Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The preparation of lead tetrmethyl for mass spectrometer analysis Ulrych, Tadeusz Jan 1960

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1960_A6_7 U5 P7.pdf [ 2.68MB ]
Metadata
JSON: 831-1.0085412.json
JSON-LD: 831-1.0085412-ld.json
RDF/XML (Pretty): 831-1.0085412-rdf.xml
RDF/JSON: 831-1.0085412-rdf.json
Turtle: 831-1.0085412-turtle.txt
N-Triples: 831-1.0085412-rdf-ntriples.txt
Original Record: 831-1.0085412-source.json
Full Text
831-1.0085412-fulltext.txt
Citation
831-1.0085412.ris

Full Text

THE PREPARATION OF LEAD TETRAMETHYL for MASS SPECTROMETER ANALYSIS by TADEUSZ JAN ULRYCH B.Sc, University of London, 1957 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of PHYSICS We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1960 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t permission f o r e xtensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted, by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of Thr t> ic$  The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 6, Canada. Date g Aj>rM l f^co  i ABSTRACT This thesis i s concerned with the problems of sample preparation a r i s i n g i n the study of lead isotope abundances. The importance of t h i s study to geophysics has been amply shown by R.D. Russell, R.M. Farquhar, F.G. Houtermans, J.T. Wilson, H.F. Ehrenberg and many others. Chapter 1 gives an outline of lead isotope measurement techniques, including types of mass spectrometers generally used and some of the problems encountered. The mass spectro-meter used i n the present research was designed and con-structed by R.D. Russell and F. Ko l l a r and descriptions of i t w i l l be found i n t h e i r publications and i n F. Kollar's Ph.D. thesis. The present techniques of producing lead tetramethyl for iso t o p i c analysis from ore samples are discussed i n Chapter 2. The remaining chapters deal with the p u r i f i c a t i o n of lead tetramethyl for mass spectrometer analysis, using vapour phase chromatography. This technique has found immediate application i n the precise intercomparison of lead samples recently c a r r i e d out i n the Geophysics Laboratory at the University of B r i t i s h Columbia by F. Kollar and others (F. K o l l a r , R.D. Russell and T.J. Ulrych, i n press). The long range object for developing t h i s technique i s to p u r i f y lead tetramethyl prepared by free methyl r a d i c a l s reacting with m e t a l l i c lead (cf. A.J. Surkan 1956) pr i o r to i s o t o p i c analysis. The presence of impurities i n samples prepared t h i s way has i i discouraged the development of this method in the past. The final chapter deals with this aspect of the proposed problem. This thesis is intended as a preliminary to the writer's Ph.D. research which wil l also deal with isotopic lead analy-sis. i i i TABLE OF CONTENTS ABSTRACT i LIST OF ILLUSTRATIONS i v ACKNOWLEDGEMENTS v CHAPTER 1 Lead Isotope Abundances. 1 Introduction. 1 Mass spectrometer methods. 4 CHAPTER 2 The Lead Tetramethyl Technique. 6 Mass spectrum of lead tetramethyl. 6 Synthesis of lead tetramethyl. 8 CHAPTER 3 Gas Chromatography. 10 General aspects of ga s - l i q u i d 10 chr omat ogr aphy. Thermal conductivity sensing device. 11 Design of the f i r s t chromatographic 14 column. Fr a c t i o n a l d i s t i l l a t i o n of lead 17 tetramethyl. Design of the second chromatographic 19 column. Results of lead tetramethyl separation. 20 CHAPTER 4 Free Radicals. 22 Methods of producing free r a d i c a l s . 22 Review of methods and r e s u l t s of 24 producing lead tetramethyl by free methyl r a d i c a l s . CONCLUSIONS 26 BIBLIOGRAPHY v i i v LIST OF ILLUSTRATIONS Fi g . F i g . F i g . F i g . Table 2.1 Table 2.2 Table 2.3 Table 2.4 F i g . 2.3 F i g . F i g . F i g . F i g . F i g . 1.1 (a) 1.1 (b) 2.1 2.2 3.1 372 (a) 3.2 (b) 3.3 3.4 F i g . 3.5 F i g . 3.6 F i g . 3.7 F i g . 3.8 F i g . 3.9 To follow page Common and radiogenic lead. Uranium and thorium decay schemes. Normal lead tetramethyl spectrogram. Radiogenic lead tetramethyl spectrogram. PbH + e f f e c t i n the Pb + spectrogram. Relative i s o t o p i c abundances of lead from the Pb+ spectrogram. C 1 3 and Pb(C3Ho)+ e f f e c t s i n Pb(CH 3) 3 + spectrogram. the Relative isotopic +abundances of lead from the Pb(CH 3) 3 spectrogram. Apparatus for the synthesis of lead tetramethyl. Apparatus for gas chromatography. 1 1 6 6 7 7 8 8 8 10 Mechanical construction of katharometer. 11 Schematic 4-filament bridge. 11 Experimental apparatus. 14 Separation of ether and acetone, 15 column #1. Apparatus for the f r a c t i o n a l d i s t i l - 16 l a t i o n of lead tetramethyl. Separation of lead tetramethyl, 17 column #1. Separation of ether, acetone and 18 benzene, column #2. Separation of lead tetramethyl, 19 column #2. Typical spectrogram obtained for the 20 P b ( C H 3 ) 3 + ion group. V ACKNOWLEDGEMENTS This research was ca r r i e d out under the supervision of Professor R.D. Russell, whose help and advice were sinc e r e l y appreciated. The writer i s also indebted to F. Kollar f o r his suggestions and c r i t i c i s m s and to P. Neukirchner for a s s i s t i n g with many of the technical aspects of the research. This research was supported i n part by grants from the National Research Council of Canada. CHAPTER 1 Lead Isotope Abundances. The isotopic composition of lead i n lead ores i s ex-tremely variable. During the past s i x or seven years, the nature of t h i s v a r i a t i o n has been the subject of extensive investigation. Broadly speaking, there are two objectives of such a study. F i r s t l y , a properly formulated model to explain these va r i a t i o n s w i l l aid i n understanding the geochemical pro-cesses involving lead, uranium and thorium i n the evolution of the outer parts of the earth. Secondly, i t i s desirable to determine some of the geological aspects of lead ore formation. It i s not the aim of the writer to give an exhaustive treatment of the subject. Therefore the following summary i s greatly condensed. Most elements found i n nature consist of varying mixtures of d i f f e r e n t isotopes. The variations i n the isotope proportions are due mainly to two processes. The f i r s t i s due to f r a c t i o n a t i o n , accompanying natural chemical and physical processes,and the second i s the addition of daughter elements from radioactive decay. The element lead has four stable isotopes of atomic mass 204, 206, 207 and 208. A l l four of these isotopes are found i n lead minerals i n greatly varying proportions. Because of the r e l a t i v e l y high atomic weight of lead, the FIG l.l (a) COMMON AND RADIOGENIC LEAD 100% Thorium Lead J J L . 