ISSN:0003-2654    

DOI:10.1039/AN99318BP025

出版商:RSC    

年代:1993

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99318FX029

出版商:RSC    

年代:1993

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99318BX031

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, AUGUST 1993, VOL. 118 97N Book Reviews Applications of Fluorescence in lmmunoassays By llkka A. Hemmila. Volume I17 in Chemical Analysis: A Series of Monographs on Analytical Chemistry and Its Applications. Pp. xi + 344. Wiley. 1991. Price f67.00. ISBN 0-47 1 -5 1091 -2. This is an overview of a field that has undergone rapid expansion over the past decade. Hemmila presents a thorough and detailed review of the scientific and technical principles underlying fluorescence immunoassay. The history and evolu- tion of immunoassay techniques, the structure and properties of antibodies and the variety of separation methods are described, the relative merits of isotopic and non-isotopic assays are discussed, and non-isotopic labels are reviewed with particular attention to enzymes and luminescent labels.The basic principles of fluorescence and phosphorescence are explained, and the different types of metal-chelate fluor- escence illustrated. Consideration of means of background rejection in fluorimetry leads into a description of instrumen- tation, including discussion of the challenge of automation, and a chapter on fluorescent probes covering organic fluoro- chromes, metal chelates and polymeric materials. Later chapters explore in more specific detail the types of fluorescence immunoassay available. Specific formats of separation-based and non-separation immunoassay are covered, and such variants as fluorogenic enzyme immuno- assay and time-resolved and phase-resolved fluorescence immunoassay are described. Fluoroimmunosensors are dis- cussed, and the book closes with chapters on the use of fluorescent labelling in other specific binding assays, notably DNA hybridization assays, and on the multiparametric immunoassays pioneered by Ekins.The extensive bibli- ography contains nearly 2000 references. The book is written in a readable style, although occasional quirks in the English can lead to temporary confusion. The format takes the reader in logical sequence through general background and history, basic principles and materials to the substance of fluorescence immunoassay and related tech- niques. The scientist new to fluorescence immunoassay will find this a good general introduction to the field, but the coverage is also sufficiently detailed to make it a useful reference volume for those already familiar with the subject.M . P. Bailey Fourier Transform Raman Spectroscopy. Instrumenta- tion and Chemical Applications By Patrick Hendra, Catherine Jones and Gavin Warnes. Ellis Horwood Series in Analytical Chemistry. Pp. 312. Ellis Horwood. 1991. Price f53.00. ISBN 0-13-327023-7. In view of the considerable upsurge in interest in Fourier transform Raman (FTR) spectroscopy over the past few years the publication of this volume is very timely. The recent development of FTR systems by most of the major manufac- turers of infrared spectrometers has led to a range of relatively inexpensive, robust Raman spectrometers that have achieved, at least initially, a high level of interest and popularity. This book addresses the instrumentation and chemical applications of FTR spectroscopy in a thorough and easily understandable manner in 12 chapters with a useful appendix on spectral processing.The instrumental aspects and historical development of FTR spectroscopy are dealt with in considerable depth and the versatility of the technique from the point of view of sample handling is stressed. Several of the current commercially available systems are described, although in a rapidly chang- ing field such as this there have been further developments, particularly in the area of photon detectors, since the book was written. The greatest strength of the book lies in this section together with those on standardization and intensity measurements. The most important aspect of this book relates to the analytical applications of the technique, and it is here that there is some element of ambiguity.Many of the applications quoted are essentially applications of Raman spectroscopy and, as such, could just as easily, although at greater expense, be undertaken on a conventional dispersive system. The main advantage of the FT system lies in its ability to obtain spectra using near-infrared excitation when the major problem associated with Raman spectroscopy (that of sample fluores- cence) tends to disappear, or at least to be substantially reduced. In this respect a recently developed conventional Raman dispersive system using a Ti-sapphire laser and a charge coupled device as detector performs just as well for most fluorescing samples and has the advantage of being able to operate much more efficiently at low wavenumber shifts and with a microscope accessory.The other advantages of FTR are its low price and ruggedness compared with conventional instrumentation and the applications section does not emphasize these points sufficiently. It is easy with a novel analytical system such as FTR to fall into the trap of undertaking a wide range of analyses that could be performed just as well either by dispersive Raman or by other analytical techniques. This appears to be the case with some of the applications quoted in the book. An example of this is the application of FTR in the area of chemometrics where it has been used to determine cetane number and cetane index of gas oils, an analysis that can be carried out just as accurately but more cheaply and ruggedly by near-infrared spectroscopy using the overtone region.Most of the other applications in the book could also be carried out just as easily using alternative techniques. Nevertheless, bearing in mind the novel nature of the technique and its potential use as an ‘add-on’ to infrared spectrometers the book is a worthwhile addition to any vibrational spectroscopist’s library. D. L. Gerrard Biosensors By F. Scheller and F. Schubert. Techniques and Instru- mentation in Analytical Chemistry. Pp. x + 360. Elsevier. 1992. Price US$161.50. DFI 31 5.00. ISBN 0-444-98783-5. There has been a considerable growth of interest in biosensor research and development, since Clark’s invention of the oxygen electrode in 1962. Clark subsequently used this electrode for a glucose assay by combining it with the enzyme glucose oxidase in a layer next to the electrode behind a semi- permeable membrane.Clark’s glucose electrode was launched commercially by the Yellow Springs Instrument Co. in the USA in 1975. This example of the long development time from invention to commercial launch of a successful biosensor is rather typical. Another example is that of the ion-selective field effect transistor (ISFET), first invented by Bergveld in 1975. Much effort has been devoted to these sensors world-wide. Only last year was there a commercial launch of pH ISFETs by Sentron in the Netherlands, based on Bergveld’s work, and by Unifet in San Diego, based on the work of Sibbald and others at THORN EM1 Central Research Laboratories. Clinical appli- cations of these sensors in commercially available instruments are likely to appear during the next 12-18 months.98N ANALYST, AUGUST 1993, VOL.118 Scheller and Schubert have comprehensively reviewed the literature on a wide range of biosensors, with the major emphasis on various types of electrochemical sensor systems. There is only a limited discussion on optical and optoelec- tronic biosensors. Many very successful dry chemistry colori- metric biosensors, such as the Ames Seralyser, Kodak Ektachem and Boehringer Reflotron, are ignored. Surface plasmon resonance biosensors for immunoassay such as those now commercially available from the joint Amersham/Kodak venture, from Serono and Pharmacia are also not discussed and neither is the Amerlite luminescence biosensor system from Amersham.In the index, reflectometry has only two entries, fluorimetry one entry, fibre optics two entries, ellipsometry two entries, optoelectronic sensors thirteen entries, substance specific optical sensors fourteen entries and luminescence two entries. It would have been more approp- riate if the authors had entitled their book ‘Electrochemical Biosensors’. A much more balanced view of the wide range of techniques incorporated in biosensors is given in Hall’s ‘Biosensors’ (Open University Press, 1990). Accepting those limitations to this monograph, the authors do give a very good coverage of electrochemical biosensors. The limitations of many of the sensors are well documented, although the problems relating to biocompatibility and especially haemocompatibility receive very little critical atten- tion.Applying sensors to clinical problems requires that a great amount of attention is given to the compatibility with the fluid with which the biosensor is in contact, especially if the application is ex vivo or in vivo. Without such attention biosensors in such application areas arc unlikely to be successful and would be limited to in vitro assays. Likewise, biocompatibility is of great importance in fermentation monitoring. The authors provide a very useful service in drawing attention to the wide range of biochemical and biological systems that can and have been coupled to electrochemical transducers for application to clinical analyses in particular. Applications in food and beverage analysis, in fermentation and environmental monitoring receive much less emphasis, although the opportunities in those areas are as great as for clinical applications.J. M . Thompson Advances in Coal Spectroscopy Edited by Henk L. C. Meuzelaar. Modern Analytical Chemistry Series. Pp. xx + 416. Plenum Press. 1992. Price US$85.00. ISBN 0-306-43796-1. Coal is a complex material, which is both difficult to analyse and to characterize for a given use. However, this does not deter coal scientists from making the attempt. It would be fair to say that no single technique can adequately describe the structure of coal and this is amply demonstrated in this book, where the number of spectroscopic techniques covered is very wide. This is the main advantage of the book, in that all the spectroscopic techniques that might be applied to coal appear in one volume.There are fifteen separate chapters that cover topics from microscopic methods to the familiar IR, NMR, MS and GC techniques, often in association with pyrolysis or solvent extraction. Other techniques are also described including XAFS, ESCA, Raman spectroscopy, laser spark emission spectroscopy and microspectrophotometry of coal macerals. In many cases the emphasis is on in situ methods. Some of these techniques will be familiar to the reader and some not so familiar. In all cases the basis of the method and experimental procedures are explained in a clear way, which does not disadvantage the uninitiated. Where space does not permit, references are provided to give background information. Because of the wide range of topics covered it is not possible in this review to single out particular methods.All of the techniques described have something to offer to the under- standing of coal structure and the behaviour of coal under certain conditions. These conditions might reflect the actual uses of coal or be used as part of the analytical method. It is clear, however, that some have more to offer than others. This is because some are in the early stages of development for use with coal, some use more complex equipment than others, and some are just more applicable to this complex substance. There is a tendency for the scientist who has access to a spectrometer to try his best to apply its use to his particular area of interest. There are many examples of this in the literature that leave the reader somewhat bewildered and uncertain as to what has been achicved.The great advantage of this book is that it clearly explains how each technique can be applied to coal, gives good examples of the use of the technique and describes the limitations of the method and the results obtained. 1 would recommend it to anyone who is interested in this area so that they can make their own decisions about the applications of spectroscopic methods to coal. This is a most useful book and will enable them to do this. M . Cloke Precision and Resolution in Spectroscopic Model Fitting By J. H. Swarte. Pp. xiii + 198. Delft University. 1992. Price Dfl. 63.50; US $35.00; f20.00. ISBN 90-6275-756-6/CIP. This monograph is the published thesis of J.H. Swarte submitted for his doctorate at the Technical University of Delft. As such it is quite clearly a research text and is aimed at those interested in the development of techniques of spectral deconvolution; it is not a light or easy read. Swarte derives the equations that relate observation errors to three effects often seen in the decomposition of a spectrum into its component Gaussian or Lorentzian peaks: (i) peak displacement from the ‘true’ position; (ii) interchange of peak shape parameters for overlapping peaks; and (iii) coincidence of peaks preventing resolution. The first two chapters (34 pp.) introduce spectro- scopic peak shapes and non-linear model fitting while the next three chapters (76 pp.) develop the theoretical description of critical errors, their relation to observation errors and their classification in ability to cause the three effects.This section is not for the mathematically faint-hearted! Chapter 6 (47 pp.) describes the application of the theory to spectroscopic systems and simulation experiments demonstrating its value. The final two chapters (28 pp.) are a discussion and conclusion. An appendix of curiosities uses the theory to show how optimistic some published work has been in deconvolut- ing spectra into component peaks. While the text is not at the browsing level, it is clearly written and is remarkably free from error. The theory is developed in stages with fairly detailed descriptions and explanations of assumptions and equations at each stage. The application of the theory is well described by the simulation experiments. The objective of each simulation is clearly laid out and the results matched against the objective. These experiments also demonstrate that significant approxi- mations to the full equations introduce only minor deviations in the results. The software implementation is not described. The appendix of curiosities has been mentioned already. The other two appendices deal with the mathematical properties of peak-shape equations and the detailed math- ematical derivation of the resolution discriminant used to describe the ability to resolve adjacent peaks. A useful glossary of terms is included. The text is a must for specialists in this field and it is worthy of consideration by others concerned with the effect of errors on model fitting. R. L. Tranter

