摘要:

Journal of Analytical Atomic Spectrometry (Including Atomic Spectrometry Updates) JAAS Editorial Board" Chairman L. Ebdon (Plymouth UK) J Egan (Cambridge UK) D A Hickman (London UK) J Marshall (Middlesbrough UK) J M Mermet (Villeurbanne France) D L Miles (Keyworth UK) B L. Sharp (Loughborough UK) R D Snook (Manchester UK) "The JAAS Editorial Board reports to the Analytical Editorial Board Chairman A G. Fogg (Loughborough UK) JAAS Advisory Board F C Adams (Antwerp Belgium) R M Barnes (Amherst MA USA) L Bezur (Budapest Hungary) R F Browner (Atlanta GA USA) B V L'vov (Leningrad USSR) S Caroli (Rome Italy) A J Curtius (Rio de Janeiro BraziO N Omenetto (Ispra Italy) L de Galan (Vlaardingen The Netherlands) J B Dawson (Leeds UK) K Dittrich (Leipzig GDR) W Frech (UmeJ Sweden) K Fuwa (Tokyo Japan) A L Gray (Egharn UK) S Greenfield (Loughborough UK) G M Hieftje (Bloomington IN USA) G Horlick (Edmonton Canada) Ni Zhe-ming (Beiiling China) T C Rains (Charleston SC USA) R E Sturgeon (Ottawa Canada) R Van Grieken (Antwerp Belgium) A Walsh K B (Victoria Australia) B Welz (Uberlingen FRG) T S West (Abderdeen UK) Atomic Spectromery Updates Editorial Board Chairman "D L J Armstrong (Dumfries UK) J R Bacon (Aberdeen UK) C Barnard (Glasgow UK) R M Barnes (Amherst MA USA) S Branch (High Wycombe UK) R Bye (Oslo Norway) J Carroll (Middlesbrough UK) M R Cave (Keyworth UK) "J M Cook (Keyworth UK) "M S Cresser (Aberdeen UK) H M Crews (Norwich UK) J S Crighton (Sunbury-on-Thames UK) J R Dean (Newcastle upon Tyne UK) *J B Dawson (Leeds UKI "L Ebdon (Plymouth UK) "J Egan (Cambridge UK) *A T Ellis (Oxford UK) "D J Halls (Glasgow UK) "D A Hickman (London UK) *S J Hill (Plymouth UK) J Fazakas (Bucharest Romania) K W Jackson (Albany NY USA) R Jowitt (Middlesbrough UK) K Kitagawa (Nagoya Japan) "D Littlejohn (Glasgow UK) "J Marshall (Middlesbrough UK) Miles (Keyworth UK) H Matusiewicz (Poznan Poland) J M Mermet (Villeurbanne France) R G Michel (Storrs CT USA) T Nakahara (Osaka Japan) Ni Zhe-ming (Beying China) P R Poole (Hamilton New Zealand) W J Price (Ashburton UK) C J Rademeyer (Pretoria South Africa) M H Ramsey (London UK) A Sanz-Medel (Owedo Spain) I L Shuttler (Uberlingen FRG) S T Sparkes (Plymouth UK) R Stephens (Halifax Canada) J Stupar (Llublpna Yugoslavia) R E Sturgeon (Ottawa Canada) A Taylor (Guildford UK) A P Thorne (London UK) G C Turk (Gaithersburg MD USA) J F Tyson (Amherst MA USA) *A M Ure (Aberdeen UK) S J Walton (Crawley UK) P Watkins (London UK) B Welz (Uberlingen FRG) J Williams (Egham UK) J B Willis (Victoria Australia) "Members of the ASU Executive Committee Editor JAAS Judith Egan The Royal Society of Chemistry Dr J M Harnly Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK Telex No 81 8293 Fax 0223 423623 Assistant Editors Brenda Holliday Editorial Secretary Monique Warner US Associate Editor JAAS US Department of Agriculture Beltsville Human Nutriton Research Center Beltsville MD 20705 USA Telephone 301 -344-2569 Telephone 0223 420066 BLDG 161 BARC-EAST Paula O'Riordan Sheryl Whitewood Advertisements Advertisement Department The Royal Society of chemistry Burlington House Piccadilly London W I V CBN UK.Telephone 071-437 8656 Fax 071-437 8883 Information for Authors Full details of how to submit materials for publica- tion in JAAS are given in the Instructions to Authors in Issue 1 Separate copies are available on request The Journal of Analytical Atomic Spectrometry (JAAS) is an international journal for the publica- tion of original research papers communications and letters concerned with the development and analytical application of atomic spectrometric techniques The journal is published eight times a year including comprehensive reviews of specific topics of interest to practising atomic spectrosco- pists and incorporates the literature reviews which were previously published in Annual Reports on Analytical Atomic Spectroscopy (ARAAS) Manuscripts intended for publication must de- scribe original work related to atomic spectromet- ric analysis Papers on all aspects of the subject will be accepted including fundamental studies novel instrument developments and practical ana- lytical applications As well as AAS AES and AFS papers will be welcomed on atomic mass spec- trometry and X-ray fluorescence/emission spec- trometry Papers describing the measurement of molecular species where these relate to the char- acterization of sources normally used for the pro- duction of atoms or are concerned for example with indirect methods of analysis will also be ac- ceptable for publication Papers describing the de- velopment and applications of hybrid techniques (e g GC-coupled AAS and HPLC- ICP) will be par- ticularly welcome Manuscripts on other subjects of direct interest to atomic spectroscopists in- cluding sample preparation and dissolution and analyte pre-concentration procedures as well as the statistical interpretation and use of atomic spectrometric data will also be acceptable for pub- lication There is no page charge The following types of papers will be consid- ered Full papers describing original work Communications which must be on an urgent matter and be of obvious scientific importance Communications receive priority and are usually published within 2-3 months of receipt They are intended for brief descriptions of work that has progressed to a stage at which it is likely to be valuable to workers faced with similar problems Reviews which must be a critical evaluation of the existing state of knowledge on a particular facet of analytical atomic spectrometry Every paper (except Communications) will be submitted to at least two referees by whose advice the Editorial Board of JAAS will be guided as to its acceptance or rejection Papers that are accepted must not be published elsewhere except by permission Submission of a manu- script will be regarded as an undertaking that the same material is not being considered for publica- tion by another journal Manuscripts (three copies typed in double spacing) should be sent to Judith Egan Editor JAAS or Dr.J M. Harnly US Assoiia?e Editor JAAS. All queries relating to the presentation and sub- mission of papers and any correspondence re- garding accepted papers and proofs should be directed to the Editor or US Editor (addresses as above) Members of the JAAS Editorial Board (who may be contacted directly or via the Editorial Office) would welcome comments suggestions and advice on general policy matters concerning JAAS Fifty reprints are supplied free of charge Journal of Analytical Atomic Spectrometry (JAASI (ISSN 0267-9477) is published eight times a year by The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF.UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry Turpin Tractions Ltd. Blackhorse Road Letchwarth Herts. SG6 1 HN UK Tel. +44 (0) 462 672555; Telex 825372 Turpin G; Fax +44 (0) 462 480947.Turpin Transactions Ltd. is wholly owned by The Royal Society of Chemistry. 1991 Annual subscription rate EC f309.00 USA $728.00 Rest of World €355.00. Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11003. USA Postmaster send address changes to Journal of Analytical Atomic Spectrometry (JAAS) Publications Expediting Inc. 200 Meacham Avenue Elmont NY 11003. Second class postage paid at Jamaica NY 11431. All other despatches outside the UK by Bulk Airmail within Europe Accelerated Surface Post outside Europe. PRINTED IN THE UK. 0 The Royal Society of Chemistry 1991. All rights reserved.No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photographic recording or otherwise without the prior permission of the publishers.Journal of Analytical Atomic Spectrometry (Including Atomic Spectrometry Updates) JAAS Editorial Board* Chairman L Ebdon (Plymouth UK) J Egan (Cambridge UK) D A Hickman (London UK) B L Sharp (Loughborough UK) J Marshall (Middlesbrough UM J M Mermet (Villeurbanne France) D L Miles (Keyworth UK) R D Snook (Manchester UK) *The JAAS Editorial Board reports to the Analytical Editorial Board Chairman A G Fogg (Loughborough UM F C Adams (Antwerp Belgium) R M Barnes (Amherst MA USA) L Bezur (Budapest Hungary) R F Browner (Atlanta GA USA) S Caroli (Rome Italy) A J Curtius (Rio de Janeiro Bran4 L de Galan (Vlaardingen The Nether J B Dawson (Leeds UM K Dittrich (Leipzig GDR) W Frech (Umed Sweden) K Fuwa (Tokyo Japan) A L Gray (Egham UK) JAAS Advisory Board S Greenfield (Loughborough UK) G M Hieftje (Bloomingron IN USA) G Horlick (Edmonton Canada) B V L'vov (Leningrad USSR) Ni Zhe-ming (Beiling Chrna) N Omenetto (Ispra Italy) lands) T C Rains (Charleston SC USA) R E Sturgeon (Ottawa Canada) R Van Grieken (Antwerp Belgium) A Walsh K B (V/ctoria Austraha) B Welz (Uberlingen FRG) T S West (Abderdeen UM ~~ ~ Atomic Spectromery Updates Editorial Board Chairman *D L Miles (Keyworth UK) J Armstrong (Oumfries UM H Matusiewicz (Poznan Poland J R Bacon (Aberdeen UK) J M Mermet (Vrlleurbanne France) C Barnard (Glasgow UK) R G Michel (Storrs CT USA) R M Barnes (Amherst MA USA) T Nakahara (Osaka Japan) S Branch (High Wycombe UK) Ni Zhe-ming (Beyng China) R Bye (Oslo Norway) P R Poole (Hamilton New Zealand) J Carroll (Middlesbrough UK) W J Price (Ashburton UK) M R Cave (Keyworth UK) C J Rademeyer (Pretoria South Africa) M H Ramsey (London UK) A Sanz-Medel (Oviedo Spain) H M Crews (Norwch UK) I L Shuttler (Uberlingen FRG) J S Crighton (Sunbury-on-Thames UK) S T Sparkes (Plymouth UK) R Stephens (Halifax Canada) J R Dean (Newcastle upon Tyne UK) J Stupar (Ljubljana Yugoslavra) R E Sturgeon (Ottawa Canada) "J M Cook (Keyworth UK) "M S Cresser (Aberdeen UKI "J B Dawson (Leeds UkI "L Ebdon (Plymouth UK) *J Egan (Cambridge UK) A Taylor (Gurldford UK) *A T Ellis (Oxford UM A P Thorne (London UK) "D J Halls (Glasgow UK) "D A Hickman (London UK) "A M Ure (Aberdeen UK) "S J Hill (Plymouth UK) S J Walton (Crawley UK) P Watkins (London UK) B Welz (Uberlingen FRG) J Williams (Eghan UK) J B Willis (Victorra Australia) J Fazakas (Bucharest Romania) G C Turk (Gaithersburg MD USA) J F Tyson (Amherst MA USA) K W Jackson (Albany NY USA) R Jowitt (Middlesbrough UK) K Kitagawa (Nagoya Japan) "D Littlejohn (Glasgow UK) "J Marshall (Middlesbrough UK) *Members of the ASU Executive Committee Editor JAAS Judith Egan The Royal Society of Chemistry Dr J M Harnly Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK Telex No 81 8293 Fax 0223 423623 Assistant Editors Brenda H ol I Ida y Editorial Secretary Monique Warner US Associate Editor JAAS US Department of Agriculture Beltsville Human Nutriton Research Center Beltsville MD 20705 USA Telephone 301 -344-2569 Telephone 0223 420066 BLDG 161 BARC-EAST Paula O'Riordan Sheryl Whitewood Advertisements Advertisement Department The Royal Society of Chemistry Burlington House Piccadilly London W1V OBN UK.Telephone 071-437 8656. Fax 071-437 8883 Information for Authors Full details of how to submit materials for publica- tion in JAAS are given in the Instructions to Authors in Issue 1 Separate copies are available on reauest The Journal of Analytical Atomic Spectrometry (JAAS) is an international journal for the publica- tion of original research papers communications and letters concerned with the development and analytical application of atomic spectrometric techniques The journal is published eight times a year including comprehensive reviews of specific topics of interest to practising atomic spectrosco- pists and incorporates the literature reviews which were previously published in Annual Reports on Analytical Atomic Spectroscopy (ARAAS) Manuscripts intended for publication must de- scribe original work related to atomic spectromet- ric analysis Papers on all aspects of the subject will be accepted including fundamental studies novel instrument developments and practical ana- lytical applications As well as AAS AES and AFS papers will be welcomed on atomic mass spectro- metry and X-ray fluorescencelemission spectro- metry Papers describing the measurement of molecular species where these relate to the char- acterization of sources norrnally used for the pro- duction of atoms or are concerned for example with indirect methods of analysis.will also be ac- ceptable for publication Papers describing the de- velopment and applications of hybrid techniques (e g GC-coupled AAS and HPLC-ICP) will be par- ticularly welcome Manuscripts on other subjects of direct interest to atomic spectroscopists. in- cluding sample preparation and dissolution and analyte pre-concentration procedures as well as the statistical interpretation and use of atomic spectrometric data will also be acceptable for pub- lication There is no page charge The following types of papers will be consid- ered Full papers describing original work Communications which must be on an urgent matter and be of obvious scientific importance Communications receive priority and are usually published within 2-3 months of receipt They are intended for brief descriptions of work that has progressed to a stage at which it is likely to be valuable to workers faced with similar problems Revlews which must be a critical evaluation of the existing state of knowledge on a particular facet of analytical atomic spectrometry Every paper (except Communications) will be submitted to at least two referees by whose advice the Editorial Board of JAAS will be guided as to its acceptance or rejection Papers that are accepted must not be published elsewhere except by permission Submission of a rnanu- script will be regarded as an undertaking that the same material is not being considered for publica- tion by another journal Manuscripts (three copies typed in double spacing) should be sent to Judith Egan.Editor. JAAS or Dr J M Harnly US Associate Editor. JAA S All queries relating to the presentation and sub- mission of papers and any correspondence re- garding accepted papers and proofs should be directed to the Editor or US Editor (addresses as above) Members of the JAAS Editorial Board (who may be contacted directly or via the Editorial Office) would welcome comments suggestions and advice on general policy matters concerning JAAS Fifty reprints are supplied free of charge Journal of Analytical Atomic Spectrometry (JAAS) (ISSN 0267-9477) is published eight times a year by The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF UK All orders accompanied with payment should be sent directly to The Royal Society of Chemistry Turpin Tractions Ltd Blackhorse Road Letchworth Herts SG6 1 HN UK.Tel +44 (0) 462 672555 Telex 825372 Turpin G. Fax +44 (0) 462 480947 Turpin Transactions Ltd is wholly owned by The Royal Society of Chemistry 1991 Annual subscription rate EC €309 00 USA $728 00 Rest of World f355 00 Customers should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank Air freight and mailing in the USA by Publications Expediting Inc 200 Meacham Avenue Elmont NY 11003 USA Postmaster send address changes to Journal of Analytical Atomic Spectrometry (JAASI Publications Expediting Inc 200 Meacham Avenue Elmont NY 11003 Second class postage paid at Jamaica NY 11431 All other despatches outside the UK by Bulk Airmail within Europe Accelerated Surface Post outside Europe PRINTED IN THE UK 0 The Royal Society of Chemistry 1991 All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photographic recording or otherwise without the prior permission of the publishers

ISSN:0267-9477    

DOI:10.1039/JA99106FX005

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JASPE2 6(2) 93-1 94 March 1991 Journal of Analytical Atomic Spectrometry CONTENTS NEWS AND VIEWS 93 98 101 Book Review-Anne P. Thorne 102 Conferences and Meetings 104 Papers in Future Issues Viewpoint-Analytical Atomic Spectroscopy Learning From Its Past-John 6. Dawson Conference Reports-Phil Riby Simon Sparkes PAPERS 105 109 115 119 123 129 133 139 145 151 155 FIFTH BIENNIAL NATIONAL ATOMIC SPECTROSCOPY SYMPOSIUM (BNASS) Temperature Programmed Static Secondary Ion Mass Spectrometric Study of Phosphate Chemical Modifiers in Electrothermal Atomizers-D Christian Hassell Vahid Majidi James A Holcombe Use of Partial Least Squares Modelling to Compensate for Spectral Interferences in Electrothermal Atomic Absorption Spectrometry With Continuum Source Background Correction. Part 1.Determination of Arsenic in Marine Sediments-Douglas C Baxter Wolfgang Frech lngemar Berglund Determination of Low Concentrations of Lithium in Biological Samples Using Electrothermal Atomic Absorption Spectrometry-Barry Sampson Determination of Ultra-trace Levels of Metal ions in Sea-water With On-line Pre-concentration and Electrothermal Atomic Absorption Spectrometry-V Porta 0 Abollino E Mentasti C Sarzanini Determination of Ammonium Acetate Extractable Molybdenum in Soil and Aqua Regia (Hydrochloric Acid and Nitric Acid 3+1) Soluble Molybdenum in Soil and Sewage Sludge by Electrothermal Atomic Absorption Spectrometry-William H Rowbottom Pre-concentration by Coprecipitation. Part 1. Rapid Method for the Determination of Ultra-trace Amounts of Germanium in Natural Waters by Hydride Generation-Atomic Emission Spectrometry-Ian D Brindle Mary E Brindle Xia-chun Le Hengwu Chen Elimination of Copper Interference by Continuous Flow Matrix Isolation in the Determination of Selenium by Flow Injection Hydride Generation Atomic Absorption Spectrometry-Stephen G Offley Nichola J Seare Julian F Tyson Helen A B Kibble Effect of Long-chain Surfactants on Drop Size Distribution Transport Efficiency and Sensitivity in Flame Atomic Absorption Spectrometry With Pneumatic Nebulization-Juan Mora Antonio Canals Vicente Hernandis Determination of Trace Elements in Solid Plastic Materials by Laser Ablation Inductively Coupled Plasma Mass Spectrometry-John Marshall Jeff Franks Ian Abell Chris Tye Determination of Arsenic in Samples With High Chloride Content by Inductively Coupled Plasma Mass Spectrometry-Simon Branch Les Ebdon Mick Ford Mike Foulkes Peter O'Neill Determination of Arsenic by Hydride Generation Inductively Coupled Plasma Mass Spectrometry Using a Tubular Membrane Gas-Liquid Separator-Simon Branch Warren T Corns Les Ebdon Steve Hill Peter O'Neill LOUG H BOROUG H UK 1 8t h-20t h JULY 1990 'i 59 165 169 173 179 191 193 Correction of Mineral Acid Interferences in Inductively Coupled Plasma Optical Emission Spectrometry on Copper and Manganese Using Internal Standardization-Louise M Garden John Marshall David Lkttlejohn Matrix Interferences Observed With a Thermospray Sample Introduction System for Inductively Coupled Plasma Atomic Emission Spectrometry-Margaretha T C de Loos-Vollebregt Runzhong Peng Johan J Tiggelman Direct Determination of Chromium in Estuarine and Coastal Waters by Electrothermal Atomic Absorption Spectrometry-S C Apte S D W Comber M J Gardner A M Gunn Determination of Manganese at Trace Levels in Water by Laser-enhanced Ionization spectrometry After Solvent Extraction-Akira Miyazakt Hiroaki Tao Contribution of System Components to Dispersion in the Analysis of Micro-volume Samples by Flow Injection Flame Atomic Absorption Spectrometry-Zhaolun Fang Bernhard Welz Michael Sperling LElTERS Letter by Boris L'vov and Walter Slavin and Reply by Gary M.Hieftje CUMULATIVE AUTHOR INDEXSTANDARD 7YPE S. 81. J. JUNIPER & Co. 7 Potter Street Harlow Essex. Tel 0279 22456 ~ ~- Circle 001 for further information The Royal Society of Chemistry - The First 150 Years By David H.Whiffen This interesting new book provides a historical review from 1841 to 1991 of the Royal Society of Chemistry and the Societies from which it was formed. Contents Historical Prologue. 1941-51 by D. H. Hey. The Chemical Society. The Royal Society of Chemistry. Premises. Publications. The Nottingham Centre. Awards and Meetings. Hardcover Approximately 270 pages Price f 14.95 RSC Members Price f 10.00 plus postage ISBN 0 85186 294 2 Due Early 1991 RIC Matters and Their Continuation in RSC. Finance. Epilogue. Appendix. Bibliography of Other Historical Volumes. Subject Index. Name Index. To Order Please write to the Royal Society of Chemistry Turpin Transactions Ltd Blackhorse Road Letchworth Herts SG6 1 HN UK or telephone (0462) 672555 quoting your credit card details. We can now accept AccessNisa/MasterCard/Eurocard. Turpin Transactions Ltd distributors is wholly owned by the Royal Society of Chemistry. For information on other books and journals please write to Royal Society of Chemistry Sales and Promotion Department Thomas Graham House Science Park Milton Road RSC Members should obtain members prices and order from The Membership Affairs Department at the Cambridge address above. ROYAL SOCIETY OF CHEMISTRY 6 Cambridge CB4 4WF UK. Information Services Circle 003 for further information

