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The development of a technique for the determination of disolved chromium(III) and total dissolved chromium… Mugo, Robert K. 1991

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THE DEVELOPMENT OF A TECHNIQUE FOR THE DETERMINATION OF DISSOLVED CHROMIUM(III) AND TOTAL DISSOLVED CHROMIUM IN SEAWATER BY ELECTRON CAPTURE DETECTION GAS CHROMATOGRAPHY by ROBERT K. MUGO B.Sc. (Hons.)# U n i v e r s i t y o f N a i r o b i , 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA October 1991 © Robert K. Mugo, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CU The University of British Columbia Vancouver, Canada Date OcWr tfc 1991 • DE-6 (2/88) ABSTRACT A gas chromatographic method f o r the de t e r m i n a t i o n of d i s s o l v e d C r ( I I I ) and t o t a l d i s s o l v e d Cr i n seawater was developed. The technique uses the e l e c t r o n capture d e t e c t i o n of the 1,1,1-trifluoro-2,4-pentanedione (Htfa) d e r i v a t i v e of C r ( I I I ) , C r ( t f a ) 3 , which was prepared from s o l v e n t e x t r a c t i o n of a 15-mL seawater sample. The method was a p p l i e d t o s t o r e d a c i d i f i e d samples f o r the det e r m i n a t i o n of t o t a l Cr and t o s t o r e d , f r o z e n , u n a c i d i f i e d samples f o r the d e t e r m i n a t i o n of C r ( I I I ) and, a f t e r r e d u c t i o n , t o t a l Cr (with Cr(VI) being obtained as the d i f f e r e n c e of these two). The accuracy of the technique was assessed by the a n a l y s i s of standard r e f e r e n c e m a t e r i a l s from the N a t i o n a l Research C o u n c i l of Canada. The Cr v a l u e s obtained f o r the r e f e r e n c e m a t e r i a l s u s i n g t h i s method were i n good agreement with the c e r t i f i e d v a l u e s . The technique has a p r e c i s i o n of 1.3% a t 4.67 nM with d e t e c t i o n l i m i t s (3 an_±) f o r C r ( I I I ) and t o t a l Cr of 0.186 and 0.243 nM i n the o r i g i n a l seawater, r e s p e c t i v e l y . The method i s designed t o be a p p l i e d t o the d e t e r m i n a t i o n o f Cr i n seawater samples immediately a f t e r c o l l e c t i o n onboard s h i p d u r i n g oceanographic c r u i s e s . The attempt t o extend the technique t o the de t e r m i n a t i o n of g a l l i u m i n seawater was not s u c c e s s f u l due t o thermal i n s t a b i l i t y and/or i n s u f f i c i e n t v o l a t i l i t y of the G a ( t f a ) 3 c h e l a t e . i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v i i i LIST OF FIGURES i x LIST OF ABBREVIATIONS x i ACKNOWLEDGMENT x i i CHAPTER 1: INTRODUCTION 1.1 BACKGROUND 1 1.2 COMPOUND REQUIREMENTS 2 1.2.1 V o l a t i l i t y 2 1.2.2 S t a b i l i t y 3 1.2.3 Ease of formation 4 1.3 B-DIKETONE CHELATES 5 1.4 FLUORINATED 6-DIKETONE CHELATES 8 1.5 ELECTRON CAPTURE DETECTOR 9 1.6 DETERMINATION OF TRACE METALS BY GAS CHROMATOGRAPHY 12 1.7 THE DETERMINATION OF CHROMIUM IN SEAWATER 16 1.8 MARINE GEOCHEMISTRY OF CHROMIUM 19 1.9 AIM OF PRESENT STUDY 23 CHAPTER 2: EXPERIMENTAL 2.1 INSTRUMENTATION 26 2.1.1 Gas chromatograph 26 i v 2.1.2 Mass spectrometry 27 2.1.3 Elemental a n a l y s i s 27 2.1.4 pH 27 2.1.5 Shaking 27 2.1.6 Heating 27 2.2 MATERIALS AND REAGENTS 28 2.2.1 l , 1 , 1 - T r i f l u o r o - 2 , 4 - p e n t a n e d i o n e 28 2.2.2 Toluene 28 2.2.3 B u f f e r 29 2.2.4 Sodium s u l p h i t e 30 2.2.5 2,6 - D i c h l o r o b i p h e n y l 30 2.2.6 Separatory f u n n e l 31 2.2.7 De i o n i z e d water 31 2.2.8 Aqueous Cr standards 31 2.2.9 T r i s - ( 1 , 1 , 1 - t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) -chromiura(III) standard 32 2.3 PROCESSING 32 2.4 OPTIMIZATION 33 2.4.1 Gas Chromatography 3 3 2.4.2 S o l v e n t e x t r a c t i o n c o n d i t i o n s 34 2.4.2.1 pH 34 2.4.2.2 Ligand c o n c e n t r a t i o n 35 2.4.2.3 Temperature and r e a c t i o n time 35 2.5 SEAWATER SAMPLES 35 2.5.1 Stored a c i d i f i e d seawater samples 36 2.5.2 Frozen u n a c i d i f i e d seawater samples 36 2.6 ANALYTICAL SCHEME 37 V 2.7 GENERAL PROCEDURE 37 2.8 QUANTITATION 39 2.8.1 Organic chromium standards 40 2.8.2 Chromium e x t r a c t i o n standards 40 2.8.2.1 C r ( I I I ) standards 40 2.8.2.2 Cr(VI) standards 41 2.9 CHROMIUM RECOVERY STUDIES 41 2.10 REPRODUCIBILITY 41 2.11 ACCURACY 41 2.12 BLANKS 42 CHAPTER 3: RESULTS AND DISCUSSIONS 3.1 CHARACTERIZATION OF TRIS-(1,1,l-TRIFLUORO-2,4-PENTANEDIONO)-CHROMIUM(III) STANDARD 43 3.1.1 Mass s p e c t r a 43 3.1.2 Elemental a n a l y s i s 44 3.2 QUANTITATIVE ANALYSIS IN GC 46 3.3 QUANTITATIVE PROCEDURES IN PRESENT STUDY 47 3.3.1 C r ( t f a ) 3 c i s v t r a n s i s o m e r i z a t i o n 47 3.3.2 I n t e r n a l standard method 48 3.3.3 Organic chromium standards , 49 3.3.4 Chromium e x t r a c t i o n standards 50 3.3.5 Chromium e x t r a c t i o n blanks 50 3.3.6 C a l i b r a t i o n curves 51 3.3.7 Chromatograms 51 3.4 REDUCING AGENT 57 3.5 SOLVENT 57 3.6 OPTIMIZATION 58 v i 3.6.1 Gas chromatograph 58 3.6.1.1 ECD s e n s i t i v i t y 59 3.6.2 Solv e n t e x t r a c t i o n 60 3.6.2.1 pH 60 3.6.2.2 Ligand c o n c e n t r a t i o n 60 3.6.2.3 Temperature and r e a c t i o n time 62 3.7 ANALYTICAL FIGURES OF MERIT 65 3.7.1 P r e c i s i o n 65 3.7.2 Recovery 66 3.7.3 Accuracy 67 3.7.4 L i m i t of d e t e c t i o n 68 3.8 ANALYSIS OF SEAWATER SAMPLES 69 3.8.1 Stored a c i d i f i e d samples 69 3.8.2 Stored f r o z e n samples 72 3.8.2.1 Handling 75 3.8.3 Reagent and h a n d l i n g blank 76 3.9 DETERMINATIONS AT SEA 76 3.10 SUGGESTIONS FOR FURTHER WORK 77 3.11 SUMMARY AND CONCLUSIONS 78 CHAPTER 4: GALLIUM 4.1 INTRODUCTION 79 4.1.1 Overview 79 4.1.2 Background 79 4.2 EXPERIMENTAL 81 4.2.1 Gas chromatography 81 4.2.1.1 Column 81 v i i 4.2.1.2 GC c o n d i t i o n s 81 4.2.2 S y n t h e s i s of t r i s - ( 1 , 1 , 1 - t r i f l u o r o - 2 , 4 -p e n t a n e d i o n o ) - g a l l i u m ( I I I ) standard 8 2 4.2.3 Organic Ga standards 82 4.2.4 Sol v e n t e x t r a c t i o n 83 4.3 RESULTS AND DISCUSSION 84 4.3.1 C h a r a c t e r i z a t i o n of t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2 ,4-pentanediono)-gallium(III) standard .... 84 4.3.1.1 Mass s p e c t r a 84 4.3.1.2 Elemental a n a l y s i s 86 4.3.2 Chromatograms 86 4.3.3 ECD s e n s i t i v i t y 90 4.3.4 D i s c u s s i o n 91 4.3.5 Summary and c o n c l u s i o n s 95 REFERENCES 96 APPENDIX I. T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r C r ( t f a ) 3 + and C r ( t f a ) 2 * 100 I I . T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r G a ( t f a ) 3 + and G a ( t f a ) 2 101 v i i i LIST OF TABLES 1.5 ECD s e n s i t i v i t y t o v a r i o u s c l a s s e s of compounds 13 3.1.1 Fragmentation ions of t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2,4-pentanediono)-chromium(III) 43 3.1.2 Elemental a n a l y s i s data f o r t r i s - ( 1 , 1 , 1 -t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) - c h r o m i u m ( I I I ) 44 3.6.1 Gas chromatographic c o n d i t i o n s f o r the a n a l y s i s of chromium as t r i s - ( 1 , 1 , 1 - t r i f l u o r o - 2 , 4 -pentanediono)-chromium(III) 58 3.7.1 R e p r o d u c i b i l i t y of Cr d e t e r m i n a t i o n on seawater sample 66 3.7.2 Recovery of Cr s p i k e s from seawater samples ... 67 3.7.3 Accuracy of Cr d e t e r m i n a t i o n on seawater samples 68 3.8.1 T o t a l Cr v s . depth i n the c e n t r a l North A t l a n t i c (BDA s t a t i o n ) 70 3.8.2 C r ( I I I ) , Cr(VI) and t o t a l Cr vs. depth i n the Northeast P a c i f i c (NTK s t a t i o n ) 74 4.2.1.2 Gas chromatographic c o n d i t i o n s f o r the a n a l y s i s of g a l l i u m as t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2 , 4-pentanediono)-gallium(III) 81 4.3.1.1 Fragmentation ions o f t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2 , 4-pentanediono)-gallium(III) 84 4.3.1.2 Elemental a n a l y s i s data f o r t r i s - ( 1 , 1 , 1 -t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) - g a l l i u m ( I I I ) 86 i x LIST OF FIGURES Fi g u r e Page 1.3 S t r u c t u r e s of some B-diketone l i g a n d s 7 1.5 E l e c t r o n capture d e t e c t o r 11 1.8 pH-pE diagram f o r the major d i s s o l v e d s p e c i e s of chromium 22 3.1.1 Mass spectrum of t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2,4-pentanediono)-chromium(III) 45 3.3.6a Organic Cr standards c a l i b r a t i o n curve 52 3.3.6b C r ( I I I ) c a l i b r a t i o n curve 53 3.3.6c T o t a l Cr c a l i b r a t i o n curve obtained from r e d u c i n g Cr(VI) standards 53 3.3.7a Chromatogram of s y n t h e s i z e d C r ( t f a ) 3 standard 54 3.3.7b Chromatogram of C r ( t f a ) 3 from an e x t r a c t i o n standard 55 3.3.7c Chromatogram of C r ( t f a ) 3 from a seawater sample 56 3.6.2.1 Cr re c o v e r y v s . pH 61 3.6.2.2 Cr r e c o v e r y vs. H t f a l i g a n d volume 61 3.6.2.3a Cr recover y vs. shaking time a t room temperature 64 3.6.2.3b Cr re c o v e r y vs. shaking time a f t e r microwave i r r a d i a t i o n 64 3.8.1 T o t a l Cr vs. depth i n the c e n t r a l North A t l a n t i c (BDA s t a t i o n ) 71 3.8.2 C r ( I I I ) , Cr(VI) and t o t a l Cr vs. depth i n the Northeast P a c i f i c (NTK s t a t i o n ) 73 4.3.1.1 Mass spectrum of t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2 , 4-pentanediono)-gallium(III) 85 X 4 . 3 . 2 a C h r o m a t o g r a m o f s y n t h e s i z e d G a ( t f a ) 3 s t a n d a r d 87 4 . 3 . 2 b C h r o m a t o g r a m o f G a ( t f a ) 3 f r o m a n e x t r a c t i o n s t a n d a r d 88 4 . 3 . 2 c C h r o m a t o g r a m o f G a ( t f a ) 3 f r o m a s e a w a t e r s a m p l e 89 5 . 1 0 ( a ) T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r C r ( t f a ) 3 + 100 5 . 1 0 ( b ) T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r C r ( t f a ) 2 + 100 5 . 2 0 ( a ) T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r G a ( t f a ) 3 + 101 5 . 2 0 ( b ) T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r G a ( t f a ) 2 + 101 x i LIST OF ABBREVIATIONS DI H 20 De i o n i z e d water H t f a / t f a 1,1,1-Trifluoro-2,4-pentanedione ( T r i f l u o r o a c e t y l a c e t o n e ) GC Gas chromatography ECD E l e c t r o n capture d e t e c t o r h f a H e x a f l u o r o a c e t y l a c e t o n e fod 6,6,7,7,8,8,8-Heptafluoro-2,2-dimethyl-3,5-octanedione acac A c e t y l a c e t o n e thd 2,2,6,6-Tetramethyl-3,5-heptanedione facam T r i f l u o r o a c e t y l - d - c a m p h o r ppm P a r t s per m i l l i o n ppb P a r t s per b i l l i o n nM Nanomolar pM Picomolar UHP U l t r a h i g h p u r i t y NaAc Sodium a c e t a t e HAc A c e t i c a c i d PFA P e r f l u o r o a l k o x y x i i ACKNOWLEDGMENT I wish t o express my g r a t i t u d e t o my r e s e a r c h s u p e r v i s o r , Dr. K. J . Or i a n s , f o r her guidance and support throughout the course of t h i s study. I am a l s o g r a t e f u l t o people i n and o u t s i d e the Department who have g i v e n me encouragement and h e l p f u l suggestions a l l along. 1 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND The use of gas chromatography i n a n a l y z i n g f o r metals as metal c h e l a t e s was f i r s t suggested by Lederer i n 1955 ( 1 ) . T h i s concept r e q u i r e s t h a t a mixture of metals or metal compounds be converted t o v o l a t i l e compounds which can then be s u b j e c t e d t o gas chromatographic s e p a r a t i o n and measurement. I n i t i a l l y , the b i g g e s t o b s t a c l e was i n f i n d i n g s u i t a b l e v o l a t i l e compounds f o r t h i s purpose. I f t h i s d i f f i c u l t y was overcome, i t was reasoned t h a t the technique would be of g r e a t b e n e f i t f o r a n a l y z i n g mixtures of metals. The a b i l i t y of gas chromatography t o separate complex mixtures r a p i d l y and t o p r o v i d e d e t e c t i o n a t low l e v e l s are of g r e a t use f o r metal a n a l y s i s . Gas chromatography has a g r e a t v e r s a t i l i t y not e v i d e n t i n o t h e r t e c h n i q u e s . By simply changing one of the parameters, such as column temperature or the l i q u i d s t a t i o n a r y phase, the q u a l i t y of the data can be improved markedly. Peak r e s o l u t i o n can be enhanced and the a n a l y s i s time shortened by simple parameter changes. The wide v a r i e t y of GC-detectors a v a i l a b l e makes i t p o s s i b l e t o take advantage of s p e c i f i c i t y i n the response c h a r a c t e r i s t i c s of s e l e c t e d d e t e c t i o n t e c h n i q u e s . The 2 e l e c t r o n capture d e t e c t o r , f o r example, i s remarkably-s e n s i t i v e t o halogenated compounds, y e t i n s e n s i t i v e to hydrocarbons. The a b i l i t y t o combine gas chromatography with other techniques, such as s o l v e n t e x t r a c t i o n , t o s o l v e e s p e c i a l l y d i f f i c u l t problems of s e p a r a t i o n s i s a l s o an a t t r a c t i v e f e a t u r e f o r a n a l y s i s of metals i n a v a r i e t y of m a t r i c e s . I f two components cannot be separated by gas chromatography, o f t e n one of the components may be removed d u r i n g the p r e l i m i n a r y sample p r e p a r a t i o n s t e p by v a r y i n g any one of the s e v e r a l parameters (pH, a d d i t i o n of masking agents, etc.) a s s o c i a t e d with the e x t r a c t i o n . 1.2 COMPOUND REQUIREMENTS I f gas chromatography i s t o be s u c c e s s f u l l y a p p l i e d t o t r a c e metal a n a l y s i s , the metal d e r i v a t i v e formed has t o meet a number of requirements. 1.2.1 V o l a t i l i t y The most important and r e s t r i c t i n g requirement i s t h a t compounds sh o u l d be v o l a t i l e enough t o be chromatographed i n the gas phase. For most purposes, the metal compound must e x h i b i t a vapor p r e s s u r e of 0.1 t o 1.0 mm Hg i n order t o move through the column a t a reasonable r a t e (2) . Only a few types of metal compounds meet t h i s requirement. 3 Immediately e l i m i n a t e d are most types of charged or h i g h l y p o l a r s p e c i e s i n which i n t e r m o l e c u l a r f o r c e s are high. The e x i s t e n c e of f a c t o r s such as l a r g e d i p o l e s , adduct formation, p o l y m e r i z a t i o n and hydrogen bonding w i l l a c t t o reduce v o l a t i l i t y . The types of metal compounds t h a t are v o l a t i l e a t reasonably low temperatures are l i m i t e d i n number. They i n c l u d e some metal h a l i d e s , metal a l k o x i d e s , metal c a r b o n y l s , metal a l k y l s , metal h y d r i d e s , jr-bonded metal complexes such as the metal c y c l o p e n t a d i e n y l s , and v a r i o u s metal c h e l a t e s such as B-diketonates and p o r p h y r i n s . 1.2.2 S t a b i l i t y The importance of the s t a b i l i t y of a compound i s s t r o n g l y dependent on i t s v o l a t i l i t y . More v o l a t i l e compounds can be e l u t e d a t lower column temperatures w i t h the r e s u l t t h a t thermal s t a b i l i t y requirements are not as demanding. For q u a n t i t a t i v e work, the compounds should be s u f f i c i e n t l y t h e r m a l l y s t a b l e t h a t they can be e l u t e d without d e g r a d a t i o n . In a d d i t i o n t o being t h e r m a l l y s t a b l e , the compounds must be s o l v o l y t i c a l l y s t a b l e when d i s s o l v e d i n the l i q u i d s t a t i o n a r y phase i n the column. I f the l i q u i d phase can compete e f f e c t i v e l y as a c o o r d i n a t i n g agent s o l v o l y s i s w i l l o c cur. The compounds should a l s o be n o n - r e a c t i v e with the s o l i d s t a t i o n a r y support and wit h the c o n s t r u c t i o n m a t e r i a l s of the chromatographic flow system. From a p r a c t i c a l 4 s t a n d p o i n t , i t i s d e s i r a b l e t h a t the compounds be s t a b l e i n the ambient atmosphere so as to a v o i d s p e c i a l h a n d l i n g procedures. U n l i k e the thermal s t a b i l i t y requirement, there are ways of circumventing some of the other s t a b i l i t y requirements. C a r e f u l s e l e c t i o n of n o n - r e a c t i v e l i q u i d p a r t i t i o n i n g phases, s o l i d supports and c o n s t r u c t i o n m a t e r i a l s w i l l permit g r e a t e r s t a b i l i t y i n o p e r a t i o n . Compounds such as the metal h a l i d e s which undergo h y d r o l y s i s i n the atmosphere are, however, burdensome t o work with. I t i s a l s o important t h a t the components of the sample should not undergo mutual r e a c t i o n . For example, redox r e a c t i o n s may occur i f o x i d i z i n g and r e d u c i n g s p e c i e s are present i n a mixture. D i m e r i z a t i o n or p o l y m e r i z a t i o n may p r e s e n t a problem p a r t i c u l a r l y when hydroxo-, oxo-, c h l o r o -or other b r i d g e formation o c c u r s . Compounds t h a t are c o o r d i n a t i v e l y s a t u r a t e d and do not c o n t a i n m o i e t i e s t h a t r e a d i l y form b r i d g e s are t h e r e f o r e p r e f e r r e d . 1.2.3 Ease of Formation For q u a n t i t a t i v e work the types of compounds which can be used are l i m i t e d t o those t h a t can be r e a d i l y formed i n q u a n t i t a t i v e or n e a r l y q u a n t i t a t i v e and e a s i l y r e p r o d u c i b l e y i e l d . The metal c a r b o n y l s , h y d r i d e s and a l k y l s are u s u a l l y formed o n l y with d i f f i c u l t y and r a r e l y i n q u a n t i t a t i v e y i e l d . T h e i r syntheses cannot be c a r r i e d out i n water owing 5 t o the s o l v o l y t i c i n s t a b i l i t y of the products. On the other hand, c e r t a i n c h e l a t i n g agents form complexes of h i g h s o l v o l y t i c s t a b i l i t y by simple r e a c t i o n s t h a t occur r e a d i l y . The r e a c t i o n s can be c a r r i e d out i n aqueous or non-aqueous media and are pH dependent, a f e a t u r e a f f o r d i n g a measure of s e l e c t i v i t y i n h a n d l i n g mixtures which are d i f f i c u l t t o separate c h r o m a t o g r a p h i c a l l y . 