ISSN:0003-2654    

DOI:10.1039/AN993180097N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, AUGUST 1993, VOL. 118 99N Conference Diary Date Conference September 1-3 2-3 5-10 5-10 5-10 5-1 1 5-1 1 6-10 6-10 6-10 6-10 7-8 7-9 7-10 7-12 8-10 7th International Conference on Polymers in Medicine and Surgery 2nd UK International Meeting on Biological and Biomedical Applications of Scanning Probe Microscopy Ninth International Biodeterioration and Biodegradation Symposium 5th European Conference on the Spectroscopy of Biological Molecules Second International Conference on the Biogeochemistry of Trace Elements Euroanalysis VIII: European Conference on Analytical Chemistry Pharmacy World Congress '93 18th International Conference on Infrared and Millimetre Waves Defect Recognition and Image Processing in Semiconductors and Devices 11th Specialised Colloque Ampere on Magnetic Resonance in Homogeneous and Heterogeneous Catalysis Location Noordwijkerhout , The Netherlands Nottingham, UK Leeds, UK Loutraki, Greece Taipei, Taiwan, Republic of China Edinburgh, UK Tokyo, Japan Colchester , UK Santander, Spain Menton,.France Second International Conference on Magnetic Heidelberg, Resonance Microscopy Germany Environmental Fate of Chemicals Lancaster , UK 2nd European FTMS Workshop Antwerp, Belgium 12th International Symposium on Biomedical Applications of Chromatography and Electrophoresis and 2nd International Symposium on the Applications of HPLC in Enzyme Chemistry 12th International Symposium on Cbrdoba, Microchemical Techniques Spain Verona and Soave, Italy 4th Workshop on Chemistry and Fate of Modern Pesticides and Related Pollutants Prague, Czechoslovakia Contact Mrs.Debbie Schorer, Conference Organiser, The Institute of Materials, 1 Carlton House Terrace, London, UK SWlY 5DB Tel: +44 71 839 4071 or +44 71 235 1391. Fax: +44 71 823 1638 The SPM Laboratory, Department of Pharmaceutical Sciences, University of Nottingham, Nottingham, UK NG7 2RD Tel: +44 602 515101. Fax: +44 602 515102 The Conference Secretary (RE), Department of Chemical Engineering, The University of Leeds, Leeds, UK LS2 9JT Professor Th. Theophanides, National Technical University of Athens, Department of Chemical Engineering, Zogratou 15780, Athens, Greece Dr. Shang-Shyng Yang, Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China; or Dr. Domy C. Adriano, University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA Miss P.E. Hutchinson, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 71 437 8656. Fax: +44 71 734 1227 Professor D. J. A. Crommelin, FIP Congress Department, The Hague, The Netherlands Tel: +3170 363 1925. Fax: +31 70 363 3914 Professor T. J. Parker, Department of Physics, University of Essex, Wivenhoe Park, Colchester, UK C04 3SQ Dr. Juan JimCnez, Drip 5, Universidad de Valladolid, 4701 1 Valladolid, Spain Professor J. Fraissard, Laboratoire de Chimie des Surfaces, Universitk P. et M. Curie, 4, Place Jussieu (Boite 196), 75252 Paris Cedex 05, France Dr. Bernhard Bliimich, c/o Max Planck-Institute fur Polymerforschung, Postfach 3148, D-6500 Mainz, Germany Dr.D. Osborn, Institute of Terrestrial Ecology, Monks, Abbots Ripton, Huntingdon, UK PE17 2LS Dr. Luc Van Vaeck, Department of Chemistry, University of Antwerp, Universiteitsplein 1, B 2610 Wilrijk, Belgium Tel: +32 3 820 2348. Fax: +32 3 820 2376 Dr. Franco Tagliaro, Scientific Secretariat, c/o Istituto di Medicina Legale, Policlinico Borgo Roma, 1-37134 Verona, Italy Tel: +39 45 8074 618. Fax: +39 45 505 259 Professor M. Valcarcel, Quimica Analitica, Facultad de Siencias, 14004 Cordoba, Spain Tel: +34 57 234453. Fax: +34 57 452285 M. Frei-Haiisler, IAEAC, P.O. Box 46, CH-4123 Allschwil 2, Switzerland Tel: +4161632789. Fax: +4161482 08 051OON ANALYST, AUGUST 1993, VOL. 118 Date 8-1 1 9-15 11-15 12-15 12-15 12-17 13-17 13-17 18-23 19-22 19-22 20 20-23 20-24 20-26 21-22 21-23 Conference Location 14th International Symposium on Polynuclear Tan-Tar- A, MO, Aromatic Hydrocarbons ISEC '93, International Solvent Extraction Conference: Solvent Extraction in the Process Industries EIRELEC 1993: Electrochemistry to the year 2000 International Ion Chromatography Symposium 1993 Surfaces in Biomaterials '93 9th International Conference on Heavy Metals in the Environment International Conference on Nuclear Analytical Methods in the Life Sciences Workshop in Liquid Scintillation Counting Very High Resolution Spectroscopy with Photoelectrons 4th International Symposium on Chiral Discrimination 2nd International Symposium on Planar Chromatography: Modern Thin-Layer Chromatography Laser Spectroscopy 93 Philips X-Ray Analysis Conference Dioxin 93: 13th International Symposium on Chlorinated Dioxins and Related Compounds 173rd Annual Meeting of the Swiss Academy of Natural Sciences (including Symposia of the Swiss Society for Analytical and Applied Chemistry, the Swiss Society for Microchemistry and Instrumental Analysis, the Swiss Association on Environmental USA York, UK Adare, Co.Limerick, Ireland Baltimore, MD, USA Cambridge, MA, USA Toronto, Canada Prague, Czechoslovakia Loughborough, Leicestershire, UK Giens, France Montreal, Quebec, Canada Research Triangle Park, NC , USA Norwich, UK Durham, UK Vienna, Austria CH-1936 Bagnes-Verbier , Switzerland Research, and other Societies, in German and French) 4th German Symposium on Near Infrared Spectroscopy Germ any Essen, The Royal Society of Chemistry 1993 Autumn Warwick, Meeting UK Contact Professor E.Cavalieri, Epply Institute, Medical Center, University of Nebraska, Omaha, NE Tel: +1402 559 4090. Fax: +l 402 559 4651 Conference Secretariat, SCI, 14115 Belgrave Square, London, UK SWlX 8PS Tel: +44 71 235 3681. Fax: +44 71 823 1698 Professor M. R. Smyth, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland Tel: +353 1 7045308. Fax: +353 17045503 Century International, P. 0. Box 493, Medfield, MA 02052, USA Tel: +1508 359 8777. Fax: +1 508 359 8778 ARDEL Management, P.O. Box 26111, Minneapolis, MN 55426, USA Tel: +1 612 927 6707. Fax: +1 612 927 8127 Heavy Metals Secretariat, CEP Consultants Ltd., 26-28 Albany Street, Edinburgh, UK EH1 3QH Tel: +44 31 557 2478.Fax: +44 31 557 5749 Jan Kucera, Nuclear Research Institute, CS-250 68 Rez near Prague, Czechoslovakia Tel: +42 2 685 7831 ext. 2268. Fax: +42 2 685 7567 Dr. Peter Warwick, Nuclear Chemistry Laboratories, Loughborough University of Technology, Loughborough, Leicestershire, UK LEll3TU Tel: +44 509 222585. Fax: +44 509 233163 Dr. Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnesia, F-67080 Strasbourg, France Chiral Secretariat, Conference Office, McGill University, 550 Sherbrooke St. West, West Tower, Suite 490, Montreal, Quebec, Canada H3A 1R9 Tel: + 1 514 398 3770. Fax: + 1 514 398 4854 Ms. Janet E. Cunningham, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1301 898 3772. Fax: +1301898 5596 68198-6805, USA Dr.D. L. Andrews, School of Chemical Sciences, University of East Anglia, Norwich, UK NR4 7TJ Kate Ridgeon, Philips Analytical, York Street, Cambridge, UK CB1 2QU Symposium Secretariat, Dioxin '93, Gesellschaft Osterreichischer Chemiker, Nibelungengasse 11, A-1010 Vienna, Austria Tel: +43 222 587 398014249. Fax: +43 222 587 8966 General Secretary, Swiss Academy of Sciences, Barenplatz 2, P.O. Box 2535, CH-3001 Berne, Switzerland Professor Dr. H. W. Siesler, University of Essen, Schutzenbahn 70, P.O. Box 103764, D-4300 Essen 1, Germany Miss P. E. Hutchinson, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 71 437 8656. Fax: +44 71 734 1227ANALYST, AUGUST 1993, VOL. 118 lOlN Date 22-24 26-1/10 26-1/10 26-1/10 26-1/10 27-29 29 30 Conference Location XIIth Conference of Analytical Chemistry of Romania Romania Constanta, AXAA-93-Solutions to Everyday Problems St.Lucia, Brisbane, Queensland, Australia 15th International Nutrition Conference Adelaide, Australia 1993 European Workshop in Chemometrics Leuven, Belgium 12th Australian Symposium on Analytical Chemistry incorporating 3rd Environmental Australia Chemistry Conference Perth, Emerging Technologies in Hazardous Waste Management V USA Atlanta, GA, 26th Annual Southern California Chapter Symposium USA Pasadena, CA, Duration of Repeated Dose Toxicity Studies- Bath, A Commonsense Approach? October 4-8 5-7 5-7 5-8 5-8 8-1 3 10-15 11-13 ECASIA 93, 5th Conference on Application of Surface and Interface Analysis 34th ORNL-DOE Conference on Analytical Chemistry in Energy Technology Laboratory Exhibition and Conference 5th Meeting of the Nuclear Magnetism and Biology Group 4th ISEC.Fourth International Seminar on Electroanalytical Chemistry 5th BCEIA. Fifth International Beijing Conference and Exhibition on Instrumental Analysis Electrochemical Society Meeting VIth National Symposium on Mass Spectometry UK Catania, Italy Gatlinburg, TN, USA London, UK Toulouse, France Beijing, China Beijing, China New Orleans, LA, USA Dehradun, India Contact Dr. Gabriel-Lucian Radu, The Romanian Society of Analytical Chemistry, 13 Bul.Carol I, Sector 3, 70346 Bucharest, Romania The Convenor, AXAA-93-Solutions to Everyday Problems, P.O. Box 6198, Upper Mount Gravatt, Queensland 4122, Australia Congress Secretariat, CSIRO Division of Human Nutrition, P.O.Box 10041, Gouger St., Adelaide 5000, South Australia, Australia Timshel Conference Service, J. B. Van Monsstraat 4, B-3000 Leuven, Belgium Tel: +32 16 290010. Fax: +32 16 290510 Valerie Landgrebe, Symposium Secretariat, 12AC/ 3EC, Conference and Seminar Management, UWA Extension, The University of Western Australia, Nedlands, Perth, Western Australia 6009, Australia Tel: +619 380 318112433. Fax: +61 9 380 1088/1066 Dr. W. Tedder, School Of Chemical Engineering, Georgia Institute of Technology, Atlanta, GA Tel: + 1 404 894 2856. Fax: + 1 404 894 2866 Tony Tumbrello, Associated Vacuum Technology Inc., 814 North Grand Avenue, Covina, CA 91724, USA Tel: +1 818 967 3869. Fax: +1 818 967 1861 Dr.Paul Illing, Health and Safety Executive, R425 Magdalen House, Stanley Precinct, Bootle, UK L20 3QZ Tel: +44 51 951 3420. Fax: +44 51 922 7918 30332-0100, USA G. Marletta, Consorzio Catania Ricerche, V. Le Andrea Doria, 6, 1-95125 Catania, Italy Tel: +39 95 221635. Fax: +39 95 339734 W. R. Laing, Technical Program Chairman, Oak Ridge National Laboratory, P.O. Box 2008, MS 6127, Oak Ridge, TN 37831-6127, USA Tel: +1 615 574 4852. Fax: +1 615 574 4902 Evan Steadman Communications Group Ltd., 90 Calverley Road, Tunbridge Wells, Kent, UK TN12UN Professor M. Malet-Martino, Laboratoire LMRCP, Universite Paul Sabatier, 118, route de Narbonne, F-3 1062 Toulouse Cedex, France Professor Erkang Wang, 109 Sitalin Street, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, China General Service Office, 5th BCEIA, Room 5412, Building No.4, Xi Yuan Hotel, Er Li Gou, Beijing 100046, China Electrochemical Society Inc, 10 South Main Street, Pennington, NJ 08534-2896, USA Dr. Pradeep Kumar, Indian Institute of Petroleum, Dehradun-248 005, India, and Dr. S. K. Aggarwal, Honorary Secretary-ISMAS, c/o Fuel Chemistry Division, Bhabha Atomic Research Centre, Bombay-400 085, Maharastra, India102N ANALYST, AUGUST 1993, VOL. 118 Date 13 16-17 17-21 17-22 18-22 19-20 19-23 20-22 2 1-22 24-28 26-28 Conference FT Microscopy-10 Years On: 4th European Seminar on FT-IR Microscopy Second National Conference on Inductively Coupled Plasma Mass Spectrometry Eighth Symposium on Separation Science and Technology for Energy Application FACSS XX, 20th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies Modern Electrochemistry in Industry and for the Protection of the Environment Frederick Conference on Capillary Electrophoresis EXPOQUIMIA ’93: Applied Chemistry Technical Fair Hygiene and Health Management in the Working Environment International Conference on Analytical Chemistry, Biochemistry and Pharmaceutical Sciences 8th Symposium on Separation Science and Technology for Energy Applications The 1993 Analytical Forum-‘Meeting the Challenge ’ November 1-3 Chernyaev Conference on Chemistry, Analysis, Technology and Application of Platinum Metals 2 Electro-Membrane Processes 2-4 KEMIA 93.Finnish Chemical Congress and Exhibition 3 Pharmaceutical Applications and Sample Handling Techniques 3-5 2nd International Symposium on Characterization and Control of Odours and VOC in the Process Industries Location Manchester, UK Detroit, MI, USA Oak Ridge, TN, USA Detroit, MI, USA Krakow, Poland Frederick, MD, USA Barcelona, Spain Ghent, Belgium Casablanca, Morocco Gatlinburg, TN, USA Chepstow, UK Moscow, Russia London , UK Helsinki, Finland York, UK Contact Michelle Barker, Conference Co-Ordinator, Spectra-Tech Europe Limited, Genesis Centre, Science Park South, Birchwood, Warrington, UK WA3 7BH Tel: +44 (0) 92.5 830 2.50.Fax: +44 (0) 925 830 252 Society for Applied Spectroscopy/ICP/MS Users Group, 198 Thomas Johnson Drive, Suite-2, Frederick, MD 21702-4317, USA Tel: +1 301 694 8122. J. T. Bell, Oak Ridge National Laboratory, Post Office 2008, Oak Ridge, TN 37381, USA FACSS, 198 Thomas Johnson Drive, Suite S-2, Fredericks, MD 21702, USA Tel: +1301 846 4789.Fax: +1 301 694 6860 Dr. Andrzej Kowal, Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niczapiminajek 1, 30-239 Krakow, Poland Margaret L. Fanning, Conference Coordinator, PRI, NCI-FCRDC, P.O. Box B, Frederick, MD Tel: +1301846 1089. Fax: +1301 846 5866 Fira de Barcelona, Avda. Reina Ma Cristina, 08004 Barcelona, Spain 3rd International Symposium, ‘Hygiene and Health Management in the Working Environment’, c/o TI- K VIV, Attn. Ms. Rita Peys, Desguinlei 214, B- 2018 Antwerp, Belgium Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702.Dr. J. T. Bell, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6223, USA Tel: +l 615 574 4934; or Dr. J. S. Watson, K-25 Plant, P.O. Box 2003, Oak Ridge, TN 37831-7298, USA Tel: +1 615 574 679.5. Lisa Butler, Analytical Products Group, Hewlett- Packard Ltd., Cain Road, Bracknell, Berkshire, UK RG12 1HN 21702-1201, USA Dr. I. B. Baranovsky, Kurnakov Institute of General and Inorganic Chemistry, 31 Lenin Avenue, Moscow 117907, Russia Dr. T. R. Ralph, Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading, Berkshire, UK RG4 YNJJ Tel: +44 734 722811 ext. 2257. Fax: +44 734 723236 Ms. Anita Haatainen, Tel: +358 0 150 9207 or Mr. Seppo Niiranen Tel: +358 0 150 9215. Don Clark, Physical Sciences-265 , Pfizer Central Research, Ramsgate Road, Sandwich, Kent, UK CT13 9NJ Tel: +44 304 616036.Fax: +44 304 616726 Louvain-la-Neuve, Symposium Secretariat, Sociktk Belge de Belgium Filtration, Universitk Catholique de Louvain, Voie Minckelers 1, 1348 Louvain-la-Neuve, Belgium Tel: +32 10 47 23 26. Fax: +32 10 47 23 21ANALYST, AUGUST 1993, VOL. 118 103N Date 7-10 7-1 1 7-12 8-10 11-12 11-12 14-19 14-19 15-19 22-23 Conference Location Contact Electrophoresis '93 Charleston, SC, USA 7th International Forum-Electrolysis in Chemical Manufacture Vista, FL, Symposium on Supercritical Fluid Phenomena (1993 Annual Meeting of the AIChE) Lake Buena USA St. Louis, MO, USA International Symposium on Plasma PolymerizatiodDeposition International Conferences on Analytical Chemistry, Biochemistry, Pharmaceutical Sciences, and Water QualitylEnvironmental Pollution 7th International Conference