ISSN:0267-9477    

DOI:10.1039/JA99106BX007

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

93 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 Viewpoint Analytical Atomic Spectroscopy Learning From its Past* John B. Dawson* Department of Instrumentation and Analytical Science University of Manchester Institute of Science and Technology P. 0. Box 88 Manchester M60 I QD UK Progress in analytical science is driven by environmental need made possible by technological development and is based on progress in fundamental scientific un- derstanding which it in turn promotes by generating more accurate information. It is more ‘directed’ than the progress in basic science where chance observations and discoveries play a major part and ser- endipity is of the essence. Selected aspects of the development of analytical atomic spectroscopy with a view to iden- tifying its limitations and potential for further development will be discussed in this article.Methods of chemical analysis based on physical principles have in the past fre- quently had a long gestation period between the discovery of the physical phenomenon and the analytical applica- tion therefore if the present situation is to be understood some appreciation of the historical perspective is required. From such knowledge the reasons for the emergence of a particular technique at a given moment the timeliness can be identified. By comparing a number of related analytical procedures it might be possible to identify the fundamental factors that limit their performance and thereby either devise techniques to cir- cumvent the problems or abandon a hopeless pursuit! Arising from the author’s long association with the tech- nique particular reference will be made from time to time to developments in atomic absorption spectrometry (AAS).These examples will be presented with a view to determining how in specific in- stances accumulated knowledge can be applied to resolve current questions. While it might be possible to predict de- velopments in existing methods and such an exercise will be attempted later it is impossible to predict what new method will emerge in 10-20 years time after all who in 1940 could have pre- dicted the emergence of atomic absorp- tion spectrometry and X-ray fluorescence as major analytical tools in the mid- 1950s? * Dr. Dawson presented this review on the emergence of atomic spectroscopy as an Invited Lecture at the 5th Biennial National Atomic Spectroscopy Symposium Loughborough UK 18th-20th July 1990.Historical Perspective The development of physical methods of analysis has taken place over many centu- ries and like chemistry has been both helped and hindered by the alchemist and skilled artisan who through the ages has sought to develop his craft while conceal- ing his trade secrets behind a screen of ‘magic’. More complete accounts of the history of analytical atomic spectroscopy can be found elsewhere.1-5 For the purpose of this discourse only a limited selection of milestones in that history need be considered with a view to estab- lishing general patterns rather than a comprehensive record. There are three stages in the emergence of a new analytical method firstly the discovery of an effect secondly the in- vestigation of the effect leading to an ex- planation and finally exploitation by the analyst.Table 1 presents a summary of the history of several branches of analyti- cal atomic spectroscopy resolved into those three phases of development. Though individuals are credited with par- ticular achievements it is the date of the achievement that is probably most significant as the achievement itself might well have been presaged by the work of others and thus was an inevitable consequence of the knowledge techno- logy needs and culture of the society in which the individual lived. Conversely if all those four conditions are not fulfilled the development does not take place. These criteria for progress are graphically illustrated by the 2000 year long gestation periods of spectacles and of the spectro- scope compared with 150 years for AAS.In these examples the scientific and tech- nical expertise was accumulating during the gestation period. For spectacles the delay in exploiting a long established technology to provide a benefit to many people is somewhat surprising. The reasons for the delay can only be sur- mised but could include inadequate un- dertstanding of optical systems and cultural factors. The development of the spectroscope,6 however is an example of the positive interaction between scientific observation and technical development for though the technical skill required to construct it existed from at least 500 BC the instrument was not built until there was a demand for an improvement in the quality of the optical observations made using prisms.By facilitating precise measurements of spectra the spectro- scope promoted research into the new fields of spectrochemistry and atomic structure. The fundamental knowledge of the nature of the atom and the origin of atomic spectra so acquired made possible the development of the analytical atomic spectrometric techniques of today. On the other hand the emergence of AAS as an analytical tool was delayed by technical limitations and a lack of demand prior to the late 1940s. The independent inventor and entrepreneur might determine the precise moment when exploitation of a physical principle occurs but the general success will depend upon the timeliness. For an idea whose time has come dis- covery and exploitation are virtually assured while the converse is also almost certainly true. In general it appears that the more recent the scientific discovery the shorter the gestation period.This effect is illustrated by the interval between discovery and the analytical ex- ploitation of X-rays in X-ray fluorescence analysis (1 895-1955) artificial radioac- tivity in neutron activation analysis (1934-1955) and the Mossbauer effect for studies of iron in haemoglobin (1957- 1 960). In the early applications of analytical atomic spectroscopy visual detection must have played an essential part e.g. the characteristic colour of a flame is readily recognized. It is therefore reason- able to assume that from earliest times (3000 BC) the colour of the ‘fumes’ (flames) as described by Agricola in 1550 has been used to control the smelt- ing of ores in a primitive application of atomic emission spectroscopy (AES).In the early nineteenth century Wollaston (1802) saw the dark lines in the sun’s spectrum and Talbot (1826) and Wheat- stone ( 1833 respectively visually ob- served flame and spark spectra as being characteristic of specific substances. The next step quantitative analysis was difficult to make using the eye as the measure of light intensities. It also re- quired the development of a sound theo- retical basis of spectrum analysis by Kirchhoff and Bunsen (1860) the photo- graphic recording of spectra (Herschel,94 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 ~ ~~ Table 1 mation from references 1-5 Emergence of atomic spectroscopy as an established analytical technique.Based on infor- Technique Discovery Explanat ion Exploitation Lenses mirrors Ancient artefacts Euclid 300 BC Spectacles prisms 10oO BC Ptolemy 100 AD Amarti 1285 Snell 1621 AD Spectra Colours of rainbow/ Nature of white light Spectroscope prism Seneca 40 AD Newton 1672 Sims 1830 Emission Flame Coloured ‘fumes’ Agricola 1550 Melvill 1752 Salted flames Flame photometer Lundegardh 1930 Electrical Arc discharge Atomic origin of Quantitative analysis Davy 1802 emission/absorption Lockyer 1873 Spark spectra lines Internal standard Wheatstone 1835 Gerlach 1925 Electrodeless K i rc h ho ff/ ICP discharges Bunsen 1860 Greenfield et al. 1964 Babat 1947 I I Absorption Dark lines in sun’s spectrum Wollaston 1802 - Flame atomic absorption spectrometry Walsh 1953 Fluorescence Sodium in Molecular Flame atomic vapour cell fluorescence fluorescence Wood 1905 Stokes 1852 Winefordner 1964 1840) and before it could be fully ex- ploited the development of standardiza- tion procedures which culminated in the enunciation of the internal standard prin- ciple by Gerlach (1925).The replacement of visual detection with photoelectric devices for the measurement of spectral line intensities led to the manufacture in the late 1930s of direct reading spec- trometers using arcs sparks or flames for atomization and excitation and thus rapid and accurate quantitative analysis became possible a century after the pioneering work of Talbot and Wheatstone. This achievement was also a direct response to the industrial need for improved quality control and increasing recognition of the importance of minor and trace elements in many fields.Thus the coincidence of a sound scientific basis with technical de- velopment and ‘customer’ demand trig- gered the wider exploitation of AES that we practise today. The historical examples presented above serve to illustrate the vital roles of timeliness and fundamental understand- ing in the emergence of a new analytical technique. A more detailed examination of factors contributing to the timeliness of the exploitation of atomic absorption and atomic fluorescence spectrometry (AFS) will be presented in the next section and later an attempt will be made to identify some of the fundamental factors that limit the performance of analytical atomic spectrometric techniques.Tim el i n ess One of the most interesting examples of timeliness in recent developments in ana- lytical science is found in the period 1945-1965. At the beginning spectro- chemical analysis was a limited activity largely in the hands of the professional spectroscopist commonly a physicist though some indication of future trends could be discerned in the increasing use of flame photometry and other forms of instrumental analysis by the analytical chemist. By the end of that period AAS was established in the analytical labora- tory the merits of the inductively coupled plasma (ICP) as an emission source had been demonstrated and the potential of AFS as an analytical technique examined. The varying fortunes of these three tech- niques (i.e.AAS ICP-AES and AFS) over the years clearly demonstrate the im- portance of timeliness and might serve to identify the key factors that determine the rate of progress in the exploitation of a technique. The phenomena of atomic emission absorption and fluorescence were recog- nized and understood for many years but only emission was utilized in the analyti- cal laboratory. Earlier in this article it was proposed that lack of demand and technical limitation delayed the analytical exploitation of atomic absorption. The factors favouring the emergence of AAS as a major analytical development of the late 1950s will now be considered. They fall into two categories first general ex- ternal factors that could have applied equally to other techniques e.,q.atomic fluorescence and second the specific ad- vantages of atomic absorption. By the early 1950s all the scientific and technical knowledge and equipment necessary to exploit atomic absorption existed. In particular it was an extension of two actively developing fields absorp- tion spectrometry and flame photometry. One of the successes of those fields was to demonstrate the importance of minor and trace elements in a wide range of cir- cumstances ranging from metallurgy to clinical chemistry. This success in turn created an increased demand for such de- terminations which AAS was well suited to meet all that was lacking was the in- ventor! In 1953 Australian patent No. 23141/1953 was granted to the Common- wealth Scientific and Industrial Research Organization (CSIRO) for the application of atomic absorption to chemical analysis with A.Walsh as the inventor; his definitive paper7 on the subject was pub- lished in 1955. The environment in which the initial development of AAS took place played an important part in its dis- semination. As a government funded re- search organization it was part of the remit of CSIRO to support Australian in- dustry therefore the manufacture and use of atomic absorption equipment was ac- tively promoted both in Australia particu- larly in the mining industry and world- wide. It is doubtful whether any previous analytical technique has enjoyed such a positive launch even so the growth until 1963 was relatively slow.8 For a new ana- lytical method to be successful it should have demonstrable advantages over its predecessors.Many of the advantages attributable to AAS are also requisite for any improved analytical method. The technique combines great sensitivity with specificity by virtue of being based on resonant transitions of a large population of ground state atoms. It is applicable to most elements and samples and in most laboratories and can provide rapid analy- sis with simple equipment. As the tech- nique is particularly suited to processing solutions the necessary sample prepara- tion procedures were established labora- tory practice long before AAS came along. However probably the single most important technical factor contributing di- rectly to its success was the choice of the hollow cathode lamp as the light source their manufacture as sealed lamps in place of the usually continually pumped sources and their operation in an a.c.mode which reduced the effect of back- ground emission. Following the above review of the cir- cumstances leading to the success of AAS it is instructive to examine the for- tunes of another technique AFS,’ that emerged almost ten years later. Many of the factors favouring AAS also apply to AFS and were present in the early 1950s. Atomic fluorescence is however more difficult to generate and detect than either emission or absorption as is illustrated by the fact that it was not observed experi- mentally by Wood (1905) until almost a century after the other two even though the effect had been expected and sought for many years.Futher its exploitation asJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 1 VOL. 6 95 an analytical method did not occur as a natural extension of an existing established method of the 1950s e.g. fluorimetry but rather it needed the estab- lishment of AAS to draw attention to the possibilities of AFS. The analytical ad- vantages of atomic fluorescence over ab- sorption include the opportunity to use non-resonant atomic transitions the feasi- bility of multi-element analysis and under favourable circumstances lower detection limits. However these advan- tages have not been sufficient to prompt many researchers to attempt to overcome the technical limitations of the method which include the absence of a univer- sally applicable light source matrix inter- ference by scattering of the exciting radiation and by the quenching of fluorescence and the absence of generally available inexpensive commercial instru- mentation.Furthermore ICP-AES which enjoys many of the advantages attributed above to AFS plus the additional one of a high temperature for sample dissociation was first reported at about the same time (1964) and thus diluted the impact of AFS on the analytical community. Another consideration militating against expan- sion in the use of AFS is the fact that as the light source and sample atomizer are key components of both atomic absorp- tion and fluorescence systems it is to be expected that improvements designed to improve performance for one technique will also benefit the other. Hence it is un- likely that the early lead established by AAS will ever be overtaken by AFS as a general purpose analytical method.The interaction of AAS with the ex- ploitation of the ICP is an interesting one. With the development of the atmospheric pressure electrodeless discharge culmi- nating with Reed's publication on the ICP in 1961,IO the stage was set for further de- velopments in AES. This occurred almost instantly and in 1964 the first paper by Greenfield et al." appeared but it was a further ten years before the number of active laboratories had reached double figures.'