOOP WHILE ti <(t + 900) ‘total time sampler onOUT &HFAO4, pumpon% ‘turn on pumpFORi%=1T05file$ = “R:test.dat”file$ = “R:test” + LTRIM$(STR$(i%)) + “.DAT”OPEN file$ FOR OUTPUT AS IOUT &HFAO3, col%(i%) ‘turn on each column in its turnstartt = TIMER: totalt = startt i- 100 ‘total time per columnCALL BUFFER(col%Q, i%, buf%)DOt = TIMER: DO: ti = TIMER: LOOP WHILE ti <(t + 30)CALL FLOW(TMD%, CT2ADD%, Count&O, j%) ‘measure the flow ratePRINT #1, Count&(j%)CALL BUFFER(col%O, 1%, buf%)chk = TIMERLOOP UNTIL (chk> totalt)CLOSE #1NEXT 1% ‘if yes, start with new columnOUT &HFAO4, pumpoff% ‘once all columns done, turn off pumpOUT &HFAO3, &HFF ‘turn off valvesOUT &HFAOI, &HFFEND172SUB BUFFER (col%O, i%, buf%)nice% = col%(i%) - buf% ‘inject first bufferOUT &HFAO3, nice%onesecond = TIMERanothercheck:yikes = TIMERIF yikes < (onesecond ÷ 1) GOTO anothercheckOUT &HFAO3, col%(i%)END SUBSUB FLOW (TMD%, CT2ADD%, Count&O, j%)‘zero counter 2OUT CT2ADD%, &HFF: OUT CT2ADD%, &HFFOUT &HFAOI, &HFF ‘set port I bits HIt = TIMER: DO: ti = TIMER: LOOP WHILE ti <(t + 1.32)OUT &HFAOI, 0 ‘set port 1 bits LO‘wait for the pulse to reach the thermistort = TIMER: DO: ti = TIMER: LOOP WHILE ti <(t + 13)‘read the contents of counter 2OUT TMD%, &H80 ‘counter latchOUT TMD%, &H80 ‘latch counter 2countLo% = INP(CT2ADD%) ‘get the LO bytecountHi% = INP(CT2ADD%) ‘get the HI bytecountHi% = &HFF - countHi%countLo% = &HFF - countLo%Count&(j%) = countHi% * 256& + countLo%END SUBFigureCi.Flowmeterandvalveandpumpcontrolcircuitsoncircuitryboard.-D-U m z x C.) C) C) c -1 Cl) C) I m -I C) (1)FigureC.2.Schematicofconnectionsbetweencomputerboard, circuitryboardandphysicalcomponentsmountedontheexterioroftheprototypesampler.FigureC.3.Schematicrepresentationofthenormaloperationandcomputerconnectingplugsoftheprototypesampler.176APPENDIX D. SINGLE ION MONITOR SCANSTI*• (I2o ..-----.---,---..-----.——-“.--—-- ..- -.------—--..- --FitL jI0Tim• )Figure D.1. SIM scans of Cu, Ga and Mn.177--M1990066007000C 5000:466560 14000446200246 2000046 -.. - .-. -15 20 45 66 73 10 295 20 -. - -T1. (1) 25 20 4 II 73 00 205 12019o.. (1)-1661261120072002295• 0400090 10000000700 ... —C C4000266400 2400200100 j• ._66cr-iw’ ..- ..- -. .. . . - 0.00 . _.-.