1.3 B-DIKETONE CHELATES ft-diketonates are one of the few c l a s s e s of metal d e r i v a t i v e s which meet the requirements f o r s u c c e s s f u l q u a n t i t a t i v e gas chromatography. These c h e l a t e s have been used e x t e n s i v e l y , are r e a d i l y o b t a i n e d i n q u a n t i t a t i v e y i e l d and are s t a b l e i n the ambient atmosphere. Many metal ions form complexes under s i m i l a r c o n d i t i o n s which s i m p l i f i e s the sample p r e p a r a t i o n procedure and c o u l d be a u s e f u l aspect i n multi-element d e t e r m i n a t i o n s . Metal B-diketonates a l s o l e n d themselves w e l l t o s o l v e n t e x t r a c t i o n w i t h i t s attendant advantages i n s e l e c t i v i t y . A wide v a r i e t y of metals i n many ma t r i c e s can be converted i n t o v o l a t i l e metal B-diketonate complexes f o r gas chromatographic s e p a r a t i o n and a n a l y s i s . The B-diketone l i g a n d s s h i e l d the metal i o n from the i n t e r m o l e c u l a r f o r c e s t h a t render i t n o n - v o l a t i l e by s u r r o u n d i n g i t w i t h a hydrocarbon s h e l l . For maximum v o l a t i l i t y the combination of s t e r i c and i n d u c t i v e e f f e c t s s h ould a c t t o minimize the tendency t o form adducts or 6 polymers. The presence of c h e l a t e r i n g s i n the complex and the r e s u l t i n g enhanced s t a b i l i t y have been d e s c r i b e d as v i r t u a l l y e s s e n t i a l f o r s u c c e s s f u l gas chromatography ( 2 ) . With t h e i r oxygen donor atoms f a c i l i t a t i n g complexation w i t h v i r t u a l l y a l l A-type elements, the 8-diketonates ( F i g . 1.3.1) are amongst the most v e r s a t i l e c h e l a t i n g agents. The i o n i z a t i o n o f 6-diketones i s as f o l l o w s : R-C-CH.-C-R' R-C-CH = C-R' (1) I A "' J A-(a) (b) The complexing e n o l a t e anion (b) i n many i n s t a n c e s forms n e u t r a l c h e l a t e s w i t h metals whose c o o r d i n a t i o n number i s twice t h e i r o x i d a t i o n s t a t e . The r e s u l t i n g complexes are c o o r d i n a t i v e l y s a t u r a t e d , thus p r e c l u d i n g o t h e r adduction by s o l v e n t or o t h e r l i g a r i d s p e c i e s ( 3 ) . C h e l a t e s which are c o o r d i n a t i v e l y s a t u r a t e d , such as those of B e ( I I ) , A l ; ' " " . ' ; , and C r ( I I I ) , have been amongst the most s u c c e s s f u l l y chromatographed as B - d i k e t o n a t e s . In c o n t r a s t , metals such as N i ( I I ) , C o ( I I ) , F e ( I I ) and L a ( I I I ) , which r e a d i l y adduct a d d i t i o n a l n e u t r a l l i g a n d s t o assume a c o o r d i n a t i o n s t a t e g r e a t e r than twice t h e i r o x i d a t i o n s t a t e , have proved d i f f i c u l t t o s u b j e c t t o GC a n a l y s i s ( 4 ) . In some cases hydrates have been formed. Hydrates tend t o lower the v o l a t i l i t y and i n c r e a s e the p o l a r i t y , thereby i n c r e a s i n g peak broadening, t a i l i n g o r o t h e r u n d e s i r a b l e c h a r a c t e r i s t i c s . A l t e r n a t i v e l y , non-solvated c h e l a t e s have 7 Liqond acetytacetone trifluoroacetylacetone hexafkioroocetylacetone 2,2,6,6-tetramethyl-3,5-hepianedione 6^,7,7,8 L 8,8-h€ptofluoro-2,2-dimefhyl-3,5-octanedione l^!A5,6 ,6 ,7 ,7 ,7-decafluofO-2,4-heptonedione tri f luoroacetyl-d-camphor Structure of Anion H£-£Vc-CH, H FjC-?-C-?-CH 3 H 0© F,C-C-9 H HjC-6-C-C-CHf-CH, H £ H CHs HaC-C-C-C-C-CFrCFj-CF, FsC-C-C-C-CFV-CFfCF, H Abbreviation ocac tfa hfa thd fod dfhd facam F i g . 1.3: S t r u c t u r e o f some 6-Diketone l i g a n d s 8 polymerized or r e a c t e d on-column with a c t i v e , hydroxyl or other groups present on the supports and i n the s t a t i o n a r y phase. T h i s l e a d s to e x c e s s i v e peak broadening or even i r r e v e r s i b l e a d s o r p t i o n , p a r t i c u l a r l y a t low metal c o n c e n t r a t i o n l e v e l s ( 4 ) . 1.4 FLUORINATED fl-DIKETONE CHELATES With on l y a few e x c e p t i o n s , the simple a c e t y l a c e t o n a t e s have proven t o be u n s a t i s f a c t o r y f o r metal a n a l y s i s owing t o thermal and s o l v o l y t i c i n s t a b i l i t y d u r i n g chromatography. They o f t e n r e q u i r e column temperatures t h a t are too h i g h (approx. 170-200 °C) f o r thermal deg r a d a t i o n t o be completely absent. Only B e ( I I ) , A l ( I I I ) and C r ( I I I ) a c e t y l a c e t o n a t e s (5) showed adequate GC c h a r a c t e r i s t i c s , with minimal i n j e c t i o n or on-column de g r a d a t i o n . As was p o i n t e d out by Moshier and S i e v e r s ( 2 ) , the major breakthrough t h a t made the GC d e t e r m i n a t i o n of metal c h e l a t e s a u s e f u l a n a l y t i c a l procedure was the i n t r o d u c t i o n of f l u o r i n a t e d B - d i k e t o n a t e s . These f l u o r i n a t e d a c e t y l a c e t o n a t e analogs r e q u i r e much l e s s severe instrument c o n d i t i o n s (lower column, i n j e c t i o n p o r t , and d e t e c t o r temperatures), because of t h e i r i n c r e a s e d v o l a t i l i t i e s . T h i s e f f e c t may be e x p l a i n e d i n p a r t by e n v i s i o n i n g the e l e c t r o n e g a t i v e f l u o r i n e atoms as dominating the outer p e r i p h e r y of the complex ( 6 ) . The f l u o r o c a r b o n s h e l l may reduce the van der Waals f o r c e s and i n t e r m o l e c u l a r hydrogen 9 b o n d i n g between f l u o r i n e s u b s t i t u t e d B - d i k e t o n a t e s . C o n c e i v a b l y t h e somewhat b u l k i e r f l u o r i n e atoms c o u l d p r e v e n t c l o s e - p a c k i n g i n t h e c r y s t a l l a t t i c e , a f a c t o r t h a t s h o u l d f a v o u r g r e a t e r v o l a t i l i t y . The i n c r e a s e i n v o l a t i l i t y o f f l u o r i n e c o n t a i n i n g B - d i k e t o n a t e s c o r r e s p o n d s d i r e c t l y t o t h e e x t e n t o f f l u o r i n e s u b s t i t u t i o n . W o l f e t al. (7) measured t h e v a p o r p r e s s u r e o f s e v e r a l m e t a l B - d i k e t o n a t e s and showed t h a t c o m p l e x e s c o n t a i n i n g h i g h l y f l u o r i n a t e d l i g a n d s a r e more v o l a t i l e t h a n c o m p l e x e s w i t h f e w e r f l u o r i n e s s u b s t i t u t e s ; i n t h e o r d e r h f a » t f a » f o d » a c a c . E i s e n t r a u t (8) a p p l i e d t h e r m o g r a v i m e t r i c a n a l y s i s t o d e t e r m i n e t h e r e l a t i v e v o l a t i l i t i e s o f v a r i o u s m e t a l B - d i k e t o n a t e s and c o n f i r m e d t h e d e p e n d e n c e o f v o l a t i l i t y on t h e e x t e n t o f f l u o r i n a t i o n . 1.5 ELECTRON CAPTURE DETECTOR S e v e r a l t y p e s o f d e t e c t o r s have been u s e d i n t h e gas c h r o m a t o g r a p h i c a n a l y s i s o f t r a c e m e t a l s . E a r l y w o r k e r s u t i l i z e d t h e c o n v e n t i o n a l f l a m e i o n i z a t i o n and t h e r m a l c o n d u c t i v i t y d e t e c t o r s . L a t e r , R o s s (12) r e p o r t e d t h a t t h e e l e c t r o n c a p t u r e d e t e c t o r r e s p o n d e d t o e x t r e m e l y s m a l l c o n c e n t r a t i o n s o f f l u o r i n e - c o n t a i n i n g B - d i k e t o n a t e s , w i t h d e t e c t i o n l i m i t s on t h e o r d e r o f 1 0 ~ 1 4 g o f t h e m e t a l . W o r k e r s have a l s o e m p l o y e d t h e m icrowave e m i s s i o n d e t e c t o r w h i c h i s c o m p a r a b l e i n s e n s i t i v i t y t o e l e c t r o n c a p t u r e d e t e c t o r . 10 The e l e c t r o n capture d e t e c t o r ( F i g . 1.5) c o n t a i n s a r a d i o a c t i v e i s o t o p e e m i t t i n g high energy e l e c t r o n s ( f i - p a r t i c l e s ) . The e m i t t e r s u s u a l l y used are 6 3 N i or t r i t i u m (adsorbed on platinum or t i t a n i u m f o i l ) . The e f f l u e n t from the column i s passed over the e m i t t e r where the e l e c t r o n s cause i o n i z a t i o n of the c a r r i e r gas through c o l l i s i o n s producing a b u r s t of secondary e l e c t r o n s . F u r t h e r c o l l i s i o n s reduce the energy of these e l e c t r o n s i n t o the thermal range. In the absence of sample molecules, a constant s t a n d i n g c u r r e n t between a p a i r of e l e c t r o d e s r e s u l t s from t h i s i o n i z a t i o n p r o c e s s . The c u r r e n t decreases, however, i n the presence of molecules t h a t tend to capture e l e c t r o n s . The uncaptured e l e c t r o n s are c o l l e c t e d p e r i o d i c a l l y by a p p l y i n g s h o r t - t e r m v o l t a g e p u l s e s t o the c e l l e l e c t r o d e s . T h i s c e l l c u r r e n t i s measured and compared t o a r e f e r e n c e c u r r e n t , and the p u l s e i n t e r v a l i s then a d j u s t e d t o m a i n t a i n c o n s t a n t c e l l c u r r e n t . The p u l s e r a t e (frequency) t h e r e f o r e r i s e s when an e l e c t r o n c a p t u r i n g compound i s p a s s i n g through the c e l l . The p u l s e i s converted t o v o l t a g e which i s l i n e a r l y r e l a t e d to the amount of e l e c t r o n c a p t u r i n g m a t e r i a l i n the c e l l . The ECD i s t h e r e f o r e s e l e c t i v e i n i t s response, being h i g h l y s e n s i t i v e toward molecules c o n t a i n i n g e l e c t r o n e g a t i v e f u n c t i o n a l groups such as halogens, p e r o x i d e s , quinones, and n i t r o groups. I t i s i n s e n s i t i v e toward f u n c t i o n a l groups such as amines, a l c o h o l s , and hydrocarbons. An important 11 Ceramic insulator Radioactive N f o i l Electron «;oUsctor F i g . 1.5: E l e c t r o n c a p t u r e d e t e c t o r 12 a p p l i c a t i o n of the ECD has been i n the d e t e c t i o n of c h l o r i n a t e d p e s t i c i d e s . Table 1.5 g i v e s a g e n e r a l i n d i c a t i o n of the ECD s e n s i t i v i t y t o d i f f e r e n t c l a s s e s of compounds. 1.6 DETERMINATION OF TRACE METALS BY GAS CHROMATOGRAPHY Formation of v o l a t i l e c h e l a t e s coupled with gas chromatography s e p a r a t i o n i s an a t t r a c t i v e technique f o r t r a c e metal a n a l y s i s because of i t s speed, s i m p l i c i t y and s e n s i t i v i t y ( 2 ) . C h e l a t i o n i s achieved by e x t r a c t i o n of the metal from an aqueous medium wit h the l i g a n d i n a s u i t a b l e i m m i s c i b l e s o l v e n t , or by d i r e c t c h e l a t i o n of the l i g a n d w i t h the metal sample (no s o l v e n t ) . Although e a r l y e f f o r t s i n metal a n a l y s i s i n v o l v e d the s e p a r a t i o n of r e l a t i v e l y l a r g e q u a n t i t i e s of metals i n mixtures, r e c e n t emphasis has been on deter m i n i n g t r a c e metals i n b i o l o g i c a l substances and on determining m i c r o q u a n t i t i e s of one metal i n the presence o f m a c r o q u a n t i t i e s of o t h e r s i n a v a r i e t y of m a t r i c e s . Although Lederer (1) f i r s t put forward the id e a of a n a l y z i n g metals as v o l a t i l e metal c h e l a t e s i n 1955, no experiments were done t o c o n f i r m t h i s concept a t the time. Janak and Brandt (9,10) each b r i e f l y d e s c r i b e d t h e i r work on metal a c e t y l a c e t o n a t e s a n a l y s i s by gas chromatography i n 1960. Bierman and Gesser (11) succeeded i n chromatographing mixtures of aluminum, chromium, and b e r y l l i u m acac 13 Table 1.5: ECD s e n s i t i v i t y t o v a r i o u s c l a s s e s ofcompounds Chemical Type Relative Sensitivity Hydrocarbons 1 Ethers, esters 10 Aliphatic alcohols, ketones, amines; mono-Cl, mono-F compounds 100 Mono-Br, di-Cl and di-F compounds 1000 Anhydrides and tri-Cl compounds 1.0* Mono-I, di-Br and nitro compounds 105 Di-I, tri-Br, poly-Cl and poly-F compounds 10° 14 complexes. Complexes of acac were g e n e r a l l y u n s u i t a b l e f o r gas phase a n a l y s i s , however, because of the h i g h GC temperature requirements. The f l u o r i n a t e d t f a and fod complexes proved to be more u s e f u l . These complexes, due to t h e i r e l e c t r o n e g a t i v e f l u o r i n a t e d m o i e t i e s , were t h e r m a l l y s t a b l e and s u f f i c i e n t l y v o l a t i l e t o be measured a t low l e v e l s by e l e c t r o n capture d e t e c t i o n . Kawaguchi e t al. (13) and Dagnell e t al. (14) f i r s t a p p l i e d microwave emission d e t e c t i o n t o the d e t e r m i n a t i o n of v o l a t i l e metal B-diketonates separated by gas chromatography. Sakamoto et al. (15) a p p l i e d gas chromatography coupled with microwave emission t o the a n a l y s i s of t r a c e i m p u r i t i e s i n metal samples. Traces of copper and aluminum were e x t r a c t e d from z i n c metal i n t o a t r i f l u o r o a c e t y l a c e t o n e s o l u t i o n , and were measured a t the p a r t per m i l l i o n l e v e l (ppm) u s i n g s e l e c t i v e microwave emission d e t e c t i o n of the i n d i v i d u a l metals. Black and S i e v e r s (16) were ab l e t o measure chromium i n human blood serum a t p a r t per b i l l i o n (ppb) l e v e l s by a simple method. They u t i l i z e d the microwave emission d e t e c t o r t o monitor a l i n e of chromium, a f t e r c o n v e r t i n g the chromium i n the matrix t o C r ( t f a ) 3 and s e p a r a t i n g i t from other compounds by gas chromatography. T h i s e x t r a o r d i n a r y s e l e c t i v i t y allowed d e t e c t i o n of the c h e l a t e peak without any d e t e c t a b l e i n t e r f e r e n c e from other compounds. H i g h l y e f f i c i e n t s o l v e n t e x t r a c t i o n techniques and gas chromatographic instrument c o n d i t i o n s have been developed 15 f o r q u a n t i t a t i v e metal a n a l y s i s . The s o l u b i l i t y of metal 6-diketonates i n o r g a n i c s o l v e n t s and t h e i r i n s o l u b i l i t y i n water f a c i l i t a t e s the c h e l a t i o n and e x t r a c t i o n of metal ions from aqueous media. Morie and Sweet (17) a p p l i e d q u a n t i t a t i v e methods t o the e x t r a c t i o n and gas chromatographic s e p a r a t i o n of an aluminum and i r o n mixture. Moshier and Schwarberg (18) o u t l i n e d a g e n e r a l procedure f o r a l l o y a n a l y s i s , u s i n g q u a n t i t a t i v e c h e l a t i o n and e x t r a c t i o n . The widespread use and severe t o x i c i t y of b e r y l l i u m -c o n t a i n i n g compounds and a l l o y s n e c e s s i t a t e d the development of s e n s i t i v e a n a l y t i c a l techniques f o r the d e t e c t i o n of t h i s metal i n b i o l o g i c a l f l u i d s (19-21) and environmental samples (22-25). As l i t t l e as 4 x l 0 ~ 1 4 g of b e r y l l i u m , i n the form of the t f a complex, has been d e t e c t e d by e l e c t r o n capture gas chromatography. Using t h i s technique S i e v e r s (19) was a b l e to d e t e c t a few ppb b e r y l l i u m i n blood and u r i n e samples. E i s e n t r a u t et al. (25) determined b e r y l l i u m a t a c o n c e n t r a t i o n of l e s s than 1 ppm i n l u n a r m a t e r i a l from the A p o l l o 11 and 12 m i s s i o n s and i n m e t e o r i t e s . P y l e e t al. (24) employed c h e l a t i o n , e x t r a c t i o n and gas chromatography t o determine b e r y l l i u m c o n c e n t r a t i o n s i n ambient a i r p a r t i c l e s . C h e l a t i o n and gas chromatography have been a p p l i e d to s e v e r a l other metals i n v a r i o u s m a t r i c e s . Savory e t al. (26) measured 3 x l 0 ~ 1 4 g of chromium from human blood serum as the t f a complex. Trace q u a n t i t i e s of chromium were measured i n s o i l (23), i n l i v e r t i s s u e (27) and i n l u n a r 16 samples, w i t h a mass spectrometer as the d e t e c t i o n d e v i c e (28). Gas chromatographic a n a l y s i s was s u c c e s s f u l l y a p p l i e d t o i n o r g a n i c systems by Genty et al. (29), who d e t e c t e d 0.1 ppm of aluminum i n uranium. Measures and Burton (30) r e p o r t e d a method f o r the de t e r m i n a t i o n of d i s s o l v e d s e l e n i t e and t o t a l selenium i n n a t u r a l waters. The method e n t a i l e d the r e a c t i o n of s e l e n i t e i n a 100 mL sample with 4-nitro-o-phenylenediamine t o form 5 - n i t r o p i a z s e l e n o l which was e x t r a c t e d i n t o t oluene and then determined by ECD-GC. A d e t e c t i o n l i m i t of 10 pM ( 7 . 9 x l 0 ~ 4 ppb) was r e p o r t e d . Gosink (31) d e s c r i b e d a method f o r the d e t e r m i n a t i o n of aluminum and t o t a l chromium i n n a t u r a l waters, as H t f a c h e l a t e s , w i t h subsequent d e t e r m i n a t i o n by ECD-GC. Measures and Edmond have r e p o r t e d shipboard ECD-GC based methods f o r the d e t e r m i n a t i o n of b e r y l l i u m (32) and aluminum (33) i n seawater. Both methods use H t f a t o c h e l a t e the metals and subsequent e x t r a c t i o n i n t o t o l u e n e . D e t e c t i o n l i m i t s of 2 pM ( 1 . 8 x l 0 ~ 5 ppb) and 0.57 nM (0.015 ppb) f o r the o r i g i n a l seawater were r e p o r t e d f o r b e r y l l i u m and aluminum, r e s p e c t i v e l y . 