? The delay in the widespread ac- ceptance of the technique must be due in part at least to the preoccupation of the spectrochemical community with the ex- ploitation of AAS. However the success of AAS in determining elements and in educating the analytical chemist in the ways of atomic spectrometry along with the recognition that AAS can suffer from chemical interferences that it is primarily a single element technique and that the instruments were becoming increasingly complex and expensive all served to create a climate in which ICP spectro- metry became an attractive proposition.According to Fassel,I2 between 1973 and 1978 'the number of laboratories engaged in analytical investigations and routine applications increased from 10 to about 200 and the number of commercial suppliers of instruments from none to at least nine'. The current usage of the ICP is now widespread and it in turn has spawned a new technique inductively coupled plasma mass spectrometry (ICP- MS).I3 The nature of developments in analyti- cal atomic spectrometry is very much a consequence of the timeliness of ideas and of their interactions. Mutations competi- tive pressures and the environment all play their part in the evolution of an analytical technique just as in the biological world. Fundamental Limitations The fundamental limitations of an analyt- ical method are frequently manifested in the sensitivity and baseline stability.Both these factors are included when the detec- tion limit of a method is calculated. This composite parameter is one of the most useful for comparing the performance of one analytical method with that of another and in an attempt to 'learn from the past' can also be used as a basis for measuring progress and for identifying 'dead ends' in analytical development.Relative Detection Limits in Emission and Absorption Atomic Spectrometry AlkemadeI4 examined theoretically the relationship between sensitivity in AES and AAS at concentration levels ap- proaching the detection limit. He showed that based on the Kirchhoff law the ratio of the amount of radiation absorbed to that emitted by an atomic vapour when ir- radiated by a sharp line source was pro- portional to the ratio of the spectral radiance of a black body at the effective temperature of the radiation source to that of a body at the temperature of the atomic vapour. Based on this premise the theore- tical wavelength dependence of the ratio of the detection limits in absorption to those in emission can be deduced.15 The limiting background noise was attributed to the shot noise of the light source ato- mizing flame and the dark current of the photomultiplier.The theoretical curve in Fig. 1 was calculated on the assumptions that the effective temperature of the illu- minating source for atomic absorption was 6OOO K and that of the atomic vapour 2500 K. The alignment of the experimen- tal data points and the theoretical curve was achieved by the use of a logarithmic scale for the detection limit ratio. Vertical transposition of the theoretical curve to coincide with the data points was equiva- lent to the use of a constant multiplying factor originating in atomic constants the geometry of the apparatus and detector amplification. The general agreement between the theoretical curve and experi- mental results justifies the conclusion that Alkemade's proposed fundamental rela- tionship between emission and absorption signals is valid.Thus at wavelengths greater than 400 nm when an air- acetylene flame is used detection limits can be lower in emission than in absorp- tion. However for AES to achieve detec- tion limits comparable to AAS over the full spectral range the excitation temper- ature of the atomic vapour must be at least 6000 K. When such temperatures are present as in plasmas and provided the spectrometer has adequate resolution atomic emission is the preferred method. Thus from a knowledge of the funda- mental limitations decisions affecting practical analysis can be made. Relative Sensitivities in Flame and Electrothermal Atomic Absorption Spectrometry As absolute sensitivity in analytical atomic spectroscopy is proportional to the number of atoms contributing to the 200 300 400 500 600 700 8oo Wavelengthlnm Fig.1 Theoretical and experimental wavelength dependence of the ratios of the detection limits ob- tained by atomic absorption spectrometry to those obtained by flame atomic emission spectrometry. The theoretical curve is shown as a full line and the experimental points as individual elements with standard error bars96 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 analytical signal at a given instant the generation of the densest possible atomic vapour up to the point at which self- absorption occurs is generally desirable. Transient response systems are frequently reported in order to provide greater ana- lytical sensitivity.The reason for this im- provement can be clearly demonstrated by comparison of estimates of the instan- taneous amount of analyte in the asborp- tion path of an atomizing flame and a graphite tube furnace. If it is assumed that all the atomized sample passes through the observation zone of the flame then the instantaneous absorption signal A is given by wheref= sample flow-rate to the nebulizer approximately 5 ml min-1; e = efficiency of sample transport and atomization about 10%; a = width and height of absorption zone about 0.5 cm; u = flame speed approximately 200 cm s-I; c’ = analyte concentration in g ml-1; K = atomic ab- sorption coefficient per g of analyte. For the furnace the maximum signal A2 is obtained when all the analyte atoms are contained in the furnace at the same instant and can be calcualted from where 1’ = sample volume 20 p1; and Y = internal radius of the furnace 0.25 cm.The theoretical ratio R of the peak ab- sorbance signal of a furnace to the contin- uous signal from a flame atomizer for the same solution is given by 0.1 Kc = 1200 (3) A2 A1 8 . 3 x IO-’Kc R = - = Table 2 presents experimental values of the characteristic concentrations for 33 elements taken from published reports. Over the period 1970-1983 there was no significant changes in the sensitivities re- ported for flame AAS. On the other hand sensitivities in electrothermal AAS in- creased on average 5-fold between 1976 [Column (B)] and 1984 [Column ( C ) ] . This improvement was a result of the use of faster response electronics rapid furnace heating gas stop during atomiza- tion the L’vov platform and chemical modifiers.The 1984 data were used for calculating the sensitivity ratios. Seventy- five per cent. of the ratios are evenly spread between values of 100 and 600 with a mean of 360 the remainder are widely spread between 960 and 2400. The predicted ratio of equation (3) is Table 2 Comparison of sensitivities of flame and electrothermal atomic absorption spectrometry. Sources of data (A) Fuller,1h Welz” and Varian Techtron;lH (B) Fuller;I6 and (C) Grosser,IY SIavin et u/.~‘’.~’ and Sperling.” Where literature values were expressed as A s peak absorbance was assumed to have the same numerical value Element Ag Al As AU Ba Be Bi Ca Cd c o Cr c u Fe Li Mn Mo Ni Pb Pd Pt Rb Sb Se Si Sn Sr Te Ti T1 V Zn Hg Mi? Excitation wavelength 328.I 309.3 193.7 242.8 553.6 234.9 223.1 422.7 228.8 240.7 357.9 324.7 248.3 253.7 670.8 285.2 279.5 3 13.3 232.0 283.3 247.6 265.9 780.0 217.6 196.0 25 1.6 286.4 460.7 214.3 365.3 276.8 3 18.4 2 13.7 Flame/ mg 1-1 per 0.0044 A (A) 0.033 0.88 0.77 0.22 0.33 0.023 0.36 0.047 0.020 0.10 0.065 0.049 0.065 1.6 0.026 0.0044 0.036 0.54 0.065 0.29 0.15 1.3 0.043 0.50 0.58 I .so 0.90 0.09 I 0.36 I .9 0.3 1 1.3 0.0 12 ETA/ pg I-’ per 0.0044 A* (B) 0.25 2.5 1.25 I .o 7.5 0.10 2.0 0.20 0.05 2.0 I .o 1 .5 1.25 10.0 0.50 0.0 1 0. I0 1 .o 5 .o 1 .o 1 .o 25.0 I .o ! .O 10.0 2.5 5 .o I .o 5.0 25.0 2.5 10.0 0.05 (C) 0.080 0.63 0.80 0.60 0.33 0.04 1 .o 0.040 0.043 0.38 0.18 0.34 0.25 9.0 0.070 0.0 I6 0.1 1 0.45 0.64 0.54 1.15 5.3 0.12 1.9 I .4 2.6 0.98 0.07 0.75 3.7 0.73 2.2 0.005 Improvement ratio (ETA flame) (A:C) 410 1400 960 370 lo00 580 360 I200 470 260 360 I40 260 180 370 280 330 1200 100 540 I30 250 360 260 410 580 920 1300 480 5 10 430 5 90 2400 *Derived from estimated peak absorbance and an assumed sample volume of 20 PI.1200. A major factor in the discrepancy between theory and practice is the as- sumption in the theoretical model that in the furnace all the sample atoms are in the absorption path simultaneously. This cannot be so as atoms begin to leave the furnace with a characteristic time con- stant of the order of 0.1 s as soon as atomization takes place. It follows from the simple model of the electrothermal atomization process developed by Fuller,Ih that even if the rate constant of free atom formation is twice that of atom loss the maximum number of sample atoms in the vapour phase in the furnace at any instant will be only half of the maximum assumed in equation (2).If the rate constant of generation is half that of the loss process the peak height is then but a quarter of the theoretical maximum. Thus the effect of atom loss from the furnace could account for much of the difference between predicted and ob- served sensitivity ratios. The higher values of some of the ratios e.,?. Al As Ba Ca Mo Sn and Sr might be more a result of inefficient atom production in the flame than efficient electrothermal atomization! The ratio for Zn appears to be anomalously high for which there is no obvious explanation other than that it is the element with the highest sensitivity determined by furnace AAS.’(’ The above results clearly demonstrate the gain in sensitivity resulting from car- rying out the analytical measurement on a transient confined atomic vapour.Other systems showing varying degrees of improved sensitivity and incorporating some or all of the above principles include the Delves’ cup furnace non- thermal atomic emission spectrometry glow discharge lamps slotted tube atom retarder discrete nebulization and abla- tion techniques. On the basis of the simple models and experience to date it appears unlikely that substantial improve- ment in the production of analytical atomic vapours can be achieved. However for individual elements there appears to be improvement factors of up to 3 or 4 available by the optimization of either the flame or furnace operating con- ditions.If this view is correct then orders of magnitude improvements in an- alytical performance will have to be sought from improved detection of the analytical signal or the generation of aJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991. VOL. 6 97 different type of analytical signal e.g. ions rather than photons. Signal Processing The noise or instability of a signal deter- mines the precision of an analytical meas- urement and the smallest amount of the analyte that can be detected with a specified probability. At analyte levels above the detection limit (approximately lox) the reproducibility of the measure- ment is determined by fluctuations in the production of the atomic vapour in the excitation of emission either in the atomic vapour or in the radiation source for ab- sorption and in the radiation detection and signal processing electronics.At the detection limit the most impor- tant factor is the stability of the back- ground (baseline) signal. Signal noise is of two kinds ‘white’ (random or stochas- tic) noise when all frequencies are equally present in the noise power spec- trum and ‘coloured’ (flicker or structured) noise when some frequencies are present at a greater power level than others. Some improvement in analytical performance can be achieved by signal processing de- signed to reduce the effects of noise. Signal modulation is widely used to dis- criminate against the mean level of the background and by means of a suitable integration time to reduce the effect of high frequency noise.It is commonly acheived by ‘chopping’ the optical beam. Modulation of the atom vapour produc- tion is rare. However pulse atomization can be exploited as a signal modulation technique by matching the response of the detection system to the temporal profile of the atomization peak. It has been reported2j that by integrating the output signal of the instrument either as a linear running mean or as a time constant with a sampling interval equal to approxi- mately one half of the full width of the signal peak at half the maximum value the precision and detection limits could be improved by factors of 2-3. Correla- tion with a signal processing function identical to the atomization signal peak did not lead to detectably better perfor- mance than the optimized linear running mean.When the noise on the analytical signal is not random and when one component of the analytical system is identified as the major source of analytical imprecision modification of the instrument or proce- dure can be used to reduce the standard de- viation of the results. The introduction of the internal standard principle by Gerlach in 1925 reduced the effects of variability of atomization and excitation in AES. In the early days of AAS a two-channel instru- ment described by Menzies in I958,’-‘ was designed to overcome the effect of the in- stability of the hollow cathode lamps in use at that time. Both these techniques for reducing the effects of system instability employed pairs of spectral lines conse- quently both are limited by the differences in behaviour of the lines when excitation conditions in the source change.Other methods of overcoming the effects of system instability depend on time sharing the signal e.,?. double-beam AAS. In these circumstances noise reduction can be achieved only for changes that occur more slowly than the modulation frequen- cy. In all instances the added complexity of the instrumentation inevitably makes its own contribution to the signal noise. It appears therefore that in the light of general experience to date further attempts to reduce system noise are unlikely to lead to the general lowering of detection limits in conventional emission and absorption analysis.However there may be special circumstances where it is possible to gen- erate highly correlated reference and ana- lytical signals. For example it may be feasible to utilize the properties of polar- ized light and Zeeman effect in the atomic vapour to produce a reference signal corre- lated with the analytical signal in wave- length time and space. Such an approach could be developed based on atomic magneto-optical rotation (AMOR). The theoretical and experimental basis for this technique is established’5 and therefore theoretical predictions on the performance of the system are possible nevertheless it is only by carrying out the experiment that the true potential and limitations of the concept will be revealed. Over the years many studies of noise in analytical atomic spectroscopy have been carried out and though there is now a general understanding of the origin and effect of noise on analytical systems that understanding has not led to substantially improved performance.This somewhat disappointing conclusion stems from the predominantly random nature of the noise in the analytical system whose effect can only be overcome by repeated measure- ment and/or increasing the observation time. Prospects for Future Development in Analytical Atomic Spectroscopy Analytical atomic spectroscopy has a long and distinguished lineage going back several millenia. From history it is clear that the timeliness of innovation is all im- portant and requires the confluence of scienti tic knowledge technical ski 11 env i- ronmental demand and entrepreneurial initiative. Once established knowledge of the fundamental characteristics of a tech- nique is sought so that the performance can be optimized and limitations defined. New techniques emerge either by the application of a previously unexploited physical principle or by extension or hy- bridization of established procedures. It is impossible to predict when the former will occur but for it to occur at all it requires that the worker in analytical science should have a profound knowledge of fun- damental physics and chemistry.The extension of existing practice is more predictable as is illustrated by Alke- made’s prophesy of ‘flame ionic mass spectroscopy’ in 1973j and its realization albeit in a different form by Gray,I3 as ICP-MS in 1978.In this instance by changing the detection system from one for photons to one for ions orders of magnitude improvement in detection limit were achieved. The combination of chromatography with spectroscopy to meet the demand for speciation was in- evitable as was the incorporation of auto- mation and computers into analytical instruments to promote rapid accurate analysis and reduce the dependence on the operator. The potential applications of both these developments is far from fully exploited. Other developments equally predictable but likely to be less successful will be the continued elaboration of ana- lytical systems which are of little rele- vance to the general analytical laboratory. This is because they are too complex and expensive offer little advance over what can be acheived by a combination of stan- dard instrumentation with appropriate preparative chemistry and not infrequent- ly have difficulty in processing real samples! Also there will be continued efforts to exploit fundamentally sound and attractive ideas that are technically unlikely to be realizable in an acceptable manner e.g.simultaneous multi-element atomic absorption. For the more distant future one of the most exciting prospects must be the pos- sibility of using solid-state tunable lasers as high intensity light sources over a wide spectral range.2h How soon will such sources be available? What will they cost? How stable will they be? Can they be used in such a way that the limiting factor in the analysis is the behaviour of the atomic vapour alone independent of the generating process? As the answers to these questions emerge over the next 5-1 0 years perhaps some new technique will also appear and be competing for a place in the analytical laboratory. Who can say? Whatever the techniques of the future the analytical specification for improved methods will include accuracies of the order of 0.1% detection limits in the sub-ng I-’ or fg mass range generation of information on the state or species of the analyte element and rapid automatic op- eration. The achievement of these goals requires an environment in which analyti- cal scientists can deploy some time and resource away from the regular demands of a service load and engage in research and development of existing and new methods. Today however the very success of the present analytical atomic98 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL.6 spectroscopic techniques might for a time inhibit the search for the new methods of tomorrow because they cur- rently generally fulfil and indeed in many instances are ahead of the demands placed on them. However if historical precedent can be relied upon when the need for a new method arises then Micawber-like ‘something will turn up’ and though it is unrecognized today it is likely to be based on an already predicted or observed phenome- non! The author thanks Dr. W. J. Price for helpful comments on this manuscript. References EnLyclopedia of Spectroscopy eds. Weise E. K. and Clark G. L. Reinhold. New York 1960 pp. 188-199. Hermann R. and Alkemade C.Th. J.. Flame Photometrv. Wilev-Interscience. New 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 York 1963. Alkemade C. Th. J. Proc. Soc. Anal. Chem. 1973,10 130. Thorburn Bums D. Proc. Anal. Dil.. Chem. Soc. 1975 12 155. West T. S. Proc.. Anal. Div. Chem. SOL.. 1977. 14 177. Thorburn Bums D. J. Aiiai. At. Spectrom. 1988,3,285. Walsh A. Spectrochim. Acta. 1955 7 108. Walsh A. Appl. Opt. 1968,7 1259. Winefordner J. D. and Vickers T. J. Anal. Chem. 1964,36 161. Reed. T. B. J . Appl. Phjs. 1961,32,821. Greenfield S . Jones I. Ll. and Berry C. T. Analyst 1964,89,7 13. Fassel V. A. Science 1978,202 183. Gray A. L. J. Anal. At. Spectrom. 1986 1 403. Alkemade C. Th. J. Appl. Opt. 1968 7 1261. Dawson J. B. Proceedings of the XVI Col- loquium Spectroscopicurn Internationale Heidelberg October 4th-9th. 1971 I Adam Hilger London 197 1 pp. 347-35 1 . Fuller C. W. Electrothermal Atomization for Atomic Absorption Spectrometry Chemi- 17 18 19 20 21 22 23 24 25 26 cal Society London 1977. Welz B. Atomic Absorption Spectrometry 2nd edn. VCH Weinheim 1985. Varian Techtron Hollonr Cathode Lamp Data Varian Zug 1970. Techniques in Graphite Furnace Atomic Ab- sorption Spec.trophotometr:v ed. Grosser Z. Perkin Elmer Ridgefield 1985. Slavin W. Carnrick G. R. Manning D. C. and Pruszkowska E. At. Spectrosc. 1983 4 69. Slavin W. and Camrick G. R.. Spectra- chim. Acta Part B 1984,39,27 I . Sperling K. R. Spectrochim. Acta Part B 1984,39,37 1 . Dawson J. B. Duffield R. J. King P. R. Hajizadeh-Saffar M. and Fisher G. W. Specwochim. Acta. Part B . 1988. 43 1133. Menzies A. C. Actas Congi,. XV Int. Quim. Para ApI.. Lisbon. 1958,2,2. Stephens R. J. Anal. At. Spemom. 1988 3 227. Hergenroeder R. and Niemax K. TrAC. Trends in Anal. Chem. (Pet-s. Ed.) 1989 8 333.