__-. . - -. - . -- II 20 4 95 75 50 205 120 25 30 45 00 72 50 205 220Tl• (1) tIm. )s)Figure D.2 SIM scans of Nb, Ni, Pb and Zn.178APPENDIX E. OCEANOGRAPHICAL DATAStation Location Sea Floor Depth(m)HSI 3814.3N 14550.9E 5200HS5 3457.8N 155 02.3E 5630HS 10 27 46.5N 174 59.4E 5820HSI5 1627.6N 168.29.8W 1550HSI6 1714.ON 16807.0W 5210P26 55.OON 145.00W 4500Table E. 1. Locations and depths of the stations studied.179Station Depth Zn (nmollkg) Cd (nmol/kg) Ni (nmo/kg) Cu (nmollkg)(m)HS 1 25 2.678 ± 0.2311 0.202 ± 0.024 3.603 ± 0.578 0.920 ± 0.12250 1.969 ± 0.603 0.335 ± 0.035 2.418 ± 0.244 0.823 ± 0.09375 1.567 ± 0.078 0.277 ± 0.019 3.182 ± 0.066 0.632 ± 0.034100 1.895 ± 0.057 0.260 ± 0.007 4.762 ± 0.020 1.196 ± 0.005250 3.471±0.112 0.911±0.001 5.487±0.043 1.046±0.001499 6.299 ± 0.213 0.863 ± 0.047 7.893 ± 0.091 1.285 ± 0.039770 6.984 ± 0.25 1 1.013 ± 0.053 7.585 ± 0.192 0.867 ± 0.0481036 8.594±0.208 1.056±0.061 9.535±0.364 1.327±0.0811489 8.830 ± 0.147 1.126 ± 0.032 9.849 ± 0.365 2.096 ± 0.0912326 8.149 ± 0.653 0.950 ± 0.072 10.828 ± 0.426 3.174 ± 0.1042759 8.443 ± 0.604 0.868 ± 0.051 10.837 ± 0.497 4.070 ± 0.1824689 8.418 ± 0.3 59 0.8 17 ± 0.032 10.308 ± 0.226 4.497 ± 0.097HS5 25 0.570±0.001 0.071±0.015 3.050±0.309 1.039±0.01950 0.430 ± 0.03 1 0.026 ± 0.001 2.635 ± 0.100 0.917 ± 0.05775 0.309±0.011 0.024±0.001 2.327±0.098 0.764±0.012100 0.543 ± 0.029 0.039 ± 0.003 2.571 ± 0.011 1.079 ± 0.046250 0.258 ± 0.009 0.03 8 ± 0.00 1 1.763 ± 0.080 0.637 ± 0.016410 1.276±0.038 0.235±0.001 4.364±0.223 1.333±0.021500 1.460 ± 0.065 0.207 ± 0.005 3.794 ± 0.400 1.883 ± 0.080692 3.566 ± 0.023 0.579 ± 0.011 6.93 1 ± 0.396 2.397 ± 0.1081013 5.751 ± 0.085 0.752 ± 0.001 8.567 ± 0.393 3.177 ± 0.1101502 6.954 ± 0.386 0.886 ± 0.039 9.845 ± 0.359 3.439 ± 0.0792526 5.772 ± 0.029 0.730 ± 0.004 7.65 1 ± 0.203 1.750 ± 0.0133051 7.110±0.309 0.782±0.042 8.852±0.362 3.373 ± 0.094HS 10 50 0.511 ± 0.162 0.012 ± 0.005 2.715 ± 0.296 0.690 ± 0.03075 0.421±0.019 0.013±0.004 1.918±0.154 0.704±0.067100 0.768 ± 0.041 0.032 ± 0.001 2.934 ± 0.087 0.840 ± 0.043238 0.355 ± 0.002 0.060 ± 0.003 1.755 ± 0.014 0.699 ± 0.003388 1.029 ± 0.024 0.191 ± 0.006 4.996 ± 0.248 1.155 ± 0.032511 5.728 ± 0.163 0.355 ± 0.009 5.639 ± 0.016 1.284 ± 0.010700 5.284 ± 0.330 0.654 ± 0.032 9.016 ± 0.435 2.222 ± 0.1071009 7.142 ±0.300 0.879±0.041 11.662±0.318 2.568 ±0.1271492 7.78 ± 0.053 0.907 ± 0.011 13.068 ± 0.3 18 2.435 ± 0.0192615 8.104±0.133 0.780±0.008 9.869±0.263 2.194±0.0273116 7.473 ± 0.182 0.766±0.014 12.873 ± 0.687 2.863 ± 0.1534599 6.992 ± 0.191 0.646 ± 0.031 11.484 ± 0.138 7.922 ± 0.155Table E.2 Dissolved Zn, Cd, Ni and Cu in the western North Pacific. Each valueis the average of two measurements and the error represents therange.180Station Depth Pb Mn Ga Nb(m) (pmollkg) (nmollkg) (pmollkg) (pmollkg)HS 