ISSN:0003-2654    

DOI:10.1039/AN99520BP020

出版商:RSC    

年代:1995

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99520FX024

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

2888 Analyst, December 1995, Vol. 120 Xu, Xu-Qin, 1699 Xuejing, Xie, 1497 Yadav, R. B., 1099 Yamaguchi, Masatoshi, 1083 Yamamoto, Atsushi, 377, 1 137 Yaman, Mehmet, 101 Yaiiez-Lim6n. M., 1953 Yang, Jing-He, 2413 Yang, Jinghe, 1705 Yang, M. H., 1681 Yang, Yu, 243 Yao, Shouzhuo, 1885,2573,2833 Yau, Kei Wang, 1963 Yellig, Thomas J., 2775 Yermolaeva, T. N., 2387 Yilmaz, Selma, 1087 Yin, Wei, 2805 Yokota, Fumiaki, 2823 Young, Paul B., 2199 Yu, Ru-Qin, 499,2259,2829 Yuan, Ruo, 1055 Yuchi, Akio, 167 Zachariadis, George A,, 1593 Zachilas, Loukas N., 21 15 Zachwieja, Zofia, 943 Zagrodzki, Pawei, 943 Zaichick, Vladimir Ye., 8 17 Zaki, M. T. M., 549 Zamarreiio, M. M. Delgado, 2489 Zambenedetti, Pamela, 2425 Zambonin, Car10 G., 2185 Zambonin, Pier G., 2731 Zamrazil, Vklav, 959 Zanetti, Alberto, 1309 Zanoni, Maria Valnice B., 505 Zaratin, Laura, 1937 Zatta, Paolo F., 2425 Zelaya-Angel, O., 1953 Zen, Jyh-Myng, 5 1 1 Zhang, Aimei, 1195 Zhang, Fan, 121, 1699 Zhang, Feng-jun, 1603 Zhang, Shufen, 1599 Zhang, X.R., 463 Zhang, Yu-Hui, 2513 Zhang, Zhujun, 453, 2585 Zhao, Guohu, 2081 Zheng, Guo-Dong, 499 Zhi, Zheng-liang, 201 3 Zhou, Ge Rong, 2237 Zhu, Yu-rui, 2853 Zhuang, Hui-sheng. 121 Zolotov, Yury A., 201 Zuber, Paul A., 2873 Zufiaurre, Raquel, 75 12888 Analyst, December 1995, Vol. 120 Xu, Xu-Qin, 1699 Xuejing, Xie, 1497 Yadav, R. B., 1099 Yamaguchi, Masatoshi, 1083 Yamamoto, Atsushi, 377, 1 137 Yaman, Mehmet, 101 Yaiiez-Lim6n. M., 1953 Yang, Jing-He, 2413 Yang, Jinghe, 1705 Yang, M. H., 1681 Yang, Yu, 243 Yao, Shouzhuo, 1885,2573,2833 Yau, Kei Wang, 1963 Yellig, Thomas J., 2775 Yermolaeva, T.N., 2387 Yilmaz, Selma, 1087 Yin, Wei, 2805 Yokota, Fumiaki, 2823 Young, Paul B., 2199 Yu, Ru-Qin, 499,2259,2829 Yuan, Ruo, 1055 Yuchi, Akio, 167 Zachariadis, George A,, 1593 Zachilas, Loukas N., 21 15 Zachwieja, Zofia, 943 Zagrodzki, Pawei, 943 Zaichick, Vladimir Ye., 8 17 Zaki, M. T. M., 549 Zamarreiio, M. M. Delgado, 2489 Zambenedetti, Pamela, 2425 Zambonin, Car10 G., 2185 Zambonin, Pier G., 2731 Zamrazil, Vklav, 959 Zanetti, Alberto, 1309 Zanoni, Maria Valnice B., 505 Zaratin, Laura, 1937 Zatta, Paolo F., 2425 Zelaya-Angel, O., 1953 Zen, Jyh-Myng, 5 1 1 Zhang, Aimei, 1195 Zhang, Fan, 121, 1699 Zhang, Feng-jun, 1603 Zhang, Shufen, 1599 Zhang, X. R., 463 Zhang, Yu-Hui, 2513 Zhang, Zhujun, 453, 2585 Zhao, Guohu, 2081 Zheng, Guo-Dong, 499 Zhi, Zheng-liang, 201 3 Zhou, Ge Rong, 2237 Zhu, Yu-rui, 