摘要:

'""Ana I y s tThe Analytical Journal of The Royal Society of ChemistryAnalytical Editorial BoardChairman: J. N. Miller (Loughborough, UK)M. Cooke (Sheffield, UK)C. S. Creaser (Nottingham, UK)A. G. Davies (London, UK)J. M. Gordon (Cambridge, UK)G. M. Greenway (Hull, UK)S. J. Hill (Plymouth, UK)D. L. Miles (Keyworth, UK)A. G. Fogg (Loughborough, UK)R. M. Miller (Gouda, The Netherlands)B. L. Sharp (Loughborough, UK)M. R. Smyth (Dublin, Ireland)Y. Thomassen (Oslo, Noway)P. Vadgama (Manchester, UK)Advisory BoardJ. F. Alder (Manchester, UK)A. M. Bond ( Victoria, Australia)J. G. Dorsey (Cincinnati, OH, USA)L. Ebdon (Plymouth, UK)A. F. Fell (Bradford, UK)J. P. Foley (Villanova, PA, USA)M. F. Gine (Sao Paulo, Brazil)T. P. Hadjiioannou (Athens, Greece)W.R. Heineman (Cincinnati, OH, USA)A. Hulanicki (Warsaw, Poland)I. Karu be (Yokohama, Japan)E. J. Newman (Poole, UK)J. Pawliszyn (Waterloo, Canada)T. B. Pierce (Hawell, UK)E. Pungor (Budapest, Hungary)J. RGiiCka (Seattle, WA, USA)R. M. Smith (Loughborough, UK)K. Stulik (Prague, Czechoslovakia)J. D. R. Thomas (Cardiff, UK)J. M. Thompson (Birmingham, UK)K. C. Thompson (Sheffield, UK)P. C. Uden (Amherst, MA, USA)A. M. Ure (Aberdeen, UK)C. M. G. van den Berg (Liverpool, UK)A. Walsh, KB (Melbourne, Australia)J. Wang (Las Cruces, NM, USA)T. S. West (Aberdeen, UK)Regional Advisory EditorsFor advice and help to authors outside the UKProfessor Dr. U. A. Th. Brinkman, Free University of Amsterdam, 1083 de Boelelaan, 1081 HVAmsterdam, THE NETHERLANDS.Professor P.R. Coulet, Laboratoire de Genie Enzymatique, EP 19 CNRS-Universite ClaudeBernard Lyon 1, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex,FRANCE.Professor 0. Osibanjo, Department of Chemistry, University of Ibadan, Ibadan, NIGERIA.Professor F. Palmisano, Universita Degli Studi-Bari, Departimento di Chimica CampusProfessor K. Saito, Coordination Chemistry Laboratories, Institute for Molecular Science,Professor M. Thompson, Department of Chemistry, University of Toronto, 80 St. GeorgeProfessor Dr. M. Valcarcel, Departamento de Quimica Analitica, Facultad de Ciencias,Professor J. F. van Staden, Department of Chemistry, University of Pretoria, Pretoria 0002,Professor Yu Ru-Qin, Department of Chemistry and Chemical Engineering, Hunan University,Professor Yu.A. Zolotov, Kurnakov Institute of General and Inorganic Chemistry, 31 LeninUniversitario, 4 Trav. 200 Re David-70126 Bari, ITALY.Myodaiji, Okazaki 444, JAPAN.Street, Toronto, Ontario, CANADA M5S 1Al.Universidad de Cordoba, 14005 Cordoba, SPAIN.SOUTH AFRICA.Changsha, PEOPLES REPUBLIC OF CHINA.Avenue, 117907, Moscow V-71, RUSSIA.Editorial Manager, Analytical Journals: Janice M. GordonEditor, The AnalystHarpal S. MinhasThe Royal Society of Chemistry,Thomas Graham House, Science Park,Milton Road, Cambridge, UK CB4 4WFTelephone +44(0)223 420066.Fax +44(0)223 420247. Telex No. 818293 ROYAL.US Associate Editor, The AnalystDr Julian F. TysonDepartment of Chemistry,University of Massachusetts,Amherst MA 01003, USATelephone +1 413 545 0195Fax +1 413 545 4846Assistant EditorsSarah Williams Yasmin KhanEditorial Secretary: Claire HarrisAdvertisements: Advertisement Department, The Royal Society of Chemistry, BurlingtonHouse, Piccadilly, London, UK WIV OBN.Telephone +44(0)71-287 3091. Telex No. 268001.Fax +44(0)71-494 1134.Information for AuthorsFull details of how to submit material forpublication in The Analyst are given in theInstructions to Authors in the January issue.Separate copies are available on request.The Analyst publishes papers on all aspectsof the theory and practice of analyticalchemistry, fundamental and applied, inor-ganic and organic, including chemical,physical, biochemical, clinical, pharma-ceutical, biological, environmental, automa-tic and computer-based methods. Papers onnew approaches to existing methods, newtechniques and instrumentation, detectorsand sensors, and new areas of applicationwith due attention to overcoming limitationsand to underlying principles are all equallywelcome. There is no page charge.The following types of papers will beconsidered :Full research papers.Communications, which must be on anurgent matter and be of obvious scientifjcimportance.Rapidity of publication ISenhanced if diagrams are omitted, but tablesand formulae can be included. Communica-tions receive priority and are usually pub-lished within 5-8 weeks of receipt. They areintended for brief descriptions of work thathas progressed to a stage at which it is likelyto be valuable to workers faced with similarproblems.A fuller paper may be offeredsubsequently, if justified by later work.Although publication is at the discretion ofthe Editor, communications will be ex-amined by at least one referee.Full critical reviews, which must be acritical evaluation of the existing state ofknowledge on a particular facet of analyticalchemistry .Every paper (except Communications) willbe submitted to at least two referees, bywhose advice the Editorial Board of TheAnalystwill be guided as to its acceptance orrejection. Papers that are accepted must notbe published elsewhere except by per-mission. Submission of a manuscript will beregarded as an undertaking that the samematerial is not being considered for publica-tion by another journal.Regional Advisory Editors.For the benefitof potential contributors outside the UK andN. America, a Group of Regional AdvisoryEditors exists. Requests for help or advice onmatters related to the preparation of papersand their submission for publication in TheAnalystcan be sent to the nearest member ofthe Group. Currently serving RegionalAdvisory Editors are listed in each issue ofThe Analyst.Manuscripts (four copies typed in doublespacing) should be addressed to:H. S. Minhas, Editor, orJ. F. Tyson, US Associate EditorParticular attention should be paid to the useof standard methods of literature citation,including the journal abbreviations definedin Chemical Abstracts Service Source Index.Wherever possible, the nomenclatureemployed should follow IUPAC recommen-dations, and units and symbols should bethose associated with SI.All queries relating to the presentation andsubmission of papers, and any correspon-dence regarding accepted papers andproofs, should be directed either to theEditor, or Associate Editor, The Analyst.Members of the Analytical Editorial Board(who may be contacted directly or via theEditorial Office) would welcome comments,suggestions and advice on general policymatters concerning The Analyst.Fifty reprints are supplied free of charge.The Analyst (ISSN 0003-2654) is published monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road,Cambridge, UK CB4 4WF.All orders, accompanied with payment by cheque in sterling, payable on a UK clearing bank or in US dollars payableon a US clearing bank, should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road,Letchworth, Herts, UK SG6 1 HN. Turpin Distribution Services Ltd., is wholly owned by the Royal Society of Chemistry. 1994Annual subscriptionrate EC f340.00, USA $641.00, Canada f384.00 (excl. GST), Rest of World f366.00. Purchased with Analytical Abstracts EC f718.00, USA$1351 .OO, Canada f811 .OO (excl. GST), Rest of World f772.00. Purchased with Analytical Abstracts plus Analytical Proceedings EC f851 .OO, USA$1601 .OO, Canada f961 .OO (excl. GST), Rest of World f915.00. Purchased with Analytical Proceedings EC f432.00, USA $812.00, Canada f487.00(excl. GST), Rest of World f432.00. Airfreight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003.USA Postmaster: Send address changes to: The Analyst, Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003. Second classpostage paid at Jamaica, NY 11431. All other despatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outsideEurope. PRINTED IN THE UK. 0 The Royal Society of Chemistry, 1994. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of thepublishers

ISSN:0003-2654    

DOI:10.1039/AN99419FX031

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

ANALAO 119(8) 1641-1924,99N-l12N (1994) AUGUST 1994TUTORIAL REVIEWREVIEW'"An al y s tThe analytical journal of The Royal Society of ChemistryCONTENTS1641 Environmental Sensors Based on Atomic Fluorescence-P. B. Stockwell, W. T. Corns1647 Lead Hydride Generation Atomic Absorption Spectrometry: an Alternative to Electrothermal AtomicAbsorption Spectrometry-Yolanda Madrid, Carmen Camara1659 Orthogonal Array Design as a Chemometric Method for the Optimization of Analytical Procedures. Part 1.Two-level Design and Its Application in Microwave Dissolution of Biological Samples-Wei Guang Lan,Ming Keong Wong, Ni Chen, Yoke Min Sin1669 Orthogonal Array Design as a Chemometric Method for the Optimization of Analytical Procedures. Part 2.Four-level Design and Its Application in Microwave Dissolution of Biological Samples-Wei Guang Lan,Ming Keong Wong, Ni Chen, Yoke Min Sin1677 Characterization of Inductively Coupled Plasma Mass Spectrometry With Segmented-flow Injection-JaneM.Craig, Diane Beauchemin1683 Microwave Digestion for the Determination of Arsenic, Cadmium and Lead in Seafood Products byInductively Coupled Plasma Atomic Emission and Mass Spectrometry-Brenda S. Sheppard, Douglas T.Heitkemper, Cynthia M. Gaston1687 Development of a High-performance Liquid Chromatographic-Inductively Coupled Plasma Method forSpeciation and Quantification of Silicones: From Silanols to- Polysiloxanes-S. B. Dorn, E. M. Skelly Frame1695 Direct Analysis of Milk for Aluminium Using Electrothermal Atomic Absorption Spectrometry-Marco A.Z.Arruda, Ma. Jose Quintela, Mercedes Gallego, Miguel Valcarcel1701 Low-volume Microwave Digestion of Marine Biological Tissues for the Measurement of Trace Elements-S.Baldwin, M. Deaker, W. Maher1705 Determination of Metallic Elements in Catalysts by Flame Atomic Absorption Spectrometry FollowingMicrowave'Energy-assisted Dissolution of Samples-Oswald Platteau, Dolores Casabiell1715 Comparison of Two Digestion Methods for the Determination of Selenium in Biological Samples-Veronique Ducros, Daniel Ruffieux, Nicole Belin, Alain Favier1719 Sensitive Atmospheric Pressure Detection of Nitroaromatic Compounds and NO, ( x = 1,2) Molecules in anIonization Chamber Using Resonance-enhanced Multi-photon Ionization-A. Marshall, A. Clark, R.M.Deas, C. Kosmidis, K. W. D. Ledingham, W. Peng, R. P. Singhal1725 Characterization of Doped Strontium Sulfide Thin Films by Secondary Ion Mass Spectrometry, RutherfordBackscattering Spectrometry and X-ray Fluorescence Spectrometry-Sari Lehto, Pekka Soininen, LauriNiinisto, Jari Likonen, Reijo Lappalainen1741 Analytical Strategies to Confirm Scotch Whisky Authenticity-Ross I. Aylott, Angus H. Clyne, Anthony P.Fox, David A. Walker1747 4-( 1 -Methylphenanthro[S, 1 O-d]imidazol-2-yl)benzohydrazide as Derivatization Reagent for CarboxylicAcids in High-performance Liquid Chromatography With Conventional and Laser-induced FluorescenceDetection-Tetsuharu Iwata, Tsuyoshi Hirose, Masaru Nakamura, Masatoshi Yamaguchi1753 Automated Determination of Weakly Acidic and Basic Pollutants in Surface Water by On-line ElectrodialysisSample Treatment and Column Liquid Chromatography-Matthieu G.M. Groenewegen, Nico C. van deMerbel, Jaroslav Slobodnik, Henk Lingeman, Udo A. Th. Brinkman1759 Determination of Strontium-90 in Water and Urine Samples Using Ion Chromatography-J. Cobb, P.Warwick, R. C. Carpenter, R. T. Morrison1765 Determination of Protein and Fat in Meat by Transmission Fourier Transform Infrared Spectrometry-B.Dion, M. Ruzbie, F. R. van de Voort, A. A. Ismail, J. S. Blais1773 Derivative Fourier Transform Infrared Spectrometric Determination of Ethanol in Beers-Maxim0Gallignani, Salvador Garrigues, Miguel de la Guardia1779 Analysis of Cotton-Polyester Yarns by Near-infrared Reflectance Spectroscopy-Marcel0 Blanco, JordiCoello, Hortensia Iturriaga, Santiago Maspoch, Enriqueta BertranTypeset and printed by Black Bear Press Limited,Cambridge, EnglandContinued on inside Back Cover-0003-2654C199418:l-178717931797180118071813181982582983583984384985385986386787587988388789189389990390791 5Separation and Sensitive Determination of Metal Ions by Capillary Zone Electrophoresis With 2-(5-Bromo-2-pyridylazo)-5-( N-propyl-N-sulfopropylamino)phenol-Shoji Motomizu, Mitsuko Oshima, MasayoshiKuwabara, Yoshimitsu ObataModified Method for the Determination of Unsaponifiable Matter in Oils and Fats-Leopold Hartman,Hudson Soares Viana, Suely FreitasDetection of Phencyclidine in Urine Using a Polarization Fluoroimmunoassay-John C.Gooch, GerardGallacher, John G. Wright, lmtiaz Mahmood, Ahmad Siddiqui, David L. Colbertlmmunoassay for Parathion Without its Prior Removal From Solution in Hexane-John M. Francis, Derek H.CrastonRapid Determination of Total Biomass from a Yeast Fermentation Using Sequential Injection-P. J. Baxter,G. D. Christian, J. RGiiCkaFlow Injection Potentiometric and Voltammetric Stripping Analysis Using a Dialysis Membrane CoveredMercury Film Electrode-Joseph H. Aldstadt, Dewey F. King, Howard D. DewaldSensitive Determination of Periodate and Tartaric Acid by Stopped-flow Chemiluminescence Spectrometry-Abaji Gaikwad, Manuel Silva, Dolores Perez-BenditoPhotokinetic Determination of Riboflavin and Riboflavin 5’-Phosphate Using Flow Injection WithChemiluminescence Detection-Tomas Perez-Ruiz, Carmen Martinez-Lozano, Antonio Sanz, VirginiaTomasDetermination of Trace Amounts of Urea by Using Flow Injection With Chemiluminescence Detection-Xincheng Hu, Norimichi Takenaka, Masaru Kitano, Hiroshi Bandow, Yasuaki Maeda, Masaharu HattoriPulse Coulometric Titration in Continuous Flow-Anastas Dimitrov Dakashev, Veselina Todorova DimitrovaContinuous-flow System for the Accurate Determination of Low Concentrations of Ammonium Ions Using aGas-permeable Poly(tetrafluoroethy1ene) Tube Decontaminator and an Ammonia Gas-sensing MembraneElectrode-Hirokazu Hara, Susumu MatsumotoApplication of Biosensor With Amperometric Detection for Determining Ethanol-Maria Varadi, NoraAdanyiScreen-printed Glucose Strip Based on Palladium-dispersed Carbon Ink-Joseph Wang , Qiang ChenAldehyde-selective Polymeric Membrane Electrodes Based on a Calix[4]arene lonophore-Wing HongChan, Pei Xiang Cai, Xiao Hong GuPreconcentration and Voltammetric Measurement of Silver(i) With a Carbon Paste Electrode Modified With2,9-Dichloro-l,1 O-phenanthroline-Surfactant-Sha-Sheng Huang, Zhan-Guang Chen, Bi-Fen Li, Hui-GaiLin, Ru-Qin YuSilica Gel Modified With Zincon as a Sorbent for Preconcentration or Elimination of Trace Metals-RyszardKocjanDetermination of Endosulfan by Stripping Voltammetry-Halliah Gurumallesh Prabu, ParamasivamManisankarElectrochemical Study of Solvent Extraction With Quinolin-8-01 as Complexing Agent.Part 2. Mechanism ofElectrochemical Extraction of Cadmium and Some Other Divalent Metals lons-Xiaohui Liu, Xingen Lu,Sinru LinAccuracy of the Measurement of Purity of Sulfamic Acid by Coulornetric Titration-Akiharu Hioki, AkiraKokubun, Masaaki KubotaSpectrophotometric Method for the Determination of Total Tobacco Alkaloids and Nicotine-Manish Rai, K.N.Ramachandran, V. K. GuptaDetermination of Aluminium, Titanium and Iron Oxides in Wet-processed Phosphoric Acid by ExtractionSpectrophotometry-L. Costadinnova, N. Elenkova, T. NedeltchevaDetermination of Micro Amounts of Lanthanoids in Cast Iron after Solid-Liquid Extraction WithDiethyldithiocarbamate-Xinzhen Du, Jingguo Hou, Su Zhao, Jingwan Kang, Jinzhang GaoSensitive Spectrophotornetric Determination of Zirconium With pAcetylchlorophosphonazo in thePresence of Sodium Dodecylbenzenesulfonate-Qing-Zhou ZhaiSpectrophotometric Determination of Carbon Tetrachloride Based on a Photoactivated Colour Reaction-Anjali PalSpectrofluorimetric Determination of Molybdenum in Vegetal Tissues and a Pharmaceutical CompoundWith Alizarin Red S in Micellar Medium-A.M. Garcia CampaAa, F. Ales Barrero, M. Roman Ceba, A.Fernandez GutierrezFluorescent Detection of Hydrazine, Monomethylhydrazine, and 1,l -Dimethylhydrazine by DerivatizationWith Aromatic Dicarbaldehydes-Greg E. Collins, Susan L. Rose-PehrssonDetermination of Salicylic and Gentisic Acids in the Presence of Each Other by Matrix lsopotentialSynchronous Fluorescence Spectrometry-Jose Antonio Murillo Pulgarin, Aurelia Alanon MolinaContinued on Facing Page1921 CUMULATIVE AUTHOR INDEX99N Book Reviews104N Conference Diary109N Courses11 1 N Papers in Future Issues11 2N RSC Awards1 12N Benedetti-Pichler AwardCover picture: The Glasgow resonance-enhanced multiphoton ionization system. Reproduced by kindpermission of the laser ionization studies group, Department of Physics and Astronomy, University ofGlasgow