ISSN:0267-9477    

DOI:10.1039/JA9910600093

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

98 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 Conference Reports Fifth Biennial National Atomic Spectroscopy Symposium (BNASS) July 18thD20th 1990 Loughborough UK Do you remember attending or hearing about the Fourth BNASS meeting at York in 1988? Well just when you thought it was safe to go back to an analytical atomic spectroscopy meeting-BNASS 5-the Loughborough meeting! After the traditional welcome to the delegates in the opening ceremony the proceedings gained pace with the first plenary lecture given by Professor Bonner Denton (University of Arizona). Entitled ‘Present applications and future trends in high performance charge transfer device detectors’ the presentation dealt with ap- plications of solid state detector arrays in different branches of both atomic emis- sion and fluorescence spectrometry.Of particular interest were a device for meas- urements in the vacuum ultraviolet region of the spectrum and a device for measure- ments in the X-ray region as a possible replacement for the traditional Si(Li) and Ge(Li) detectors. Those of us who have witnessed slide-changer burn out at previ- ous papers presented by Bonner Denton were shocked to see only two carousels of slides used-he was obviously suffering from jet lag! Following the plenary lecture the Sym- posium was split into two streams for the invited and contributed papers. This lead to some difficult decisions having to be taken and also made it hard as the con- ference report writer to cover all the presentations. In the first invited lectures Dr. R.G. Brereton (University of Bristol) presented a paper entitled ‘The chemo- metric approach to optimization and in- terpretation in atomic spectroscopy’ which dealt with the fundamental aspects of chemometrics while Dr. Trevor Delves (Southampton General Hospital) discussed ‘Clinical and environmental ap- plications of atomic spectroscopy’. This paper included a look at Al Pt and Pb de- termination and also an interesting section on source identification of Pb poi- soning by ICP-MS. A break for refresh- ment ensued and before the next session took place a game of musical chairman occured. The result of this was the unex- pected arrival of Professor Les Ebdon (Polytechnic South West Plymouth) as Chairman in stream B (unexpected for both the delegates and Professor Ebdon). However his arrival was much appreciat- ed by the fashion conscious in the audi- ence as he demonstrated his latest chairmans ensemble including an African shirt in a subtle shade of orange.The re- mainder of the session saw contributed lectures including Dr. I. B. Brenner’s (Jobin-Yvon Lonaumeau France) paper discussing the difficulties of internal refe- rence selection in various solid sample in- troduction techniques into ICP-AES and glow discharges. Dr. John Marshall (ICI Wilton Materials Research Centre Mid- dlesbrough) described the application of laser ablation ICP-MS to the analysis of plastics and P. S. Goodall (Polytechnic South West) used molecular gases to modify ICPs for slurry analysis of refrac- tory materials. Wednesday’s scientific session was completed with a drink and a chance to view the 25 posters covering a wide variety of topics being presented.The relaxed atmosphere proved to be condu- cive to discussion not only about the posters but research in general. In an attempt to show some of the American delegates the more traditional side of the UK and to take advantage of Loughborough’s excel lent sports faci 1 i- ties an impromptu football (or soccer de- pending on your country of origin) game was organized. Although not well attend- Kirkbright Bursary recipients. Chris Hassell ( L ) and Gary MoitltoriJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 99 A group of delegates with Harp Minhas (centre) obviously enjoying the meeting ed because of the unusual temperatures and/or the attraction of the bar represen- tatives from the research students post- docs academic staff and exhibitors were present.Although the game generated a friendly atmosphere it soon became ap- parent why most of the players had become chemists and not professional footballers. After the physical exertions of the game came the introduction to that other British tradition-warm beer. Thursday’s lectures began with the arrival of a suit clad Professor Les Ebdon to deliver a plenary lecture entitled ‘Plasmas go green the use of plasmas to solve environmental problems’. The lecture reflected on the current interest in environmental analysis and the applica- tion of plasma based spectroscopic tech- niques for trace metal determinations in this area. Of course a lecture by Profes- sor Ebdon would not be complete without the mention of sample introduction by slurry nebulization hydride generation and speciation.After the split into the concurrent streams the first two invited lectures of the day were presented. Professor Jean- Michel Mermet (Universiti Claude Bernard Lyon) considered noise and drift in a paper entitled ‘Internal standard in inductively coupled plasma spectrochem- istry do we need it?’ The long-term sta- bility with respect to several instrumental parameters and their effect on internal standard selection were discussed. The second invited lecture featured Dr. Andy Ellis (Oxford Instruments Oxford) with an informative lecture on ‘Instrumental and calculation methods for improving accuracy and precision in EDXRF spectrometry’ which dealt with the im- provements in accuracy and precision afforded to EDXRF by the develop- ments in computer hardware deconvolu- tion software and pulse processing electronics. Further discussion of these lectures was held over a break for coffee before the six contributed papers of the morning.Of these papers Fraz Mukhtar (Thames Polytechnic London) demon- strated the ability of TXRF to carry out trace level speciation. Chris Hassell (University of Texas Austin) one of the two Kirkbright Bursary recipients both of whom were attending the BNASS meeting showed how static SIMS could be used to study surface reactions in graphite furnaces and Dr. E. B. M. Steers produced some enlightening data on the excitation mechanisms in glow dis- charges.Following the break for lunch we re- turned for a plenary lecture by Professor Bob Michel (University of Connecticut) entitled ‘Laser excited atomic fluores- cence and ionization in graphite furnaces. An overview of instrumentation and real sample analyses for the determination of metals down to the femtogram level’. The technique used conventional furnace tech- nology but with laser enhanced fluores- cence to determine femtogram levels of T1 Mn and Pb. Data were also presented for the determination of fluorine by laser enhanced molecular fluorescence of MgF. From one of the newest techniques under development there followed an overview of atomic spectroscopy and its develop- ment from Dr. John Dawson (DIAS UMIST Manchester) with his invited lecture entitled ‘Analytical atomic spec- troscopy learning from its past’.Alterna- tively Dr. Ernie Newman’s (BDH Poole Dorset) invited lecture ‘Analysis of fine chemicals by atomic spectrometry’ dealt with a wide range of spectroscopic methods used at BDH. The last section of contributed papers for the day included an excellent presentation by Simon Branch (Polytechnic South West) on the determi- nation of As in urine by ICP-MS J. A. Armstrong (Polytechnic South West) on the use of white spirit dilution and DCP- AES analysis of grease additives and Dr. Alan Batho (Thermo Electron Warring- ton) on the simultaneous determination of trace metals in Sn-Pb solder. The final event of the day was the poster session again an informal opportunity to talk to the presenters and also a chance to visit the exhibitors.One well known micro- wave manufacturer was attracting custom- ers by demonstrating the worlds most expensive pop-corn maker! The main social event of the confer- ence occured on Thursday evening-the BNASS conference dinner. Just when we thought we had finished the technical pro- gramme for the day the BNASS Chair- man (Dr. David Hickman Metropolitan Police London) gave an after dinner speech on the use of the antenna in the modem police force-most enlightening. After his critically acclaimed appearance at the R & D topics meeting and various busking spots throughout London Dr. Steve Haswell (Thames Polytechnic/Hull University) was talked into playing his melodeon as part of his 1990 RSC Con- ference Tour. In honour of the Chairman Steve sang a song about hard working and honest policemen followed by several tunes reflecting the international nature of the conference.The perfomance certainly made the evening and I’m sure was being talked about well after the meeting. For those delegates full of party spirit or those filling up with it from the bar the event continued until early the next morning and included a football match at 2.00 a.m. which was enjoyed by the participants but was not as well re- ceived by the occupants of the halls of residence. (I would like to state that Dr. Haswell had nothing to do with this event despite certain rumours-put the cheque in the post Steve!). Fellow survivors of the conference dinner who made it to the first plenary lecture on Friday morning were able to see Professor David Littlejohn (University of Strathclyde Glasgow) present a lecture en- titled ‘The state and status of electrother- mal atomization in atomic spectrometry’.The lecture reviewed the area of ETAAS The highlight of the Conference DinnerSteve Haswell utid his melodeon100 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 1 VOL. 6 its development and current research inter- ests. Also discussed was the use of graph- ite furnaces as emission sources either thermally generated emission or excitation by non-thermal hollow cathode discharges within the furnace. Applications using the graphite furnace as a sample introduction device for ICP-AES and ICP-MS were also assessed. The theme of multi-element determinations in graphite furnaces was carried into stream A where Dr.Jim Harnly (United States Department of Agri- culture Beltsville MD) discussed ‘Multi- element graphite furnace atomic spectro- metry the search for photons in the UV’. The lecture was an overview of the re- search carried out at USDA on simulta- neous multi-element atomic absorption with a continuum source (SIMAAC) and furnace atomization non-thermal excita- tion spectrometry (FANES). In the con- tributed papers section Robin Nicholl (University of Strathclyde) described a computer controlled detection system for simultaneous multi-element determina- tions in AAS and AES based on optical fibres and PMTs. Finally in this section Gary Moulton (University of Maryland) the second Kirkbright Bursary recipient detailed a multi-element ETAAS system with a pulsed xenon arc lamp source with detection limits comparable with conven- tional ETAAS.The final session of the conference on Friday afternoon had been organized with the plenary lecture as the final presenta- tion presumably to minimize delegate fall-out during the afternoon so the session began with invited lectures. Dr. John Carroll’s (ICI Chemicals and Poly- mers Runcorn) presentation ‘Applica- tions of atomic spectroscopy in the chlor- alkali industry’ discussed the analysis of saturated brines by ICP-OES and ICP- MS. ‘Automatic hydride generation from alkaline solutions’ by Dr. Ragner Bye (University of Oslo Norway) considered the generation of volatile hydrides from neutral and alkaline media rather than the acidic solutions normally used.In the last series of contributed lectures Stephen Offley (Loughborough University of Technology) showed how Cu interferenc- es could be removed on-line for the deter- A weary organizing committee at the end of the meeting L to R Colin Watson. David Hickman Judith Egan. John Marshall. Ste\pe Hill and Harp Minhas mination of Se. Dr. I. B. Brenner suggest- ed the occurrence of particle-plasma in- teractions during slurry nebulization of refractory compounds in ICPs and Dr. Mike Foulkes (Polytechnic South West) discussed matrix enhancements from cali- brants and slurries in ICP-AES. The final contributed paper come from the master musician Dr. Steve Haswell who in an alternative to slurries suggested the use of on-line microwave digestion using a continuous-flow system.This seemed ap- propriate as the final plenary lecture from Dr. Skip Kingston (NIST Gaithersburg) entitled ‘Sample preparation for atomic spectrometric analysis’ dealt with the standardization of microwave dissolution procedures and the development of a computer controlled digestion system with a pseudo-learning ability. The final act of the meeting was for Colin Watson chairman of the session to present awards for the best student poster to A. T. Ince and in a long tradition of prizes for Polytechnic South West the award for best student oral presentation went to Simon Branch. For those remaining in Loughborough on Friday night one last social event was organized-a steam train journey where once again Dr. Haswell was persuaded to play and the Editor of a well known journal was seen stoking the boiler (I bet those photos don’t get published ! ).Finally on behalf of the delegates I would like to thank the organizing com- mitte and also as a former bursary recipi- ent I would like to thank ASU BDH and ICI for funding of this year’s bursaries without which I am sure some of the stu- dents would not have been able to attend. For those of you who missed this meeting the sixth BNASS will be held in 1992 and to the football players remember to bring your shorts. Phil Riby USDA NCL Beltsville MD USA Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) XVII October 7th-I2th 1990 Cleveland OH USA The stark contrast between grey London and the rich autumn colours of Cleveland will long remain one of my strongest im- pressions of this my first visit to North America.My other main impression was that of size with everything being on a grand scale compared with my previous experiences. This was particularly true of the seventeenth meeting of the Federation of Analytical Chemistry and Spectro- scopy Societies which ran up to seven- teen parallel streams and approximately 160 sessions each dealing with a different branch of analytical science. In these ses- sions at least 20% of the papers con- cerned analytical atomic spectrometry. Size was both the strength and the weakness of this meeting. The strength being the substantial number of high- quality papers presented the weakness in that it was impossible because of the mul- tiple streams to cover all of the papers that one wished to.This was certainly true for the atomic spectrometry sessions.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991. VOL. 6 101 The highlights of the scientific pro- gramme included the symposium on ad- vances in applied spectrometry and analytical chemistry in honour of Ted Rains and the memorial symposium in regard of Professor C. Th. J. Alkemade on the subject of atomic physics and ana- Time for- a quick drink and a chat hempeen ses- sions for delegates Jim Harnly. Da1.e Styr-is and Phil Rib! lytical spectrometry. It is difficult to isolate any individual session or paper above the rest as the quality was consis- tently high but I did find that I particu- larly enjoyed several sessions on ETAAS and ICP-MS which were both stimulating and entertaining.Unfortunately the meeting lacked a strong European style poster session. Poster sessions particularly when com- bined with a light buffet or ‘cocktail’ rather a sad reflection on the mistake of viewing this medium as a lower status form of communication compared with a conventional lecture. Any conference is more than just a scientific meeting it is also a social event. Somehow I managed to miss the conference social evening of video games and stand-up comedy by being waylaid and finding the local brewery (which was busy with a significant number of confer- ence attendees). I also observed the dangers of Tequila and beer drinking with Texans. Although they were in no way in- volved in any of the above I would like to thank Judith Egan Jim Hamly and Phil Riby for introducing me to a group of friendly people who certainly made me feel welcome. A commendation should also go to Nancy Miller-Ihli who as Chair of the Governing Board spared no effort in ensuring that the meeting ran smoothly. As I sat in the airport at the end of a hectic week I couldn’t help but reflect upon the previous six days. A lot had happened and 1 had learned great deal. I looked out of the window the Indian summer had been replaced with grey rain- clouds. It was time to leave. Chair of the Goiurning Board N a n q Miller-ihli at the Conference Dinner event provide an excellent opportunity for the transmision of scientific data and allow interchange of ideas and experience between participants. This is not a criti- cism of the conference organizers but Simon Sparkes Analytic*al Chemistry Research Unit Department cf Eniir-onmental Sciences Polytechnic South West Plymouth. UK

ISSN:0267-9477    

DOI:10.1039/JA9910600098

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991. VOL. 6 101 Book Review Fourier Tansforms in NMR Optical and Mass Spectrometry Alan G. Marshall and Francis R. Verdun. Pp. xvi+210. Elsevier. 1990. Price $107.25 Df1222.00 (hardback); $46.25 Df195.00 (paperback). ISBN 0 444 87360 0 (hardback); 0 444 87412 7 (paperback). The object of this book is to present a unified treatment of the three most common types of Fourier transform (FT) spectrometry-optical mass (MS) and nuclear magnetic resonance (NMR). This unified treatment extends over six chap- ters and the three separate forms are covered in the last three chapters. Specifi- cally Chapter 1 introduces fundamental line shapes by discussing the complex amplitude of forced oscillations of a damped harmonic oscillator. The reader is then introduced to the usual FT pairs the convolution and shift theorems the effects of discrete sampling and phase correction in Chapters 2 and 3.Some common features of the three spectrome- tries (the mutiplex principle resolution modulation ell-.) are discussed in Chapter 4. The other two general chapters Chap- ters 5 and 6 cover respectively noise and non-FT methods of signal handling (Laplace transforms auto-regression and auto-correlation and maximum entropy). After the two chapters on FT ion cyclo- tron resonance MS and FT-NMR we reach optical spectrometry under the title of FT-interferometry . From the point of view of an optical spectroscopist which is the background against which this review is written the book does not offer the easiest way into the subject.Chapter 1 in particular seems to add unnecessary confusion. When the damped oscillator concept is applied to a bound electron the real part of the complex amplitude gives rise to disper- sion while the imaginary part gives ab- sorption. In the very next chapter however we find the absorption spec- trum referred to as real and the disper- sion spectrum as imaginary. To add confusion the real and imaginary parts of the oscillator amplitude are designated by .r’ and Y’ as if they were the first and second time derivatives. The mathematical treatment in Chap- ters 2 and 3 is fairly standard but I per- sonally find it harder to follow than a ‘classic’ such as Bracewell’s ‘The Fourier transform and its applications’. One difficulty for optical spectroscopists is the exclusive use of the time-frequency Fourier pair for which causality does not allow signals at KO.The path differenc- es-wavenumber pair (s o) for which signals can be acquired at .\-<O is not in- troduced until Chapter 9. Thus the use of a short two-sided section of the interfero- gram to determine phase and then correct it the method commonly used in optical spectrometry does not appear in the dis- cussion of phase correction in Chapter 4. A further consequence which is a curio- sity to optical spectroscopists is the use of zero filling to recover the complete spectral information. As the above example indicates some of the general features of FT spectro- metry discussed in the book are much more relevant to MS and NMR than to optical spectrometry.Another example is the discussion of polarization quadrature excitation and heterodyning that occupies most of the second half of Chapter 4.102 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 1 VOL. 6 This partial specialization would matter less if the reader had a clearer idea of the origin of the input signals and the infor- mation required from the FT output in . each instance. It is a pity that Chapter 1 has not been used to give a brief explana- tion of each of the three experimental techniques so as to provide this back- ground. On the credit side there is a much fuller discussion of noise than is offered by most books and Chapter 6 presents a useful introduction to general methods of signal handling (transfer functions auto- regression maximum entropy etc.) which is not normally found in texts on spectrometric methods. Finally there are both positive and negative points to be made about the pres- entation. The liberal use of diagrams and the sections on problems and hints for so- lutions at the end of each chapter are plus points. On the minus side the format of both diagrams and text makes them rather unnecessarily difficult to read; the dia- grams have a cluttered appearance and the captions of the figures and tables are not easily distinguished from the text. Anne P. Thorne Imperial College of Science Technology and Medicine London UK