93.3% Uranium Lead 6.7% - I : 1_ Ordinary Lead ead M | ^ Jj 204 205 206 207 208 FIG 1.1 (b) URANIUM AND THORIUM DECAY SCHEMES TO FOLLOW P. I -2-f i r s t process mentioned above has never been observed i n nature and i s quite d i f f i c u l t to achieve i n the laboratory (Russell 1959). The v a r i a t i o n s i n the lead isotope r a t i o s are, therefore, explained by the second process. It i s known that lead-206, lead-207 and lead-208 are i d e n t i c a l with the lead produced i n the radioactive decay of uranium-238, uranium-235 and thorium-232 respectively and therefore the addition of radiogenic lead to the mineral lead w i l l increase the amount of lead-206, lead-207 and lead-208 r e l a t i v e to lead-204 (Fig. 1.1 (a) and (b))„ An excellent example of the application of lead i s o -tope r a t i o s has been given recently by Stanton and Russell (Stanton and Russell 1959) with regard to lead sulphide ores. They studied a c e r t a i n class of conformable lead sulphide ore and found that the isotope r a t i o s of such deposits are very uniform and simply r e l a t e d , while the isotope r a t i o s of c e r t a i n vein deposits contain anomalous additions of radiogenic leads. These r e s u l t s support the hypothesis that these conformable deposits are the product of a subcrustal source and have been i n contact with c r u s t a l rocks for only a short time before deposition„ The vein deposits, on the other hand, seem to have migrated through s i g n i f i c a n t thicknesses of older c r u s t a l rocks. The beginning of absolute geological age determi-nations based on radioactive decay can be traced to Ruther-ford and Soddy (Wilson, Russell and Farquhar 1956, p. 295), -3-who put forward the hypothesis that lead isotopes are formed by means of uranium and thorium decay. The standard methods used for t h i s work are those based on the decay of the two isotopes of uranium and the one isotope of thorium. The reasons for t h i s choice are clear. 1) . A l l three isotopes are radioactive and therefore three ages can be obtained as a check for consistency, 2) . The decay schemes are well known. 3) . The parents are highly concentrated i n minerals l i k e uraninite, which are formed with n e g l i g i b l e amounts of lead. The early work i n age determination was done through chemical analyses (Ellsworth 1932, Holmes 1937). It was found however that there was an uncertainty due to common lead contamination, and an isotopic analysis,, as well as a chemical analysis i s now made0 The proportion of common lead contamination i s in f e r r e d from the abundance of lead-204 o One age value can be obtained from the is o t o p i c analysis alone using the equation (Nier 1939) where -\ and x a-^e the decay constants of uranium-238 and uranium-235, A = 0„153 7 x 10~ 9 y r s . - 1 , A 1 = 0„972 2 x 10" 9 y r s . - 1 (Fleming, Ghlorso and Cunningham 1951 and 1952), t i s the age. U 2 3 5 : U 2 3 8 =1 : 137.8 (Inghram 1947). The analysis of lead isotopes i s performed with the p b206 n238 ( e A t _ i ) - 4 -aid of a mass spectrometer, whose basic operation i s as follows. Ions are formed from the sample to be analysed either by electron bombardment or by evaporation from a hot f i l a -ment. The ions leave the i o n i s a t i o n chamber through a narrow s l i t , are accelerated to a f i x e d energy by a strong e l e c t r o s t a t i c f i e l d and pass through collimating s l i t s . A magnetic f i e l d p a r a l l e l to the s l i t s d iverts the ions into c i r c u l a r paths, the r a d i i of which depend on the momentum of the ions. Thus sorted, the ions of a certa i n mass pass through resolving s l i t s and s t r i k e a c o l l e c t o r . The charge given up by the ions at the c o l l e c t o r produces an e l e c t r i c current which i s amplified and recorded. By varying the magnetic f i e l d , the complete mass spectrum of the sample i s obtained. In the s o l i d source mass spectrometer, the sample i s introduced into the i o n i s a t i o n chamber i n the form of a s o l i d , usually by being painted on a tungsten filament from which i t i s evaporated. In the gas source instrument, the sample i s introduced i n a gaseous form and i s bombarded with electrons. For routine analysis, the gas source mass spectrometer has several advantages over the s o l i d source instrument, the main one being the ease of operation. In the s o l i d source mass spectrometer the introduction or removal of a sample usually necessitates breaking the vacuum, whereas t h i s i s not necessary i n the former type. Another im-portant factor i s the r e p r o d u c i b i l i t y of r e s u l t s ; the -5-s o l i d i o n source gives widely v a r y i n g i o n e f f i c i e n c i e s i n some cases (Mair 1958). In a n a l y s i s of lead isotopes the s o l i d source mass spectrometer o f f e r s one important advantage. In some lead-bearing m i n e r a l s , e.g. z i r c o n s , a p a t i t e s , f e l d s p a r s , the lead i s present i n very s m a l l amounts, ranging upward from one p a r t per m i l l i o n . Because the minimum sample s i z e which can be r e a d i l y handled u s i n g the c l a s s i c a l gaseous techniques i s of the order of 10 mg. ( C o l l i n s , Freeman and Wilson 1951, and C o l l i n s , R u s s e l l and Farquhar 1953) (see Chapter 2) i t would be necessary t o process s e v e r a l kilograms of the sample i n order t o o b t a i n s u f f i c i e n t lead from the mi n e r a l . By us i n g a surface i o n i s a t i o n source, however, good r e s u l t s have been obtained f o r mineral separates from g r a n i t e s ( T i l t o n et a l . 1955) and a sample c o n t a i n i n g as l i t t l e as 2p,g. of lead has been reasonably w e l l analysed (Mair 1958). The problem which the w r i t e r has undertaken i s the extension of the range of a p p l i c a t i o n of the gas source mass spectrometer t o s t u d i e s of lead isotopes i n minerals i n which the lead i s contained as a minor c o n s t i t u e n t . The f i r s t stages of t h i s problem formed a b a s i s of the w r i t e r ' s M„Sc. research. - 6 -CHAPTER 2 The Lead Tetramethyl Technique. The f i r s t mass spectrographic studies of lead were made by F.W. Aston (1933) who u t i l i z e d a discharge through lead tetramethyl vapours i n a discharge tube. In his extensive studies of the is o t o p i c composition of lead, Nier (1938, 1939, Nier, Thompson and Murphey 1941) used a method i n which lead iodide was evaporated i n the vacuum system of a gas source mass spectrometer. This method, however, suffers from several disadvantages. Since lead iodide i s a s o l i d , both source and tube must be heated to 350°C to give suf-f