ISSN:0003-2654    

DOI:10.1039/AN99419BX033

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, August 1994, Vol. I I 9 99N Book Reviews Hand book of Nea r-lnf rared Analysis Edited by Donald A. Burns and Emil W. Ciurczak. Practical Spectroscopy Series. Volume 13. Pp. xiv + 682. Marcel Dekker. 1992. Price US$l95.00. ISBN 0-8247-8657-2. The editors have drawn together the efforts of 29 contributors with a wealth of experience in the application of near-infrared (NIR) in diverse fields. The book is divided into four parts: background, instrumentation and computerization, method development and an applications section covering a wide range of industrial products. For example, NIR spectroscopy can replace the octane engine in gasoline testing, the Kjeldahl nitrogen in flour protein testing, and the differential scanning calorimeter in heat-set temperature determination of nylon yarn.These examples illustrate the diversity of applications cited. The resurgence of interest in NIR stems from the prolifera- tion of computers and the application of multivariate calibra- tion software. The compelling advantages of speed, precision and convenience in non-destructive testing has pressed NIR into service in almost every industry, replacing laborious traditional methods. The introduction outlines the development of NIR spectro- scopy; the principles and the theory of diffuse reflectance. It has to be said that the theory lags behind the applications of NIR which have developed empirically. The chapter on the theory of diffuse reflectance by Olinger and Griffiths attempts to remedy this lack of knowledge in the most readable form seen to-date.‘“he criterion for a ‘‘handbook” is that it merits more frequent handling than a monograph which spends more time on the bookshelf. This book passes that test.’ The section on instrumentation and data analysis is a useful summary of available hardware and software, from fixed-filter to monochromator instruments. Emphasis is given to data treatments such as multiplicative scatter correction (MSC) , Fourier transform (FT) , principal components analysis (PCA), multiple linear regression (MLR) and partial least squares (PLS) in NIR calibration. The chapters on data analysis by Mark and calibration basics by Workman are particularly lucid for the non-statistician who needs to grasp concepts without getting lost in matrix algebra. NIR spectro- scopy has been a proving ground for new chemometric methods of calibration.In particular the PLS algorithm promoted by Harald Martens has significantly improved calibration reliability and performance over traditional mul- tiple linear regression which can prove to be haphazard due to multicollinearity in the spectra. The applications section begins with an authoritative chapter on NIR analysis of agricultural products by Shenk, Workman and Westerhaus. Their advice on these most complex of natural products is of general applicability to any sample population. Applications chapters follow on tobacco, textiles, dairy and baked products, pharmaceuticals, petro- chemicals and polymers, wool, wood and beverages. While each application may seem to attract the interest of only the target industry involved, these applications are prescribed reading for all users as they highlight the common problems of sample set selection, calibration and validation. Medical and life science applications of NIR are a glaring omission which the editors should remedy in the next edition.The criterion for a ‘handbook’ is that it merits more frequent handling than a monograph which spends more time on the bookshelf. This book passes that test. The editors have strived to bring the jargon of NIR down to earth with a useful volume for existing and intending NIR users who need to implement NIR in their workplace. This handbook serves the purpose well and will be welcome on the bench (rather than the bookshelf!) of every NIR user involved in method development.Ian Murray Senior Analytical Chemist Scottish Agricultural College, UK ~ Experimental Design: A Chemometric Approach. Second, revised and expanded edition By Stanley N. Deming and Stephen L. Morgan. Data Handling in Technology. Volume 11. Pp. xvi + 430. Elsevier. 1993. Price US$177.25; DF1310.00. ISBN 0-444- 891 11 -0. Unfortunately, many scientists fight shy from sound experimental design because of difficulties in understanding the statistics. In this second, revised and expanded edition of the volume first published in 1987, an understanding of experimental design is the primary objective and the necessary statistics are developed alongside. The book’s structure serves to highlight its value, which is as a teaching text rather than a reference book. Indeed the reader is explicitly directed to read the chapters in order, working through the exercises presen- ted at each chapter’s conclusion.The first two chapters, ‘Systems Theory’ and ‘Response Surfaces’, provide the introductions and definitions of terms. There is the welcome addition to Chapter 1 of a section on measurement scales. Detailed statistics make their first appearance in Chapter 3, which again has an additional section, this time on enumarative versus analytic studies, describing the differences between studies on populations and systems. Lunderstanding experimental design is the primary objective’ The next two chapters consider single- and two-experiment systems and the models that can be developed to approximate the observed responses. Matrix algebra is introduced here and this is a section that needs careful understanding.Statistical theories are further developed in the next two chapters on ‘Hypothesis Testing’ and the ‘Variance-Covariance Matrix’. These concepts are key to the understanding of the adequacy of linear models and to the positioning of experiments in factor space. Chapter 8 continues the practical theme looking at the three possible designs for three experiments with a single factor, and the fitting of first- and second-order models. Many people will be familiar with analysis of variance (ANOVA), but probably not with the very helpful way it is presented in Chapter 9. Rather than the conventional tabular approach, a ‘sum of squares and degrees of freedom’ tree is used. The tree diagrams are an excellent means of presenting least squares results for linear models.The entirely new Chapter 10 presents an example of regression analysis applied to observed data, in this case the operation of a finance department. The descriptive develop- ment of a model is interesting to read, but its relationship tolOON Analyst, August 1994, Vol. 11 9 data from the natural sciences may not be immediately obvious. However, Chapter 11 provides direct practical help by using a model enzyme reaction to illustrate how to exploit just ten experiments to examine a single factor system. The familiar factorial, star and central composite designs are considered in Chapter 12, which has been extended in this second edition by a section on mixture designs. I was disappointed to find that there is still no discussion of sequential or iterative processes, D-optimal designs, or multi-criteria or pareto-optimal systems, for example, although this is partly remedied by a new Chapter 14 which further develops factorial designs.The final chapter discusses confounding and randomization. Three appendices, on matrix algebra (including problems with answers), critical values of t and F, complete the book. Compared with the first edition, some of the more amusing index entries have been omitted. Nevertheless, looking up ‘simplex’ still leads only to an excercise which says ‘look up the definition of a simplex’. In summary, this is a useful book, especially as a teaching text, but less-so as a more encyclopaedic text into which one can dip for a quick solution.If you already have the first edition, you may find the second edition of limited additional value. John C. Berridge Analytical Research and Development Pfizer Central Research, Kent, UK Instrumentation in Analytical Chemistry. Volume 1 Edited by J. Zyka. Ellis Horwood Series in Analytical Chemistry. Series Editor, Mary Masson. Pp. 368. Ellis Horwood. 1991. Price f53.00. ISBN 0-13-472218-3.- The series of volumes, Instrumentation in Analytical Chemistry, are intended to provide basic information on a variety of techniques in condensed form and survey new developments in analytical methods. Volume 1 contains 16 chapters and is written mainly by authors from Charles University, Prague. The techniques covered include isotacho- phoresis, differential-pulse polarography and voltammetry, ion-selective potentiometry, optical emission spectrometry, gas chromatography, X-ray spectroscopy, Mossbauer spectro- scopy, modern radioanalytical methods, neutron activation analysis and particle-induced X-ray emission spectroscopy.There are also chapters on analytical measurements in flowing liquids, the uses of computers in gas chromatography, the long range detection of atmospheric species with lasers, methods for decomposition of inorganic compounds, the chromato- graphic analysis of phenols and the study of inclusion compounds in chromatography. ‘I find it difficult to recommend this book as a general text for undergraduate or postgraduate study.’ Although the coverage of technique is reasonable for a general text book in analytical chemistry, I cannot help thinking that it would probably have been better to consider fewer techniques in greater depth in this first volume of the series.The background theory given in some of the chapters will be useful to many readers, but many of the chapters give disappointing introductions to the techniques and procedures. The main weakness of the book is that it is not particularly up-to-date. Most of the references quoted are pre-1985. The chapter on the uses of computers in gas chromatography is dated, the sources described in the emission spectrometry chapter are not new (e.g., the ICP) and the ‘modern’ methods of decomposing inorganic substances do not include micro- wave digestion. The coverage of applications is also patchy, which some chapters giving a better guide to the literature than others.If the series editors had been more selective about the chapters included in Volume 1, a more useful and attractive text book would have been produced, which would comple- ment others published recently on instrumental analytical chemistry. As it is, I find it difficult to recommend this book as a general text for undergraduate or postgraduate study. Perhaps later volumes will be more successful in achieving the aims of the series. David Littlejohn Department of Pure and Applied Chemistry University of Strathclyde, UK Modern Methods for Trace Element Determination By C. Vandecasteele and C. B. Block. Pp. xiv + 330. Wiley. 1993. Price f45.00. ISBN 0-471-94039-9. This book attempts to cover an enormous subject in the confines of its relatively small size and therefore involves a number of compromises in the depth of the explanation of the various subjects.Although titled ‘Modern Methods for Trace Element Determination,’ it could have been more accurately called something like ‘Spectroscopic Methods for Trace Analysis’, as this occupies most of the book and is what it is mainly concerned with. The book starts with a short introductory chapter that notes the importance of trace analysis in a number of fields, this is followed by a longer chapter (43 pages) on the subject of sample preparation. This covers most generally used methods of sample preparation and deals with systematic errors, but reference to a more comprehensive work would be needed before a new practitioner would be able to tacke much of the methodology.Detection limits, quality, standardization and calibration are dealt with in a brief chapter of 18 pages followed by the principles of spectrochemical analysis in 15 pages! ‘It is reasonably priced and will be a useful addition to the literature for those who need a source of basic information on trace analysis methods using atomic spectrometry.’ Atomic absorption spectrometry is covered by a fuller chapter of some 45 pages which gives a useful summary of the uses of the technique in trace analysis at the current time. The chapter on atomic emission spectrometry seems overly brief and requires a fuller list of references if it is indended to provide a gateway to the subject. Atomic fluorescence and a comparison of atomic spectrometric analytical techniques are covered briefly, followed by a much more comprehensive chapter on mass spectrometry, which rightly concentrates on ICP-MS and which gives more emphasis to the use of high resolution instruments than is usual in an introductory text.The subject of X-ray methods is dealt with in a wide ranging chapter, which will be useful to the non-expert needing to evaluate the possibilities of the technique. Neutron activation receives 20 pages and the book concludes with 5 pages on metal speciation and mentions three common examples, but it does not provide sufficient references or explore the nature of the subject sufficiently to be of much use to workers seriously interested in the subject.Analyst, August 1994, Vol.119 101N Despite the criticisms of the overly brief treatment of some of the subjects, the book is well written, almost free of typographical errors and is well indexed. I have some difficulty in identifying the target audience; for a novice, it does not provide sufficient information to really get started and the expert will have most of the information already to hand. It is reasonably priced and will be a useful addition to the literature for those who need a source of basic information on trace analysis methods using atomic spectrometry. Colin Watson Atomic Spectroscopy Consultancy Ilford, UK Practical Organic Mass Spectrometry. A Guide for Chemical and Biochemical Analysis. Second Edition By J. R. Chapman. Pp. xiv + 330. Wiley. 1993. Price f39.95. ISBN 0-471-92753-8.A colleague retiring recently gave us the advice not to waste time and energy running after a bus, a pretty young student, or a new application in analytical chemistry, because there would be another one along in a minute. Dr. Chapman has been brave to sit down to write an up-to-date textbook on analytical organic mass spectrometry at a time when new ionization methods, instruments and computer embellishments to all of them seem to arrive increasingly frequently, and spawn rashes of mnemonics like MALDI, ESP, NICI, MIKES, and (MS)n which mystify even experienced spectroscopists let alone students on final year degree, masters and research degree courses. There has been nothing published since Chapman’s first edition in 1985 which attempts to address the need for a clear authoritative balanced view of where analytical organic mass spectrometry is at, except Matsuo et al.’s ‘Biological Mass Spectrometry; Present and Future’ (1994), also published by Wiley but at three times the price, so unsuitable for either students or smaller mass spectrometry laboratories to buy.A glance at the first edition (only 197 pages) shows how much has happened since then-only 6 pages on fast atom bombard- ment and nothing on spray or atmospheric pressure inlet systems, or of course time-of-flight MS applied to molecular weight determinations in excess of 100 000 Daltons! ‘There are many strengths to this book. Chap- man has the gift of explaining theory clearly for beginners, and summarizes the “pros and consyy of the many techniques available nowadays carefully and in a very balanced way.’ The new edition includes sections on instrumentation, sample introduction, chemical ionization and negative chemical ionization, ionization of labile materials (in two parts), tandem mass spectrometry, quantitative analysis, and a most useful appendix on calibration compounds with their masses for all ionization modes.It retains the effective division of material used in the first edition: theory, practical require- ments and applications treated consecutively within each section, and it is amply referenced up to 1992 with 1004 citations plus 150 more in the appendices’ bibliography for chemical ionization applications. The latter are reprinted from the first edition without additions. This is a pity since they cover only the period up to 1982.An updated listing with additions for the other techniques would have been invalu- able, but perhaps impossible within the scope of a reasonably priced volume. There are very few errors or misprints and the diagrams are admirably clear. There are many strengths to this book. Chapman has the gift of explaining theory clearly for beginners, and summarizes the ‘pros and cons’ of the many techniques available nowadays carefully and in a very balanced way. This will help the many in industry who need to make difficult choices of which type of instrument and accessories to go for, and having acquired them how to set them up and get the best results out of them. The latter is not covered in any other book I know (and not always in the makers’ manual!).Sections on sensitivity tests and the use of the Grob mixture for assessing GC-MS performance will help chromatographers to ensure that the benchtop GC peak analyser gives results that are as sensitive and reliable as possible. This is a book which should be on the bench of every laboratory running any sort of organic mass spectrometer. Indeed, within a couple of days of its arrival in our library, it was. It can also be recommended to students and postgradu- ates, especially if a paperback edition at the standard price of f24.95 is made available-John Wiley please note. So, has Dr. Chapman caught the bus? I think the answer is a resounding yes and he is to be congratulated on producing a timely textbook which I believe stands comparison with Beynon and Biemann’s classic books of the 1960s.Martin Frearson Chemical Sciences University of Hertfordshire, UK Analysis with Supercritical Fluids: Extraction and Chro- matography. Edited by Bernd Wenclawiak. Pp. xiv + 214. Springer- Verlag. 1992. Price DM1 48.00. ISBN 3-540-55420-3; 0-387- 55420-3. Owing to their favourable physicochemical properties, the use of supercritical fluids has proved to be advantageous over other methods for the extraction of components from complex matrices and for chromatographic separations. This book is a collection of eleven chapters written by leading practitioners of supercritical fluid chromatography (SFC) and supercritical fluid extraction (SFE). The major emphasis of the volume is on SFC with the basic principles of SFE being dealt with in a chapter by King and France and applications being limited to those described by Hawthorne in an elegant chapter on coupled SFE-capillary gas chromatography.The basic prin- ciples of SFC are well delineated by Schneider and are followed by discussions on the use of gradients (Klesper and Schmitz); injection techniques (Greibrokk), and stationary phases for packed-column SFC (Poole, Oudsema, Dean and Poole) . ‘a very useful introduction into supercritical fluids’ Chiral separations are becoming increasingly important in many areas of the pharmaceutical and agrochemical indus- tries. SFC, particularly with the packed-column approach, has advantages over high-performance liquid chromatography (HPLC) in this area in that method development and analysis times are much faster and, in addition in many cases, higher efficiencies are obtained.Schleimer and Schurig review this area well. In the area of detection, Pinkston gives an erudite account of the systems developed for supercritical fluid chromatography-mass spectrometry (SFC-MS) and their relative merits. Mass spectrometry, whilst being a very powerful detection system for SFC is not perfect, particularly when studies concern differentiation of isomers. SFC-Fourier102N Analyst, August 1994, Vol. 119 transform infrared (SFC-FTIR) has advantages in this area over SFC-MS and it is also complementary to SFC-MS in other areas. Taylor and Calvey elegantly discuss systems of this type. Supersonic jet spectroscopy with supercritical fluids is the subject of the final chapter by Lin, Coates, Lee and Lubman.A useful bibliography is appended at the end of the book. The book is well written and compiled. More attention could have, perhaps, been given to SFE, but on the positive side, for once capillary SFC does not totally dominate over packed-column SFC. This volume will form a very useful introduction into supercritical fluids for new practitioners and there is also much in it for practitioners of SFC and SFE. It will be of interest for analytical scientists in a wide range of areas and will be a useful reference volume for many years. D . E. Games Mass Spectrometry Research Unit University College of Swansea, UK 13C-NMR of Natural Products. Volume 2. Diterpenes By Atta-ur-Rahman and Viqar Uddin Ahmad.Pp. x + 796. Plenum. 1992. Price US$125.00. ISBN 0-306-43898-4. This book is the second of a series on The 13C-NMR Data of Natural Products and deals with diterpenoids. It contains over 1300 entries with references up to and including 1989. The entries are grouped largely according to skeletal type, of which there are about seventy. The most abundant groups are the clerodanes (204), the labdanes (202), the kauranes (107), the pimaranes (72), the abietanes (64) and the cembranes (65). There is also a large miscellaneous section (113) that includes a couple of polyketides (latrunculin A and B) and several compounds belonging to the other groups. Com- pounds can be accessed via a name index, a botanical index, a molecular formula index, a molecular weight index and a skeletal type index.Compounds which lack a trivial name are assigned a code based on the botanical source and hence are unrecognizable in the name index. In most of these cases it would have been possible and preferable to use a systematic name. Some judicious pruning of nomenclature excesses ( e . g . , 13-furyllabda-8( 17)-ene) from the literature would also have been desirable. It is advantageous for a natural product chemist to have easy access to 13C data. Although it is limited in coverage and several years out of date this large volume provides a considerable amount of data, useful for identifying known compounds and part structures and for providing reference shifts. It can even be used for browsing to spot mistakes in the literature. For example, is the structure of the abietane derivative neotriptonorterpene really consistent with the presence of a methoxyl at 6c 55.3 or does the methyl ester of carnosic acid really have a methoxyl at 6c 61.0? It would have been helpful to have some indication of the definitive sets of chemical shifts, i.e., those assigned by direct and long range carbon-proton correlation experiments.‘the variable quality of the diagrams and the haphazard nature of the nomenclature detract from the value of this book.’ I cannot avoid making some comments on the diagrams since they represent the ‘text’ of this book. The authors have chosen not to redraw literature structures and as a result there is often no consistency in drawing or in the presentation of stereochemistry (e.g., in the kauranes, dolabellanes, spon- gianes, etc.). This makes comparison of structures more difficult.The fact that the spongiane derivative aplyroseol-1 and the entry which follows it are identical, but drawn differently, makes this point. The unnecessary use of confor- mational diagrams from the literature also creates problems. For example sarcodictyin C, D and E accidentally acquire a cyclopropane ring while the ten yucalexin diterpenoids appear among the kauranes instead of in the beyeranes and atisanes. In certain series (e.g., the ginkgolides, spongianes, etc.) there is a tendency to misdraw bonds which are crossing, thus giving an Escher-like quality to the structures. The inclusion of all the stereochemistry, especially at the ring junctions of less common skeletal types, would have been beneficial.More assiduous checking of structures would have revealed these omissions and other errors. In summary, the variable quality of the diagrams and the haphazard nature of the nomenclature detract from the value of this book. A much more critical approach to nomenclature and to the presentation of structures is required. I hope that the authors will consider these matters very carefully before producing further volumes in this series. J . D. Connolly Department of Chemistry University of Glasgow, UK Biomolecular Spectroscopy. Part B Edited by R. J. H. Clark and R. E. Hester. Advances in Spectroscopy. Volume 27. Pp. xx + 344. Wiley. 1993. Price fllO.00. ISBN 0-471-93832-7. This book is number 21 in the highly acclaimed series Advances in Spectroscopy, and as with Part A of the title (published as Volume 20) it is concerned with spectroscopic studies of a wide range of biomolecular species and their reactions in solution.The present volume concentrates on ultrafast molecular dynamics together with photobiology and vibrational chirality. The volume contains seven chapters (each generally 40-50 pages in length) written by experts in the fields, developed from research presentations given at the Fourth European Conference on the Spectroscopy of Biolog- ical Molecules. Chapter 1 gives an authoritative review of time-resolved infrared (TRIR) spectroscopy and protein dynamics. The fundamentals are clearly presented and applications given using haem proteins, bacteriorhodopsin and photoreaction centres.The excited states of retinoids, carotenoids and chlorophylls as revealed by time-resolved electronic absorp- tion and resonance Raman spectroscopy are presented in chapter 2 (89 pages). No experimental details are given but each section on the pigments consists of the physiological functions and questions addressed, experimental results and their interpretation, and conclusions and answers to the above questions. ‘a valuable introduction to the non-expert and a timely overview to those already familiar with the subject’ Dynamic properties of proteins are often essential to their function, and time-resolved resonance Raman (TR3) spectro- scopy is the technique discussed in chapter 3 with particular attention to the study of haem proteins. The authors, in addition to reviewing experimental methods, demonstrate the application of the method to the characterization of reaction intermediates involving cytochrome P-450, the peroxidases, and cytochrome oxidase.Analyst, August 1994, Vol.11 9 103N In chapter 4 the spectroscopy, dynamics and function of cytochrome oxidase are discussed. Evidence from optical absorption, infrared and Raman spectroscopy is compared with that from electron paramagnetic resonance (EPR) and other methods. That the potential value of vibrational spectroscopy is greatly enhanced by adding the dimension of optical activity is clearly demonstrated in chapters 5 and 6. In chapter 5 , following an account of the theory of Raman optical activity, the application to conformational studies of amino acids, peptides, proteins, carbohydrates, and nucleosides is given.Chapter 6 (Structural Studies of Biological Macromolecules using Vibrational Circular Dichroism) focuses on newer developments in the application of VCD to protein structural studies, but results obtained from the complementary elec- tronic circular dichroism (ECD) and infrared techniques are used to interpret and extend the newer data. The final chapter is concerned with the use of X-ray absorption spectroscopy for the characterization of transition metal sites in proteins. The book concludes with a useful index, and SI units and standard IUPAC nomenclature have been used throughout. The typography and quality of printing are excellent, and the editors should be congratulated in achieving their aim of providing a text that is both a valuable introduction to the non-expert and a timely overview to those already familiar with the subject.Brian Everatt Ciba - Geigy Plc Cheshire, UK Advances in Biosensors. Volume 2 Edited by Anthony P. F. Turner. Pp. xii + 344. JAI Press. 1992. Price f53.00; US$90.25. ISBN 1-55938-270-8. As a burgeoning subject area, biosensors have begun to accumulate a distinctive body of review literature of their own. However, this can be scattered among general analytical review material. This second in the Advances series dedicated to biosensors provides a useful focus, summarizing the thrust of some academic and industrial activity. The authorship, taken from leading US and European groups, provide comprehensive detailed reviews, with at long last, some serious recognition of practical problems and the needs of the applied scientist.An introductory chapter (Yacynych) on amperometric enzyme electrode construction gives a description of ‘old’ and ‘new’ as regards membrane films and electrode interfaces. The description of new electropolymerized films will be of particular interest to the specialist, but if the message here is, thin is ‘beautiful’, one wonders at the survivability of such films in aggressive environments. The next contrasting chapter covers the electrochemistry of redox protein behavi- our at solid electrode surfaces, and how surface modifiers and electron mediators, respectively, may be made to harness such behaviour, ultimately for a useful analytical purpose. For those for whom success in enzyme biosensors coincides with a redox enzyme ‘hardwired’ to a transducer, the following chapter on conducting films and mediated amperometric devices will provide ample self-justification.In fact, not only do the authors (Schuhmann and Schmidt) present some excellent new insight into mediatorhonductor chemistry, but their remarks about pitfalls to practical adaptation adds the right note of caution to this approach. So called technological imperatives come to the fore in the case of in vivo glucose sensors, which pose formidable (re-)calibration and biocom- patibility challenges, as illustrated in the chapter by Koudelka- Hep et al. It may, of course, be that eventually, optical sensors with more sophisticated optics will make electrochemical devices redundant; however, the summary of work presented by Coulet on amperometric and optical (luminescence-based) biosensars, reassuringly suggests that the former still has some time to run. ‘Authoritative reviews representing an inter- national perspective on biosensors and begjnning to now get to grips with practical realities’ To the extent that biosensors represent an interfacial science, it is important that many groups continue work on the basic chemistry of bioreagent attachment to surfaces and of modified surface behaviour. It is useful, therefore, to have a full chapter devoted to this topic, confirming progress and the specialist nature of the work. A thorough, detailed chapter on the principles of operation of fluorescent sensors provides insight into both their steady-state and dynamic behaviour, and for once how theory can actually give direct assistance in the construction of practical systems. For those not content with the transducer element as a ‘black box’, the chapter giving the unbridled basic physics of coupled waveguides should be especially satisfying, however, here, any practical lessons are more difficult to gauge. Also, with surface and waveguide optics, the salutary story of the Pharmacia BIA- core immunosensor development shows the major and collab- orative effort that even a large organization must engage in to eventually bring a product to the market. This is, overall, a worthy collection of reviews that certainly those in the field will find of interest. The first volume was a good start, this volume, if anything, does a more thorough job, that will see it through as a future reference source. P. Vadgama Department of Medicine (Clinical Biochemistry) University of Manchester, UK