1.7 THE DETERMINATION OF CHROMIUM IN SEAWATER Seawater i s a h i g h l y complex matrix, from an a n a l y t i c a l p o i n t of view, because of the l a r g e c o n c e n t r a t i o n of d i s s o l v e d s a l t s (3.5% by weight). S i x i o n s ; C l ~ , Na +, K +, S 0 4 2 ~ , C a 2 + , and Mg 2 +, account f o r 99% of these d i s s o l v e d 17 s a l t s . Cr and other t r a c e elements, on the other hand, e x i s t at c o n c e n t r a t i o n s of l e s s than 1 M9/k<3 (ppb). V e r t i c a l or depth d i s t r i b u t i o n s of t r a c e metals i n seawater are i n v e s t i g a t e d t o he l p e l u c i d a t e the major biogeochemical. processes which c o n t r o l the c o n c e n t r a t i o n and d i s t r i b u t i o n of these elements. S e v e r a l methods f o r the de t e r m i n a t i o n of chromium i n n a t u r a l waters have been r e p o r t e d . Some of the methods have been used f o r the d e t e r m i n a t i o n of t o t a l chromium on l y while others have allowed the d e t e r m i n a t i o n of C r ( I I I ) o r Cr(VI) e i t h e r s e p a r a t e l y or t o g e t h e r . Most of the methods used have i n v o l v e d s u b s t a n t i a l sample h a n d l i n g and pretreatment procedures which are c l e a r l y u n d e s i r a b l e from a t r a c e a n a l y s i s viewpoint; none of the methods has had shipboard a p p l i c a t i o n . Subramanian (34) r e p o r t e d a method f o r the de t e r m i n a t i o n of C r ( I I I ) and Cr(VI) by g r a p h i t e furnace atomic a b s o r p t i o n spectrometry a f t e r an i n i t i a l s o l v e n t e x t r a c t i o n s t e p u s i n g the ammonium p y r o l i d i n e c a r b o d i t h i o a t e -m e t h y l i s o b u t y l ketone e x t r a c t i o n system. The procedure i n v o l v e d d e t e r m i n a t i o n of Cr(VI) f o l l o w e d by the simultaneous d e t e r m i n a t i o n of [ C r ( I I I ) + C r ( V I ) ] with C r ( I I I ) being o b t a i n e d by d i f f e r e n c e . A d e t e c t i o n l i m i t of 5.8 nM f o r both Cr s p e c i e s was o b t a i n e d . Cranston and Murray (35) used a technique i n which C r ( I I I ) was s e l e c t i v e l y c o p r e c i p i t a t e d u s i n g i r o n ( I I I ) hydroxide, and a f t e r d i s s o l u t i o n of the p r e c i p i t a t e , Cr was 18 d e t e r m i n e d by g r a p h i t e f u r n a c e a t o m i c a b s o r p t i o n s p e c t r o m e t r y . T o t a l chromium was d e t e r m i n e d i n a s i m i l a r way u s i n g i r o n ( I I ) h y d r o x i d e , w h i c h r e d u c e s C r ( V I ) t o C r ( I I I ) w h i l e b e i n g s i m u l t a n e o u s l y o x i d i z e d t o i r o n ( I I I ) h y d r o x i d e . A d e t e c t i o n l i m i t o f 0.02 nM was r e p o r t e d . W i l l i e e t al. (36) u s e d an i m m o b i l i z e d d i p h e n y l c a r b a z o n e c h e l a t i n g a g e n t t o p r e c o n c e n t r a t e t o t a l chromium as C r ( I I I ) f r o m s e a w a t e r f o l l o w e d by d e t e r m i n a t i o n by g r a p h i t e f u r n a c e a t o m i c a b s o r p t i o n s p e c t r o m e t r y . P r i o r t o t h e i o n - e x c h a n g e s t e p , a l l t h e d i s s o l v e d C r ( V I ) was r e d u c e d t o C r ( I I I ) by t h e a d d i t i o n o f S 0 2 - w a t e r t o a 200 mL s e a w a t e r sample and a l l o w i n g i t t o s t a n d f o r s e v e r a l m i n u t e s . A d e t e c t i o n l i m i t o f 0.76 nM was r e p o r t e d . L u m i n o l c h e m i l u m i n e s c e n c e was e m p l o y e d by Chang e t al. (37) f o r t h e d e t e r m i n a t i o n o f C r ( I I I ) i n s e a w a t e r . Magnesium i o n s were f o u n d t o i n t e r f e r e , a l t h o u g h d i l u t i o n o f t h e s e a w a t e r and u t i l i z i n g b r o m i d e - i o n c h e m i l u m i n e s c e n c e s i g n a l enhancement e l i m i n a t e d t h e i n t e r f e r e n c e . A d e t e c t i o n l i m i t o f 3.84 nM was o b t a i n e d . S i m u l t a n e o u s d e t e r m i n a t i o n o f C r ( I I I ) and C r ( V I ) u s i n g i o n c h r o m a t o g r a p h y w i t h c h e m i l u m i n e s c e n c e d e t e c t i o n was r e p o r t e d by W i l l i a m s e t al. (38) . The s e p a r a t i o n s y s t e m i n v o l v e d b o t h a n i o n and c a t i o n e x c h a n g e c o l u m n s c o n n e c t e d i n p a r a l l e l . P o s t - c o l u m n r e a c t i o n w i t h l u m i n o l c h e m i l u m i n e s c e n c e a l l o w e d f o r h i g h s e n s i t i v i t y d e t e c t i o n . The d e t e c t i o n l i m i t f o r C r ( I I I ) was 1.92 nM and t h a t f o r C r ( V I ) was 5.76 nM. 19 Lan e t al. (39) r e p o r t e d a two step c o - p r e c i p i t a t i o n procedure f o r d i f f e r e n t i a t i n g Cr(VI) and C r ( I I I ) i n n a t u r a l waters f o l l o w e d by d e t e r m i n a t i o n of chromium by neutron a c t i v a t i o n . The method i n v o l v e d the c o p r e c i p i t a t i o n a t two d i f f e r e n t pH v a l u e s of the two chromium s p e c i e s with l e a d p y r o l i d i n e d i t h i o c a r b a m a t e . They r e p o r t e d a d e t e c t i o n l i m i t of 0.58 nM u s i n g sample volumes of 2 l i t e r s . S i u e t al. (40) used i s o t o p e d i l u t i o n gas chromatography/mass spectrometry t o determine t o t a l chromium from seawater by complexing the chromium with H t f a and monitoring the C r ( t f a ) 2 + mass fragments with a s e l e c t e d i o n monitoring mode. A d e t e c t i o n l i m i t of 0.15 nM was r e p o r t e d . 1.8 MARINE GEOCHEMISTRY OF CHROMIUM Chromium (atomic number 24) has an outer s h e l l p o p u l a t i o n of 3 d 5 4 s 1 and tends t o e x i s t i n nature i n two main o x i d a t i o n s t a t e s , C r ( I I I ) and C r ( V I ) . The r e p o r t e d abundance i n the e a r t h ' s c r u s t v a r i e s from 100 t o 300 ppm. There are f o u r n a t u r a l l y o c c u r r i n g chromium i s o t o p e s : 5 0 C r (4.35%), 5 2 C r (83.79%), 5 3 C r (9.50%) and 5 4 C r (2.36%). In a d d i t i o n t h e r e are a number of r a d i o a c t i v e i s o t o p e s of which the l o n g e s t l i v e d i s 5 1 C r with T1/f2 = 27.8 days. The t o x i c i t y of t h i s metal t o a q u a t i c and t e r r e s t r i a l organisms, i n c l u d i n g humans, depends on i t s o x i d a t i o n s t a t e (41). C r ( I I I ) i s c o n s i d e r e d t o be e s s e n t i a l t o mammals f o r the maintenance of g l u c o s e , l i p i d , and p r o t e i n metabolism. 20 Cr(VI) on the o t h e r hand i s r e p o r t e d t o be t o x i c because of i t s a b i l i t y t o o x i d i z e o t h e r s p e c i e s and i t s adverse impact on the lung, l i v e r and kidneys (42). Both chromium s p e c i e s e n t e r the waterways p r i m a r i l y as a r e s u l t of e f f l u e n t d i s c h a r g e s from c o o l i n g towers, e l e c t r o p l a t i n g and t a n n i n g i n d u s t r i e s , o x i d a t i v e dyeing, and l e a c h i n g s from s a n i t a r y l a n d f i l l s (43), as w e l l as from n a t u r a l i n p u t s of c r u s t a l m a t e r i a l s through r i v e r s and the atmosphere. Chromium(III) has t h r e e 3d e l e c t r o n s . In o c t a h e d r a l c o o r d i n a t i o n these t h r e e e l e c t r o n s are i n the high s p i n s t a t e s and the c r y s t a l f i e l d s t a b i l i z a t i o n energy i s 6/5 &Q, the l a r g e s t o c t a h e d r a l s i t e p r e f e r e n c e energy a v a i l a b l e t o t r a n s i t i o n metals (44). As a r e s u l t , C r ( I I I ) tends t o form s t r o n g k i n e t i c a l l y i n e r t complexes (45). For example, the r a t e s of s u b s t i t u t i o n of the waters of h y d r a t i o n are extremely slow, w i t h a r e s i d e n c e time of about two hours (46,47). The l a c k of l a b i - l i t y of the c o o r d i n a t i o n sphere imposes l i m i t a t i o n s on the mechanisms of e l e c t r o n t r a n s f e r r e a c t i o n s . The s o l u b i l i t y o f C r ( I I I ) hydroxides o r oxides i s low. The s o l u b i l i t y maximum of s o l i d C r ( O H ) 3 i s about 400 nM a t pH 8.5 and i s c o n t r o l l e d by the i n t e r s e c t i o n of C r ( O H ) 2 + and C r ( O H ) 4 " (48). Cr (VI) tends t o form mostly oxo compounds. Because of i t s l a r g e i o n i c p o t e n t i a l , i t i s an extremely s t r o n g a c i d and the s o l u b l e t e t r a h e d r a l chromate i o n C r 0 4 - 2 i s the common s p e c i e s . 21 E l d e r f i e l d (49) has suggested'that Cr ( I I I ) and Cr (VI) are the o n l y s i g n i f i c a n t o x i d a t i o n s t a t e s i n n a t u r a l waters, the most probable s p e c i e s being C r ( O H ) 2 + ( H 2 0 ) 4 and C r 0 4 ~ 2 , r e s p e c t i v e l y . In o x i d i z i n g waters, thermodynamic c a l c u l a t i o n s p r e d i c t t h a t the s t a b l e form should be C r ( V I ) ; s i g n i f i c a n t amounts of C r ( I I I ) have been found, however, as reviewed by Brewer (51). The v a r i e t y of techniques t h a t have been used t o determine Cr s p e c i e s , probable o x i d a t i o n s t a t e changes d u r i n g sample h a n d l i n g , as w e l l as environmental v a r i a b i l i t y may account f o r the d i s c r e p a n c i e s i n the r e p o r t e d r e s u l t s . The r e d u c t i o n of Cr(VI) as C r 0 4 2 ~ t o Cr ( I I I ) as C r ( O H ) 2 + takes p l a c e as f o l l o w s : C r 0 4 2 - + 6H + + 2H 20 + 3e" = C r ( H 2 0 ) 4 ( O H ) 2 + (2) l o g K = 66.1 The e q u i l i b r i u m r a t i o of d i s s o l v e d chromium i s then: l o g C r ( V I ) / C r ( I I I ) = 6 pH + 3 pE - 66.1 (3) Taking the average pH and pE of oxygenated s u r f a c e seawater a t 8.2 and 12.6, r e s p e c t i v e l y , the r a t i o equals 20.9 and Cr(VI) should predominate. The pE-pH r e l a t i o n s h i p i s shown i n F i g . 1.8 (51). The k i n e t i c s of the o x i d a t i o n are known t o be slow. E a r l e y and Cannon (52) concluded t h a t t h i s i s due i n p a r t t o the d i f f e r e n c e s i n c o o r d i n a t i o n between C r ( I I I ) ( o c t a h e d r a l ) and Cr(VI) ( t e t r a h e d r a l ) . Using C r ( I I I ) s p i k e s added to 22 23 Columbia R i v e r e s t u a r y water, Cranston and Murray (53) observed a f i r s t o rder o x i d a t i o n h a l f - l i f e of one month. The changes i n the o x i d a t i o n s t a t e can i n f l u e n c e input and removal from the ocean. Murray et al (48) i n a study of Cr d i s t r i b u t i o n i n the e a s t e r n t r o p i c a l P a c i f i c (a r e g i o n where i n t e r m e d i a t e waters have low oxygen l e v e l s ) r e p o r t e d t o t a l Cr c o n c e n t r a t i o n s of between 3.0 and 4.0 nM a t the s u r f a c e with a sharp decrease to a minimum of l e s s than 2.5 nM a t the top of the oxygen minima. The Cr c o n c e n t r a t i o n s then i n c r e a s e d t o about 5.0 nM i n the deep water with the deep p r o f i l e s being s i m i l a r t o those of s i l i c a (a n u t r i e n t element). C o i n c i d e n t with the minimum i n t o t a l Cr were hi g h v a l u e s of C r ( I I I ) and p a r t i c u l a t e Cr. They concluded t h a t Cr(VI) was reduced to C r ( I I I ) a t the oxygen minima, much of which was r a p i d l y scavenged by the v e r t i c a l p a r t i c l e f l u x . 1.9 AIM OF PRESENT STUDY The d e s i r e t o understand the f a c t o r s t h a t c o n t r o l the d i s t r i b u t i o n of t r a c e metals i n the oceans has l e d t o the search f o r s e n s i t i v e , r a p i d and a c c u r a t e techniques f o r t h e i r d e t e r m i n a t i o n i n the seawater matrix. Accurate d e t e r m i n a t i o n of t r a c e metals depends on the a b i l i t y t o c o l l e c t samples f r e e of contamination or o t h e r sampling a r t i f a c t s . Much work i n d e v e l o p i n g c o n d i t i o n s aimed a t e l i m i n a t i n g or c o n t r o l l i n g contamination d u r i n g t r a c e element sampling, storage and a n a l y s i s has t h e r e f o r e been 24 done ( 5 4 ) . I t i s v e r y i m p o r t a n t t o e n s u r e t h a t c o n t a m i n a t i o n c o n t r o l p r o c e d u r e s a r e o b s e r v e d a t a l l s t a g e s ; t h e a b i l i t y t o do t h e d e t e r m i n a t i o n s a t s e a w o u l d be o f g r e a t b e n e f i t i n m o n i t o r i n g and c o n t r o l l i n g p o t e n t i a l c o n t a m i n a t i o n . C u r r e n t l y most p r o c e d u r e s i n v o l v e c o l l e c t i n g s a m p l e s , p o s s i b l y d o i n g some p r e l i m i n a r y t r e a t m e n t a t s e a ( e . g p r e c o n c e n t r a t i o n ) , and t h e n t r a n s p o r t i n g t h e s a m p l e s t o a s h o r e - b a s e d l a b o r a t o r y f o r d e t e r m i n a t i o n s a t a l a t e r d a t e . The a b i l i t y t o a c q u i r e p r e c i s e and a c c u r a t e d a t a r a p i d l y u n d e r t h e a d v e r s e c o n d i t i o n s t h a t e x i s t o n b o a r d s h i p i s o f b e n e f i t . T h i s p r o v i d e s t h e p o s s i b i l i t y o f m o d i f y i n g s a m p l i n g s t r a t e g i e s a s d a t a g a t h e r i n g p r o c e e d s and a f f o r d s t h e a b i l i t y t o i d e n t i f y and s o l v e any u n f o r e s e e n c o n t a m i n a t i o n p r o b l e m s i n t h e f i e l d . The h i g h s e n s i t i v i t y o f e l e c t r o n c a p t u r e d e t e c t i o n g a s c h r o m a t o g r a p h y (ECD-GC) o f f l u o r i n a t e d v o l a t i l e c h e l a t e s o f t r a c e m e t a l s p e r m i t s t h e u s e o f s m a l l , e a s i l y c o l l e c t e d v o l u m e s o f s e a w a t e r . The compact n a t u r e and g e n e r a l i n s e n s i t i v i t y o f t h e e q u i p m e n t t o m o t i o n c o u p l e d w i t h t h e f a c t t h a t a GC i s r e l a t i v e l y i n e x p e n s i v e makes i t p a r t i c u l a r l y s u i t a b l e f o r u s e o n b o a r d s h i p s . T h i s s t u d y was t h e r e f o r e aimed a t t h e d e v e l o p m e n t o f a method f o r t h e d e t e r m i n a t i o n o f d i s s o l v e d C r ( I I I ) a n d t o t a l d i s s o l v e d C r , a f t e r r e d u c t i o n , ( w i t h C r ( V I ) b e i n g o b t a i n e d a s t h e d i f f e r e n c e o f t h e s e two) i n s e a w a t e r by ECD-GC w h i c h w o u l d have a s e a - g o i n g a b i l i t y . S i m i l a r methods t h a t have a l r e a d y b e en d e v e l o p e d f o r Se ( 3 0 ) , Be (32) and A l (33) have 25 allowed the d e t e r m i n a t i o n of these elements a t sea on s e v e r a l oceanographic c r u i s e s . Cr c o n c e n t r a t i o n s i n seawater are r e p o r t e d t o f a l l between 2-5 nM with a n u t r i e n t - t y p e d i s t r i b u t i o n ( s u r f a c e d e p l e t i o n and enrichment a t depth as a r e s u l t of involvement i n b i o l o g i c a l c y c l e s ) , complicated i n suboxic or anaerobic areas due t o the i n f l u e n c e of changing redox c o n d i t i o n s (54). I t i s hoped t h a t the r a p i d sea-going method developed here w i l l g r e a t l y enhance our understanding and i n s i g h t i n t o these and other f a c t o r s t h a t are r e s p o n s i b l e f o r the g e n e r a l oceanic chemistry of chromium. 26 CHAPTER 2 EXPERIMENTAL 2.1 INSTRUMENTATION 2.1.1 Gas chromatograph A Hewlett Packard 5890 s e r i e s I I GC equipped with a 10-15 mCi 6 3 N i e l e c t r o n capture d e t e c t o r was used i n t h i s study. The ECD-GC was run i n the s p l i t mode with a s p l i t r a t i o of approximately 10:1. A J & W S c i e n t i f i c DB 210 15 m x 0.25 mm o.d. c a p i l l a r y column with a 0.5-fim f i l m t h i c k n e s s was used. The c a r r i e r gas was hydrogen u l t r a h i g h p u r i t y (UHP) grade. I t was p u r i f i e d f u r t h e r by f i r s t p a s s i n g i t through a molecular s i e v e t r a p then through a hydrocarbon t r a p b e f o r e being s u p p l i e d t o the GC. The d e t e c t o r makeup gas was UHP grade n i t r o g e n and was f e d i n t o the d e t e c t o r a f t e r p a s s i n g i t through a heated c a r r i e r gas p u r i f i e r t r a p which removes any t r a c e amounts of moisture o r oxygen pr e s e n t i n the stream. The N 2 gas was subsequently passed through an i n d i c a t i n g oxygen t r a p which complements the heated t r a p . Data h a n d l i n g from GC was performed on an o n - l i n e Hewlett Packard p e r s o n a l computer equipped with HP-Chemstation 3 365 software. 27 2 . 1 . 2 M a s s s p e c t r o m e t r y Mass s p e c t r a l d a t a u s i n g e l e c t r o n i m p a c t i o n i z a t i o n w e r e o b t a i n e d w i t h t h e u s e o f a K r a t o s MS 50 mass s p e c t r o m e t e r i n t h i s D e p a r t m e n t . 2 . 1 . 3 E l e m e n t a l a n a l y s i s C a r b o n a n d h y d r o g e n e l e m e n t a l a n a l y s i s were p e r f o r m e d o n t h e s y n t h e s i z e d m e t a l c h e l a t e s b y M r . P . B o r d a o f t h i s D e p a r t m e n t . 2 . 1 . 4 p_H pH m e a s u r e m e n t s w e r e p e r f o r m e d u s i n g a n O r i o n SA 520 pH m e t e r e q u i p p e d w i t h a 9 1 - 0 2 g e n e r a l p u r p o s e c o m b i n a t i o n e l e c t r o d e . 2 . 1 . 5 S h a k i n g S h a k i n g was a c c o m p l i s h e d w i t h a B u r r e l l M o d e l 75 w r i s t a c t i o n s h a k e r . 2 . 1 . 6 H e a t i n g A Samsung MW2570UC home m i c r o w a v e o v e n was e m p l o y e d t o s p e e d u p t h e c h r o m i u m e x t r a c t i o n s . 28 2.2 MATERIALS AND REAGENTS 2.2.1 1 , 1 , 1 - t r i f l u o r o - 2 , 4 - p e n t a n e d i o n e The l i g a n d , 1 , 1 , 1 - t r i f l u o r o - 2 , 4 - p e n t a n e d i o n e ( H t f a ) , was purchased from the A l d r i c h Chemical Company. P r i o r t o use, t h i s compound was d i s t i l l e d a t atmospheric pressure i n a T e f l o n s t i l l as d e s c r i b e d by Measures et al. (32), to minimize or remove o r g a n i c and metal contaminants. The T e f l o n s t i l l was c o n s t r u c t e d from a 100 mL d i s t i l l a t i o n f l a s k connected by a ground g l a s s t u b i n g adaptor t o a 15 cm l e n g t h of 10 mm o.d. x 8 mm i . d . T e f l o n t u b i n g . The d i s t i l l a t i o n head was o b t a i n e d by running t h i s t u b i n g i n t o a Cole-Palmer (T-63970-30) T e f l o n elbow j o i n t and then running another 25 cm p i e c e of T e f l o n t u b i n g out and through the middle of a c o n v e n t i o n a l L i e b i g condenser. In order t o get the i n i t i a l l y impure m a t e r i a l t o h i g h enough p u r i t y f o r use i n t h i s study, i t was necessary t o d i s t i l l i t a t l e a s t t h r e e times. Once d i s t i l l a t i o n was complete, the l i g a n d was s t o r e d i n a stoppered T e f l o n b o t t l e i n the f r e e z e r . With use, however, extraneous peaks developed; a s i n g l e d i s t i l l a t i o n was s u f f i c i e n t t o r e s t o r e i t s p u r i t y . 