i c i e n t vapour pressure. Free lead i s deposited on the i n -side of the mass spectrometer tube giving r i s e to e l e c t r i c a l leakage and there may also be a memory e f f e c t . Thus f r e -quent and troublesome cleaning i s necessary making the rate at which samples can be analysed rather slow. Another d i s -advantage i s that i f mercury d i f f u s i o n pumps are used, the Pb + spectrum i s complicated by the mercury isotope of mass 204. The P b l + ions can be used for analysis but the r e s o l u t i o n required i s f i f t y percent higher than i n the previous case. O i l pumps may reduce the f i r s t l i m i t a t i o n but the advantage i s p a r t i a l l y cancelled by the variable hydrocarbon background. Because of the above d i f f i c u l t i e s , C B . C o l l i n s i n 1951 turned back to a lead tetramethyl technique. On bombardment with 50-150 vo l t electrons, lead FTG 2 .1 . Pb(CHj ) , + Normal Lead TetramethiilSpectrogram Sample source : Ethyl Corporation. Detroit TO FOLLOW R 6 Pb(CH 3), + Pb(CH 3) 2 + L_n_ SO N - 0> dole* M Pb' •am — O o> csl C M C M C M — CM CM NNM O O O O CM CM CM CM o CM FIG 2.2. (CH3)3 Radiogenic Lead Tetramethul Spectogram Congo pitchblende Age: 6.30xio8years TO FOLLOW R 6 Pb(CH})2+ t- • en m CM CM Pb (CH3), Ji l / u . C I — O Ok CM CM CM — CM CM CM CM PI> r- • o o CM CM - 7 -tetramethyl dissociates into the following ion groups. Pb +, Pb(CH 3) 2 +, Pb(CH 3) 3+ and a small proportion of Pb(CH 3> 4 +. C o l l i n s , Russell and Farquhar (1953) and Diebler and Mohler (1951) have reported the abundances of ions observed from lead tetramethyl. The magnitudes of the abundances of PbH + 13 + ions and the e f f e c t of C i n the Pb(CH 3) 3 spectrogram ob-tained i n the two laboratories are not i n close agreement. The v a r i a t i o n i n the two determinations i s probably due to d i f f e r e n t ion source conditions. F i g , 2.1 and Fig» 2.2 show spectrograms for ordinary and radiogenic lead respectively. The most useful spectro-grams for c a l c u l a t i n g the abundances of lead isotopes are those of the Pb + and P b ( C H 3 ) 3 + ion groups. Interpretation of the d i f f e r e n t ion groups i s complicated by the presence of hydrides, the loss of one, two or three hydrogen atoms and by the carbon-13 e f f e c t . The analysis of the Pb + spectrogram can best be i l l u s -trated by Table 2.1 which shows the contribution of the PbH + ions to the i n t e r e s t i n g mass numbers and Table 2.2 which also shows the calculated r e l a t i v e abundances of the four lead isotopes from the Pb + ion spectrogram. From the figures i n these tables i t i s possible to calculate the s i g n a l obtained from the PbH + ion group. In t h i s case i t comes to 8»3 percent of the t o t a l ion s i g n a l from the Pb"*" ion group. Several disadvantages present themselves i f the Pb + ion spectrogram i s used for measuring the abundances of TABLE 2.1 PbH + EFFECT IN THE Pb + SPECTROGRAM Mass number Ions 204 P b 2 0 4 205 P b 2 0 4 H 206 p b206 207 P b 2 0 7 + p b 2 0 6 H 208 P b 2 0 8 + Pb 2 0 7H 209 P b 2 0 8 H TABLE 2c 2 RELATIVE ISOTOPIC ABUNDANCES FROM THE Pb + SPECTROGRAM Relative Mass number Relative i n t e n s i t y Lead isotope abundance, % 204 1.448 ± 0.003 204 10574 ± 0.005 205 0.135 ± 0.003 206 20.31 ± 0.02 206 22.07 ± 0.03 207 23.23 ± 0 . 0 2 207 23.33 ± 0 . 0 3 208 50.65 ± 0.03 208 53.02 ± 0.05 209 4„23 ± 0.01 to f o l l o w b . 7 -8-the isotopes of lead. The PbH +/Pb + f r a c t i o n depends on the energy of the i o n i s i n g electrons and on the temperature of the ion source, both of which may vary. Secondly, t h e O i s o -tope mercury-204 which r e s u l t s from the use of mercury d i f f u s i o n pumps complicates the quantitative determination of lead-204. In the analysis of radiogenic lead, because of the very small lead-204 and very variable lead-208 contents, no d i r e c t measure of the PbH + contribution may be possible. Tables 2.3 and 2.4 i l l u s t r a t e the analysis of a t y p i c a l Pb(CH ) + ion spectrogram. Corrections have been «j 3 made for the carbon-13 e f f e c t and the loss of one hydrogen atom. From the numbers i n these tables i t can be shown that the contribution of the Pb(C 3Hg) + ions amounts to 0.8% of that from the P b ( C 3 H g ) + ions. The major cor-r e c t i o n to be applied i s that for carbon-13 and i s not dependent on the energy of the i o n i s i n g electrons or the temperature of the ion,source. Because of the above mentioned advantages and be-cause i t i s the most abundant,, the Pb(CHg) 3 + ion group spectrogram i s preferred to the Pb + ion group spectrogram, when s u f f i c i e n t r e s o l u t i o n of the mass spectrometer i s available. Jones and Werner (1918) have described the synthesis of lead tetramethyl from lead chloride and Grignard re-agent. (The term Grignard reagent r e f e r s to any solution TABLE 2 ,3 C 1 3 AND Pta(C 3H g) + EFFECTS IN THE P b ( C H 3 ) 3 + SPECTROGRAM Mass number Ions 248 Pb 2 0 4(C 1 2H3)2(C 1 2H2) 249 P b 2 0 4 ( C 1 2 H 3 ) 3 250 P b 2 0 4 ( C 1 2 H 3 ) 2 ( C 1 3 H 3 ) + P b 2 0 6 ( C 1 2 H 3 ) 2 ( C 1 2 H 2 ) 251 P b 2 0 6 ( C 1 2 H 3 ) 3 + P b 2 0 7 ( C l 2 H 3 ) 2 ( C 1 2 H 2 ) 252 P b 2 0 7 ( C 1 2 H 3 ) 3 + P b 2 0 6 ( C 1 2 H 3 ) 2 ( C 1 3 H 3 ) + P b 2 0 8 ( C 1 2 H 3 ) 2 ( C 1 2 H 2 ) 253 P b 2 0 8 ( C 1 2 H 3 ) 3 + P b 2 0 7 ( C l 2 H 3 ) 2 ( C 1 3 H 3 ) 254 P b 2 0 8 ( C 1 2 H 3 ) 2 ( C 1 3 H 3 ) TABLE 2o4 RELATIVE ISOTOPIC ABUNDANCES FROM THE P b ( C H 3 ) 3 + SPECTROGRAM Relative Mass number Relative i n t e n s i t y Lead isotope abundance s % 248 0,01 + 0.005 249 1.51 + 0.005 204 1,569+ 0o005 250 0.23 ± 0.01 251 2 1 . 2 6 ± 0 . 0 2 206 2 1 , 9 7 + 0 . 0 3 252 23,56 + 0.02 207 23,41 ± 0.03 253 51.67 ± 0.03 208 53.04 ± 0.05 254 1.77 ± 0.005 (absolute error i s believed to be less than 1%) \o \O\\O\N b.Q B F I G . 