1 25 57.5 ± 5.7 0.988 ± 0.145 9.3 ± 3.1 28.8 ± 12.150 45.2±7.2 1.129±0.193 9.7±0.6 72.6±1.475 36.2 ± 2.7 0.778 ± 0.036 10.3 ± 0.5 63.8 ± 5.4100 43.1 ± 0.4 0.733 ± 0.001 9.8 ± 0.6 52.4 ± 5.2250 49.2±0.5 0.882±0.014 7.5±0.1 42.8±3.4499 31.4±2.3 0.816±0.027 5.2±0.4 86.7±0.3770 26.3±1.7 0.726±0.019 4.7±0.1 27.1±4.51036 31.1 ±2.1 0.423 ± 0.042 5.4 ±0.2 104.6 ±6.51489 23.4 ± 0.6 0.435 ± 0.014 6.3 ± 0.3 169.3 ± 13.52326 23.5 ± 0.6 0.230 ± 0.024 9.8 ± 1.7 38.4 ± 1.62759 24.3 ±2.2 0.240±0.019 12.1±0.6 32.6 ±0.74689 21.3±0.8 0.257±0.019 14.1±1.1 42.0±1.8HS 5 25 27.1 ±2.6 1.160±0.112 11.7 ±0.2 52.1 ±6.350 23.4±0.8 1.180±0.046 12.3±0.3 25.4±1.575 22.8±1.5 0.983±0.002 11.5±0.3 31.7±0.9100 22.3 ± 1.2 1.135 ± 0.054 12.5 ±0.3250 12.4 ± 0.1 0.801 ± 0.002 10.9 ± 0.6 45.4 ± 0.2410 5.9 ± 0.4 0.594 ± 0.047 12.0 ± 0.5500 19.0 ± 0.1 11.6 ± 0.0 71.1 ± 3.1692 18.1 ±0.4 0.594±0.028 6.7±0.2 37.2±3.21013 15.7±0.5 1.154±0.021 4.8±0.5 29.9±2.61502 13.4±1.0 0.762±0.058 6.2±0.8 191.1±2.72526 8.2 ±0.1 0.314±0.024 6.6 ±0.2 51.3 ±4.43051 7.4±0.1 0.223±0.018 7.5±0.2 27.1±1.4HS 10 50 40.7 ± 4.4 0.757 ± 0.069 14.5 ± 0.6 9.8 ± 2.675 37.2 ± 3.1 0.621 ± 0.048 14.5 ± 3.0 14.1 ± 1.6100 39.7 ± 1.5 0.981 ± 0.076 18.4 ± 1.5238 26.0±0.5 0.317±0.004 16.4±0.8 24.7±0.1388 46.4 ± 1.8 0.207 ± 0.006 16.8 ± 1.8 14.7 ± 4.8511 43.9 ± 2.1 0.286 ± 0.014 16.0 ± 1.0 35.3 ± 0.3700 40.1 ± 1.8 0.393 ± 0.036 10.2 ±0.3 16.7 ±2.81009 38.7±0.1 0.600±0.023 8.5±0.2 22.7±4.731492 21.7±1.6 0.302±0.029 9.9±0.3 50.7±1.72615 19.0±0.4 0.185±0.008 15.4±0.8 22.0±1.43116 13.2 ± 0.4 0.213 ± 0.014 22.3 ± 1.1 22.9 ± 1.04599 17.1 ± 0.9 0.115 ± 0.008 23.2 ± 0.2 14.4 ± 0.1Table E.3. Dissolved Pb, Mn, Ga and Nb in the western North Pacific. Eachvalue is the average of two measurements with the error being therange.181Station Depth Zn (nmollkg) Cd (nmollkg) Ni (nmollkg) Cu (nmollkg)(m)HS 15 50 0.277±0.170 0.007±0.002 0.965 ± 0.164 0.613 ±0.163100 0.467 ± 0.188 0.013 ± 0.003 1.957 ± 0.132 0.529 ± 0.047300 1.745 ± 0.055 0.321 ± 0.017 5.513 ± 0.158 1.579 ± 0.074300 2.830±0.002 0.186±0.005 3.791 ±0.358 0.909±0.018600 3.711 ± 0.126 0.518 ± 0.017 6.175 ± 0.134 1.070 ± 0.062800 6.534 ± 0.259 0.680 ± 0.029 8.818 ± 0.040 1.144 ± 0.0151000 6.483 ± 0.050 0.681 ± 0.013 9.622 ± 0.229 2.062 ± 0.0101200 7.123 ± 0.088 0.719 ± 0.036 9.173 ± 0.071 1.982 ± 0.0261500 8.861 ± 0.152 0.725 ± 0.034 10.657 ± 0.004 1.656 ± 0.039HS 16 25 0.900 ± 0.172 0.016 ± 0.000 1.429 ± 0.051 0.684 ± 0.09750 0.683 ± 0.194 0.016 ± 0.003 2.255 ± 0.116 