ISSN:0267-9477    

DOI:10.1039/JA9910600101

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

102 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 1 VOL. 6 Conference and Meetings Total Reflection X-ray Fluorescence Spectrometry April 23-24 1991 University of Hull Hull UK This seminar is the Second UK Work- shop to provide an opportunity for attend- ees to both learn about and use the technique of total reflection X-ray fluo- rescence spectrometry. The workshop will be held at the University of Hull and the fee will be &99 to include accommo- dation tea dinner coffee and lunch. For further information contact Mrs Sandie McCollin The Short Course Office School of Chemistry The Univer- sity Hull HU6 7RX UK; telephone (0482) 465464; telefax (0482) 4664 10. Third International Conference on Progress in Analytical Chemistry in the Iron and Steel Industry May 1616,1991 Luxembourg The Commission of the European Com- munities and the European Committee for the Study and Application of Analyti- cal Work in the Steel Industry (CETAS) will organize this conference in Luxem- bourg Plateau du Kirchberg Jean Monnet Building rue Alcide De Gasperi.The aim of the conference is to bring to- gether chemists from all over the world working in connection with iron and steel for an exhange of experience covering the different analytical tech- niques used in their laboratories. Ana- lysts working in the iron and steel application sector in affiliated research institutes universities and in governmen- tal control bodies are also encouraged to participate. The conference will include invited lecturers papers and posters. Papers or posters can cover the following possible topics progress in analytical methods; automation including sampling sample preparation and measurement; data and information management and qua1 i ty assurance concepts; calibration and drift correction procedures including com- puter support; analysis of steel products environmental materials and organics; speciation of elements in steel; analysis of coatings interfaces and surfaces; ana- lysis of raw materials additives and by- products; international standardization of methods and certification of reference materials; and re-cycling and waste man- agement problems.For further further information contact the Presidium of Cetas Mrs. M. R. Posch P.O. Box 185 NL-1940 Ad Be- verwijk The Netherlands. XXVII Colloquium Spectroscopicum Internationale June 9-14 1991 Grieg Hall Bergen Norway The Final Circular with Abstract and Registration Forms is now available.To enhance the scientific stature of the CSI the Organizing Committee has estab- lished the CSI Award for major scientific contributions to analytical spectroscopy. Sir Alan Walsh has been selected as the first recipient of the award for his extra- ordinary contribution to atomic spectros- copy. The Organizing Committee takes pleasure in announcing that Sir Alan and Lady Walsh have accepted an invitation to attend the XXVII CSI. In a special plenary CSI Award Session L. R. P. Butler P. Larkins and R. Sturgeon will commemorate and put into perspective Sir Alan’s scientific contributions. Inaugural Lectures will be given by Pro- fessor I.Sobelman and Dr. B. E. Woodgate on the topic of ‘Spectroscopy in space’. Invited Lectures will be given by Professor Dietrich Behne; Dr. Michael Bol’shov; Professor M. de Bruin; Dr. A. R. Byme; Dr. Jiri Dedina; Dr. J. J. Del- puech; Professor Klaus Dittrich; Dr. Heinz Falk; Professor Zhaolun Fang; Professor Yohichi Gohshi; Professor M. Grasserbauer; Professor R. Van Grieken; Dr. Hiraki Haraguchi; Professor Willard W. Harrison; Professor David Hercules; Professor Gary Hieftje; Professor James A. Holcombe; Professor Benli Huang; Professor Sven Johansson; Dr. Tibor Kantor; Dr. Reinhold Klockenkamper; Dr. Peter Larkins; Professor Milton L. Lee; Professor Boris L’vov; Dr. Harald Martens; Dr. James W. McLaren; Pro- fessor J. M. Mermet; Professor Nico M. M. Nibbering; Dr.N. Omenetto; Dr. J. C. Riviere; Professor Peter J. Sadler; Professor Bernhard Schrader; Dr. J. H. Scrivens; Dr. Markus Stoeppler; Dr. Ralph Sturgeon; Dr. Dimiter Tsalev; Dr. W. Ulsamer; Dr. John G. Williams; and Dr. Brenda P. Winnewisser. Submitted papers will be presented on the following topics. Basic theory and instrumentation of atomic spectroscopy (emission absorption fluorescence) molecular spectroscopy (UV VIS IR) X-ray spectroscopy gamma spectro- metry mass spectrometry (inorganic and organic) electron spectroscopy Raman spectroscopy Mossbauer spectroscopy nuclear magnetic resonance spectro- metry surface analysis and depth profil- ing and photoacoustic spectroscopy. Applications of spectroscopy in the ana- lysis of metals and alloys geological materials industrial products biological samples food and agricultural products and reference materials.An exhibition of scientific equipment analytical reagents as well as books and journals will be held adjacent to the main auditorium. Satellite meetings will be held on Graphite Atomizer Techniques in Analyt- ical Spectroscopy Characterization of Oil Components Using Spectroscopic Methods Measurements of Radionu- clides After the Chernobyl Accident and Speciation of Elements in Environmental and Biological Sciences. For further general information contact XXVII CSI HSD Congress-Conference P.O. Box 1721 Nordnes N-5025 Bergen Norway; telephone 47 5 23 88 40; telex 42607 hsd n; telefax 47 5 23 88 01. For further information on the scienti- fic programme contact Dr.Y. Thomas- sen National Institute of Occupational Health P.O. Box 8149 DEP N-0033 Oslo 1 Norway; telephone 47 2 46 68 50; telefax 47 2 60 32 76 or Professor F. J.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 103 The Sixth Biennial National Atomic Spectroscopy Symposium wd.. be held at the Polytechnic South West Plymouth tith BNASS 22-24 July 1992 6 t h BNASS The symposium will provide a forum where interesting and useful applications of atomic spectroscopy can be reported and discussed. In addition to plenary invited and submitted lectures a particular feature of the meeting will be the presentation of posters. There will also be an exhibition and a social programme for delegates and their guests. This meeting is organized by the Atomic Spectroscopy Group Analytical Division of The Royal Society of Chemistry Further information can be obtained from the Chairman of the organizing committee Dr S Hill Department of Environmental Sciences Polytechnic South West Drake Circus Plymouth Devon PL4 SAA UK.Langmyhr Department of Chemistry University of Oslo P.O. Box 1033 Blin- dern N-0315 Oslo 3 Norway. Fourth Surrey Conference on Plasma Source Mass Spectrometry and King- ston Conference on Plasma Spectro- metry in the Earth Sciences July 14-18 1991 University of Surrey Guilford UK The Surrey Conference is the fourth bien- nial meeting to be held at the Surrey Uni- versity site. Papers are invited on all aspects of plasma source mass spectro- metry. Following the success of the 1989 meetings the I99 1 Surrey Conference will be followed by a second meeting (previously held at Kingston Polytechnic) dedicated to Earth Science applications of plasma spectrometry.The scientific programmes will consist of invited and open lectures discussion sessions and poster events. There will also be full social programmes. Further details can be obtained from the conference organizers Drs. Kym E. Jarvis and John G. Williams NERC ICP- MS Facility Department of Geology. RHBNC Egham Surrey TW20 OEX UK or Dr. Ian Jarvis School of Geological Sciences Kingston Polytechnic Penrhyn Road Kingston on Thames Shrrey KTl 2EE. UK. IUFAC International Congress on An- alytical Sciences August 25-3 1 199 1 Makahuri-Messe Chiba Japan Papers are solicited in the following areas Separation Sciences; Chemical Speciation and Characterization; New Principles Reactions and Techniques; Chemometrics and Robotics; Biochem- ical/Biomedical; Environmental; High- Tech Materials.Authors wishing to contribute oral or poster presentations should contact The Japan Society of Analytical Chemistry 1-26-2 Nishig- otanda Shinagawa Tokyo 141 Japan (Telefax +8 1-3-5487-2790 BITNET KK9822QJPNSUT20) as soon as possible. Deadline for sub- mission of abstracts is March 31 1991. Pre- and Post-Symposia will include 199 1 Pacific International Congress on X-ray Analytical Methods August 12- 16 1991 Honolulu Hawaii USA contact Dr. R. Jenkins International Centre for Diffraction Data 1601 Park Lane Swarthmore PA 1908 1 USA; and New Approaches in Trace Element Ana- lysis by Atomic Spectroscopy September 2-4 199 1 Kitami Japan contact Profes- sor I.Atsuya Kitami Institute of Techno- logy 165 Kouencho Kitami Hokkaido 090 Japan. Federation of Analytical Chemistry and Spectroscopy Societies (FACSS)- Pacific Conference Joint Meeting October 6-1 1 199 1 Anaheim CA USA The 1991 FACSS meeting is a combined meeting with the Pacific Conference on Chemistry and Spectroscopy. The joint meeting will provide a programme of ex- panded technical coverage with an em- phasis on emerging technologies in analytical spectroscopic chemical and biochemical science. In addition the Tomas Hirschfeld Student Awards will be presented at the meeting to the gradu- ate students submitting the most outstand- ing papers. The scientific programme will also include various Award Symposia There will also be an Instrument Exhibi- tion and Workshops and Short Courses on topics such as ICP-MS GC-MS LC- MS sample preparation lasers in analyti- cal chemistry and chemometrics.The104 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 Employment Bureau will be operated by the national office of the American Chemical Society. For general information contact one of the General Chairman Richard Deming Department of Chemistry and Biochemis- try California State University at Fuller- ton Fullerton CA 92634 USA (714 773 2170); or Connie Sobel 1800 N. Altade- na Drive Passadena CA 91 107 USA (818 794 0737). For other information contact FACSS P.O. Box 278 Manhattan KS 66502 USA (301 846 4797). Laboratory Exhibition and Conference November 5-7 199 1 London The 1991 event will be known as the Laboratory Exhibition and Conference and will be held at the New Earls Court 2 Exhibition Centre.The timing of the event has also been changed to Novem- ber. Not only will the new event bring to- gether the world’s leading scientific companies it will also introduce further conferences in addition to the existing Analyticon conference alongside the ex- hibition. Discussions with potential con- ference sponsors are at an advanced stage; the likely outcome includes a con- ference in conjunction with The Chro- matography Society a Clinical Biochemistry meeting in conjunction with the Southern Region of the Associa- tion of Clinical Biochemists and a con- ference organized by The Royal Society of Chemistry. The move to the new venue of Earls Court 2 has enabled the organizers to structure the exhibition into clearly defined technology zones Analytical Science Biotechnology Laboratory Automation Environmental Analysis Laboratory Fittings Laboratory Ware and Medical Laboratory Sciences.Further information is available from Evan Steadman Communications Group The Hub Emson Close Saffron Walden Essex CH 10 1 HL UK. Third International Symposium on An- alytical Chemistry in the Exploration Mining and Processing of Materials August 2-7 1992 Randburg South Africa Interested people are invited to submit titles and abstracts under the general theme ‘The Role of Contemporary Chemical Analysis in Mining and In- dustrial Technology’. The following topics will be covered Geochemical Exploration; Extraction and Beneficia- tion of Materials Value-added Prod- ucts; Environmental Aspects; Coal; Metals and Alloys; Rare Earths; Noble and Base Metals; Analytical Assurance and Laboratory Management; Automa- tion and Process Control; and High- technology Materials.Innovation in ana- lytical techniques would be particularly welcome. Titles and abstracts (not more than 250 words) should be submitted so as to arrive not later than September 30 1991. Extended abstracts will be required before March 30 1992. All correspondence and submissions must be addressed to The Conference Secretary Mintek Private Bag X3015 Randburg 2 125 South Africa. SAC92 September 20-26 1992 Reading UK An International Conference on Analyti- cal Chemistry (SAC92) organized jointly by the Analytical Division of The Royal Society of Chemistry and the Laboratory of the Government Chemist will be held at the University of Reading. This is the tenth in the series of triennial conferences originally started by the Society for Ana- lytical Chemistry (hence SAC) and on this occasion also celebrates the 150th anniversary of the founding of the Labo- ratory of the Government Chemist (LGC). The scientific programme will be organized around plenary invited and contributed papers and posters covering the whole field of analytical chemistry. The language of the conference will be English. The programme will include workshops where research workers can demonstrate new apparatus and tech- niques. An opportunity will be made for all participants to visit The Laboratory of the Government Chemist and other scien- tific establishments. Further information is available from The Secretary Analytical Division Royal Society of Chemistry Burlington House Piccadilly London W 1 V OBN UK.

ISSN:0267-9477    

DOI:10.1039/JA9910600102

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

104 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 Future Issues will Include- Optimization of Cold Vapour Atomic Ab- sorption Spectrometric Determination of Mercury With and Without Almagama- tion by Subsequent Use of Complete and Fractional Factorial Designs With Uni- variate and Modified Simplex Methods- George A. Zachariadis and John A. St rat is High-performance Liquid Chromato- graphy-Atomic Absorption Spectro- metry Interface for the Determination of Selenoniocholine and Trimethylselononi- um Cations Application to Human Urine-Jean-Simon Blais A. Hu- yghues-Despointes Georges Marie Momplaisir and William D. Marshall Optimization of Mass Scanning Rate for the Determination of Lead Isotope Ratios by an Inductively Coupled Plasma Mass Spectrometer-Naoki Furuta Flow Injection Flame Atomic Spectro- metric Determination of Aluminium Iron Calcium Magnesium Sodium and Potassium in Ceramic Materials by On- line Dilution in a Stirred Chamber-V.Carbonell A. Sanz A. Salvador and M. de la Guardia Direct Solid Sampling in Capacitively Coupled Microwave Plasma Atomic Emission Spectrometry-J. D. Wine- fordner Abdalla H. Ali and Kin C. Ng Evaluation of a 13.56 MHz Capacitively Coupled Plasma as a Detector for Gas Chromatographic Determination of Or- ganotin Compounds-Degui Huang and Michael W. Blades Application of a High Resolution Induc- tively Coupled Plasma Mass Spectrome- ter to the Measurement of Long-lived Radionuclides-Chang-Kyu Kim Riki Seki Shigemitsu Morita Yuichi Takaku Yasuhito Igarashi and Ma- sayoshi Yamamoto Atomic Spectrometry Update The Update in the April issue is- Clinical Materials Foods and Beverag- es-David J. Halls Helen M. Crews Andrew Taylor and Simon Branch