2.2.2 Toluene The s o l v e n t used was t o l u e n e BDH A.C.S. or Omnisolve grade (whichever was a v a i l a b l e ) . I t was p u r i f i e d by d i s t i l l a t i o n through a 4 f t x 1.5 i n c h g l a s s s t i l l . Two or 29 three d i s t i l l a t i o n s were necessary to c l e a r t h i s s o l v e n t of extraneous peaks from o r g a n i c contaminants. The r e d i s t i l l e d t oluene was then s p i k e d with 2 , 6 - d i c h l o r o b i p h e n y l , which was used as the i n t e r n a l standard a t a c o n c e n t r a t i o n of approximately 100 ng/mL. 2 . 2 . 3 B u f f e r The b u f f e r used was prepared from BDH a n a l y t i c a l grade sodium a c e t a t e (NaAc) which had been r e c r y s t a l l i z e d once t o remove t r a c e amounts of Cr and other metal contaminants present. The r e c r y s t a l l i z a t i o n procedure was as f o l l o w s : 100 g of NaAc was d i s s o l v e d i n 100 mL of d e i o n i z e d water (DI H 2 0) i n a 250-mL T e f l o n b o t t l e . The s o l u t i o n was f i l t e r e d through a 0.40-juM polycarbonate f i l t e r u s i n g a p r e v i o u s l y a c i d - c l e a n e d M i l l i p o r e f i l t r a t i o n u n i t . To the f i l t e r e d s o l u t i o n was added 100 mL of a b s o l u t e ethanol which had been p u r i f i e d by double d i s t i l l a t i o n i n the T e f l o n s t i l l d e s c r i b e d above. The f i l t r a t e was then s t o r e d i n the r e f r i g e r a t o r o v e r n i g h t t o a l l o w f o r r e c r y s t a l l i z a t i o n . The r e c r y s t a l l i z e d m a t e r i a l was c o l l e c t e d by f i l t r a t i o n and d r i e d by l e a v i n g i t f o r a few hours i n a laminar flow c l e a n bench. The y i e l d was approximately 60% . An a l t e r n a t e c l e a n i n g procedure f o r the sodium a c e t a t e i n v o l v e d t r e a t i n g the impure sodium a c e t a t e b u f f e r s o l u t i o n i n the same way as the seawater samples and u s i n g the r e d i s t i l l e d H t f a l i g a n d t o scavenge any Cr p r e s e n t . T h i s was done by a d j u s t i n g the b u f f e r pH t o approximately 6 with 30 double d i s t i l l e d a c e t i c a c i d (HAc) f o l l o w e d by s o l v e n t e x t r a c t i o n with toluene i n a s i m i l a r manner t o the samples ( d e s c r i b e d i n the ge n e r a l procedure). The b u f f e r was r i n s e d s e v e r a l times with the r e d i s t i l l e d t o luene t o ensure t h a t a l l the H t f a had been removed. Both procedures were e q u a l l y e f f e c t i v e i n producing NaAc which was c l e a n enough f o r use i n t h i s study and the ch o i c e of the r e c r y s t a l l i z a t i o n procedure f o r a l l subsequent work was made p u r e l y on the b a s i s of time and labour s a v i n g s . 2.2.4 Sodium s u l p h i t e The 1 M sodium s u l p h i t e (BDH ACS grade) s o l u t i o n used f o r the r e d u c t i o n of Cr(VI) t o C r ( I I I ) , was clea n e d by the use of the r e d i s t i l l e d H t f a l i g a n d as d e s c r i b e d f o r the sodium a c e t a t e b u f f e r above. 2.2.5 2 , 6 - d i c h l o r o b i p h e n y l T h i s compound was used as the i n t e r n a l standard as purchased from Chem. S e r v i c e Inc., Westchester, PA. I t was sp i k e d d i r e c t l y i n t o the tol u e n e a f t e r the l a t t e r had been p u r i f i e d by d i s t i l l a t i o n as d e s c r i b e d above. A l l o t h e r reagents were of a n a l y t i c a l grade q u a l i t y and were used without f u r t h e r p u r i f i c a t i o n . 31 2.2.6 Separatorv funnel The s m a l l e s t commercially a v a i l a b l e T e f l o n s e p a r a t o r y f u n n e l s are 125 mL and t h e i r use with the r e l a t i v e l y low sample volumes i n t h i s study would have r e s u l t e d i n the l o s s of some of the o r g a n i c l a y e r on the w a l l s of the v e s s e l . T h i s n e c e s s i t a t e d the c o n s t r u c t i o n of a makeshift low-volume (ca 20 mL) T e f l o n s e p a r a t o r y f u n n e l . T h i s was done q u i t e e a s i l y by t a k i n g an 18 cm x 1.5 cm p i e c e of heat s h r i n k T e f l o n t u b i n g and s h r i n k i n g one of the ends onto a standard T e f l o n s e p a r a t o r y f u n n e l stopcock. S e p a r a t i o n of the aqueous and o r g a n i c phases a f t e r r e a c t i o n was achieved u s i n g t h i s c o n s t r u c t e d f u n n e l . 2.2.7 Dei o n i z e d Water Dei o n i z e d water (DI H 20) used i n t h i s study was obtained from a Barnstead Nanopure S e r i e s 630 D e i o n i z a t i o n System i n s t a l l e d i n the l a b o r a t o r y . 2.2.8 Aqueous Cr standards C e r t i f i e d atomic a b s o r p t i o n standards f o r C r ( I I I ) and Cr(VI) were used t o prepare a p p r o p r i a t e e x t r a c t i o n standards. 1000 ppm C r ( I I I ) i n 1 wt. % HC1 and 1000 ppm Cr(VI) as ammonium dichromate s o l u t i o n i n water were d i l u t e d with DI H 20 t o a p p r o p r i a t e c o n c e n t r a t i o n ranges f o r use i n t h i s study. 32 2.2.9 T r i s - ( 1 , 1 . 1 . - t r i f l u o r o - 2 . 4 - p e n t a n e d i o n o 1 - chromium(111) standard Chromium t r i f l u o r o a c e t y l a c e t o n a t e ( C r ( t f a ) 3 ) was s y n t h e s i z e d as d e s c r i b e d by Fay e t al. (55). Chromium ( I I I ) c h l o r i d e (1.58 g, 10 mmol)) was added to p u r i f i e d H t f a (1.53 g, 34.5 mmol) i n a 250-mL round bottomed f l a s k . 20 g of urea and 100 mL DI water were added and the mixture then r e f l u x e d over a steam bath f o r 7 hr with constant s w i r l i n g . At the end of t h i s p e r i o d h e a t i n g was stopped and the mixture was allowed to c o o l t o room temperature. The o l i v e -drab product formed was c o l l e c t e d on a buchner f u n n e l and washed s e v e r a l times with DI water a f t e r which i t was d r i e d i n the oven a t 65 °C f o r 1 hr. The crude C r ( t f a ) 3 was p u r i f i e d by r e c r y s t a l l i z a t i o n two times w i t h e t h y l a c e t a t e as the s o l v e n t . The f i n a l y i e l d was 2.61 g (51%). Mass s p e c t r a as w e l l as C and H elemental a n a l y s i s data f o r the compound were ob t a i n e d ( r e s u l t s presented l a t e r ) . I n j e c t i o n of a 1 )iL s o l u t i o n of the C r ( t f a ) 3 compound i n t o l u e n e i n t o the GC r e v e a l e d t h a t t h i s compound e l u t e d as two peaks f o r i t s t r a n s and c i s isomers which were w e l l r e s o l v e d . 2.3 PROCESSING Sample p r o c e s s i n g i n the l a b o r a t o r y took p l a c e i n a f i l t e r e d a i r environment w i t h i n a laminar flow bench i n an 33 e f f o r t t o reduce p o s s i b l e contamination from the surroundings. The e x t r a c t i o n s were c a r r i e d out i n T e f l o n PFA b o t t l e s . Before t h e i r f i r s t use, these 60-mL b o t t l e s , a l l the reagent c o n t a i n e r s , and the T e f l o n s e p a r a t o r y f u n n e l , were leached i n 4 N h y d r o c h l o r i c a c i d a t 60 ° C f o r thr e e days f o l l o w e d by a weak (approx. 1%) n i t r i c a c i d l e a c h f o r about a week. During u s u a l l a b o r a t o r y runs the T e f l o n r e a c t i o n b o t t l e s and s e p a r a t o r y funnel were clea n e d between e x t r a c t i o n s by r i n s i n g t h r e e times w i t h approximately 5-10 mL of acetone. 2.4 OPTIMIZATION The optimum c o n d i t i o n s f o r the gas chromatograph o p e r a t i o n and the s o l v e n t e x t r a c t i o n procedure s t e p were both i n v e s t i g a t e d i n t h i s study. 2.4.1 Gas chromatography The o p e r a t i n g c o n d i t i o n s f o r the gas chromatograph were op t i m i z e d i n order t o o b t a i n the h i g h e s t s e n s i t i v i t y of the ECD t o the C r ( t f a ) 3 c h e l a t e and t o achieve reasonable r e t e n t i o n times f o r the c h e l a t e and i n t e r n a l standard peaks, w h i l e m a i n t a i n i n g good r e s o l u t i o n . The GC c o n d i t i o n s which were monitored and o p t i m i z e d were the i n j e c t i o n p o r t temperature, oven temperature, d e t e c t o r temperature, c a r r i e r gas flow r a t e and the d e t e c t o r makeup gas flow r a t e . 34 2.4.2 S o l v e n t e x t r a c t i o n c o n d i t i o n s The optimum c o n d i t i o n s f o r the r e a c t i o n / e x t r a c t i o n of chromium from seawater were determined on the b a s i s of the r e c o v e r i e s of a chromium s p i k e from a seawater matrix. A s p i k e of 4.31 nM C r ( I I I ) was added t o seawater c o l l e c t e d i n Nootka Sound (49°N 127°W) o f f the west c o a s t of Vancouver I s l a n d , B.C., which had been s t o r e d a c i d i f i e d a t pH 2.1. T h i s amount of Cr i s roughly equal t o the t o t a l amount of Cr a l r e a d y present i n the seawater. A s e r i e s of seawater "blanks" with the same amount of reagent but with no Cr s p i k e s were run a l o n g s i d e the s p i k e d samples. The f o l l o w i n g f a c t o r s were i n v e s t i g a t e d : the sample pH, the amount of l i g a n d added, and the e f f e c t of i n c r e a s i n g the e x t r a c t i o n temperature. The r e c o v e r y of Cr was q u a n t i f i e d by the use of a c a l i b r a t i o n curve o b t a i n e d by running o r g a n i c Cr standards prepared from the C r ( t f a ) 3 c h e l a t e i n t o l u e n e . 2.4.2.1 pH The pH was a d j u s t e d by the a d d i t i o n of v a r i o u s amounts of NaAc/HAc b u f f e r t o o b t a i n samples w i t h pH v a l u e s of between approx. 2 t o 8. These samples were then s u b j e c t e d t o Cr e x t r a c t i o n s as i n the g e n e r a l procedure. 35 2.4.2.2 L i g a n d c o n c e n t r a t i o n The e f f e c t on t h e C r r e c o v e r y o f i n c r e a s i n g t h e amount o f p u r e H t f a l i g a n d added, w h i l e k e e p i n g o t h e r r e a c t i o n c o n d i t i o n s c o n s t a n t , was i n v e s t i g a t e d . L i g a n d v o l u m e s r a n g i n g f r o m 20 t o 200 juL were added t o t h e r e a c t i o n b o t t l e s . 2.4.2.3 T e m p e r a t u r e and r e a c t i o n t i m e A v a r i e t y o f r e a c t i o n / e x t r a c t i o n c o n d i t i o n s t o d e t e r m i n e t h e optimum p a r a m e t e r s f o r t h e f o r m a t i o n and e x t r a c t i o n o f t h e C r ( t f a ) 3 c h e l a t e were i n v e s t i g a t e d . D i f f e r e n t c o m b i n a t i o n s o f s h a k i n g w i t h and w i t h o u t h e a t i n g were i n v e s t i g a t e d . 2.5 SEAWATER SAMPLES Two t y p e s o f s t o r e d s e a w a t e r s a m p l e s were a n a l y z e d i n t h i s s t u d y : 1. F i l t e r e d s e a w a t e r s a m p l e s t h a t had b e e n s t o r e d a c i d i f i e d . 2. F i l t e r e d s e a w a t e r s a m p l e s t h a t had b e e n f r o z e n i m m e d i a t e l y a f t e r c o l l e c t i o n w i t h o u t b e i n g a c i d i f i e d . I n a d d i t i o n , f i l t e r e d a c i d i f i e d s e a w a t e r c o l l e c t e d i n t h e N o o t k a Sound ( a m i x t u r e f r o m two d i f f e r e n t d e p t h s ) was u s e d whenever a s e a w a t e r m a t r i x was r e q u i r e d . 36 2.5.1 Stored a c i d i f i e d seawater samples Samples from the c e n t r a l North A t l a n t i c Ocean, near Bermuda, were c o l l e c t e d u s i n g 5 - l i t e r N i s k i n b o t t l e s (General Oceanics) mounted on a s t a i n l e s s s t e e l hydrowire, by E.A. Boyle and c o l l e a g u e s a t Massachusetts I n s t i t u t e of Technology. The samples were f i l t e r e d then a c i d i f i e d t o a pH of approx. 2 with 1 mL per l i t e r of 6N HC1, and s t o r e d i n a c i d leached p o l y e t h y l e n e b o t t l e s . 2.5.2 Frozen u n a c i d i f i e d seawater samples Samples f o r C r ( I I I ) and t o t a l Cr were c o l l e c t e d from the Northeast P a c i f i c Ocean near Nootka Sound u s i n g 3 0 - l i t e r Go F l o b o t t l e s (General Oceanics) mounted on a K e v l a r l i n e , by members of our r e s e a r c h group. A f t e r f i l t r a t i o n they were immediately f r o z e n without a c i d i f i c a t i o n . Under these c o n d i t i o n s , i t was hoped t h a t the i n t e g r i t y of the t r a c e metals would be maintained, with l i t t l e or no changes i n the redox s p e c i a t i o n . J u s t p r i o r t o p r o c e s s i n g the samples were allowed t o thaw f o r about 4-5 hr on the bench and t o achieve room temperature f o l l o w e d by d e t e r m i n a t i o n of C r ( I I I ) and, a f t e r r e d u c t i o n , t o t a l Cr. 2.6 ANALYTICAL SCHEME T o t a l d i s s o l v e d Cr was determined as C r ( I H ) from seawater samples t h a t had been s t o r e d a c i d i f i e d ; the reduc i n g agent was not added t o these samples as a c i d i f i c a t i o n causes r e d u c t i o n of Cr(VI) t o C r ( I I I ) i n l e s s than 24 hr (58). Seawater samples t h a t had been s t o r e d f r o z e n were f i r s t allowed t o thaw f o r immediate d e t e r m i n a t i o n of C r ( I I I ) , with t o t a l Cr being determined a f t e r r e d u c t i o n with sodium s u l p h i t e . Cr(VI) was then obtained as the d i f f e r e n c e of these two v a l u e s . A c o n c e n t r a t i o n f a c t o r of 15 was achieved by u s i n g 15 mL of sample and 1 mL of t o l u e n e . For seawater samples t h a t had been s t o r e d a c i d i f i e d t o pH 2, the e x t r a c t i o n pH of 6 ± 0.2 was achieved by adding 1000 (iL of 2 M NaAc/HAc b u f f e r . The pH of the p r e v i o u s l y f r o z e n samples was 8.2 and i t was necessary t o add 20 nh of 10% HAc t o achieve the d e s i r e d e x t r a c t i o n pH. The g e n e r a l procedure d e s c r i b e d below was a p p l i e d t o the d e t e r m i n a t i o n o f Cr i n a l l samples with the o n l y e x c e p t i o n being the a d d i t i o n of 200 JUL of 1 M sodium s u l p h i t e t o the p r e v i o u s l y f r o z e n samples d u r i n g /the de t e r m i n a t i o n of t o t a l Cr. 2.7 GENERAL PROCEDURE 15 mL seawater samples were measured a c c u r a t e l y i n t o the r e a c t i o n b o t t l e s u s i n g an a d j u s t a b l e 10 mL Eppendorf 38 p i p e t and then b u f f e r e d with NaAc/HAc b u f f e r t o pH 6.0 ± 0.2. Next, 1 0 0 /JL of the p u r i f i e d H t f a l i g a n d was added, then 1 mL of toluene which had been s p i k e d with the i n t e r n a l standard. For the de t e r m i n a t i o n of t o t a l Cr i n the p r e v i o u s l y f r o z e n samples, i n a d d i t i o n 2 0 0 /uL of 1 M sodium s u l p h i t e was added. The b o t t l e s were shaken manually f o r f i v e seconds t o ensure mixing of the v a r i o u s reagents, then p l a c e d i n the microwave and heated f o u r a t a time f o r 3 min a t microwave power l e v e l 20 ( e q u i v a l e n t t o 1 3 0 watts power with t h i s microwave). To reduce p r e s s u r e b u i l d - u p i n s i d e the b o t t l e s d u r i n g microwave h e a t i n g , b o t t l e s were p a r t i a l l y d e f l a t e d by squeezing the w a l l s b e f o r e capping t o a l l o w room f o r expansion. The b o t t l e s were removed from the microwave and shaken manually f o r f i v e seconds and then r e t u r n e d f o r another 3 min a t the same power l e v e l . At the end of t h i s p e r i o d the samples were a t a temperature of 6 5 - 7 0 °C. During c o o l i n g , samples were shaken f o r 1 0 min on the mechanical w r i s t a c t i o n shaker, a f t e r which they were allowed t o c o o l f u l l y a t room temperature b e f o r e commencing the s e p a r a t i o n s t e p . The contents of the b o t t l e were c a r e f u l l y t r a n s f e r r e d t o the T e f l o n s e p a r a t o r y f u n n e l , the aqueous l a y e r was separated and d i s c a r d e d . The o r g a n i c l a y e r was shaken f o r 1 0 s with 1 mL of d e i o n i z e d water t o h e l p prevent the for m a t i o n of emulsions from Ca and Mg hydroxides which can occur when NaOH i s added i n the next s t e p . The l a y e r s were allowed t o separate and the o r g a n i c 39 l a y e r then shaken f o r 20 s with 1 mL of 1 M NaOH. T h i s washing s t e p with base i s c r i t i c a l as i t dest r o y s the excess l i g a n d which would o v e r s a t u r a t e the d e t e c t o r i f not removed. A f t e r s e p a r a t i o n the o r g a n i c l a y e r was r i n s e d two times with a t o t a l of 2 mL of DI water t o r i n s e o f f a l l the NaOHi, The e x t r a c t was t r a n s f e r r e d t o a c l e a n g l a s s v i a l with a T e f l o n l i n e d cap. I t was ready f o r i n j e c t i o n i n t o the GC a t t h i s stage or i t c o u l d be s t o r e d f o r a n a l y s i s l a t e r on. For long term storage, the e x t r a c t s were s t o r e d i n the f r e e z e r a t -15 °C and were s t a b l e f o r s e v e r a l weeks a t these c o n d i t i o n s . C r ( I I I ) and Cr(VI) standards were t r e a t e d i n the same manner with the o n l y e x c e p t i o n being the a d d i t i o n of 200 jxL of l M sodium s u l p h i t e r e d u c i n g agent t o the l a t t e r s tandards. 2.8 QUANTITATION Q u a n t i t a t i v e d e t e r m i n a t i o n i n t h i s study was made by the use of the i n t e r n a l standard method and c a l i b r a t i o n s tandards. Two types o f standards were used: 1. Organic Cr standards made from the p u r i f i e d C r ( t f a ) 3 2. Cr e x t r a c t i o n standards 40 2.8.1 Organic chromium standards The standard s o l u t i o n s of C r ( t f a ) 3 were made by-weighing 0.0039 g of the p u r i f i e d c h e l a t e and d i s s o l v i n g i t i n 23.5 mL of the r e d i s t i l l e d t o luene which had been s p i k e d with the 2 , 6 - d i c h l o r o b i p h e n y l i n t e r n a l standard, producing a s o l u t i o n of 1.66xl0~ 4 g/mL C r ( t f a ) 3 . T h i s s o l u t i o n was f u r t h e r d i l u t e d 1:1000 with toluene t o produce a f i n a l primary o r g a n i c Cr standard with a c o n c e n t r a t i o n of 16.8 ppb. T h i s standard was then used t o prepare a range of d i l u t e standards f o r a c a l i b r a t i o n curve. E x t r a c t i o n e f f i c i e n c i e s f o r o p t i m i z i n g Cr r e c o v e r i e s were determined from t h i s curve. Once the Cr r e a c t i o n / e x t r a c t i o n optimum c o n d i t i o n s had been found and the r e c o v e r i e s shown t o be q u a n t i t a t i v e , t h i s curve c o u l d a l s o be used, i n s t e a d of the Cr e x t r a c t i o n c a l i b r a t i o n c urves, t o compute the a c t u a l Cr c o n c e n t r a t i o n s i n the seawater samples a f t e r blank c o r r e c t i o n . 