2.3. A P P A R A T U S F O R T H E S Y N T H E S I S O F L E A D T E T R A M E T H Y L T O F O L L O W P. 8 A of an alkyl magnesium halide in ether, the reagent most often used being methyl magnesium bromide in diethyl ether.) The method used has been improved slightly over the years to give a better yield of lead tetramethyl, but the basis of their method is the same. The following is a typical technique. Lead chloride is obtained from a sample (e.g. galena) by boiling i t in hydrochloric acid^, and after recrystallization the chloride is converted to lead iodide by reaction with potassium iodide., 200-500 mg. of lead iodide is thoroughly dried and placed in the apparatus shown in Fig. 2.3 through the side arm A. BCD is a simple water-cooled "finger" re-flux condenser. A l l the air in the apparatus is displaced by passing dry oxygen-free nitrogen or argon by way of the lead-in E. Two cubic centimeters of ether are added to form a slurry and then an excess (5-10 ml.) of 0.5 mole-per-litre Grignard reagent is added and the mixture refluxed for one or two hours at about 35°C. After the reaction is complete water is added to consume the excess Grignard re-agent and to wash out the water-soluble byproducts. The ether layer is then separated in a separatory funnel and the resulting ether solution dried with anhydrous calcium sulphate. In the past, separation of ether and lead tetra-methyl has been effected by a crude dist i l lat ion followed by a second disti l lat ion under vacuum in the mass spectro-meter sample line. -10-CHAPTER 3 Gas Chromatography. Etherington (1957) f i r s t attempted to separate lead tetramethyl from a mixture containing lead tetramethyl and ether using g a s - l i q u i d chromatography. This experiment, which forms the smaller part of Etherington's thesis, gave no p o s i t i v e r e s u l t . Before describing the d e t a i l s of the procedure de-veloped by the writer, i t i s well to consider some general aspects of g a s - l i q u i d chromatography. The main features of t h i s method are shown in F i g . 3.1. The apparatus embodies a column which can be a s t r a i g h t , U shaped or c o i l e d tube, containing a suitable inert, s i z e -graded s o l i d which acts as a s o l i d support for the s t a t i o n -ary phase. The stationary phase i s a l i q u i d possessing a very low vapour pressure at the temperature of the experi-ment o A small sample of the v o l a t i l e mixture to be separated i s introduced into the top of the column. The components of the mixture are transported through the column i n a vapour phase by an inert gas r e f e r r e d to as the eluent or c a r r i e r gas. Because of t h e i r d i f f e r e n t physical properties, the constituents are transported through the column at d i f f e r e n t rates and emerge from i t i n d i v i d u a l l y . The compositions of the e f f l u e n t can be analysed q u a n t i t a t i v e l y and q u a l i t a t i v e l y by a detector s e n s i t i v e to some property of the vapours, usually the F I G . 3. I. D I A G R A M O F A P P A R A T U S F O R G A S C H R O M A T O G R A P H Y T O F O L L O W P. 10 GAS REGULATING VALVE COLUMN SAMPLE INTRODUCING )EVICE Ivy THERMOSTAT J DIFFERENTIAL DETECTOR 1 T GAS FLOW METER HIGH PRESSURE GAS SOURCE -11-thermal conductivity,, There are various methods of analysing the ef f l u e n t . Thermal conductivity, vapour-density balance, heat of ad-sorption are but a few. Thermal conductivity, however, i s the most widely employed and i s the method used by the writer. F i g . 3.2 (a) and (b) show the mechanical construction of the sensing instrument (Katharometer) and the detector c i r c u i t . The p r i n c i p l e of the method i s that heat i s conducted away from a hot body, situated i n a gas, at a rate depending on the nature of the gas, other factors being constant. The temperature of the sensing elements and hence t h e i r resistance i s determined by the conductivity of the surrounding gas. Since absolute measurements using thermal conductivity are d i f f i c u l t , a d i f f e r e n t i a l technique was adopted by the writer, using two gas channels and two matched pairs of tungsten filamentso (Type 9225 20 ohms Gow-Mac Instrument Company;, New Jersey.) Pure c a r r i e r gas was passed through channel #1, through the column and then through channel #2. The d i f f e r -ences i n resistance of the heated wires due to the presence of v o l a t i l e components i n the ef f l u e n t were then recorded by means of the Wheatstone bridge arrangement shown i n F i g . 3.2 (b) which gave an out of balance voltage recorded on a Brown 10 m i l l i v o l t chart recorder. The p a r t i c u l a r mechanical arrangement shown i n F i g . 3»2 (a) was chosen to minimize e f f e c t s of flow f l u c t u a t i o n s at the expense of a f a s t r e-sponse. The c a r r i e r gas should s a t i s f y the following two re-F I G . 3 . 2 . D E T A I L S O F T H E R M A L C O N D U C T I V I T Y S E N S I N G D E V I C E T O F O L L O W P II FILAMENTS F I G . 3. 2 . ( a ) S C H E M A T I C 4 F I L A M E N T B R I D G E F I G . 3 . 2 . ( b ) -12-quirements„ (1) It should be in e r t . (2) Its thermal conductivity should be either somewhat greater or less than that for the vapours to be detected. The above requirements are s a t i s f i e d by a number of gases, the most r e a d i l y available being hydrogen, helium and nitrogen. The thermal conductivities of the above r e l a -t i v e to a i r are 7.10, 5.53 and 0.996. Hydrogen however i s not recommended for safety reasons and helium i s rather ex-pensive for routine work where nitrogen w i l l do. Although the s e n s i t i v i t i e s with nitrogen are much ^ smaller than with either hydrogen or helium^ they were ample for t h i s problem. Columns are usually constructed of pyrex or copper tubing. The i n t e r n a l diameter of such columns usually l i e s between 4 and 8 millimeters and th e i r lengths vary with application from 1 to 20 meters. Since the resolution or the separating power of a column i s proportional to the number of t h e o r e t i c a l plates, the resolution can be i n -creased by increasing the length and i s roughly proportion-a l to the square root of the column length. An increase i n column diameter r e s u l t s in a decrease i n resolution owing to the decrease i n sharpness and uniformity of the moving fronts of the component bands. However a column of greater diameter can be used for large samples since the capacity of a column i s proportional to the square of the diameter. -13-The s o l i d support must meet the following requirements. (1) It must have a large surface area to provide the maximum number of t h e o r e t i c a l plates. (2) It must be inactive with respect to the com-ponents of any given sample. (3) It must permit a reasonable rate of flow without an excessive pressure drop. The materials which give the best r e s u l t s have so far been limited to diatomaceous earths and several kinds of f i r e b r i c k . The best compromise between column resistance and surface area i s obtained from a type C-22 f i r e b r i c k with p a r t i c l e s i z e ranging from 60 to 80 mesh. The narrow l i m i t s of the p a r t i c l e s i z e are necessary to ensure uni-formity of packing with the consequent sharp and undisturbed moving fronts i n the column. The stationary phase i n g a s - l i q u i d chromatography i s an ent i r e f i e l d of study i n i t s e l f . The choice of a s u i t a -ble p a r t i t i o n l i q u i d i s the most important factor i n ob-taining