2853 Zhuang, Hui-sheng.121 Zolotov, Yury A., 201 Zuber, Paul A., 2873 Zufiaurre, Raquel, 75 12888 Analyst, December 1995, Vol. 120 Xu, Xu-Qin, 1699 Xuejing, Xie, 1497 Yadav, R. B., 1099 Yamaguchi, Masatoshi, 1083 Yamamoto, Atsushi, 377, 1 137 Yaman, Mehmet, 101 Yaiiez-Lim6n. M., 1953 Yang, Jing-He, 2413 Yang, Jinghe, 1705 Yang, M. H., 1681 Yang, Yu, 243 Yao, Shouzhuo, 1885,2573,2833 Yau, Kei Wang, 1963 Yellig, Thomas J., 2775 Yermolaeva, T. N., 2387 Yilmaz, Selma, 1087 Yin, Wei, 2805 Yokota, Fumiaki, 2823 Young, Paul B., 2199 Yu, Ru-Qin, 499,2259,2829 Yuan, Ruo, 1055 Yuchi, Akio, 167 Zachariadis, George A,, 1593 Zachilas, Loukas N., 21 15 Zachwieja, Zofia, 943 Zagrodzki, Pawei, 943 Zaichick, Vladimir Ye., 8 17 Zaki, M.T. M., 549 Zamarreiio, M. M. Delgado, 2489 Zambenedetti, Pamela, 2425 Zambonin, Car10 G., 2185 Zambonin, Pier G., 2731 Zamrazil, Vklav, 959 Zanetti, Alberto, 1309 Zanoni, Maria Valnice B., 505 Zaratin, Laura, 1937 Zatta, Paolo F., 2425 Zelaya-Angel, O., 1953 Zen, Jyh-Myng, 5 1 1 Zhang, Aimei, 1195 Zhang, Fan, 121, 1699 Zhang, Feng-jun, 1603 Zhang, Shufen, 1599 Zhang, X. R., 463 Zhang, Yu-Hui, 2513 Zhang, Zhujun, 453, 2585 Zhao, Guohu, 2081 Zheng, Guo-Dong, 499 Zhi, Zheng-liang, 201 3 Zhou, Ge Rong, 2237 Zhu, Yu-rui, 2853 Zhuang, Hui-sheng. 121 Zolotov, Yury A., 201 Zuber, Paul A., 2873 Zufiaurre, Raquel, 75 12888 Analyst, December 1995, Vol. 120 Xu, Xu-Qin, 1699 Xuejing, Xie, 1497 Yadav, R. B., 1099 Yamaguchi, Masatoshi, 1083 Yamamoto, Atsushi, 377, 1 137 Yaman, Mehmet, 101 Yaiiez-Lim6n.M., 1953 Yang, Jing-He, 2413 Yang, Jinghe, 1705 Yang, M. H., 1681 Yang, Yu, 243 Yao, Shouzhuo, 1885,2573,2833 Yau, Kei Wang, 1963 Yellig, Thomas J., 2775 Yermolaeva, T. N., 2387 Yilmaz, Selma, 1087 Yin, Wei, 2805 Yokota, Fumiaki, 2823 Young, Paul B., 2199 Yu, Ru-Qin, 499,2259,2829 Yuan, Ruo, 1055 Yuchi, Akio, 167 Zachariadis, George A,, 1593 Zachilas, Loukas N., 21 15 Zachwieja, Zofia, 943 Zagrodzki, Pawei, 943 Zaichick, Vladimir Ye., 8 17 Zaki, M. T. M., 549 Zamarreiio, M. M. Delgado, 2489 Zambenedetti, Pamela, 2425 Zambonin, Car10 G., 2185 Zambonin, Pier G., 2731 Zamrazil, Vklav, 959 Zanetti, Alberto, 1309 Zanoni, Maria Valnice B., 505 Zaratin, Laura, 1937 Zatta, Paolo F., 2425 Zelaya-Angel, O., 1953 Zen, Jyh-Myng, 5 1 1 Zhang, Aimei, 1195 Zhang, Fan, 121, 1699 Zhang, Feng-jun, 1603 Zhang, Shufen, 1599 Zhang, X. R., 463 Zhang, Yu-Hui, 2513 Zhang, Zhujun, 453, 2585 Zhao, Guohu, 2081 Zheng, Guo-Dong, 499 Zhi, Zheng-liang, 201 3 Zhou, Ge Rong, 2237 Zhu, Yu-rui, 2853 Zhuang, Hui-sheng. 121 Zolotov, Yury A., 201 Zuber, Paul A., 2873 Zufiaurre, Raquel, 75 1