2.8.2 Chromium e x t r a c t i o n standards 2.8.2.1 C r ( I I I ) standards Aqueous C r ( I I I ) e x t r a c t i o n standards were prepared from a primary standard s o l u t i o n of 384.6 nM C r ( I I I ) by s e r i a l d i l u t i o n . Standards with 0.190, 0.380, 3.850, 7.690 nM C r ( I I I ) were prepared and u s u a l l y analyzed i n d u p l i c a t e . 41 2.8.2.2 Cr(VI) standards Aqueous C r ( V l ) e x t r a c t i o n standards were prepared from a primary standard of 380.8 nM C r ( V I ) . Two r e p l i c a t e s each of 1.620, 3.850 and 7.690 nM Cr(VI) were e x t r a c t e d as i n the g e n e r a l procedure with the a d d i t i o n of the sodium s u l p h i t e r e d u c i n g agent. 2.9 CHROMIUM RECOVERY STUDIES The r e c o v e r y of both C r ( I I I ) and Cr(VI) i n seawater was ev a l u a t e d by s p i k i n g seawater samples w i t h each of the two Cr s p e c i e s a t two d i f f e r e n t c o n c e n t r a t i o n l e v e l s . C r ( I I I ) was s p i k e d a t the 2.150 and 4.310 nM l e v e l s whereas Cr(VI) was s p i k e d a t the 3.850 and 7.690 nM l e v e l s . Both s p i k e d samples p l u s the unspiked seawater "blanks" were then analyzed f o r Cr u s i n g the procedure developed. 2.10 REPRODUCIBILITY r The p r e c i s i o n o f the technique was determined by running 6 r e p l i c a t e a n a l y s i s on a seawater sample. 2.11 ACCURACY The a n a l y s i s of standard r e f e r e n c e m a t e r i a l s from the N a t i o n a l Research C o u n c i l of Canada was an important t e s t f o r the accuracy of the technique. Two samples, the Open 42 Ocean Seawater Reference Standard (NASS-3) and the C o a s t a l Seawater Reference Standard (CASS-2) were analyzed f o r t o t a l d i s s o l v e d Cr u s i n g our method. The samples as purchased were a t pH 1.9 and were thus t r e a t e d i n the same way as the samples t h a t had been s t o r e d a c i d i f i e d i n the l a b o r a t o r y (7 r e p l i c a t e s f o r each r e f e r e n c e m a t e r i a l ) . 2.12 BLANKS DI water samples were analyzed f o r C r ( I I I ) and t o t a l Cr as p a r t of the Cr e x t r a c t i o n standards. When averaged over a p e r i o d of time, these r e s u l t s p r o v i d e d an e s t i m a t i o n of the l i m i t of d e t e c t i o n of the technique. To determine how much of the s i g n a l observed i n the DI H 20 e x t r a c t i o n s came from the water and how much came from the reagents and h a n d l i n g , samples of d i f f e r e n t aqueous phase volumes but with c o n s t a n t reagent amounts added were analyzed. DI H 20 volumes of 5, 10, and 15 mL t o which i d e n t i c a l reagent amounts had been added, were analyzed i n d u p l i c a t e f o r C r ( I I I ) and t o t a l Cr. A l e a s t squares f i t of the s i g n a l v e r s u s DI H 20 volume gave an i n t e r c e p t a t zero volume which was the e q u i v a l e n t of the reagent p l u s h a n d l i n g blank. 43 CHAPTER 3 RESULTS AND DISCUSSION 3.1 CHARACTERIZATION OF TRIS-(1,1,l-TRIFLUORO-2,4-PENTANEDIONO)-CHROMIUM(III) STANDARD The s y n t h e s i z e d C r ( t f a ) 3 standard was c h a r a c t e r i z e d by i t s mass s p e c t r a l data and as the r e s u l t s of C and H elemental a n a l y s i s . 3.1.1 Mass s p e c t r a Table 3.1.1 shows the r e s u l t s o f the mass s p e c t r a l a n a l y s i s of the C r ( t f a ) 3 c h e l a t e . Table 3.1.1: Fragmentation i o n s o f t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2,4-pentanediono)-chromium(III) Fragment mass I n t e n s i t y Assignment (m/z) (% base peak) 513 1.5 5 4 C r ( t f a ) 3 + 512 7.5 5 3 C r ( t f a ) 3 + 511 25.8 5 2 C r ( t f a ) 3 + 359 21.5 5 3 C r ( t f a ) 2 + 358 100.0 5 2 C r ( t f a ) 2 + 44 The most important aspect of the mass spectrum ( F i g . 3.1.1) was the v e r i f i c a t i o n of the molecular i o n with m/z 511 and r e l a t i v e i n t e n s i t y 25.8% c o n f i r m i n g the f o r m a t i o n of the c h e l a t e by c h e l a t i o n of the most abundant Cr i s o t o p e ( 5 2 C r ) with the l i g a n d ( 5 2 C r ( t f a ) 3 + ) . A l s o observed were peaks wi t h m/z 512 and 513 ( r e l a t i v e i n t e n s i t i e s of 7.5% and 1.5%, r e s p e c t i v e l y ) r e s u l t i n g from c h e l a t i o n of the l i g a n d w i t h the 5 3 C r and 5 4 C r i s o t o p e s . The base peak was as a r e s u l t of the l o s s of one of the t f a m o i e t i e s t o form the 5 2 C r ( t f a ) 2 + molecular i o n . S i m i l a r l y a peak with m/z 359 and r e l a t i v e i n t e n s i t y 21.5% was as a r e s u l t of the l o s s of a t f a molecule t o form 5 3 C r ( t f a ) 2 + . 3.1.2 Elemental a n a l y s i s The r e s u l t s of C and H elemental a n a l y s i s on C r ( t f a ) 3 are presented i n Table 3.1.2 and are c o n s i s t e n t with the s t r u c t u r e of the c h e l a t e . Table 3.1.2: Elemental a n a l y s i s data f o r t r i s - ( 1 , 1 , l -t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) - c h r o m i u m ( I I I ) % C H C r ( t f a ) 3 C a l c d . 35.24 2.37 found 35.33 2.43 I n t e n s i t y » » « J L _ l i I I L _ i l _ l I I I I I I I I I I I a s» s o> &? § g T o o XX Ml Set B n § m I ft •1 H -H i H * c o •1 o I i ! 46 3.2 QUANTITATIVE ANALYSIS IN GC In GC, q u a n t i t a t i v e a n a l y s i s i s based upon a comparison of e i t h e r the peak h e i g h t or the area of the a n a l y t e peak with t h a t of one or more standards. The h e i g h t of a chromatographic peak i s o b t a i n e d by c o n n e c t i n g the base l i n e s on e i t h e r s i d e of the peak by a s t r a i g h t l i n e and measuring the p e r p e n d i c u l a r d i s t a n c e from t h i s l i n e t o the peak. Prov i d e d t h a t column temperature, e l u e n t flow r a t e , and r a t e of sample i n j e c t i o n are so c o n t r o l l e d as not t o a l t e r the peak widths d u r i n g the p e r i o d r e q u i r e d t o o b t a i n chromatograms f o r sample and standards, t h i s measurement can o r d i n a r i l y be made wit h reasonably h i g h p r e c i s i o n and y i e l d a c c u r a t e r e s u l t s . Peak areas on the o t h e r hand are independent of broadening e f f e c t s due t o v a r i a b l e s mentioned above. Thus from t h i s s t a n d p o i n t , peak areas are a more s a t i s f a c t o r y a n a l y t i c a l parameter than peak h e i g h t s d e s p i t e the f a c t t h a t the l a t t e r are more e a s i l y measured. 47 3.3 QUANTITATIVE PROCEDURES IN PRESENT STUDY 3.3.1 C r ( t f a ) ^ t r a n s ^ c i s i s o m e r i z a t i o n A c a l i b r a t i o n problem a r i s e s f o r C r ( t f a ) 3 . T h i s compound i s made up of two isomers, c i s and t r a n s , but the r a t i o of the two can vary a c c o r d i n g t o the experimental procedures i n v o l v e d . In t h e i r d e t e r m i n a t i o n of t r a c e q u a n t i t i e s of aluminum and chromium i n uranium, Genty e t a l . (29) used a packed column and opted t o s e l e c t GC o p e r a t i n g c o n d i t i o n s where r e s o l u t i o n of the two Cr peaks was not a c h i e v a b l e , thus avoided having t o d e a l w i t h q u a n t i t a t i o n based on e i t h e r isomer. The optimum GC o p e r a t i n g c o n d i t i o n s employed i n t h i s study, however, allowed f o r good r e s o l u t i o n of the two isomers. Unless both peaks are q u a n t i f i e d i n the a n a l y s i s , the r e s u l t s depend on the constancy of the r a t i o between the two isomers. L o v e t t e t al. (56) r e p o r t e d a cons t a n t 4:1 t r a n s : c i s r a t i o a t t a i n e d a f t e r d i s s o l u t i o n o f i n i t i a l l y 100% t r a n s o n l y C r ( t f a ) 3 i n benzene. They thus proceeded t o use the t r a n s isomer o n l y f o r q u a n t i t a t i o n . C r ( t f a ) 3 c i s £ t r a n s i s o m e r i z a t i o n i n the gas phase has been r e p o r t e d t o take p l a c e a t t y p i c a l GC oven temperatures (e.g., 120 °C) ( 5 ) ; t h i s can r e s u l t i n e r r o r s i f q u a n t i t a t i v e a n a l y s i s i s based on the p r e d i c t e d magnitude of one of the peaks. Attempts were made i n t h i s study t o monitor the area r a t i o of the two Cr peaks. The r a t i o was not cons t a n t throughout and q u a n t i t a t i o n based on o n l y one of the peaks would have been 48 u n r e l i a b l e . I t was t h e r e f o r e decided t o q u a n t i f y Cr u s i n g the sum area of the two peaks i n s t e a d of r e l y i n g on e i t h e r peak. 3.3.2 I n t e r n a l Standard Method The i n t e r n a l standard method r e q u i r e s t h a t an e x t r a component, the i n t e r n a l standard, be added i n a known amount t o every sample and standard. Since t h i s e x t r a component i s present i n both unknown and c a l i b r a t i o n samples, i t s presence i s d e t e c t e d i n a l l analyses and i t serves as a r e f e r e n c e o r n o r m a l i z i n g f a c t o r . Some of the requirements f o r an i n t e r n a l standard compound i n c l u d e : 1. I t must be a v a i l a b l e i n hi g h (or a t l e a s t known) p u r i t y . 2. I t must be s t a b l e , both on the s h e l f and d u r i n g a n a l y s i s . 3. I t must not r e a c t with any of the sample components. 4. I t must chromatograph w e l l , y i e l d i n g a well-formed peak. 5. I t must have a r e t e n t i o n time d i f f e r e n t from any of the sample components. 6. I t must be s o l u b l e i n the sample or i n the s o l v e n t used f o r the sample. 7. I t should have a r e t e n t i o n time comparable t o t h a t of the components of i n t e r e s t . 49 The advantages of u s i n g i n t e r n a l standards i n gas chromatography are many: instrument s e t p o i n t , flow, column d r i f t , and oth e r p o s s i b l e v a r i a t i o n s are compensated f o r by the standard. In a d d i t i o n the sample s i z e i s not c r i t i c a l and o n l y the peaks of i n t e r e s t need be e l u t e d and c a l i b r a t e d . The r a t i o of the a n a l y t e t o i n t e r n a l standard peak areas (or h e i g h t s ) s e r v e s as the a n a l y t i c a l parameter. In t h i s work 2 , 6 - d i c h l o r o b i p h e n y l , which had been shown t o be a good i n t e r n a l standard i n s i m i l a r GC work on Be (32) and A l (33), was used. The i n t e r n a l standard had a r e t e n t i o n time of 2.03 min under the GC c o n d i t i o n s used. The r e t e n t i o n times f o r the t r a n s and c i s Cr isomers were 2.66 and 3.35 min r e s p e c t i v e l y . 3.3.3 Organic chromium standards The o r g a n i c Cr standards were i n i t i a l l y made on a d a i l y b a s i s but p e r i o d i c checks on standards s t o r e d i n the f r e e z e r f o r up 2-3 weeks proved t h a t t h i s was not necessary. The standards were remarkably s t a b l e and showed no evidence of decomposition even when s t o r e d a t room temperature f o r a few days. Three standards, w i t h Cr c o n c e n t r a t i o n b r a c k e t i n g the sample and any added Cr s p i k e c o n c e n t r a t i o n s , were made up i n t he p u r i f i e d t o l u e n e ( a l r e a d y s p i k e d with the i n t e r n a l standard) and i n j e c t e d i n t o the GC. I n i t i a l l y these standards were used o n l y t o q u a n t i f y the Cr recover y d u r i n g 50 the s o l v e n t e x t r a c t i o n stage. Once the c o n d i t i o n s f o r q u a n t i t a t i v e (100 ± 4%) Cr recover y were found, however, these standards c o u l d be used d i r e c t l y t o determine Cr c o n c e n t r a t i o n s i n r e a l samples a f t e r blank c o r r e c t i o n . 3.3.4 Chromium e x t r a c t i o n standards Both C r ( I I I ) and Cr(VI) standards were r o u t i n e l y e x t r a c t e d from d e i o n i z e d water and these were used t o q u a n t i f y the amounts of the two Cr s p e c i e s i n seawater samples. The Cr(VI) standards were used t o q u a n t i f y t o t a l Cr i n the p r e v i o u s l y s t o r e d f r o z e n seawater samples a f t e r r e d u c t i o n . The use of the o r g a n i c Cr standards was u s e f u l i n c o n f i r m i n g the t o t a l Cr re c o v e r y from these standards a f t e r the s o l v e n t e x t r a c t i o n procedure. L i k e the o r g a n i c standards, these e x t r a c t s , d e s p i t e c o n t a i n i n g a host of othe r e x t r a c t e d m e t a l - t f a c h e l a t e s , were e g u a l l y s t a b l e . 3.3.5 Chromium e x t r a c t i o n blanks D e i o n i z e d water blanks (0 nM standards) were run a l o n g s i d e the Cr e x t r a c t i o n standards throughout. I t was observed t h a t these d i d not vary much from day t o day pr o v i d e d the same batch o f reagents were used. The blank v a l u e f o r C r ( I I I ) and t o t a l Cr averaged 0.390 ± 0.062 and 1.017 ± 0.081 nM r e s p e c t i v e l y . The main source of Cr i n the blank was from the DI H 20. T h i s blank i s t h e r e f o r e o n l y used w i t h the e x t r a c t i o n standards which c o n t a i n the 51 e q u i v a l e n t amount of DI H 20. from reagents and h a n d l i n g ( S e c t i o n 3.8.3), and used t o samples. C o n t r i b u t i o n t o t h i s blank was determined s e p a r a t e l y blank c o r r e c t the seawater 3.3.6 C a l i b r a t i o n curves In a l l cases, a c a l i b r a t i o n curve was o b t a i n e d by p l o t t i n g the area r a t i o (area of Cr peaks/area of i n t e r n a l standard peak) a g a i n s t the Cr c o n c e n t r a t i o n . T h e o r e t i c a l l y the c o n c e n t r a t i o n r a t i o i . e . , Cr c o n c e n t r a t i o n / i n t e r n a l standard c o n c e n t r a t i o n should be used. The i n t e r n a l standard was, however, p r e s e n t i n e x a c t l y the same c o n c e n t r a t i o n i n a l l cases both f o r sample and standards. F i g s . 3.3.6a, 3.3.6b and 3.3.6c shows the c a l i b r a t i o n curves obtained by running o r g a n i c Cr, C r ( I I I ) and Cr(VI) standards, r e s p e c t i v e l y . 3.3.7 Chromatograms F i g . 3.3.7 shows chromatograms of c i s and t r a n s C r ( t f a ) 3 from (a) s y n t h e s i z e d C r ( t f a ) 3 standard, (b) C r ( I I I ) e x t r a c t i o n standard and (c) seawater sample. The peaks f o r the t r a n s and c i s isomers of Cr have r e t e n t i o n times of 2.66 and 3.35 min, r e s p e c t i v e l y . The i n t e r n a l standard e l u t e s a f t e r 2.03 min. A l s o i d e n t i f i e d on the chromatograms i s a peak wi t h r e t e n t i o n time 1.57 min, c o r r e s p o n d i n g t o the A l - t f a c h e l a t e formed from t r a c e A l p r e s e n t i n the samples 52 0.4-r 0.3--0.0 A 1 ! 1 1 0 2 4 6 8 Chromium concentration (pg/ul) F i g . 3.3.6(a): Organic Cr standards c a l i b r a t i o n curve (each p o i n t the mean o f two r e p l i c a t e s ) 53 F i g . 3 . 3 . 6 ( b ) : C r ( I l l ) c a l i b r a t i o n curve F i g . 3 . 3 . 6 ( c ) : T o t a l Cr c a l i b r a t i o n curve o b t a i n e d from r e d u c i n g Cr(VI) standards 54 >< M cn W 2 — o • » OB •ft TIME (min) CO CO CO F i g . 3.3.7(a): Chromatogram of s y n t h e s i z e d C r ( t f a ) 3 s t a n d a r d (peak r e t e n t i o n times (min): I n t e r n a l standard, 2.042; Cr, 2.682 & 3.351) 55 en H w 55 W E-< H CO f A A o TIME (min) F i g . 3.3.7(b): Chromatogram o f C r ( t f a ) 3 from an e x t r a c t i o n s t a n d a r d (peak r e t e n t i o n times (min): A l , 1.572; I n t e r n a l s tandard, 2.043; Cr, 2.682 56 EH H CO 55 w 2 A co i f? o C C cc TIME (min) F i g . 3.3.7(c): Chromatogram of C r ( t f a ) 3 from an e x t r a c t i o n s t a n d a r d (peak r e t e n t i o n times (min): A l , 1.572; I n t e r n a l s t a n d a r d , 2.042; Cr, 2.682 & 3.351) 57 and standards. The i d e n t i t y of the peak was confirmed by the a n a l y s i s of a pure A l ( t f a ) 3 standard ( d e t a i l s i n Chapter 4 ) . 3.4 REDUCING AGENT The r e a c t i o n between chromium as C r ( I I I ) and 1,1,1-t r i f l u o r o - 2 , 4 - p e n t a n e d i o n e t o form T r i s - ( 1 , 1 , 1 - t r i f l u o r o -2,4-pentanediono)-chromium(III) i s s p e c i f i c f o r C r ( I I I ) and does not occur with C r ( V I ) . I t i s t h e r e f o r e necessary t o reduce Cr(VI) t o C r ( I I I ) i n seawater samples and standards f o r d e t e r m i n a t i o n of t o t a l Cr b e f o r e c h e l a t i o n w i t h H t f a can occur. In t h i s study sodium s u l p h i t e was chosen f o r t h i s purpose as i t s e f f e c t i v e n e s s has a l r e a d y been demonstrated by L o v e t t e t al. (53). Thus 200 M L of the 1 M Na 2S0 3 r e d u c i n g agent was added t o 15 mL samples to g e t h e r w i t h the o t h e r reagents and the c o n v e r s i o n of Cr(VI) t o C r ( I I I ) was achieved r a p i d l y under these c o n d i t i o n s . T h i s was an excess amount but l e s s e r r e d u c i n g agent amounts r e s u l t e d i n l o n g e r o v e r a l l r e a c t i o n times. 3.5 SOLVENT Toluene was the s o l v e n t used i n t h i s study. Other o r g a n i c s o l v e n t s such as hexane, benzene e t c . , c o u l d a l s o have been used. Whatever the c h o i c e of s o l v e n t , i t must be o b t a i n a b l e i n h i g h p u r i t y f r e e of o t h e r o r g a n i c contaminants 58 t h a t might i n t e r f e r e w i t h the GC a n a l y s i s . The toluene used here was e a s i l y p u r i f i e d by d i s t i l l a t i o n and presented no contamination problems p r o v i d e d i t was s t o r e d i n a T e f l o n b o t t l e a f t e r d i s t i l l a t i o n . 