good r e s u l t s g since i t s chemical composition w i l l greatly a f f e c t p a r t i t i o n c o e f f i c i e n t s . Several c r i t e r i a a f f e c t i n g the choice of the p a r t i t i o n l i q u i d can however be treated generally. The stationary l i q u i d chosen should be v i r t u a l l y non-v o l a t i l e at the operating temperature, i . e . the temperature of the mean b o i l i n g point of the sample. A vapour pressure of 1 micron at t h i s temperature i s usually considered the maximum permissible value consistent with long column l i f e . -14-To function properly, the stationary l i q u i d must produce a d i f f e r e n t i a l p a r t i t i o n i n g of the components to be separated and must have a s u f f i c i e n t solvent power for the vapourised components. The l a t t e r requirement demands a cer t a i n s t r u c t u r a l resemblance between the mobile and the stationary phase, since then i d e a l solutions are more c l o s e l y r e a l i s e d i n the column. P o l a r i t y of the stationary l i q u i d can also play an important r o l e i n separation e f f i c i e n c y . Liquids with i n -creasing p o l a r i t y w i l l create stronger a t t r a c t i v e f i e l d s around the dissolved molecules of the v o l a t i l e constituents and exert strong a t t r a c t i v e forces causing considerable deviations i n the order of e l u t i o n . Gas-liquid chromatography can be a very precise technique. For t h i s to be so, the column and the detecting device are enclosed i n a thermostat capable of being regu-lated to + 1°C, the gas flow i s adjusted by a p r e c i s i o n gas regulating valve and the pressure at the i n l e t and outlet of the column i s usually regulated. In t h i s work the writer was interested i n a q u a l i t a t i v e rather than a quanti-t a t i v e study and so discarded many of the f i n e r d e t a i l s . The apparatus used i s shown i n F i g . 3.3. It embodies a high pressure nitrogen cylinder, a gas regulating valve, the column, kept at an approximately constant temperature in a water bath i n a dewar f l a s k , the thermal conductivity sensing device previously described, a flow meter and a c o l l e c t i n g arrangement. F I G . 3 . 3 . E X P E R I M E N T A L A P P A R A T U S T O F O L L O W P. 14 C O L L E C T I N G A R R A N G E M E N T -15-The immediate purpose of this work was to investigate in general the use of gas-liquid chromatography in the separation of contaminants from lead tetramethyl and to purify samples prepared by the method described in Chapter 2. With this purpose in mind, the writer f i rs t constructed a 4 mm. internal diameter, 50 cm. long, U shaped pyrex column. The solid support used was a type C-22 crushed firebrick, particle size 40-100 mesh. A. Keulemans (1957) l is ts the principle types of stationary liquids used in gas-liquid chromatography and their applications to various problems. It appears that organic esters, i . e . esters of an aromatic carboxylic acid and an aliphatic alcohol make stationary liquids of very general applicability. (Some of them are also used as diffusion pump oi ls , e.g. Octoils.) Keule-mans summarises their properties in the following manner. "The esters derived from aromatic acids, in particular, usually show no pronounced selectivity over a wide range of compound types, since they contain phenyl, aliphatic and polar groups. They separate many classes of solutes roughly according to volati l i ty and can be employed, if pure, for long periods up to 140°C." In view of these considerations, the stationary liquid chosen was dinonyl phthalate, a member of the phthalate group or organic esters. The ratio of stationary liquid to solid support was chosen to be 30:100 parts by weight. If the proportion of -16-liquid is large, diffusive phenomena tend to impair the sepa-ration, while if the proportion is small, residual adsorpti-vity causes tailing of the elution peaks. The column material was prepared by dissolving the partitioning liquid in ether, mixing the dissolved liquid and the stationary support thoroughly and evaporating the ether at 50°C. The material was packed into the column and plugs of glass wool were placed at the ends. The liquid sample was introduced by means of a syringe. For this purpose a serum cap was used to close the front end of the column. An obvious method of checking the separating efficiency of a column is by introducing a sample composed of two con-stituents of comparable volati l i t ies and observing the sepa-ration. Ether and acetone serve this purpose well. Since theory shows that the efficiency of separation in a gas-liquid chromatographic column improves with reduction in sample size, throughout the experiments dealing with acetone and ether the sample introduced was in the form of the vapours of the constituents. Fig. 3.4 shows the various chromatograms obtained with the f i rs t column. Curves (a) and (b) show the chromatograms for pure samples of ether and acetone respectively, at a temperature of 75°C and a flow rate of 50 ml./min. The f i rs t peak obtained in each case is due to air and is opposite in direction to the ether and acetone peaks since the thermal conductivity of air is higher than that of nitrogen, which in turn is higher than that of ether and J \ C O L D W A T E R F I G . 3 . 5 . A P P A R A T U S F O R T H E T R A C T I O N A L D I S T I L L A T I O N O F L E A D T E T R A M E T H Y L T O F O L L O W P. 16 W A R M W A T E R -17-acetone. Curves (c), (d) and (e) show the separation of ether and acetone at 75°C, 70°C and 65°C respectively using a flow rate of 50 ml./min. i n each case. Since the range of v o l a t i l i t i e s of interest i n the writer's case was far larger than the one employed i n the above experi-ments, these r e s u l t s indicate that the separating ef-f i c i e n c y of even a short column was s u f f i c i e n t for small samples, e s p e c i a l l y i f the temperature was kept close to the median b o i l i n g point of the sample. The writer next attempted to apply t h i s method to the p u r i f i c a t i o n of lead tetramethyl obtained by the procedure described i n Chapter 2. The s o l u t i o n containing lead tetramethyl and ether was f r a c t i o n a l l y d i s t i l l e d down to 1/4 cc. i n the appa-ratus shown i n F i g . 