ISSN:0003-2654    

DOI:10.1039/AN995200X026

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

1839 Generalized Method for Simultaneous Multicomponent Determinations Through a Single Catalytic KineticRun by Using the Rate Spectrum-Xian-De Wang, Zhi-Cheng Gu1843 Complexometric Determination of Thallium(rii) Using Sodium Sulfite as a Selective Releasing Agent-C. HRaghavan Nambiar, B. Narayana, B. Muralidhara Rao, Biju Mathew1847 CUMULATIVE AUTHOR INDEXNEWS AND VIEWS 73N Book Reviews79N Conference Diary84N Courses85N Papers in Future Issues86N Lists of Abbreviations and AcronymsCover picture: Nickel sulfide fire assay for precious metals (see p. 1675). Photograph kindly supplied by TheCentre for Analytical Research in the Environment, Imperial College of Science, Technology and Medicine

ISSN:0003-2654    

DOI:10.1039/AN99520BX030

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Analyst, June 1995, VoL. 120 73N Book Reviews Environmental Sampling for Trace Analysis Edited by Bernd Markert. Pp. xxx + 524. VCH. 1994. Price DM248.00; f99.00. ISBN 3-527-30051-1. This book contains a wealth of knowledge on sampling of all types of environment materials and I would thoroughly recommend it to environmental analytical chemists. Its principle strength is an emphasis on practical matters (includ- ing sampling costs, logisitics and unexpected environmental hazards, e.g., the likelihood of a sediment pore water sampler being uprooted by a curious catfish)! However, theoretical considerations are in no way neglected, and the literature reviewed is extensive and comprehensive. The book is generally well written. The text is divided into three sections. Part I is a short, historical review, and Part I1 a general discussion, whilst Part I11 (which forms the bulk of the book) deals with sampling various environment compart- ments: air, water, soils and sediments, and plants and animals.The rationale for the book (reiterated by many of the authors) is that, however good the analytical procedures applied to environmental samples, the validity of the results obtained will depend, critically, on the aptness of the samples for the particular study undertaken. Thus, it is important for analytical scientists to be aware of what constitutes good sampling practice. In Chapter 4, an account is given of methods to estimate sampling precision and bias so as to set realistic limits on the quality of data required for any particular study and, in Chapter 5 , a simple chemometrics approach is described to overcome errors associated with statistically incorrect handling of below-detection-limit results.The two chapters on air sampling discuss particle and gas measurement using filters (where results can vary widely depending on exactly how the particulate material is trapped for analysis) and sampling of organic gases (by both passive and active means). A useful list is included of those samplers that have passed US government tests for PMlo particle monitoring. Seven chapters are devoted to waters. Chapter 8 deals with general problems of freshwater sampling, such as contamina- tion from sampling equipment, and outlines the sampling methods available. The need to understand the dynamics of a water body (inflows, outflows, mixing and stratification) before deciding on a sampling strategy is exemplified in the following two chapters which deal with eutrophication man- agement and a case study of the highly polluted River Elbe.Waste water sampling is then discussed (a particularly good description of available automatic samples is included here) whilst the final two chapters deal with the problems associated with groundwater sampling. ‘contains a wealth of knowledge on sampling and I would thoroughly recommend it to en- vironmental analytical chemists’. The soils and sediments section begins with a discussion on how to use statistical methods (frequency, neighbourhood and variogram analysis) to determine the validity of a sampling grid. This is followed by a description of the development of the international standard for soil sampling, ISORC 90, then by a contribution on fixed versm hypothesis-driven soil sampling protocols. Specific advice is included on derivation of specialized, hypothesis-driven sampling plans based on the IHEARU scheme.The emphasis then moves to sediments with a description of corers, suspended sediment collectors, sedimendwater interface collectors and methods for pore water sampling (both in the laboratory and in situ). The final contribution to this section describes case studies involving contamination of rice-growing soils by industrial pollution. A recurring theme of the chapters dealing with plants is whether or not samples should be washed before analysis. This is discussed particularly extensively in Chapter 21.Amongst the factors also important in constructing a valid plan for sampling plants