A HYDRIDE GENERATION-ATOMIC ABSORPTION SPECTROMETRIC PROCEDURE FOR THE QUANTIFICATION OF GERMANIUM AND OTHER ELEMENTS IN IRON METEORITES A thesis presented in partial fulfiL~ent of the requirements for the degree of MASTER OF SCIENCE Department. of Chemistry and Biochemistry ~Essey University NEW ZEALAND XUN GUO 1989 MASSEY UNIVERSITY LIBRARY i A B S T R A C T Covalent hydride-forming elements were investigated to explore their fX)tential use in chemical classification of iron meteorites. Only As , Ge and Pb were detectable in these samples . A simple and inexpensive combined hydride generation atomic absorption spectrc:metric method (HGAAS) was developed and was the first to be applied to quantification of these elements in iron meteorites. Variable studies were: flame type, generation reaction conditions, interferences, and atcxnization. A convenient nitrogen­ nydrogen- air entrained flame was used to determine germanium in meteorites. 'l'he determination of germaniu,n in 22 iron meteorites using the above method gc:1ve data in good agreement with those obtained by J . T i'iasson et al who used radiochemical neutron activation analysis (.Ri-iAA). From practical applications of my method, it was clear that the technique afforded a reliable, inexpensive, and sensitive method for tne c;uantification of germanium in iron meteorites. Various methods of sa~ple attack were tried and included acid attack in an open container, under a reflux , or with a Teflon bo.-nb, and fusion with sodium peroxide. The optimum method was acid attack under reflux or with a Teflon bomb . Nitric acid was more suitable than other acids. The method has applied to various samples which resulted in: identification of a bogus meteorite(HANAU), classification of a newly discovered meteorite(TASSAJARA), and confirmation that the Antarctic "Oi-J~UM VALLEY " iron was in fact part of the previously known DERRICK PfAKS shower. ii ACKNOWLEDGEMENTS I would like to express my gratitude to my supervisor, Professor R.R. Brooks, for his advice, instruction, and encouragement throughout the period of this work. Thanks are also due to the Department of Chemistry and Biochemistry, the University Library and the Computer Unit for their advice and assistance. My grateful thanks go to Dr. T. N. M. Waters, Vice­ Chancellor of Massey University, for his encouragement and support throughout my stud ies here. I a cKnowledge the receipt of a fellowship from Massey University, which enable me to study here . I am gra teful to the Depa rtment of Pharmacology, Guiyang Colle ge of Traditiona l Chine se Med icine, Guizhou, P. R. China for granting me l e ave from their employ in order to further my education. Finally, I gratefully acknowledge my wife, Xiaohong Fan, for her encouragement, support and assistance, and also my parents and my son, who are in P. R. China, for their great support during my studies at Massey Unive rsity, New Zealand. iii TABLE OF CONTENTS Abstract............................................................ i Acknowledgments. • . • . • . • . • • . • • . • • . • . ii Table of Contents .••..••.•............••......•.......•....•.....••. iii LJ.s. t o f F".igures ........•.••.................••.......••....•....•.•• vi List of Tables. • . • . viii CHAPTER ONE GENERAL INTRODUCTION ...•.................•............. l I.l Hydride Generation........................................... l I.1.1 A Review of Hydride Generation .....................•.... 2 1.1.2 Developnent of Reduction Methods for Hydride Generation .........•......•.••.•....••••.•• 5 I .1. 3 Applications. • . • . • • . • . 7 I.2 Iron Meteorites and Their Classifications .................... 9 I .2.1 Iron i\\eteorites ......................................... 11 I.l.2 The Met.nod of Classification of Iron Meteorites ......... 12 1.3 Aim of Present v~ork .......................................... 15 CHAPTER Tv.O STUDIES ON HYDRIDES OF VARIOUS ELE.V£.t~TS. 19 II . 2 Instrumentation. 20 II.2.1 Apparatus .............................................. 20 II. 2. 2 Collecting Unit. 21 II. 2. 3 Instrument .......................•....................• 21 II. 2. 4 Standards and Reagents . • . 23 11.3 Atomisation Conditions ...................................... 25 II. 3 .1 The Type of Flame. 25 II.3.2 The Effects of Different Burner Heights ...............• 26 II.3.3 The Effects of Gaseous Flow Rate in the Flame .......... 28 II.3.4 Carrier Gas Flow Rate .•....................•......••... 28 iv II. 4 Experimental.. • • • . • • • • • • • . • • • • . • . • . • . • • • • . 30 II. 4 .1. The Effect of Different Acids and Acidities .•••••.••••• 30 II.4.2 Interference fran Non-analyte Elements .•...••.•.......• 34 II.4.3 The Optimum Amount of Sodiu~ Borohydride ..•.••.•••....• 38 II.4.4 The Effects of the Total Reaction Volume ..