on Plasma Chemistry and Technology XV International Congress of Clinical Chemistry OPTCON '93 Las Vegas, NV, USA New Delhi, India San Diego, CA, USA Melbourne, Australia San Jose, CA, USA 32nd Annual Eastern Analytical Symposium International Conferences on Analytical Shanghai, Chemistry, Biochemistry, Pharmaceutical China Sciences, and Water QualitylEnvironmentaI Pollution New Jersey, USA 30-3/12 13th International Symposium on HPLC of San Francisco, Proteins, Peptides and Polynucleotides CA, USA December 6-8 Symposium on Purity Determination of Drugs Stockholm, Sweden 7-9 The First Conference in Chemistry and its Doha, Applications Qatar 8-1 0 Laser M2P, Materials Engineering, Medicine Lyon, and Biology, Physics and Chemistry France 1994 January 5-7 6th Winter Conference on Flow Injection San Diego, CA, An a 1 y s i s USA 10-15 1994 Winter Conference on Plasma San Diego, CA, Spectrochemistry USA Mrs.Janet Cunningham, Electrophoresis '93, c/o The Electrophoresis Society, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: +1301898 5596 Dr. N. Weinberg, 72 Ward Road, Lancaster, NY Tel: +1716 684 0513. Fax: +1 716 684 0511 Michael A. Matthews, Chemical Engineering Department, University of Wyoming, Box 3295, University Station, Laramie, WY 82071-32, USA Tel: + 1 307 766 5769 Fax: + 1 307 766 4444. Or: Ted W. Randolph, Chemical Engineering Department, Yale University, 9 Hillhouse Avenue, New Haven, CT 06520-2159, USA Tel: + 1 203 432 4375.Fax: +1 203 432 7232 K. L. Mittal, Skill Dynamics (an IBM Company), 500 Columbus Ave., Thornwood, NY 10594, USA Tel: +1 914 742 5747. Fax: +1 914 742 5594 Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702. Research Institute of Plasma Chemistry and Technology, P.O. Box 1653, Carlsbad, CA 92008, USA 1993 IFCC Congress Secretariat, 232 Bridge Road, Richmond, Victoria, Australia Tel: +61 3 429 4322. Fax: +61 3 427 0715 IEEELEOS, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA Tel: +1 908 562 3896. Fax: + 1 908 562 1571 EAS Program Committee, P.O. Box 633, Montchanin, DE 19710-0633, USA Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: +1 613 932 7702.Ms. Paddy Batchelder, Conference Manager, 7948 Foothill Knolls Drive, Plcasanton, CA 94588, USA Tel: + 1 51 0 426 9601. Fax: + 1 510 846 2242 14086-9779, USA Swedish Academy of Pharmaceutical Sciences, P. 0. Box 1136, S-111 81 Stockholm, Sweden Tel: +46 8 245085. Fax: +46 8 205511 Professor Abdel-Fattah M. Rizk, Department of Chemistry, Faculty of Science, University of Qatar, P.O. Box 2713, Doha, Qatar Richard Moncorgk, Universitk de Lyon 1, Biit. 205, F-69622 Villeurbanne Cedex, France Professor G. D. Christian, Department of Chemistry BG-10, University of Washington, Seattle, WA 98195, USA Tel: +1206 543 1635. Fax: +1 206 685 3478 Dr. R. Barnes, 1994 Winter Conference on Plasma Spectrochemistry, % ICP Tnformation Newsletter, Department of Chemistry, Lederle GKC Towers, University of Massachusetts, Amherst, MA 01003- 0035, USA Tel: +1413 545 2294.Fax: +I 413 545 4490104N ANALYST, AUGUST 1993, VOL. 118 Date Conference Location 11-14 5th International Symposium on Supercritical Baltimore, MD, Fluid Chromatography and Extraction USA 19-21 2nd International Conference on Reactive Yokohama, Plasmas and 11th Symposium on Plasma Processing Japan February 21-25 OFC '94: Optical Fibre Communications San Jose, CA, Conference USA 22-25 HTC 3: Third International Symposium on Antwerp, Hyphenated Techniques in Chromatography Belgium 2 8 4 3 Pittcon '94: The 45th Pittsburgh Conference Chicago, TL, on Analytical Chemistry and Applied Spectroscopy USA March 13-16 13-18 27-30 April 6-8 10-13 10-15 10-16 12-14 Third European Federation of Corrosion Workshop on Microbial Corrosion Portugal Estoril, 207th American Chemical Society National Meeting USA San Diego, CA, International Federation of Automatic Control (IFAC) Symposium on Modeling and Control in Biomedical Systems Galveston, TX, USA Electroanalysis: A Tribute to Professor J.D. R. Thomas UK Cardiff, ANATECH 94: 4th International Symposium on Analytical Techniques for Industrial Process Control France Mandelieu La Napoule, 207th ACS National Meeting and 5th Chemical Congress of North America (with Sessions of Analytical Chemistry, Environmental Chemistry, Chemical Health and Safety, etc.) 3rd International Conference on Methods and Kailua-Kona, Applications of Radioanalytical Chemistry Hawaii USA Mexico City, Mexico 13th Pharmaceutical Technology Conference Strasbourg, France Contact Larry T.Taylor, Department of Chemistry, Virginia Polytechnic Institute, Blacksburg, VA 24061, USA T. Goto, Department of Quantum Engineering, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, Tel: +1 202 223 9034. Fax: +1 202 416 6100 Dr. R. Smits, p/a BASF Antwerpen N.V., Central Laboratory, Scheldelaan, B-2040 Antwerp, Belgium Tel: +32 3 568 2831. Fax: +32 3 568 3250 Mrs. Alma Johnson, Program Secretary, The Pittsburgh Conference, Department CFP, 300 Penn Center Boulevard, Suite 332, Pittsburgh, PA 15235, USA DC 20036-1023, USA C6sar Sequeira, Tnstituto Superior Tkcnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal, or A. K. Tiller, Corrosion Centre, 23 Grosvenor Gardens, Kingston-upon-Thames, UK KT2 5BE, or D. Thierry, Swedish Corrosion Institute, Roslagsvagen 101, Hus 25, S-10405 Stockholm, Sweden Department of Meetings, American Chemical Society, 115516th St., NW, Washington, DC 20036, USA Tel: +1 202 872 4396. IFAC Biomedical Symposium, University of Texas Medical Branch, Box 55176, Galveston, TX 77555- 5176, USA Tel: + 1 409 770 6628 or 770 6605. Fax: + 1 409 770 6825 Dr. J. M. Slater, Department of Chemistry, Birkbeck College, University of London, 29 Gordon Square, London, UK WC1H OPP Tel: +44 71 380 7474. Fax: +44 71 380 7464 ANATECH 94 Secretariat, Elsevier Advanced Technology, Mayfield House, 256 Banbury Road, Oxford, UK OX2 7DH Tel: +44 (0)865 512242. Fax: +44 (0)865 310981 Mr. B. R. Hodson, American Chemical Society, 1155-16th Street N.W., Washington, DC 20036, USA Tel: +1 202 872 4396. Ned A Wogman, Battelle, Pacific Northwest Laboratories, P.O. Box 999, P7-35, Richland, WA 99352, USA Tel: + 1 509 376 2452. Fax: + 1 509 376 2373 Professor Mike Rubinstein, 13th Pharmaceutical Technology Conference, 24 Menlove Gardens North, Liverpool, UK L18 2EJ Tel: +44 51 737 1993. Fax: +44 51 737 1070 Entries in the above listing are 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/AN993180099N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, AUGUST 1993, VOL. 118 10SN New Editorial Board Members Professor Michael Cooke BSc., Ph.D., C.Chem., FRSC Michael Cooke graduated from the University of Bristol in 1967 and completed his Ph.D. in the autumn of 1969. A two year Post-Doctoral post working on the electrochemical synthesis of organometallic compounds was followed by a year as a Research Fellow at the University of Arizona working with Professor Bob Feltham. He then returned to the University of Bristol to work with Professor Gordon Stone F.R.S. on synthetic organometallic chemistry for a few years before moving into analytical chemistry under the guidance of Graham Nickless. Throughout the eighties he developed his interests in chromatography and hyphenated chromato- graphic techniques and in using analytical science to solve problems and answer questions.In 1988 he left academic life to take up an industrial post with a multinational company based in Germany. He returned to England in 1990 to join a laboratory services company with a brief to develop environ- mental analytical services. In September 1991 he was appointed Professor of Analytical Science at the newly created Sheffield Hallam University. Although his research interests are still centred on the use of chromatography and hyphenated techniques to investigate problems analytically, a recent area for research has been the development of field based analytical methodology and portable equipment. Dr. Gillian M. Greenway BSc., Ph.D., C.Chem., MRSC Dr. Gillian M. Greenway started her career in Analytical Science when she enrolled for a degree in Applied Chemistry at Sheffield City Polytechnic (now Sheffield Hallam Univer- sity) in 1978.During that time she got her first real taste of analytical chemistry on industrial placements at the MAFF, ADAS laboratories in Starcross, Devon, Yorkshire Water Authority and British Steel Chemicals in Sheffield. After surviving these experiences and only flooding two laboratories she decided that analytical science had the potential to be very interesting but routine analysis was not for her. After completing a final year research project on chemilumi- nescence with Paul J. Worsfold (now a Professor at the University of Plymouth) and getting enough results to think that research might be worthwhile she decided to embark on a Ph.D.In 1982 she started her Ph.D. project on sample introduc- tion into a microwave-induced plasma emission spectrometer. The project, which was in collaboration with the Health and Safety Executive, involved the use of thermal desorption and gas chromatographic sample introduction methods for or- ganometallic compounds. The GC-MIP worked well despite being balanced on breeze blocks but the thermal desorption caused problems. Despite Gordon Kirkbright’s untimely death in 1984 she completed the work for her Ph.D. and became a physical/ analytical chemistry lecturer at Hum berside College of Higher Education (now the University of Humberside) in 1985. After the first year, which was an initiation by fire with a huge teaching commitment and laboratory classes at least two nights a week, she started some research with two M.Phil.students. The work involved the use of immobilized enzymes in flowing systems and included the development of wire- coated enzyme electrodes and the use of immobilized enzyme reactors. In 1988 Gillian became a lecturer in the Analytical Group at the University of Hull, working with Professor Alan Town- shend and her ex-project supervisor Paul Worsfold (who has now been replaced by Dr. Steve Haswell). She has an active research group working in several areas of analytical chemistry including on-line sample preparation (dialysis, SFE, microwave digestion, preconcentration and speciation), on- line adsorptive stripping voltammetry, chemiluminescence and electrochemiluminescence , molecular recognition and sensor design, sample introduction for ICP-MS and some chromatography. Analytical Science runs in Gillian’s family with both her husband and brother having the same calling; however, her one year old daughter showed very little interest when she briefly attended the XXVIII CSI at York.

ISSN:0003-2654    

DOI:10.1039/AN993180105N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

106N ANALYST, AUGUST 1993, VOL. 118 RSC Sponsored Awards The recipients of the analytical-related awards. L to R: Professor A . McCaffery, Professor K . D. Bartle, Professor C. W. Rees (President of the Royal Society of Chemistry) and Professor P. Sudler Professor Charles Rees, President of the Royal Society of Chemistry, presented the RSC's annual industrially sponsored awards for 1992 at a ceremony on June 2,1993, at the Society's headquarters at Burlington House, in Piccadilly, London. Awards presented relevant to analytical chemistry are as follows: Analytical Separation Methods (Sponsored by Roche Products Ltd.) Awarded to Professor Keith D. Bartle, University of Leeds, for his outstanding contribution to column chromatography and, in particular, to developments in the use of supercritical fluids for chromatography and extraction.Keith has been a member of The Analyst Editorial Board for the past three years. Inorganic Biochemistry (Sponsored by Chapman & Hall, Scientific Data Division) Awarded to Professor Peter Sadler, Birkbeck College, London, for his distinguished work on the application of inorganic biochemistry to medicine and particularly in the study of potential drugs against rheumatoid arthritis and in the treatment of cancer. Spectroscopy (Sponsored by Varian NMR Division) Awarded to Professor Anthony McCaffery , University of Sussex, who is distinguished for the development and application of polarization spectroscopy techniques to the study of atomic and molecular interactions, particularly in the gas phase.Chemical Analysis and Instrumentation (Sponsored by Perkin- Elmer Ltd.) Awarded to Professor Melvin Comisarow, University of British Columbia, Canada, for the introduction and develop- ment of ion cyclotron resonance mass spectrometry, a technique which improves the accuracy that can be obtained by spectrometry. Future Issues will Include- Examination of Sampling Methods for Assessment of Per- sonal Exposures to Airborne Aldehydes-Rein Otson, Philip Fellin, Quang Tran and Robert Stoyanoff Determination of Nanogram Amounts of Iodine in Foods by Radiochemical Neutron Activation Analysis-Amares Chatt and Raghunadha R. Rao Comparison of Liquid Chromatographic Methods for Analy- sis of Homologous Alkyl Esters of BiphenyL4,4'-dicarboxylic Acid-Joel K. Swadesh, Charles W.Stewart, Jr. and Peter C. Uden Characterization of Trace Amounts of Aluminium in Bio- logical Reference Materials by Electrothermal Atomic Absorption Spectrometry-Norine Motkosky and Byron Kratochvil Flow Injection Spectrophotometric Method for the Speciation of Aluminium in River and Tap Waters-Ma Jod Quintela, Mercedes Gallego and Miguel Valcarcel Characterization of Planar Concentration Gradients in a Sequential-injection System for Cell-perfusion Studies-Cy H. Pollema and Jaromir RfiHiEka Electrochemical Reduction at Mercury Electrodes and Dif- ferential-pulse Polarographic Determination of Pentamidine Isethionate-M. Valnice B. Zanoni and Arnold G. Fogg Comparison of Instrumental Methods for the Determination of Total Selenium in Environmental Samples-Philip M.Haygarth, A. Philip Rowland, Stefan Sturup and Kevin C. Jones Cathodic Stripping Voltammetric Determination of Pentam- idine Isethionate at a Hanging Mercury Drop Electrode-M. Valnice B. Zanoni and Arnold G. Fogg Selective Extraction and Voltammetric Determination of Gold at a Chemically Modified Carbon Paste Electrode- Peng Tuzhi, Li Huiping and Wang Shuwen Spectroscopic Probes for Hydrogen-bonding, Extraction Impregnation and Reaction in Supercritical Fluids-Andrew I. Cooper, Steven M. Howdle, Catherine Hughes, Margaret Jobling, Sergei G. Kazarian, Martyn Poliakoff, Lindsey A. Shepherd and Keith P. Johnston Quantitative Structure-Extraction Relationships: A Model For Supercritical Fluid Extraction-Mark Kane, John R. Dean, Steve M. Hitchen, William R. Tomlinson, Roy L. Tranter and Christopher J. Dowle Estimating and Using Sampling Precision in Surveys of Trace Constituents of Soils-Michael Thompson and Michael Maguire Direct Determination of Ethanol in all Types of Alcoholic Beverages by Near-infrared Derivative Spectrometry- MBximo Gallignani, Salvador Garrigues and Miguel de la Guardia Assessment of Three Azophenol Calix[4]arenes as Chro- mogenic Ligands for Optical Detection of Alkali Metal Ions- Mary Mc Carrick, Stephen J. Harris and Dermot Diamond Nitrogen Factors for Beef: A Reassessment-Analytical Methods Committee