are knowledge of (i) plant physiology (to determine which tissues to collect), (ii) genetics (in particular, the occurrence of clonal forms), and (iii) agehtage in growth or reproductive cycle. Particular problems are experienced in sampling fine roots and in obtaining representative samples from lichen thalli and moss cushions. Although the latter are excellent bioindicators, metal concentrations vary both within and between neighbouring growths. Chapter 23 introduces the concept of multi-element cadas- tar investigations, where developments in chemical analysis are allowing ecologists to determine the chemical composition of components (e.g., plants, soils etc.) of characteristic ecosystems throughout the globe; information which can be used, for example, to tell where particular metals are accumulated in the biomass. The importance of obtaining representative samples for use in this type of research cannot be over-estimated. Next, is a contribution on sampling tropical plants (those from remote, montane forests may give an excellent indication of trends in global atmospheric pollution) and a chapter on the importance of throughfall and, in particular, stemflow, in influencing soil properties (pH, plant and animal population) close to the base of trees. The final chapter (and, unfortunately, the only one dealing with sampling animal populations) concens Red Wood ants where indications of the effects of pollution can only be gained through understanding of the social structure of the ant colony.Christine Davidson University of StrathcLyde GLasgow, UK Practical Surface Analysis. Second Edition Edited by D. Briggs and M. P. Seah. Volume 1. Auger and X-ray Photoelectron Spectroscopy. Pp. xiv + 658. Wiley. 1994. Price f49.95. ISBN 0-471-95340-7. Practitioners of Auger electron spectroscopy (AES) and X- ray photoelectron spectroscopy (XPS) will certainly be familiar with the first edition of this book, which has now become established as a standard working text in most surface science laboratories. This is not without good reason. The first edition successfully combined a description of the principles behind each method and the fundamentals of quantitation, with real examples taken from both academic and industrial areas of interest.This comprehensive though concise approach, has been preserved in the second edition in which the contributing authors effectively trace the development of each technique from their historical origins in solid-state physics, to their current impact in the fields of metallurgy, heterogeneous catalysis, polymer technology and corrosion studies. The book is structured into ten chapters plus nine appen- dices that provide more detailed considerations of the problems associated with spectral interpretation, curve fitting and calibration. For example, Chapters 1-5, in effect, establish the techniques to the reader by outlining their74N Analyst, June 1995, VoE. 120 evolution from early work in low energy electron diffraction and studies of the photoelectric effect, describing the instru- mental techniques necessary for efficient electron counting and spectral accummulation and finally, developing the theoretical bases for spectral interpretation and quantitation.It is within this section that the practicalities of achieving the ultra-high vacuum conditions (UHV) are treated, as well as the various methods available for the in situ production of near atomically clean surfaces. The later chapters (3-5), concen- trate on the use of spectral data to elucidate chemcial state and establish surface atomic compositions. Accordingly, the reader is re-introduced to the fundamentals of atomic structure and the origins of the energy loss processes that are responsible for the principal spectroscopic features, as well as the secondary effects arising from energy level perturbations and diffraction. The interpretation of such effects is exempli- fied by references to valence band studies of polymer systems, the use of binding energy shifts to reveal oxidation state, and the use of ‘shake-up/shake-off‘ features in the study of organic systems involving n-n* transitions.Chapter 5 addresses the question of quantification by developing some of the fun- damental relationships between measured spectral intensity and surface atomic composition. Practical examples are chosen from XPS analysis to demonstrate the principal methods adopted for inelastic background correction and peak area quantitation using established values for photoemis- sive atomic cross-sections.Some of the ideas in this chapter are developed further in Appendix 3 which focuses on data analysis in both XPS and AES. ‘The f i t edition successfully combined a des- cription of the principles behind each method and the fimdamentals of quantitation; this com- prehensive though concise approach, has been preserved in the second edition’ The