•.•.....•.... 40 II.4 .5 Total Reaction Time. • • . • • . • • • . • . • . • • . • • • . • . • . • • . 41 II.4.6 The Effects of Different Oxidation States .•.•••.••...•. 42 II.4.7 The Use of Oxidation agents before Generation of Hydrides. • • • . • • • • . • • • • . • . • . • . • . • . 4 5 II. 4. 8 The Effects of Connecting Tubes of Different Materials. 48 II. 4. 9 Detection Limits. • • • • . • • . • . • • . • • • . • . • . • • . • 50 II.5 Discussion and Conclusion •.•...•.•......•..•.....••..•.....• 51 CP.API'ER THREE THE DETERMINATION OF GERMANIUM HJ IRON METEORITES ...• 58 III. l Introduction. • . • • • . • • • . • . 58 111.2 The Role of Germanium in Chemical Classification of Iron Meteorites. • . • . • . • . • . 59 IlI.3 Determination of GeGmniu~ in Iron Meteorites .........•.... 60 III.3.1 Conditions of Analysis ....••..................•....... 60 i. Apparatus and Instru~ent. • 60 ii. Acid Strength. • • . • . • . 61 iii. The Amount of Sodium Tetrahydroborate(III) ...•....•.• 61 iv. Reaction Time for Hydride Generation ................• 63 v. Flame Type. • • • . • . • • . • . • . • . • . • • . 63 vi . Flow Rate of Gases . • • • • . • • . • . • • . • . • . • 6 5 vii. Carrier Gas ...•........•............................. 65 viii. General Operation Procedure •••.........•.••.•........ 65 III. 3. 3 Interfering Elements. • • • • . • . • . • . • . • . • • . 67 III.3.4 IVia.sking Agent ••••...•.•.•.••....•.....•...••.••.•.•••• 69 V III.3.5 Treatrnent of Samples . ••. .••••.. ••.• .••.•..•••••••••••• 71 i. Acid Attack in an Open Container •. .....•.......•.. •. 73 ii. Acid Attack under Reflux. • • . • • . • . 73 iii. Acid Attack in a Teflon Bomb ••••••••••••• ••• •• • •••••• 74 iv. Fusion with SOdiuu Peroxide •.. • ..••.....•.••..•• •• ••• 74 II I. 4 A Ccrnpar ison with the Other Methods . • . • • • . • . • . • • . • . • • . • • • 77 III. 5 surrmary and Conclusions •.•...•.•.•....••••.•.••.••••••.••.• 79 CHAPTER FOUR SCME PRACTICAL APPLICJI.TIONS OF Gffi'-1.ANIUM O.ETERiV.INATIONS IN METEORITES . • . • • • . • . • . • . • • . • • . • • • • • 82 IV .1 Introduction. • • • . • • . • • . • . • • • . • . • • . • • • • • 82 IV. 2 The Hanau Harbour "Meteorite" ..•.....•..........•••••..••..• 82 IV. 3 The Derrick Peaks Shower..... • . • . • . • • 84 IV.4 The Wali<.er County Meteorite .•...............•...••....•...•. 85 IV. 5 The Tassa jara .Meteorite. 85 IV . 6 Conclusions. • . • 87 CHAPTER FIVE SUMLV,ARt AND GENERAL CONCLUSION .•••.•.........•.•..•... 88 V.l Sum-nary of Methodology for Hydride Generation .. ... .• ........ 88 V. 2 Probleins in the Application of the f•lethod to Iron lYieteorites .. .. ....... .. ...................•..... 89 V. 3 The Significance of the :Viethc<l for r,;-eteor i te Research. • . 90 V.4 Reca~uendations for Future \tvork . .•.•................•........ 91 References . • . • 9 2 vi LIST OF FIGURES FIGURES PAGE 1.1 Plot of Ga vs. Ni for Iron Meteorites ...•....•.•..•..•...•••. 16 l. 2 Plot of Ge vs. Ni for Iron Meteorites ........•.....•...•••.•. 16 1.3 Plot of Ir vs. Ni for Iron Meteorites ..............•••.•.•••. 16 2.1 Apparatus for Hydride Generation .............•.•.•....••.••.. 22 2.2 Sensitivities for Various Types of Flame ......•.....•..••.... 27 2.3 Absorbance as a Function of Burner Height .....••..•...••...•. 29 2. 4 Flame Gases Flow Rate •.•......•......•.........•......•..•••• 31 2.5 Carrier Gas Flow Rate ......•.•.•.............••...••..•.••••• 33 2.6 Absorbance as a Function of Acidity ...............•..•...•.•• 35 2.7 Interferences of Several Ions .................•..........•... 37 2.8 Hydride Generation Reaction T~~e ............................. 43 2. 9 Analytical Curves for Arsenic ..........................•...•. 46 2.10 Signal Height as a Function of amount of Am.-r10nium Pe.csulpha te ( l M) .................................. ¼9 2 .11 Analytical Cu.eves ......................................•..... 52 3.1 Signal as a Function of the A111ount of Sodium Tetrahydroborate(III) ........ ....................... 62 3.2 Reaction TD~e for Hydride Generation ...........•..........•.. 64 3. 3 Flow Rates of Flame Gases ............................•..•..•• 66 3.4 Flow Rate of Carrier Gas ........................•........... 68 3.5 Amount of Ascorbic Acid (L~) for Masking Fe ..........•.....•. 70 3.6 Amount of Trisodium Citrate (L~) for Masking Interfering Elements ....................................... 72 3.7 Apparatus for Digestion of Sarnples ................•....•..... 75 vii 4.1 Photographs of the Hanau Harbour Iron Meteorite in Its Original State •••.•••..•...•.•...•...•.•.•••...•.... 86 4.2 Photograph of a Cross Section of The Hanau Harbour Iron Meteorite Showing Plessite Bands .••••....•••.•.••..•.. 87 viii LIST OF TABLES FABLE PAGE 1.1 Minerals Ccmnonly