3.6 OPTIMIZATION 3.6.1 Gas chromatography The GC c o n d i t i o n s were s e l e c t e d t o ensure the h i g h e s t p o s s i b l e s e n s i t i v i t y of the e l e c t r o n capture d e t e c t o r f o r the C r ( t f a ) 3 c h e l a t e , as w e l l as good r e s o l u t i o n and reasonable r e t e n t i o n times f o r the peaks of i n t e r e s t . Table 3.6.1 shows the o p t i m i z e d parameters used f o r a l l q u a n t i t a t i v e work. Table 3.6.1: Gas chromatographic c o n d i t i o n s f o r the a n a l y s i s of chromium as t r i s - ( 1 , 1 , 1 - t r i f l u o r o -2,4-pentanediono)-chromium(III) I n j e c t i o n p o r t temperature 200 °C Oven temperature 130 °C De t e c t o r temperature 350 °C Column head p r e s s u r e 15 p s i Hydrogen c a r r i e r gas flow 2.6 mL/min Ni t r o g e n makeup gas flow 49 mL/min 5 9 C a p i l l a r y c o l u m n s , d e s p i t e c a r e f u l c o n d i t i o n i n g d u r i n g m a n u f a c t u r e , do s t i l l h ave a c t i v e s i t e s i n them w h i c h t e n d t o a f f e c t t h e g a s c h r o m a t o g r a p h y o f m e t a l c h e l a t e s ( 3 2 ) . S i l y l - 8 ( C h r o m a t o g r a p h i c S p e c i a l t i e s I n c . ) was i n j e c t e d t o d e a c t i v a t e t h e c a p i l l a r y c o l u m n a t t h e b e g i n n i n g o f e a c h d a y s r u n . T h i s was f o u n d t o i n c r e a s e t h e ECD s e n s i t i v i t y f o r t h e C r ( t f a ) 3 c h e l a t e somewhat, p r e s u m a b l y by t e m p o r a r i l y s e q u e s t e r i n g any a c t i v e s i t e s i n t h e column and t h u s i m p r o v i n g i t s p e r f o r m a n c e . 3 . 6 . 1 . 1 ECD s e n s i t i v i t y The e l e c t r o n c a p t u r e d e t e c t o r i s e x t r e m e l y s e n s i t i v e t o t h e C r ( t f a ) 3 c h e l a t e a s e x p e c t e d . As l i t t l e a s 0 . 1 5 pg C r i n j e c t e d as t h e c h e l a t e c o u l d be d e t e c t e d and t h e d e t e c t o r r e s p o n s e was l i n e a r f o r up t o t h r e e o r d e r s o f m a g n i t u d e . The s e a w a t e r s a m p l e s i n t h i s s t u d y a l l had C r c o n c e n t r a t i o n s between 0 . 6 a n d 4.2 nM and a c o n c e n t r a t i o n f a c t o r o f 1 5 was o b t a i n e d r e s u l t i n g i n 0 . 4 7 - 3 . 2 9 pg C r i n e a c h 1 JUL i n j e c t i o n . The ECD r e s p o n s e as a f u n c t i o n o f t e m p e r a t u r e was m o n i t o r e d and showed no a p p r e c i a b l e v a r i a t i o n between 1 5 0 - 3 5 0 °C w i t h r e g a r d t o t h e peak a r e a s o f t h e C r ( t f a ) 3 c h e l a t e . T h i s i s u n l i k e t h e f a c t o r o f 2 i n c r e a s e i n s e n s i t i v i t y s e e n i n t h e c a s e o f B e ( t f a ) 2 ( 3 2 ) . The d e t e c t o r r e s p o n s e f o r t h e i n t e r n a l s t a n d a r d was however r e d u c e d a t l o w e r t e m p e r a t u r e . 60 3.6.2 S o l v e n t e x t r a c t i o n 3 . 6 . 2 . 1 pH The h i g h e s t r e c o v e r y of Cr was achieved a t pH range 5 . 6 - 6 . 5 . At pH v a l u e s g r e a t e r than t h i s , the r e c o v e r y of Cr was observed t o decrease ( F i g . 3 . 6 . 2 . 1 ) . /In t h e i r s t u d i e s of Cr content i n b i o l o g i c a l m a t e r i a l s , Savory e t al. ( 2 6 ) r e p o r t e d a pH range of 5 . 8 - 6 . 2 f o r Cr e x t r a c t i o n with H t f a . The wide pH range f o r Cr e x t r a c t i o n found i n t h i s study allowed a s a f e t y margin p r e c l u d i n g the n e c e s s i t y t o make the b u f f e r a d d i t i o n extremely a c c u r a t e l y . In g e n e r a l use the samples were a d j u s t e d t o pH 6.0 ± 0.2. 3.6.2.2 Ligand c o n c e n t r a t i o n The e x t r a c t i o n of Cr was found t o depend on the amount of l i g a n d added. At c o n s t a n t pH and r e a c t i o n time, the more l i g a n d added, the g r e a t e r the e x t r a c t i o n e f f i c i e n c y f o r l i g a n d volumes i n the 2 0 - 8 0 /iL range ( F i g . 3 . 6 . 2 . 2 ) . 1 0 0 ML of the pure l i g a n d was used f o r a l l e x t r a c t i o n s i n t h i s study and t h i s was s u f f i c i e n t f o r r e c o v e r y of a l l the Cr i n a 1 5 mL sample p l u s any added s p i k e s . Taking an average t o t a l Cr c o n c e n t r a t i o n of 1 0 nM i n a 1 5 mL sample (approximately the sum of the Cr present i n the seawater i n i t i a l l y p l u s the h i g h e s t s p i k e added) o n l y 5.5 x 1 0 ~ 5 /iL of the l i g a n d should t h e o r e t i c a l l y be 61 100-x u o > o a 4) OS K 80--6 0 -40-20-PH 6 8 lOO-Ps u, a > o a QS 40 BO 120 160 Htfa (pL) 200 240 F i g . 3.6.2.1: Cr r e c o v e r y vs. pH (top) (each p o i n t the mean of two r e p l i c a t e s ) F i g . 3.6.2.2: Cr r e c o v e r y vs. H t f a l i g a n d volume (bottom) (each p o i n t the mean o f two r e p l i c a t e s ) 62 necessary f o r complete ,Cr e x t r a c t i o n . The t e s t s showed t h a t a l a r g e excess (at l e a s t 10 6) of H t f a was r e q u i r e d f o r q u a n t i t a t i v e Cr e x t r a c t i o n a t the c o n d i t i o n s used here. T h i s excess c o u l d be d i s t r i b u t e d as f o l l o w s : an u n d i s s o c i a t e d f r a c t i o n i n the o r g a n i c phase; an u n d i s s o c i a t e d f r a c t i o n i n the aqueous phase (probably being n e g l i g i b l e ) ; a f r a c t i o n combined with i o n s of the aqueous phase which cannot be e x t r a c t e d under the experimental c o n d i t i o n s used; and a f r a c t i o n complexed i n the o r g a n i c phase as t f a complexes of metals ot h e r than Cr. The presence of an excess of H t f a i n the o r g a n i c phase causes problems i n the d e t e c t o r d u r i n g a n a l y s i s due t o the extremely h i g h s e n s i t i v i t y of the ECD t o t h i s f l u o r i n a t e d l i g a n d . Shaking the o r g a n i c phase wi t h 1 mL of IM NaOH f o r 20 s e l i m i n a t e s t h i s problem by d e s t r o y i n g t h i s excess l i g a n d . A comparison of the chromatogram b e f o r e and a f t e r washing wi t h the base shows t h a t the C r ( t f a ) 3 c h e l a t e was not d e s t r o y e d by the washing. 3.6.2.3 Temperature and r e a c t i o n time I n i t i a l attempts t o o b t a i n q u a n t i t a t i v e e x t r a c t i o n of Cr by r e a c t i o n w i t h the l i g a n d , 1 , 1 , 1 - t r i f l u o r o - 2 , 4 -pentanedione a t room temperature showed t h a t a t l e a s t 3-4 hours shaking time were r e q u i r e d . F i g . 3.6.2.3a shows the percentage e x t r a c t i o n e f f i c i e n c y of Cr as a f u n c t i o n of shaking time a t room temperature. L o v e t t et al. (56) have 63 r e p o r t e d a room temperature shaking time of a t l e a s t 2 h f o r Cr c o n c e n t r a t i o n s of below 10 nq/raL with the l i g a n d i n g r e a t excess (0.164 M i n benzene) i n order t o o b t a i n maximum Cr e x t r a c t i o n . Measures (57) estimates 87% Cr recovery u s i n g 15 mL seawater samples a f t e r shaking a t room temperature f o r 2 hr u s i n g 100 ixL of H t f a . In order t o reduce the r e a c t i o n time necessary f o r q u a n t i t a t i v e e x t r a c t i o n of Cr, i t was found necessary t o change the temperature of the r e a c t i o n mixture. I n i t i a l i n v e s t i g a t i o n s i n t o t h i s were done u s i n g a water bath a t about 65-70 °C and i n v o l v e d immersing the T e f l o n r e a c t i o n b o t t l e s f o r d i f f e r e n t times w i t h r e g u l a r shaking i n between. Good Cr r e c o v e r i e s were achieved i n s i g n i f i c a n t l y reduced r e a c t i o n times (30-40 min was enough f o r 90% Cr recovery) although r e p r o d u c i b i l i t y between r e p l i c a t e samples was poor. Using a microwave oven t o heat the samples, however, e l i m i n a t e d t h i s problem. Not o n l y was Cr recovery e x c e l l e n t (100 ± 4%), but the r e a c t i o n time and the power l e v e l c o u l d be v e r y w e l l c o n t r o l l e d , a l l o w i n g f o r good r e p r o d u c i b i l i t y . V a r i o u s r e a c t i o n times/microwave power l e v e l combinations were i n v e s t i g a t e d . A t o t a l r e a c t i o n time of 6 min, s p l i t between two 3 min s e s s i o n s , w i t h a 5 s manual shaking time i n between was chosen. The microwave power l e v e l adopted was 20 ( e q u i v a l e n t t o 130 Watts on t h i s microwave) and t h i s combination gave Cr r e c o v e r i e s t h a t were not o n l y e x c e l l e n t but were ve r y r e p r o d u c i b l e . 64 100--80--% 60--o a K 40--20--0--1 2 3 Shaking time at room temp, (hrs) 20 40 60 Shaking time (min) after microwave (b) 60 F i g . 3 . 6 . 2 . 3 ( a ) : F i g . 3 . 6 . 2 . 3 ( b ) : C r r e c o v e r y vs. s h a k i n g t ime (hrs ) a t room temperature (each p o i n t the mean o f two r e p l i c a t e s ) C r r e c o v e r y vs. s h a k i n g t ime (min) a f t e r microwave i r r a d i a t i o n (each p o i n t the mean o f two r e p l i c a t e s ) 65 The b o t t l e s were put i n the microwave f o u r a t a time. At the end of the 6 min microwave time, samples were at a temperature of approximately 70 °C and i t was necessary t o c o o l them t o room temperature b e f o r e completing the e x t r a c t i o n s t e p . During the i n i t i a l p e r i o d of c o o l i n g , b o t t l e s were shaken on the shaker although i t was estimated t h a t the Cr was c h e l a t e d w i t h the l i g a n d by t h i s time. E x t r a c o n t a c t time, nonetheless, does serve t o ensure t h i s . As can be seen i n F i g . 3.6.2.3b, by 10 min of shaking a f t e r microwave r e a c t i o n , Cr r e c o v e r y i s e s s e n t i a l l y q u a n t i t a t i v e . In u s u a l l a b o r a t o r y runs, samples were shaken f o r 10 min and then allowed t o c o o l t o room temperature on the bench f o r approximately 15 min w h i l e a new s e t of samples were being processed. 3.7 ANALYTICAL FIGURES OF MERIT 3.7.1 P r e c i s i o n The p r e c i s i o n of the technique was e v a l u a t e d by performing r e p l i c a t e Cr a n a l y s i s on a seawater sample. The seawater sample used f o r t h i s purpose was the Nootka seawater matrix which had been s t o r e d a c i d i f i e d a t pH 2.1. The r e s u l t s are shown i n Table 3.7.1. 66 Table 3.7.1: R e p r o d u c i b i l i t y of Cr d e t e r m i n a t i o n on a seawater sample. Sample No Chromium (nM) 1 4.69 2 4.58 3 4.69 4 4.67 5 4.76 6 4.63 Mean 4.67 s t d dev 0.06 % r e l s t d dev 1.31 The r e l a t i v e p r e c i s i o n of the technique a t 4.67 nM Cr i s t h e r e f o r e 1.3%. 3.7.2 Recovery Absolute r e c o v e r y s t u d i e s of both C r ( I I I ) and Cr(VI) s p i k e s added t o seawater were performed by s p i k i n g known amounts of the two Cr s p e c i e s i n t o seawater samples and then s u b j e c t i n g the samples t o the f u l l e x t r a c t i o n procedure. Two r e p l i c a t e s f o r each sample were analyzed and as shown i n 67 Table 3.7.2, e x c e l l e n t r e c o v e r i e s of both s p e c i e s were achieved. Table 3.7.2: Recovery of Cr s p i k e s from seawater samples Chromium (nM) I n i t i a l Spike Cr T o t a l Percentage T o t a l added s p e c i e s added recovd. r e c o v e r y 4 .70±0.08 2.15 C r ( I I I ) 6.62±0.19 97 4 .70±0.08 4.31 C r ( I I I ) 8.99±0.04 100 4 .70±0.08 3.85 Cr(VI) 8.62±0.21 101 4 •70±0.08 7.69 Cr(VI) 12.3±0.03 99 Absolute q u a n t i t a t i v e r e c o v e r y i s not, as p o i n t e d out by Measures e t al. (32), a requirement f o r an a n a l y t i c a l technique although good p r e c i s i o n i s u s u a l l y a s s o c i a t e d w i t h h i g h y i e l d s . That the r e c o v e r y of both Cr s p e c i e s i n t h i s study was e x c e l l e n t shows t h a t even w i t h the case of Cr(VI) s p i k e s , r e d u c t i o n t o C r ( I I I ) f o l l o w e d by c h e l a t i o n was s u c c e s s f u l . 3.7.3 Accuracy The accuracy of the technique was assessed by the a n a l y s i s o f Cr i n t r a c e metal seawater r e f e r e n c e standards from the N a t i o n a l Research C o u n c i l of Canada. Two r e f e r e n c e 68 seawater samples, the Nearshore Seawater Reference M a t e r i a l (CASS-2) and the Open Ocean Seawater Reference M a t e r i a l (NASS-3) were analyzed f o r t o t a l d i s s o l v e d Cr u s i n g the technique developed i n t h i s study (7 r e p l i c a t e s f o r each sample). The r e s u l t s are shown i n Table 3.7.3. Table 3.7.3: Accuracy of Cr d e t e r m i n a t i o n on seawater samples Chromium (nM) Found C e r t i f i e d CASS-2 2.331 ± 0.068 2.327 ± 0.308 NASS-3 3.333 ± 0.011 3.365 ± 0.192 Good agreement between the c e r t i f i e d v a l u e s f o r the r e f e r e n c e m a t e r i a l s and the v a l u e s o b t a i n e d by a p p l y i n g the technique t o the samples p r o v i d e d s u f f i c i e n t evidence f o r the accuracy o f the method. The accuracy, i n d i c a t e d by the percent e r r o r , was 0.17% and -0.95% f o r CASS-2 and NASS-3, r e s p e c t i v e l y . The r e l a t i v e p r e c i s i o n o b t a i n e d was 2.9% and 0.3%; the cor r e s p o n d i n g v a l u e s f o r the m a t e r i a l s are 13.2 and 5.7% f o r CASS-2 and NASS-3, r e s p e c t i v e l y . 3.7.4 L i m i t of d e t e c t i o n The l i m i t of d e t e c t i o n (LOD) i s d e f i n e d as the l e a s t amount of a n a l y t e t h a t can be d e t e c t e d w i t h reasonable 69 c e r t a i n t y . The LOD was estimated by the r e p l i c a t e a n a l y s i s of DI water f o r C r ( I I I ) and t o t a l Cr. These blanks were run on a r e g u l a r b a s i s as p a r t of the Cr e x t r a c t i o n standards and thus the numbers r e p r e s e n t the LOD over a p e r i o d of time (a t l e a s t 10 r e p l i c a t e s i n each c a s e ) . The LOD f o r C r ( I I I ) and t o t a l Cr d e f i n e d as t h r e e times the standard d e v i a t i o n of t h e i r blanks were 0.186 nM and 0.243 nM r e s p e c t i v e l y . 3.8 ANALYSIS OF SEAWATER SAMPLES The method was a p p l i e d t o the d e t e r m i n a t i o n of Cr i n seawater samples t h a t had been s t o r e d a c i d i f i e d and t o samples t h a t had been s t o r e d f r o z e n without a c i d i f i c a t i o n . 3.8.1 S t o r e d a c i d i f i e d samples Cr i n seawater samples t h a t have been s t o r e d a c i d i f i e d a t pH approx. 2 with h y d r o c h l o r i c a c i d f o r p e r i o d s l o n g e r than 24 hours a l l e x i s t s i n the C r ( I I I ) s t a t e (58). The r e d u c t i o n of Cr(VI) t o C r ( I I I ) i s achieved simply by a c i d i f y i n g the seawater sample. T h i s was v e r i f i e d by a c i d i f y i n g a sample t o pH 2 t h a t had p r e v i o u s l y been s t o r e d f r o z e n . A n a l y s i s f o r C r ( I I I ) a t r e g u l a r i n t e r v a l s showed t h a t a l l the Cr was i n the reduced s t a t e a f t e r about a day. F u r t h e r v e r i f i c a t i o n of t h i s was achieved by running r e p l i c a t e a n a l y s i s with and without the a d d i t i o n of the sodium s u l p h i t e r e d u c i n g agent i n seawater samples t h a t had 70 been s t o r e d a c i d i f i e d . The r e s u l t s showed no d i f f e r e n c e i n t o t a l Cr content. Thus, i n the a n a l y s i s of seawater samples t h a t had been s t o r e d a c i d i f i e d , the Cr measured r e p r e s e n t s the t o t a l amount of d i s s o l v e d Cr present i n the sample i . e . , C r ( I I I ) + C r ( V l ) . T a b l e 3.8.1: T o t a l Cr vs. depth i n the c e n t r a l North A t l a n t i c (BDA s t a t i o n ) Depth (m) T o t a l Cr (nM) 19 2.85 38 2.96 56 3.64 77 3.39 121 3.42 171 3.66 299 3.76 640 3.10 1468 3.17 2088 3.09 2463 3.42 3000 3.94 3500 3.33 4000 3.64 71 1000 2000 -Q 3000 -4000 — Chromium (nM) 1 2 3 4 F i g . 3.8.1: T o t a l Cr vs.depth i n the c e n t r a l North A t l a n t i c (BDA s t a t i o n ) (each p o i n t the mean of two r e p l i c a t e s ) 72 Table 3.8.1 shows the t o t a l Cr c o n c e n t r a t i o n i n a c i d i f i e d samples obtained from v a r i o u s depths from a s t a t i o n i n the A t l a n t i c Ocean near Bermuda. T h i s data i s p l o t t e d i n F i g . 3.8.1 which shows the Cr c o n c e n t r a t i o n vs. depth p r o f i l e a t t h i s s t a t i o n (BDA). T o t a l Cr c o n c e n t r a t i o n s between 2.85 and 3.94 nM were found i n a l l samples. The p r o f i l e i s c o n s i s t e n t with the d i s t r i b u t i o n of t o t a l Cr seen i n other s t u d i e s ( c r " . (58)), but does not g i v e any i n f o r m a t i o n about the p r o p o r t i o n of the two Cr s p e c i e s i n the seawater analyzed. The complex geochemical c y c l e s which c o n t r o l the d i s t r i b u t i o n of chromium i n the oceans can o n l y be u n r a v e l l e d by a more thorough i n v e s t i g a t i o n of not o n l y the t o t a l chromium, but the d i f f e r e n t Cr s p e c i e s and a comparison with depth d i s t r i b u t i o n s of o t h e r chemical p r o p e r t i e s i n c l u d i n g n u t r i e n t s and o t h e r t r a c e metals. 3.8.2 S t o r e d f r o z e n samples Frozen samples c o l l e c t e d o f f the c o a s t of Vancouver I s l a n d , B.C., near Nootka Sound, were analyzed f o r d i s s o l v e d C r ( I I I ) , Cr(VI) and t o t a l Cr. The r e s u l t s are presented i n T a b l e 3.8.2 and p l o t t e d i n Fig.3.8.2 (NTK s t a t i o n ) . The r e s u l t s show t h a t Cr(VI) was the dominant Cr s p e c i e s i n these seawater samples and was roughly t h r e e times g r e a t e r than C r ( I I I ) . Thermodynamic c a l c u l a t i o n s on 73 Chromium (nM) 1 2 3 4 F i g . 