ISSN:0003-2654    

DOI:10.1039/AN994190099N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

104N Analyst, August 1994, Vol. 11 9 Conference Diary Date Conference 1994 September Location 4-7 5-6 5-9 6-8 8 11-16 12-15 12-15 12-15 13-14 13-18 14-15 18-22 19-20 19-21 19-21 East European Furnace Symposium Warsaw, Poland First International Symposium on Coimbra, Neuroelectrochemistry Portugal VIIth International Symposium on Synthetic Tiibingen, Membranes in Science and Industry Germany RSC Autumn Meeting (with Analytical Session Glasgow , on Analytical Challenges in Toxicology and UK Pollution) Trace Analysis Symposium London, UK EUCMOS XXII: XXIInd European Congress on Molecular Spectroscopy Germany Essen, Separations for Biotechnology Reading, UK IIIrd International Symposium on Krakow, Environmental Geochemistry Poland The 108th AOAC International Annual Meeting and Exposition USA Portland, Recent Advances in Thermal Analysis Techniques UK Leeds, 3rd International Symposium on Mass Spectrometry in the Health and Life Sciences San Francisco, USA Waterborne Coatings and Additives Manchester , UK Geoanalysis 94: An International Symposium on the Analysis of Geological and Environmental Materials Ambleside, UK Chiral Europe '94 Nice, France The Second International Conference on Applications of Magnetic Resonance in Food Science The Fourth Annual CIM Field Conference Aveiro, Portugal Ontario, Canada Contact Dr.Ewa Bulska, University of Warsaw, Department of Chemistry, UI. Pasteura 1,02 093 Warsaw, Poland Fax: +48 22 225996 Profa. Dra. Ana Maria Oliveira Brett, Departamento de Quimica, Universidade de Coimbra, 3049 Coimbra, Portugal Tel: +35139 22826.Fax: +35139 27703 Dechema, P.O. Box 970146, D-W-6000 Frankfurt am Main 97, Germany Dr. J. F. Gibson, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 (0)71 437 8656. Fax: +44 (0)71 734 1227 Dr. Graham MacKay, Lab 6-10, Laboratory of the Government Chemist, Queens Road, Teddington, Middlesex, UK TWll OLY Tel: +44 (0)81 943 7496. GDCh-Geschaftsstelle, Abt. Tagungen, Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358. Fax: +49 69 791 7475 SCI Conference Office, 14/15 Belgrave Square, London, UK SWlX 8PS Tel: +44 (0)71 235 3681. Fax: +44 (0)71 823 1698 Helios Rybicka, Faculty of Geology, Geophysics and Environmental Protection, University of Mining and Metallurgy, Al.Mickiewicza 30, PL-30-059 Krakow , Poland Tel: +48 12 333290. Fax: +48 12 332936 Margaret Ridgell, AOAC International, 2200 Wilson Boulevard, Suite 400, Arlington, Tel: + 1 703 522 3032. Edward Charsley/Stephen Warrington, Thermal Analysis Consultancy Service, Leeds Metropolitan University, Calverley Street, Leeds, UK LS1 3HE Tel: +44 (0)532 833121/833122. Fax: +44 (0)532 833120 Marilyn Schwartz, Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 9413-0446, USA Mrs. C. L. Sharp, Conference Secretary, 41 Exeter Road, Davyhulme, Manchester, UK M41 ORF Tel: +44 (0)61 747 4961. Fax: +44 (0)61 747 4961 D. L. Miles, Analytical Geochemistry Group, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, UK NG12 5GG Tel: +44 (0)602 363100.Fax: +44 (0)602 363200 Spring Innovations Ltd, 216 Moss Lane, Bramhall, Stockport, UK SK1 1BD Tel: +44 (0)61 440 0082. Fax: +44 (0)61 440 9127 Dr. A. M. Gil, Department of Chemistry, University of Aveiro, 3800 Aveiro, Portugal VA 22201-3301, USA 1994 CIM Field Conference, c/o Sudbury Geological Discussion Group, P. 0. Box 1233, Station B, Sudbury, Ontario, Canada, P3E 4S7Analyst, August 1994, Vol. 11 9 105N Date 19-23 21 21-23 21-24 22-24 25-28 26-28 26-30 29-30 Conference Location XIIIth International Symposium on Medicinal Paris, Chemistry France Sampling: A One Day Symposium Manchester , UK 7th International Symposium on Bournemouth, Environmental Radiochemical Analysis UK 5th International Symposium on Stockholm, Pharmaceutical and Biomedical Analysis Sweden 12th National Conference on Analytical Chemistry Romania Const anta , 5th International Symposium on Chiral Discrimination Sweden Stockholm, Protozoan Parasites and Water York, UK 16th International Symposium on Capillary Chromatography Italy Riva del Garda, Food and Feed Analysis: A Focus on Methods Nyon, with Mineral Hazards to Health and the Switzerland Environment October 2-7 3-6 10-13 11-13 14-15 17-19 29th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy USA Societies PREP '94: 11th International Symposium on Preparative and Industrial Chromatography Germany St.Louis, Baden-Baden, International Symposium on Bled, Chromatographic and Electrophoretic Slovenia Techniques 35th ORNL-DOE Conference on Analytical Chemistry in Energy Technology USA Tennessee, CITAC '94 Hong Kong Symposium on Traceability and Comparability of Analytical Measurements Hong Kong 3rd International Symposium on Supercritical Strasbourg, Fluids France 30411 OPTCON '94 Boston, USA 3 1-211 1 ANABIOTEC '94: 5th International Minneapolis, Symposium on Analytical Methods, Systems and Strategies in Biotechnology USA Contact CONVERGENCES/ISMC '94,120 Avenue Gambetta, 75020 Paris, France Fax: +33 14031 0165 Linda Catterson, Laboratory of the Government Chemist, Queens Road, Teddington, Middlesex, UK TWll OLY Dr.P. Warwick, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, UK LEll 3TU Tel: +44 (0)509 222585. Fax: +44 (0)509 233163 Swedish Academy of Pharmaceutical Sciences, P.O.Box 1136, S-111 81 Stockholm, Sweden Tel: +46 8 245085. Fax: +46 8 205511 Dr. G.-L. Radu, Romanian Society of Analytical Chemistry 13 Bul. Carol I, Sector 3,70346 Bucharest, Romania Swedish Academy of Pharmaceutical Sciences, P.O. Box 1136, S-11181 Stockholm, Sweden Tel: +46 8 245085. Fax: +46 8 205511 IFAB Communications, Institute for Applied Biology, University of York, York, UK YO1 5DD Tel: +44 (0)904 432940. Fax: +44 (0)904 432917 Professor Dr. P. Sandra, IOPMS, Kennedypark 20, B-8500 Kortrijk, Belgium Tel: +32 56 204960. Fax: +32 56 204859 T. Rihs, Swiss Federal Research Station for Animal Production, CH-1725 Posieux, Switzerland Tel: +41 37 877111. FACSS, P.O. Box 278, Manhattan, KS 66502-0003, USA Tel: +1 301 846 4797.GDCh-Geschaftsstelle, Abt. Tagungen, Varrentrappestr. 4042, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358. Fax: +49 69 791 7475 Dr. M. ProSek, National Institute of Chemistry, SLO-Ljubljana, Slovenia Fax: +386 61 125 9244 W. R. Laing, Technical Program Chairman, Oak Ridge National Laboratory, P.O. Box 2008, MS 6127, Oak Ridge, TN 37831-6127, USA Tel: +1615 574 4852. Fax: +1 615 241 4599 Dr. T. L. Ting, CITAC '94 Secretariat, c/o Government Laboratory, Ho Man Tin Government Offices, 88 Chung Hau Street, Hong Kong Tel: +852 762 3706. Fax: +852 714 4083 Congres 'Fluides Supercritiques', ENSIC B .P. 451-1, Rue Grandville, F-54001 Nancy Cedex, France Tel: +33 8317 5003. Fax: +33 8335 0811 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, Tel: +1 202 223 9034.Fax: +1202 416 6100 Anabiotec Conference Secretariat, Elsevier Advanced Technology, Mayfield House, 256 Banbury Road, Oxford, UK OX2 7DH Tel: +44 (0)865 512242. Fax: +44 (0)865 310981 DC 20036-1023, USA106N Analyst, August 1994, Vol. 119 Date Conference Location Contact November 9-11 11th Montreux Symposium on Liquid Montreux, Chromatography-Mass Spectrometry (LC/ Switzerland MS; SFCMS; CE/MS; MSMS) 10-11 17th International Conference on Chemistry, New Delhi, Bio Sciences, and Environmental Pollution India 6-12 Third Rio Symposium on Atomic Spectrometry Caracas, Professor Jose Alvarado, Universidad Simon Bolivar, Departamento de Quimica, Laboratorio de Absorcion Atomica, Apartado Postal No.89000, Caracas, 1080-A, Venezuela Fax: +58 2 938322 M. Frei-Hausler, Postfach 46, CH-4123 Allschwil 2, Switzerland Tel: +41614812789. Fax: +41614820805 Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702. Venezuela 18-22 Joint Oil Analysis Program International Pensacola, Condition Monitoring Conference USA 24-26 5th International Symposium on Advances in Madras, Electrochemical Science and Technology India 1995 January 8-13 1995 Winter Conference on Plasma Spectrochemistry Cambridge, UK February 6-8 International Conference on Arsenic in Calcutta, Ground Water: Cause, Effect and Remedy India 15 Alternatives to Chemical Solvents Restricted London, by the Montreal Protocol UK 19-24 OFC '95: Optical Fibre Communication San Diego, Conference USA April 10-13 Annual Chemical Congress (with Analytical Edinburgh, Session) UK May 7-1 1 16-18 21-26 Seventeenth International Symposium on Virginia, Capillary Chromatography and USA Electrophoresis Fourth International Conference on Progress in Analytical Chemistry in the Steel and Metals Industry Luxembourg CLEO '95: Conference on Lasers and Electro- Baltimore, Optics USA Technical Support Center, Joint Oil Analysis Program, Building 780, Naval Air Station, Pensacola, FL 32508, USA Tel: +1904 452 3191.The Secretary, Society for Advancement of Electrochemical Science and Technology, Karaikudi, 623 006, India Janice M. Gordon, Winter Conference on Plasma Spectrochemistry, Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF Tel: +44 (0)223 420066.Fax: +44 (0)223 420247 D. Chakraborti, School of Environmental Studies, Jadavpur University, Calcutta -700 032, India Tel: +9133 473 5233. Fax: +9133 473 4266 Ms. Paula Elliott, Secretary, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 (0)71 437 8656. Fax: +44 (0)71 734 1227 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, Tel: +1202 223 9034. Fax: +1202 416 6100 DC 20036-1023, USA Dr. J. F. Gibson, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 (0)71 437 8656. Fax: +44 (0)71 734 1227 Dr. Milton L. Lee, Department of Chemistry, Brigham Young University, Provo, Tel: +1801378 2135.Fax: +1 801 378 5474 R. Jowitt, British Steel PLC, Technical, Teesside Laboratories, P.O. Box 11, Grangetown, Middlesbrough, Cleveland, UK TS6 6UB Fax: +44 (0)642 460321 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, Tel: +1202 223 9034. Fax: +1202 416 6100 UT 84602-4672, USA DC 20036-1023, USAAnalyst, August 1994, Vol. 11 9 107N Date Conference Location Contact 21-26 QELS '95: Quantum Electronics and Laser Baltimore, Meetings Department, Optical Society of America, Science Conference USA 2010 Massachusetts Avenue, NW , Washington, DC 20036-1023, USA. Tel: + 1 202 223 9034. Fax: + 1 202 416 6100 28-2/6 19th International Symposium on Column Innsbruck , HPLC '95 Secretariat, Tyrol Congress, Liquid Chromatography Austria Marktgraben 2, A-6020 Innsbruck, Austria Tel: +43 512 575600.Fax: +43 512 575607 June 5-8 5th Symposium on our Environment and 1st Convention City, Asia-Pacific Workshop on Pesticides Singapore Environment, c/o Department of Chemistry, The Secretariat, 5th Symposium on our National University of Singapore, Kent Ridge, Republic of Singapore 0511 Fax: +65 779 1691 July 9-15 SAC95 Hull, UK 10-13 Vth COMTOX Symposium on Toxicology and Vancouver, _ _ Clinical Chemistry of Metals August 27-2/9 CSI XXIX: Colloquium Spectroscopicum Internationale 27-1/9 46th Annual Meeting of the International Society of Electrochemistry (ISE46) 27-30 EUROTOX September 25-28 5th Symposium on 'Kinetics in Analytical Chemistry' (KAC '95) October 1-5 21st World Congress of the International Society for Fat Research (ISF) November 5-10 OPTCON '95 14-15 International Conference for Chemical Information Users Canada Leipzig, Germany Xiamen, China Prague, Czech Republic Moscow, Russia The Hague, The Netherlands San Jose, USA Manchester , UK Analytical Division, The Royal Society of Chemistry, Burlington House , Piccadilly , London, UK W1V OBN Tel: +44 (0)71437 8656.Fax: +44 (0)71 734 1227 F. William Sunderman, Jr., M.D., Departments of Laboratory Medicine and Pharmacology, University of Connecticut Medical School, P.O. Box 1292, Farmington, CT 06034-1292, USA Tel: +I 203 679 2328. Fax: +1203 679 2154 GDCh-Geschiiftsstelle, Abt. Tagungen, Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358.Fax: +49 69 791 7475 Secretariat, XLVIth ISE Annual Meeting, P.O. Box 1995, Xiamen University, Xiamen 361005 , China Tel: +86 592 208 5349. Fax: +86 592 208 8054 Czech Medical Association J. E. Purkyng, EUROTOX '95, P.O. Box 88, Sokolska 31,120 26 Prague 2, Czech Republic Tel: +42 2 24 915195. Fax: +42 2 24 216836 Dr. I. F. Dolmanova, Analytical Chemistry Division, Chemical Department, Lomonosov Moscow State University, 119899 Moscow, Russia Tel: +7 095 939 3346. Fax: +7 095 939 2579 Mrs. J. Wills, ISF Secretariat, P.O. Box 3489, Champaign, IL 61826-3489, USA Tel: +217/359 2344. Fax: +217/3518091 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW , Washington, Tel: +1 202 223 9034. Fax: +1 202 416 6100 Dr.M. P. Coward, Chemistry Department, UMIST, P.O. Box 88. Manchester, UK M60 1QD Tel: +44 (0)61 200 4491. Fax: +44 (0)61 228 1250 DC 20036-1023, USA108N Analyst, August 1994, Vol. 119 Date Conference Location Contact 1996 February 6-9 June 16-21 July 8-12 Fourth International Symposium on Bruges, Dr. R. Smits, Royal Flemish Chemical Society Hyphenated Techniques in Chromatography Belgium (KVCV), Working Party on Chromatography, (HTC 4); Hyphenated Chromatographic BASF Antwerpen N.V., Central Laboratory, Anal yser s Haven 725, Scheldelaan 600, B-2040 Antwerp, Belgium Tel: +32 3 561 2831. Fax: +32 3 561 3250 HPLC '96: 20th International Symposium on High Performance Liquid Chromatography USA San Francisco, Mrs. Janet Cunningham, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: +1301898 5596 XVI International Congress of Clinical Chemistry UK Clinical Chemistry, P.O. Box 227, Buckingham, London, Mrs. Pat Nielsen, XVIth International Congress of UK MK18 5PN Fax: +44 (0)280 6487 September 1-7 Euroanalysis IX 15-20 21st International Symposium on Chromatography Bologna, Italy Professor Luigia Sabbatini, Euroanalysis IX, Dipartimento di Chimica, Universith di Bari, Via Orabona, 4, 70126 Bari, Italy Tel: +39 80 242020. Fax: +39 80 242026 Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358. Fax: +49 69 791 7475 Stuttgart , GDCh-Geschiiftsstelle, Abt. Tagungen, Germany

ISSN:0003-2654    

DOI:10.1039/AN994190104N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, August 1994, Vol. 11 9 109N Courses Date Conference Location Contact 1994 September 4-8 Molecular Graphics and Modelling Short Course 5-6 Workshop on Evaluation of Measurement Uncertainty in Chemical Analysis 5-9 AMCP-AES-ICP-MS Short Course 6-9 The Leeds Course in Clinical Nutrition 21-22 Statistical Tools for Analytical Quality Assurance Workshop 25-30 1994 European Workshop in Chemometrics York, UK Graz , Austria Loughborough, UK Leeds, UK London, UK Bristol, UK Dr. T. L. Threlfall, Industrial Liaison Executive, University of York, Department of Chemistry, Heslington, York, UK YO1 5DD Tel: +44 (0)904 432576. Fax: +44 (0)904 432516 Professor W. Wegscheider, Technische Universitat Graz, TechnikerstraB 4, A-8010 Graz, Austria Tel: +43 316 873 8303. Fax: +43 316 810926 Mrs.S. J. Maddison, Department of Chemistry, Loughborough, University of Technology, Loughborough, Leicestershire, UK LE11 3TU Tel: +44 (0)509 22575. Mrs. Hilary L. Thackray, Department of Continuing Professional Education, Continuing Education Building, Springfield Mount, Leeds, UK LS2 9NG Tel: +44 (0)532 333233. Leslie Coveney, 144 Porstmouth Road, Cobham, Surrey, UK KTll 1HX Tel: +44 (0)32 864 915. Fax: +44 (0)32 864 915 Janice Green, School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS Tel: +44 (0)272 303030 (ext. 4421) or +44 (0)272 303672. Fax: +44 (0)272 251295 October 18-19 Mass Spectrometry for Beginners Manchester , Dr. M. P. Coward, Chemistry Dept. UMIST, UK P.O. Box 88, Manchester, UK M60 1QD Tel: +44 (0)61 200 4491.Fax: +44 (0)61 228 1250 November 7-8 Short Course on LC/MS, SFC/MS and CE/MS Montreux, M. Frei-Hausler, Workshop Office IAEAC, Switzerland Postfach 46, CH-4123 Allschwil2, Switzerland December 15-17 Capillary Electrophoresis Short Course Loughborough, Mrs. S. J. Maddison, Department of Chemistry, UK Loughborough University of Technology, Loughborough, Leicestershire, UK LEll 3TU Tel: +44 (0) 509 22575. 1995 April 4-5 Workshop in Chemical Information Retrieval Manchester, UK Dr. M. P. Coward, Chemistry Department, UMIST, P.O. Box 88, Manchester, UK M60 1QD Tel: +44 (0)61200 4491. Fax: +44 (0)61 228 1250 September 6-8 5th Workshop on Chemistry and Fate of Paris, Professor M-C. Hennion, ESPCI, Labo. Chimie Modern Pesticides France Analytique, 10 Rue Vauquelin, 75005 Paris, France Entries in the above listing are included at the discretion of the Editor and are free of charge. If you wish to publicize a forthcoming meeting please send full details to: The Analyst Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF. Tel: +44 (0)223 420066. Fax: +44 (0)223 420247.