ISSN:0267-9477    

DOI:10.1039/JA9910600104

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 105 Temperature Programmed Static Secondary Ion Mass Spectrometric Study of Phosphate Chemical Modifiers in Electrothermal Atomizers* D. Christian Hassell Vahid Majidit and James A. Holcombe* Department of Chemistry and Biochemistry The University of Texas at Austin Austin TX 78772 USA Temperature programmed static secondary ion mass spectrometry is used to investigate surface chemical reactions of phosphate chemical modifiers used for the determination of Cd and Ag in electrothermal atomic absorption spectrometry. Cadmium-xyphosphorus reactions are initiated on the surface at dry cycle temperatures with further stabilizing reactions occurring on the surface in the char cycle temperature range. This leads to a delay in the atomization of Cd to a higher appearance temperature.However for the determination of Ag addition of phosphate results in an attenuation in the atomic absorption spectrometric signal intensity with no change in appearance temperature. Similar Ag-xyphosphorus surface reactions are not observed. Keywords Secondary ion mass spectrometry; electrothermal atomic absorption spectrometry; phosphate chemical modifier; cadmium; silver Various analytical techniques have been used in attempts to elucidate electrothermal atomizer surface reactions. These include electron microscopy,I X-ray crystallography2 and surface spectroscopies such as electron spectroscopy for chemical analysis' and A ~ g e r . ~ While these techniques have been useful in many mechanistic studies they are relatively insensitive to the sub-ppm analyte concentrations normally encountered in electrothermal atomic absorption spectro- metry (ETAAS).A further drawback is that reactions have not been studied during the actual thermal heating of the surface (i.e. during the drying or charring cycles) since the sample surfaces were usually cooled prior to analysis. Prod- ucts stable at these elevated temperatures might react to form new products when cooled or undergo a reaction upon contact with the atmosphere during transfer between instru- ments. Temperature programmed static secondary ion mass spectrometry (TPS-SIMS) was used in order to examine A B C D Translational rod Fig. 1 TPS-SIMS sample introduction system A Cu gasket; B conflat- flanged stainless-steel chamber; C polytetrafluoroethylene spacer; D.Furon seal; E port to rotary-vane roughing vacuum pump; F port to tur- bomolecular vacuum pump; G graphite sample platform; H thermocou- ple; I Ta strip heater; and J Cu electrodes * Presented at the Fifth Biennial National Atomic Spectroscopy Sympo- t Present address Department of Chemistry. University of Kentucky. $ To whom correspondence should be addressed. sium (BNASS). Loughborough UK 18th-20th July. 1990. Lexington. KY 40506 USA. surface reactions occurring during the thermal treatment. The technique combined high sensitivity with minimal surface perturbation hence permitting surface interrogation using analyte concentrations more closely associated with routine ETAAS. An investigation of the chemical role of phosphates used as chemical modifiers with ETAAS served both to gain insights into reaction mechanisms and to evaluate the utility of TPS-SIMS.Temperature programmed thermal desorption mass spectrometry (TP-TDMS) a method used to study gas- phase electrothermal atomization reaction products,s.6 was also utilized to support conclusions drawn from the TPS- SIMS data. Phosphates are often used for the determination of Cd Pb and Zn leading to a delay in atomization to higher tempera- tures and removal of more volatile interfering matrices during the thermal pre-treatment steps. Czobik and Matou- sek7 originally postulated the formation of a metal pyrophos- phate which then decomposed to release the free metal vapour. While the existence of a metal-oxyphosphorus com- pound was later corroborated by Bass and Holcombe6 and Wendl and Miiller-Vogt,2 it is unclear whether the stabiliza- tion occurs via a gas-phase reaction or on the graphite surface.Experimental Apparatus and Solutions The TPS-SIMS system consists of an extractor type ion gun for generation of primary ions (Leybold-Heraeus Model IQE 12/38). The secondary-ion optics include an electrostatic einzel lens pre-filter and a quadrupole mass spectrometer with pulse-counting detection and an effective mass range of 2-456 u (Leybold Vacuum Products Export PA USA). Turbomolecular pumps maintain a base pressure of 1.3 x Pa. The stainless steel ultra-high vacuum chambers transla- tional rod and heating-block assembly were designed and manufactured in the University of Texas Chemistry Depart- ment. The sample introduction system is illustrated in Fig.1. The heating block consists of a corrugated tantalum strip heater po- sitioned between two copper electrodes and a thermocouple temperature probe in contact with the pyrolytic graphite coated graphite sample platform (10 x 5 x I mm Stackpole/ Ultracarbon Bay City MI USA). The platform is secured to the heating block directly above the tantalum strip with a stain- less-steel screw and ceramic washer thereby ensuring that heating is predominantly by radiation rather than conduc- tion. The tantalum strip heater and thermocouple are connect-106 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 ed to a feedback and proportional control circuit which permits programmable heating and cooling.Also shown in Fig. 1 are the two separate pumping stages which isolate the main ultra-high vacuum chamber from atmosphere. The precision ground stainless steel translational rod is sealed by spring-energized polymer seals (Furon Los Alamitos CA USA) such that when the heating block is trans- lated from atmosphere it first passes through the roughing- pumped chamber then through the turbomolecular-pumped chamber before being positioned for analysis in the main ultra-high vacuum chamber. This differentially pumped ar- rangement allows rapid sample introduction and pump-down to working pressure (<1.3 x 104 Pa) within approximately 15 min. Mass scanning and data collection are performed with software written in ASYST (Asyst Software Technologies Rochester NY USA) running on a PC-AT compatible com- puter in conjunction with a Keithley Series 500 data acquisi- tion and control system (Keithley Instruments Cleveland OH USA) which incorporates analogue to digital digital to analogue and pulse counting interface boards. The software permits full mass spectral scanning multiple individual ion monitoring (i.e.‘mass hopping’) selective scaling auto- matic gain and numerous data reduction and analysis capa- bilities. The TP-TDMS system consists of a quadrupole mass analy- ser with a 70 eV electron impact ionizer and a programmable peak selector (Uthe Technology International Sunnyvale CA USA). An Apple 11+ computer is used for data collection and control of the heating programme which is capable of reach- ing temperatures of 3000 K.This system has been described previously in greater detaiL6 Electrothermal AAS studies were performed on a Varian GTA-95 graphite tube atomizer and an AA-875 spectrometer interfaced to a PC compatible computer via a Keithley 570 data acquisition system. ASYST software was used for data collection and analysis. Vaporization was from the wall of a standard pyrolytic graphite coated graphite tube. The cadmium and phosphate stock solutions were prepared by dissolving ACS reagent grade Cd(N03)2 and NH4H,P04 in distilled de-ionized water. Working solutions were prepared by serial dilution of the stock solutions. Procedure For the TPS-SIMS studies 2 p1 aliquots of the aqueous solu- tions were deposited on a pyrolytic graphite coated graphite platform and allowed to dry at ambient temperatures.The sample platform was then secured to the heating block assem- bly and translated through the differentially pumped vacuum stages into the main vacuum chamber for analysis. The tem- perature range of the system used in this study was between ambient and 900 K thus permitting mechanistic studies in the dry and char cycle regimes. The heating rate was 1 K s-I. The primary Ar+ ion beam current was 1 nA at 3 keV using a 1 0 p m spot. The beam was rastered in the x-y plane to achieve a scan area of 4 mm2 thus ensuring a static mode of operation. ‘Static’ implies that at this low ion flux only the outermost surface layers are probed; furthermore this mode is considered to be non-destructive since total surface damage to the scan area due to primary ion collisions is minimized. For the TP-TDMS studies the sample was deposited on a pyrolytic graphite coated graphite platform and thermally treated in the pre-treatment chamber under nitrogen at atmo- spheric pressure.This chamber was evacuated to <I .3 x Pa before the sample was translated into the high-vacuum ana- lysis chamber and positioned below the quadrupole. When a pressure of 2.6 x 1W Pa was achieved the sample was ato- mized and subsequently detected by an electron multiplier located at the end of a quadrupole mass analyser. 1 .00 c 0.80 u) 3 * 4 0.60 : 0.40 - (0 C CII .- w .- - Q g 0.20 z 0 .I Cd+ I CdNO’ CdNO,’ Cd,’ Cd,O’ Cdo+ x 100 k+ 100 150 200 250 300 m/z Fig. 2 graphite coated graphite surface T = 298 K Secondary ion mass spectrum (positive) Cd(N03)? on pyrolytic c C I 0.80 - 2 0.60 - c a 0 C 0 v) .- 2 0.40 - E ; 0.20 - N (0 .- - z CdO+Cd p+ OIUC’ - 100 150 200 250 300 m/z Fig.3 Secondary ion mass spectrum (positive) Cd(NO3)? and NH4H2PO4 on pyrolytic graphite coated graphite surface T = 298 K Results and Discussion Fig. 2 is static SIMS spectrum of 260 ng of Cd [as Cd(N03)2] on a graphite surface at 298 K without any prior heating. While the Cd isotope peaks dominate the oxide and nitrate ions and their fragments are clearly evident. (The presence of dimer ions and associated oxides does not necessarily indicate the presence of dimers on the surface; these are often an arti- fact of secondary ion collisions between nearest neighbour surface or second-layer species.*) With the addition of 1200 ng of NH4H2P04 to the original aqueous solution (Fig.3) Cd(N0,)2 and its fragments are not detected and CdPO,+ species are evident. The CdO+ peaks are diminished to 25% of their former intensity. These observations clearly indicate the formation of a Cd-oxyphosphorus compound on the surface by the end of the desolvation step. Fig. 4 displays the signal from several Cd species monitored during sample heating. Between 340 and 410 K the Cd+ signal which could include a small contribution of daughter fragments in addition to the ionized free Cd decreases rapidly. In this local region the decrease of the Cd+ signal is accom- panied by an increase of the CdP02+ signal. This suggests a chemical coupling of these two species and a nearly complete conversion into a surface-bound CdPO species by 400 K.The increase in the CdPO+ intensity at still higher tempera- tures suggests interconversion of the CdPO species. The dis- similar thermal behaviour of CdPO+ and CdP02+ also indicates that these two are not simply daughter fragments of the same higher order CdP,O species on the surface. While changes in surface character or composition can alter the ionization cross-JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 1 07 10.0 > 70.0 c1 .- v) Q c - 50.0 > .- c - 30.0 4 - ..--’ I I I I I I I Fig. 4 TPS-SIMS Cd(NO3I2 and NH4H2P04 on graphite surface heated at 1 K s-l. A Cd+; B CdP02+; and C CdPO+ 400 300 200 - v) 4- ‘E 100 2 I 2 0 - k lo00 .- E v) 800 c - 600 400 200 n 300 600 900 1200 1500 1800 2100 TIK Fig.5 TP-TDMS temperature programme of 300 K s-I. (a) Cd(N03)2 on graphite surface; and (h) Cd(N03)* and NH4H2P04 on graphite surface section of surface species and thus significantly affect the SIMS signal inten~ities,~ the dissimilarity between CdPO+ and CdP02+ suggests that such ‘SIMS matrix effects’ are not a logical first choice to explain the signal intensity variation with temperature. By using the TP-TDMS system the gaseous products also can be monitored during a temperature ramp (Fig. 5 ) . The Cd+ and CdN03+ peaks at 650 K in the absence of phosphate [Fig. 5 (a)] are probably due to crystal fracturing which is often ob- served while heating salts in a vacuum.6 The first PO2+ peak centred at 500 K in the presence of phosphate [Fig.5(6)] is the result of vaporization of excess of phosphate. The absence of CdN03+ peaks in the presence of phosphate substantiates the previous suggestions from the SIMS observations of rapid low- temperature conversion of any nitrate species into the more stable oxyphosphorus compound. The observed delay in peak atomization temperature from 970 K [Fig. 5(a)] to 1330 K [Fig. 5(b)] is consistent with the appearance temperature shift of the Cd atomic absorption signal in ETAAS. The P307+ peak is coin- cident with the Cd+ peak and indicates the decomposition of a higher order CdP,.O species which might exist on the surface prior to atomization; however it is possible that a relatively low ionization cross-section of such a large molecule combined 1 .oo r 0.80 cn 3 L C c1 CI 8 0.60 .- 0.40 A E 0.20 b .- - 0 z 0 1 I I 1 J 100 150 200 250 300 m/z Fig.6 SIMS spectrum (positive) AgN03 and NH4H2P04 on graphite surface T = 298 K 0.30 A 0 1 .o 2.0 3.0 4.0 t/S Fig. 7 ETAAS Ag absorbance profiles (328.1 nm 400 K s-I thermal ramp from 673 K) for A 0.1 ng Ag; and B 0.1 ng Ag and 100 ng Pod3+ as NH4H2P04 with the low transmission efficiency of the TPS-SIMS system at higher masses might preclude its detection on the surface. The static SIMS data suggest that relatively low temperature reactions (i.e. within the drying cycle region) ‘stabilize’ the Cd in the presence of phosphates although thermal pre- treatment beyond 500 K is required to remove the bulk of the unreacted phosphate in order to minimize gas phase chemical and spectral interferences.l o Silver has been reported as an element which is ‘stabilized’ by phosphates in a fashion similar to that observed for Cd.7-11 However the static SIMS studies of Ag with NH4H2P04 (Fig. 6) show no significant Ag analogues of the CdP,.O species. Repeating conventional ETAAS studies of Ag with NH4H2P04 has shown no shift in the appearance temperature but rather has demonstrated an attenuation of the Ag atomic absorption signal with the addition of NH,H,PO,; for Cd the shift to a higher appearance temperature with the addition of NH4H2P04 is not accompanied by such attenuation. Fig. 7 illustrates typical absorbance profiles for Ag with and without the addition of NH4H2P04 modifier at a thermal ramp-rate of 400 K SKI. Slower ramp-rates result in further attenuation which is consistent with gas-phase interference since the vapour temperature is not sufficiently high to promote dissoca- tion prior to diffusional loss.Thus contrary to ‘accepted dogma’ no chemical basis exists for the practice of using phosphate modifiers for the determination of Ag. Although the ammonium cation might help remove any interfering chloride matrix as NH,Cl(g) indiscriminate use of phosphate modifiers for the determination of Ag might actually reduce analytical sensitivity and accuracy.108 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 In summary while a mechanism cannot be assigned based upon these data it is clear that Cd-oxyphosphorus reactions are initiated on the graphite surface at relatively low tempera- tures during or immediately following desolvation.Intercon- versions of CdP,O species continue to occur at char cycle temperatures. Finally based on both TPS-SIMS and ETAAS data phosphate chemical modifiers are relatively counter- productive for the determination of Ag. This work was supported by National Science Foundation grant CHE-8704024. References 1 Welz B. and Schlernmer G. and Ortner H. M. frog. Anal. Spec- trosc. 1989 12 1 1 1. 2 Wend] W. and Muller-Vogt G. J. Anal. At. Spectrom. 1988,3,63. 3 4 9 10 1 1 Sabbatini L. and Tessari G. Ann. Chim. (Rome) 1984,74,779. Wu S. Chakrabarti C. L. Marcantonio F. and Headrick K. L. Specwochim. Acta Part B 1986,41,65 1 Styris D. L. and Kaye J. H. Spectrochim. Acta Part B 1981,36,41. Bass. D. A. and Holcornbe J. A. Anal. Chem. 1987 59,974. Czobik E. J. and Matousek J. P.. Talanta 1977,24 573. Benninghoven A. Rudenauer F. G. and Werner H. W. Secmdury ion Mass Spectrometry Wiley New York 1987 p. 215. Benninghoven A. Rudenauer F. G. and Werner H. W. Secondary Ion Mass Specmmem-y Wiley New York 1987 p. 824. Ohlsson K. E. A. and Frech W. J. Anal. At. Spectrom. 1989,4,379. Slavin W. Carnrick G. R. Manning D. C. and Pruszkowska E. At. Spectrosc. 1983,4 69. Paper 0104009F Received September 4th I990 Accepted October 12th 1990