3.8.2: C r ( I I I ) ( 0 ) r C r ( V I ) ( * ) and t o t a l Cr( • ) vs. depth i n tiie Northeast P a c i f i c (NTK station) (each point the mean of two re p l i c a t e s ) 74 Cr s p e c i a t i o n i n seawater p r e d i c t t h a t Cr(VI) should be the dominant s p e c i e s a t n a t u r a l seawater pH and pE (49). The r a t i o of C r ( V I ) / C r ( I l l ) p r e d i c t e d under these c o n d i t i o n s i s approximately 1 0 2 0 . However, C r ( V I ) / C r ( I I I ) r a t i o s of between 50 t o 1 have been found e x p e r i m e n t a l l y (59). Arhennius and B o n a t t i (60) have p o i n t e d out t h a t t h i s T able 3.8.2: C r ( I I I ) , C r ( V I ) , and t o t a l Cr vs the Northeast P a c i f i c (NTK s t a t i o n ) . depth i n Depth C r ( I I I ) T o t a l Cr Cr(VI) C r ( I I I ) (m) (nM) (nM) (nM) (%) 20 0.71 3.29 2.69 22 50 1.17 4.19 3.43 28 100 0.71 3.54 2.86 20 300 1.02 3.66 2.66 28 v a r i a t i o n and c o n t r a d i c t i o n w i t h t h e o r y might be due t o the in situ c o p r e c i p i t a t i o n of Cr(VI) o n l y , w i t h s t r o n t i u m or barium s u l p h a t e . The k i n e t i c s t a b i l i z a t i o n of C r ( I I I ) by h y d r a t i o n would a l s o be expected t o h i n d e r the o x i d a t i o n t o the h i g h e r s t a t e and some workers have r e p o r t e d h i g h e r p r o p o r t i o n s of C r ( I I I ) than Cr(VI) (39). In anoxic environments, Cr i s p r e d i c t e d t o be i n the C r ( I I I ) o x i d a t i o n s t a t e . Murray e t a l . (48) and Cranston and Murray (53) have 75 r e p o r t e d Cr(VI) and C r ( I I I ) l e v e l s t h a t are c o n s i s t e n t w i t h these p r e d i c t i o n s f o r both the e a s t e r n t r o p i c a l P a c i f i c and Saanich I n l e t . The e f f e c t s of h a n d l i n g and storage on the s p e c i a t i o n of metals i n seawater samples are s t i l l u n c l e a r . U n c e r t a i n t i e s e x i s t i n any form of sample storage with regard t o i t s e f f e c t on the s p e c i a t i o n of the t r a c e metal i o n s , e s p e c i a l l y i n cases l i k e Cr where the o x i d a t i o n s t a t e changes can occur r e l a t i v e l y e a s i l y . C l e a r l y the most r e l i a b l e r e s u l t s w i l l be those f o r samples where det e r m i n a t i o n s have been performed i n as s h o r t a time as p o s s i b l e a f t e r c o l l e c t i o n . 3.8.2.1 Handling Since Cr(VI) i s f a i r l y e a s i l y reduced t o C r ( I I I ) on a c i d i f i c a t i o n t o pH approx. 2 i n l e s s than 24 hours, i t was important t o v e r i f y t h a t t h i s c o n v e r s i o n d i d not occur d u r i n g sample p r e p a r a t i o n f o r the d e t e r m i n a t i o n of C r ( I I I ) from the p r e v i o u s l y f r o z e n samples. These samples had t o be thawed then pH a d j u s t e d from approx. 8 t o 6 b e f o r e adding the r e s t of the reagents and performing the s o l v e n t e x t r a c t i o n s t e p . I t was important i n t h i s study t o assure t h a t the C r ( I I I ) measured was what was o r i g i n a l l y i n the sample and d i d not r e s u l t from unintended r e d u c t i o n of C r ( V I ) . The v e r i f i c a t i o n was done by s p i k i n g Cr(VI) i n t o a f r e s h l y thawed sample a t the l e v e l of 38 nM and running the 76 C r ( I I I ) d e t e r m i n a t i o n procedure on f o u r r e p l i c a t e s each of t h i s and a non-spiked sample. The r e s u l t s showed no d i f f e r e n c e i n the amount of C r ( I I I ) i n the two samples d e s p i t e a Cr(VI) s p i k e of roughly 10 times the n a t u r a l Cr l e v e l s present i n the seawater sample. T h i s was proof t h a t Cr(VI) was not reduced t o C r ( I I I ) d u r i n g the p r e p a r a t i o n and h a n d l i n g process f o r the d e t e r m i n a t i o n of C r ( I I I ) i n these samples. I t does not, however, e x p l a i n the f a c t t h a t C r ( I I I ) l e v e l s found i n these samples were h i g h e r than p r e d i c t e d by thermodynamic c a l c u l a t i o n s . 3.8.3 Reagent and h a n d l i n g blank The c o n t r i b u t i o n t o the a n a l y t e s i g n a l from the reagents and h a n d l i n g o n l y was determined s e p a r a t e l y from the aqueous Cr e x t r a c t i o n standards blank, which a l s o c o n t a i n e d a c o n t r i b u t i o n from DI H 20. The reagent and h a n d l i n g blank was r o u t i n e l y checked, e s p e c i a l l y when a batch of reagents were used f o r the f i r s t time. I t averaged 0.066 nM f o r C r ( I I I ) standards and 0.326 nM f o r Cr(VI) standards. In the a n a l y s i s of seawater samples, t h e r e f o r e , the v a l u e s were a d j u s t e d a c c o r d i n g l y . 3.9 DETERMINATIONS AT SEA The method developed i n t h i s study was designed t o be a p p l i c a b l e t o the d e t e r m i n a t i o n of d i s s o l v e d C r ( I I I ) and t o t a l Cr (and Cr(VI) by d i f f e r e n c e ) a t sea. The method has 77 been a p p l i e d i n the l a b o r a t o r y on s t o r e d seawater samples from p r e v i o u s oceanographic c r u i s e s , and so f a r has y i e l d e d data on Cr t h a t are c o n s i s t e n t with those o b t a i n e d by workers u s i n g other t e c h n i q u e s . The i n h e r e n t advantage of t h i s technique over ot h e r such methods, however, i s i t s seagoing a b i l i t y . As noted elsewhere i n t h i s t h e s i s , the a b i l i t y t o perform t r a c e metal d e t e r m i n a t i o n s on board s h i p s w i t h i n a f a i r l y s h o r t time a f t e r sampling has many advantages. The f a c t t h a t Cr e x i s t s i n both C r ( I I I ) and Cr(VI) s t a t e s i n seawater and t h a t i n t e r c o n v e r s i o n of these s p e c i e s d u r i n g storage and h a n d l i n g may occur, warrants the e f f o r t t o perform d e t e r m i n a t i o n s as soon as p o s s i b l e a f t e r sample c o l l e c t i o n , and the need t o minimize sample h a n d l i n g . The method w i l l soon be used i n the f i e l d . 3.10 SUGGESTIONS FOR FURTHER WORK I t has been suggested t h a t p a r t i c u l a t e Cr i n seawater e x i s t s i n the C r ( I I I ) o x i d a t i o n s t a t e as C r ( 0 H ) 3 (48). A n a t u r a l e x t e n s i o n o f the technique i s t o i n c l u d e d e t e r m i n a t i o n of p a r t i c u l a t e Cr. T h i s would i n v o l v e d i s s o l v i n g the Cr( O H ) 3 r e s i d u e c o l l e c t e d a f t e r f i l t r a t i o n i n a c i d and proceeding as f o r C r ( I I I ) d e t e r m i n a t i o n i n the d i s s o l v e d s t a t e . T h i s w i l l be u s e f u l i n p r o v i d i n g i n f o r m a t i o n about the o v e r a l l geochemistry of Cr i n a l l forms i n seawater. 78 There a l s o e x i s t s the p o s s i b i l i t y of developing a multi-element procedure i n c o r p o r a t i n g Cr and A l provided the c o n d i t i o n s f o r one element are compatible w i t h those of the oth e r . In t h i s study, t h i s was examined on l y q u a l i t a t i v e l y ( S e c t i o n 3.3.7) but appeared f e a s i b l e and warrants f u r t h e r i n v e s t i g a t i o n . 3.11 SUMMARY AND CONCLUSIONS An a c c u r a t e and r a p i d ECD-GC technique f o r the de t e r m i n a t i o n of d i s s o l v e d C r ( I I I ) and t o t a l Cr i n seawater was developed. The method uses s m a l l sample volumes (15 mL) and has a seagoing a b i l i t y t h a t w i l l a l l o w d e t e r m i n a t i o n immediately a f t e r sample c o l l e c t i o n . T h i s w i l l be u s e f u l i n red u c i n g p o s s i b l e contamination and oth e r s p e c i a t i o n changes which may occur d u r i n g sample s t o r a g e . Of p a r t i c u l a r importance w i l l be the a p p l i c a t i o n of t h i s method t o areas where the seawater environment i s expected t o have a g r e a t i n f l u e n c e on the redox s p e c i a t i o n of Cr. Such areas i n c l u d e areas w i t h pronounced oxygen minima and i n t e r m i t t e n t l y r e d u c i n g f j o r d s which are e a s i l y found i n the c o a s t a l areas of B r i t i s h Columbia. The p o s s i b l e e x t e n s i o n of the technique t o i n c l u d e d e t e r m i n a t i o n of p a r t i c u l a t e Cr i n seawater w i l l h e l p e l u c i d a t e the geochemistry of Cr i n the oceans. The technique a l s o o f f e r s the p o s s i b i l i t y o f being extended t o multi-element d e t e r m i n a t i o n s . 79 CHAPTER 4 GALLIUM 4.1 INTRODUCTION 4.1.1 Overview A method f o r the d e t e r m i n a t i o n of aluminum i n seawater which uses the e l e c t r o n c apture d e t e c t i o n o f the 1,1,1-t r i f l u o r o - 2 , 4 - p e n t a n e d i o n e d e r i v a t i v e formed a f t e r c h e l a t i o n was r e c e n t l y d e s c r i b e d (33). In t h i s chapter the attempt t o adapt t h i s technique t o the d e t e r m i n a t i o n of g a l l i u m i n seawater i s d e s c r i b e d , p o s s i b l e reasons f o r the f a i l u r e are p o s t u l a t e d and some sugg e s t i o n s are put forward. 4.1.2 Background G a l l i u m i s immediately below aluminum i n the p e r i o d i c t a b l e o f elements and i t i s expected t h e r e f o r e t h a t these two Group I I I metals should have s i m i l a r chemical behavior. D i s s o l v e d g a l l i u m c o n c e n t r a t i o n s i n the P a c i f i c are r e p o r t e d to be 2-30 pM and 20-60 pM i n the northwest A t l a n t i c . The co r r e s p o n d i n g c o n c e n t r a t i o n s f o r d i s s o l v e d aluminum are h i g h e r a t 0.06-6.0 nmol/kg and 5-40 nmol/kg, r e s p e c t i v e l y . Both these elements e x i s t as h y d r o l y z e d s p e c i e s i n seawater 80 and s i m i l a r f a c t o r s may be r e s p o n s i b l e f o r t h e i r v e r t i c a l d i s t r i b u t i o n s (61). A s h i p b o a r d method f o r the de t e r m i n a t i o n of aluminum i n seawater which uses the l i g a n d 1 , 1 , 1 - t r i f l u o r o - 2 , 4 -pentanedione t o c h e l a t e the metal has been r e p o r t e d ( 33 ) . The technique u t i l i z e s the h i g h s e n s i t i v i t y of e l e c t r o n capture d e t e c t o r gas chromatography (ECD-GC) f o r f l u o r i n a t e d v o l a t i l e metal c h e l a t e s and allows f o r the use of smal l sample volumes. Determinations a t sea improve contamination c o n t r o l which i s c r i t i c a l when d e a l i n g w i t h t r a c e metals e s p e c i a l l y A l due t o i t s h i g h n a t u r a l abundance i n c r u s t a l m a t e r i a l s (8.2%). The c h i e f l i m i t a t i o n i s t h a t the elements i n q u e s t i o n must form c h r o m a t o g r a p h i c a l l y s t a b l e , v o l a t i l e c h e l a t e s w i t h h i g h e f f i c i e n c y i n aqueous s o l u t i o n and t h a t these be e x t r a c t a b l e i n t o a s u i t a b l e o r g a n i c phase. I t was the purpose of t h i s study t o i n v e s t i g a t e the p o s s i b i l i t y of adapting t h i s ECD-GC technique t o the de t e r m i n a t i o n of g a l l i u m i n seawater. Such a technique, i t was reasoned, would a l l o w f o r the e l u c i d a t i o n of the f a c t o r s r e s p o n s i b l e f o r i t s d i s t r i b u t i o n i n seawater as w e l l as g i v i n g us the p o s s i b i l i t y f o r a comparison of i t s ocea n i c c h e m i s t r y w i t h t h a t of aluminum, p r e f e r a b l y i n a m u l t i -element method f o r the two elements. 81 4.2 EXPERIMENTAL 4.2.1 Gas chromatography 4.2.1.1 Column The DB 210 c a p i l l a r y column ( J & W S c i e n t i f i c ) which had been used f o r ECD-GC work on Be (32), A l (33), and gave good s e p a r a t i o n f o r Cr i n t h i s t h e s i s f a i l e d t o work f o r Ga. The A l and Ga peaks were un r e s o l v e d d e s p i t e attempts t o r e s o l v e them by changing the GC o p e r a t i n g c o n d i t i o n s . A v a r i e t y of other columns were i n v e s t i g a t e d ; a J & W S c i e n t i f i c DB 5 15 m x 0.25 mm o.d. with 0.25-/im f i l m t h i c k n e s s gave the b e s t r e s u l t s . 4.2.1.2 GC c o n d i t i o n s The GC c o n d i t i o n s f o r the a n a l y s i s of g a l l i u m as the t f a complex are presented i n Table 4.2.1.2 Table 4.2.1.2: Gas chromatographic c o n d i t i o n s f o r the a n a l y s i s of g a l l i u m as t r i s - ( 1 , 1 , 1 -t r i f l u o r o - 2 , 4 p e n t a n e d i o n o ) g a l l i u m ( I I I ) I n j e c t i o n p o r t temperature 200 °C Oven temperature 140 °C Detector temperature 300 °C Column head p r e s s u r e 15 p s i Hydrogen c a r r i e r gas flow 2.6 mL/min Nitr o g e n makeup gas flow 52 mL/min 82 4.2.2 S y n t h e s i s of t r i s - ( l , l . 1 - t r i f l u o r o - 2 , 4 p e n t a n e d i o n o )  q a l l i u m ( I I I ) standard. The procedure f o l l o w e d f o r the s y n t h e s i s of g a l l i u m t r i f l u o r o a c e t y l a c e t o n a t e ( G a ( t f a ) 3 ) was adapted from the Wold e t al.(62) d e s c r i p t i o n f o r the s y n t h e s i s of g a l l i u m a c e t y l a c e t o n a t e . G a l l i u m ( I I I ) n i t r a t e (2.86 g, 11.2 mmol) i n 25 mL of DI water was added t o 1,1, l - t r i f luoro-2,4-pentanedione (5.78 g, 37.5 mmol) i n 7 mL of con c e n t r a t e d NH4OH s l o w l y with shaking. The white p r e c i p i t a t e which formed was c o l l e c t e d on a buchner f u n n e l and r i n s e d s e v e r a l times w i t h DI water. I t was d r i e d i n the oven a t 60 °C f o r approximately 2 hr a f t e r which i t was r e c r y s t a l l i z e d twice from e t h y l a c e t a t e . The y i e l d of the white c r y s t a l l i n e product was 3.850 g (65%). I t had a m e l t i n g p o i n t of 128-130 °C (the l i t e r a t u r e m e l t i n g p o i n t value f o r the t r a n s isomer of t h i s c h e l a t e i s 128.5-129.5 °C ( 2 ) ) . The compound was c h a r a c t e r i z e d by mass s p e c t r a and C and H elemental a n a l y s i s d a t a . 4.2.3 Organic Ga standards The p u r i f i e d G a ( t f a ) 3 c h e l a t e was used t o make the GC standards f o r the o p t i m i z a t i o n procedures. The st o c k s o l u t i o n was made by d i s s o l v i n g 0.022 g of the c h e l a t e i n 47.12 mL of p u r i f i e d t o l u e n e g i v i n g a s o l u t i o n c o n t a i n i n g 4.67 x 10~ 4 g/mL G a ( t f a ) 3 . The a c t u a l c o n c e n t r a t i o n of 83 g a l l i u m i n t h i s s o l u t i o n was 6.10 x 10~ 5 g/mL. App r o p r i a t e standards c o n t a i n i n g lower g a l l i u m c o n c e n t r a t i o n s were made from t h i s primary standard by s e r i a l d i l u t i o n with the toluene s o l v e n t . 4.2.4 S o l v e n t e x t r a c t i o n A 10 ppb g a l l i u m standard made up i n a seawater matrix was used i n an attempt t o determine the optimum pH f o r the c h e l a t i o n of g a l l i u m . V a r i o u s samples volumes were i n v e s t i g a t e d . The s o l v e n t e x t r a c t i o n procedure i n v o l v e d pH adjustments w i t h 1 M NaAc/HAc b u f f e r , f o l l o w e d by the a d d i t i o n of l i g a n d and s o l v e n t w i t h subsequent shaking on the mechanical shaker. The o r g a n i c l a y e r was then separated and r i n s e d w i t h 1 M NaOH s o l u t i o n and DI water b e f o r e being analyzed. 84 4.3 RESULTS AND DISCUSSION 4.3.1 C h a r a c t e r i z a t i o n of t r i s - ( l . l . l - t r i f l u o r o - 2 , 4 - pentanediono) a a l l i u m ( I I I ) standard The p u r i f i e d G a ( t f a ) 3 was c h a r a c t e r i z e d by the r e s u l t s of C and H elemental a n a l y s i s and mass spectrometry data. 4.3.1.1 Mass s p e c t r a The r e s u l t s of the mass s p e c t r a l a n a l y s i s f o r the G a ( t f a ) 3 c h e l a t e are presented i n Table 4.3.1.1. Table 4.3.1.1: Fragmentation ions of t r i s - ( 1 , 1 , 1 -t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) - g a l l i u m ( I I I ) Fragment mass I n t e n s i t y Assignment (m/z) (% base peak) 530 2.2 7 1 G a ( t f a ) 3 + 528 3.0 6 9 G a ( t f a ) 3 + 377 68.4 7 1 G a ( t f a ) 2 + 375 100.0 6 9 ( t f a ) 2 + 71 2.7 7lGa+ 69 4.9 69 Ga+ 43 72.6 CH 3C0 + The mass spectrum ( F i g . 4.3.1.1) pr o v i d e d evidence f o r the for m a t i o n of the G a ( t f a ) 3 c h e l a t e and the s p l i t t i n g 85 II +* - H M c © c 7» (f If 4f 1* 2* If * Iff M •f 7f tf If 4f 31 If 1* • ^ T " iff t l f ' i i I I | I I l 4M T 4 If 1 ( 1 1 1 1 i t i f f r ' I 1 I I I I I I I I I I tff IM F i g . 4.3.1.1 Mass spectrum of t r i s - ( 1 , 1 , 1 - t r i f l u o r o - 2 A -pentanedione)-gallium(lii) t r i r A u o r o 2 ' 4 " 86 p a t t e r n of the compound. The molecular i o n with m/z 528 had a r e l a t i v e i n t e n s i t y of 3.0% and corresponds t o 6 9 G a ( t f a ) 3 + . A s m a l l e r peak with m/z 530 ( r e l a t i v e i n t e n s i t y 2.2%) corresponds t o g a l l i u m - t f a c h e l a t e molecular i o n formed from the 7 1 G a i s o t o p e . The base peak i s the r e s u l t of the l o s s of one of the t f a m o i e t i e s from the parent i o n and has m/z 375; a l s o seen i s a peak corre s p o n d i n g t o 7 1 G a ( t f a ) 2 + with m/z 377 and r e l a t i v e i n t e n s i t y 68.4% . Peaks with r e l a t i v e i n t e n s i t i e s of 2.7% and 4.9% correspond t o 7 1 G a + and 6 9 G a + r e s p e c t i v e l y . 3.1.2 Elemental a n a l y s i s R e s u l t s of C and H elemental a n a l y s i s p r o v i d e d a d d i t i o n a l evidence f o r the f o r m a t i o n of G a ( t f a ) 3 (Table 4.3.1.2). Table 4.3.1.2: Elemental a n a l y s i s data f o r t r i s - ( 1 , 1 , 1 -t r i f l u o r o - 2 , 4 - p e n t a n e d i o n o ) - g a l l i u m ( I I I ) % C H G a ( t f a ) 3 C a l c d . 34.03 2.27 found 3 3.88 2.26 4.3.2 Chromatograms F i g u r e 4.3.2 shows the chromatograms o b t a i n e d f o r the G a ( t f a ) 3 c h e l a t e from: (a) the s y n t h e s i z e d G a ( t f a ) 3 87 X EH M W 55 w EH M 1 . Z e - 4 -1 . 1 • 1 .0« - 4 ^ O O O • e o o o 7 0 0 0 -•i J 4ooo -i « o o o -Ok o G> — s o 3 TIME (min) F i g . 4.3.2(a) Chromatogram o f s y n t h e s i z e d G a ( t f a ) 3 s t a n d a r d (peak r e t e n t i o n times (min): Ga, 1.440; I n t e r n a l s t a n d a r d , 3.015) 88 TIME (min) Chromatogram of G a ( t f a ) 3 from an e x t r a c t i o n s t a n d a r d (peak r e t e n t i o n times (min): A l , 1.123; Ga, 1.488; I n t e r n a l s tandard, 3.094) 89 F i g . 4 . 3 . 