ISSN:0003-2654    

DOI:10.1039/AN993180106N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, AUGUST 1993, VOL. 118 953 Analytical Perspective Relationship Between Geochemical Reference Material Characterization and the Development of New Methods for Geoanalysis” Jean S. Kane National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Reference materials (RMs) have a number of uses in the geoanalytical laboratory. Prime among them is the stimulus RMs provide to the continuous improvement of established analytical methods and the development of new methods. As demands increase for certifying the concentrations of elements to higher levels of accuracy and/or with greater precision, old methods of analysis are refined and new ones are developed. This paper traces the parallel histories of the issue of geochemical reference materials and the development of today‘s principal methods for geoanalysis, showing the relationships between the two.Keywords: Geochemical reference materials; geoanalysis It is a truism that the very highest quality analyses with respect to both accuracy and precision are required in order to characterize fully certified reference materials (CRMs) and other non-certified geochemical reference materials (GRMs). Once certifiedhest estimate1 concentrations have been estab- lished, these materials can fill a number of roles in the geoanalytical laboratory. They can be used reliably as calibration standards for many analytical instruments. They can be analysed as the principal means of method validation, with the results of such analyses forming the basis of the accuracy and precision statement in any given laboratory’s standard operating procedure.Regular inclusion of GRMs with unknown samples provides the means by which analytical drift can be distinguished from geochemical diversity, espe- cially when analyses for a single study are performed over a period of months or years, in different laboratories or using changed analytical methods. Finally, the need for well characterized reference samples has provided an important stimulus to the continuous improvement of established analytical methods and to the development of new methods. Characterization of reference materials requires that, first, good analytical methods be available for use. The route to well characterized reference materials and to sound method development is unavoidably circular.Reference materials cannot help but reflect the state of the art at the time of their first characterization. The process is on-going, as analysis of reference materials prompts continual method refinement and this results in improved characterization of the succeeding generation of materials. CRMs Versus Uncertified Reference Materials Before developing parallel historical perspectives of the actual production and issue of reference materials and analytical methods used in characterizing those materials, a brief review of the terminology for reference materials and their analysis is necessary. This will include both general terminology as * Presented at the Meeting Geoanalytical Techniques: Current Capabilities, Future Potential, Milton Keynes, Buckinghamshire, UK, October 1 , 1992.presented in the International Organization for Standardiza- tion (ISO) Guide 301 and more specific terminology as used at the National Institute of Standards and Technology (NIST) .2 The TSO Guide defines a reference material as one for which one or more properties are sufficiently well established to be used for the calibration of an apparatus, the assessment of a measurement method or assigning values to unknown samples. Historically, ‘certifying bodies’, e.g., NIST and the Com- munity Bureau of Reference (BCR), have produced CRMs, which are issued with Certificates of Analysis. [NIST has a trademark pending on the term Standard Reference Material (SRM) for its CRMs.31 Certified values are the best possible estimates of the ‘unknowable’ true concentration.4 They result when the systematic errors in analysis are small reiative to the precision error, which itself is not large.At NIST, certified values are established either from results of a single definitive method275 of analysis, or from results of at least two reliable independent, comparative methods216.7 whose results are in statistical agreement. Collectively, CRMs account for approximately 25% of the materials in widespread distribu- tion to geochemical laboratories today. Certified values typically are provided for a limited range of elements in each CRM. Additional GRMs are produced by a number of other agencies,8-12 including the United States Geological Survey (USGS) and the International Working Group (IWG) of the Centre de Recherches Pktrographiques et Gkochemiques (CRPG) .Currently, the I S 0 Guide1 defines two terms, consensus value and best estimate, that apply to the concentration values reported for uncertified materials (and presumably to uncerti- fied values of constituents in CRMs). When NIST reports an uncertified value for one of its SRMs, the term ‘Information Value’ is used. In discussing the methods of analysis, it is necessary to distinguish between broad instrumental or chemical tech- niques and the specific details of their use in a given laboratory. The latter includes all aspects of chemical or physical preparation of sample prior to measurement, specific conditions during measurement and data reduction after measurement in addition to the generic properties of the technique used.In all that follows, it is the total method that is954 ANALYST, AUGUST 1993, VOL. 118 most important: however, in order to structure the presenta- tion, examples will be grouped according to broader instru- mental or classical chemical techniques. Historical Peppective The iterative process of method development and ever improving SRM/GRM characterization can be illustrated in several ways. One is to look at the initial characterization of G-1 and W-1, based on the collaborative study of Fairbairn et al. 13 At the time of that study, the principal techniques used in analytical geochemistry were classical chemistry and d .c. arc spectrography. One of the aims of the study was to establish best estimate constituent concentrations based on classical chemistry so that the materials could be used for majodminor element calibration in d .c.arc spectrographic analysis. The classical methods were well established and highly precise. They were thought to be equally accurate, qualifying as definitive methods in most laboratories using them, but Fairbairn et aE.’s study13 proved otherwise. Data ranges between laboratories greatly exceeded the within-laboratory measurement precision. 13914 Despite this, consensus best estimates values were derived, based on approximately 50% of the total data submitted. These values both met the goals of the study and have withstood the test of time.14-16 Establish- ment of these best estimates of true concentration was a milestone in geoanalysis. Methods based on d.c. arc spectrography had been under development for approximately 20 years at the time of Fairbairn et al.’s study.13 The technique is a comparative one, measuring a concentration-dependent physical property (characteristic emission line intensity) and quantifying the concentration through concurrent measurement of calibration standards.Selection of calibration standards, then, was a major aspect of the method development needed in each laboratory using the technique. Correction for any spectral interferents occurring differently in a sample and the calibra- tion standard was another. A third was establishing the arcing conditions that matched excitation of sample and standard. All of these factors contributed to a measurement uncertainty for the d.c. arc technique that was expected to exceed that of classical chemical analysis.Finally, sampling errors due to the multi-mineralic nature of the samples can be considerable,l7.18 as measurements are made on 15-20 mg sample sizes. Nevertheless, the use of d.c. arc spectrography permitted the measurement of concentrations far lower than those measured chemically. The results obtained through use of the technique prompted the on-going drive to lower and lower determination limits and changed the focus for SRM/GRM characterization to include trace elements in addition to major and minor constituents. None of the instrumental techniques that today might be considered the mainstays of geochemical analysis, 19 namely atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), instrumen- tal neutron activation analysis (INAA) , X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS), were in use in the routine analytical laboratory at the time of Fairbairn et d ’ s study.13 All had their historical roots in the mid-1800s to carly 1900s, but none began to be routinely developed for geochemical analysis until the 1940s or later.Each of these techniques expanded the range of elements that could be determined, or lowered the quantifiable concentration at which the element could be measured, or both. Additionally, the new instrumental techniques were all capable of producing more precise data than could be obtained with d.c. arc spectrography. This greatly improved the precision with which best estimates of ‘true’ concentration for CRM/GRM constituents could be made.At the same time, the development of all techniques was aided by the availability of G-1 and W-1 and the other GRMs that followed, beginning in the 1960s. Today’s Mainstay Techniques for Geoanalysis Many methods of analysis19 are currently used in geoanalysis. As already noted, however, a relatively small number of instrumental techniques dominate, and these are being used for the analysis of extensive suites of elements by large numbers of laboratories. It must be emphasized that, while the discussion that follows is organized around those dominant techniques, it is the detailed method of application in each individual laboratory that ultimately determines the useful- ness of the analytical result in characterizing SRMs/GRMs.Having emphasized that distinction between technique and method, the historical framework in which the dominant geoanalytical techniques developed, and their respective contributions to the characterization of CRMs/GRMs for geoanalysis, can be outlined. Atomic absorption spectrometry, including not only flame but also electrothermal and vapour generation variants of AAS, will be considered first. In 1955, independent publica- tions described the first measurements and instrumentation for the method.20 Beginning in the mid-1960s, application of AAS to geoanalysis was extensive. Atomic absorption measurements were not yet in use when Stevens et al.’s study21 of G-1 and W-3 was conducted. However, by the time Flanagan22 published his 1972 compila- tion for the USGS standard rock series including BCR-1, AAS (predominantly flame) had been used to determine approxi- mately one quarter of all elements reported in that work.The SRM 1633 Coal Fly Ash was the first silicate material to be certified23 by NIST for several trace constituents. Atomic absorption methods, including cold vapour for mercury, were used in determining seven of the twelve elements certified, and was used extensively in the round-robin analysis of SRM 1633 conducted concurrently by the Environmental Protection Agency (EPA).24 Most recently, AAS analyses contributed to 20% of the certified values of the new NIST soil SRMs, 2709- 2711,25 and to 31% of the best estimate concentrations (16 of 51) for SDO-1.26 Achieving agreement between results obtained using AAS and other techniques required the development of decomposi- tion methods free from volatilization losses (e.g., Hg in SRM 1633, As in SDO-1), of analyses either free from, or accurately correcting for, matrix effects (e.g., Cd and Co by electrother- mal AAS in SRMs 1633 and 2709, respectively; As by hydride generation AAS in SRM 2709).Each of the required method development studies improved the understanding of the AAS instrumental technique generally, in addition to refining other equally important aspects of the methods of analysis. Today, as a result, differences of 3% relative or less between results obtained by AAS and other techniques are frequently achieved in CRM certification and GRM characterization programmes (e.g., Co, Cu and Hg in SRM 2709;25 A1203, Fe203, CaO, MgO, Na20, Cu, Ni and Zn in SDO-126).By the mid-1980s, ICP-AES was pushing in front of AAS as a mainstay laboratory technique ,27 particularly for the refrac- tory elements that had always been particularly difficult to determine using AAS. Inductively coupled plasma atomic emission spectrometry had clear advantages over AAS. First, it was possible using commercial instrumentation to determine many elements simultaneonsly, rather than sequentially. Also, for many elements, the detection limits obtained in ICP- AES measurement were lower for a given element than those obtained by flame AAS. However, the spectra produced were far more complex and subject to many more spectral interferences than the AA spectra, so that data reduction after measurement was more prone to systematic error.Identifica- tion of the spectral overlaps respon5ible for measurement bias and the development of correction algorithms had to precede the extensive use of ICP-AES in characterizing new CRMs/ANALYST, AUGUST 1993, VOL. 118 955 GRMs. Additionally, the technique was not totally free from systematic errors due to matrix effects, as had been initially postulated.28 These also had to be investigated, and correction strategies such as the method of additions employed. Analysis of existing CRMs/GRMs contributed greatly to ensuring complete identification of both spectral and matrix effects of ICP-AES methods. The National Institute of Standards and Technology first used ICP-AES analyses in the certification of SRMs used by the geoanalytical community while producing the sediment SRM 1646 in 1982.29 The National Research Council of Canada (NRCC) also used the method extensively in produc- ing its CRM sediments, MESS-1 and BCSS-1.30 Since then, use of the procedure has become widespread in new certifica- tion/characterization programmes.Eleven of 24 certified values for the NIST soils, SRMs 2709-2711,25 were based in part on ICP-AES data. The ICP-AES method developed only slightly more rapidly than AAS. However, a genuinely explosive growth occurred with ICP-MS .31732 The first commercial instrument (1983) followed the first developmental prototype by only 3 years, and by 1986 a number of application papers focusing on GRM analysis had been published.This speed of development was possible largely because ICP-MS is a composite method whose development can be shown to begin with the merger of the two, rather than with the inception of either plasma tech- nology in 1942 or mass spectrometry in the 1920s. Both ICP- AES and ICP-MS have greatly expanded the ability to obtain data by two or more independent methods for many elements, not the least of which are the rare earth elements (REE), Nb and Ta, all important in petrogenic modelling applications. These elements were determined in geoanalytical labora- tories initially by d.c. arc spectrography and subsequently by either INAA (most REE, Ta) or XRF (La, Ce, Nb), with little overlap between methods. However, the availability of the resulting single-technique databases for CRMs/GRMs facili- tated method validation when ICP-MS was first applied to these elements. The importance of pre-measurement chemistry in addition to instrumental technique is well illustrated by key reports on the development of ICP-MS methods. To cite just two, Sholkovitz33 used CRWGRM analyses to document decomposition problems affecting REE data reliability, while McLaren et al.34 investigated isobaric interferences in ICP-MS analyses due to the choice of decomposition acid. Inductively coupled plasma mass spectrometry has been used for geochemical analyses for almost 10 years now, and many reports of analyses on previously existing CRMs/GRMs have been published, but the use of the method for the characterization of new CRMs/GRMs is not yet widespread, as is use of the other four mainstay analytical techniques.The NRCC has made the most extensive use of ICP-MS in certification of its marine CRMs34 and in developing cooperat- ive laboratory data for NIST SRM 2704.35 The National Institute of Standards and Technology used ICP-MS analyses coupled with other methods in the certification of Ag, Cd and Ni in the three soil SRMs.25 All of the mainstay instrumental techniques for geochemical analysis discussed thus far have required sample dissolution as a critical first step in the analytical method. The development and validation of dissol- ution procedures is the subject of full texts or chapters there0f.~C3~ Reference has already been made to the Sholko- vitz33 study of errors in some Zr and REE analyses that resulted from incomplete dissolution prior to ICP-AES and ICP-MS measurement.Mainstay instrumental techniques for geoanalysis that do not require prior sample decomposition are INAA and XRF. Both developed similarly to the atomic spectrometric methods already discussed. That is, there was a considerable time lag between the fundamental discoveries leading to the instru- mental techniques and the development of routine laboratory methods for applying them in geoanalysis. While neutron activation analyses can be traced back to the discovery of radioactivity in the 1890s and to fission experi- ments first performed in 1934 by Fermi,40 there was an absence of INAA data in Fairbairn et aZ.’s report13 and only limited inclusion in the Stevens et al.’s 1960 report21 on G-1 and W-1.Extensive use of INAA in geoanalysis began in the early 1970~22 and is relatively unchanged today. Some of the early uses of the method focused on characterizing the USGS BCR-1, more analysed than any other GRM; BCR-1 consti- tuted the control sample throughout the lunar programme.41 Determinations of the REE, Co, Cr, Ta, Hf and other constituents by INAA were basic to that programme. More recently, INAA provided one of the independent methods of analysis for Pt and Pd in the chromatite GRMs;42 ICP-MS following fire assay provided the other. Instrumental neutron activation analysis also provides an independent method for several elemetats in which dissolution losses, due either to volatility (e.g., Hg, As) or to incomplete solubilization of a constituent mineral (e.g., Zr, Cr) in a sample, can lead to error.The absence of such error can be inferred if a decomposition method and INAA give results that agree statistically. The basis of the XRF technique lies in the study of fluorescence excitation by deBroglie, beginning in 1914. In 1948, an instrument that could be exploited commercially was described by Friedman and Birks.40 Shortly thereafter, application of the technique for analytical geochemistry began. Full exploitation of XRF, however, depended on developments in computer technology a decade later, which permitted accurate correction43-45 of matrix and mineralogical effects. Early applications of XRF used compressed powder pellets; subsequent improvements in both the precision and accuracy achievable with the technique resulted when samples were instead prepared as fused-glass discs.This preparation both reduced matrix and mineral effects requiring correction and provided a more homogeneous sample for measure- ment.19 Stevens et aZ.’s report (1960)21 of data for G-1 and W-1 includes some XRF data, presumably the first such data for GRM characterization. By the time of Flanagan’s 1972 compilation,22 XRF was being used in analyses for approxi- mately 30% of all elements for which concentrations were reported. The XRF major oxide data from these early applications exhibited a precision of approximately 2% relative, and interlaboratory discrepancies suggested systematic errors of similar or greater magnitude. Twenty years later, when XRF was used as the predominant method for establishing best estimatekertified values for the major constituents in both the NIST soil SRMs 2709-271125 and USGS SDO-1,26 the precision approached 0.2% in some instances, and inter- laboratory discrepancies indicated considerable improve- ments in accuracy, with systematic errors under 1% relative.Both imprecision and systematic errors are larger factors in SRM/G-RM characterization using XRF for trace element analysis. However, as improved matrix correction algor- ithms43-45 were developed, and improved detection limits were achieved with instrument modifications and changes in sample preparation for analysis, XRF competed favourably with other techniques in providing concentrations of both trace and major elements for certifications.25 One factor that has a considerable impact on the accuracy and precision of results achievable in certifying or otherwise characterizing SRMs/GRMs is the availability of suitable calibration standards.Because error is propagated in the analysis, the final result can be no better than the calibration standards used. Theoretically, the solution techniques, AAS, ICP-AES and ICP-MS, can be calibrated with high-purity single-element solutions with a calibration error kept at or below 0.3% relative. However, it is much more difficult to achieve this level of calibration accuracy with d.c. arc spectrography, TNAA and XRF, because of the common956 ANALYST, AUGUST 1993, VOL. 118 practice of using natural matrix standards. The entire focus of the initial study by Fairbairn et a1.13 on G-1 and W-1 was to provide two natural matrix calibration standards for the spectrographic laboratory, and a major use of today’s SRMs/ GRMs is for instrument calibration.A draft I S 0 guide for calibration46 based on CRMs/GRMs recommends the use of ten o’r more such materials in establishing the calibration line. This recommendation is easily followed for major oxide calibrations, but cannot be for trace element calibration, owing to the unavailability of sufficient well characterized SRMs/GRMs for the element in question. It must be said, however, that the common practice of single-point calibration should be discontinued. Sufficiently accurate calibration for GRM characterization is not achiev- able based on a single CRM/GRM standard.The calibration error introduced by this practice is an important factor in generating systematic errors through successive generations of materials. At NIST, primary high-purity chemicals are used for the calibration of certification analyses, by XRF and INAA, in addition to the solution techniques. Independence of cali- brants and of measurement technique is the goal, not always realizable, in certifications based on two or more independent techniques.6 Although such a practice is not practical for the routine geoanalytical laboratory, it has much to recommend it in those instances where laboratories are participating in collaborative characterization programmes for new GRMs. It would eliminate the concern that, without a prior SRM/GRM having established values for a given constituent, characteriza- tion of a new material cannot be accomplished.Conclusions Clearly, many improvements have occurred both in the development of analytical methods for geochemical investiga- tions and in the availability of CRMs/GRMs for calibration and method validation over the last 40 years or more. G-1 and W-1 had established best estimate values for the major oxides; certifications today also achieve equal or better accuracies and precisions for many trace elements. The ability to detect and correct for ever smaller matrix and spectral interferences by all of the techniques has been critically important in this regard, as has been previously discussed. Modifications in equipment design will continue to generate improvements in accuracy and precision of analyses, in the availability of two or more independent techniques for the analysis o f individual elements and in efficiency in the laboratory.For example, the development of the stabilized temperature platform furnace technique for AAS47 has improved accuracy by reducing systematic errors due to matrix interferences and improved precision by reducing temperature fluctuations in the furnace during atomization. The use of epithermal activation in conjunction with Compton suppression in NAA48 is permitting that technique to be used for determinations of Cd, Hg and other elements that had previously been undetectable at any but greatly enriched levels without prior radiochemical separation. The availability of commercial instrumentation for simultaneous multi- element determinations49 using AAS makes that technique more efficient and better able to compete with newer multi- element techniques than it was when originally developed.50 Equally important are new approaches to sample prepara- tion for, and sample introduction into, the instrument.Developments in the last 10 years for sample preparation include microwave decomposition ,51 which should eliminate the difficulty of open beaker systems in completely attacking refractory minerals, equipment for the highly controlled, automated preparation of fused discs for XRF analyses52 and ion-exchange separation of the REE53 before ICP-AES analysis. Sample introduction for TCP-AES and ICP-MS by slurry,S4 electrothermal vaporization,ss laser ablations6 and glow discharges7 techniques will create opportunities. At the same time, because the sample sizes introduced for measure- ment with these approaches are well below those on which CRM/GRM homogeneity is established, degradation of the precision due to sampling error is distinctly possible.17.18 This highlights the need for SRMs/GRMs specifically intended for use in microanalysis, as all of these new sample introduction techniques may be viewed as non-traditional forms of microanalysis.These SKMs/GRMs must be more homogeneous at small sample sizes than are current materials for bulk analysis. A brief review of the CRMs/GRMs that arc available shows that standards development today for micro- analysis is only slightly ahead of the point that GRM development for mainstream geochemical analysis was at the time G-1 and W-1 first appeared on the scene.The available materials are few in comparison with the very large number for bulk chemical analysis.8,1*-12 Some promising adaptations of the use of NIST SRMs 610-617 to calibration for ICP-MS microanalysis are beginning to appear in the literature.S*,59 However, the homogeneity of SRMs 610-617 has been established only with respect to use of the total sample for a single analysis, in which event a 5-10% relative sampling uncertainty is not unexpected. The instrumental techniques in most extensive use today are likely to continue so for a considerable time. Broader availability of SRMs/GRMs for isotopic analysis60 would facilitate applications that more fully utilize the full capacity of ICP-MS to provide isotopic and compositional data. Specialty techniques have always played a major role for selected elements; these, too, will continue to have a role, and new techniques are likely to develop. Further, computer enhance- ments will permit ever more sophisticated chemometric methods of data reduction .6* Through all of these developments, the ability to certify, or give best estimates of, concentrations of SRM/GRM constitu- ents will continue to improve.As a result, the confidence intervals of 1-3% relative that typify major/minor constituent certified and best estimate values today will become more frequently achievable for trace constituent values also. The author acknowledges the invitation extended by P. J. Potts to present the thoughts in this paper at the meeting on Geoanalytical Methods: Current Capabilities and Future Potential, held at the Open University, Milton Keynes, UK, in October 1992.T. E. Gills and C. M. Beck, 11, of NIST, and one of the referees, are thanked for their comments, which contributed to improving the presentation of those ideas in this paper. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 References Guide 30, International Organization for Standardization, Geneva, 1978. Uriano, G. A., and Gravatt, C. C., CRC Crit. Rev. Anal. Chem., 1977, 6, 361. Administrative Memorandum, NIST, Gaithersburg, MD, 1992. Youden, W. J., Anal. Chem.. 1960,32, 23A. Moody, J . R., and Epstein, M. S . , Spectrochim. Acta, Part B, 1991, 46, 1571. Epstein, M. S . , Spectrochim. Acta, Part B, 1991, 46, 1583.Schiller, S. B., and Eberhardt, K. R., Spectrochim. Acta, Purr B, 1991, 46, 1607. Geostand. Newsl., 1989, 13, special issue. Kane, J. S . , J. Geochem. Explor., 1992, 44, 37. Potts, P. J . , Tindle, A. G., and Webb, P. C., Reference Material Compositions, CRC Press, Boca Raton, PL., 1992. Flanagan, F. J . , U.S. Geol. Surv. Bull., 1986, No. 1582. Roelandts, I., Spectrochim. Acta, Part B, 1991, 46, 1639. Fairbairn, H. W., Schlccht, W. G., Stevens, R. E., Dennen, W. H . , Ahrens, L. H., and Chayes, F., U.S. Geol. Surv. Bull., 1951, No. 980, 71. Kane, J. S . , Spectrochim. Acta, Part B, 1991, 46, 1632. Gladney, E. S . , Burns, C. E . , and Roelandts, I., Geostand. Newsl., 1983, 7, 3.ANALYST, AUGUST 1993, VOL. 118 957 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Gladney, E.S., and Roelandts, I., Geostand. Newsl., 1988, 12, 63. Ondrick. C. W.. and Suhr, N. H., Chem. Geol., 1969,4, 429. Ingamells, C. O., and Pitard, F. F., Applied Geochemical Analysis, Wiley, New York, 1986, ch. 1. Potts, P. J . , in Analysis of Geological Materials, ed. Riddle, C., Marcel Dekker, New York, ch. 4, in the press. Koirtyohann, S. R., Anal. Chem., 1991, 63, 1024A. Stevens, R. E., Niles, W. W., Chodos, A. A., Filby, R. H., Leininger, R. K., Ahrens, L. H., Fleischer, M., and Flanagan, F. J., U.S. Geol. Surv. Bull., 1960, No. 1113. Flanagan, F. J., U.S. Geol. Surv. Pro5 Pap., 1976, No. 840. Cali, J. P., NBS Certificate of Analysis, SRM 1633, National Bureau of Standards, Gaithersburg, MD, 1975. Von Lehmden, D.J., and Fleur, P. D., EPA-NBS Round- Robin Analysis Results (unpublished), 1977. Reed, W. P., NIST Certijicates of Analysis, SRMs 2709-2711, NIST, Gaithersburg, MD, 1992. Kane, J. S., Arbogast, B., and Leventhal, J., Geostand. Newsl., 1990, 14, 169. Slavin, W., Anal. Chem., 1986, 58, 589A. Thompson, M., and Walsh, J. N., Handbook of ICP Analysis, Chapman and Hall, New York, 1989, ch. 5 . Uriano, G. A., NBS Certificate of Analysis, SRM 1646, National Bureau of Standards, Gaithersburg, MD. 1982. Berman, S. S . , NRC Certificates of Analysis, MESS-I, BCSS-1, PACS-I, and BEST-I, National Research Council of Canada, Ottawa, 1990. Fassel, V. A., Anal. Chem., 1979, 51, 1290A. Date, A. R., and Hutchison, D., Spectrochim. Acta, Part B, 1986, 41, 175. Sholkovitz, E.R., Chem. Geol., 1990, 88, 333. McLaren, J . W., Beauchemin, D., and Berman, S. S., Anal. Chem., 1987, 59, 610. Rasberry, S. D., NBS Certijicate of Analysis, SRM 2704, National Bureau of Standards, Gaithersburg, MD, 1988. Dolezal, J., Povandra, P., and Sulcek, Z . , Decomposition Techniques in Inorganic Analysis, Elsevier, New York, 1966. Sulcek, Z . , and Povandra, P., Methods of Decomposition in Inorganic Analysis, CRC Press, Boca Raton, FL, 2nd cdn., 1989. Boch, R., A Handbook of Decomposition Methods in Analytical Chemistry, International Textbook, London, 1979. Potts, P. J., A Handbook of Silicate Rock Analysis, Blackie, Glasgow, 1989. 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 A History of Analytical Chemistry, eds. Laitinen, H. A., and Ewing, G. W., Maple Press, York, PA, 1977. Science, 1970. 167 (whole issue). Potts, P. J., Bowing, C. J. B., and Govindaraju, K . , Geostund. Newsl., 1992, 16, 81. Rasberry, S. D., and Heinrich, K. F. J., Anal. Chem., 1974,46, 81. Lachance, G. R., andTraill, R . J., Can. J . Spectrosc., 1966, 11. 43. Lucas-Tooth, H. J., and Pyne, C., Adv. X-Ray Anal., 1964, 7. 523. Committee Draft ISOICL) 11095, International Organization for Standardization. 1992. Slavin, W., and Manning, D. C., Anal. Chem., 1979, 51, 261. Wu, D., and Landsberger, S . , J. Radioanal. Nucl. Chem. Articles, 1993, in the press. Retzick, M., and Bass, D., Am. Lab., 1988, September, 70. Harnly, J. M., and O'Haver, T. C., Anal. Chem.. 1981. 53, 1291. Lamothe, P. J., Fries, T. L., and Consul, J. J., Anal. Chem., 1986, 58, 1881. Taggart, J. E., Jr.. and Wahlberg, J. S . , Adv. X-Ray Anal., 1980, 23. 257. Crock, J. G., Lichte, F. E., and Wildeman, T. R., Chem. Geol., 1984, 45, 149. Williams, J. G., Gray, A. L., Norman, P., and Ebdon, L., J. Anal. At. Spectrom., 1987. 2, 469. Falk, H., and Tilch, J., J. Anal. At. Spectrorn., 1987, 2, 527. Jackson, S. E . , Longerich, H. P., Dunning, C;. R., and Fryer, B. J . , Can. Mineral., in the press. Winchester, M. R., and Marcus, R. K.. Appl. Spectrosc., 1988, 42, 941. Rivers, M. L., Jones, K. W., and Sutton, S. R., Abstract5, Microanalysis Techniques in the Geosciences, October 2, 1992, Milton Keynes, UK. Perkins, W., Abstracts, Microanalysis Technique5 in the Geo- sciences, October 2, 1992, Milton Keynes, UK. Vockc, R. D., Jr., Abstracts, USGS Workshop on Isotopics, September 14-16, 1992, Reston, V A . Chemometrics: Theory and Applications, ed. Kowalski, B. R. ~ American Chemical Society. Washington, DC, 1977. Paper 2106456A Received December 3, 1992 Accepted April 15, 1993