ISSN:0267-9477    

DOI:10.1039/JA9910600105

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 I09 Use of Partial Least Squares Modelling to Compensate for Spectral Interferences in Electrothermal Atomic Absorption Spectrometry With Continuum Source Background Correction Part 1. Determination of Arsenic in Marine Sediments* Douglas C. Baxter Wolfgang Frech and lngemar Berglund Department of Analytical Chemistry University of UmeA S-90 I 87 UmeA Sweden When arsenic is to be determined in samples containing aluminium such as sediments by electrothermal atomic absorption spectrometry (ETAAS) at the most sensitive line (1 93.7 nm) spectral interferences occur when continuum source background correction is used. In this work the possibilities of resolving the spectral interference from aluminium mathematically using multivariate calibration have been investigated.A calibration set consisting of arsenic and aluminium standard solutions and mixtures of the two is analysed by ETAAS and the absorbance signals obtained are used to construct a partial least squares model. This model is then used to predict the arsenic (and aluminium) concentrations in dissolved sediment samples from their absorbance signal patterns. The multivariate calibration method employed is described and results for the determination of arsenic in two marine sediment reference materials are discussed. Keywords Arsenic determination; electrothermal atomic absorption spectrometry; marine sediment reference material; spectral interference; partial least squares modelling In the determination of arsenic in environmental samples by electrothermal atomic absorption spectrometry (ETAAS) prob- lems may arise in the form of non-spectral and spectral interfer- ence effects. However by utilizing optimal ETAAS conditions including the platform technique,'.? chemical modification2" and evaluation of peak area^,^,^,^ non-spectral interference effects have largely been eliminated.Such conditions are readily accessible and are incorporated in the stabilized tem- perature platform furnace (STPF)2 concept; a collection of ana- lytical conditions which in the majority of instances facilitates interference-free graphite furnace performance. An additional important requirement for the STPF concept is the use of 'Zeeman-effect background correction for all but the simplest situations'.? In general this is the only STPF con- dition that cannot be fulfilled by all ETAAS instruments hence the problem of spectral interferences in the determina- tion of arsenic may arise.By using continuum source background correction Saeed and Thomassens observed spectral interferences from phos- phate matrices in the determination of arsenic. Riley6 noted un- dercorrection errors at the primary arsenic wavelength ( 1 93.7 nm) resulting from aluminium auto-ionization lines (see Table 1 data from reference 7) and proposed using the line at 197.2 nm which is approximately half as sensitive instead. A more recent study by Martinsen er al.x revealed potential problems from concomitant cobalt and iron at the 193.7 cm line and from cobalt and nickel at the alternative 197.2 nm wavelength. (It should be noted that the use of Zeeman-effect background cor- rection eliminates all the aforementioned spectral interference problems.') For environmental samples such as sediments as discussed here spectral interferences from aluminium at the 193.7 nm arsenic line are likely to be the major problem1() as the other species are not present in sufficiently high concentra- tions to cause background correction errors.In this work the possibilities of mathematically resolving the spectral interference from aluminium in the determination of arsenic in sediments at the 193.7 nm line by ETAAS with con- tinuum source background correction are investigated. It is shown that accurate arsenic results for two marine sediment reference materials [ BCSS- 1.Coastal Marine Sediment and MESS- 1 Estuarine Sediment (National Research Council * Presented at the Fifth Biennial National Atomic Spectroscopy Sympo- sium (BNASS). Loughborough. UK 181h-201h July. 1990. Table 1 Aluminium ion vacuum wavelengths in a 1.0 nm interval centred around the arsenic 193.759 nm line' Wavelength/nm Wavelength/nm 193.4503 11" 193.5949 IIIt 193.4713 I1 193.6907 11 193.5840 111 193.9261 I1 193.5863 111 * 11 Singly ionized aluminium. i. 111 Doubly ionized aluminium. Canada)] can be obtained using multivariate calibration based on partial least squares (PLS) m0del1ing~I-l~ of the signal profiles. Theory Problem Formulation and Notation To achieve accurate background correction in ETAAS using a continuum source the non-specific signal component must be a broad band with an unstructured n a t ~ r e .~ The presence of any structure within the spectral bandwidth isolated by the monochromator other than that due to the analyte (and which can be considered negligibleI4) leads to inaccurate back- ground corre~tion,~ i.e. a spectral interference implies that the background corrected absorbance signal contains contributions from both the analyte and some interfering species. Therefore for the determination of arsenic in matrices with high alumin- ium contents such as sediments the problem is one of resolv- ing the contributions of these two species. The notation used in the following discussions is that ma- trices are represented by boldface uppercase italic letters e . g . R and vectors by boldface lowercase italic characters e.g.r. Partial Least Squares Modelling The problem of spectral interferences is frequent in analytical chemistry and various approaches to their resolution have been proposed.15-'x For the present application PLS model- ling1 1-13.17 of the absorbance signals was used. A calibration set was first prepared by ETAAS analysis of standard solutions of arsenic and aluminium and mixtures of the two. The known110 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 concentrations in these solutions were arranged in an n x 2 matrix C (n standard solutions and two species arsenic and al- uminium) and the corresponding absorbance signals in an n x rn response matrix R . Each of the n rows of R describes the absorbanc. signal as a function of time and each of the m columns the absorbance at a specific time for the n standard solutions.The goal in PLS is to model R and C as well as possible and to maximize correlation between these matrices thus confer- ring good predictive capabilitie~.~1.12.'7 To achieve this the mean value of each column in R and C (row vectors F and f of dimensions 1 x rn and 1 x 2 respectively) is first subtracted from each variable in the column making the subsequent com- putations-well conditioned. Next the matrices are decomposed R = l F + T P + E (1) C = 1C + UQ + F (2) where P and Q are the loading for the matrices R and C re- spectively and T and U the sc0res.~*-1~ The column vectors 1 contain ones in all positions and have dimensions n x 1. The loadings and scores matrices are of a lower dimension than the R and C blocks and consist of a number of PLS components which describe the systematic variation in R and C.Matrices E and F are residual matrices containing the non-modelled parts of the data. The relation between U and T is given by U = T B + H (3) where B is a diagonal matrix of model regression coefficients12 and H a residual matrix which is minimized in the least- squares sense. Predictions of the concentrations of arsenic and aluminium in an unknown sample are then obtained from the absorbance signal vector (Tunk) inserted into the PLS model in the sequence runk +funk *uunk j C u n k (4) Number of Significant PLS Dimensions The PLS components are calculated one at a time using an iter- ative a l g o r i t h m ~ ~ ~ ~ 2 ~ ~ 7 which extracts the first component to de- scribe the largest amount of variance in the data the second the greatest part of the remaining variance after the first com- ponent and so on.Iteration continues until no significant vari- ance and hence no information remains. The number of PLS components or dimensions required to predict concentrations accurately is an important factor to con- sider in constructing the model. In the ideal situation predic- tion of arsenic and aluminium concentrations should require only two PLS components. However should the two species interact in any way or detector non-linearities be evident then more than two PLS dimensions will be necessary if accurate estimates of concentration are to be made. To establish the optimum number of PLS components the method known as cross-validationlg is used.After each new PLS component is calculated the predictive capabilities are compared with those of the previous lower-dimensioned model. Cross-validation on newly calculated dimensions continues until predictions are no longer improved and the optimum number of PLS compo- nents to use in the model is established. If too few dimensions are included in the PLS model an adequate description of the system under consideration cannot be obtained and biased estimates of concentration will result.I2JO When too many components are used overfitting of the data in the calibration set occurs which generally means that noise in the measurements is given predictive significance. I x20 Experimental Instrumen tation A laboratory-constructed graphite furnace incorporating side- Table 2 Instrumental parameters for the platform equipped ETAAS system. For sample volume see Table 3; modifier volume 5 pl of 0.15% palladium; wavelength 193.7 nm; lamp current* 9W; and spectral band- width 1.0 nm Stage TemperatureTC Time/s Drying I30 40 Atom izationt 2000 6 Clean-out 2400 3 Ashing 900 45 * Westinghouse arsenic electrodeless discharge lamp.Continuum source t Heating rate approximately 2000 "C s-I. Read command selected. background correction using a Varian hydrogen hollow cathode lamp. heated integrated-contact tubes" was installed on the optical bench of a research spectrometer system based on a modified Varian Techtron AA-6 monochromator.21.22 The furnance was heated by a power supply (LL-Elektronik Bygdsiljum Sweden) equipped with an optical feed-back temperature control system.23 Instrumental parameters are given in Table 2.Absorbance data and tube temperature profiles were acquired at 90.9 Hz using an Ericsson personal computer via a Tecmar Labmaster interface. The ETAAS software was obtained from B. Radziuk (Bodenseewerk Perkin-Elmer Germany) and permits storage of background corrected absorbance signals as ASCII files. Reagents and Materials Standard solutions of arsenic and aluminium were prepared in 0.4 mol dm-3 hydrochloric acid from analytical reagents of the highest available purity. All acids employed in the dissolution of sediment samples were of pro analysi quality supplied by Merck and used without further purification. A 0.15% palladi- um (as nitrate) solution was used as chemical modifier throughout being prepared from a Merck ETAAS standard.Spectroscopic-reagent grade argon was utilized as the furnace purge gas. Integrated-contact tubes (I9 x 5.7 mm i.d.) were manufac- tured from single pieces of RWO quality graphite and were coated with pyroltic graphite (Ringsdorff-Werke GmbH Germany). Solid pyrolytic graphite platforms as supplied by Perkin-Elmer were used. Two marine sediment reference materials (BCSS- I and MESS- 1 ) were obtained from the National Research Council Can ad a Dissolution Procedure The sediments were dissolved following the procedure of Stur- geon et ~ 1 . ' ~ After drying to constant mass at 105 O C 0.5 g of sediment was placed in a 100 ml polytetrafluoroethylene beaker and wetted with 4 ml of water.Then 5 ml of concen- trated hydrochloric acid 2 ml of concentrated nitric acid and 5 ml of concentrated hydrofluoric acid were added the beaker was covered and heated for 2 h at about 90 "C on a hot-plate. The cover was removed and the solutions slowly brought to dryness then 5 ml of copcentrated nitric acid 2 ml of concen- trated hydrochloric acid and 100 p1 of concentrated perchloric acid were added to effect dissolution of the organic material. On evaporation to dryness the residue was dissolved in 20 ml of warm 1 mol dm-3 hydrochloric acid and diluted to 50 ml with water. The supernatant liquid was carefully decanted to leave the small amounts of undissolved materiaP behind. Blank dissolutions were performed in parallel.Following dissolution the sediment samples were finally further diluted in 0.4 mol dm-3 hydrocholoric acid giving di- lution factors of 1 k 335 for BCSS- 1 and 1 k 301 for MESS-1. To confirm that no arsenic was lost during the digestion pro- cedure the dissolved sediment samples were also analysedJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 I. Table 3 Experimental design for calibration. Four replicates performed at each point marked x in the design; 10 pl blank volumes and 5 pl of standard (plus 5 p1 of blank where appropriate). Manual injections. Note that 5 p1 of the dissolved sediment samples were injected then 5 p1 of the blank or an arsenic standard were added the latter for the results discussed later in Table 5 Arsenic Aluminium concentration/mg I-' concentrat ion/ PE I-' 0 100 200 0 50 100 X X X X X X - - X using a Perkin-Elmer Zeeman 3030 equipped with HGA 600 and AS-60 peripherals.Arsenic was determined using STPF conditions,2 and the results obtained were in agreement with the certified values. Verification that no spectral interferences were observed at the 193.7 nm arsenic line was also made using Zeeman-effect background correction for aluminium concentrations of up to 500 mg 1-I (about three times higher than in the sample digests). No significant arsenic (or alumin- ium) concentrations were observed in the blanks following di- gestion. Data Analysis by PLS A program was written to convert the ASCII files stored by the ETAAS software into a format suitable for evaluation by PLS using the SIMCA 3B pa~kage.2~ An editing program was also used which permitted the averaging of several absorbance signals.'3 The calibration set was constructed by ETAAS analysis of arsenic and aluminium standard solutions according to the ex- perimental design given in Table 3. Background corrected ab- sorbance data were collected from the spectrometer every 11 ms during the atomization step using the ETAAS software. The total number of data points acquired for the calibration set thus amounted to about 1.5 x 104 which cannot be convenient- ly handled by the personal computer therefore two methods of data reduction were used. First only the 240 points in the time interval 0.88-3.52 s were used for calibration purposes as the entire signal appeared in this temporal window (see also Fig.1). Second the four replicates at each calibration point were averaged. The latter procedure had no great effect on the predictive properties as verified by comparing results using PLS models based on both reduced and non-reduced data sets. 0.15 (a) L 0.15 9 0.075 0 2.5 5 VOL. 6 1 1 1 Reduction of the data set by signal averaging did on the other hand decrease the required computation time considerably. The results reported here are all based on the reduced data set as this permits fairly rapid processing (about 2 h in total). For the prediction of concentrations in the sediment samples no signal averaging was used so that an approximate assessment of the variations in the results could be made. A more thor- ough evaluation of the uncertainty in the predicted results in- cluding the effect of variance in the calibration set would require an alternative PLS alg~rithm,'~,'~ and is not considered further here.Results and Discussion Graphite Furnace Conditions Preliminary studies showed that the ashing conditions were not critical as the use of the palladium modifier was efficient in stabilizing arsenic to even higher temperatures than the 900 "C given in Table 2. However at higher ashing tempera- tures the arsenic signal appeared somewhat earlier in time before the tube wall temperature had stabilized during the atomization step. An ashing temperature of 900 "C was thus made to ensure a stablized tube wall temperature for the dura- tion of the absorbance pulses (see Fig. 1). For the atomization temperature 2000 "C was used which is lower than that typically recommended for arsenic deter- mination by ETAAS.2.4 At higher temperatures the arsenic peaks were narrower higher and of smaller area.Aluminium signals were also narrower and higher but were of greater area as expected from the larger degree of ionization at ele- vated temperatures. Furthermore the separation between the arsenic and aluminium peak maxima was reduced and thus the conditions for mathematically resolving these signal components were less favourable at temperatures above 2000 "C. It was also confirmed that none of the other sample compo- nents (phosphates iron cobalt)s.x were present in the dissolved sediments at sufficiently high concentrations to produce spec- tral interferences at the 193.7 nm arsenic line.This was achieved by preparing standard solutions having approximate- ly the same concentrations of these components as are present in the dissolved sediments using the relevant data from the certificates of analysis. The data given in Table 4 indicate that the measurement pre- cision is not very good. This may be partly owing to the use of 0.3 (4 0.3 A I Time/s Fig. 1 Averaged absorbance signals for the calibration set (Tables 3 and 4) (peak-area values are given in parentheses). (u) A 50 pg I-' As (peak area = 0.043); and B 10 mg I-' Al (0.073). ( h ) A 50 pg I-' As plus 100 mg I-' A1 (0.122) and B numerical addition of the two signals in (u) (0.1 16). (c) A 100 pg I-' As (0.074); and B. 200 mg I-' A1 (0.151). ( d ) A 100 pg I-' As plus 200 mg I-' A1 (0.241); and B numerical addition of the two signals in (c) (0.225).All signals have been corrected for the blank. Tube temperature (2000 "C) profile C is also shown in (0)112 JOURNAL OF ANALYTICAL A.TOMIC SPECTROMETRY MARCH 1991 VOL. 6 Table 4 Peak characteristics for the calibration set and sediment samples Peak characteristics* Sample Peak areat Peak height fFak/s 50 pg I-' As 100 pg I-' As 100 mg I-' Al 200 mg 1-' Al 50 pg I-' As + 100 mg I-' Al 100 pgl-IAs+ 200 mg I-' Al BCSS- 1 BCSS-1 + 50 pg 1-' As BCSS-1 + 100 pg I-' As MESS- 1 0.043 f 0.005 0.074 f 0.007 0.073 k 0.006 0.151 f 0.002 0.122 f 0.004 0.241 f 0.004 0. I55 f 0.005 0.194 k 0.017 0.228 f 0.010 0.164 f 0.010 0.072 f 0.005 0.127 f 0.007 0.087 f 0.006 0.161 k0.007 0.140 f 0.005 0.254 f 0.007 0.176 k 0.002 0.273 f 0.0 13 0.388 k 0.0 15 0.179 f 0.014 * Mean value f one standard deviation (n = 4).i Peak areas have been corrected for blanks. I .57 k 0.04 1.51 f 0.01 2.03 f 0.05 2.02 f 0.04 1.77 f 0.01 1.78 f 0.03 1.82 f 0.02 1.64 f 0.07 1.58 f 0.06 1.85 k 0.04 Table 4 the results of the univariate calibration approaches may be rejected.3O Tables 4 and 5 also show data and results for the determina- tion of arsenic in BCSS-1 using univariate calibration by the standard additions method. The peak area result is similar to (or as inaccurate as) that based on the calibration graph proce- dure indicating the lack of non-spectral interference effects in the arsenic determination. This is an important finding for the use of aqueous standard solutions in the multivariate calibra- tion procedure discussed below.Although the use of standard additions and peak height measurements gives an arsenic concentration closer to the certified value (see Table 5 ) the result is still seriously in error. We1z3l has also emphasized that the use of standard ad- ditions cannot correct for spectral interferences. Thus unvari- ate calibration is unsuitable for this application and for the analytical conditions used. The considerable danger of obtain- ing erroneous results by assuming that the peak height is unaf- fected by the presence of a component that causes spectral interference is also evident. manual pipetting but is mostly a result of drift in the arsenic lamp intensity which caused slight base-line shifts leading to some uncertainties in peak evaluation.Univariate Calibration For the instrumental conditions used here the arsenic peak absorbance is observed earlier in time than that of alumin- ium (see Table 4). However the peaks are not sufficiently separated to allow calibration based on the peak height method as has been done in several ETAAS applications where spectral interferences have been Indeed for the results given in Table 4 the arsenic concentrations evaluated on a univariate peak height basis would give results approximately four times higher than the certified values (Table 5 ) . Peak area results are even more seriously overestimated. It can be seen in Table 4 that the times at which the peak ab- sorbances occur (cFak) are significantly earlier for the pure arsenic standards relative to those samples which also contain aluminium.Harnly3O has suggested using various temporal characteristics to assess the accuracy of peak height and area measurements for analytes in the absence and presence of a matrix. On the basis of the differences in rPak apparent in Interaction Effects The experimental design shown in Table 3 allows the inclu- sion of interaction effects between arsenic and aluminium. That such an effect exists can be seen in Fig. 1. Here the average signals for the calibration samples are plotted togeth- er with those obtained by numerically adding the pure compo- nent absorbance profiles. All signals shown have had the average blank signals subtracted. It is obvious that while the leading edges of the signals are similar for the mixed standards (arsenic plus aluminium) and the added absorbance profiles [Fig. l(h) and (41 the peak heights are much greater and the tailing less in the former.This means that the signal shape ob- tained on atomizing arsenic and aluminium together is not simply a linear combination of the individual single-component signals. For this reason it is important for the PLS model to include interaction effects. l7 From the results given in Table 4 and Fig. 1 it is also obvious that there are some non-linearities present in the cali- bration set. Thus the PLS model will require more than two di- mensions to enable accurate predictions of the arsenic concentrations in unknown samples i.e. the system under consideration is not ideal (see Number of Significant PLS Dimensions under Theory).Fortunately the PLS method is capable of handling such non-linearities.I3.l7 Table 5 methods. Data from Table 4 Results for the determination of arsenic in sediments by ETAAS with continuum source background correction using univariate calibration Arsenic concentration/pg g-' Calibration graph Standard additions Sample Dilution factor Peak area Peak height Peak area Peak height Certified value BCSS-1 1 +335 69 46 72 27 1 1 . 1 f 1.4 MESS- 1 1 + 301 66 42 - - 10.6 k 1.2 Table 6 ate calibration* Results for the determination of arsenic and aluminium in sediments by ETAAS with continuum source background correction using multivari- Arsenic concentration@& g-' Aluminium concentration (96) Sample PLS t Certified PLSf Certified BCCS- 1 12.3 f 1.7 11.1 f 1.4 9.77 f 0.10 11.83 f 0.41 MESS- I 9.7 f 1.7 10.6 f 1.2 9.85 k 0.85 I 1.03 k 0.38 * A three-component PLS model was used which explained 99.7% and 99.5% of the variance in the response ( R ) and concentration (C) matrices t Error terms are one standard deviation of the concentrations obtained by fitting four individual absorbance signals to the PLS calibration model.respectively.JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY. MARCH 1991 VOL. 6 113 Time/s Fig. 2 Averaged absorbance signals for the sediment samples solid line BCSS-1; and broken line MESS-1. Signals have been corrected for the blank 16.7 11.1 13.47 11.83 -in 5.5 1 0 I T 10.6 A 10.19 5 C .- U I c 8 a 12.55 11.03 1 3 5 No. of PLS components Fig. 3 Predicted C arsenic and C aluminium concentrations in ( u ) BCSS- 1 and ( h ) MESS- 1 as a function of the number of PLS components used in the model.Solid line is the certified concentration and broken lines are the 95% confidence limits. Error bars are one standard deviation of the predicted concentrations for four individual absorbance signals fitted to the model Multivariate Calibration by PLS Modelling Average absorbance signals for the sediment samples are shown in Fig. 2 and it can be seen that the shapes closely correspond to those of the mixed arsenic plus aluminium standards in Fig. 1. The concentrations for these two species as determined by a three-component PLS model are reported in Table 6. Fig. 3 shows the predicted arsenic and aluminium concentrations for the two marine sediment reference materials as a function of the number of PLS dimensions employed in the model where it is clear that three components are optimum particularly with respect to arsenic in BCSS- 1 .One of the attractive features of multivariate calibration using PLS modelling is that both the analyte element and the spectrally interfering component can be determined simultane- ously by employing a suitable experimental design for the cali- bration set (see Table 6). However while acceptable results for arsenic are obtained the aluminium concentrations deter- mined are in error. This is probably owing to the presence of residual fluorides in the sample which severely depress the formation of free aluminium atoms32 (and hence ions) under the graphite furnace conditions used.Such an effect cannot be accounted for in a PLS model based on aqueous standard solu- tions as used here. An alternative experimenta1 design making standard additions of both aluminium and arsenic to sediment samples prior to construction of the PLS model,12 might improve the predictive capabilities for aluminium. This would of course complicate the calibration step being considerably more time consuming. Nevertheless the main objective of this work to determine arsenic in sediments accurately by ETAAS with continuum source background correction at the 193.7 nm line where severe spectral interferences from aluminium are present has been realized. Conclusions Multivariate calibration based on PLS modelling can be used to correct for spectral interferences in ETAAS.Although the spectral interference problems observed in the determination of arsenic in sediments can be avoided by selection of the less sensitive 197.2 nm wavelength6.I0 or using Zeeman-effect background correction? such alternatives might not always be convenient or indeed available. Thus the method used here may offer a solution to the general problem of background cor- rection errors in ETAAS. One disadvantage of this method may however lie in the need to know a priori the cause of the spectral interference and design the experiments accord- ingly. Furthermore a computer based data acquisition and storage system and access to suitable software,2s is necessary. This work was supported by the Swedish Centre for Environ- mental Research and the Natural Sciences Research Council.We are indebted to E. Lundberg Norrby Marine Research Laboratory Hornefors Sweden for the provision of the sedi- ment reterence materials and to B. Hiitsch Ringsdorff-Werke Bonn Germany for supplying us with graphite parts. The as- sistance of K. Olsson in dissolving the sediment samples and M. Berglund with the computer programs is also gratefully acknowledged. 1 2 3 4 5 6 7 8 9 10 I I 12 13 14 15 16 References L'vov B. V.. Spectrochirn. Actu. Port B 1978,33 153. Slavin W. Gruphite Fi4rnar.e AAS - A Source Book. Perkin-Elmer Norwalk CT 1984. Ediger R. D. At. Ahsorpt. NeM,sl. 1975 14 127. Schlemmer G. and Welz B. Spectrochirn. Actu. Part B 1986 41 1157. Saeed K. and Thomassen Y. Anal. Chirn. Actu 198 I 130,28 I . Riley K. W.At. Spectinsc. 1982 3 120. CRC Hutidhook of Chemistry utid Physics ed. Weast R . C. CRC Press Boca Raton FL. 62nd edn. 198 1 pp. E206-E2 10. Martinsen I. Radziuk B. and Thomassen Y . . J . A w l . At. Spec,ti-om. 1988.3 1013. Slavin W. and Camrick. G.R.. CRC Crir. Re\.. A w l . Cheni.. 1988 19,95. Bettinelli M. Pastorelli. N. and Baroni. V.. Anul. Chini. Aem 1986. 185 109. Wold S. Ruhe A. Wold. M.. and Dunn. W. J.. 111 SlAM .I. S . i . Stutist. Conrpiit. 1984. 5 735. Geladi. P.. and Kowalski. B. R.. A w l . Ckinr. Ac.tu 1985. 185 I . Baxter. D. C. and Ohman. J.. SpecmxAini. Ac.tu. Purt B. 1990. 45 481. Welz. B.. Atoniic Ahsoiptioii Specrronic>ti.\'. VCH. Weinheim. 2nd edn. 1985. p. 136. Ho C.-N.. Christian G. D. and Davidson. E. R.. A m / . Cheni.. 1978. 50 1 108. Saxberg B. E. H . and Kowalski B. R.. A w l . C/wni.. 1979. 51 1031.114 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 17 18 19 20 21 22 23 24 Lindberg W. Person J.-A. and Wold S . Anal. Chem. 1983 55 643. van Veen E. H. and de Lms-Vollebregt M. T. C. Spectrochim. Acra Part B 1990,45,313. Wold S. Technometrics 1978,29,397. Martens H. PhD Thesis Technical University of Norway Trond- heim 1985. Frech W. Baxter D. C. and Hutsch B. Anal. Chem. 1986 58 1973. Lundberg E. and Frech W. Anal. Chem. 1981.53 1437. Lundgren G. Lundmark L. and Johansson G. Anal. Chem. 1974 46 1028. Sturgeon R. E. Desaulniers J. A. H. Berman S. S. and Russel D. S . Anal. Chim. Acra 1982 134,283. 25 26 27 28 29 30 31 32 Wold S. SIMCA-3B Users Manual with Examples Research Group for Chemometrics Department of Organic Chemistry University of Umei 1983. Lorber. A. and Kowalski B. R. J. Chemometrics 1988,2,93. Lorber A. and Kowalski B. R. Appl. Specrrosc. 1988,42 1572. Sampson B. J. Anal. At. Spectrom. 1987,2,447. Jacobson B. E. and Locklitch G. Clin. Chem. 1988,34,709. Harnly J. M. J. Anal. At. Specrrom. 1988,3,43. Welz B. Ft-esenius 2. Anal. Chem. 1986,325,95. Dittrich K. CRC Crir. Rev. Anal. Chem. 1986 16 223. Paper 010292621 Received July 2nd I990 Accepted August 29th I990