2 ( c ) : Chromatogram o f G a ( t f a ) 3 from a seawater sample (peak r e t e n t i o n t i m e s (min) : A l , 1 .115; G a , 1 .475; I n t e r n a l s t a n d a r d , 3.087) 90 standard, (b) 100 ppb Ga e x t r a c t i o n standard and (c) Ga from a seawater sample. G a ( t f a ) 3 e l u t e s a f t e r 1.46 min. The i n t e r n a l standard ( 2 , 6 - d i c h l o r o b i p h e n y l ) has a r e t e n t i o n time of 3.08 min under the GC c o n d i t i o n s used here, a l s o seen i s a peak f o r A l ( t f a ) 3 with a r e t e n t i o n time of 1.12 min. 4.3.3 ECD s e n s i t i v i t y S e n s i t i v i t y problems were encountered very e a r l y on i n t h i s study. The d e t e c t o r response f o r the G a ( t f a ) 3 c h e l a t e was not o n l y remarkably low when compared t o the response f o r A l ( t f a ) 3 c h e l a t e but a l s o v a r i e d g r e a t l y from day t o day. That these o r g a n i c standards were u n s t a b l e on storage f o r a few days even a t v e r y low temperatures (-15 °C) was confirmed by monitoring the response of the ECD t o one p a r t i c u l a r s tandard s t o r e d i n the f r e e z e r over a p e r i o d of time. The d e t e c t o r response t o a s i n g l e Ga standard prepared f r e s h d a i l y a l s o showed v a r i a t i o n from day t o day. The attempt t o o p t i m i z e the s o l v e n t e x t r a c t i o n c o n d i t i o n s w i t h r e g a r d t o pH was a l s o u n s u c c e s s f u l . The amount of g a l l i u m r e covered was i m p o s s i b l e t o q u a n t i f y s i n c e the d e t e c t o r response c h a r a c t e r i s t i c s f o r the G a ( t f a ) 3 c h e l a t e c o u l d not be determined. On average, a 10 ppb Ga standard seemed t o be the l e a s t amount d e t e c t a b l e even with the changing d e t e c t o r response. To o b t a i n a reasonable s i g n a l from an a c t u a l seawater sample 91 (with Ga c o n c e n t r a t i o n of 2-60 pM) , l a r g e seawater volumes (250-500 mL) were r e q u i r e d and even then the r e s u l t s were i r r e p r o d u c i b l e . 4.3.4 D i s c u s s i o n The f a c t t h a t G a ( t f a ) 3 was s y n t h e s i z e d , p u r i f i e d and s u c c e s s f u l l y c h a r a c t e r i z e d suggests t h a t the c h e l a t e i s a t l e a s t s t a b l e i n i t s n a t u r a l s o l i d form a t room temperature. In s o l u t i o n , however, the c h e l a t e seems t o l o o s e i t s s t a b i l i t y a f t e r a few days which perhaps e x p l a i n s why the d e t e c t o r response f o r a s i n g l e G a ( t f a ) 3 standard made up i n t o l u e n e v a r i e d from day t o day on s t o r a g e . When the same standard was prepared f r e s h l y each day and analyzed, the r e s u l t s were not much b e t t e r . One can argue t h a t the problem might l i e i n the i n s t a b i l i t y of the d e t e c t o r response from day t o day. I f t h i s were so, then the d e t e c t o r would be expected t o behave i n a s i m i l a r way f o r the t f a c h e l a t e s of o t h e r metals, e s p e c i a l l y A l which i s j u s t above Ga i n the p e r i o d i c t a b l e . However, A l ( t f a ) 3 was a l s o s y n t h e s i z e d i n t h i s study and i t s chromatographic behavior i n v e s t i g a t e d : no s i m i l a r problems were experienced. The f o r e g o i n g l e a d s t o the c o n c l u s i o n t h a t e i t h e r G a ( t f a ) 3 i s u n s t a b l e i n s o l u t i o n on s t o r a g e and/or t h a t the c h e l a t e experiences decomposition i n the gas chromatograph d u r i n g a n a l y s i s r e s u l t i n g i n poor and i r r e p r o d u c i b l e response c h a r a c t e r i s t i c s . Thermal and chromatographic 92 s t a b i l i t i e s are mandatory i f the GC of metal c h e l a t e s i s t o have any a n a l y t i c a l a p p l i c a t i o n s . As noted i n a comprehensive review on gas chromatography of metal complexes by Uden e t al. (5) t f a complexes of G a ( I I I ) , I n ( I I I ) , S c ( I I I ) , V ( I V ) , R h ( l l l ) , and C u ( l l ) , though having been gas chromatographed with no apparent evidence of decomposition, have not y e t been proved t o e l u t e q u a n t i t a t i v e l y a t below the microgram l e v e l . C u ( t f a ) 2 has i n f a c t been shown t o undergo c o n s i d e r a b l e on-column degradation below t h i s l e v e l and i s t h e r e f o r e not s u i t a b l e f o r t r a c e a n a l y s i s (63). The H t f a c h e l a t e s of F e ( I I I ) , M n ( I I I ) , Z r ( l V ) , H f ( l V ) and Zn(II) are a l l noted t o e l u t e a t hig h sample l e v e l s w i t h some decomposition and show c o n s i d e r a b l e d e t e r i o r a t i o n below microgram l e v e l s ( 2 ) . The ECD has been employed as a c r u c i a l t e s t f o r the chromatographic s t a b i l i t y of a metal complex s p e c i e s by Burgett and F r i t z (64) who observed d e t e c t o r s a t u r a t i o n a t the 100-ng l e v e l but the t o t a l disappearance of d e t e c t a b i l i t y below t h i s l e v e l . I t i s c l e a r i n t h i s i n s t a n c e t h a t the observed d e t e c t i o n l i m i t was a f u n c t i o n of the GC t o e l u t e the complex s p e c i e s and not the a b i l i t y of the d e t e c t o r s t o d e t e c t i t . I t i s p o s s i b l e t h a t o t h e r complexes f o r which the ECD d e t e c t i o n l i m i t s are not good (such as was the case here f o r G a ( t f a ) 3 ) s u f f e r from s i m i l a r problems of inadequate chromatography r a t h e r than poor d e t e c t o r s e n s i t i v i t y . When t r a c e and u l t r a - t r a c e l e v e l a p p l i c a t i o n s have been s u c c e s s f u l and t h e r e f o r e the chromatography i s not 93 suspect, the d e t e c t i o n l i m i t s of the ECD have been c o n s i s t e n t l y i n the low picogram range f o r pure complexes. T h i s would appear t o exonerate the ECD s e n s i t i v i t y as the source of problems. While t h e r e i s s t i l l some u n c e r t a i n t y as t o whether the e l e c t r o n c a p t u r i n g a b i l i t y o f these complexes a r i s e s from the f l u o r i n a t i o n , the metal or the presence of s e v e r a l pseudo-aromatic r i n g s ( 5 ) , i t i s c l e a r t h a t a l l of the f l u o r i n a t e d complexes are good e l e c t r o n -c a p t u r i n g s p e c i e s and should g i v e good d e t e c t i o n l i m i t s i f the GC c h a r a c t e r i s t i c s are adequate. In t h e i r ECD-GC study of the d e t e r m i n a t i o n of t r a c e q u a n t i t i e s of aluminum and chromium i n uranium u s i n g H t f a as l i g a n d , Genty e t a l . (29) observed t h a t the ECD s e n s i t i v i t i e s f o r A l , Cr and Be were w i t h i n the same order of magnitude but t h a t the d e t e c t o r ' s s e n s i t i v i t y f o r Ga was th r e e o r d e r s of magnitude lower. By the use of r a d i o a c t i v e g a l l i u m ( 7 2 G a , T 1 / / 2 ~ 14.1 h r ) , they were a b l e t o show t h a t the major p a r t of the compound i n t r o d u c e d i n t o the apparatus remained f i x e d on i t s v a r i o u s components ( i n j e c t i o n p o r t and column m a i n l y ) , w h i l e o n l y a smal l f r a c t i o n was e l u t e d ; t h i s c o u l d e x p l a i n the s e n s i t i v i t y d i f f e r e n c e s n o t i c e d . S i m i l a r d i f f i c u l t i e s were encountered f o r copper, the use of r a d i o a c t i v e copper s i m i l a r l y showed t h a t s o l v e n t e x t r a c t i o n was q u a n t i t a t i v e but t h a t copper was trapped i n v a r i o u s p a r t s of the GC. The f a c t t h a t two metals, A l and Ga, which d i s p l a y f a i r l y s i m i l a r chemical behavior should behave so 94 d i f f e r e n t l y as t f a c h e l a t e s i n the gas chromatograph suggests a dependence of the c h e l a t e p r o p e r t i e s on the metal i o n . The dependence of the v o l a t i l i t y of B-diketonate complexes on the s i z e of the metal i o n was noted f o r the r a r e e a r t h metals (65) and the a l k a l i n e e a r t h metals (66). In e i t h e r case, the complexes with s m a l l e r i o n i c r a d i i were much more v o l a t i l e than those with l a r g e i o n i c r a d i i . P o s s i b l e e x p l a n a t i o n s f o r the s i z e - r e l a t e d t r e n d i n v o l a t i l i t y have been advanced (65). The s i z e of the complex decreases with the r a d i u s of the metal i o n , and the l o c a l d i p o l e can e i t h e r decrease i n s i z e or become more e f f e c t i v e l y s h i e l d e d from the a t t r a c t i v e f o r c e s of n e i g h b o r i n g molecules. The s m a l l e r complex may a l s o have a reduced tendency t o form oligomers. A l l of these f a c t o r s enhance the v o l a t i l i t y of the B-diketonate with a s m a l l e r metal i o n i c r a d i u s . One s u g g e s t i o n put forward as a p o s s i b l e s t e p towards s o l v i n g the problems of decomposition of the c h e l a t e s i n the v a r i o u s components of the GC i s t o dope the c a r r i e r gas with a continuous l e v e l of l i g a n d vapor ( 5 ) . At the moment however, t h i s does not appear f e a s i b l e f o r the ECD with i t s h i g h s e n s i t i v i t y t o f l u o r i n a t e d l i g a n d s ; the excess l i g a n d would most c e r t a i n l y contaminate the d e t e c t o r . 95 4 . 3 . 5 Summary and c o n c l u s i o n s The a t t e m p t t o u s e t h e ECD-GC t e c h n i q u e f o r t h e d e t e r m i n a t i o n o f g a l l i u m i n s e a w a t e r t h r o u g h c h e l a t i o n o f t h e m e t a l w i t h H t f a was u n s u c c e s s f u l . The g a l l i u m - t f a c h e l a t e was u n s t a b l e and s u f f e r e d d e c o m p o s i t i o n i n t h e g a s c h r o m a t o g r a p h . The f a c t t h a t A l ( t f a ) 3 shows none o f t h e p r o b l e m s e x p e r i e n c e d w i t h G a ( t f a ) 3 s u g g e s t s a m e t a l i o n s i z e - v o l a t i l i t y r e l a t i o n s h i p w h i c h h a s a l r e a d y b een n o t e d f o r m e t a l s i n t h e o t h e r g r o u p s . One p o s s i b l e s o l u t i o n w o u l d be t o t r y o t h e r B - d i k e t o n e l i g a n d s w i t h a g r e a t e r d e g r e e o f f l u o r i n a t i o n w h i c h h o p e f u l l y w i l l r e s u l t i n g r e a t e r v o l a t i l i t y o f t h e c h e l a t e . 96 REFERENCES 1. Lederer, M., Nature, 176, 462, (1955). 2. Moshier, R. W., S i e v e r s , R. E., "Gas Chromatography of Metal C h e l a t e s " , Pergamon Press, Oxford, (1965). 3. Welcher, F, "Organic A n a l y t i c a l Agents", V o l . 1, Van Nostrand, P r i n c e t o n , N.J., (1947). 4. J a c q u e l o t , P., Thomas, G. , Bull. Soc. Chem. Tr. , 702, (1971) . 5. Uden, P. C , Henderson, D. E., Analyst, 102(122), 889, (1977) and r e f e r e n c e s quoted t h e r e i n . 6. S i e v e r s , R. E., Ponder, B. W., M o r r i s , M. L., Moshier, R. W., Inorg. Chem. 2, 693, (1963). 7. Wolf, W. R. , S i e v e r s , R. E., Brown, G. H. , ibid., 11, 1995, (1972). 8. E i s e n t r a u t , K. J . , S i e v e r s , R. E., J. Inorg. Nucl. Chem. 29, 1931, (1967). 9. Brandt, W. W. , In "Gas Chromatography", S c o t t , R. P. W. , ed.,. Buttersworths, Washington, pp. 305, (1960). 10. Janak, J . , ibid., pp. 306. 11. Biermann, W. J . , Gesser, H. , A n a l . Chem., 32, 1525, (1960) . 12. Ross, W. D., ibid., 1596, (1963). 13. a) Kawaguchi, H. , Sakamoto, T. , Mizuike, A., Talanta, 20, 321, (1973). b) Kawaguchi, H., Sakamoto, T., Yoshida, Y., Miz u i k e , A., Bunseki Kagaku, 22, 1434, (1973). 14. D a g n a l l , R. M., West, T. S., Whitehead, P., Analyst, 98, 647, (1973). 15. Sakamoto, T., Kawaguchi, H., Miz u i k e , A., J. Chromatogr., 121, 383, (1976). 16. Black, M. S. , S i e v e r s , R. E., A n a l . Chem., 48, 1872, (1976). 97 17. Morie, G. P., Sweet, T. R., Anal. Chim. Acta, 34, 1872, (1976). 18. Moshier, R. W. , Schwarberg, J . E., Talanta, 13, 445, (1966). 19. S i e v e r s , R. E. , T a y l o r , M. L. , A r n o l d , E. L. , A n a l . Lett. 1, 735, (1968). 20. T a y l o r , M. L. , A r n o l d , E. L. , A n a l . Chem., 43, 1328, (1971). 21. Wolf, W. R. , A r n o l d , E. L. , Hughes, B. M. , Tierman, T.O., S i e v e r s , R. E., ibid., 44, 616, (1972). 22. S i e v e r s , R. E., Black, M. S., ibid., 45, 1773, (1973). 23. Ross, W. D., P a r t s , L. P., Black, M. S. , Winniger, M. T., U.S. NTIS AD Rep. AD A016760, (1975). 24. P y l e , J . L., Ross, W. D., S i e v e r s , R. E., Environ. Sci. Technol., 11, 467, (1977). 25. E i s e n t r a u t , K. J . , G r i e s t , D. J . , S i e v e r s , R. E., A n a l . Chem., 43, 2003, (1971). 26. Savory, J . , Mushak, P., Sundermann, F. W. , E s t e r s , E. M., R o z e l , N. O., Anal. Chem., 42, 294, (1970). 27. Booth, G. H. J r . , Darby, W. J . , iJbid. , 43, 831 (1971). 28. Isenhour, T. L., Frew, N. M., Leary, J . J . , ibid., 44, 665, (1972). 29. Genty, C., Houin, C., Malherbe, P., Sc h o t t , R., ibid., 43, 235, (1971). 30. Measures, C. I . , Burton, J . D., A n a l . Chim. Acta, 120, 177, (1980). 31. Gosink, T. A., Anal. Chem., 47, 165, (1975). 32. Measures, C. I . , Edmond, J . M., A n a l . Chem., 58, 2065, (1986). 33. Measures, C. I . , Edmond, J . M., A n a l . Chem., 61, 544, (1989). 34. Subramanian, K., A n a l . Chem., 60, 11, (1988). 35. Cranston, R. E., Murray, J . W., A n a l . Chim. Acta., 99, 275, (1978). 98 36. W i l l i e , S. N. , Sturgeon, R. E., Berman, S. S., Anal. Chem., 55, 981, (1983). 37. Chang, C. A., P a t t e r s o n , H. H., Mayer, L. M., Bause, D. E., A n a l . Chem., 52, 1264, (1980). 38. W i l l i a m s , T., Jones, P., Ebdon, L., J . Chromatgr., 482, 361, (1989). 39. Lan, C. R., Tseng, C. L., Yang, M. H. , A l f a s s i , Z. B. , Analyst, 116, 35, (1991). 40. S i u , K. W. M. , Bednas-, M. E. , Berman, S. S., A n a l . Chem. 55, 473, (1983). 41. Stollenwerk, K. G., Grove, D.B., J. Environ. Qual., 14, 396, (1985). 42. Langard, S., Norseth, T. , "Handbook on the T o x i c o l o g y of Metals", F r i b e r g , L. , e t al., eds., E l s e v i e r / N o r t h -H o l l a n d Biomedical P r e s s : Amsterdam, pp. 383-397, (1979). 43. Pankow, J . F. , Janauer, G. E. , A n a l . Chim. Acta. 69, 97, (1974). 44. Burns, R. G. , " M i n e r a l o g i c a l A p p l i c a t i o n of C r y s t a l F i e l d Theory", U n i v e r s i t y P ress, London, pp. 224, (1970). 45. Pearson, R. G., Science, 151, 172, (1966). 46. Taube, H., " E l e c t r o n T r a n s f e r R eactions of Complex Ions i n S o l u t i o n " , Academic P r e s s , New York, pp. 103, (1970). 47. L i n c k , R. G., "Survey of Progress i n Chemistry" S c o t t , A. F, ed., Vol.7, Academic P r e s s , pp. 89 (1976). 48. Murray, J . W., S p e l l , B., Pa u l , B., In "Trace Metals i n Seawater," Wong, C. S. e t al., eds., Plenum Press, New York, pp. 643, (1983). 49. E l d e r f i e l d , H., Earth Planet. Sci. Lett., 9, 10, (1970). 50. Brewer, P. G., In "Chemical Oceanography", 2 n d Edn. R i l e y , J . P., Skirrow, G., eds., Academic Press, London, pp. 463, (1975). 51. Cranston, R. E., Ph.D. T h e s i s , U n i v e r s i t y of Washington, S e a t t l e , pp. 304, (1979). 99 52. E a r l e y , J . E. , Cannon, R. D., Trans. Metal Chem., 1, 34, (1965). 53. Cranston, R. E. , Murray, J . W. , Limnol. Oceanogr., 25, 1104, (1980). 54. Bruland., K. W. , In "Chemical Oceanography", R i l e y , J . P., Chester, R., eds., Academic Press, London, pp. 157, (1983). 55. Fay, R. C , P i p e r , T. S., J . Am. Chem. S o c , 85, 500, (1963). 56. L o v e t t , R. J . , Lee, G. F., Environ. Sci. Technol., 10(1), 69, (1976). 57. Measures, C. I . , pe r s o n a l communications, (1991). 58. Campbell, J . A., Yeats, P. A., E a r t h Planet. Sci. Lett., 53, 427, (1981). 59. F l o r e n c e , T. M. , B a t l e y , G. E. , CRC Crit. Rev. Anal. Chem., 9, 219, (1980). 60. A r r h e n i u s , G., B o n a t t i , E. , Prog. Oceanogr., 3, 7, (1965). 61. a) Orian s , K. J . , Bruland, K. W. Geochim. Cosmochim Acta, 52, 2955, (1988). b) O r i a n s , K. J . , Bruland, K. W. Nature, 332, 717, (1988). c) O r i a n s , K. J . , Bruland, K. W. Nature, 316, 427, (1985) . 62. Wold, A., B a i r d , J . H., Hough, C. R., A n a l . Chem., 26(3), 546, (1954). 63. B e l c h e r , R., M a r t i n , R. J . , Stephen, W. I . , Henderson, D. E., Kamalizad, A., Uden, P. C., A n a l . Chem., 45, 1197, (1973). 64. B u r g e t t , C. A., F r i t z , J . S., A n a l . Chem., 44, 1738, (1972). 65. S i c r e , J . E., Dubois, J . T., E i s e n t r a u t , K. J . , S i e v e r s , R. E., J . Am. Chem. Soc, 91, 3476, (1969). 66. Schwarberg, J . E., S i e v e r s , R. E., Moshier, R. W., A n a l . Chem., 42, 1828, (1970). 100 APPENDIX I TOTAL'ABUNDANCE" 0.99939 AVCRAiE MASS- Sll.239700 MOST A8IJN0ANT PEAK- 510.939557 N0M MASS EXACT MASS INTENSITY 50S. 509.995095 5.19_ 510. 509.998385 0.S9 511. 510.989557 100.00 512. 511.991749 28.59 513. 512.991829 7.41 514. 513.994011 1.04 515. 514.995115 0.11 F i g . 5.10(a): T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r C r ( t f a f 3 TOTAL A2UN0ANC E» 0.9994S AVESA^E MASS* 3S3.1S8467 MOST 4BUN0AMT PEAK- 357.971:15 NOM MASS EXACT MASS INTENSITY 355. 3S5.978742 S.19 357. 355.982097 0.58 358. 357.973215 100.00 359. 358.974960 22.85. 360. 359.974549 5.55 361. 360.976759 0.57 362. 361.977584 0.05 F i g . 5.10(b): T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r C r ( t f a ) o + 101 APPENDIX I I TOTAL ABUNDANCE" 0.99977 AVERAGE MASS" 528.966294 MOST A8UN0ANT PEAK- 527.974600 MASS EXACT MASS INTEN! 523. 527. 974600 100. .00 529. 528 . 977970 17 .27 530. 529. 973898 68 .34 531 . 530. 977245 1 1 .71 532. 531 . 979397 1 .75 533. 532 . ,981972 0 .18 534. 533. .984688 0 .01 F i g . 5.20(a): T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r G a ( t f a ) 3 + TOTAL ABUNDANCE- 0.99967 AVERAGE MASS- 375.83*303 MOST ABUNOANT PEAK- 374.953257 NOM MASS EXACT MASS INTENSITY 375 .• • 374 . 9S82S7 100.«f0 376. 375 .961644 U . S l " 377. 376.957470 67.64* 378. 377.960843 7 . 7 l " 379. 378.962626 0.93* 330. 379.964990 0.06 F i g . 5.20(b): T h e o r e t i c a l i n t e n s i t y p a t t e r n s f o r G a ( t f a ) 2 + 

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