ISSN:0003-2654    

DOI:10.1039/AN994190109N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

110N Analyst, August 1994, Vol. 11 9 Conference Report ~ The International Symposium on Electroanalysis, University of Wales College of Cardiff, April 6-8, 1994 The conference subtitle was ‘A Tribute to J . D. R. Thomas’, to whom the meeting was dedicated. Professor Townshend initiated the conference with a tribute to Professor Thomas, which included his academic career to date, his scientific achievements and his influence on and contribution to analytical chemistry. This was followed by a presentation on sequential injection analysis, by Professor Christian. The meeting continued with a talk by Dr. Sasaki, a late replacement speaker for Professor Karube, on the development and application of microbiosensors. The last presentation of the day was given by Dr. Sanghera on the modification of electrodes to mimic binding sites of enzymes.Later, at the evening reception most delegates took the opportunity to enjoy a drink or two, before dinner. However, the end of the evening meal was by no means the end of the evening! Two distinct groups seemed to emerge from the delegates and both toured the city centre in search of a lively night out. Judging by the look on most faces at breakfast the following day, it was apparent that they had been successful! Professor Pungor opened the second day with an interpreta- tion of the operation of ion-selective electrodes, which was followed by Professor Frant’s review on the history of the early commercialization of ion-selective electrodes. Professor Covington described the development of refer- ence methods for determination of ionized calcium and magnesium in blood serum and plasma.He explained that ionized calcium can be measured in whole blood by electro- chemical potentiometric analysis with ion-selective electrodes quicker than by flame photometry on diluted samples, and that ionized magnesium is becoming very important clinically. Professor Covington also explained that the primary reasons for the discrepancies between commercial instruments include calibration solutions of widely different compositions, vari- able residual liquid junction potentials arising from the use of different geometries of the liquid junction or differing electrolyte compositions of the junction, and the sources and levels of heparin used to prevent blood coagulation. Ionized calcium and magnesium have no definitive methods of measurement, hence there is an urgent need for reference methods to achieve accuracy in health care measurements. He described an inter-laboratory test in twenty-four laboratories in fifteen countries of prototype reference method and commercial instruments in which salient factors affecting the accuracy and precision were evaluated.Dr. Birch talked about the industrial applications of sensing systems, how Unilever Sensor Technology are using thick-film technology to develop a multisensor for waste water analysis in collaboration with Southampton University. Leading up to lunch, Professor Janata gave a review on the history of ion-selective field-effect transistors. Professor Buck gave a talk on the mechanisms of transport in carrier-based ion- selective electrodes.Professor Machado gave a presentation on epoxy-based ion-selective electrodes. This was followed by a poster session. Delegates were given the chance to discuss presentations already given by speakers, as well as catching up on current research being undertaken by the students present. Later that evening, delegates attended the Conference Banquet held at Cardiff Castle. On arrival, all were impressed by the beautiful grounds and parading peacocks. Once inside the castle, we were greeted with melodic harp music, played by a local musician. The relaxed and informal atmosphere gave all the delegates present a chance to socialize before an excellent five course dinner. On the final day of the conference, Professor Bond gave a review on voltammetric microelectrodes and their contribu- tions to analytical chemistry. He explained how microelec- trodes had been in existence for around forty years and how technology had permitted these to become small enough to go into individual neurones or cells.Dr. Jascowicz gave a presentation on the application of conducting polymers in electroanalysis. Gases can be incor- porated into conducting polymer layers, liquids and solids. Dr. Jascowicz talked about the synthesis of conducting polymers and their resulting properties and functionality as a result of the conditions used for synthesis. This was followed by Professor Guilbault’s talk, which gave an overview on piezoelectric immunobiosensors. The final presentation at the conference was given by Professor Williams on vibrating microband electrodes.A portable reagentless, one-shot electrochemical sensor for the determination of chlorine in water has been developed using microband electrodes. Line electrodes are macroscopic in one dimension and microscopic in another. To prepare inexpen- Mrs. G. Thomas, The Master of Ceremonies and Professor J . D . R. Thomas at the Conference Banquet. Delegates at the Conference Banquet held at Cardiff Castle.sive line electrodes, Professor Williams has used screen- printed ceramic tiles which are scored and snapped before use, resulting in gold line electrodes. The main objective is cost-effective electrodes. He explained that vibrating micro- band electrodes are a new approach to hydrodynamic modula- tion studies. The vibration modulates the diffusion limited current, and all background currents are rejected as they are not modulated. Professor Williams stated that vibrating electrosystems are ‘cheap and cheerful’ and very effective electroanalytical tools. His presentation was acknowledged by Analyst, August 1994, Vol. 119 l l l N Professor Thomas, who added that ‘successful technology is simple technology’. Professor Thomas concluded the conference and thanked all those who had participated. The meeting was closed by Jonathan Slater who also gave an insight on what it was like to work with Professor Thomas. Yasmin Khan Assistant Editor The Analyst

ISSN:0003-2654    

DOI:10.1039/AN994190110N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, August 1994, VoI. 119 l l l N Future Issues will Include- Determination of BRL 46470 in Human Plasma by High- performance Liquid Chromatography With Ultra-violet Absorbance Detection Followed by Post-column Photochem- ical Reaction and Fluorescence Detection-Nigel J. Deeks, Richard W. Abbott, Graham D. Allen, Frank J. Hollis and Gerald Rhodes Characterization of Doped Strontium Sulfide Thin Films by Secondary Ion Mass Spectrometry, Rutherford Backscatter- ing Spectrometry and X-ray Fluorescence Spectrometry- Lauri Niinisto, Sari Lehto, Pekka Soininen, Jari Likonen and Reijo Lappalainen Detection of Phencyclidine in Urine Using a Polarization Fluoroimmunoassay-John C. Gooch, Gerard Gallacher, John G. Wright, Imtiaz Mahmood, Ahmad Siddiqui and David L. Colbert Catalytic Fluorimetric Determination of Copper Using Aerial Oxidation of Ascorbic Acid in the Presence of o-Phenylene- diamineCusumu Kawakubo, Hirofumi Kato and Masaaki Iwatsuki Object-orientated Programming on Personal Computers- R.G. Brereton Adsorptive Cathodic Stripping Voltammetric Determination of Theophylline at a Hanging Mercury Drop Electrode-Ali Z. Abu Zuhri, Raqi M. Shubietah and Arnold G. Fogg Imaging Glucoamylase by Scanning Tunnelling Microscopy- A. Patrick Gunning, Victor J. Morris, Gerrard F. H. Kramer, Gary Williamson and Nigel J. Belshaw Determination of Salicyclic and Gentisic Acids in the Presence of Each Other by Matrix Isopotential Synchronous Fluores- cence Spectrometry-Jo& A. Murillo and Molina A. Alaiih Orthogonal Array Design as a Chemometric Method for the Optimization of Analytical Procedures.Part 2. Four-level Design and Its Application in Microwave Dissolution of Biological Samples-Wei Guang Lan, Ming Keong Wong, Ni Chen and Yoke Min Sin Determination of Endosulfan by Stripping Voltammetry- Prabu H. Gurumallesh and P. Manisankar Voltammetric Study of Salbutamol, Fenoterol and Meta- proterenol at Unmodified and Nafion-modified Carbon Paste Electrodes-Malcolm R. Smyth, Damien Boyd, Jo& Ramh Barreira Rodriguez, Arturo Jose Miranda Ordieres and Paulino Tuiion Blanco Screen-printed Glucose Strip Based on Palladium-dispersed Carbon ink-Joseph Wang and Qiang Chen Aldehyde-selective Polymeric Membrane Electrodes Based on a Calix[4]arene Ionophore-Wing Hong Chan, Pei Xiang Cai and Xiao Hong Gu Use of Nuclear and Nuclear-related Analytical Techniques in Studies of Trace and Minor Elements in Air Pollution-Borut Smodig and Boris Stropnik Determination of Trace Amounts of Urea by Flow Injection Analysis With Chemiluminescence Detection-Yasuaki Maeda, Xincheng Hu, Norimichi Takenaka, Masaru Kitano, Hiroshi Bandow and Masaharu Hattori Separation and Sensitive Determination of Metal Ions by Capillary Zone Electrophoresis with 2-(5-Bromo-2- pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br- PAPS) Shoji Motomizu, Mitsuko Oshima, Masayoshi Kuwabara and Yoshimitsu Obata Flow Injection Potentiometric and Voltammetric Stripping Analysis Using a Dialysis Membrane Covered Mercury Film Electrode-Howard D.Dewald, Joseph H. Aldstadt and Dewey F. King Determination of Aluminum, Titanium and Iron Oxides in Wet-Processed Phosphoric Acid by Extraction Spectropho- tometry-L. Costadinnova, N. Elenkova and T. Nedeltcheva Pulse Coulometric Titration in Continuous Flow-A. D. Dakashev and V. T. Dimitrova COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (0)71-437 8656. Fax: +44 (0)71-287 9798. Telecom Gold 84: BUR210. Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society's Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge.

ISSN:0003-2654    

DOI:10.1039/AN994190111N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

112N Analyst, August 1994, Vol. 11 9 RSC Sponsored Awards 1993 The Royal Society of Chemistry’s industrially-sponsored awards for 1993 were presented at a ceremony held in Burlington House, London, on June 1, 1994. The following awards of analytical interest were presented. The prize for Analytical Reactions and Analytical Reagents, sponsored by Merck Ltd., was presented to Professor P. C. Uden of the University of Massachusetts, USA. The prize for Electroanalytical Chemistry, sponsored by ABB Kent-Taylor Ltd., was presented to Dr. D. Band of Guy’s and St. Thomas’s Medical and Dental Schools. In addition, the 1992 prize for Chemical Analysis and Instrumentation, sponsored by Perkin-Elmer Ltd. , was pre- sented to Professor M. Comisarow of the University of British Columbia, Canada, who had been unable to attend the ceremony in 1993.The photograph shows (L-R): Professor P. C. Uden, Professor C. W. Rees (President of the RSC), Dr. D. Band and Professor M. Comisarow. Nominations for the 1995 Benedetti-Pichler Award The American Microchemical Society is soliciting nominations for the prestigious 1995 Benedetti-Pichler Award. The award, established in 1966, is given annually to recognize outstanding achievements in microanalytical chemistry. The award consists of a plaque and expenses to attend the Eastern Analytical Symposium in Somerset, New Jersey, in November 1995 in order to receive the award at a session in honour of the awardee. Nominations, including at least two supporting letters, should be sent no later than October 30, 1994, to Len Klein, Secretary, American Microchemical Society, FMC Corporation, Agricultural Chemical Group., P.O. Box 8, Princeton, New Jersey 08543, USA. For further information, please contact Dr. Joseph Sneddon, Head, Department of Chemistry, McNeese State University, Lake Charles, Louisiana 70609, USA. Telephone: (318) 475-5777 Fax: (318) 475-5234.