3.5 which was designed with the help of Prof. J.S. Forsyth. In such a f r a c t i o n a t i n g column, the vapour of the s o l u t i o n to be separated i s passed through the column and brought into contact with part of the condensate which flows down the column. The less v o l a t i l e components of the ascending vapour are condensed, while the more v o l a t i l e components are b o i l e d out of the descending l i q u i d phase. The d i s t i l l a t i o n through the column i s thus equivalent to a number of successive simple d i s t i l l a t i o n s . The e f f i c i e n c y of separation of a f r a c t i o n a t i n g column increases as the amount of vapour condensed at the top of the column and returned as reflux^ increases. In the writer's case, the r e f l u x r a t i o was -18-1 : 1. The purpose of the packing shown i n Fig . 3.5, which was composed of small glass h e l i c e s , was to provide good contact between the vapour and. l i q u i d phases i n the column. The d i s t i l l e d mixture was introduced into the column with a syringe and the lead tetramethyl was coll e c t e d for analysis i n the mass spectrometer. The method of c o l l e c t i o n was as follows. The dual stop-cock T^, shown i n Fig. 3.3, was set to allow the vapours emerging from the gas-chromato-graphic column to bypass the c o l l e c t i n g apparatus and escape to the atmosphere v i a a d i l u t e n i t r i c acid bubbler. When the katharometer began to indicate the lead tetramethyl peak, stop-cock Tg was opened and was turned to allow the lead tetramethyl to enter the c o l l e c t i n g arrangement which con-s i s t e d of a l i q u i d a i r trap and a sample storage tube. At the end of the lead tetramethyl peak, as shown by the sensing device, T-^  was closed, the c a r r i e r gas was pumped from the c o l l e c t i n g apparatus with the aid of a rotary vacuum pump and the apparatus was is o l a t e d by closing Tg. The dewar f l a s k containing l i q u i d a i r was then transferred to the sample storage tube into which the lead tetramethyl condensed. The sample storage tube consisted of a break-seal tube for long storage, or a tube terminated with a stop-cock for convenient handling for immediate use. Fig . 3.6 curve (a) shows the chromatogram obtained. The separation was not complete due largely to the long ether t a i l . This t a i l i n g was probably due to two reasons. F i r s t l y , the sample was not introduced as a "plug" at the CD CD Ol o o O 4 AIR -^j CD Ol O o O AIR -19-front end of the column, owing to the length of tubing be-tween the serum cap and the layer of column material, re-sulting in "exponential" flow and secondly the sample size was very large for the column. Curve (b) shows the sepa-ration obtained for a sample size of \ cc. which has de-teriorated considerably with the large increase in sample size. Owing to the inherent inefficiency of the disti l lation process and the incomplete separations obtained with the 50 cm. column, the writer constructed a column with a higher sample capacity and higher separating power. As mentioned previously, the f i rs t of these two factors can be attained by an increase in column diameter, while the second factor can be attained by an increase in column length. A new column was therefore constructed using 1 cm. internal diameter pyrex tubing wound into a 1^ meter helix as shown in Fig. 3.3. The column material was prepared as before except that a solid support of a more uniform particle size, ranging from 60 to 80 mesh, was used. Preliminary experiments were performed using ether, acetone and benzene in amounts 25%, 70% and 5% respectively. The sample size was 1/8 cc. in each case at a flow rate of 50 ml./min. Fig. 3.7 shows the chromatograms obtained. The separation attained between benzene and ether was complete and could be further increased by decreasing the temperature as shown in curve (b). Since the boiling point of lead tetra-methyl is approximately twice that of benzene and since the FIG 3.8 . SEPARATION OF LEAD TETRAMETHYL COLUMN # f 2 TO FOLLOW R 19 fccc (62° C) — i :—: 1 1 1 1 1 1 1_ 0 10 20 3 0 40 5 0 60 70 TIME (MINUTES) -20-column separates roughly according to b o i l i n g point, the re-s u l t s would indicate that the new column s a t i s f i e s the re-quirements. The column was therefore applied to the problem of separating lead tetramethyl from the unwanted constituents. Before introduction into the column, a p a r t i c u l a r sample was d i s t i l l e d down to approximately J cc. to avoid the possi-b i l i t y of column saturation. Before commencing each run, the temperature of the water i n the dewar f l a s k was raised to approximately 95°C and nitrogen was passed through the column to drive out any vapours which may have remained i n the column material. Typical r e s u l t s obtained are shown i n F i g . 3.8. Nitro-i gen at a flow rate of 50 ml./min. was used as the c a r r i e r gas i n each of the runs. Only two factors were altered from run to run, the temperature and sample Size as shown on the curves . Curve (a) shows the separation obtained when water was present i n the sample. The long t a i l i n g following the water peak was due to the f a c t that few stationary l i q u i d s are compatible with i t and i t i s often adsorbed to a c e r t a i n extent by the s o l i d support. Curve (b) shows the separation obtained when water was removed completely p r i o r to the separation. A contaminant peak, probably masked by the water peak i n curve (a), follows the ether peak. This contaminant could be mercury dimethyl which i s often observed i n the mass spectrometer. Curve (c) shows the chromatogram of the d i s t i l l a t e T Y P I C A L Pb (CH 3) 3 S P E C T R O G R A M O B T A I N E D T O F O L L O W P. 20 -21-obtained from the i n i t i a l separation. No lead tetramethyl peak i s present, showing that the d i s t i l l a t i o n as used i s nearly 100 percent e f f i c i e n t . The time required for the complete separation was of the order of 70 minutes, but t h i s time can be greatly shortened, i f desired, by increasing the temperature as indicated by the curves i n F i g . 3.7. The technique developed was applied to the analyses of s i x samples from the conformable lead deposits at Broken H i l l , New South Wales, A u s t r a l i a and one sample from the conformable lead deposits at Mount Isa, Queens-land, A u s t r a l i a with r e s u l t s being published by K o l l a r , Russell and Ulrych ( i n press). Using a mass spectrometer technique developed by F. Kollar a p r e c i s i o n ten times better than previously possible was obtained. This has made i t possible to d i s t i n g u i s h an age difference of 10 m i l l i o n years between formations 1500 m i l l i o n years old, a p r e c i s i o n that has never been possible before by any radioactive age determination method. Fi g . 