0.466 ± 0.033100 1.03 1 ± 0.102 0.012 ± 0.000 2.309 ± 0.088 0.487 ± 0.058300 1.230 ± 0.011 0.280 ± 0.003 3.774 ± 0.082 0.470 ± 0.021500 3.636 ± 0.037 0.652 ± 0.0 13 7.073 ± 0.206 1.276 ± 0.013706 5.651 ± 0.050 0.690±0.003 8.511 ± 0.166 1.349±0.012906 5.229±0.204 0.707±0.039 7.611 ±0.143 0.658±0.0351204 5.759 ± 0.216 0.679 ± 0.013 6.401 ± 0.127 0.917 ± 0.0301504 8.111 ±0.104 0.697±0.019 9.716±0.160 1.126±0.0012032 9.535 ± 0.387 0.697 ± 0.026 10.595 ± 0.351 2.848 ± 0.0692532 9.141 ± 0.195 0.663 ± 0.024 9.292 ± 0.118 1.235 ± 0.0203034 9.906 ± 1.093 0.635 ± 0.050 9.945 ± 0.833 2.524 ± 0.2113534 7.972±0.672 0.622±0.038 7.843±0.454 3.354±0.1844041 10.032 ± 0.541 0.609 ± 0.047 10.006 ± 0.236 3.299 ± 0.0094500 9.884 ± 0.0 12 0.628 ± 0.0 10 9.472 ± 0.004 4.543 ± 0.035Table E.4. Dissolved Zn, Cd, Ni and Cu in the central North Pacific. Each valueis the average of two measurements and the error represents therange.182Station Depth Pb (pmollkg) Mn (nmollkg) Ga (pmollkg) Nb (pmollkg)(m)HS 15 50 10.9 ±2.2 0.6946±0.086 9.5 ±0.1 (368.2)100 10.1±1.4 1.063±0.039 11.0±1.0 79.2±17.3300 21.3±1.2 0.184±0 13.2±0.1 33.8±1.8300 34.2 ± 3.1 0.363 ± 0.013 10.3 ± 0.4 60.6 ± 15.4600 19.6 ± 0.6 0.339 ± 0.013 9.9 ± 0.4 80.6 ± 5.5800 14.1 ± 1.0 0.248 ± 0.012 9.5 ± 0.2 109.3 ± 10.21000 10.5 ± 1.2 0.308 ± 0.011 9.5 ± 0.9 57.0 ± 10.21200 8.1 ± 1.1 0.329±0.008 10.1 ±0.8 101.4 ±4.81500 7.7 ± 0.2 0.287 ± 0.0 12 13.7 ± 1.0 80.0 ± 0.9HS 16 25 16.7 ± 0.6 0.934 ± 0.007 14.4 ± 1.3 35.3 ±050 25.5±2.1 2.377±0.315 11.1±0.5 49.8±12.8100 38.3±0.3 2.755±0.161 9.1±0.7 64.7±5.4300 38.3 ± 0.4 0.617 ± 0.007 8.5 ± 0.2 106.0 ± 1.1500 31.9±0.6 0.816±0.035 6.7±0.4 21.0±2.9706 28.7 ± 1.0 0.619 ± 0.024 7.2 ± 0.3 37.0 ± 5.2906 19.0 ± 1.3 0.472 ± 0.016 7.4 ± 0.6 23.9 ± 1.91204 14.3±0.3 0.652±0.001 8.6±1.3 31.1±2.21504 13.3 ± 0.2 0.490 ± 0.009 10.3 ± 0.4 36.8 ± 3.82032 16.3 ± 1.1 0.468 ± 0.003 15.6 ± 1.2 63.7 ± 8.52532 12.3±0.8 0.289±0 18.6±0.8 150.1±7.93034 15.3 ±0.7 0.256±0.040 25.3±1.3 61.2±0.13534 1 1.5 ± 0.7 0.277 ± 0.037 23.0 ± 0.4 46.9 ± 2.34041 11.8±0.5 0.216±0.027 27.1±0.1 79.4±0.44500 15.6±0.1 0.160±0.005 27.8±0 69.4±1.2Table E.5. Dissolved Pb, Mn, Ga and Nb in the central North Pacific. Each valueis the average of two measurements with the error being the range.Values in brackets believed to be contaminated.183Station Depth Zn (nmollkg) Cd (nmol/kg) Ni (nmoL/kg) Cu (nmollkg)(m)P26 25 0.388±0.012 0.143±0.015 2.806±0 0.897±0.10250 0.293 ± 0.001 0.204 ± 0.009 2.471 ± 0.048 0.827 ± 0.00775 0.463 ± 