ISSN:0003-2654    

DOI:10.1039/AN9931800953

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, AUGUST 1993, VOL. 118 959 Complexation of Poly(oxyethy1ene) in Analytical Chemistry A Review Tetsuo Okada Faculty of Liberal Arts, Shizdoka University, Shizuoka 422, Japan Summary of Contents Introduction Chemistry of Poly(oxyethy1ene) Complexation General Thermodynamic Aspects of Poly(oxyethy1ene) Complexation Effect of Solvents Separation of Poly(oxyethy1ene) Poly( oxyet h ylene) Complexat ion in Separation Solvent extraction and related methods Chromatography Separation with poly(oxyethy1ene) Separation with synthetic ionophores having poly(oxyethy1ene) as a part of the structure Separation of Metal Ions Poly(oxyethy1ene) Complexation in Electrochemistry Poly(oxyethy1ene) Complexation in Potentiometry Pol y( oxyet hy lene) Com plexation in Vo Ita m met ry Usual solution-phase voltammetry Solid-phase volta mmetry Conclusion References Keywords: Poly(oxyeth ylene) complexation with metal ions; thermodynamics; application to separation and electrochemistry; novel ionophores; review Introduction The complexation of the polyethers with metal ions is of fundamental and practical importance.Tn particular, the cyclic polyethers, such as the crown ethers, have received much attention since their synthesis by Pedersen in 1967,' whereas the acyclic polyethers have been recognized as compounds of less interest and less effectiveness2 because of their weaker complexation ability and poorer selectivity. However, the fundamental interest and the practical versatil- ity of acyclic polyether complexation have attracted a number of researchers.3.4 Poly(oxyethylene)(POE) i s one of the most commonly used synthetic acyclic polyethers, and often acts as a hydrophilic moiety of non-ionic surfactants."." The synthesis and purifica- tion of monodisperse POE, which has a relatively short chain length, are much easier than for a POE with a longer chain length [POE with less than 8 oxyethylene (OE) units is commercially available]. As the resemblance in the physical and chemical properties between POE oligomers makes the purification of longer monodisperse chains difficult, the preparation needs more complicated procedures.Therefore , polydisperse POE is often used instead of monodisperse POE. Although the use of polydisperse POE is convenient in some cases, it has tended to cause confusion and misunderstanding of the chemistry taking place in the system.In order to avoid such misunderstandings as well as to facilitate the develop- ment of analytical means of using POE complexation, it is essential to elucidate the basic features of the complexation and to interpret the analytical results on the basis of an accurate understanding of the chemistry. Therefore, both the complexation ability of POE with some hard metal ions and the micellization of POE that takes place when POE bears a hydrophobic terminal group, are important characteristics. Although micellization of these compounds has played a significant role in analytical chemistry, a number of reviews and papers dealing with the utilization of micelles in spectrophotometry7~8 and separation9.10 have been published.Therefore, the present review focuses mainly on the analytical utilization of the complexation ability of POE and its derivatives. The problems that remain unsolved and the possibilities of using the POE complexes as analytical tools are discussed together with the perspective of POE complexation in analytical chemistry. Chemistry of Poly(oxyethy1ene) Complexation General Thermodynamic Aspects of Poly(oxyethy1ene) Corn- plexation Most of the synthetic acyclic polyethers contain POE moi- eties, because: (i) chemical modification of POE is relatively easy; (ii) POE of various relative molecular mass is available, which allows systematic experimentation; and (iii) POE can be easily dissolved in various solvents. Crystals of POE and its complexes have been studied by X-ray crpstallography. 11-14 In the solid state, POE adopts a 7/2 helix, and traps a metal ion in the cavity (Fig.1). Although the complexation of POE resembles that of a crown ether, a POE chain is obviously much more flexible than the cyclic counterparts. A conforma- tional change might, therefore, play a more important role in POE complexation than in a crown ether complexation. In the gas phase, the extended zigzag form, consisting of all-trans conformations, is thought to be the most stable [Fig. l(a)]. However, the helical form [Fig. l(b)], which comprises a succession of TGT along 0-C-C-0 bonds, becomes more stable with increases in the relative permittivity and the polarity of the media; an equilibrium is established betwecn these two conformers.15-20 In addition, the helix form becomes more stable with an increasing number of OE units20 (hereafter n and ii denote the numbers of repeating OE units contained in the monodisperse and polydisperse POE chains, respectively).In Table 1, some thermodynamic parameters of the POE complexation are summarized.21-24 The complexation energy960 ANALYST, AUGUST 1993, VOL. 118 is the sum of the energy needed for the conformational change of a ligand, the bond formation energy, the desolvation energy of a ligand and the desolvation energy of a metal ion. Changes in AH (enthalpy) and AS (entropy) for the K+ and Cs+ complexation with n are also depicted in Fig. 2. The complexation of POE has mostly been discussed on the basis of the comparison with that of a crown ether.22 The greater complexation ability of the latter is explained by the term ‘macrocyclic effect’.25?26 The macrocyclic effect stems from synergistic effects rather than from a single origin, such as the match of ligand cavity size with the crystalline size of the metal ion, the conformational change needed for the arrange- ment of donor atoms at the distance required by the metal ion, the desolvation of the ligand, etc. Table 2 lists some complex Fig.1 Illustrations of POE and a POE-metal ion complex. (u) An extended zig-zag form of diMe-PEG(4). (b) A helical form of diMe- PEG(4) comprising TGT along 0-C-C-0 bonds. (c) A complex of diMe-PEG(11) and a metal ion; the oxygen atoms are shown by shaded circles formation constants of simple POE compounds, the structures of which are shown in Scheme 1.25-33 Although acyclic ethers have, in general, lower complexation abilities than their cyclic counterpart, as shown in Fig.2, the complexation ability of POE continues to be enhanced with increasing n; e.g., log K ( K represents the 1 : 1 complex formation constant) of POE ( n > 15) with K+ in methanol is larger than 3.5, which corresponds to a value such as that of 24-crown-8.26Jl This fact can be explained by a numerical effect; the number of alignments of oxygen atoms at the coordination sites, as required by the metal ion, increase with increasing n. The general order of the selectivity of POE complexation is K+ 3 Rb+ > Cs+ > Na+ > Li+ in polar solvents. Smaller ions, which are more favourably solvated by polar molecules, are more strongly complexed with POE; i.e., POE preferably forms an Li+ complex .24,34,35 However, a large desolvation enthalpy loss is unfavourable for complexation with such a 3.5 k 0) J 3.0 2.5 40 r I - E 2 9 d I 30 - I - E“ s r 30 a I 60 40 10 20 n Fig.2 Changes in log K , AH and AS for PEG-metal ion complexation. Circles and triangles represent data for K+ and Cs+ complexation, respectively. Log K values and other thermodynamic data are taken from refs. 31 and 21, respectively Table 1 Thermodynamic parameters for POE complexation. Values in parentheses are measured in 99% methanol22 and the others in methanol. ( A H in kJ mol-* and AS in J K-I mol-I) Ligand Na+ K+ Poly(ethy1ene glycol) (5)* AH (-26.7) -24.9 AS (-50.1) -45 Poly(ethy1ene glycol) (6)t A H - -26.3 AS - -40.0 Poly(ethy1ene glycol) (8)t AH - -30.8 AS - -48.7 MeOH* AHs -357 -271 Rb + -24.7 - 46 -27.9 -4s.1 -34.1 -59.4 -239 cs+ -44.2 - - 124 - - -59.4 -64.8 - 208 Ba?-+ -28.4 (-28.2) -25 (-18.5) - * From ref. 23. t From ref. 21. * Solvation enthalpy from ref. 24ANALYST, AUGUST 1993, VOL. 118 961 Table 2 Log K (at 25 "C) for POE complexation Ligand diMe-PEGt(4) diMe-PEG(5) diMe-PEG( 6) PEG(6) POE(6)D POE(8)D PEG( 10) PEG(l5) PEG(18) ~ ~ ~ ( 3 1 6 ) Metal ion (anion) Li+ (picrate) Na+ (Cl- ) K+ (I-) Na+ (Cl-) K+ (CI-) K+ (I-) K+ (I-) K+ (I-) K+ (I-) K+ (I-) K+ (I-) K+ (I-) K+ (I-) Rb+ (I-) Na+ (Cl-) cs+ (Cl-) K+ (N03-) cs+ (I -) Log K 1.39t 1.28 1.72 1.45 1.44,1.47 2.27 1.98 2.20 2.55 2.37 2.13 2.57,2.82 3.02 3.39 3.44 (1.88) 4.08 3.53 (1.60)s 3.30 (1.00) Method* Spec Pot Pot Cond Cal, Pot Cal Cal Pot Pot Chro Cond Cond, Chro Chro Chro Chro Chro Chro Pot Reference 32 30 30 30 22,30 22 23 30 30 31 27 27,31 31 31 31 31 31 28 * Method: Spec = spectrophotometry, Cond = conductimetry , Cal = calorimetry, Pot = potentiometry and Chro = chromatography.t PEG = polyethylene glycol. 9 1 : 2(POE : metal ion) complex formation constant. In dioxane, and other values obtained in methanol. H-O-(CH2-CH2-O-)- H C8HI7 e O < C H 2 r C H 2 - O k H PEG(n) PEG(n) POE( ii)OP CH3 fo-CH2-CH2- 0 i CH3 CgH19 </ \ t o f C H i C H 2 - O k H di Me-PEG( n) - POE( n)NP POE(n)D POE(n)D Scheme 1 small ion; i.e., as far as the desolvation enthalpy is concerned, Cs+ complex formation is most preferable. According to molecular mechanics calculations, a larger conformational enthalpy change is required for complexation with a smaller ion.If the D3d arrangement is assumed for dime thylpoly (ethylene glycol) [ diMe-PEG( 5 ) ] , the enthalpy change necessary for Cs+ complexation is about 34 kJ mol-l smaller than for K+ complexation.3~ These results imply that POE is pre-organized for Cs+ complexation. As shown in Table 1, in methanol Cs+ complex formation is more exothermic than K+ complex formation.34>35 Therefore, the fact that K+ complexation takes place more favourably than Cs+ complexation can be explained by a larger entropic gain in the desolvation process for the former. The intrinsic selectivity of the POE complexation among heavy alkali metal ions thereby originates in the desolvation entropy.In contrast, its selectivity among light alkali metal ions might be explained by the dominant enthalpy changes.21 Although only a few data are available, the POE complexa- tion selectivity for the alkaline earth metal ions can be discussed in the same way.36The order of complexation will be Ba2+ > Sr2+ > Ca2+ > Mg2-t. Although the data are not shown, this order can be inferred from results of solvent ex traction, poten tiome try, etc. It is known that an alkali metal ion, for example K+, adopts coordination numbers of 6-lO,37 suggesting that the ligand involves at least 6 donor atoms (5 OE units) in the molecule to satisfy all the coordination sites of K+. This has been shown by solvent extraction,38 nuclear magnetic resonance,39 and chro- matography,31 albeit with a subtle disagreement.Although a 1 : 1 complexation has usually been assumed in order to analyse the experimental results, mu1 tiple complexa- tion also takes place. When a POE with n = 4 was used as the ligand, a 2 : 1 (POE : metal ion) complexation was detected in 1,2-dichloroethane, which is similar to that for benzo-15- crown-5 complexation with K+.40 On the other hand, a 1 :2 complex formation has also been reported between K+ or Rb+ and POE ( n 3 17), and between Cs+ and POE ( n 3 18) .31 Effect of Solvents The POE complexation has mostly been investigated in methanol. As is known for crown ether complexation, water is an unfavourable solvent for such a reaction because of its increased ability to solvate ions. However, it appears that POE complexation does possibly occur in the water phase, judging from the results of some experiments; i.e., POE behaves as a cationic surfactant in the presence of metal ions,41342 and binding between POE with a very high relative molecular mass (2 x 104) and a metal ion was detected directly using an ion-selective electrode and ultrafiltration .43 The effect of solvents on POE complexation has been very clearly explained by Ono and co-workers .4447 They proposed conductimetric measurements and a one-dimensional lattice model to determine the binding constants between PEG and metal ions,44,45 and elucidated the effects of different solvents on the complexation.4~~47 In a solvent containing a mixture of molecules each with an equal donor ability, AG (Gibbs energy) is expressed by the electrostatic energy, which can be represented by the Born equation; there is a linear relation between log K and E-1 (E = relative permittivity). In solvents of identical relative permittivity, AG is governed by the desolvation energy, finally leading to the linear relation between log K and the donor number (DN) of the solvent.Thus, high DN solvent molecules coordinate strongly with a metal ion, and the enthalpy disturbs the POE complexation.962 ANALYST, AUGUST 1993, VOL. 118 The POE complexation possibly takes place in a solvent having a lower DN than diethyl ether (DN = 19.2), which is regarded as a small analogue of POE. This might explain why K+ is more favourably complexed than Na+ in a solvent with a high DN, but is unfavourably complexed in a solvent with a low DN.In a high DN solvent, Na+ is more strongly solvated than K+, and less preferably complexed with POE, whereas, in a low DN solvent, the solvation effect becomes less important, and the stabilization effect of the bond formation between POE and the metal ion is the dominant factor governing the complexation pr0cess.~7 However, as the ion- pair formation, which plays a significant role in determining the overall selectivity in solvents of low relative permittivity, has to be taken into account, the apparent selectivity is not necessarily explained by solvation alone. Poly(oxyethy1ene) Complexation in Separation Separation of Poly( oxyethylene) Solvent extraction and related methods The complexation ability of POE with metal ions has been utilized for the determination of POE itself.The POE complexes are extracted as ion-pairs with a bulky, less hydrated, and mostly coloured anion, and then determined spectrophotometrically. Such an extraction-spectrophoto- metric method has been commonly employed to determine non-ionic surfactants containing POE, and has been thoroughly investigated. Of primary interest is the choice of anion , which should have large absorptivity and hydrophobic- ity. From these standpoints, picrate48-52 and tetrathiocyanato- cobalt(11)53-57 have been most extensively used in such analyses. Furthermore, the methods have been improved to enhance the sensitivity,56.57 to reduce the analysis time51 and to be made applicable to flow injection techniques.52 The anions used in the separation and determination of POE are summarized in Table 3.48-71 In some cases, indirect measurements have been carried out; metal ion concentra- tions in the organic phase or in the precipitates were determined by an appropriate and sensitive method.56,57,61-@ In order to enhance the precision, two-phase titration methods have also been proposed.69-71 From a practical point of view, however, all these methods involve a serious and essential drawback; the non-ionic Table 3 Anions used for the determination of POE based on ion-pair formation Anion* Procedure+ Reference Picrate CO( SCN)42- Fe( SCN)& Zn ( S CN)42 - MoO(SCN)52- CdI42- P WA-Ca" TB PP TPB F-TPB Cl-TPB Absorption at about 350-380 nm Absorption at, e.g., 620 nm Co" determination with Nitroso-R Co" determination with PAR Absorption at about 520 nm Zn" determination with AAS Zn" determination with PAN Bi"' determination Absorption at 470 nm Cd" determination with AAS Call determination with AAS Absorption at 609 nm Two-phase titration Two-phase titration Two-phase titration with potentiometric titration 48-52 53-55 56 57 58-60 61,63 62 64 65 66 67 68 69 70 71 * PWA = phosphotungstic acid; TBPP = tetrabromophenol- phthalein ethyl ester; TPB = tetraphenyl borate; F-TPB = tetrakis(4- fluoropheny1)borate; and CI-TPB = tetrakis(4-ch1orophenyl)borate.+ Nitroso R = l-nitroso-2-naphthol-3,6-disulfonic acid; PAR = 4- (2-pyridy1azo)resorcinol; PAN = 1-(2-pyridylazo)-2-naphthol; and AAS = atomic absorption spectrometry. surfactant is usually polydisperse in POE chain lengths, which strongly affects the complexation ability and extractability.Favretto et ~ 1 . 4 9 ~ 5 0 studied factors affecting the determination of POE surfactants using the ion-pair formation between a POE-metal ion complex and a picrate ion, and reported that the apparent molar absorption increased with increasing n up to a maximum, and then decreased to a constant value. In contrast, Lin et a1.54 reported a constancy of the apparent molar absorptivity value per OE unit for a POE-metal ion- tetrathiocyanatocobaIt(I1) adduct. Selected results reported by several groups are illustrated in Fig. 3 on the same basis. A POE of n < 5 shows low responses in all cases, as can be inferred from the complexation ability. Hence, these methods can be used in practice for: ( i ) the determination of a surfactant provided as a particgar trademark, e.g., Triton X-100 I_octylphenyl-POE(10)] [POE(m)OP], Brij 35 IPOE(23) dodecyl ether] [POE(Z)D], etc.; and (ii) the determination of surfactants having a very narrow range of POE chain lengths. Chromatography The separation of POE oligomers has been one of the most interesting and challenging tasks in separation science.A number of liquid chromatographic approaches have been proposed,7'-79 most of which are based on the lipophilic or hydrophobic interaction between POE and the stationary phase. Although, interestingly, such interaction involves conformational changes of the POE chains,74 this is outside the scope of this review. In order to utilize the POE complexation in the chromato- graphic separation, a mobile phase must not contain solvents that are unfavourable for the complexation.Kraus and Rogers80 reported that the retention behaviour of POE in size- exclusion chromatography was modified by the addition of a salt to the tetrahydrofuran mobile phase, and implied that this phenomenon was caused by the structural changes of the POE molecules as a result of complexation. Recently, Okadaxl succeeded in separating POE oligomers by utilizing complexation with a metal ion in an ion-exchange resin phase. In this separation, POE forms a complex with the metal ions, which are bound by the resin, and the POE is separated according to its complexation ability; as the complexation ability of POE is enhanced as the chain becomes 0 10 n 20 Fig.3 Changes in relative responses of some methods for POE determination. Solid circles are data for the two-phase titration (ref. 71), and others are apparent molar absorptivity for extraction- spectrophotometry using picrate (open circles, from ref. 50), tetra- thiocyanatocobalt(r1) (open triangles, from ref. 54) and hexathiocya- natoiron(m) (solid triangles, from ref. 55) as a counter anion, respectively. Monodispersed POE was used in ref. 50, while polydispersed POE was used in other casesANALYST, AUGUST 1993, VOL. 118 963 longer, the retention becomes larger with increasing n. Fig. 4 shows two chromatograms, one obtained with a routine reversed-phase stationary phase and the other with a K+-form cation-exchange resin. Both have complementary aspects from the practical point of view; the separation between oligomers becomes worse with increasing n in reversed-phase chromatography, whereas POE with n < 6 cannot be retained by a K+-form cation-exchange resin; the hydrophobic chain length rather than the POE chain length governs retention in the former separation , whereas the effect of the hydrophobic chain length is marginal in the latter.This different charac- teristic between the two separation modes led to the two- dimensional separation of POE surfactants.82 A POE separation using an ion-exchange resin has been applied to the indirect conductimetric detection of POE having no effective chromophores,83 the evaluation of the POE complexation ability in both the mobile phase31 and the stationary phase84 and the temperature gradient separation of POE oligomers.85 Separation of Metal Ions Separation with poly(oxyethy1ene) Two methods are classified in the separation of metal ions using POE: (i) a solute ion is complexed directly with POE; and (ii) an anionic metal complex forms an ion-pair with a POE complex of a Group 1 or 2 metal ion.Both are basically similar to the extraction of non-ionic surfactants. Case I . Target ions of this scheme are hard metal ions, such as alkali, alkaline earth,407*6-93 lanthanides and actinides."