ISSN:0003-2654    

DOI:10.1039/AN994190112N

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, August 1994, Vol. 11 9 1641 Environmental Sensors Based on Atomic Fluorescence P. B. Stockwell and W. T. Corns P.S. Analytical Ltd., Arthur House, B4 Chaucer Business Park, Watery Lane, Kemsing, Sevenoaks, Kent, UK TN15 6QY Specific atomic fluorescence detectors have been designed for several elements. Interference problems are minimized by coupling these detectors to vapour generation techniques. Mercury is analysed by generating the metallic vapour coupled to a mercury specific detector. The hydride forming elements, arsenic, selenium and antimony are coupled to a flexible atomic fluorescence detector which can be tailored to each element by exchange of the lamp source (boosted discharge hollow cathode lamp). Cadmium is determined by generating the volatile diethyl compound and by using a specific atomic fluorescence detector.Performance data on all three systems are also presented. Keywords: Atomic fluorescence; vapour generation; mercury; hydride forming elements Introduction Considerable attention has been drawn to the levels of the toxic elements mercury, arsenic, selenium and antimony in the last decade. Legislative and environmental pressure has forced the acceptable levels to be lowered and this puts an additional burden on the analytical chemist. Not only does the analysis have to reach lower detection levels, but also to be seen to be correct. Of the trace-element analysis techniques, atomic fluores- cence rather puzzlingly has received little attention. In the 1960s and 1970s, atomic absorption techniques were all the vogue, in the late 1970s and 1980s, inductively coupled plasmas (ICPs) and direct-current plasmas became increas- ingly predominant and in the 1990s the emphasis seems more and more to be directed to the coupling of ICPs with mass spectrometers.The latter instruments offer increasing capa- bilities and much lower detection levels for many elements, but they are extremely expensive and somewhat difficult to operate in a routine environment. Fluorescence techniques, however, offer extremely good advantages in terms of linearity and detection levels. By its inherent nature the signal obtained can be enhanced by the intensity of the lamp or excitation source. The limitations being scatter and back- ground levels of impurities. Atomic fluorescence detection, especially when coupled with vapour-generation techniques, offers both sensitivity and specificity.In this manner the benefits of atomic fluorescence are fully realized. Developments in the design of specified atomic fluores- cence detectors for mercury, for the hydride-forming elements and for cadmium have been described.1-2 Each of these systems is capable of analysing samples in the parts per 1012 (ppt) range reliably and economically. Several analytical applications will be described here. Background There has been considerable concern about pollution in the environment. The focus of much of this concern has been on the heavy metals such as mercury, arsenic, selenium, anti- mony and cadmium. A brief rdsumC of why some of these elements are important and where they are used is given below.Mercury The toxicological effect of mercury compounds on both plant and animal life has long been recognized, but it was not until the disaster at Minamata Bay in 1953 that the subject received worldwide attention.4 Mercury occurs naturally in the envi- ronment in the form of mineral deposits and also anthro- pogenically from industrial and agricultural wastes. Because of its high toxicity there has been extensive research and development into techniques that can be used to determine mercury in a variety of samples. Mercury is often present in natural gas and petroleum products, each of which can form the basis of feedstock for industrial reactions. Many reactions take place in the presence of aluminium rotors or condensers. Unfortunately, low levels of mercury can attack these aluminium components, causing stress fractures,s which can result in plant shutdown, which is extremely costly.Arsenic In nature, arsenic seldom occurs in the free state, but is usually found as mineral sulfides, as arsenides and sulforarsenides of heavy metals, as the oxide or as arsenates. All the inorganic and organic compounds of arsenic in the environment are in the 3-, 3+ or 5+ oxidation states. Arsenic and its various inorganic and organic compounds figure in many industrial processes and applications, for example, the manufacture of certain glasses, and semiconduc- tor and photo-conductor materials, amongst others. For many years there has been environmental concern regarding the possible contamination by arsenic of water, soil and food. Selenium The element selenium is of great significance in environmental analysis, biochemistry and medical chemistry.On the grounds of its ambivalent character (toxic as well as essential), there exists a particularly urgent need for an exact knowledge of the selenium content of biological and environmental materials. This is the reason that there is a requirement for methods permitting analytical access to selenium concentrations rang- ing between increased (toxic) via normal to low (deficiency) levels. Selenium specifically renders this task more difficult because the difference between increased and normal concen- tration levels is small, being only about one order of magnitude. Antimony Although the element antimony is non-essential for life it is found in biological specimens from persons who have been1642 Analyst, August 1994, Vol. I19 / I exposed to industrial sources of antimony or who are being treated with drugs containing antimony.The most likely route into the body from industrial exposure is by inhalation. This can arise from breathing the dust or fume from the grinding and high-temperature processing of anti- mony and its compounds or from stibine (antimony hydride), which is particularly poisonous. Cadmium Cadmium is toxic to humans; it accumulates in the kidneys, and too high a level results in renal failure. Cadmium metal is very volatile compared with many other toxic metals and this is another major area of risk. If cadmium alloys are heated, there is a very serious risk from the resulting cadmium vapour. These elements discussed above are of environmental concern and, therefore, there is a need to determine them accurately and reliably.Unfortunately, there are (i) often present in small amounts, and (ii) difficult to determine by conventional techniques. Of the trace-element analysis techniques, atomic fluores- cence offers improved selectivity compared with optical emission spectroscopy (OES) , because the resolution is determined by the linewidth of the source, rather than by the detection system. Fluorescence techniques offer extremely good advantages in terms of linearity and detection levels. Atomic absorption, on the other hand, although it has been extensively used, suffers from the fact that it is non-linear and measurements at lower levels are extremely difficult. As legislative and environmental pressures increase, detec- tion levels are required to be lower and lower.To maximize the analytical precision it is also important that the measure- ments and, therefore, the sample pre-treatment are optimized to ensure reliable determinations; this often leads to single- element analytical systems. When the analyst is faced with the analysis of soil, biological samples etc., the limit of detection required stretches analytical techniques. Fluorescence tech- niques often offer two orders of magnitude sensitivity improvement over absorption techniques and allow the analyst the capability of reaching the required detection limits required and traceability of the results.In atomic absorption, non-specific absorption from molecular species can occur, resulting in positive bias. This phenomenon is not usually observed with fluorescence techniques.6 Theoretical Aspects of Atomic Fluorescence A typical atomic fluorescence arrangement, shown in Fig. 1, consists of an intense excitation source focused on to an atom population in a flame. Fluorescence radiation, which is Hydrogen diffusion flame I / I / i I Lens 1 I Lens 1 Boosted discharge hollow cathode lamp Interference filter Solar blind K- - PMT Fig. 1 excitation source, atom cell and detection optics. Schematic representation of a fluorescence detector showing emitted in all directions, then passes to a detector, usually positioned at right angles to the incident light. The source can be either an atomic line or a continuum, and this serves to excite atoms by the absorption of radiation at specific wavelengths.The atoms are then de-activated, partly by collisional quenching with flame gas molecules and partly by emission of fluorescence radiation in all directions. The wavelength of the fluorescence radiation is generally the same or longer than the incident radiation, The wave- length of the emitted radiation is characteristic of the absorbing atoms, and the intensity of the emission can be used as a measure of their concentration. At low concentrations, this intensity is governed by the following relationship: If = K@I,C where If is the intensity of fluorescence radiation, C is the concentration of metal ion in solution, K is a constant, I0 is the intensity of the source at the absorption-line wavelength, @ is the quantum efficiency for the fluorescence process, which can be defined as the ratio of the number of atoms that fluorescence from the excited state to the number of atoms that undergo excitation to the same excited state from the ground state in unit time.There are five basic types of fluorescence that occur in flame measurements: (i) resonance fluorescence, (ii) direct-line fluorescence, (iii) stepwise-line fluorescence, (iv) thermally assisted direct-line fluorescence, and ( v ) thermally assisted anti-Stokes fluorescence. These have been described in detail by Thompson and Reynolds.7 Maximizing the Benefits of Atomic Fluorescence Despite its inherent advantages, atomic fluorescence has not been successful commercially.This has been due to the matrix-interference effects that occur when real samples are analysed. Coupling a fluorescence-measurement technique with a vapour-generation technique has the potential to overcome all of these problems with an additional bonus. The pre-treatment required to generate the vapour will in itself remove a great majority of the interfering species, and the bonus is the increased transfer of efficiency of the element of interest to the measurement cell. Stockwell8 has illustrated the improvements afforded by a vapour-generation technique to the sensitivity of an ICP-OES system, i.e., by a factor of 500. Each of the elements discussed here can be determined by the vapour-generation technique, and each has accessible atomic fluorescence lines and high-intensity light sources and, therefore, provide good prospects of measurement.The vapour-generation techniques required involve (i) generation of mercury itself as a vapour, (ii) generation of the hydrides of arsenic, selenium, antimony and tellurium, and (iii) genera- tion of the diethylcadmium species. P.S. Analytical, in association with Yorkshire Water Laboratory Services and the University of Plymouth, has pioneered the development of these coupled techniques, and several instruments are now readily available for routine use. Determination of Mercury by Atomic Fluorescence Mercury is an ideal element for determination by fluores- cence, as it is atomic at room temperature and has an intense resonance line at 253.7 nm.Intense mercury sources are readily available and there is little problem in producing an atom cell when the technique is coupled with vapour generation. Thompson and Godden9 proposed the use of fluorescence for the determination of mercury in 1975. Godden and Stockwelllo have described the modification of a commercial fluorescence spectrometer for mercury determi-Analyst, August 1994, Vol. 11 9 1643 nation, which, in turn, resulted in a new instrument, the PSA Merlin (P. S. Analytical Ltd. Kemsing, Kent, UK), being specifically developed for this purpose. The determination of mercury at low levels requires considerable care and attention to detail. Appropriate metho- dologies are described in detail in the Yorkshire Water 'Methods of Analysis', 5th edition." Basically, the method requires the reaction of the samples in an acid medium with tin(I1) chloride. This procedure is automated by the use of a vapour generator in which the sample, blanks and tin(@ chloride are introduced, by means of peristaltic pumps, into a gadliquid separator.Fig. 2 shows a schematic representation of an automated instrument for mercury determination. The mercury is sparged from the gadliquid separator by a flow of argon gas, and the stream containing the mercury is fed into the Merlin fluorescence detector, via a specific interface, for analysis. The instrument is used to determine total inorganic mercury, and samples that contain organic mercury must be digested before analysis. The preferred bromate/ bromide digestion method ensures that complete breakdown of organomercury compounds is achieved within 1 h.11 The reductant, reagent blank and samples are presented to the vapour generator, and the equipment is calibrated over the range of interest.Where the blank and sample matrices are completely matched, the resulting signal represents the true level of mercury in the sample. The calibration graphs are computed by the method of least squares and show excellent correlations, which confirm the linearity and sensitivity of the method and Merlin's applicability to the analysis of mercury. The Merlin system provides a rapid, sensitive, fully automated system for mercury determinations at ultra-trace levels. It can be applied to a wide range of samples, and systems have been installed in both laboratory and process-control situations. The accuracy and precision of the technique is shown in Table 1.Its performance exceeds that of all other commercial systems, even those relying on some method of preconcentra- tion on gold traps, etc. The instrument can be used to analyse samples over a wide order of magnitude (0-10 ppm) and with excellent detection levels (0.37 ppt). The determination of mercury by the cold-vapour technique is virtually interference free. Compounds that form strong complexes with mercury, e.g., halides and sulfides, can cause suppression; such Fig. 2 Schematic arrangement of mercury analysis system compris- ing A, autosampler; B, hydride vapour generator; C, Merlin atomic fluorescence detector; and D, computer. The computer software provides complete control and data management software.Table 1 Certified reference materials for mercury Certified reference material Certified value Value obtained NIST SRM Urine BCR CRM 186 0.105 f 0.008 pg ml-1 0.103 f 0.005 pg ml-1 Pig kidney 1.97 f 0.04 ng g-1 1.987 f 0.003 ng g-1 BCR 143 Sewagesludge 3.92 f 0.23 pgg-I 3.82 -C 0.13 pgg-l River sediment NIST SRM 8407 50 rt 2 pg g-1 50 f 1 pgg-1 interference is normally overcome during the sample-diges- tion stage. Several metals, e.g., silver and gold, form strong amalgams with mercury. These elements, however, are seldom found at high concentrations in environmental and industrial samples. Determination of Arsenic, Selenium and Antimony While mercury is a relatively simple element to determine by fluorescence, the technique can be extended to other ele- ments. Research has been camed out in conjunction with The University of Plymouth. Fundamental scientific work has been undertaken, as well as instrument optimization and simplification.The instrumentation concepts have focused on four main areas: (i) the light source, (ii) the atom cell, (iii) the optical design, and (iv) the read-out and data-processing system for the instrumentation. For the determination of arsenic and other hydride-forming Table 2 Certified reference materials for arsenic Certified reference CASS2 material Certified vaiue/pg 1-1 Value obtainedpg I-* (Nearshore sea- water 1.01 -C 0.07 1.08 f 0.18 (Estuarine water) 0.765 ? 0.093 0.697 f 0.020 SLEW1 Table 3 Certified reference materials for cadmium Certified reference material Certified value Value obtained NIST SRM 1643c (Water) 12.2 rt 0.1 pgl-1 12.6 f 0.5 pg1-I BCR 144 (Sewage Sludge) 3.41 k 0.25 pgg-l 3.34 f 0.15 pgg-l BCR 145 (Sewage Sludge) 18.0 & 1.2 pg g-1 18.24 rt 0.7 pg g-1 Timdmin Fig.3 Chromatogram of mercury speciation: A, 53 pg ethylmercury chloride; B, 51 pg diethylmercury. Arrow indicates solvent injection, hexane.1644 Analyst, August 1994, Vol. 119 elements, boosted-discharge hollow-cathode lamps have been found suitable for the excitation source of the detectors. A simple hydrogen-diffusion flame provides the atom cell. The optical design is more complex than that required for mercury and requires attention to the selection of optical filters and reduction of background scatter.Changing a lamp allows a range of detectors to be available commercially with little additional modification to the design. Data processing and control facilities are provided, with software similar to that used with the Merlin detector. Instrumentation for arsenic atomic fluorescence basically consists of a boosted-discharge hollow cathode lamp as an excitation source, a hydrogen- diffusion flame as an atom cell, a collection of lenses to collect and focus useful radiation, an interference filter to achieve wavelength isolation and a solar-blind photomultiplier tube. Illumination from the excitation source is at right angles to the detection axis to suppress detection of radiation from the excitation source. A multi-reflectance filter specifically deve- loped to maximize the optical transmission at the wavelength of interest has proved to be a versatile and sensitive option, which allows determination of arsenic, selenium, antimony and tellurium at significantly lower levels than can be achieved elsewhere .z The analytical operation of the arsenic fluorescence detec- tion system is similar to that for mercury, albeit involving Time/s Fig.4 Fluorescence response of dimethylselenide standard (a) and that from a typical sea-water sample (6). different chemistry. Sodium tetrahydroborate is used instead of tin(I1) chloride and its reaction with hydrochloric acid produces a steady stream of hydrogen. The hydride anion converts the arsenic(I1r) into the hydride form, and the excess of hydrogen provides the fuel for the atom cell (i.e., hydrogen flame).Arsine produced by the reaction of the tetrahydrobor- ate with the acid is transferred by the argon stream into the hydrogen-diffusion flame. The signal shape is similar to that produced for mercury except that the plateau is achieved somewhat quicker and the memory effects are also minimized. The hydride-generation process is subject to several chemical interferences. Transition metal ions, e.g., nickel, copper and cobalt, are known to cause suppression of the hydride- generation signal. These effects can be minimized by using high acidity and low reductant concentrations. Under these conditions the interfering species is supposedly reduced to a lesser extent and kept in solution with the high acid concentrations. One of the advantages of using atomic fluorescence is that the additional sensitivity allows dilution of the sample to overcome these interference effects.Since the signal follows the on-going kinetic reaction taking place in the reaction vessel, any interfering species can easily be diagnosed by evaluation of the peak shape. This information adds to the confidence in the resulting data. The calibration graph is linear between 0 and 100 pg 1-1 of arsenic. Typically, detection levels in the region of 0.010 pg 1-1 are achievable by use of the vapour generator coupled with the specific fluorescence detection system described above. The accuracy of the technique is shown in Table 2, where the results for certified water reference materials are presented. Selenium, antimony and tellurium can be determined in a similar fashion.Determination of Cadmium as the Diethyl Compound With the success of vapour generation approaches for mercury and the hydride-forming elements, the extension to other elements, especially those with good excitation sources such as cadmium and lead, is an obvious priority. Several groups3J2J3 have investigated the conversion of cadmium and lead into the die thy1 and te traethyl compounds, respectively. Recently, Goodall et aZ.3 have coupled the PSA vapour generation technology to a specific atomic fluorescence detector for cadmium determination. The technology is similar to that used from the hydride atomic fluorescence detector, except that no hydrogen is produced by the chemical reaction to form the diethyl compound: Cd2+ + 2BEtd- = CdEtz + 2BEt3 The efficiency of the ethylation process can be reduced by Table 4 Comparison of vapour generation-atomic fluorescence spectrometry techniques Analyte Generated species Excitation source Filterhm Hg Mercury vapour Low-pressure vapour 254 k 10 discharge lamp hollow cathode lamp (multi- As Covalent hydrides Boosted-discharge 199-220 Se reflectance Sb filter) Te Cd Diethyl compound Vapour discharge lamp 228 k 10 Wavelengths detectednm 253.57 193.76 (As) 197.26 (As) 196.09 (Se) 203.99 (Se) 206.28 (Sb) 217.58 (Sb) 214.27 (Te) 228.33 Atom cell Detector Flow cell UV-VIS PMT Argon-Air Solar-blind PMT Hydrogen flame from reagents Argon Solar-blind PMT Air Hydrogen flame from cylinder * PMT = photomultiplier tube.Analyst, August 1994, Vol.11 9 1645 compounds that decompose the ethylating reagent.High acidity and transition-metal ions have been shown to suppress the analytical signal. Careful control of the pH and the use of citratekitrate masking agents effectively overcome these problems. An additional flow of hydrogedargon is required to create the atomization cell. In addition, a cadmium discharge lamp is used as the excitation source rather than a boosted hollow cathode lamp; the power supply module is simpler in concept. Moreover, the optics and data-collection systems are basically the same as those designed for the hydride fluores- cence detector. A prototype instrument has been constructed along the above lines, and initial results show significant promise. Detection levels in the low ppt range are possible; the performance for certified reference materials is shown in Table 3.Speciation The sensitivity of each of these detectors is such that they are also suitable for speciation studies, and the results presented here show considerable promise. Organomercury species have been separated by high-performance liquid chromatography14 and gas chromatography (GC) techniques. 15 Both approaches are compatible with the PSA Merlin detector. The latter approach utilizes a pyrolyser to break down organomercury species thermally as they exit the GC column. This is typically maintained at 800°C. The resulting mercury vapour is then detected by atomic fluorescence. Recently, Ebdon et aZ.16 have used this approach to speciate mercury in oil samples. Fig. 3 shows a typical chromatogram for 51 pg of monoethylmercury and 53 pg of diethylmercury.The GC column (SGE (UK) Ltd., Milton Keynes, UK) (BP-5, 60 cm x 0.53 mm, 5% phenyldiethylsiloxane) was maintained at 100°C. The transfer line between the column and the pyrolyser was heated to 150°C to prevent condensation of mercury species. Helium was the carrier gas (at 7.5 ml min-1). A make-up gas of argon then conveyed the analyte to the detector. A readily available economic system can, therefore, be provided by using the fluorescence detector. Similar approaches can also be made with the hydride-type detectors in order to speciate arsenic, selenium and antimony compounds. Donard et al.17 have used a cryogenic trap coupled to the atomic fluorescence detector to determine selenium species in sea-water.Fig. 4 shows a typical chromato- gram for 1 ppt of dimethylselenide standard solution and a sea-water sample containing dimethylselenide and dimethyl- diselenide. Conclusions Atomic fluorescence is already proving to be a very reliable and sensitive means for determining mercury, arsenic, sele- nium, antimony and tellurium. Recent research has shown the potential for extension of those concepts to cadmium and lead. Table 4 shows the variation between the requirements for each of the types of fluorescence detector described here. Sensors are commercially available for mercury and the hydride- forming elements, and the potential for cadmium and lead is clearly demonstrated here. The sensitivity of each of these detectors is such that they are also suitable for speciation studies, and the results presented here show considerable promise.The advancements in the analytical applications of atomic fluorescence could not have been achieved so successfully and in such a short timescale without assistance from a number of sources. Their assistance is gratefully acknowledge here. Professor L. Ebdon, Dr. P. Goodall, Dr. S. Hill and A. Mohammad from the University of Plymouth are thanked, as is Dr. C. Thompson at Yorkshire Water LabServices, Sheffield. Methods for mercury in water have been developed at Yorkshire Water LabServices, Sheffield Laboratory, Char- lotte Rd., Sheffield, UK, S2 4EQ. Professors 0. Donard and D. Armouroux from the Laboratory of Photophysics and Photochemistry at the University of Bordeaux, France, are thanked for their co-operation on the selenium speciation. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 References Stockwell, P. B., Thompson, K. C., Henson, A., Temmerman, E., and Vandecasteele, C., Znt. Labmate, 1989, 14,45. Corns, W. T., Stockwell, P. B., Ebdon, L. C., and Hill, S. J., J. Anal. At. Spectrom., 1993, 8,71. Goodall, P., Hill, S. J., Ebdon, L. C., Stockwell, P. B., and Thompson, K. C., J. Anal. At. Spectrom., 1933,8,723-729. Smith, W. E., and Smith, A. E. (eds.), Minamata, Holt, Rinehardt and Winston, New York, 1975. English, J. J., Paper presented at the First Ethylene Producers Conference Houston, Texas, USA, April 4th, 1989, American Institute of Chemical Engineers, New York, USA. Microfiche no. 39, paper 74 C. West, C. D., Anal. Chem., 1974,46, 797. Thompson, K. C., and Reynolds, R. J., Atomic Absorption, Fluorescence and Flame Emission Spectroscopy. A Practical Approach, Griffin, London, 1978, pp. 264-265. Stockwell, P. B., Lab. Pract., 1990,39,6,29. Thompson, K. C., and Godden, R. G., Analyst, 1975,100,544. Godden, R. G., and Stockwell, P. B., J. Anal. At. Spectrom., 1989,4, 301. Yorkshire Water, Methods of Analysis, Yorkshire Water, Leeds, 5th ed., 1988, (1989), sect. 9. D’Ulivo, A., and Chen, Y ., J. Anal. At. Spectrom., 1989,4,319. Sturgeon, R. E., Willie, S. N., and Berman, S. S., Anal. Chem., 1989,61, 1867. Bushee, D. S., Analyst, 1988, 113, 1167. Lansens, P., Meuleman, C., Laino, C. C., and Baeyens, W., Appl. Organomet. Chem., 1993, 7 , 45. Ebdon, L. C., Mohammad, A. S. A., and Stockwell, P. B., unpublished results. Donard, O., Amouroux, D., and Stockwell, P. B., unpublished results. Paper 3107021 B Received November 25, I993 Accepted February 8, 1994