ISSN:0267-9477    

DOI:10.1039/JA9910600109

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991 VOL. 6 1 I5 Determination of Low Concentrations of Lithium in Biological Samples Using Electrothermal Atomic Absorption Spectrometry* Barry Sampson Department of Chemical Pathology Charing Cross Hospital Fulham Palace Road London W6 8RF UK A method is described for the determination of endogenous lithium concentrations in serum and urine using electrothermal atomic absorption spectrometry. The method has also been applied to the analysis of nanolitre samples of micro-puncture fluid from rat kidney tubules containing pharmacological concentrations of lithium. The graphite tubes are coated in situ with tantalum to give improved sensitivity and increased pre-atomization stability. A mini-flow of gas at a flow-rate of 30 ml min-l is used during atomization to eliminate background interference.Background correction is not necessary. The characteristic mass is 0.98 pg of lithium. Serum samples are de- proteinized with an equal volume of 10% nitric acid before analysis. Urine samples are diluted 5-fold with 5% nitric acid. The normal range of serum lithium is up to 0.39 pmol I-' and normal urinary excretion is up to 9 pmol over a period of 24 h. Keywords Lithium; electrothermal atomic absorption spectrometry; tantalum coated tubes; serum; urine Lithium is used clinically to treat manic depression the thera- peutic concentration in plasma being 0.4-0.8 mmol 1-I.\ At this level the determination of lithium presents no problem and most clinical laboratories measure lithium routinely using air- propane flame emission spectrometry or air-acetylene flame atomic absorption spectrometry (FAAS).Ion-selective elec- trodes for lithium are also available. Naturally occurring concentrations of lithium are far lower than those used therapeutically (given above). The concensus from recent publications is that the normal serum concentra- tion is less than 1 pmol l-1.24 The flame techniques referred to are not sufficiently sensitive at this concentration. Standard flame photometers incorporating a fixed ratio pre-dilution of the sample with a reference solution of potassium or caesium can achieve a detection limit of 3&50 pmol 1-I. Flame atomic absorption spectrometry can give a detection limit for lithium in aqueous solutions of about 2 pmol 1-I but for real samples matrix effects raise this limit considerably.Flame emission spectrometry using a dinitrogen oxide-acetylene flame is much more sensitive2 and can rival electrothermal atomization in detection limits but is also subject to matrix effects with real samples. Flame assays also require comparatively large volumes of sample. Laboratories involved in clinical studies may be reluctant to install a dinitrogen oxide flame system for which there is little other application in clinical analysis. In- ductively coupled plasma mass spectrometry has also been used for low level lithium assays in clinical samples.6 The determination of lithium at these low concentrations is needed for several areas of study in medicine pharmacology and physiology. Examples from this laboratory include studies of the physiology of renal clearance of lithium in animals and humans and clinical studies.Animal studies include the deter- mination of lithium in nanolitre samples of kidney tubular fluid obtained by micro-puncture in experiments to study the renal handling of lithium in rats. This technique involves the collec- tion of tubular fluid \*;a a sharpened micropipette inserted into a superficial nephron in the exposed kidney of an anaesthetized animal. Analysis of the fluid obtained can provide valuable in- formation about renal tubular fun~tion.~ Renal clearance of lithium is used as a marker for proximal sodium and water re- sorptionx.' in the kidney. In clinical studies clearance of exoge- nous lithium at near pharmacological doses (serum concentration of up to 0.3 mmol 1-I) has been used however there is evidence that lithium may have dose related effects on * Presented at the Fifth Biennial National Atomic Spectroscopy Sympo- sium (BNASS) Loughborough.UK 18th-20th July. 1990. sodium clearance. It has been suggested that measurement of the clearance of endogenous lithium may give equally valid results without the need for the administration of a pharmaco- logically active susbtance.' A further application is the study of the absorption of lithium from a topically applied ointment containing lithium succinate that is used to treat skin condi- tions;IoJ1 such treatment has been applied to the control of uraemia induced pruritis.I2 Measurements of low lithium con- centrations have also been used to monitor industrial exposure to lithium resulting from the use of lithium alloy^.^"^^ Electrothermal atomization techniques should provide a sen- sitive assay but there are severe matrix interferences notably from inorganic components of the sample.s The addition of ammonium nitratels and/or potassium phosphateI6 have been used to minimize these intereferences and to stabilize the lithium during the pre-atomization step; however in most in- stances matrix-matched standards have been required. Lithium carbide formation is also a problem in the furnace.Use of tan- talum foil a tantalum boat or a tantalum carbide coated tube have been proposed as possible solutions.s Published methods for using coated tubes have normally used tubes pre-soaked in a solution of the coating metal often dissolved in hydrofluoric acid at reduced p r e ~ s u r e .~ . ~ ~ A recently published method for the determination of lithium in micro-puncture samples in- volved direct deposition of up to 6 nl of sample onto a tanta- lum platform which was then inserted into the furnace.'* Background correction has also been required in most assays. The method presented here involves coating of the tube in situ with a water soluble salt of tantalum eliminating the need for hydrofluoric acid solutions. Background correction is not required. Experimental Apparatus All work was performed with a Perkin-Elmer 3030 atomic ab- sorption spectrometer with an HGA 600 furnace and AS-60 autosampler. For background absorption studies a hollow cathode lamp with neon fill gas was used.Perkin-Elmer pyro- lytic graphite coated graphite tubes were used for all experi- ments. Argon was used as the purge gas except where oxygen was used as indicated. Results and peak plots were recorded on a Perkin-Elmer PR 100 printer. Atomic emission spectrometry of samples containing high concentrations of lithium was performed using an IL 943 flame photometer with a diluent containing caesium.116 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 1991. VOL. 6 Reagents A lithium standard solution 1 mmol I-I (IL flame photometer standard with I40 mmol 1-1 of Na and 5 mmol I-' of K) was diluted to a stock standard of 40 pmol I-' in 1% v/v nitric acid (BDH Poole Dorset UK Aristar grade). Working standards were prepared as required by dilution with de-ionized water.Ammonium nitrate and ammonium phosphate modifier solu- tions were prepared by mixing equimolar amounts of ammonia solution and nitric acid or ammonia solution and phosphoric acid ( 2 + 1). All reagents were BDH Aristar grade. Triton X- 100 (BDH scintillation grade) was added to the modifiers as indicated. In the initial experiments the tantalum modifier solution was tantalum AAS standard ( 1 g I-' as ammonium hexafluorotantalate in water Aldrich Gillingham Dorset UK). A revised method was later adopted using a saturated solution of ammonium heptafluorotantalate (about 50 g I-' of tantalum) (Aldrich) was used. Other reagents used were of Aristar grade or equivalent where possible otherwise the purest grade available was used. Sample Collection Blood samples were collected in cleaned 10 ml polystyrene tubes or 10 ml glass Vacutainer tubes (Becton-Dickinson Toronto Canada) and allowed to clot.The serum was separat- ed into 3 ml polystyrene tubes and stored frozen (-20 "C) until analysed. No difference was observed in the results from the different tube types and no lithium contamination was detect- ed. Twenty-four hour urine samples were collected in 4.5 1 polyethylene bottles without any added preservative. Aliquots were transferred into 25 ml polystyrene universal containers and stored frozen. The final step in the preparation of the serum samples was to precipitate the proteins with an equal volume of 10% v/v nitric acid. Urine samples were diluted 5- fold with 5% v/v nitric acid. Micro-puncture samples from rat kidneys were collected with glass constriction pipettes of 3&70 nl capacity and diluted with 50 p1 of de-ionized water in polystyrene microvi- als (400 p1 capacity) for direct use in the furnace autosampler. Samples were stored frozen until analysed.The dilution of these samples was at least 1000-fold and they were treated as pure aqueous solutions for analysis. Table 1 flow of 300 ml min-' was used throughout the programme Furnace programme for tantalum coating of tubes. An argon gas Hold/s Step TemperatureTC Ramp/s I * 2* 3* 4 80 120 600 2500 20 I 99 10 5 10 I 5 * 75 or 99 pl sample volume injected and programme steps 1-3 repeat- ed up to ten times before step 4. Table 2 analysis Instrumental parameters and furnace programme for sample Instrumentul puiumeters- Wavelength 670.8 nm Slit width 0.7 mm Measurement Integrated absorbance Integration time 5 s Sample volume 25 pl Replicates 2 Furnace progiumme- Step TemperatureTC Ramp/s Hold/s rate/ml min-' Read Internal gas flow- - 1 90 1 1 300 2 120 20*/30t 5 300 - 300 1*/5t 5*/10f 3 1250 4 20 1 10 300 5 2100 0 5 30 On 6 2400 I 5 300 - - - * Water and micro-puncture samples. t Serum and urine samples.Table 3 pmol I-' lithium standard Effect of tantalum coating on the signal from 20 p1 of 1 Amount of tantalum/mg Peak area/A s 0 0.1 I .0 5.0 0.035 f 0.002 0.280 f 0.004 0.290 f 0.004 0.300 k 0.003 Results and Discussion Method Development It was found that careful alignment of the furnace and selec- tion of atomization temperature was needed to minimize inter- ference from emission from the hot graphite tube during atomization.It is also important to use the lowest possible atomization temperature in order to minimize emission. The atomization characteristics of lithium were studied in aqueous solutions with and without the addition of chemical modifiers. Without any additions it was found that the maximum pre-atomization temperature possible was less than 750 "C. An atomization temperature of 2100 "C was used as this gave the optimum compromise between analytical sensi- tivity and low emission noise. While the addition of phosphate results in increased stability of the lithium and can allow the use of higher pre-atomization temperatures it can also contrib- ute to non-specific absorbance. The peak shape was poor; con- siderable tailing was observed on numerous occasions as the absorbance had not returned to the base line within 10 s of atomization.Tubes were coated with tantalum by replicate injections of 99 p1 of the 1 g I-' modifer solution with a furnace pro- gramme drying the solution between each injection at the tem- peratures indicated in Table 1. About 1 mg of tantalum was deposited in the tube. The tube was taken through several com- plete programmes (Table 2 ) until no further signal was record- ed. Both the phosphate modifier and tantalum coating allow the use of higher pre-atomization temperatures; the phosphate modifier gives a similar sensitivity compared with untreated tubes and the tantalum coating provides a higher sensitivity. The benefit of tantalum coating is shown in Table 3.Uncoated graphite tubes were used in some early experiments but showed a low sensitivity. Tantalum coated tubes were used for all subsequent work. By using the saturated solution of tanta- lum slightly improved results for sensitivity were obtained and the sensitivity remained constant for longer. The tube coating process was also much faster. Two replicate injections of 75 1.11 were used. By using this technique the characteristic mass (0.0044 A s) is 0.98 k 0.14 pg (ten determinations). Despite the improve- ment shown with tantalum tailing can remain a minor problem and with high-concentration samples at least 5 s are required for the signal to return to the base line. Micro-puncture Samples Micro-puncture samples can be analysed by use of the method developed up to this point.As stated above it was considered possible to treat the samples as pure aqueous solutions and they were assayed against aqueous standards. Errors may ariseJOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY. MARCH 1991 VOL. 6 117 Table 4 Accuracy of micro-puncture sample analysis Concentration calculated/ Concentration found/ mmol I-' mmol I-' 0.42 0.36* 0.72 0.62 0.9 1 0.84 1.37 1.41 1.87 I .86 * Mean of two samples. Table 5 Effect of internal gas flow-rate during atomization on lithium absorbance measured as peak area and background signal. Sample 30 pl of undiluted normal urine; and lithium concentration approximately 1.5 pmol 1-I Internal gas flow-rate/ml min-' LithiumlA s BackgroundtA s 300 200 100 50 30 10 0 0.14 - 0.I9 - 0.24 - 0.28 0.004 0.30 0.007 0.31 0.018 0.3 1 0.027 in these experiments owing to uncertainty in the exact volume of the constriction pipettes which were made in the labora- tory. Although accuracy could not be assessed from recovery experiments because of the small volumes involved it was as- sessed in two alternative ways. One method was to prepare di- lutions of standard solutions in the same manner as samples using the same constriction pipettes. The results are shown in Table 4. Accuracy was also determined by comparing results obtained by analysing serum samples containing pharmacolog- ical amounts of lithium after a 1000-fold dilution (Fig. 1). Within-batch precision of the micro-puncture fluid assay was assessed by repeated injection of a single sample into the furnace.At all concentrations the within-batch precision found was 1-2%. The detection limit (3 x standard deviation of the blank) is 0.04 Fmol 1-1. Serum Samples As the deuterium arc background corrector cannot function at the long wavelength (670.8 nm) of lithium the presence of background absorption was assessed by measuring absorbance at the non-resonance line of 671.6 nm obtained from a neon filled hollow cathode lamp. For this study urine diluted with an equal volume of 10% nitric acid was used. Using gas-stop during atomization was found to give a rapid but significant smoke peak. Introducing a mini-flow of argon gas during atomization reduced this to negligible amounts (Fig. 2) but had a smaller effect on the lithium atomization signal (Table 5).A gas flow-rate of 30 ml min-I was found to be adequate. For the determination of lithium in serum attempts were first made to assay samples after aqueous dilution. A sample dilution of 1 + 1 with 0.1% v/v Triton X-100 and a 30 pl sample volume gave adequate sensitivity. Oxygen ashing was introduced to minimize the build-up of carbon residues in the tube however this was found to cause a decrease in the life- time of the tube and marked changes in sensitivity were ob- served during a batch of 30 samples. The oxygen ashing step was felt to be the major contributor to the problems encountered. A modification which involved de-proteinizing the samples with an equal volume of 10% nitric acid containing 100 mg 1-I tantalum was introduced. The tantalum was added to replenish the tantalum coating on the graphite tube surface otherwise it was found that the sensi- tivity decreased during a run although the tube life was greater than 400 firings.In subsequent work when a higher density of tantalum coating (up to 5 mg per tube) was used the c '- 2.0 3 0 0.4 0.8 1.2 1.6 2.0 Li concentration (AESVmmol I-' Fig. 1 Comparison of assays by atomic emission spectrometry (AES) and electrothermal atomic absorption spectrometry (AAS) for samples with pharmacological concentrations of lithium. Samples for AAS were diluted 1 + lo00 with water before assay. The equation of the line is given by v = 1.03s - 2.85 x correlation coefficient ( R 2 ) = 0.94 0.05 (a) 0.025 - 0 5.0 Time/s Fig. 2 Comparison of background absorbance (671.6 nm) for urine with (a) internal gas flow-rate of 30 ml min-' or (h) gas stop during atomiza- tion.Sample 30 pl of undiluted normal urine; and Li concentration ap- proximately 1.5 pmol I-' loss of sensitivity was found to be reduced and tantalum was no longer added to the de-proteinizing solution. The furnace programme used is shown in Table 2. The slopes of standard additions lines for de-proteinized serum were similar to aqueous standards and aqueous calibra- tion was used. Recovery experiments using aqueous standards gave good recoveries (Table 6). Within-batch precision for normal serum was 7.8% at a concentration of 0.15 pmol I-'. Between batch precision using the same serum was 19% ( n = 7). Urine Samples For the initial studies on urine samples the same methods as for serum samples were used however at a 1 + 1 dilution there was a marked variation in the standard additions slopes.By using a higher dilution and/or smaller sample volume this variation was reduced but remained significant for some urine samples. The reason for the high variability has not been in- vestigated but is thought to be due to the calcium and/or phos- phate content. Urine samples were assayed at a 5-fold dilution with 5% nitric acid and a recovery sample was included with118 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY MARCH 199 I VOL. 6 Table 6 Recovery of lithium from serum and urine Lithium added/ Lithium found/ Sample pmol I-' pmol I-' Recovery* (96) Serum 0.5 0.47-0.58 101 f8 1 .o 0.9 1-1.16 101 f 10 2.0 I .76-2.05 9 5 f I I Urine 1 .o 0.90-1.07 98 f 8 *Recovery f standard deviation n = 7.Table 7 Results of assays on clinical samples Lithium/pmol I-' Sample Median Range Serum- Normal subjects 0.17 0.05-0.39 (n = 19) Chronic renal failure 0.53 0.39-1.28 (n = 10) Normal subjects 1 S O 0.264.9 (n = 13) Urine- 3.8 0.5-9. I (pmol per 24 h) each urine. If the recovery was low the assay was repeated using standard additions. The furnace programme used was the same as for serum samples. Recovery data for the urine assay are given in Table 6. Within-batch precision for normal urine at a concentration of 2 pmol 1-i was 2.5% and between-batch precision was 9.8%. Clinical Samples Serum samples from normal subjects and from patients with chronic renal failure treated by haemodialysis or peritoneal dialysis and urine samples from normal subjects (Table 7) were analysed.Most normal subjects have serum lithium levels not much above the detection limit of the assay. Patients with chronic renal failure have higher concentrations but there is no clinical significance associated with this. The urine lithium ex- cretion in normal subjects is variable and may be related to dietary intake." Conclusions The use of tantalum coated tubes is shown to give an en- hanced sensitivity for lithium determination in the electrother- mal atomizer. In situ coating of the tubes with the water soluble ammonium heptafluorotantalate is rapid and avoids the need for use of hydrofluoric acid solutions. Tantalum coating allows the use of higher pre-atomization temperatures. Use of a mini-flow of argon at a flow-rate of 30 ml min-1 in the furnace during atomization gives a substantial reduction in the residual background absorbance with a minimal effect on assay sensitivity.The assay has been applied to lithium deter- mination in nanolitre volumes obtained from rat kidney micro-puncture experiments and to serum and urine. Serum is de-proteinized with nitric acid before being assayed; urine samples are diluted with nitric acid. This assay may be suit- able for the determination of lithium in samples other than those used here. I wish to thank Drs. S. Walter and D. Shirley Department of Physiology Charing Cross and Westminster Medical School for the micro-puncture samples Prof. G. MacGregor and Dr. D. Singer Department of Medicine St. Georges Hospital Medical School for some of the patient samples and Dr.J. R. Curtis Department of Medicine Charing Cross and Westmin- ster Medical School for samples from patients with chronic renal failure. 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 References Srinavasen D. P. and Hullin R. P. Br. J. Hosp. Med. 1980,24,466. Matusiewicz H. Anal. Chim. Actu 1982 136,215. Miller N. L. Durr J. A. and Alfrey A. C. Anal. Biochem. 1989 182,245. Fridrich L. Zazgomik J. Kopsa H. Schmidt P. Hinterberger W. and Maly K. J. Clin. Chem. Clin. Biochem. 198 I 19,672. Shen L. Shan X.-q.. and Ni Z.-m. J. Anal. At. Spectrom. 1988 3 989. Abou-Shakra F. R. Havercroft J. M. and Ward N. I. Truce Elem. Med. 1989,6 142. Quamme G. A. and Dirks J. H. Kidney Int. 1986,30 152. Thomsen K. Nephron 1984,37,2 17. Thomsen K. Kidney Inr. 1990,37 (suppl. 281 S10. Skinner G. B. Lancet 1983,2,288. Boyle J. and Burton J. L. BI-. Med. J. 1986,292,28. Sampson B. Curtis J. R. Stewart J. C. M. and Cream J. J. Truce Elem. Med.. in the press. Barber D. Braithwaite R. A. and Brown S. S. Proceedings of the National Meeting of the Association of Clinical Biochemists Birmingham UK 15-19 May 1989 A61. Bencze K. Pellikan Ch. and Kronseder A. Arfzl. Luh. 1989 35 102. Ehrlich B. E. and Diamond J. M. Biochem. Biophvs. A m 1978 532,264. Trapp G. A. Anal. Biochem. 1985,148 127. Zatka V. J. Anal. Chem. 1978,50,538. Willis. L. R. Broughton M. C. and Foster R. Kidney Int. 1990,37 575. Paper- Ol03313H Received July 24th I990 Accepted October- 5th 1990

ISSN:0267-9477    

DOI:10.1039/JA9910600115

出版商:RSC    

年代:1991

数据来源: RSC