-95 The extraction selectivity is the same as expected from the POE complexation, i.e., K+ > Rb+ > Cs+ > Na+ > Li-t.86 0 1 I 20 40 Ti me/mi n Fig. 4 Comparison of chromatograms. Sample, POE(23)D-3,5- dinitrobenzoate.Detection, UV (at 254 nm). (u) Reversed-phase chromatogram obtained with Wakosil 5C8 (octylsilanized silica gel with 5 pm particle size packed in a 4 X 150 mm column) as a stationary phase, and 70% v/v acetonitrile as a mobile phase. (b) A chromato- gram obtained with K+-form ion-exchange resin (TSKgel IC-Cation- SW with 5 pm particle size packed in a 4.6 x 50 mm column) as a stationary phase, and methanol-7.5 mol 1-1 KCI methanol (30 min) as a mobile phase Kikuchi and co-workers40~87 elucidated the detailed extrac- tion mechanism of alkali metal ions with Triton X-10087 or monodisperse POE-monododecyl ether,4* and showed that it was important to take the dissociation of ion-pairs between picrate and a POE-metal ion complex, in 1 ,2-dichloroethane7 into account.They verified a 1 : l : l stoichiometry of the extracted species by analysing the results with a model involving the dissociation of the ion-pair in the organic phase. There have been a few reports dealing with chromato- graphic or isotachophoretic separation of Group 1 and 2 metal ions utilizing POE complexation.9~93 Although Fujita et a1.92 attempted chromatographic separation with POE-bonded polystyrene gel, a very long analysis time was needed for the entire separation, and the performance was much worse than with crown ether stationary phases. A similar extraction has been applied to the separation of lanthanides and actinides.94.95 Although it is interesting to investigate the metal size selectivity of the POE complexation systematically,96 this method is not, in general, very effec- tive."' Case 2.The POE acts, in this case, as a phase-transfer catalyst by forming a complex with a hard metal ion, and thus facilitates the extraction of a bulky and less hydrated solute anion. Cobalt(ii), Fell1 and Zn" were, for example, quanti- tatively extracted with PEG into an organic phase as thiocyanato complexes,97~98 but Cd" and Pb" were extracted as halide complexes. The extractability of the metal ions as thiocyanate or iodide complexes was enhanced in the order, Nil1 < Pb" < Cd" < Hg" < Cu' < VIV < Fe"' < Co" < MoV < Znll, which correlated with the complexation ability of these transition metal ions.97 A similar concept has been applied to the separation of U02(SCN)3- from coexistent NpV and PaV.99 Solid-phase extraction using POE-bonded polyurethane has also been reported,100.1"1 where the extractability of tetra- thiocyanatocobalt(I1) and tetrathiocyanatozinc(i1) increased in the order Li+ < Na+ < Cs+ < Rb+ < K+ = NH4+ < Ag+ < TI+ < Ba2-t < Pb2+, which almost coincides with the selectivity of POE complexation. Similar schemes have been applied to a slightly unusual type of solvent extraction, that is, cloud-point extraction. Aqueous solutions of POE are spontaneously separated into two phases, when the temperature is raised. One phase is a diluted POE aqueous solution, and the other is a concentrated POE solution. The temperature at which the phase separation occurs is defined as the cloud point. This phenomenon has interested not only analytical chemists102-114 but also theor- etical chemists.115-121 A surfactant-rich phase can be regarded as a kind of organic phase that possibly possesses unique solution properties. This pseudo-organic phase has been utilized to extract some metal chelates.In some cases, POE acts as both an organic phase and a phase-transfer catalyst. Kawamorita et al.104 studied the extraction of Ni", Zn" and Cd" &elates, with several coloured ligands, into the POE(7.5)NP-rich phase [nonylphenyl-POE (7.5)]. They sug- gested that these coloured chelates were extracted, to some extentss ion-pairs with the POE complexes. Extraction with POE(7.5)NP has been used for Zn"-1-(2-pyridylaz0)-2-naph- thol,102 Zn11-2-(8-quinolylazo)-4,5-diphenylimidazole,~~~ Au"'-CI- ,lo5 etc.Coexistent salts, e.g., NH4(S04)*, lower the cloud points of other POE derivatives, and permit the extraction of Arsenazo 111 chelates of Z P , Uvl, Fe"', Pb", Sc'", LarI1, Th'", PrIV and other chelates into the POE- rich phase.106-112 Although there was no description it appears that the POE complexation facilitates the extraction in some cases. The extraction of thiocyanato complexes into POE-rich phases has also been reported.112-1 l 4 According to recent work,113 although tetrathiocyanato complexes of Co" and Cu" were the main extracted species, the extraction of bisthio- cyanato complexes should be taken into account to explain the extraction behaviours. The analysis of a Triton X-lOO-Coll-964 ANALYST, AUGUST 1993. VQL. 118 CN--K+ adduct also confirmed the 2 : 1 : 4 : 2 stoi- chiometry .I14 Although it appears that these results show that the extraction into the POE-rich phase is analogous to the usual solvent extraction, the cloud point was not affected by the cation but by the anion, suggesting that the hydration energy (or hydrophobicity) of the anion is the principal factor governing the partition of the ~alt.113 As the desolvation process of the cation is the main factor determining the selectivity of the POE complexation, it is somewhat doubtful whether the usual POE complexation takes place in the POE- surfactant rich phase. This requires furtherinvestigation.Separation with synthetic ionophores having poly(oxyethy1ene) as a part of the structure Analytical applications of POE complexation are most extensive in this area.One reason that crown ethers have been widely used to separate alkali and alkaline earth metal ions is their unique selectivity. Therefore, less attention has been paid to the use of acyclic polyethers for this separation because of their common selectivity.26 Some researchers have thought that chemical modifications might facilitate the enhancement of the POE complexation ability and selectivity, and hence have synthesized a number of POE derivatives and related pol yethers. 122-142 Some examples are shown in Scheme 2. The characteristics of these polyethers can be summarized as follows: ( i ) some compounds are modelled on natural acyclic polyethers, such as monensin, negricin, etc., known to be highly selective to a particular ion; (ii) most of the compounds have terminal carboxylic acid(s), which not only act as an electron donor but also facilitate the phase transfer of an ion to the organic phase by eliminating the charge of the resulting complex; and (iii) some are thought to be pre-organized for complexation with a particular ion.The selectivities of some of the compounds are summarized in Table 4. In general, compounds having fewer oxygen atoms show a higher selectivity toward smaller ions; e.g., compounds 3, 14, 16 and 18 are Li+-selective.l26.12~,12~ However, the extraction or membrane transport efficiencies are not, in such cases, very high. A molecular dynamics study indicated that the first coordination sphere consisted of four donor atoms arranged in a tetrahedral manner for Li+, whereas an octahedral coordination shell is formed around K+ or Rb+.143 'The POE derivatives that have four or five oxygen atoms can wrap around Li+, and satisfy all the possible coordination sites of Li+. However, for larger metal ions some coordination sites remain unoccupied, which results in an unstable complexa- tion. Ligands that have sufficient numbers of donor atoms can satisfy all the possible coordination sites of the larger ion, and thus the Li+-selectivity is lost. One strategy to build a Li+- selective ionophore indicated that a structure having branched chains that form a three-dimensional cage was effective, but that it was difficult to keep an effective conformation without a cyclic part of the structure.142 Thus, although there will be limitations in the design of effective acyclic ligands, which are selective to smaller ions, no one doubts that it is an interesting challenge to find such ligands. Most of the compounds in Scheme 2 have two or more terminal aromatic groups.Analysis by X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and infrared (IR) spectrometry showed that by stacking the aromatic terminals the cyclic structure of the ligand is stabilized (Fig. 5) when the ligand coordinates an ion.l"-l39 The roles of the carboxylic acids are also interesting; they act as an efficient electron donating group and vary the selectivity. The crystal structure of the benzo-14-crown-4- oxyacetate-Li+ complex showed that a carboxylate group was coordinated to the Li+ through a water bridge.144 This prevented Li+ distribution into the organic phase, and lowered the extractability. Infrared and NMR spectra indi- cated that the interaction of 14 with Mg" was different from that with Call in the symmetry of the resulting complexes. As shown below, the asymmetric interaction with Mg" resulted in Mg" being wrapped in the pseudocavity, whereas the sym- metric interaction with Call caused intermolecular binding.137 0 In most of work carried out in the references listed in Table 4, the authors have thought that the pseudocyclic structures are important, and, in some cases, indispensable for selective complexation. This might stem from conventional discussion on the origins of the selectivity of crown ethers. Such discussion has been mostly based on CPK (Corey-Pauling- Koltun) modelling and speculation; it is not possible to say whether the pseudocyclic structure is more stable than other conformations or not, unless the structure with the lowest energy is sought by solution-phase spectroscopy or computa- tion.As shown above, ligands often form pseudocyclic structures in the complexes, hence the conformational energy loss will be minimized for cyclically pre-organized ligands. However, to explain the selectivity, it is obvious that the contribution of the conformational change to the overall energy of the complexation should be calculated. In addition, an idea of the match of the cavity size with the crystalline size of the metal ion is not necessarily valid even for the crown-ether complexation. The complexation between K+ and dibenzo-30-crown-10 (log K = 4.626 in methanol at 25 "C) is an example.Although this ligand size is much larger than K+, stable complexation takes place because the crown ether adopts a three-dimensional cage, and wraps around the metal i0n.3~ Further evidence for this consideration was presented for the complexation of a compound having carboxylates at both end-terminals. 122 The size-fit theory suggests that this compound forms a pseudocyclic structure by hydrogen bonding between the terminal carboxylic acids. The complexation of neutral carboxylic acids was one order of magnitude weaker than that of anionic ones, indicating that the neutralization of the charge of a metal ion by the binding of an anionic group is more important than the pre-organized pseudocyclic structure of the ligand.Pseudocyclic pre-organi- zation of POE derivatives is, therefore, one of the factors affecting the selectivity, but not necessarily the principal one. Poly(oxyethy1ene) Complexation in Electrochemistry Poly(oxyethy1ene) Complexation in Yotentiometry The POE-me tal ion-te traphen y 1 borate (TPB) precipitates can be used as ion exchangers for ion-selective electrodes (ISEs) for Ba2+, Sr2+ and Pb2+.145-147 There was good correlation between an ISE response to a metal ion and the extractability of the metal ion into an organic phase.148 Moody and CO-workers14y-151 prepared 21 and 22 (Scheme 2), and utilized them as neutral ISE ionophores with various solvent mediators. The selectivity of an electrode containing 21 depended on the solvent mediators incorporated;l4y in some cases, it was Ca2+ selective, but in other cases, Li+ selective. In contrast, an ISE based on 22 was most responsive toward K+.In addition, an electrode using 22 favourably responded to uranyl ion, when sodium tetraphenylborate was incorporated in the membrane as the anion excluder.150 Tripodal ionophores (23 and 24) were also tested for use in a Barl-ISE, but were inferior to POE.152 However, the tetra- hedral tripodal structure was favourable for the formation of the pseudocavity in order to maximize the number of stable ion-dipole interactions. Potentiometric titration using POE complexation has been successfully employed for the titration of Ba", Call, Sr", Cd" and rare earth metal ions;153-15X the POE-metal ion-TBPANALYST, AUGUST 1993, VOL. 118 965 COOH 3 n = o 4 n = l 5 n = 2 \" / n COOH HOOC nC1 OH 12 6 n = O 7 n = l 8 n = 2 9 n = 3 10 n = 2 COOH 0 OH '6'""" 11 X = O-(CH2)3-0 12 X = O-(CH2--CH2-0)2- 13 X = O-(CH*-CH2-0)3- But Bu 16 n = l 17 n = 2 18 0 / COOH c0-0 9 COOH 19 R = H 10u03 20 R CH3 d 21 R = H 22 R = CH2 0 L O O-R 23 R = CH2 a 14 n = l 15 n = 2 - 5 Scheme 2966 ANALYST, AUGUST 1993, VOL.118 precipitation was monitored potentiometrically. However, in general, the selectivity is not high as would be expected. Potentiometry based on POE has been used to investigate complex formation or solvation of metal ions in non-aqueous solvents. Nakamura and co-workers*59-163 studied potentio- metric responses of polyacrylamide electrodes containing POE(4)D or POE(6)D as ionophores.The POE(4)D elec- trode showed Nernstian responses toward Li+, Mg2+ and Ba2+ in acetonitrile (AN) and Ag+ in dimethyl sulfoxide (DMSO), and the POE(6)D electrode showed Nernstian responses toward Mg2+ and Ba2f in dimethylformamide (DMF) and Ag+ and Cu2+ in DMSO.159 These electrodes have been used for the determination of the complexation constants of MgZ+-DMF, -DMSO or -hexamethylphosphoric triamide(HMPA), Ba2+-DMF, -DMSO or -HMPA,16o and Li+-DMF in AN. 161 The potentiometric response mechan- isms were elucidated by voltammetry using these elec- trodes;l62 i.e., the ions were accumulated within the vicinity of the electrodes by the complexation with POE, and transferred to the polymer phase. Such methods have been shown to be efficient in determining the Gibbs free enrgy transfer.163 As mentioned already, the interaction between POE and a metal ion in an aqueous medium is very weak.However, an electrode containing POE showed a linear response to POE, with a slope of 50-70 mV in the presence of a monovalent cation, and with a slope of 30 mV in the presence of a divalent cation.42 This suggests that POE interacts with the metal cation at the watedmembrane interface, and forms the Fig. 5 Typical stacking structure n complex. This phenomenon has been applied to the poten- tiometric determination of POE.41,42,164-171 It may be obvious that direct potentiometric measurements of POE suffer interference from concomitant metal ions capable of forming stable POE complexes. Thus in order to reduce the interferences and to enhance the reliability, titration has also been studied.167-'69 As POE complexation depends on the POE chain length, the potentiometric response is also a function of the POE chain lengths.Polyfoxyethylene) Complexation in Voltammetry Usual solution-phase voltammetry Triton X-100, a non-ionic POE surfactant, has often been used in polarography to reduce the maximum wave, but usually has no effect on quantitative or qualitative values such as half- wave potentials and diffusion currents. However, recently, POE complexation has been used to improve voltammetric selectivity172-174 and to elucidate POE complexation at liquid/ liquid interfaces. 175- 181 Recently, it was found that PEG, when adsorbed onto a mercury electrode, shifts the half-wave potentials of Sn", Inlrr, Cd" and Zn" to the negative,172-174 and the reduction waves of Cd" and In"' comprised two waves in the presence of PEG. A mechanism for this phenomenon was speculated to be PEG- metal complexation on the electrode.172 In particular, PEG was an efficient shift agent for Cd"; the reduction wave of Cd" was separated from that of In"' in the presence of PEG.Simultaneous determination of Cd" and In"', the intrinsic reduction potentials of which are close to each other, was made possible by the addition of PEG.173.174 Current scan polarography has proved to be an effective method in evaluating the transfer of ions from a particular solvent to another immiscible solvent.182.183 Both POE and crown ethers have been used in this way, and POE was shown to facilitate the transfer of some metal ions by complexation.Triton X-lOO,175 for example, lowered the Gibbs free energy transfer of alkali and alkaline earth metal ions from water to nitrobenzene by 37-40 kJ mol-l. It was shown that PEG also acted as an effective ionphore, facilitating the transfer of Ba", Sr" and Pb" from water to the organic pha~e~177-179 and that Table 4 Selectivity of ionophores listed in Scheme 2 Ionophore Selectivity* Method? Reference Monocurboxylic acid- 1 Li>Na=K>Rb>Cs - Ba > Ca - 2 K>Rb>Na>Cs>Li - 3 Li > N a > K; Rb > Cs Li:Na = 4.9 4 Li > Na > K; Rb > Cs Li:Na = 3.1 5 Li > Na; K > Rb > Cs Li : Na = 2.4 6 Ca>>Sr=Ba Ca: Sr = 6 7 Ba>Sr>>Ca Sr : Ca = 8-9 8 Ba>>Sr=Ca Ba: Sr > 6 9 Ba>Ca>Sr 10 Ba>>Sr>Ca Ba:Sr=50 11 Ba>Ca 12 Ba>>Ca Ba : Ca = 6 13 Ca>Ba 14 Dicarboxylic ucid- Ca > Ba > Mg (pH = 8.28-9.10) Mg >> Ca > Ba(0.14.3 moll-' LiOH) Li > Na > K 16 Li>Na>K 17 Na>Li>K 18 Li>Na>K Li : Na = 5.8, Li : K = 14 19 K: Na = 3.9, K : Li > 10 20 K>Na>Li K:Na = 5.1,K:Li > 10 Low efficiency Monocarboxylute with u quinoline ring- K > Rb > Cs > Na > Li M M M E E E E E E E E M M M M M M M M M M M 140 141 140 126 126 126 124 124 123 124 124 132 132 132 131 131,137 129 128 128 133 130,136 136 * Valency of metal ions is omitted for simplicity.7 E = solvent extraction; and M = membrane transport.ANALYST, AUGUST 1993, VOL. 118 967 these cations could be determined voltammetrically.177 Kakiuchi et a1.18(),181 found that POE adsorbed at the water/ nitrobenzene interface forms a complex with the metal ion on the aqueous side of the interface.The adsorption of POE(4)D was explained on the basis of Gouy-Chapman theory by assuming complexation with Li+. According to the model developed, the complex formation constants of Li+ with POE(4)D, POE(6)D and POE(8)D at the interface were estimated to be 20,180 80 and 1000,181 respectively. Although POE has been used to modify electroactive molecules,184,18s the author has not been able to find examples where POE complexation plays a significant role. Solid-phase voltammetry Poly(oxyethy1ene) when doped with a metal ion has conduct- ing properties,18&189 and has been applied for analytical purposes in addition to poly(pyrro1e) ,190 poly(ani1ine) 191 and poly(thiophene).192 This material is one of the most interest- ing conductive polymers because of its variety of chemical forms. The conductance of POE doped with a metal ion was explained by cation migration within the POE helix tunnels, however, later it was proposed that the conduction principally took place in the amorphous region of POE, where the metal ions are coordinated by POE as well as being in solution; cations are bound inter-chain rather than intra-chain .I87 The high ionic conductivity is ascribed to the high mobility of the ionic carriers induced by the segmental motion of the POE chains. The high conductance of POE, when doped with a metal ion, allowed the fabrication of C02 and H2 sensors.193 Although the sensing mechanisms have not been elucidated, the sorption of these gases changed the conductance.Oliver et al. Iy4 reported diffusion-controlled voltammetry of a redox protein in a Li+-doped POE solid solvent. The peak current linearly increased with increasing square roots of the potential scan rates, indicating that the electrode reaction was governed by the diffusion of redox protein through the POE membrane. In voltammetric measurements, it was found that a high water content increased the diffusion rate. This fact led to the following idea on voltammetric gas sensing using a POE membrane. As POE-based conducting polymers are usually either dissolved or swollen by a variety of solvents, it is difficult to use them in solution.They are, however, applicable to media used for electrochemical gas sensors. Murray and coworkers19~-19* designed a voltammetric gas chromatographic detector using POE-based conductive polymers, and investigated the res- ponse mechanisms in detail. Fig. 6 shows a schematic representation of a detector in which derivatives of ferrocene or [R~(bipyridy1)~]2+ act as the electroactive compounds, and the oxidation is monitored voltammetrically. When the membrane is exposed to air containing the vapour of an organic solvent, the organic solvent is partitioned into the network of the polymer strand. This plasticization results in an increase in voltammetric current . According to an investigation into the response of this gas sensor,19* the peak area can be described by where Y is the microdisc radius, Do, and C, are the diffusion coefficient and the concentration of the electroactive solute in the absence of partitioned organic solvent, fi is the polymer- solute specific constant, VG is the specific retention volume, ps is the density of the stationary phase, T, is the column temperature, f i s the volumetric flow rate, n is the number of electrons, F is the Faraday constant and M , is the moles of an injected organic sample.This equation involves specific terms (Do,, and p) and a sensitivity term ( V G ) . The VG value can be evaluated by measuring the retention of the solute on the POE-based stationary phase (identical with the POE mem- brane used for the detector). This value suggests that solutes that have stronger retention ability are detected with higher sensitivity in contrast to the usual gas-chromatographic detectors, the sensitivities of which are generally worse for solutes of stronger retention abilities.Nagashima and co-workers199,2~ reported a galvanic cell using Ag+-doped POE for NO2 and 03. The cell geometry and detection mechanisms are shown in Fig, 7. In this sensor, oxidizing solutes are reduced on the surface of the POE-based membrane, and the Ag+ doped in the membrane is changed into Ag20. The ion that acts as a supporting electrolyte participates in the electrode reaction in this case, whereas in Murray's detector it does not. These two sensors differ on this point, but both ingeniously utilize the conducting nature of metal ion-doped POE membranes.Conclusion Analytical and fundamental features of POE-complexation have been discussed in this review. From an analytical point of view, POE is characterized as follows: (i) POE permits systematic studies because of the variety of chain lengths and terminal groups; (ii) the ability and selectivity of POE complexation are not high; (iii) modification of POE mol- ecules is generally easy, which usually enhances the complexa- tion ability and/or the selectivity; and (iv) POE complexation facilitates the phase transfer of hydrophilic ions, and thereby permits solvent extraction, membrane separation, fabrication of ion sensors, etc. As can be seen in Scheme 2, a variety of compounds have been studied, and an increasing number of compounds will be synthesized to improve and enhance the complexation ability GC Carrier gas ~ ~~ 0- Organic vapour 0 Plasticization -It POE Red ox Ref WE Aux Fig.6 Schematic representation of a gas sensor plasticization. This figure was drawn with reference to in ref. 198 in order to show the cell geometry clearly. based on the the description Ref, reference electrode; WE, working electrode; Aux, auhiary electrode NO7 NO Gas e- I--------- ' 1 I L - i +?