ISSN:0003-2654    

DOI:10.1039/AN9941901641

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Analyst, August 1994, Vol. 11 9 1647 Lead Hydride Generation Atomic Absorption Spectrometry: An Alternative to Electrothermal Atomic Absorption Spectrometry A Review Yolanda Madrid and Carmen Chmara" Departamento de Quimica Analitica, Facultad de Quimicas, Universidad Complutense, 28040 Madrid, Spain Historical, theoretical and practical aspects of lead hydride generation and its application to spectrochemical analysis, especially atomic absorption spectrometry, are reviewed. Lead hydride generation conditions (particularly the need to use oxidizing agents), possible generation and atomization mechanisms and interferences are described and discussed in detail. The main applications of lead hydride generation atomic absorption spectrometry to the determination of lead in a wide variety of matrices and its advantages over graphite furnace atomic absorption spectrometry in the determination of low levels of lead are addressed. Keywords: Lead determination; hydride generation; atomic absorption spectrometry; lead hydride; review Introduction and Scope of the Review Hydride generation combined with atomic absorption spec- trometric detection has become one of the most powerful analytical tools for the determination of elements such as As, Se, Bi, Sn, Ge, Pb, Sb and Te.The advantages of hydride generation atomic absorption spectrometry (HGAAS) over other atomic absorption spectometric techniques such as the flame and graphite furnace methods are increased atomization efficiency, higher selectivity because the analyte is removed from the matrix as a volatile compound and detection limits at the pg 1-1 level or lower for the elements cited above.Considering these advantages, it is not surprising that HGAAS has become well accepted for the determination of elements that form hydrides at low concentrations. However, certain key aspects of this technique remain unclarified and require further investigation. The generation of lead hydride has been relatively little studied in comparison with the generation of other hydrides. This can be attributed to the difficulties with lead hydride formation, namely the low yield and low stability of the volatile hydride. Since the first report on the analytical applications of lead hydride by Thompson and Thomersonl in 1974, several papers have described attempts to increase the efficiency of lead hydride generation and to make the HGAAS competitive with electrothermal atomic absorption spectrometry (ETAAS) [this review refers specifically to graphite furnace atomic absorption spectrometry (GFAAS)], which is the most popular technique for the determination of low levels of lead in complex matrices.* To whom correspondence should be addressed. This paper reviews the current statuts of lead HGAAS with emphasis on its capabilities and shortcomings, and discusses key aspects such as the lead hydride generation mechanism and interferences. Its performance is compared with that of GFAAS. Problems Related to the Low Efficiency of Lead Hydride Generation: Need to Use Oxidizing Agents Lead hydride, PbH4, is unstable at room temperature (a boiling-point of approximately - 13 "C has been reported2) and so far it has not been prepared in pure form.Further, the synthetic methods successfully applied to obtain the hydrides of the Group IVB elements have not provided good results with lead.3 Early attempts to prepare lead hydride involved the reaction of HCl on Mg-Pb alloy, electrolysis of dilute H2S04 using a lead electrode and direct reaction of lead and atomic hydrogen. However, for none of them was direct evidence of lead hydride formation reported.4 In 1963, Saalfeld and Svec5 determined the heats of formation and M-H bond energies of the Group IVB and VB hydrides using mass spectrometry. Lead hydride was prepared by the reaction of HCI with Mg2Pb, although the low efficiency of formation and rapid decomposition made the use of several batches necessary to complete the mass spectrometric studies.The results obtained for bismuthine and lead hydride were only approximate owing to the low precision of the analytical measurements. The heat of formation and M-H bond energy for plumbane were 59.7 and 49.0 kcal mol-1, respectively, which were higher than those nbtained for the other Group IVB and VB hydrides. Later, Jeffes and McKerrell6 calculated the values of the thermodynamic functions (AWt, AS", and AGOt) of the Group l A , IIA, IIIB, IVB, VB and VIB hydrides. They found PbH4 and BiH3 to be more unstable than those hydrides most commonly used for analytical purposes (AsH3, G e b , H2Te, H2Se, SnH4). The low stability and the volatility of lead hydride explain the lack of data on its physical, chemical and thermodynamic properties and the poor development of the lead hydride technique for the determination of lead using NaBH4 as reducing agent.Thompson and Thomerson' published the first report on lead hydride generation for analytical purposes. Lead hydride was generated by the direct reaction of an acidified sample (0.2 mol 1-1 HCI) and sodium tetrahydroborate (NaBH4) solution T YO d v ) . Atomization was carried out in a silica tube mounted in an air-acetylene flame. The poor sensitivity obtained for lead with respect to the other hydride-forming elements indicated the poor efficiency of conversion to the hydride (less than 5%). The detection limit was 0.1 pg ml-1.1648 Analyst, August 1994, Vol.119 However, the breakthrough in the attempt to increase the efficiency of lead hydride generation came from Fleming and Ide7 and Vijan and Wood,s who pioneered the use of the oxidizing agents K2Cr207 and H202, respectively, and of NaBH4 to improve the efficiency of lead hydride production. In both instances the prior oxidation of lead markedly increased the sensitivity of determination by improving the efficiency of lead hydride generation. These papers were the starting point of lead HGAAS and nowadays it is accepted that an oxidant must be used to determine lead by this technique. The increased efficiency of lead hydride generation in the presence of oxidizing agents has been attributed to the formation of metastable Pb'" compounds before the formation of lead hydride in the reaction of Pb with NaBH4. This reaction path and the nature of acid-oxidant mixtures employed in lead hydride generation are discussed in detail in the following sections.Description of Acidaxidant Mixtures Employed in Lead Hydride Generation Compared with other hydrides, little work has been published on lead HGAAS. All previous studies have tried to increase the efficiency of PbH4 generation and decrease the detection limit in order to include this element in multi-element analysis schemes involving hydride generation. In 1974, Thompson and Thomersonl reported a method for the determination of Pb and also As, Bi, Ge, Sb, Se and Sn by HGAAS. The hydrides were generated by adding the acidified sample (0.2 moll-1 HCI) to dilute YO m/v) NaBH4 solution using nitrogen as the carrier gas.The liberated hydrides were atomized in a silica tube mounted in an air-acetylene flame. Both the acid and NaBH4 concentrations were critical for the lead analyte and the efficiency of conversion to hydride was poor (less than 5%). The detection limit and characteristic concentration were 0.1 and 0.08 pg ml-1, respectively. In 1976, Fleming and Ide7 published a method for the determination of As, Pb, Bi, Se and Te in steel by the formation of their volatile hydrides and detection by AAS. Lead hydride was generated in the presence of K2Cr20r tartaric acid and the generation efficiency was about 10%. The enhancement provided by the oxidizing agent was attributed to a modifying effect of the K2Cr207 on the reduction by NaBH4.The method was presented as a viable alternative for the determination of lead in iron and steel. In the same year, Vijan and Woods described the semi- automated determination of lead by HGAAS. Lead was converted into its hydride by reaction of the sample, contain- ing 0.7% v/v of nitric acid or 1% vlv of perchloric acid, with 12% hydrogen peroxide and 4% d v NaBH4. The generated hydride was swept by a stream of nitrogen into an electrically heated silica tube at 860 "C and the absorbance of lead was recorded at 217.0 nm. The characteristic concentration and detection limit were 0.6 and 0.1 pg 1-1, respectively. The acid-oxidant mixture was also employed by Hon et al. ,9 who used 10% v/v H202 and 0.5% vlv HN03 and hydride atomization in a silica T-tube heated in an air-acetylene flame.The characteristic amount and detection limit of 11 and 24 ng, respectively, confirmed that the prior oxidation of lead markedly increased the sensitivity. The HN03 concentration was critical and had to be strictly controlled to achieve good precision. In an interesting study, Jin and TagalO compared K2Cr20T- malic acid, HN03-H202 and (NH4)2S208-HN03 oxidant- acid mixtures in terms of generation efficiency, sensitivity and selectivity. Peroxodisulfate-nitric acid was the most efficient oxidizing agent but it gave high blanks and poor selectivity compared with the others. The influence of the type of oxidizing agent [K2Cr207, Ce(SO&, KMn04, H202 and Na2S208] on lead hydride generation was also reported by Castillo et al. 11 They found an exponential relationship between the atomic absorption signal obtained and the E" value of the oxidizing agent.Recent studies have reported new lead hydride generation media. Thao and Zhou12 achieved a detection limit of 0.37 pg 1-l for lead in food samples using 10% d v K3Fe(CN)6- 0.2-0.6 mol 1-1 HC1 medium and 2% m/v NaBH4. Li et al.13 successfully used 0.3% m/v oxalic acid and 3% m/v cerium(rr1) ammonium nitrate with KBH4 reducing agent to determine lead by AAS in soil reference materials. Madrid et a1.14 studied the effect of different acids on the efficiency of lead hydride generation in potassium dichromate medium. Potassium dichromate was chosen as being a more selective medium than hydrogen peroxide or ammonium perodisulfate. The acids tested were lactic, malic, tartaric, citric, oxalic, benzoic and nitric acids.Fig. 1 shows that lactic, malic and tartaric acids give the best results, whereas citric and oxalic acids provide inadequate lead hydride generation, possibly owing to partial dichromate reduction by these acids before addition of NaBH4. Benzoic acid is unsuitable because it is insoluble in water. Nitric acid, the most widely applied reagent for lead hydride generation, is unsatisfactory in this medium. Lactic acid gave optimum lead hydride generation and its presence in the reaction medium considerable en- hanced the efficiency of lead hydride generation and acceler- ated the reaction kinetics. The NaBH4 concentration had a more marked effect for lead than for the elements such as selenium and arsenic, and the optimum concentration was significantly lower (4%) in lactic acid-K2Cr207 than in ammonium peroxodisulfate-HN03 (8%) or peroxide-nitric acid (10%) media. The detection limit (30) was 0.4 pg 1-1 and the method was applied to determine lead in fish, vegetables and liquid samples.A different lead hydride generation method was developed by Zhang et al. 15 using a nitroso-R salt (1-nitroso-2-naphthol- 3,6-disulfonic acid disodium salt). A characteristic concentra- 0.200 8 9 0.100 0 2.0 6.0 Acid (% m/v) 10.0 Fig. 1 Effect of different acids on lead hydride generation in 1% m/v potassium dichromate oxidant medium: (a) lactic acid; (b) tartaric acid; (c) malic acid-oxalic acid; (d) citric acid; (e) nitric acid. (a) 50 ng of Pb; (b)-(e) 100 ng of Pb. From reference 14.Analyst, August 1994, Vol.11 9 1649 tion of 0.8 pg 1-1 was reported. The mechanism suggested involved the oxidation of lead(1r) to lead(rv) while chelated with the nitroso-R salt. The proposed method was applied to the determination of lead in reference materials (soil and vegetable samples). Hengwu et aZ. 16 used a similar procedure in a systematic study of the effect of chelating agents and found that l-(2-pyridylazo)-2-naphthol-6-sulfonic acid (PAN- S), Bromopyrogallol Red, Pyrocatechol Violet and Alizarin Red S significantly enhanced the efficiency of lead hydride generation. PAN-S was among the most effective. A charac- teristic concentration of 1.3 yg 1-1 was reported. The method was validated by determining lead in spiked tap and natural water samples and the recoveries were between 90 and 105%.The mechanism proposed is the direct generation of lead hydride from chelated Pb" instead of from metastable Pb'V. Lead hydride generation from organic media has also been reported. However, the results are contradictory as to whether or not lead hydride is actually generated. Aznarez et aZ.17 were the first to report a vapour-phase method for lead in a non-aqueous extraction phase. Lead hydride was generated in an aliquot of lead pyrrolidine-l- carbodithioate extract in chloroform by the addition of NaBH4 in N,N-dimethylformamide (DMF). The proposed method gave a detection limit of 1 pg 1-1 of lead in the chloroform extract. Selectivity was improved by extracting the lead into the organic phase. The authors claimed that the generation of lead hydride from an organic phase obviated the need for oxidizing agents in the reaction medium.The method was applied to the determination of lead in BCS standard steels and airborne particulates. The same group18 later developed a similar method for the determination of lead in gasoline by AAS. The sample (1 ml of gasoline) was diluted with DMF and hydride was generated by direct injection of NaBH4-DMF solution. The method was applied to the determination of lead in commercial gasolines, with good accuracy and precision. Nerin et a1.19 studied the behaviour of several lead compounds in organic media with a hydride generator. A wide range of NaBH4 concentrations, different types and concen- trations of acid media and various oxidants were tested, but no lead hydride was generated and the analytical signal obtained was due to the volatilization of the Pb& itself and not to the formation of PbH4, as might have been expected.The same effect was observed when NaHC03 was used instead of NaBH4. The in situ decomposition of NaHC03 in an acid medium released C02 which, together with the carrier gas, carried the Pb& to the silica tube of the atomizer. This paper demonstrated that PbH4 is not generated from organic media under similar conditions to those required in water. The method was applied to the determination of volatile lead compounds in gasoline by dissolution in Me2S02 and volatili- zation of the volatile lead with NaHC03 in acid medium. The detection limit was 17 pg 1-1 of lead in 20 ml of sample.Atomization Mechanism of Lead Hydride Generation in Externally Heated Quartz Tube Dedina and Rubeska20 and Welz and Melcher21 proposed that atomization in flames and quartz tubes proceeds by a hydrogen radical reaction: +H +H +H +H PbH4 + PbH3 + PbH2 + PbH + Pb + 4H2 The required H radicals are generated by the reaction of oxygen (residual oxygen in the argon and the sample solution) and hydrogen (generated from the NaBH4 reaction) and are formed mostly near the gas inlet to the heated portion of the atomizer: H + 0 2 + OH + 0 0 + H2 + OH + H OH + H2 + H20 + H Optimum sensitivity is achieved by minimizing the oxygen concentration, which depends not only on the type of hydride, but also on the atomization temperature. At high tempera- tures (about lo00 "C) the very small amount of oxygen dissolved in the sample may be enough for optimum sensitiv- ity.At low temperatures the oxygen present in the system as a contaminant may not be sufficient for optimum sensitivity and additional oxygen may be required. Agterdenbos and Bax22 stated that the radicals are not abundant enough for this kind of reaction and proposed a reaction catalysed by H and 0 radicals: 3PbH4 + 3 0 2 -+ 3Pb + 6H20 Forsyth and Marshall23 concluded that hydrogen radicals formed in the heated quartz tube not only participate in lead hydride atomization but can also volatilize lead deposited on the quartz surface: Pb(s) + 2H + PbH2 (8) Thermal dissociation was not excluded, but it was assumed that this reaction leads to decomposition products which are retained in the tube, and atomized to some extent when hydrogen enters the quartz tube by formation of hydrogen radicals. The quality of the inner quartz surface considerably influences the sensitivity. At high temperatures (about lo00 "C), SiOH groups of the quartz tube surface react with hydrogen, resulting in the release of H radicals.Optimum performance is most conveniently maintained by rinsing the tube in 40% HF.21 Mechanism of Lead Hydride Generation Hydride is generated by the NaBH4-acid reduction system according to the reaction NaBH4 + 3H20 + H+ + H3B03 + Na+ + 8H+ + MH, + H2 (excess) The presence of oxidizing agents in the lead generation system before the reduction step accelerates the reaction rate and increases the sensitivity of lead determination.Although the effect of these oxidizing agents is not well characterized, the enhancement has been attributed to the formation of metastable PbIV compounds before lead hydride is produced in the reaction of Pb with NaBH4. There is an exponential relationship between the efficiency of lead hydride generation and the EO value of the oxidizing agents with this efficiency increasing in the order K2Cr207 (E" = 1.33 V) < H202 (E" = 1.78 V) < (NH4)&O8 (E" = 2.01 V) .I1 The role of NaBH4 in lead hydride generation would be to act as a hydrogen ion donor to metastable Pb'" compounds as shown in the reaction BH4- + 3H2O + PbIV + H3B03 + 3H+ + PbH4 The formation of lead chelates would reduce the E" value of the lead system and favour the conversion of Pb" into Pb'".This would explain the need to use chelating agents when lead hydride is generated with K2Cr207 as oxidizing agent. Consequently, nitric acid, which is the most widely used reagent for lead hydride generation, is unsatisfactory in this medium, perhaps because the Crlv--Crlll system is not a strong enough oxidant to form metastable PbIV compounds, produc- ing an intermediate species in the lead hydride formation and stabilized by chelating agents such as lactic, malic or tartaric1650 Analyst, August 1994, Vol. 11 9 acid, thereby increasing the efficiency of lead hydride genera- tion. Other workers, such as Wang and Barnes,24 consider that the oxidizing agents, act as depolarizers, which decrease the overpotential created on the lead by hydrogen.This over- potential significantly decreases the rate of reaction of the NaBH4 with lead species. Interferences in Lead Hydride Generation: Phenomenology and Mechanism As the analyte is separated from the matrix by volatilization in the form of the gaseous hydride, spectral interferences are usually insignificant in HGAAS. However, there are two types of non-spectral interferences: those affecting the analyte in the gaseous phase and those arising in the liquid phase during hydride generation. Owing to the very limited number of elements that can be volatilized by hydride generation, vapour-phase interferences other than mutual interferences of hydride-forming elements are very unlikely. The liquid-phase interferences have been more fully investi- gated.They cause changes in the hydride release rate and decrease the efficiency of the hydride release and may be classified as follows: (1) Interferences due to the chemical form of the analyte.25 (2) Matrix interferences arising when the matrix affects the efficiency of hydride generation. The main matrix interfer- ences are those caused by metal ions. Their methodology, mechanism and elimination have been covered by a number of reviews.2&28. The predominant mechanism is the capture and catalytic decomposition of the volatile hydride by the finely dispersed metal. (3) Incomplete mineralization, which may alter the effi- ciency of hydride generation. Some of these interferences, especially those from transi- tion metals, can even inhibit lead hydride generation.However, because of the specificity of lead hydride generation (need to use an oxidizing agent) the interference studies are inconclusive and show that selectivity depends on the medium, oxidizing agent, chelating agent and atomization system. In an attempt to systematize the selectivity of lead HGAAS, five types of interferences have been identified, caused by hydride-forming elements, alkali and alkaline earth metals, anions and transition metals, with the last receiving particular attention. Hydride-fonning Elements Inter-element interferences among volatile hydride-forming elements generally occur in the atomizer. The mechanism of these interferences is still largely unknown and their effect depends on the generation procedures and on the atomizer design and temperature.They are thought to be due to the formation of stable diatomic molecules such as AsSb29 or to the competition of hydrides for free H radicals in the atomizer .21 Lead is less affected by this kind of interference than other hydride-forming elements because of the particular conditions of lead hydride generation, in which the efficiency of the hydride reaction is very low. Studies of the effect of hydride-forming elements on the efficiency of lead hydride generation with (NH&S208, K2Cr207 and H202 as oxidizing agents10 showed that Sb, As and Sn do not interfere up to a Pb-to-interferent ratio of 1 : 50000 and that potassium dichromate is the most interfer- ence-free agent. Selenium and tellurium severely suppressed the Pb signal at Pb-to-interferent ratios of 1 : 1 and 1 : 10, respectively, in the hydrogen peroxide and peroxodisulfate systems.D'Ulivo and Papoff30 also found severe suppression of the 5 pg 1-1 lead signal in the presence of Se and Te at the 200 pg 1-1 level whereas the same level of the other hydride-forming elements did not significantly affect the signal. The lead hydride was generated in HCl-Hz02 medium. Bonilla et al.31 found that in HN03-H202 medium there was 65% and 84% depression of the lead signal by Te and Se, respectively, at a Pb-to-interferent ratio of 1 : 5. No suppres- sion of the signal was observed up to Pb-to-interferent ratios of 1 : loo00 for As"', BilIr and SblI1. Madrid et aZ.32 noted that in HN03-(NH4)2S208 generation medium Serv completely suppressed the signal at a Pb-to-Se ratio of 1 : 100.Snrv, BilIr and As"' did not affect the analytical signal even at Pb-to-interferent ratios of 1 : 1OOOOO. Interferences due to SeIV, Snrv, BPI1, SbrlI, Terv and Ad1' were also tested by generating lead hydride in lactic acid- K2Cr207 medium14 and in all instances, including those with SeIV and TeIV, the changes in the signal at ratio up to 1 : 1OOOOO were insignificant. These results suggest that, except for Se and Te, the interferences caused by the hydride-forming elements are not important in the determination of lead by HGAAS. However, there are sometimes considerable discrepancies in the magni- tude of the interferences reported. Also, it should be noted that the work cited in the above references was performed using a variety of hydride generators and that the atomization systems were of flame, quartz tube and electrically heated tube types.Depending on which of these atomizers is used, the sensitivity and severity of interferences will differ. Further, the need for an oxidizing agent adds other possibil- ities. The action of foreign ions may be different in the presence of H202 and (NH&S208 and the interference mechanism may also be different. In this respect, most workers simply mention the existence of interference and observe that too little work has been done to allow discussion of the possible interference mechanisms. The same can be said of the other