3,9 shows the P b ( C H 3 ) 3 + mass spectrum of a sample prepared and p u r i f i e d as described. -22-CHAPTER 4 Free Radicals. It was f i rs t shown in an experiment by Paneth and Hofeditz that free methyl radicals could be detected by their removal of lead mirrors. In this experiment, methyl free radicals were obtained from the thermal decomposition of lead tetramethyl, and the reaction was assumed to be: Pb(CH3)4 - Pb + 4CH3 The free methyl radicals thus formed reacted with the lead mirror to form lead tetramethyl by Pb + 4CH2= Pb(CH 3) 4. The latter reaction is the basis of the method of producing lead tetramethyl which the writer hopes to employ in conjunction with his Ph.D. research programme. The feasability of this method has been well demonstrated by A. Surkan (1956) who, however, was discouraged from developing i t into a useful technique owing to the presence of contaminants in the cr i t ical mass ranges. The dissociation of a compound with the resulting production of free radicals may be performed in one of several ways, the chief methods being thermal (pyrolyses), photolyses and electric discharges. Dissociation occurs when the thermal energies of the molecules exceed their bond dissociation energy. This method has been widely used since 1933 when Leermakers -23-showed that free methyl radicals could easily be obtained in quantity by heating azomethane to 400°C. In 1934, - F.O. Rice et a l . showed that at temperatures of 800°C or greater, the pyrolyses of the vapours of a whole range of stable organic compounds, such as paraffin hydrocarbons, ether, alcohols, aldehydes, ketones and amines yield the simple alkyl radicals methyl and ethyl. The disadvantages of this method are the high temperatures necessary with the resulting experimental difficulties and the fact that investigations have shown that, in pyrolyses of organic molecules, free radical formation often compromises only a small proportion of the total reaction. Between 1931 and 1934, Norrish et a l . , after detailed study of the photochemical decomposition of aldehydes and ketones, concluded that when acetone vapour is exposed to ultraviolet light, the i n i t i a l reaction is the decomposition into free methyl radicals. Pearson in 1934 substantiated this conclusion by using Paneth's mirror technique. There is now abundant evidence that the photochemical decompo-sition of molecules of a l l types, in the liquid or gaseous phase, leads to the production of active free radicals. Two fundamentally different types of electrical discharge occur. The silent or non-disruptive and the disruptive discharge. The former includes types such as the ozoniser, corona, electrodeless discharge. From i n -vestigations with a variety of substances there can be no -24-doubt that the s i l e n t discharge decomposes organic and i n -organic compounds into atoms and r a d i c a l s , but the s i t u a t i o n i s usually too complex to enable precise predictions to be made. The disruptive discharge, the arc and the spark, i s much more vi o l e n t , with the r e s u l t that p r a c t i c a l l y every possible atom or r a d i c a l i s produced. This makes the analy-s i s of the r e s u l t s of such a discharge almost impossible. The main e f f e c t s of these discharges are thermal i n nature, corresponding to l o c a l i s e d heating of the gas to a very high temperature. Other methods e x i s t , such as e l e c t r o l y s i s , but for various reasons these do not lend themselves to the routine preparation of lead tetramethyl. Surkan i n 1956 attempted to produce lead tetramethyl by the reaction of lead with free r a d i c a l s i n s u f f i c i e n t quantity for use i n a mass spectrometer. It i s of intere s t here to summarise his methods and r e s u l t s . Surkan experimented with two types of free r a d i c a l forming mechanisms. High frequency discharge and thermal decomposition. The sources of free methyl r a d i c a l s used were acetaldehyde, acetone, methyl alcohol, methane, ethane and propane. Of the two mechanisms used, Surkan found the high frequency discharge to be superior i f used at low power to avoid impurities. By attack of standard lead mirrors he found that acetone and methyl alcohol gave the greatest y i e l d of free methyl r a d i c a l s . However, from the point of view of low impurities and high y i e l d , methane -25-gaye the best r e s u l t s . Surkan produced s u f f i c i e n t lead tetramethyl to y i e l d high i n t e n s i t y ion beams i n the mass spectrometer from 500 p.g. of lead, which i s less by a factor of twenty than the amount necessary i n the present method of preparing lead tetramethyl. A serious problem i n Surkan's method was the contamination of the reaction products, making impossible the accurate determination of the isotope abundances. -26-Conclusions. Two types of mass spectrometer are used for lead i s o -tope studies. Gas source and s o l i d source instruments. The former type has advantages which resulted i n i t s choice for use i n t h i s laboratory. Two problems aris e when the gas source instrument i s used for lead isotope analyses. The f i r s t problem concerns the sample s i z e . The lead to be analyses i s introduced into the mass spectrometer i n the form of lead tetramethyl vapour. The present chemical technique used i n preparing lead tetramethyl necessitates the use of a minimum of 8 mg. of lead. It would be highly impractical to t r y and obtain lead i n such quantities from ce r t a i n types of minerals, e.g. zircons, i n which the lead concentration i s small. The writer therefore investigated a new method of producing lead tetramethyl from microgram quantities of lead, a problem f i r s t studied by Surkan. Surkan, using free methyl r a d i c a l s produced by high frequency discharge i n propane, methane and acetone, obtained s u f f i c i e n t lead tetramethyl f o r analysis i n a mass spectrometer. A large amount of contaminants were however obtained, some in the mass range of i n t e r e s t , making any useful isotope measure-ments impossible. The writer's b r i e f investigations into free r a d i c a l s would indicate that photolysis of acetone vapour i s capable of producing large quantities of free methyl r a d i c a l s with smaller amounts of contaminants than e l e c t r i --27-c a l discharge and i s more convenient a method than pyrolyses. The experiments performed with g a s - l i q u i d chromato-graphy show that lead tetramethyl can r e a d i l y be separated from any contaminants obtained. The writer hopes to develop the free r a d i c a l technique as part of his Ph.D. research. The second problem concerns the pur i t y of the lead tetramethyl sample obtained by the usual technique described i n Chapter 2, i n which the main contaminant i s ether. D i s t i l l a t i o n , i f c a r r i e d too f a r w i l l r e s u l t i n loss of lead tetramethyl. Other contaminants may be