-----.. Fig. 7 Schematic representation of a POE-based galvanic cell. This figure was drawn with reference to the description in ref. 199 in order to show the cell geometry clearly968 ANALYST, AUGUST 1993, VOL. 118 iH 25 n = 0 = 2 R = H, pNO2, o-OCH~ 0 i- TMA+ i- But SO2 SO2 But 0 0 26 R = CH3 R R /” hv, \ / N=N N=N 7 / R 27 n = 1 = 2 28 Fig.8 Structural changes of some ligands induced by the precomplexation (25 and 26), photo-exposure (27), and reduction (28) and the selectivity. In order to facilitate the development of such novel and efficient compounds, it is necessary to elucidate and understand further the fundamental aspects of the complexation of simple POE and conventionally prepared compounds. In this sense, it is to be regretted that too many authors have attempted to explain their results only by the match of the crystalline size of a metal ion with the cavity size of the pseudocyclic structure of an acyclic polyether, without direct evidence. Such explanations would appear to be acceptable in some cases, but invalid in others. Theoretical calculation and spectroscopic measurements should be used to explain the analytical results.The use of energies other than that of POE complexation is also important in the development of novel analytical methods. It has been found that 25 and 26 (Fig. 8) show template effects;201,202 tetramethylammonium ion was coex- tracted by forming a bridge between the anionic amide groups of 25, and the enhancement of the complexation was observed by precomplexation of 26 with Ni”. Photoenhancement203 and redox enhancement204 of membrane transport have also been reported using 27 and 28. Compound 27 changed structure on exposure to light, and thus varied its complexation ability. Compound 28 was reduced to the anion radical or dianion, and the efficiency of metal ion transport was thereby enhanced.Although it is known that POE interacts with iodine205 and cyclodextrin,206-20* for example, and even with anions such as polyacrylic acid,209-211 dodecyl sulfate ,212,213 and chloride ,214 these have not been employed to design a novel analysis. A convenient method215 recently developed to synthesize a variety of monodisperse POE is also expected to facilitate both the understanding of POE chemistry and the develop- ment of analytical methods. This author believes that POE will continue to make a significant contribution to analytical chemistry. References 1 2 3 Pedersen, C. J . , J. Am. Chem. SOC., 1967,89,7017. Balasubramanian, D., and Chandani, B . , J . Chem. Educ., 1983, 60, 77. Vogtle, F., and Weber, E., Angew. Chem. Int. Ed. Engl., 1979, 18,753.ANALYST, AUGUST 1993, VOL.118 969 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 Fenton. D. E., in Comprehensive Coordination Chemistry, ed. Wilkinson, G . , Pergamon, Oxford, 1987, vol. 3, p. 1. Rosen, M. J . , Surfactants and Interfacial Phenomena, Wiley Interscience, New York, 1978. Cross, J., in Nonionic Surfactants, ed. Cross, J., Marcel Dekker, New York, 1987, ch. 1. Georges, J., Spectrochim. Acta Rev., 1990, 13, 27. Hayashi, K., Sasaki, Y., Tagashira, S . , and Kosaka, E., Anal. Chem., 1986,58, 1444. Armstrong, D. W., Sep. Purif. Methods, 1985, 14, 213. Borgerding, M. F., Quina, F. H., Hinze, W. L., Bowemaster, J., and McNair, H. M., Anal. Chem., 1988, 60, 2520. Cross, J., in Nonionic Surfactants, ed. Cross, J., Marcel Dekker, New York, 1987, ch.2. Yamaguchi, I . , Miki, K., Yasuoka, N., and Nobutami, K., Bull. Chem. SOC. Jpn., 1982, 55, 1372. Chatani, Y., and Okamura, S . , Polymer, 1987, 28, 1815. Chatani, Y., Fujii, Y., Takayanagi, T., and Honma, A , , Polymer, 1990, 31, 2238. Viti, V., Indovina, P. L., Podo, F., and Radics, L., Mol. Phys., 1974,27, 541. Andersson, M., and Karlstrom, G., J. Phys. Chem., 1985, 89, 4957. Matsuura, H., Fukuhara, K., Masatoki, S . , and Sakakibara, M., J. Am. Chem. SOC., 1991, 113, 1193. Matsuura, H., Fukuhara, K., Sakakibara, M., and Masatoki, S . , J. Phys. Chem., 1991, 95, 10800. Siew, D . C. W., Cooney, R. P., and Taylor, M. J., J. Raman Spectrosc., 1991,22, 183. Fukuhara, K., and Matsuura, H ., Chem. Lett., 1987, 1549. Okada, T., J. Chem. SOC., Chem. Commun., 1991. 1209. Haymore, B. L., Lamb, J. D., Izatt, R. M., and Christensen, J. J., Inorg. Chem., 1982, 21, 1598. Buschmann, H.-J., Polyhedron, 1985, 4, 2039. Cox, B. G., Hedwig, G . R., Parker, A. J., and Watts, D. W., Aust. J. Chem., 1974, 27,477. Cabbiness, D. K., and Margerum, D. W., J. Am. Chem. SOC., 1969, 91, 6540. Izatt, R. M., Bradshaw, J . S . , Nielsen, S. A., Lamb, J . D . , and Christensen, J. J., Chem. Rev., 1985, 85, 271. Burger-Guerrisi, C., and Tondre, C., J . Colloid Interface Sci., 1987, 116, 100. Gokel, G. W., Goli, D . M., and Schultz, R. A., J. Org. Chem., 1983,48,2837. Yanagida, S . , Takahashi, K., and Okahara, M., Bull. Chem. SOC. Jpn., 1978, 51, 1294. Chaput, G . , Jeminet, G., and Juillard, J., Can.J . Chem., 1975, 53, 2240. Okada, T., Macromolecules, 1990, 23, 4216. Tsvetanov, Ch. B., Petrove, E. B., Dimov, D . K., Panayotov, I. M., and Smid, J., J. Solution Chem., 1990, 19, 425. Buschmann, H.-J., Inorg. Chim. Acta, 1992, 195, 51. Adams, M. D . , Wade, P. W., and Hancock, R. D., Talanta, 1990,37, 875. Wipff, G., Weiner, P., and Kollman, P., J. Am. Chem. SOC., 1982, 104, 3249. Ono, K., Honda, H . , and Murakami, K., J . Macromol. Sci. Chem., 1989, A26, 567. Truter, M. R., Struct. Bonding, 1973, 16, 71. Yanagida, S . , Takahashi, K., and Okahara, M., Bull. Chem. SOC. Jpn., 1977, 50, 1386. Liu, K., Macromolecules, 1968. 1, 308. Kikuchi, Y., Nojima, Y., Kita, H., Suzuki, T., and Sawada, K., Bull. Chem. SOC. Jpn., 1992,65, 1506. Masadomc, T., Imato, I., and Ishibashi, N., Anal.Sci., 1990,6, 605. Sugawara, M., Nagasawa, S., and Ohashi, N., J. Electroanal. Chem., 1984, 176, 183. Sartori, R., Sepulveda, L., Quina, F., Lissi, E., and Abuin, E., Macromolecules, 1990, 23, 3878. Ono, K., Konami, H., and Murakami, K . , J . Phys. Chem., 1979,83,2665. Awano, H., Ono, K., and Murakami, K., Bull. Chern. SOC. Jpn., 1982, 55, 2525. Awano, H., Ono, K., and Murakami, K., Bull. Chem. SOC. Jpn., 1982,55, 2530. Honda, H . , Ono, K., and Murakami, K., Macromolecules, 1990, 23, 515. Favretto, L., and Tunis, F., Analyst, 1976, 101, 198. 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 Favretto, L., Stancher, B., and Tunis, F., Analyst, 1979, 104, 241.Favretto, L., Stancher, B . , and Tunis, F., Analyst, 1980, 105, 833. Merino-Teillet, M. de la Luz, Leon-GonzAlez, M. E., Santos- Delgado, M. J., and Polo-Diez, L. M., Analyst, 1987,112,1323. Ledn-Gonzalez, M. E., Santos-Delgado, M. J . , and Polo-Diez, L. M., Fresenius'J. Anal. Chem., 1990,337, 389. Calzolari, C., Favretto, L., and Tunis, F., Analyst, 1974, 99, 171. Lin, J. T., Cornell, D. G., and Micich, T. J., J. A m . Oil Chem. SOC., 1986, 63, 1575. Murai, Y., Suzuki, H., Hasei, M., and Koh, T., Bunseki Kagaku, 1989,38, T15. Anderson, N. H., and Girling, J . , Analyst, 1982, 107, 836. Inaba, K., Int. J. Environ. Anal. Chem., 1987, 31, 63. Crisp, P. T., in Nonionic Surfactants, ed. Cross, J., Marcel Dekker, New York, 1987, ch.3. Murai, S . , Bunseki Kagaku, 1984, 33, T18. Kautzner, B., and Laby, R. H . , GIT Fachz. Lab., 1988,32,527; Chem. Abstr., 1988, 109, 233218m. Crisp, P. T., Echert, J. M., and Gibson, N. A., Anal. Chim. Acta, 1979, 104, 93. Crisp, P. T., Echert, J. M., Gibson, N. A., and Webster, I. J., Anal. Chim. Acta, 1981, 123, 355. Van Hoof, F. M., Van Craenenbroeck, W. J . , and Dewaele, J. K., Znt. J. Environ. Anal. Chem., 1985, 19, 155. Fornoro, G., and Ferrero, F., Tinctoria, 1989, 86, 68; Chem. Abstr., 1990, 112, 79975j. Qi. W., Huang, C., and Xu. G., Huaxue Shiji, 1991, 13, 6; Chem. Abstr., 1991, 115,94841t. Chen, S . , Yu, B., and Ma, Y., Fenxi Huaxue, 1992, 20, 578; Chem. Abstr., 1992,117, 55481~. Grasso, G., and Bufalo, G . , At. Spectrosc., 1986, 7, 93. Toei, K., Motomizu, S ., and Umano, T . , Talanta, 1982,29,103. Tsubouchi, M., and Tanaka, Y., Talanta, 1984, 31, 633. Tsubouchi, M., Yamasaki, N., and Yanagisawa, K., Anal. Chem., 1985, 57, 783. O'Connell, A. W., Anal. Chem., 1986, 58, 669. Kondoh, Y., Yamada, A . , and Takano, S . , J. Chromatogr., 1991, 541,431. Szymanowski, J., Kusz, P., and Dziwinski, E . , J. Chrornatogr.. 1990, 511, 325. Melander, W. R., Nahum, A., and Horvath, Cs., J. Chromat- ogr., 2979, 185, 129. Desbkne, P. L., Desmaziitres, B., Basselier, J. J., and Monvernay, A . D., J. Chromatogr., 1989,461, 305. Bear, G . R., J. Chromatogr., 1988, 459, 91. Noguchi, K., Yanagihara, Y., Kasai, K., and Katayama, B., J. Chromatogr., 1989, 461, 365. WiSniewski, M., Szymanowski, J., and Atamahczuk, B., J. Chromatogr., 1989,462, 39.Jandera, P., Urbanek, J., ProkeS, B., and ChurBEek, J . , J. Chrornatogr., 1990, 504, 297. Kraus, S., and Rogers, L. B., J. Chromatogr., 1983, 257, 237. Okada, T., Anal. Chem., 1990, 62, 327. Okada, T., J. Chromatogr., 1992, 609,213. Okada, T., Anal. Chem., 1990, 62, 734. Okada, T., J. Chem. SOC., Faraday Trans., 1991, 87, 3027. Okada, T., Anal. Chem., 1991, 63, 1043. Niitsu, M., and Mukai, Y., Bunseki Kagaku, 1983, 32, E367. Kikuchi, Y., Takahashi, N., Suzuki, T., and Sawada. K., Anal. Chim. Acta, 1992, 256, 311. Inokuma, S . , Hayase, T., Azechi, S . , and Kuwamura, T., Yukagaku, 1988,37,28. Makrlik, E . , HAlovB, J., and Vafiura, P., Collect. Czech. Chem. Commun., 1992, 57, 276. Okada, T., J. Chromatogr., 1991, 586, 277. Kasanskii, K. S . , and Ptitsyna, N.V., Makromol. Chem., 1989, 190, 255. Fujita, H., Yanagida, S . , and Okahara, M., Anal. Chem., 1980, 52, 869. Kaniansky, D., Zelenskg, l . , VarBSkova, I . , Marhk, J., and Zelenska, V., J . Chrornatogr., 1990, 502, 143. Vanura, P., Chem. Listy, 1990, 84, 141; Chem. Abstr., 1990, 112, 224272j. Yoshida, I., Takeshita, R., Ueno, K., and Takagi, M., Anal. Sci., 1986, 2, 53. BarthBlemy, P. P., Desreux, J. F., and Massaux, J . , J. Chem. SOC., Dalton Trans., 1986, 2497.970 ANALYST, AUGUST 1993, VOL. 118 97 98 99 100 101 102 103 104 105 I06 107 108 109 I10 111 112 113 114 115 116 117 118 I19 120 12 1 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 Sotobayashi, T., Suzuki, T., and Tonouchi, S., Chem. Lett., 1976, 585. Suzuki, T., Murakami, N., and Sotobayashi, T., Bull.Chem. Soc. Jpn., 1980, 53, 1453. Sotobayashi, T., Suzuki, T., and Kudo, H., J. Radioanal. Chem., 1977, 36, 145. Maloney, M. P., Moody, G. J., apd Thomas, J. D. R., AnalyJt, 1980, 105, 1087. Hamon, R. F., Khan, A. S . , and Chow, A., Talanta, 1982,29, 313. Watanabe, H., and Tanaka, H., Talanta, 1978, 25, 585. Watanabe, H., and Yamaguchi, N., Bunseki Kagaku, 1984,33, E211. Kawamorita, S., Watanabe, H., Haraguchi, K., and Miyajima, M., Nippon Kagaku Kaishi, 1986, 901. Kojima, H., and Onishi, H., Nippon Kagaku Kaishi, 1986,889. L,i, B., and Huang, D., Huaxue Shiji, 1991, 13, 205; Chem. Ahstr., 1991, 115, 22210%. Buhai, L., and Rigan, M., Talunta, 1990,37, 885. Zvarova, T. I., Shkinev, V. M., Vorobeva, G. A., Spivakov, B. Ya. and Zolotov, Yu.A., Mikrochim. Acta, 1984, 111, 449. Shkinev, V. M., Molochnikova, N. P., Zvarova, T. I., Spivakov, B. Ya., Myasoedov, B. F . , and Zolotov, Yu. A., J. Radioanal. Nucl. Chem., 1985, 88, 115. Molochnikova, N. P., Frenkel, V. Ya., and Myasoedov, B. F., J. Kadioanul. Nucl. Chem., 1988,121,409. Molochnikova, N. P.. Shkinev, V. M., and Myasoedov, B. F., Solvent Extr. Ion Exch., 1992, 10, 697. Nafant’eva, T. I., Belyaeva, V. K., Gatinskaya, N. G., Shkinev, V. M., Marov, I. N., and Spivakov, B. Ya., Zh. Neorg. Khim., 1989, 34, 1256; Chem. Abstr., 1989, 111, 65051~. Okada, T., Anal. Chem., 1992,64,2138. Takamoto, S., Sakai. C., Ichikawa, K., Ogura, A., and Wakui, K., Nippon Kagaku Kaishi, 1990, 759. Kjellander, R., and Florin, E., J. Chem. SOC., Faraday Trans.I , 1981, 77, 2053. Kjellander, R., J. Chem. SOC., Furaday Trans. 2,1982,78,2025. Karlstrom, G., J . Phys. Chem., 1985, 89, 4962. Jonsson, R., Nilsson, P.-G., Lindman, B., Guldbrand, L., and Wennerstrom, H., in Surfactants in Solution, eds. Mittal, K. L., and Lindman, B . , Plenum, New York, 1984, p. 3. Land, J. C., in Surfactants in Solution, eds. Mittal, K. L., and Lindman, V., Plenum, New York, 1984, p. 35. Blankschtein, D., Thurston, G. M., Fisch, M. R., and Benedek, G. B., in Micellar Solutions and Microemulsions, eds. Chen. S.- H., and Rajagopalan, R., Springer-Verlag, .New York, 1990, p. 185. Thurston, G. M., Blankschtein, D., Fisch, M. R., and Benedek, G. B., J. Chem. Phys., 1988, 84, 4558. Tummler, B., Maass, G., Vogtle, F., Sieger, H., Heimann, U., and Weber, E., J.Am. Chem. SOC., 1979, 101,2588. Kang, S. I., Czech, A., Czech, B. P., Stcyart, L. E., and Bartsch, R. A., Anal. Chem.. 1985,57, 1713. Walkowiak, W., Stewart, L. E.. Lee, H. K., Czech, B. P., and Bartsch, R. A., Anal. Chem., 1986,58, 188. McDowell, W. J.. Case, G. N., Bartsch, R. A., and Czech, B. P., Solvent Extr. Ion Exch., 1986,4,411. Walkowiak, W., Ndip, G. M., Desai, D. €I., Lee, H. K., and Bartsch, R. A., A n d . Chem., 1992, 64, 1685. Hiratani, K., Aiba, S . , and Nakagawa, T., Chem. Lett., 1980, 477. Hiratani, K., Chem. Lett., 1981, 21. Hiratani, K., Chem. Lett., 1982, 1021. Hiratani, K., Bull. Chem. SOC. Jpn.. 1982, 55, 1963. Hiratani, K., Supihara, H., Taguchi, K., and Iio, K., Chem. Lett., 1983, 1657. Taguchi, K., Hiratani, K., Sugihara, H., and Iio, K., Chem.Lett., 1984, 1457. Hiratani, K., Taguchi, K . , Sugihara, ‘fl., and Iio, K., Bull. Chem. Soc. Jpn., 1984, 57, 1976. Hiratani, K., and Aiba, S., Bull. Chem. SOC. Jpn., 1984, 57, 2657. Hiratani, K., andTaguchi, K., Bull. Chem. SOC. Jpn., 1987,60, 3827. Hiratani, K., Taguchi, K., Sugihara, H., and Iio, K., J. Membr. Sci., 1987, 35, 91. Hiratani, K., Taguchi, K., and Sugihara, H., J . Membr. Sci., 1991.56, 153. 138 139 140 141 142 143 144 145 146 147 148 I49 150 1.51 152 1.53 154 155 156 157 . 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 Kuboniwa. H., Yamaguchi, K., Hirao, A., Nakahama, S., and Yamazaki, N., Chem. Lett., 1982, 1937. Kuboniwa, H., Yamaguchi, K . , Nakahama, S . , Hori, K., and Ohashi, Y., Chem.Lett., 1988, 923. Yamaguchi, K . , Negi. S., Kozakai, S., Nagano. R., Kuboniwa, H., Hirao, A., Nakahama, S . , and Yamazaki, N., Bull. Chem. Sac. Jpn., 1988, 61, 2047. Yamaguchi, K., Kuboniwa, H., Murakami, N., Hirao, A , , Nakahama, S . , and Yamazaki, N., Bull. Chem. SOC. Jpn., 1989, 62, 1097. Dale, J., and Fredrikson, S. B., Pure Appl. Chem., 1989, 61, 1587. Grootenhuis, P. D. J., and Kollman, P. A., J . Am. Chem. SOC., 1989,111,2152. Shoham, G., Christianson, D. W., Bartsch, R. A., Heo, G. S . , Olsher, U., and Lipscomb, W. N., J. Am. Chem. SOC., 1984, 106, 1280. Levins, R. J., Anal. Chem., 1971, 43, 1045. Baumann, E. W., Anal. Chem., 1975,47, 959. Jaber, A. M. Y., Moody, G. J., and Thomas, J . D. R., Analyst, 1988, 113, 1409. Alexander, P.H. V., Moody, G. J . , and Thomas, J. D. R., Analyst, 1987, 112, 113. Moody, G. J., Saad, B. B., Thomas, J. D. R., Kohnke, F. H., and Stoddart, J. F., Analyst, 1988, 113, 1295. Johnson, S., Moody, G. J . , Thomas, J. D. R., Kohnke, F. H., and Stoddart. J. F., Analyst, 1989, 114, 1025. Beswick, C. W., Moody, G. J., and Thomas, J. D . R., Anal. Proc., 1989, 26, 2. Feng, Y. P., Goodlet, G., Harris, N. K., Islam, M. M., Moody, G. J., and Thomas, J. D. R., Analyst, 1991, 116, 469. Levins, R. J., and Ikeda, R. M., Anal. Chem., 1965, 37, 671. Selig, W. S., Fresenius’ 2. Anal. Chem., 1986, 325, 616. Selig, W. S., Microchem. J., 1988, 37, 155. Sanchez, M. L. R., and Vytfas, K., Analyst, 1988, 113, 959. Jaber, A. M. Y., Moody, G. J., and Thomas, J . D. R., Analyst, 1976,101, 179.Moody, G. J., Thomas, J . D. R., Lima, J. L. F. C., and Machado, A. A. S. C., Analyst, 1988, 113, 1023. Nakamura, T., Ogiwara, K., Izutsu, K., and Rechnitz, G. A . , Bull. Chem. SOC. Jpn., 1985, 58, 3409. Naka’murg, T., Higuchi, H., and Izutsu, K., Bull. Chem. SOC. Jpn., 1988,61, 1020. Nakamura, T., Higuchi, H., and Izutsu, K., Bull. Chem. SOC. Jpn., 1989, 62, 3089. Nakamura, T., Nakamura, Y., Kojima, T., and lzutsu, K., Bull. Chem. SOC. Jpn., 1900, 63, 2615. Nakamura, T., Komai, M., Hosono, S . , and Izutsu, K . , Anal. Chim. Acta, 1990, 238, 351. Moody, G. J . , and Thomas, J. D. R., in Nonionic Surfactants, ed. Cross, J., Marcel Dekker, New York, 1987, ch. 4. Jones, D. L., Moody, G. J., Thomas, J . D. R., and Birch, B. J., Analyst, 1981, 106, 974. Jones, D.L., Moody, G. J., and Thomas, J. D. R., Analyst, 1981, 106, 439. Vytfas, K., DvofakovB, V., and Zeman, I., Analyst, 1989, 114, 1435, and references cited therein. Ivanov, V., Bavykina, N. I . , and Pravshin, Yu. S . , Zh. Anal. Khim., 1985, 40, 2265; Chem. Abstr., 1986, 104, 188721d. Ivanov, V. N., andpravshin, Yu. S . , Zh. Anal. Khim., 1986,41, 360; Chem. Abstr., 1986, 104, 1887248. Chernova, R. K., Kulapina, E. G . , Materova, E. A., and Tret’yachenko, E. V., Zh. Anal. Khim., 1989, 44, 408; Chem. Abstr., 1989, l l i , 136466. Masadome. T., Imato, T., and Ishibashi, N., Bunseki Kagaku, 1991,40, 7. Kurotu, T., Bull. Chem. SOC. Jpn., 1990, 63, 592. Kurotu, T., Bull. Chem. SOC. Jpn., 1990, 63, 597. Kurotu, T., Anal. Chim. Acta, 1990, 233, 325. Yoshida, Z., and Kihara, S ., J. Electroanal. Chem., 1987, 227. 171. Chen, Q . - Z . , Iwamoto, K., and Seno, M., Electrochim. Actu, 1992, 37, 643. Sun, Z., and Wang. E., Talanta, 1988, 35, 673. Sun, Z., and Wang, E., Electroanalysis, 1989, 1, 441. Sun, Z., and Vanysek, P., Anal. Chim. Acta, 1990, 228, 241. Kakiuchi, T., Usui, T., and Senda, M., Bull. Chem. SOC. Jpn., 1990, 63, 2044. Kakiuchi, T., Usui, T., and Senda, M., Bull. Chem. SOC. Jpn., 1990, 63, 3264.ANALYST, AUGUST 1993, VOL. 118 97 1 182 183 184 185 186 I87 188 189 190 191 192 193 I94 195 196 197 198 199 Koryta, J., Electrochim. Acta, 1988, 33, 189. Senda, M., Kakiuchi, T., and Osakai, T., Electrochim. Acta, 1991,36,259. Hale, P. D., Lan. H. L., Boguslavsky, L. I., Karan, H . I., Okamoto. Y., and Skotheim, T. A . , A n d . Chim. Acta, 1990, 251, 121. Giraudeau, A., Meray, M. El., Gross, M., Peichocki, C., and Bernard, M., Anal. Chim. Acta', 1991, 251, 39. Watanabe, M.. and Ogata, N., in Dodensei Kohunshi, ed. Ogata, N., Kodansha, Tokyo, 1990. Ratner, M. A., and Shriver, D. F., Chem. Rev., 1988,88, 109. Farrington, G . C.. Yang, H., and Huq, R., Muter. Res. Soc. Symp. Proc., 1989, 135, 319. Huq, R., Farrington, G. C., and Gregory, C., Int. Symp. Polym. Electrolytes, 2nd, 1989, 273. Fan, F. F., and Bard, A. J., J. Electrochem. Soc., 1986, 133, 301. Syed, A. A., and Dinesan, M. K., Talanta, 1991, 38, 815. Roncali, J., Chem. Rev., 1992, 92, 711. Egashira, M., Shimizu, Y., and Eshita, A . , J . Electrochem. Soc., 1988, 135, 2546. Oliver, B. N., Egekeze, J. O., and Murray, R. W., J . Am. Chem. Soc., 1988, 110, 2321. Geng, L., Longmirc, M. L., Reed, R. A . , Parcher, J. F.. Barbour, C. J., and Murray, R. W., Chem. Muter.. 1989,1,58. Parcher, J. F., Barbour. C. J . , and Murray, R. W., Anal. Chem., 1989, 61, 584. Geng, L., Reed, R. A., Kim, M.-H., Wooster, T. T., Oliver, B. N., Egekeze, J., Kennedy, R. T., Jorgenson, J. W., Parcher, J . F., and Murray, R . W., J. Am. Chem. Soc., 1989, 111, 1614. Barbour, C. J., Murray, R. W., and Parcher, J. F., Anal. Chem., 1991,63,604. Nagashima, K., Meguro, K., and Hobo, T., Fresenius' J. Anal. Chem., 1990, 336, 571. 200 201 202 203 204 205 206 207 208 209 210 21 1 212 213 214 215 Nagashima, K., Yajima, I., and Hobo, T., Bunseki Kagaku, 1991,40, T77. Bochenska, M., Biernat, J. F.. Topolski, M., Bradshaw, J . S . , Bruening, R. L., Izatt, R. M., and Dalley, N. K., J. Inclusion Phenom. Mol. Recogn. Chem., 1989, 7, 599. Schepartz, A . , and McDevitt, J. P., J . Am. Chem. Soc., 1989, 111, 5976. Echegoyen, L. E . , Yoo, H. K., Gatto, V. J . , Gokel, G . W., and Echegoyen, L., J . Am. Chem. Soc., 1989, 111, 2440. Haberfield, P., and Rizzo, T. P., J. Inclusion Phenom. Mol. Recogn. Chem., 1990, 9, 367. Chang, J.-H., Ohno, M., Esumi, K., and Meguro, K., J. Am. Oil Chem. SOC., 1988, 65. 1664. Cserhati, T., and Szejtli, J., Cavhohydr. Res., 1992, 224, 165. Harada, A.. and Kamachi. M., Macromolecules, 1990,23,2821. Harada, A., Li, J., and Kamachi, M., Nature (London), 1992, 356, 325. Ohno, H., Matsuda, H., and Tsuchida, E., Makromol. Chem., 1981, 182, 2267. Scranton, A. B., Klier, J., and Aronson, C. L., ACS Symp. Ser., 1992,480, 171. Chatterjce, S. K., Khan, A. M., Ghosh, S . , and Yakav, D., Angew. Makromol. Chem., 1990, 181, 93. Dubin, P. L., Gruber, J . H., Xia, J . , and Zhang, H., J. Colloid Interface Sci., 1992, 148, 35. Maltesh, C., and Somasundaran, P., Langmuir, 1992, 8, 1926. Nakanishi, T., Seimiya, T., Sugawara, T., and Iwamura, H., Chem. Lett., 1984, 2135. Kinugasa, S., Takatsu, A., Nakanishi, H . , Nakahara, H., and Hattori, S . , Macromolecules, 1992, 25, 4848. Pup er 2/06 778A Received December 21, I992 Accepted March 2, 1993