hydride-forming elements. The first systematic work in this field was by Welz and Melcher21 and Dedina and Rubeska.20 They proposed a hydride radical reaction as the mechanism of flame and quartz tube atomization, the same as that given for lead earlier. The required H radicals are generated in flames by combustion processes.When another hydride-forming ele- ment is present in the sample in addition to the analyte, the required H radicals are consumed by the matrix hydrides. Hence for trace amounts of hydride the degree of atomization is inefficient or low.21 Apart from the explanation proposed by Welz and Melcher, the following interference mechanism based on the formation of stable mixed diatomic molecules was suggested by Dittrich and Mandry? Mtrace + 3 Mrnatrix excess + MtraceMrnatrix + M2matrix Pb + 3 Se -+ PbSe + Se2 Pb + 3 Te + PbTe + Te2 Although inter-element interferences among volatile hy- dride-forming elements generally occur in the atomizer, they can also take place during hydride formation in the liquid phase by a competitive reaction between the interfering elements and lead for N a B b .The magnitude of the effect might be highly dependent on the oxidizing agent selected for lead hydride generation. Alkali and Alkaline Earth Metals These elements are present at high concentrations in a wide variety of matrices and do not interfere at commonlyAnalyst, August 1994, Vol. 119 165 1 encountered levels. In some cases the presence of consider- able amounts of alkali and alkaline earth metals (Pb-to- interferent ratio of 1 : 106) had a positive effect on lead hydride generation by increasing the analytical signals. The reason for this enhanced generation is still not well understood.31 Anions Castillo et a1.33 reported a complete study of interferences when H202 or S2082- was used as the oxidizing agent.They differentiated two interference mechanisms depending on whether an anion or a chelating agent is present in the reaction medium. The first type is related to the reducing character of the anion or chelating agent (hydrogensulfides, iodides or organic matter) which reduces the hydrogen peroxide and prevents the subsequent oxidation of lead to the metastable tetravalent state. Moreover, it is necessary to consider chelating agents such as phosphates, EDTA and oxalates, which prevent both the oxidation of lead to the tetravalent state and its reduction to lead hydride. The interferences caused by anion interferents and chelat- ing agents differed significantly depending whether hydrogen peroxide or ammonium peroxodisulfate medium was used, with the exception that EDTA totally suppressed the signal.When S2082- medium was used, hydrogensulfides and iodides did not interfere and the suppressing effect of phosphates, borates, sulfates, oxalates and citrates was minimal compared with that in H202 medium. Among the anion and chelating agent interferences studied, the strongest was by the EDTA, as a Pb-to-interferent ratio of 1 : 1 completely suppressed the signal for both generation media. The presence of large amounts of C1- or Br- at Pb-to-anion ratios of 1 : 1OOOOO does not affect lead hydride generation. Their high concentration in natural matrices means that this is important, particularly for chloride, which is one of the main interferents in the determination of lead by GFAAS.Some workers have reported up to a 50% lead signal enhancement in the presence of Cl- and Br-.W This effect was found to be independent of the lead concentration within the dynamic range studied and it was explained by hypothesizing that PbI" forms more a stable complex than PbI1 with chlorine, so that the redox reaction c1 PbCl,(m - 2) + 2H202 + 4H+ + PbCl,(n - 4) + 4H2O is shifted towards the right and the yield of PbH4 in the subsequent reaction with NaB& is increased. The same workers showed that sulfate (5 x 10-3 moll-1) percolate (0.2 mol 1-I), phosphate (2 x 10-3 moll-1) and EDTA (5 X 10-7 mol 1-1, 0.2 ppm) do not affect the lead signal at the 5 pg 1-1 level if the solution is made 10-5 mol 1-1 in Zn.The strong effect of complexing agents such as EDTA was eliminated by addition of Zn salts. To determine lead in wines by HGAAS, Cacho et al.34 studied the influence of ethanol, tartaric acid and S02. as characteristic components of wine. The hydride generation efficiency decreased markedly in a generation medium con- taining up to 5% of ethanol, above which the efficiency varied very little. This behaviour was attributed to variations in pH and in the oxidation-reduction potentials of the substances present in the reaction medium. The presence of tartaric acid also affected the lead hydride generation efficiency, and at working acid concentrations above 8 g 1-1 the lead signal was depressed by 60%.Sulfur dioxide in the range 0.2-1.0 g 1-1 studied did not affect the lead signal. When lead hydride generation was later carried out in water containing propor- tions of these compounds similar to those found in wine, an acidity study showed that the effect of HCl concentration was much stronger than in water or DMF and a lower HCl concentration than in water was needed to produce the maximum signal. Further, the variation of the atomic absorp- tion signal with NaBH4 concentration was completely differ- ent from that found in water. Using optimum conditions for HCl and H202, the maximum sensitivity was achieved at an NaBH4 concentration of 21%, compared with 7% in water. It was pointed out that even with different optimum conditions for lead hydride generation, the signals are the same in water and ethanol media and the interferences due to ethanol and tartaric acid are eliminated by increasing the NaBH4 concen- tration.Catalysis and Interference by Transition Metals: a Controversiul Issue One of the major drawbacks of HGAAS is the severe interference effects associated with Group VIII (Fe, Co, Ni) and IB (Cu, Ag) elements. Several reviews have been published on this topic, but few include information about the possible mechanisms involved. Smith35 and Welz and Melcher36 proposed the preferential reduction of the interfer- ing metal in solution to a different oxidation state or to the free metal. The latter forms a precipitate, which can then either coprecipitate the element of interest or adsorb the volatile hydride and catalytically decompose it.Aggett and Hayashi37 suggested that interference occurs because the interferent in a low oxidation state, stabilized by tetrahydroborate(Iu), reacts with the hydride-forming element to form a soluble species. As mentioned in previous sections, the magnitude of these interferences depends on the method of hydride generation (batch, continuous or flow-injection mode), on the atomiza- tion system and on the reagents added. Selectivity is also dependent on the oxidant-acid medium used. In general terms, selectivity decreases in the order K2Cr2OTmalic or tartaric acid > H2O2-HC1 > (NH4)4S20s- HN03. Of these media, H202-HN03 appears to be the best compromise in terms of sensitivity, reagent blank and interference effects.30 The literature is contradictory as to the effect of transition metals on lead hydride generation efficiency.Both enhance- ment and depression of the analytical signal have been reported. The most serious interferences are due to Cu, Ni and Fe. Jin and TagalO found that Ag, Au, Cd, Cu and Ni interfered seriously in all reaction systems. The presence of Cu in the reaction medium at a Pb-to-interferent ratio of 1 : 10 led to a decrease of 60% in sensitivity in K2Cr207, 33% in H202 and 75% in (N&)2S208. D'Ulivo and Papoff30 developed an empirical equation for predicting the effect of Cu on the lead signal at various concentration ratios: 'YO decrease = 1.15 C4&,0.55 (C expressed in pg 1-1) Castillo et al.33 concluded that the presence of FeIrl and especially of Vv at a Pb-to-interferent ratio of 1:0.016 increases the sensitivity by 17 and l a % , respectively, when lead hydride is generated in H202-HN03 medium.This behaviour was attributed to an increase in the kinetics of the reduction process. In contrast, the positive effect of Fe3+ and V5+ was not observed when peroxodisulfate was used as an oxidizing agent. The presence of FelI1 at a Pb-to-interferent ratio of 1 : 1 produced a 54% suppression of the signal. The double catalytic and interference effect of these elements has also been reported by Bonilla et al.31 The effect of transition metals such as Ni, Co and Mn on lead hydride generation in H202-HN03 showed that there are several Concentration ranges of these metals in which the efficiency of lead hydride generation is greatly increased. The highest sensitivity was achieved with Ni at a concentration of 2.5 pg ml-1. The increase in the peak height of 2.5 pg ml-1 Ni was1652 Analyst, August 1994, VoE.I1 9 dependent on the NaBH4 concentration. Increases of 173% and 373% were obtained when working at 4 and 10% m/v NaBH4, respectively. The enhanced sensitivity was noted in both peak height and peak area, which suggests that the improvement in lead hydride generation is due not only to a kinetic effect (greater peak height) but also to increased efficiency (greater peak area). A similar but less intense effect was obtained in peroxodi- sulfate medium.32 The presence of the transition metals Mn, Fe, Co, Zn, Cu and Ni increased the efficiency of lead hydride generation by 20-60%, Ni was the most effective and its optimum concentration range was 0.1-0.2 pg ml-1.A similar study was performed in K2Cr20Tlactic acid medium.14 None of the elements cited above had a positive effect on the lead hydride generation efficiency; on the contrary, serious suppression of signal was observed in all instances. Comparison of the results obtained in the three generation media showed that the increase in lead hydride generation efficiency in the presence of these transition metals was greater in H202-HN03 (300%) than in (NH4)2S208- HN03 (60%) and K2Cr2OTlactic acid (0%). This could be explained by the faster reaction kinetics in the latter medium, as evidenced by the analytical peak shape in the presence and absence of Ni in the three media (Fig.2). Further, the optimum concentration at which these elements increased lead hydride generation was lower in (NH4)2S208-HN03 (0.1 pg ml-1 of Ni) than in H202-HN03 (2.5 pg ml-1 of Ni), indicating that the oxidant medium used had a considerable influence on the selectivity of the method. Although not yet well understood, the catalytic effect of Ni can be attributed to its participation in a very unstable transitional Ni hydride that favours lead hydride formation.38 To sum up, the transition metals produce the most serious interferences in the determination of lead by hydride genera- tion, suppressing the analytical signal. However, it is possible to find a concentration range in which these elements do not affect the signal and even produce a positive (catalytic) effect.The magnitude of the two effects is strongly dependent on the medium, oxidizing agent and atomization system used. Elimination or reduction of transition metal interferences The interferences by the transition metals in lead hydride generation are sometimes so significant that they must be eliminated or reduced. Several methods have been proposed to alleviate these interferences, including optimization of the acid and tetrahydroborate concentrations, separation proce- dures, use of masking agents and application of a flow injection system instead of the more usual batch or continu- ous-flow systems. Flow injection hydride generation (FI-HG) is commonly used to generate hydrides,39-42 although no work on lead hydride has been reported. The use of FI-HG improves the tolerance towards transition metals in the determination of Fig.2 Analytical peak shape (a) HN03-H202; (b) HN03- (NH4)2S208 and (c) lactic-K2Cr207. A, in the presence of Ni; and B in the absence of Ni. elements such as Bi and As.39740 As-the reduction rate of metal ions is slow in comparison with the rate of hydride generation, the use of flow injection, which shortens the sample-reagent interaction period, decreases the magnitude of interferences. Further, the inclusion of a microcolumn in the system allows 'on-line' removal of these interferences. There are few reports of continuous-flow systems for hydride generation with on-line matrix removal. Ikeda43 used a system incorporating a microcolumn packed with chelating resin to remove Cu and Ni in the HGAAS determination of selenium.Riby et a1.M used a microcolumn of strong cation-exchange material to remove Ni in the determination of arsenic in a nickel-based alloy. The application of flow injection techniques could considerably extend the capabilities of the hydride generation technique. The benefits obtained may include smaller samples, high generation efficiency, reduced interferences and on-line preconcentration. No particular difficulties from contamina- tion have been encountered in determinations at low working concentrations, which further demonstrates the benefits of the closed, inert flow-injection system in hydride generation. These benefits could be applied in the future to improve the analytical performance of lead determination by HGAAS. Separation procedures are widely used when lead is determined by hydride generation in the presence of high levels of transition metals.Lead was extracted with dithizone in chloroform and back-extracted into acid, where it was determined by AAS following hydride generation in peroxo- disulfate-nitric acid medium. 10 Vijan and Sadanads eliminated Cu interference by coprecipitating lead with Mn02 in acidic solution. To avoid tedious separation procedures some workers recommend the use of masking agents such as citric acid-potassium cyanide mixture,8 thiourea,& 1 ,lo-phenan- throline, sodium cyanide and oxalic acid47 and sulfosalicylic acid and sodium cyanide dissolved in NaBb.48 The use of ion-exchange resins has also been explored as a means of decreasing transition metal interferences.@ Certain resins that retain interfering metals do not retain As, Se and Pb.The resins studied included Chelex 100, AG 500W-Xl6 and Dowex 5OW-X16. Chikuma and AokisO proposed a method for determining lead in environmental water samples by HGAAS combined with a resin-water suspension sampling technique after preconcentration using a chelating resin (a sulfonated dithizone-loaded anion-exchange resin). After the loading period, the resin was suspended in water and added to the hydride generation system with 1 moll-1 HCl, 15% H202 and 5% NaBH4. Lead in the resin was effectively converted into its hydride and no interferences from sulfonated dithizone (DzS) or DzS-load resin were observed. This method elimi- nates the interferences from As"', Gel" and SeIV which are not absorbed by the resin, and decreases the interferences from transition metal ions which are immobilized and inactivated through complex formation.Graphite Tube Atomization of Lead Hydride: an Alternative to the Classical Quartz Atomization Cell The graphite furnace has been used for hydride atomization almost since the introduction of hydride generation. There are two approaches to using graphite furances: in situ trapping of the hydrides in the furnace and on-line atomization. In the in situ trapping system, the graphite furnace is used both as a trapping medium and as an atomization cell. Hydride purged from a generator is trapped in a heated graphite furnace, usually in the range 300-600 "C, until the evolution of hydride is complete.The trapped analyte is subsequently atomized at temperatures generally over 2000 "C. The data on the temperature dependence of trapping efficiencies of individual hydrides are contradictory. For example , one study found that the trapping efficiency of bismuthine was optimumAnalyst, August 1994, Vol. 119 1653 at temperatures between 25 and 350 "C,51 whereas Brovko et ~ 1 . ~ ~ reported that the optimum temperature was above 250 "C. In summary, the trapping temperature should be optimized for each experimental set-up. Generated hydrides are delivered either via an internal gas line in commercial furnaces or through an interface made of graphite or quartz. None of these arrangements is ideal. Quartz interfaces have to be removed before atomization53 and graphite interfaces are apt partially to capture hydride during the trapping stage.Using a 207Bi tracer, Lee54 showed that 61% of generated bismuthine was captured in the graphite interface, 11% in the atomizer tube and the remainder was lost. Similar difficulties are found for hydrides in the internal gas line, because the hydride comes into contact with metal components, with graphite tube ends and with graphite cylinders that are cold during both the trapping and the atomization stages.55 The quality of the graphite surface plays an important role in the trapping efficiency of hydrides. As a rule, uncoated tubes are more efficient than pyrolytic graphite t~bes.5675~ In the on-line atomization approach, the generated hydride is transferred directly from generator to the furnace, which is usually pre-heated to above 2200 "C.Generated hydride is almost always run through the internal gas line of commercial furnaces, which has the same disadvantage as in situ trapping that hydrides can be captured on cooler metal or graphite parts. Sensitivity is generally lower for on-line atomization than for in situ trapping. It is also lower than that provided by quartz tube atomizers, as the small size of commercial graphite furnaces and their high atomization temperature decrease the residence time of free analyte atoms, and consequently the sensitivity.58 Dittrich and Mandry59.a tailored a large-sized 'graphite paper furnace' for hydride generation that is similar in size to the quartz tube atomizer and improves sensitivity while retaining the main advantage of graphite furnaces, i.e., the high temperature suppresses atomization interferences. Advantages Over the Standard Atomization System Using Externally Heated Quartz Tubes Graphite furnace atomization, especially with in situ trapping, has proved to be the most sensitive atomic spectrometric method for the detection of As, Se, Sb and Sn because the graphite furnace is utilized as both a concentration medium and an atomization cell.Also, in situ trapping is an effective tool for decreasing matrix interferences by transition metals, because it eliminates the variable rates of hydride evolution caused by them. Using the on-line atomization mode, Dittrich and Mandry59.60 observed a significant alleviation of selenium, bismuth and arsenic interferences in Sb when the temperature was increased to 1600-2000 "C.The mutual interferences among volatile hydride-forming elements in graphite furnaces with on-line atomization and in situ trapping are less severe than in externally heated quartz tubes, perhaps owing to the higher temperature in the graphite furnace and to the different atomizer material and gaseous phase ~omposition.53~5~~57 For example interferences by antimony, selenium and bismuth in arsenic analysis (90% depression of sensitivity) were almost completely eliminated in the graphite furnace using the on-line atomization mode, even at a temperature of 1600 "C.60 This atomization approach has been used by Aroza et aZ.61 for lead hydride atomization with in situ trapping to determine lead in food samples.The lead hydride generated in HN03- H202 medium was transported into the graphite tube by means of the device shown in Fig. 3 and adsorbed for 60 s at 500 "C. After adsorption, the device was removed from the furnace and the hydride was atomized at lo00 "C. The method was five times more sensitive (1 ng) than that based on HGAAS alone. Further, the selectivity of the combined technique was higher than that of the standard atomization system. The results for Ca, Ba, Na, As", Sn, Hg, Crl*', Cu and Ag were similar to those obtained previously. However, the improved method tolerated three-fold higher concentrations of SeIV, SbV, Fe and Zn and 100-fold higher concentrations of Sr and K. In general, the selectivity was slightly higher than that using an atomization cell, maybe because, as a result of the 60 s delay, elements able to affect the kinetics of the lead hydride generation reaction no longer had an appreciable influence on the signal.Further advantages were the ability to choose a significantly lower working concentration of NaBH4 (7% d v ) than when using an atomization cell where the sensitivity increased for up to 16% m/v NaBH4. This is because the reaction kinetics increase exponentially with increasing NaBH4 concentration and the atomization cell is used on-line. However, by delaying the lead vaporization step until 60 s after lead hydride generation, it is possible to circumvent the slow reaction kinetics at low tetrahydroborate concentrations and achieve considerable savings in the cost of analysis compared with the use of a silica atomization cell.The sensitivity was also highly dependent on the nature of the graphite tube. The results showed that the adsorption efficiency increased in the order new uncoated graphite tubes < old pyrolytic graphite tubes < old uncoated graphite tubes. Old tubes adsorbed lead hydride better, perhaps because tube porosity increases with age. A similar approach was adopted by Yang and Ni,62 but a Zr-coated graphite tube was used for the sorption of lead hydride generated in H202-HN03 medium. The hydride was run into the graphite tube, via a quartz tube, where it was collected at 100 "C for 100 s, after which the quartz tube was withdrawn from the graphite furnace and the analyte was atomized at 2200 "C for 5 s.Under these conditions, the sensitivity (52.8 ng) was six times higher than that obtained using a pyrolytic graphite-coated tube for the sorption of lead From hydride generation system - PTFE device Fig. 3 PTFE device for transporting lead hydride to the graphite furnace. From reference 61.1654 Analyst, August 1994, Vol. 11 9 hydride and lower adsorption temperatures (100-400 "C) could be chosen. A detection limit (30) of 242 pg was obtained and the proposed method was applied to determine lead in reference materials and tap-water samples. Sturgeon et al.63 proposed a method for the determination of lead based on the generation of PbEt, using NaBEt, and subsequent trapping in a graphite tube at 400 "C. The PbEt, was generated as follows: 4NaBEt4 + 2Pb2+ -+ PbEt, + 4BEt3 + 4NaC1 + PbO and transferred via a quartz delivery tube and atomized at 1600 "C after collection was completed.This highly selective method with a detection limit of 14 pg of lead was applied to determine lead in marine reference materials using aqueous calibration graphs. Atomization Mechanisms The mechanism by which the volatile hydrides are sequestered by a heated graphite furnace and subsequently atomized is not well understood. Sturgeon et al.57 investigated the hydride trapping and analyte atomization mechanisms for arsenic, bismuth, anti- mony, selenium, tin and lead. Volatile hydrides delivered into a pre-heated graphite furnace are deposited there by thermal decomposition. A porous tube surface increases the efficiency of trapping as a consequence of the higher surface area available.The deposited metal may subsequently re-oxidize during the trapping stage. The atomization of arsenic, antimony, selenium and tin in the graphite furnace is identical with that occurring when these elements are injected directly into an aqueous solution and the condensed-phase species resulting from hydride deposition are the same as those resulting from dehydration-ashing of aqueous solutions of these elements. This is not so for Pb and Bi. The atomization of the deposited hydride appears to originate with the reduced metal, in contrast to the thermal decomposition