water, which can usually be removed by c a r e f u l chemistry, and such compounds as mercury dimethyl or other byproducts of the reaction be-tween the Grignard reagent and the somewhat impure lead iodide obtained from the mineral. Contaminants can have serious e f f e c t s on the p r e c i s i o n of analysis. Ether, because i t i s a large proportion of the sample and because of i t s high vapour pressure, r a i s e s the pressure of the mass spectrometer vacuum system and causes pressure scattering with the r e s u l t i n g t a i l i n g of the i s o -tope peaks. Other contaminants, i f f a l l i n g i n the mass range of i n t e r e s t , can d r a s t i c a l l y change the isotope r a t i o s , a f f e c t i n g p a r t i c u l a r l y the abundance of lead-204. The technique developed by the writer has overcome the d i f f i c u l t i e s mentioned above. Analyses recently completed i n t h i s laboratory by F. Kollar and others involved lead samples from 200 square mile areas i n Broken H i l l , A u s t r a l i a and Mount Isa, A u s t r a l i a . The isotope r a t i o s i n each -28-d i s t r i c t are predicted to be i d e n t i c a l (Stanton, Russell 1959). In attempting to v e r i f y t h i s theory, Kollar ob-tained a 0.05% precision by using a s p e c i a l l y constructed gas source mass spectrometer with a new technique involving the d i r e c t intercomparison of two samples. In order to do t h i s , he required very pure samples of lead tetramethyl, since only then can conditions i n the mass spectrometer be kept the same f o r both samples and the p o s s i b i l i t y of con-tamination be avoided. Six samples from Broken H i l l , New South Wales and one from Mount Isa, Queensland were analysed by the time t h i s 207 206 thesis was prepared. It was found that the Pb /Pb and Pb 2^ 4/Pb 2^ 6 isotope r a t i o s i n each d i s t r i c t were i d e n t i c a l within 0.05%. Furthermore there was a 0.5% difference i n the isotope r a t i o s from the two l o c a l i t i e s separated by eight hundred miles. From these r e s u l t s i t can be in f e r r e d that the leads from the two d i s t r i c t s l i e approximately on the same lead-uranium-thorium curves and that the Mount Isa lead i s about 50 m i l l i o n years younger than the Broken H i l l lead. The l a t t e r r e s u l t i s of great importance since the age difference i s only 3% of the ages of the two deposits and represents a s i g n i f i c a n t increase i n the precision with which ages i n t h i s range can be compared by t h i s or s i m i l a r methods. v i BIBLIOGRAPHY Aston, F.W., The isotopic c o n s t i t u t i o n and atomic weight of lead: Proc. Roy. Soc. Lond., 140A, 535 (1933). C o l l i n s , C.B., Farquhar, R.M., and Russell, R.D., Isotopic const i t u t i o n of radiogenic leads and the measure-ment of geological time: B u l l . Geol. Soc. of Amer., 65, 1-22 (1954). C o l l i n s , C.B., Freeman, J.R., and Wilson, J.T., A modifi-cation of the is o t o p i c lead method for determi-nation of geological ages: Phys. Rev., 82, 966-967 (1951). C o l l i n s , C.B., Russell, R.D., and Farquhar, R.M., The maximum age of the elements and the age of the earth's crust: Can. Jour. Phys., 31, 402-411 (1953). Diebler, V.H., and Mohler, F.L., Mass spectra of some organo-lead and organo-mercury compounds: Jour. Res. Natl. Bur. Standards, Washington, 47, No. 5, 337-342 (1951). Ellsworth, H.V., Rare-element minerals of Canada: Geol. Surv. Canada, Econ. Geol. Ser. No. 11 (1932). Etherington, E.W., Migration rates of substances along columns: M.A. Thesis, University of Toronto (1957). Fleming, G.H.Jr., Ghiorso, A., and Cunningham, B.B., The 235 s p e c i f i c alpha a c t i v i t y of U : Phys. Rev., 82, 967-968 (1951). v i i F l e m i n g , G.H.Jr., G h i o r s o , A., and Cunningham, B.C., S p e c i f i c a l p h a a c t i v i t i e s and h a l f - l i v e s o f U 2 3 4 , U 2 3 5 and U 2 3 6 : Ph y s . Rev., 88, 642-644 ( 1 9 5 2 ) . Holmes, A., The age o f t h e e a r t h - N e l s o n and Sons, ( 1 9 3 7 ) . Inghram, M.G., M a n h a t t a n p r o j e c t , t e c h n i c a l s e r i e s , N a t i o n a l n u c l e a r e n e r g y s e r i e s , d i v i s i o n I I , 14 Chap. 5, 35, M c G r a w - H i l l Co. ( 1 9 4 7 ) . J o n e s , L.W., and Werner, L., H y d r o c a r b o n b a s e s and a s t u d y o f o r g a n i c d e r i v a t i v e s o f m e r c u r y and o f l e a d : J o u r . Am. Chem. S o c , 40, 1257-1275 ( 1 9 4 8 ) . K e ulemans, A . I . , Gas C h r o m a t o g r a p h y : R e i n h o l d P u b l i s h i n g C o r p o r a t i o n ( 1 9 5 7 ) . M a i r , J.A., S o l i d s o u r c e mass s p e c t r o m e t r y : a p p l i c a t i o n s t o g e o c h r o n o l o g y : Ph.D. T h e s i s , U n i v e r s i t y o f T o r o n t o ( 1 9 5 8 ) . N i e r , A.O., V a r i a t i o n i n t h e r e l a t i v e a b u n d a n c e s o f t h e i s o t o p e s o f common l e a d f r o m v a r i o u s s o u r c e s : J o u r . Am. Chem. S o c , 60, 1571-1576 ( 1 9 3 8 ) . N i e r , A.O., The i s o t o p i c c o n s t i t u t i o n o f r a d i o g e n i c l e a d s and t h e measurement o f g e o l o g i c a l t i m e I I : Phy s . Rev., 55, 153-163 ( 1 9 3 9 ) . N i e r , A.O., Thompson, R.W., and Murphey, B.F., The i s o -t o p i c c o n s t i t u t i o n o f l e a d and t h e measure-ment o f g e o l o g i c a l t i m e I I I : P h y s . Rev., 60, 112-116 ( 1 9 4 1 ) . R u s s e l l , R.D., Some g e o c h e m i c a l c o n s i d e r a t i o n s o f l e a d i s o -t o p e d a t i n g o f l e a d d e p o s i t s : E c o n o m i c v i i i G e o l o g y , 54, No. 5, 951-953 ( 1 9 5 9 ) . ( D i s -c u s s i o n o f p u b l i c a t i o n by B o y l e , R.W. i n E c o n o m i c G e o l o g y , 54, 130-135 ( 1 9 5 9 ) . S t a n t o n , R.L., and R u s s e l l , R.D., Anomolous l e a d s and t h e emplacement o f l e a d s u l f i d e o r e s : E c o n o m i c G e o l o g y , 54, No. 4, 588-607 ( 1 9 5 9 ) . S u r k a n , A . J . , S o u r c e s o f l e a d i o n s f o r mass s p e c t r o m e t r y : M.A. T h e s i s ( 1 9 5 6 ) . T i l t o n , G.R., P a t t e r s o n , C . C , Brown, H., Inghram, M. C., Hayden, R. J . , H e s s , D . C , and L a r s e n , E.S. J r . , I s o t o p i c c o m p o s i t i o n and d i s t r i b u t i o n o f l e a d , u r a n i u m and t h o r i u m i n a p r e c a m b r i a n g r a n i t e : B u l l . G e o l . Soc. Amer., 66, 1131-1148 ( 1 9 5 5 ) . W i l s o n , J . T . , R u s s e l l , R.D., and F a r q u h a r , R.M., R a d i o -a c t i v i t y and age o f m i n e r a l s : Handbuch d e r P h y s i k , X L V I I , p. 295 ( 1 9 5 6 ) . 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0085412/manifest

Comment

Related Items