ISSN:0003-2654    

DOI:10.1039/AN9931800959

出版商:RSC    

年代:1993

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ANALYST, AUGUST 1993, VOL. 118 973 Electrocatalytic Reduction of Hydrogen Peroxide at a Stationary Pyrolytic Graphite Electrode Surface in the Presence of Cytochrome c Peroxidase: A Description Based on a Microelectrode Array Model for Adsorbed Enzyme Molecules Fraser A. Armstrong" Department of Chemistry, University of California, Irvine, CA 92717, USA Alan M. Bond* Department of Chemistry, La Trobe University, Bundoora, Victoria 3083, Australia Felix N. Buchi Paul Scherrer Institute, CH-5232 Villigen, Switzerland Andrew Hamnett Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, UK NE 1 7RU H. Allen 0. Hill, A. Martin Lannon and Olwen C. Lettington Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK OX? 3QR Cynthia G.Zoski Department of Chemistry, University of Rhode Island, Kingston, 02881, USA Electrochemical reduction of H202 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versusthe standard hydrogen electrode) in the presence of yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear- sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules.A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment. Keywords : Peroxide vo Ita m m e tric biosensor; c ytoc h ro m e c pe roxidase a dso rp ti0 n ; micro e lec tro de array model The use of electrodes modified with redox-active biologically important molecules represents a rapidly expanding area of analytical voltammetry (amperometry) .I-3 These so-called biosensors may achieve remarkable specificity for detection of their biological partners (or other molecules) and enhanced specificity for catalysing the process relative to that which occurs at a bare ( i .e . , unmodified) electrode. In the voltammetric determination of H202, the reduction process at carbon electrodes is extremely irreversible and not particularly selective .4-6 Vacuum deposition of gold and palladium may be used to provide an inorganic-based catalytic system for amperometric determination of peroxide over the concentration range 1 x 10-7-1 x 10-3 moll-l.4 As H202 is an important entity in many biological processes, it is not surprising that electrode surface modification with enzymes has been examined as a method of catalysing the reduction of H202.1-3,5 It has been observed7-9 that voltammetric waves due to the reduction of H202 at potentials of around 600 mV or higher versus SHE (standard hydrogen electrode) at neutral pH can be obtained with pyrolytic graphite 'edge' (PGE) electrodes in the presence of cytochrome c peroxidase (CcP) , Cytochrome c peroxidase is a soluble enzyme of relative molecular mass (M,) 34000, containing a single b-type haem group, for which the catalytic intermediates are reasonably well characterized.10111 In addition, the three-dimensional structure of the enzyme is known.12 As the mechanistic aspects of voltammetric biosen- sors are very complex and not well understood, this system could provide an important model for understanding how enzymes interact with electrodes and catalyse a reaction, and how the resulting voltammetry may be interpreted. Bowden and co-workers899 have provided evidence, from rotating disc studies, that the enzyme adsorbs strongly at a PGE electrode in a form that exhibits the essential properties of the enzyme in solution.Armstrong and Lannon7 noted that linear-sweep voltammograms obtained with a freshly polished stationary PGE electrode after introduction into electrolyte containing CcP and H202 show an interesting time dependence of the voltammetric response. From the time of initial contact between the electrode and the enzyme-substrate solution, the waveform changes from sigmoidal to peak-like. This change is not predicted on the basis of mass transport by linear diffusion, although the final peak-shaped response observed at long times is consistent with linear diffusion of peroxide to the electrode surface and was used to calculate the diffusion coefficient.The rate of this transition was seen to depend on the enzyme concentration, thus indicating that the various waveforms reflect different stages of adsorption. It follows from the above brief review of the literature that apart from the demonstration that reduction of peroxide and adsorption of the enzyme are interrelated, few details of the mechanism of the CcP-catalysed electrode reduction of H202 are understood. However, from what is known from conven- tional studies, the stages of catalysis may be described in terms of three discrete redox steps (1)-(3): Ferrl + H202 -+ {FerV=O, R+} + H20 (1) ~~~ ~~~ ~~~~ * Authors to whom correspondence should be addressed. (2) {Fe'"=O, R+} + e- -+ FeIV=O974 ANALYST, AUGUST 1993, VOL.118 Fel"=O + e- + 2H+ + Ferrl + H20 (3) over-all : H202 + 2H+ + 2e- -+ 2H20 (4) in which the initial reaction of the FerI1 form with peroxide produces a two-equivalent oxidized intermediate containing oxyferrylhaem(1v) and a protein-bound cation radical (R+) .11 In yeast mitochondria, the FerIr state is regenerated by two rapid reactions with reduced cytochrome c, via the one- electron oxyferryl form. The over-all reaction is highly exergonic. At pH 7, the formal two-electron reduction potential EO' for H202 is approximately 1.3 V versus SHE.13 Relevant formal potentials for the intermediate couples [eqns. (2) and (3)] have not been determined but values may be expected to be of similar magnitude to those measured14 for horseradish peroxidase, i.e., each about 0.9 V versus SHE.In contrast, the reduction potential of cytochrome c is approxi- mately 0.26 V versus SHE.15 Hence, the electrode potential at which electrochemical reduction of H202 is observed, about 600 mV versus SHE, is actually much more positive (i.e., the reaction occurs readily with a much lower driving force) than that apparent with its physiological partner, but is still considerably less positive than the electrode potential expec- ted for reversible electrochemical reduction of H202. The over-all multi-step process is highly irreversible, although the rate-determining process has not been established. Given the gaps in the existing state of knowledge, it is clear that a full theoretical treatment of the voltammetry is not possible. In this paper, while recognizing that we cannot provide a complete description of the voltammetry, we address a question that ultimately must be of importance in the interpretation of any voltammetry due to bioelectrocatalysis by direct electron transfer to enzymes:7-9.1&22 How do the density and arrangement of enzymes at the electrode surface define the diffusional geometry of small substrate molecules and hence determine the appearance of the voltammetric response at a stationary electrode? In a recent examination of the electrochemistry of cytochrome c at pyrolytic graphite electrodes, we proposed23-27 that electron transfer between an electrode and freely diffusing protein molecules could be very fast but it might occur only at suitable interaction sites on the graphite surface.The shape and form of the voltammetric wave was proposed to be a function of the size and density of these sites rather than of the heterogeneous electron-transfer rate constant. With the biocatalytic electrochemistry of cytochrome c peroxidase , obvious and important similarities are apparent. In this case, however, it is the small substrate, H202, which diffuses and exhibits electrode site specificity, in this instance for adsorbed enzyme molecules. Here then lies an interesting extension of the microscopic hypothesis, as the size and density of active electrode sites, and thus the shape and form of the voltammetric wave, should be related to the extent of adsorption of the enzyme. In order to determine a correlation between the time- dependent changes in voltammetric waveform and the process of adsorption, we performed electrochemical experiments in coiljunction with ellipsometry.28 The latter technique provides independent information on the adsorption of species at an electrode surface.The combined measurements have led us some way towards establishing the fidelity of a microscopically defined dynamic picture of an enzyme-electrode interface and therefore, by implication, to an improved understanding of H202 and related biosensors. Experimental Cytochrome c peroxidase (EC 1.11.1.5) was prepared from baker's yeast according to the procedure of English et aZ.29 Concentrations of stock solutions (prepared by dissolving crystals in buffer solution at pH 7) were determined from the absorbance at 408 nm ( E = 98 1 mmol-l cm-l).3" Neomycin (92% B form) and HEPES [N-(2-hydroxyethyl)piperazine- N'-(2-ethanesulfonic acid)] were purchased from Sigma.All other reagents were of at least analytical-reagent grade. Water was purified using a Milli-Q de-ionizing system (Millipore). Stock solutions of H202 (prepared from BDH 100 volume solution) were standardized by titration with KMn04. For conventional voltammetric experiments, an all-glass cell featuring a three-electrode configuration was used. The saturated calomel reference electrode (SCE) was maintained at room temperature (20°C) and linked to the sample compartment by a long L-shaped arm terminating in a Luggin capillary tip. The sample chamber was designed to hold 0.5 ml of solution that could be stirred, when this was required, by a magnetic 'microflea'.The counter electrode was a semi- cyclindrical piece of platinum gauze positioned opposite to the Luggin tip. The working electrode was a disc, radius 2.5 mm, of pyrolytic graphite cut so that the basal (a-b) plane would be perpendicular to the electrode-solution interface; hence the term PGE electrode. The disc was housed in a Teflon sheath, within which contact was made with a brass rod, and sealed with epoxy resin. Prior to each experiment the electrode surface was polished with 0.3 pm alumina (Banner) and sonicated thoroughly. On lowering the electrode into the sample solution, care was taken to ensure that the electrode surface was positioned reproducibly close to the Luggin tip. Unless stated otherwise, experiments were carried out at 5 "C with the sample compartment partially immersed in a circulating water-bath.At the more usual temperature of 25 "C the voltammetric response developed more rapidly than at 5 "C but also deteriorated more rapidly (see later). Linear- sweep voltammetry was carried out using an Ursar Instru- ments potentiostat and accessories. Voltammograms were recorded on a Bryans Gould 60000 recorder. All potentials were corrected to correspond with the SHE (we used EsCE = +250 mV versus SHE at 20 "C). For ellipsometry, the working electrode consisted of a 9 mm square of pyrolytic graphite mounted on the side of a vertical support which could be lowered into the sample solution. The cell, miniaturized to hold 7 ml of solution, featured a main glass chamber of i.d.2.0 cm with two short (0.4 cm) coplanar side-arms positioned at 120 " to each other. The ends of these were precision ground so that silica windows could be glued into place to give perfect alignment for light incident at 60" on the centrally positioned working electrode. A platinum counter electrode was positioned in a recess on one side of the cell so that it did not obstruct the light path. The SCE reference electrode was located in a side-arm that featured a Luggin capillary tip. The tip was positioned close to the working electrode without obstructing the light path. The cell was thermostated at 5°C by a tightly wound jacket of poly(viny1 chloride) (PVC) tubing through which fluid from a Churchill refrigerator-circulator was circulated. Thorough mixing of solutions was achieved by stirring with a 'microflea'.Dry air was directed at the optical windows to prevent condensation. A Rudolph Research RR2000 automatic ellipsometer was used. The light source was a 100 W tungsten halogen lamp powered by a mains-driven smoothed 12 V supply. An interference filter placed before the photomultiplier tube gave incident light of wavelength 633 nm. Values of ellipticity (E), azimuthal angle (0) and intensity of reflection ( I ) were measured and stored in the random access memory of a Matmo Z-80-based personal computer. Values of 8 and E were converted into values of phase change A and amplitude change W, where the relative phase change A between parallel and perpendicular components of the reflected light is given by tan A = tan 2~/sin 28 and the corresponding relative amplitude change Y is given by cos 2Y = -cos 2E cos 20 Values calculated from these relationships were compared with those calculated by standard literature procedures.28 (5) (6)ANALYST, AUGUST 1993, VOL. 118 975 Results and Discussion Fig.l ( a ) shows linear-sweep voltammograms recorded at various times following the injection of CcP into a solution of 56 pmol 1-1 HzOz contained in the ellipsometry cell described above. The electrolyte consisted of 0.1 mol 1-1 KC1, 5 mmol 1-1 neomycin and 5 mmol I-' HEPES at pH 7.0. In this experiment, the concentration of CcP in the resulting solution was 0.2 pmol 1-'. Although there is some variability in the results obtained between experiments, the form and develop- ment of the waves are essentially as reported previously.7 That is, at short times, a sigmoidal curve with a small limiting current is obtained, whereas at longer times a peak-shaped response is found.The ellipsometry of the electrode-solution interface was monitored, whilst stirring the solution and holding the electrode potential at 850 mV. Corresponding normalized changes in I, A and Y were measured as a function of time, and these are shown in Fig. 2(a). Intervals during which the voltammograms were recorded (in each instance with the stirrer switched off) are indicated. Although changes in the ellipsometric parameters occur over at least two time phases, development of the peak-shaped voltammetric wave- form is complete within the time course of an initial large, dominant change (the first phase). This conclusion was substantiated by the results of several experiments in which the concentration of CcP was varied.The rate of development of the peak-shaped waveform (as evaluated from the increase 300 400 500 600 700 800900 300 400 500 600 700 800 900 EImV versus SHE Fig. 1 Linear-sweep voltammograms (scan rate 8 mV s-') of solutions of H202 (56 pmol 1-I) in 0.1 mol I-' KCl, 5 mmol 1-1 neomycin, 5 mmol 1-1 HEPES (pH 7.0) at various times following addition of CcP. (a) To a concentration of 0.2 pmol I-'. Scans initiated at times: A, 30; B, 178; C, 325; D, 750 and E, 1080 s. ( b ) To a concentration of 0.5 pmol 1-I. Scans initiated at times: A, 60; B, 180; C, 310; and D, 710 s 5.0 4.5 19.0 18.8 18.6 17.2 1 , , , 1 0 1000 2000 21.2 21.0 20.8 20.6 - 0 1000 2000 3000 Ti mels Fig.2 Changes in ellipsometric parameters over the time course of voltammetric scans shown in (a) Fig. l ( a ) and (b) Fig. l(b), indicating points at which voltammograms were recorded. The electrode potential was held at +850 mV versus SHE in peak potential) and the rate of changes in the first phase of ellipsometry each increased as the enzyme concentration was raised. Figs. l(6) and 2(6) show voltammograms and ellip- sometric changes, respectively, obtained following the injec- tion of CcP to a final concentration of 0.5 pmol 1-l. With the concentration of enzyme as high as 1 pmol I-', sharp peak- shaped voltammetric curves were obtained on the first scan and the first, large phase of ellipsometric changes was complete after 2 min.In contrast, with 0.1 pmol1-* of enzyme, sigmoidal curves were dominant; the development of peak- shaped voltammetric curves was slow and incomplete and the end of the first phase of ellipsometric changes was poorly defined. The voltammetric and ellipsometric results could be repro- duced readily at a qualitative level. Further, the voltammetry was observed to develop in the absence of neomycin, although very sharp waves were not obtained. The observation of activity in the absence of neomycin is in contrast to work reported earlier7 and is in broad agreement with the results of Paddock and Bowdens in their work on this system. It is now believed that the presence of an aminoglycoside in this system may assist adsorption, but is not essential.Perhaps, more important, aminoglycosides probably offset the deleterious effects of contaminants which inhibit the activity of CcP. The enzyme-electrode surface interface is clearly a highly critical region the stability of which is influenced by subtle alterations in solution and electrode conditions. Paddock and Bowden8 reported that the stability of the biocatalytic response was substantially poorer when using HEPES buffer as compared with potassium phosphate. On the other hand (in what is a clearer type of experiment because one addresses the charac- teristic reversible voltammetry of the protein redox centre) we have found31 that the direct electrochemistry of negatively charged ferredoxins is promoted very effectively by aminogly- cosides such as neomycin.These reagents, presumably through multiple salt-bridge interactions, induce strong adsorption of the protein molecules with retention of charac- teristic properties32-33 and minimize effects of contaminants, although their effectiveness in these roles will vary for different proteins. Addition of CcP causes the reflected intensity to fall dramatically in the ellipsometry experiments irrespective as to whether the solution was stationary or stirred. This phenomenon must therefore be associated with a change in the absorbance of the enzyme on adsorption. If we assume that a complete monolayer of enzyme molecules exists a t the end of the initial phase and that the native conformation of the enzyme is retained on adsorption, then we expect t? have the equivalent of an organic layer approximately 40 A thick.The effective thickness of a monolayer of CcP molecules was estimated from the radius of 21 8, used by Northrup et al.34 (their 'Model 1') in a Brownian dynamics simulation of the kinetics of precursor complex formation with cytochrome c. Refractive indices, n (real) = 1.6 and k (imaginary) = 0.3, can be derived28335 under these assumptions. The n value is close to those commonly observed for monolayers of protein molecules.36 However, the k value is substantially larger than would be expected on the basis of the absorption spectrum of CcP in any of its catalytic states and it would appear that optical transitions from the enzyme to the underlying carbon material are taking place. At lower coverages of enzyme, i.e., within the early rapid change, the A and \I, values cannot be understood within the basis of any simple effective medium model,37 as such models inevitably lead to predicted k values below that of the underlying carbon substrate for sub-monolayer enzyme cover- age.As kfilm is smaller than ksubstrate, the direction of change of A according to this model will invert, but experimentally A is seen to change monotonically from zero to complete average. In fact, this type of change can be understood in terms of 'island films'.38,39 Dignam and Markovits39 showed that the optical properties for such films were best described in terms of a film with a refractive index that remains essentially976 ANALYST, AUGUST 1993, VOL. 118 constant and equal to that of a complete monolayer, but where the apparent thickness increases monotonically with coverage. This corresponds far more closely to the observed ellipsome- tric behaviour of our film, and gives us considerable con- fidence that the island model is far closer to the correct physical model than any model involving essentially randomly distributed molecules at sub-mopolayer coverage.Models based on developing clusters have also been considered in some detail by Greef and CO-workers.40~41 The transformation from a sigmoidal to peak-shaped waveform was analysed in terms of a microscopic array model in which catalytic reduction of H202 occurs only at the active sites of enzyme molecules that are adsorbed on the electrode surface. From the description in the introduction, it is obvious that the process is complex and involves many steps.However, it is known in the limiting case that, assuming that all the electrode surface is electroactive and using a model based on linear diffusion, a diffusion coefficient is calculated which is in agreement with that expected for H202. It is also known that the over-all process is irreversible. Thus, combin- ing all the steps (homogeneous and heterogeneous) enables a ‘heterogeneous equivalent’ description of the type developed by Ruiik and Feldberg42.43 to be employed. For an irreversible process occurring under conditions of linear diffusion at a planar (macroscopic) electrode surface , the relevant equation44 is planar P = P’ - (R7‘/a’naF){0.0O534(F/R7‘) + In[ (na’n,FvD,lR T)1/2/k’]} (7) where E;lanar is the peak potential (in volts), Eo’ is the formal reduction potential for the substrate undergoing reduction, a’ is the apparent transfer coefficient, n, is the number of electrons transferred in the rate-determining step, Y is the scan rate, Do is the diffusion coefficient of H202 and k’ is the heterogeneous equivalent rate constant consisting of first- order heterogeneous and homogeneous rate constants. The other symbols have their usual meanings.In the microscopic array model, the enzyme molecules behave as if they adsorb as expanding clusters, in other words, generating microelectrodes of increasing size. Fig. 3 shows an idealized microelectrode array used for the theoretical calcu- lations. The radius of each microelectrode (r,) and the inter- electrode spacing (d,) is variable. With this model, it is instructive to consider first the condition r, << d,, in which the diffusion layers generated for each microelectrode are isolated and do not overlap with each other.For an irreversible process, we may write45 for the steady-state voltammetry obtained with each idealized hemispherical microelectrode having a radius r, at time t EZ2 = EO’ + (RT/a’n,F)ln(k’r/D,) (8) where Es:,2 is the potential at half-limiting current. In the limit of these microelectrodes being well spaced so that diffusion layers do not overlap, then the current is the sum of the individual microelectrodes. I i I 4 0 0 01 I rt H Fig. 3 trodes where r, = radius at time t and dt = spacing at time t Schematic diagram showing a hexagonal array of microelec- Combining eqns.(7) and (8), we obtain (I$anar -E?2), = (-RT/a’naF){0.00534(F/RT) + In [ ( z (X ’naFvDo/R T ) 1’2/rt]} (9) from which it can be seen that the average effective radius of the cluster of electroactive enzyme molecules at any time t may be determined from the difference between the final observed value of and the corresponding value of (EF2),. Obviously, if the linear diffusion model had been employed assuming that the entire electrode surface was electroactive, then a peak-shaped response would have been expected for all times. In other words, neither the change in wave shape nor the change in the position of the response would have been predicted. Hence, despite the obvious approximations and uncertainties in the microscopic model, the hypothesis at least has the virtue of providing a qualitative understanding of the voltammetry.Fig. 4 shows computer simulations of the development of voltammograms at a single site (for an irreversible process with a = 0.5) as r, increases. The values Do = 1.1 X m2 s-1 and n, = 2 as determined by Scott et al.9 were used. Although there is qualitative similarity, in that there is a trend from sigmoidal to peak-shaped waveform, the quantitative similarity is poor. However, excellent agreement between experiment and theory is obtained once we consider the more realistic case, in which r, becomes comparable to d, so that overlap of diffusion layers occurs as illustrated in Fig. 5 . Fig. 6(a) and (b) shows simulations based on an array of microelectrodes with different parameters, using the theory of Gueshi et al.46-48 The transformation to a peak-shaped waveform is now in close agreement with the time-dependent change observed in our experiments.Applying eqn. (9) to the experiment shown in Fig. l(a), one calculates an avera e reached by the time of the first scan (initiated after 30 s). Such a result is obtained using the observed value of EF2 = 525 mV, and E;lanar value of 660 mV that is typically obtained under these conditions and an a’ value of 0.2. As a hemisphere, this would consist of ( 2 d 3 ) x 109 enzyme molecules of effective diameter approximately 40 A. How- ever, a more plausible situation is that r, corresponds to the radius of an expanding flat disc. This is consistent with the ellipsometry and is more realistic in view of the probability that the only CcP molecules contributing to the activity are those which are in direct contact with the electrode and able to provide unrestricted entry and exit for H202 and H20 (see also below).Using a rotating disc electrode, Paddock and Bowdens obtained an value of 700 mV. However, our own observation that EZ2 occurs at a more negative potential is not inconsistent with this result. The value obtained at a effective radius of approximately 4 X m (40000 w ) 0 -2 -4 I .P -6 .> -8 -10 - 400 -200 0 200 400 E - e&rnV Fig. 4 Simulation for the development of voltammograms with increasing size (radius rl) of a single electrocatalytically active cluster of CcP molecules on the electrode surface. Simulation parameters are given in the text.The ordinate unit i is the steady-state limiting current obtained when r, = 10 pm. Y,: A, 10; B, 34; C, 50; D, 65; and E, 79 pmANALYST, AUGUST 1993, VOL. 118 977 (a) Electrode J Redox Redox active inactive site part of electrode Fig. 5 Schematic dia ram showin overlap of diffusion layers as ( a ) time increases or (b) cf decreases (% is the diffusion layer thickness) 0 20 40 ' 60 ' 80 N $100 120 140 0 60 120 180 I I -0.6 -0.4 -0.2 0 -0.5 -0.3 -0.1 0.1 E-PN Fig. 6 Simulations showing the development of voltammograms for reduction of H202 based on an array model according to the theory of Gueshi et al.4648 Parameters in ( a ) are Y = 8 mV s-l, k' = 1 x cm s-l, a' = 0.35, Do = 1 x cm2 s-l, n, = 2, T = 278 K, i is the current normalized to an electrode area of 1 cm2 and a concentration of 1 x mol l-l, d, = 40 pm, r, and 8 (the fraction of surface that is electroinactive given by the expression [(d? - rF)/dF]) are: A, 1.8 pm, 0.988; B, 12.6 pm, 0.90; C, 20 pm, 0.75, D, 03 pm, 0; and E, 33.5 pm, 0.30.Parameters in (b) are as for ( a ) except a' = 0.8, d, = 4 pm and r, and 8 are: A, 0.22 pm, 0.993; B, 0.69 pm, 0.970; C, 2.8 pm, 0.5; and D, co pm, 0 stationary array of microelectrodes would indeed be expected tc be more negative than that measured at a rotating disc electrode because of the much higher sensitivity to kI.46-48 Our analysis has focused on the coincidence of the development of a peak-shaped voltammetric response with the first and dominant phase of the changes in ellipsometry. We have no completely convincing explanation at present for the subsequent further changes, although it is plausible that secondary adsorption is occurring, that is, formation of a second layer of enzyme, perhaps over denatured, flattened primary adsorbed molecules.Secondary adsorption is expec- ted to be counterproductive because second-layer enzyme molecules will not be able to receive electrons easily from the electrode and should impede the diffusion of substrate molecules to the more electroactive primary layer. The consequence of this is that the sites for H202 reduction are progressively destroyed. In support of this idea, we have always noted that over longer periods the voltammetric peak broadens with some attenuation and its position shifts back to more negative potentials. Eventually, a sigmoidal waveform, similar to that observed at very early times, is obtained.In the framework of our model, the system reverts back to being an array of isolated microelectrodes. The concepts proposed in this paper also have important implications with regard to biosensors as the data and mechanism suggest that an effectively fully covered surface must be maintained at all times when analytical measurements are being undertaken. At less than monolayer coverage, the signal can be expected to be irreproducible and time dependent as the current will be proportional to the fraction of electrode coverage and not to the total electrode area. To emphasize the difficulty in making a reliable biosensor, it also appears that greater than monolayer coverage may also lead to a decrease in reproducibility so that achieving the optimum surface state may be far from a trivial problem.F. A. A. is indebted to the Royal Society for a 1983 University Research Fellowship held at Oxford, 1983-89, during the tenure of which part of this work was carried out. A.M.B. gratefully acknowledges the Trustees of the Analytical Trust of the Royal Society of Chemistry for the award of the Robert Boyle Fellowship in Analytical Chemistry (on the occasion of the 150th Anniversary of the Royal Society of Chemistry and coincidentally the 300th anniversary of the death of Robert Boyle) which made possible the collaboration required for this research, the Inorganic Chemistry Laboratory at Oxford University for acting as hosts for the duration of the award and La Trobe University for granting leave to take up the Fellowship.We thank Professor E. Bowden for making available to us a preprint of ref. 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 References Analytical Voltammetry, eds. Smyth, M. R., and Vos, J. G. (Comprehensive Analytical Chemistry), Elsevier, Amsterdam, 1992, vol. 27. Chemical and Biochemical Sensors, Parts I and I I , eds. Gopel, W., Jones, T. A., Kleitz, M., Lundstrom, I., and Seiyama, T., (Sensors-a Comprehensive Survey), VCH, Weinheim, 1992, vols. 2 and 3. Bartlett, P. N., Tebbutt, P., and Whitaker, R. G., Prog. React. Kinet., 1992, 16, 55. Gorton, L., and Svensson, T., J. Mol. Catal., 1986, 38, 49. Higgins, I. J., and Hill, H. A. O., Essays Biochem., 1985, 21, 119.Sugiyama, K.. and Aoki, K., J. Elecroanal. Chem., 1989, 261, 437, and references cited therein. Armstrong, F. A., and Lannon, A. M., J. Am. Chem. SOC., 1987, 109, 7211. Paddock, R. M., and Bowden, E. F., J. Electroanal. Chem., 1989, 260,487. Scott, D. L., Paddock, R. M., andBowden, E. F., J. Electroanal. Chem., 1992, 341,307. Yonetani, T., in The Enzymes, ed. Boyer, P. D., Academic Press, New York, 1976, vol. 13, pp. 345-361. Chance, M., Powers, L., Kumar, C., and Chance, B., Biochemistry, 1986, 25, 1259. Finzel, B. C., Poulos, T. L., and Kraut, J., J. Biol. Chem., 1984, 259, 13027. Hoare, J. P., in Encyclopaedia of Electrochemistry of the Elements, ed. Bard, A. J., Marcel Dekker, New York, 1974, vol. 11, p. 194. Hayashi, Y., and Yamazaki, I., J. Biol. Chem., 1979,254,9101.Taniguchi, I., Funatsu, T., Iseki, M., Yamaguchi, H., and Yasukouchi, K., J. Electroanal. Chem., 1985, 193, 295. Tarasevich, M. R., Yarapolov, A. I., Bogdanovskaya, V. A., and Varfolomeev, S. D., Bioelectrochem. Bioenerg., 1979, 6, 393. Lee, C.-W., Gray, H. B., Anson, F. C., and Malmstrom, B. G., J. Electroanal. Chem.. 1984, 172, 289. Ikeda, T., Fushimi, F., Miki, K., and Senda, M., Agric. Biol. Chem., 1988, 52, 2655.978 ANALYST, AUGUST 1993, VOL. 118 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Guo, L. H., Hill, H. A. O., Lawrance, G. A., Sanghera, G. S., and Hopper, D. J., J. Electroanal. Chem., 1989, 266, 379. Gorton, L. , Jonsson-Pettersson, G., Csorcgi, E., Johansson, K., Dominguez, E., and Marko-Varga, G., Analyst, 1992, 117, 1235. Sucheta, A., Ackrell, B.A. C., Cochran, B., and Armstrong, F. A., Nature (London), 1992, 356, 361. Sucheta, A , , Cammack, R., Weiner, J. H., and Armstrong, F. A., unpublished work. Armstrong, F. A., Bond, A. M., Hill, H. A. O., Psalti, I. S. M., and Zoski, C. G., J. Phys. Chem., 1989,93, 6485. Armstrong, F. A., Bond, A. M., Hill, H. A. O., Oliver, B. N., and Psalti, I. S. M., J. Am. Chem. SOC., 1989, 111, 9185. Biichi, F. N., and Bond, A. M., J. Electroanal. Chem., 1991, 314, 191. Bond, A. M., and Hill, H. A. O., in Metal Ions in Biological Systems, eds. Sigel, H., and Sigel, A., Marcel Dekker, New York, 1991, vol. 27, ch. 12, pp. 431-494. Bond, A. M., Anal. Proc., 1992,29, 132. Azzam, R. M. A., and Bashara, N. N., Ellipsometry and Polarized Light, North-Holland, Amsterdam, 1987. English, A. M., Laberge, M., and Walsh, M., Znorg. Chim. Acta, 1986, 123, 113. Yonetani, T., and Anni, H., J. Biol. Chem., 1987, 262, 9547. Armstrong, F. A., Adv. Znorg. Chem., 1992, 38, 117. Armstrong, F. A., Butt, J. N., and Sucheta, A., Methods Enzymol., in the press. Butt, J. N., Armstrong, F. A., Breton, J., George, S. J., Thomson, A. J., and Hatchikian, E. C., J. Am. Chem. SOC., 1991, 113, 6663. 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Northrup, S. H. , Reynolds, J . C. L. , Miller, C. M., Forrest, K. J., and Boles, J. O., J. Am. Chem. Soc., 1986, 108, 8162. Rothen, A., Prog. Surf Membr. Sci., 1974, 8, 81. Toth, K., Vuye, G., Vainer, H., Ronto, G., and Aslanian, D., J. Phys. C., 1983, 10, 521. Aspnes, D. E., in Microelectronics Processing, cd. Casper, L. A., (ACS Symposium Series, No. 295), American Chemical Society, Washington, DC, 1986, ch. 11. Strachan, C. S., Proc. Cambridge Philos. SOC., 1933, 29, 116. Dignam, M. J. and Moskovits, M., J. Chem. SOC., Faraday Trans. 2, 1973, 69, 56. Greef, R., Ber. Bunsenges. Phys. Chem., 1984, 88, 150. Bobbert, P. A., Vlieger, J., and Greef, R., Thin Solid Films, 1988, 164, 63. RuiiC, I., and Feldberg, S., J. Electroanal. Chem., 1974, 50, 153. RuiiC, I., J. Electroanal. Chem., 1983, 144, 433. Bard, A. J., and Faulkner, L. R., Electrochemical Methods; Fundamentals and Applications, Wiley, New York, ch. 6. Bond, A. M., Oldham, K. B., and Zoski, C. G., Anal. Chim. Acta, 1989, 216, 177. Gueshi, T., Tokuda, K., and Matsuda, H., .I. Electroanal. Chem., 1978, 89, 247. Gueshi, T., Tokuda, K., and Matsuda, H., J. Electroanal. Chem., 1979. 101, 29. Tokuda, K., Gueshi, T., and Matsuda, H., J. Electroanal. Chem., 1979, 102, 41. Paper 2106371 I Received November 30, 1992 Accepted February 3, 1993

ISSN:0003-2654    

DOI:10.1039/AN9931800973

出版商:RSC    

年代:1993

数据来源: RSC