of oxides observed for aqueous samples of these elements. Pb and Bi are deposited in the metallic state during hydride deposition and remain so until atomized.Auger electron microprobe spectrometry and electron microscopy with energy-dispersive X-ray fluorescence spectrometry have also been used to characterize the sample deposits. Hydride deposition appeared to be non-uniform. Once a metallic deposition was initiated on a surface site, analyte tended to preferentially deposit on this nucleus.57 Sequestration of Volatile Lead Hydride by Platinum Group Metals In situ trapping procedures that utilize the graphite furnace as both concentration medium and atomization cell provide the most sensitive atomic spectrometric method available for the detection of As, Se, Sn and Pb. Incomplete trapping lowers the analytical performance of the in situ concentration method and is the most important factor limiting its application.This problem can be overcome by the use of tubes coated with platinum group metals (PGM) as both the hydride trapping medium and the atomization cell. The method has been successfully applied to collect As, Se, Bi, Sb, Sn, Ge and Pb hydrides and Hg vapour.62~-7 Under these conditions, hydrides are effectively adsorbed on the surface of the PGM-coated tubes at relatively low temperatures (about 200 "C) and the sensitivity is greatly enhanced. During the deposition step, hydrogen produced by the hydrolysis of excess of BH4- may promote hydride decomposition and trap the analyte as an alloy or intermetallic compound, thus lowering the risk of losses and improving sensitivity. Rapid, dissociative chemisorption of arsine on Pt has been reported64 even at -80 "C.Determination of Lead Organic Compounds by Hydride Generation Alkyllead compounds in the environment have more pro- nounced physiological effects than inorganic lead because they are more toxic. Many automobile gasolines still contain tetraalkyllead compounds as anti-knock agents, although this use is diminishing. The study of organolead compounds in the environment is particularly difficult because of the decomposi- tion, redistribution and disproportionation of the original alkyllead compounds and environmental methylation. The determination and speciation of ionic alkyllead have been accomplished mainly by coupled techniques as GC-AAS, GC-microwave plasma detector (MPD) and HPLC-AAS.68 HGAAS with modified chemical conditions of hydride generation has been applied to the selective determination of alkyllead compounds.However, the use of this technique is limited because of instability of the alkyllead hydride molecule and hydrogen-alkyl exchange. Yamauchi et aZ.69 determined triethyllead, diethyllead and inorganic lead ions in urine by selective generation of their hydrides and AAS detection. Several generation media were used: 0.5 mol 1-1 lactic acid from the generation of Et,Pb+, 0.75 moll-' H202-0.004 moll-' HC104 for the generation of Et2Pb2+ and 1.6 moll-' mallic acid-0.05 moll-1 H202 for the generation of Pb2+. The gaseous hydrides were collected on silica wool in a U-trap cooled to liquid nitrogen temperature. The trap was then warmed to room temperature and the hydrides were passed into a silica cell (heated electrothermally to lo00 "C).Recoveries of spikes added to urine were >90% for all species and detection limits of 5 ng of Pb for Et,Pb+ and Et,Pb+ and 0.1 pg for Pb2+ were reported. However, these species could not be determined simultaneously because a different generation medium was required for each com- pound. The speciation technique proposed by D'Ulivo et aZ.,70 which is based on modified chemical conditions of lead hydride generation in the aqueous phase and a system of mathematical equations, enables trimethyl-, triethyl-, dimethyl- and diethyllead compounds and Pb*+ to be deter- mined by AAS. The presence of EDTA in the generation medium inhibits h ydride generation from inorganic lead but not from organic compounds. Also, it was found that the presence of H202 oxidant does not affect the analytical signal from Me,Pb+ and Et,Pb+ but significantly improves the efficiency of hydride generation from Et2Pb+, MePb+ and Pb2+.These results suggested that the role of hydrogen peroxide is to stabilize the lead in oxidation state IV and promote the formation of volatile hydrides. With inorganic lead, the peroxide promotes the formation of Pb*" and dramatically increases lead hydride formation. Hydride generation has been also used as a derivatization method for the speciation of organolead compounds by GC-AAS. Baussand et aZ.71 used the coupled GC-AAS to determine lead in the atmosphere and in drinking water. Volatile lead compounds are generated by hydrogenating inorganic bonds using N a B b as reducing agent in KOH- K2Cr207 or H202 generation medium.The volatile hydrides were trapped in a chromatographic column (Chromosorb W) immersed in liquid nitrogen. After desorption, the volatile hydrides were determined by AAS. The detection limits of this technique were 1 pg 1-1 Pb, 100 ng 1-1 Pb(CH3)4, 200 ng 1-1 Pb(CH3)3H, 1 pg 1-1 Pb(C2H5),H and 1 ng 1-1 Pb2(C2H5)2. The lead hydride generation efficiency of Pb- fromn Pb2+ and Pb(CH3)Cl was 10% and 100%, respectively.Analyst, August 1994, Vol. 119 1655 A higher efficiency of generation is obtained from organic compounds because the process is easier as the lead is already in the form of a stabilized Pb*" compound, which participates in a simple complexation reaction with H+: BH4- + 3H2O + 4Pb(CH3)3+ --+ H3B03 + 3H+ + 4Pb (CH3) 3H Therefore, the use of an oxidizing agent is no longer needed.Hydride generation has had only limited application in the selective determination of organolead compounds owing to their low stability and hydrogen alkyl exchange. Other speciation techniques (CG-AAS, HPLC-AAS) or derivatiza- tion methods (with alkylating agents) are currently preferred. Lead Hydride Generation from Slurries In recent years, interest has grown in the direct analysis of suspensions or slurries of solids by AAS methods, which have the advantages of speed, ease of analysis and reduction of blank levels. Many of these studies have employed flame AAS, but the atomization efficiency depends on sample transport, particle size, atomization temperature and sample matrix. Electrothermal atomization AAS can tolerate large particle sizes and has been used successfully for the determination of lead in solid, environmental, food and biological samples, although sample inhomogeneity , sampling difficulties and high matrix salt levels may cause significant errors.Hydride generation offers an attractive way of overcoming many of the problems described above, but very little work has been reported to date on slurry methods, which involve the generation of a covalent hydride from a suspension of solid sample. This approach has been applied for the determination of As72 and Sb73 in complex matrices. Slurry HGAAS offers the advantage of simpler and faster sample pre-treatment than conventional methods, plus a detection technique (hydride generation) that is selective and sensitive enough to determine low analyte levels in complex matrices and is easy and cheap to operate.These advantages are very useful for the analyses of materials such as foodstuffs and biological samples, which is of great importance as the lead concentration in such samples is often very low, the favoured technique is often GFAAS. Unfortunately, there are numerous interferences in these determinations and they are even worse when a slurry or suspension is analysed, manifest- ing themselves in the form of background effects, sampling difficulties, build-up of carbonaceous residues and increases in the cost of the analysis due to Zeeman correction and the use of scanverger gases such as 02. The drawbacks of lead determination by conventional wet digestion are possible losses of analyte and the risk of sample contamination (a cleaned pre-chamber and highly-purity reagents and acids are necessary).Slurry HGAAS appears to offer a viable alternative for overcoming many of these problems in the determination of lead. Madrid et al.74 reported a simple and rapid method for the determination of lead in foodstuffs and biological samples that combines a slurry procedure with lead hydride generation. Powdered samples were suspended in Triton X-100 as dispersing agent and shaken with 10.0 g of blown zirconia spheres until the slurry was formed. A few drops of silicone antifoaming agent were added before the slurry was diluted to minimize the foam formed on addition of NaBH4 to the viscous slurry. This grinding procedure ensured that 90% of the particles had a diameter of less than 25 pm, a particle size small enough to permit lead determination by HGAAS.Three oxidant media, namely H202-HN03, K2Cr20Tlactic acid and (NH4)2S208-HN03, were evaluated for the genera- tion of lead from slurry samples and their application to the determination of lead in vegetables and fish by HGAAS was investigated .75 The results of a comparative study of vegetable and fish samples are given in Tables 1 and 2. Detection and quantifica- tion limits (LOD and LOQ, respectively) were calculated using IUPAC rules. Standard additions graphs were prepared for blanks and samples and from these the blank-to-sample slope ratios (slope ratio) were calculated to compare the selectivities of the method.HN03-HZ02 medium was unsuitable for the generation of lead hydride from slurry samples because of decomposition of the hydrogen peroxide by the organic matrix. Further, the low sensitivity provided by this medium made it necessary to increase the concentration of the powdered sample in the slurry, resulting in higher errors owing to sampling difficulties and increased matrix effects. (NH&S208-HN03 gave reliable results for the determina- tion of lead in vegetables but only semi-quantitative results with fish slurry samples. Table 1 Lead concentration in foods determined using the ammonium peroxodisulfate-nitric acid medium75 Sample IAEA V10 Hay (powdered)? BCR CRM 281 Ryegrass* Lettuce Mussel Sardine Atlantic bluefin tuna Anchovy Atlantic pomfret Prawn IAEA H9 Diet? Concentration of powdered sample in slurry (% m/v) 2.0 2.0 2.0 2.0 2.0 2.0 4.0 2.0 2.0 10.0 Lead content procedure)/ 1.60 f 0.07 2.32 f: 0.10 2.87 f 0.16 1.96 f: 0.06 <LOD <LOD (slurry g-'* <LOD <LOD 0.10 k 0.07 Certified value or value obtained by other procedure/ LOD/ LOQ/ PLg g-' Mg-' ILgg-' 1.614 0.30 0.90 2.38 _+ O.ll§ 0.20 0.60 2.90 f: 0.167 0.40 1.20 1.98 k 0.087 0.30 0.9 - 0.20 0.6 - 0.6 1.8 - 0.3 0.9 - 0.7 2.1 No hydride generation 0.098§ 0.07 0.21 Slope ratio 1.11 1.7 1.16 1.5 1.48 7 2.5 6.5 1.6 * Mean value expressed as x f: u.t IAEA = International Atomic Energy Agency. * BCR CRM = Community Bureau of Reference. Certified Reference Material. 9 Certified value. 7 Value obtained by other procedure (sample solutions prepared by mineralization in a FTFE pressure bomb with nitric acid and V205).1656 Analyst, August 1994, Vol.11 9 K2Cr2OTlactic acid provided the best results for the determination of lead in slurried vegetable and fish samples, and also resulted in lower detection limits owing to its high sensitivity and low blanks. When mussel was analysed, mineralization, decreasing the risk of sample contamination. However, the oxidant-acid medium must be chosen carefully to achieve good recoveries in the determination of lead. - , however, this medium gave lower results than the (NH4)&0*-HN03 and wet digestion procedures, perhaps because potassium dichromate was unable to remove the lead completely from this sample, unlike ammonium peroxodisul- fate, which is a sufficiently strong oxidant to eliminate lead completely .In conclusion, slurry HGAAS is a simple and rapid method for the determination of lead in a wide variety of samples. Slurry preparation requires less sample manipulation than Major Applications of Lead HGAAS HGAAS has been successfully applied to determine lead in a wide variety of matrices such as steel, soil, food and environmental samples, with Pb concentrations ranging from pg ml-1 to pg 1-1 levels. In most instances the technique was sensitive and selective enough to determine lead directly without preconcentration or separation procedures. Table 3 summarizes the major applications to the determination of Table 2 Lead concentration in foods determined using the potassium dichromate-lactic acid medium75 Sample IAEA V10 Hay (powdered)+ BCR CRM 281 Ryegrass* Lettuce Mussel Sardine Atlantic bluefin tuna Anchovy Atlantic pomfret Prawn IAEA H9 Diet? *, t, *, 7 See Table 1.Concentration of powdered sample in slurry (% m/v) 2.0 2.0 2.0 2.0 2.0 2.0 4.0 2.0 2.0 10.0 Lead content procedure)/ 1.64 k 0.07 2.36 k 0.15 2.90 k 0.03 1.26 k 0.10 0.14 k 0.01 0.43 k 0.04 0.24 k 0.01 0.40 ? 0.09 (slurry g-'* Certified value or value obtained by other procedure/ LOD/ LOQ/ 1.610 0.10 0.30 2.38 f 0.llP 0.14 0.32 - 0.16 0.48 - 0.10 0.30 0.42 k 0.031 0.09 0.27 0.23 k 0.047 0.05 0.15 - 0.09 0.27 8-l pgg-' Pgg-' 0.13 k 0.021 0.04 0.12 No hydride generation No hydride generation Slope ratio 3.00 2.6 1.8 0.9 1.31 1.2 2.3 1.5 Table 3 Application of HGAAS to the determination of lead Sample Oxidant Detection method Wine H202-HC1 AAS (silica tube) K2Cr20Tlactic aicd AAS (silica tube) Gasoline Not needed AAS (silica tube) Not needed AAS (silica tube) Food Steels H202-HN03 AAS (silica tube) HN03-(NH4)2S208 AAS (silica tube) HN03-(Nb)2S208 AAS (silica tube) K2Cr20T-lactic acid AAS (silica tube) H202-HN03 AAS (in situ trapping in graphite tube) H202-HN03 AAS (in situ trapping in Zr- coated graphite tube) (Nb)?Ce(N03)6- AAS (silica tube) K2Cr20Ttartaric acid AAS (silica tube) Not needed Air-acetylene flame oxalic acid H202-HCl ICP-MS Soils (NH4)2S20THN03 Atomization under low pressure using AAS (silica tube) Nitroso-R salt AAS (silica tube) * LOD = limit of detection, calculated as 3a.LOD* 24 pg 1-1 2.5 pg 1-1 20 pg 1-1 17 pg 1-1 0.1 pgg-1 0.05 pg g-' Not given 0.04 pg g-1 4 ng g-1 0.4 ng g-' Not given 7pgml-l 1 pgl-1 0.05 pg 1-1 0.10 pg 1-1 Not given Remarks 21% NaBH4 Samples pre-treated with HN03 Samples diluted in DMF and addition of N a B b solution in DMF Samples diluted in Me2S0 and addition of NaBH4 or NaHC03 in acid medium Samples digested in a PTFE pressure bomb with v 2 0 5 Comparison of wet digestion procedures Digestion with HN03-HC104 Extraction with dithizone- Digestion with HN03-Vz05 Comparison of wet digestion procedures Digestion with HN03-HC104 in PTFE pressure bomb Digestion with HN03 C1CH3 Digestion with acid mixture Pb is separated using APDC in CH3Cl and mixed with NaBH4 in DMF Lead isotope determination Digestion with HN03-HC104 Digestion with HF-HC1 Reference 34 14 18 19 31 32 10 14 61 62 13 7 16 48 76 15Analyst, August 1994, Vol.11 9 1657 lead in solid and liquid samples and lists the detection limits (30) and digestion procedures used in each instance. Advantages of Lead HGAAS Over GFAAS in the Determination of Low Levels of Lead So far, GFAAS has been the most widely applied spectro- scopic method for the determination of very small amounts of lead in biological samples. Unfortunately, numerous interfer- ence effects have been reported for these determinations. Because of the large matrix interferences, most determina- tions are carried out at 283.3 nm and not at the more sensitive wavelength of 217.0 nm. The interferences make it necessary to use chemical modifiers in analyses for lead, which increases the risk of contamination. However, hydride generation appears to offer a viable alternative.The presence of soluble oxidants such as potas- sium dichromate , hydrogen peroxide and ammonium peroxy- disulfate increases the efficiency of lead hydride generation , making it useful for the determination of lead in biological samples. This method has several advantages over elec- trothermal atomic absorption spectrometry (ETAAS) for the determination of lead: (i) greater selectivity because lead is separated from the matrix, avoiding possible matrix interfer- ences; (ii) the ability to work at 217.0 nm, which offers greater sensitivity than the wavelength of 283.3 nm usually employed in GFAAS; (iii) simpler separation and lower cost than GFAAS; (iv) shorter analysis time; (v) suitability for automa- tion or semi-automation; and (vi) HC104 mineralization reagent can be used in HGAAS but is usually inconvenient in graphite furnace methods.The detection limits of conventional HGAAS are at low pg 1-1 levels, which enables lead to be determined in a wide variety of samples without preconcentration procedures. The analytical performance of HGAAS can be improved by preconcentration methods such cryogenic trapping and in situ trapping in a graphite furnace. Cryogenic collection with subsequent temperature jump injection directly into the atomizer can improve the hydride detection limit, but unfortunately this collection method is not suitable for unstable hydrides such as that of lead and is cumbersome for routine analysis. The use of the graphite furnace as both the hydride trapping medium and the atomization cell significantly enhances the sensitivity of lead determination and effectively eliminates interferences in the atomizer and those due to variations in the rate of hydride generation from sample to sample.The detection limits for lead are at the ng 1-1 level, making it one of the most sensitive methods for the determination of lead at the ultra-trace level. Conclusions The expanding literature dealing with the determination of lead by hydride generation indicates that this method has gained a certain level of acceptance among analytical scien- tists. However, certain major improvements must be made before better results will be possible. One such improvement is the coupling of flow injection to lead hydride generation to provide advantages including the possibility of micro-sampling analysis, increased sample throughput, on-line preconcentra- tion and better detection limits.The authors thank M. Gormann for revision of the manu script and the Comision Interministerial de Ciencia y Tegnolo- gia (Project 88/0094) for financial support. References 1 Thompson, K. C., and Thomerson, D. R., Analyst, 1974, 99, 595. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 Paneth, F., and Rabinonowish, E., Chem. Ber., 1925,58,1138. C. J. Porrit, Chem. Ind. (London), 1985,398. Mueller, W. M., Blackledge, J. P., and Libowitz, G., Metal Hydrides, Academic Press, New York, 1968. Saalfeld, F. E., and Svec, H.J., Inorg. Chem., 1963, 2, 46. Jeffes, J. H., and McKerrell, H., J. Iron Steel Inst., 1964, 666. Fleming, H. D., and Ide, R. G., Anal. Chim. Acta, 1976,83,67. Vijan, P. N., and Wood, G. R., Analyst, 1976, 101, 966. Hon, P. K. Lau, 0. W., Cheung, W. C., and Wong, M. C., Anal. Chim. Acta, 1980, 115,355. Jin, K., and Taga, M., Anal. Chim. Acta, 1982, 143,229. Castillo, J. R., Mir, J. M., Martinez, C., Val, J., and Colon, P., Mikrochim. Acta, 1985, 1,253. Thao, R., and Zhou, H., Fenxi Huaxue, 1985, 13,283. Li, J., Liu, Y., and Lin, T., Anal. Chim. Acta, 1990, 231, 151. Madrid, Y., Meseguer, J., Bonilla, M., and CQmara, C., Anal. Chim. Acta, 1990,238, 181. Zhang, S., Hanj, H., and Ni, Z., Anal. Chim. Acta, 1989,221, 85. Hengwu, C., Fulong, T., Chang, G., and Brindle, I.D., Talanta, 1993,40, 1147. Aznarez, J., Palacios, F., Vidal, J. C., and Galban, J., Analyst, 1984,109, 13. Aznarez, J., Vidal, J. C., and Carnicer, R., J. Anal. At. Spectrom., 1987,2, 55. Nerin, C., Olavide, S., and Cacho, J., Anal. Chem., 1987,59, 1918. Dedina, J., and Rubeska, I., Spectrochim Acta, Part B, 1980, 35, 119. Welz, B., and Melcher, M., Analyst, 1983, 108, 213. Agterdenbos, J., and Bax, D. , Fresenius’ Z. Anal. Chem., 1986, 323, 783. Forsyth, D. S., and Marshall, W. D., Anal. Chem., 1985, 57, 1299. Wang, X., and Barnes, R. M., Spectrochim. Acta, Part B, 1987, 42, 139. Bye, R., Talanta, 1990,37, 1029. Robbins, W. B., and Caruso, J. A., Anal. Chem., 1979, 51, 889A. Pierce, F. D., and Brown, H. R., Anal. Chem., 1976,48, 693. Kirkbright, G. F., and Taddia, M., Anal.Chim. Acta, 1978, 100, 145. Dittrich, K., and Mandry, R., Analyst, 1986, 111, 277. D’Ulivo, A., and Papoff, P., Talanta, 1985, 32, 383. Bonilla, M., Rodriguez, L., and Camara, C., J. Anal. At. Spectrom., 1987,2, 157. Madrid, Y., Bonilla, M., and Camara, C., J. Anal. At. Spectrom., 1988,3, 1097. Castillo, J. R., Mir, J. M., Val, J., Colon, M. P., and Martinez, C., Analyst, 1985, 110, 1219. Cacho, J., Ferreira, V., and Nerin, C., Analyst, 1992, 117, 31. Smith, A. E., Analyst, 1975, 100, 300. Welz, B., and Melcher, M., Analyst, 1984, 109, 569. Aggett, J., and Hayashi, Y., Analyst, 1987, 112,277. Holah, G. D., Hughes, N. A., Hui, C. B., and Kand, C. H., Can. J. Chem., 1978, 56,2552. Astrom, O., Anal. Chem., 1982, 54,W. Yamamoto, M., Yashuda, Y., and Yamamoto, Y., Anal. Chem., 1985, 57, 1382. Weltz, B., and Schubert-Jacobs, M., At. Spectrosc., 1991, 12, 91. Weltz, B., and Guo, T., Spectrochim. Acta, Part B, 1992, 47, 645. Ikeda, M., Anal. Chim. Acta, 1985, 170, 217. Riby, P. G., Haswell, S. J., and Grzeskowiak, R., J. Anal. At. Spectrom., 1989,4, 181. Vijan, P. N., and Sadana, R. S., Talanta, 1980,27, 321. Rigin, V. I., Zh. Anal. Khim., 1986, 41, 46. Zhang, P., and Hu, Z., Fenxie Huaxue, 1985, 15,404. Wang, X., Viczian, M., Lasztiky, A., and Barnes, R. M., J. Anal. At. Spectrom., 1988, 3, 821. Hershey, J. W., and Keliher, P. N., Spectrochim. Acta, Part B, 1969,44,329. Chikuma, M., and Aoki, H., J. Anal. At. Spectrom., 1993, 8, 415. Narasaki, H., and Ikeda, M., Anal. Chem., 1989,56, 2059.1658 Analyst, August 1994, Vol. 119 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Brovko, I. A., Tursunov, A., Rish, M. A., and Davirov, A. D., Zh. Anal. Khim., 1984,34, 1768. Willie, S. N., Sturgeon, R. E., and Berman, S. S., Anal. Chem., 1986,58, 1140. Lee, D. S., Anal. Chem., 1982,54, 1682. Sturgeon, R. E., Willie, S. N., and Berman, S. S., Anal. Chem., 1985,57,2311. Andreade, N., Anal. Chem., 1984,56,2064. Sturgeon, R. E., Willie, S. N., Sproule, G. I., and Berman, S. S., J. Anal. At. Spectrom., 1987, 2,719. Dittrich, K., Mandry, R., Udelnow, R., and Udelnow, A., Fresenius’ Z. Anal. Chem., 1986,323,793. Dittrich, K., and Mandry, R., Analyst, 1986,111,269. Dittrich, K . , and Mandry, R., Analyst, 1986,111,277. Aroza, I., Bonilla, M., Madrid, Y., and Ciimara, C., J. Anal. At. Spectrom., 1989, 4, 163. Yang, X.-P., and Ni, Z;M., J. Anal. At. Spectrom., 1991, 6, 483. Sturgeon, R. E., Willie, S. N., and Berman, S. S., Anal. Chem., 1989, 61, 1867. Sturgeon, R. E., Willie, S. N., and Berman, S. S., Spectrochim. Acta, Part B, 1989,44, 667. Doidge, P. S., Sturman, B. T., and Rettberg, T. M., J. Anal. At. Spectrom., 1989, 4, 251. ~ 66 67 68 69 70 71 72 73 74 75 76 Zhang, L., Ni, Z.-M., and Shan, X.-G., Spectrochim. Acta, Part B, 1989,44,751. Yang, X.-P., Ni, Z.-M., and Gao, Q . , Anal. Chim. Acta, 1993, 272, 105. Hamson, R. M., and Rapsomanikis, S., Environmental Analy- sis Using Chromatography Interface with Atomic Spectroscopy, Ellis Horwood, Chichester, 1989. Yamauchi, H., Arai, F., and Yamamura, Y., Ind. Health, 1981, 19, 115. D’Ulivo, A., Fuoco, R., and Papoff, P., Talanta, 1986,33,401. Baussand, P., Foster, P., Besson, J., Laverlocher, J., and Heinhart, A. O., Analusis, 1985, 13,53. Haswell, S. J., Mendham, J., Butler, M. J., and Smith, D. C., J. Anal. At. Spectrom., 1988,3,731. de la Calle-Guntifias, B., Madrid, Y., and CAmara, C., Analyst, 1991,116,1029. Madrid, Y., Bonilla, M., and CAmara, C., J. Anal. At. Spectrom., 1988,3, 1097. Madrid, Y., Bonilla, M., and CAmara, C., Analyst, 1990, 105, 563. Zhang, B., Tao, K., and Feng, J., J. Anal. At. Spectrom., 1992, Paper 3106503K 7, 171. Received November 1, 1993 Accepted March 7, 1994

ISSN:0003-2654    

DOI:10.1039/AN9941901647

出版商:RSC    

年代:1994

数据来源: RSC