0.047 0.340 ± 0.005 NA 1.045 ± 0.005100 0.338 ± 0.004 0.413 ± 0.013 2.376 ± 0.03 1 0.996 ± 0.003100 0.416±0.019 0.748±0.078 NA 1.224±0150 NA 0.951±0.057 NA NA200 NA 0.922±0.057 2.827±0 0.728±0250 1.53 1 ± 0 NA 2.554 ± 0.189 0.788 ± 0.030300 NA 0.847±0.067 NA 1.549±0.142500 2.600 ± 0.034 0.849 ± 0.058 2.289 ± 0.027 1.362 ± 0.126500 2.536±0.116 NA 1.870±0.291 1.196±0.019750 4.553 ± 2.572 0.833 ± 0.034 4.543 ± 0.444 1.599 ± 0.010750 6.130±0.127 NA NA NA1000 6.905 ± 0.150 0.928 ± 0 5.445 ± 1.3 17 2.002 ± 0.0091000 5.156±0.303 NA NA NA1250 5.496±0 0.702±0.048 7.857±0 NA1500 7.242±0.614 NA NA 1.926±0.1672000 8.219± 1.181 0.716 ± 0.008 9.438 ± 0.430 1.425 ± 0.0052250 8.818 ± 0.346 0.758 ± 0.019 9.53 1 ± 0.290 3.703 ± 0.0912500 10.253 ± 0.815 0.855 ± 0.072 9.199±0.737 2.041 ± 0.0602500 NA 0.752 ± 0.027 9.403 ± 0.050 2.380 ± 0.1383000 9.394 ± 0.468 0.747 ± 0.048 9.530 ± 0.207 2.773 ± 0.3883000 NA 0.606±0 9.523±0.415 3.929±0.1453900 8.940±0 0.842±0.029 9.633±0 3.042±0_____4200 NA NA 9.147 ± 0.123 6.663 ± 0.522Table E.6. Dissolved Zn, Cd, Ni and Cu in the eastern North Pacific. Each valueis the average of two measurements and the error represents therange.NA = not analyzed.184Statio Depth Pb (pmollkg) Mn (nmollkg) Ga (pmollkg) Nb (pmollkg)n (m)P 26 25 23.5 ± 2.1 0.548 ± 0.064 4.0 ± 0.8 35.4 ± 0.750 41.3±4.5 0.539±0.025 4.8±0.2 51.9±4.175 31.3±4.3 0.423±0.007 3.1±2.2 15.6±1.5100 38.2 ± 2.3 0.490 ± 0.021 7.3 ± 1.5 16.4 ± 0.3100 NA 0.301 ± 0.013 NA NA150 18.0±2.0 NA 8.0±3.4 6.3±0200 NA NA 11.8±3.5 NA250 22.3 ± 2.2 0.278 ± 0.035 NA 3.3 ± 1.2250 NA 0.496±0.024 NA NA300 21.3±2.8 NA 11.9±3.1 NA500 26.8±1.5 0.816±0.004 13.8±2.1 12.3±2.3750 28.5 ± 1.1 0.626±0.019 7.1 ±2.8 34.0 ±2.2750 18.8±2.0 NA NA 30.4±1.91000 20.9±6.6 0.511 ±0.005 4.4± 1.4 22.7±8.41000 NA NA 3.1±0.5 NA1250 15.3 ±0 NA 7.1±0.4 23.9±3.91250 NA NA 7.5±0.2 NA1500 19.6±1.4 0.430±0.042 NA 123.8±10.62000 14.3 ± 0.5 0.380 ± 0.004 9.4 ± 2.3 34.2 ± 6.62000 8.3 ± 2.3 NA NA 51.2 ± 3.82250 7.9 ± 0.2 NA 8.4 ± 1.6 29.2 ± 02500 10.0 ± 1.3 0.346 ± 0.025 12.0 ± 0.6 51.5 ± 2.52500 8.5 ± 1.3 NA 17.5 ± 1.9 NA3000 8.8±0.8 0.339±0.027 11.7±0 104.5±21.33000 8.8±0.1 NA 10.7±2.0 NA3500 5.0 ±0.1 0.363 ± 0.029 NA NA3900 5.3 ±0 NA 20.4±0 NA4200 5.2±5.9 0.479±0.023 31.7±3.8 107.7±13.8____4200 NA NA NA 104.6± 11.0Table E.7. Dissolved Pb, Mn, Ga and Nb in the eastern North Pacific. Each valueis the average of two measurements with the error being the range.NA = not analyzed.


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