remaining chapters (6-10) concentrate on the applica- tion of XPS and AES in diverse fields of industrial interest. Thus, the application of AES to quality control problems in the microelectronics industry, is described with studies of passivation, diffusion, material bonding and etching. The use of AES in metallurgical studies is exemplified by measure- ments of atomic segregation including kinetic studies of mobility in a variety of complex metal-alloy systems. The practical consequences of atomic segregation are described in terms of material failure mechanisms such as embrittlement and stress corrosion cracking. The subject of heterogeneous catalysis provides special challenges for the practising spectro- scopist since here, the analyses frequently involve studies of mixed metal-insulator systems and the attendant problems of differential charging.In addition, consideration must be given to the possibility of actually inducing surface compositional changes through beam damage and the use of UHV, resulting in the analysis of entirely unrepresentative surfaces. Both issues are addressed in Chapter 8 with examples chosen from Pt-based and zeolite-based catalytic systems.The bulk of the volume finishes with descriptive accounts of the use of both techniques in polymer analysis showing, for example, the use of valence band spectra as a fingerprint for polymer structure elucidation. In the study of corrosion, techniques for improv- ing spatial resolution, quantification and the method of depth profiling are exemplified through numerous systems involving metals largely from the first and second transition series. The series of appendices, that bring the book to an end, provide useful practical guidance in the achievement of energy scale calibration, charge referencing, curve-fitting and decon- volution, and the use of AES chemical shifts in structure determination. Finally, the book provides a useful database of the principal photoelectron and Auger energies, atomic sensitivity factors and spectral line positions derived from the most widely used Mg and A1 X-ray sources. As with the first edition, this book is destined to become the much dog-eared, over-subscribed text in all surface analysis laboratories, providing students and established spectro- scopists alike with an easy reference manual for ‘Practical Surface Science’.Stephen Bailey ICI Katalco Cleveland, UK Spectroscopic Techniques for Food Analysis Edited by Reginald H. Wilson. Pp. xv + 246. VCH. 1994. DM1 65.00. ISBN 1-56081 -037-8. An overview of the general principles of spectroscopic analysis in which both established and newer techniques are classified according to the type of information they provide is given in Chapter 1 and includes a tabulated guide to spectroscopic methods used in food science.Within the core of the book the subsequent six chapters cover near-infrared, mid-infrared, NMR, atomic, mass and UVNIS spectroscopy. The theory associated with each technique, the types of instrumentation available, the advantages and limitation and the scope for future developments are discussed. Sampling techniques, detection, calibration and the application of chemometric methods (where appropriate) are generally well covered. As is claimed on the cover notes, there are numerous illustrative examples of real food applications providing insight to new approaches and problem solving. The applica- tion of spectroscopy to both the analysis of macro food components such as water, proteins, lipids and poly- saccharides and micro food components such as nutrients, additives, contaminants and toxicants is comprehensively covered with reference to their nutritional, physiological, toxicological and functional properties. The determination of metallic elements by emission, absorption and other atomic spectroscopic techniques (e.g., ICP-MS) is well covered and is illustrated with several worked examples for the identification and measurement of minerals, trace metals, and toxic elements in foods.The chapter on UVNIS spectroscopy is restricted to methods where it is the predominant technique, i.e., not including chromatographic methods. Food-specific applica- tions are presented mostly in tabular form and cover general food categories, enzymic methods and various classes of micro components.The chapter on mass spectroscopy is well presented and a comprehensive range of applications is given, many of them employing GC-MS methods. ‘recommended as a collective reference text for all practising food analysts and food scientists who wish to keep abreast of the latest develop- ments in this area.’ The book essentially achieves its aim to provide a critical review of the latest state-of-the art spectroscopic techniques used for food analysis, but in a somewhat disparate manner. The coverage across the different spectroscopic disciplines is inconsistent both in depth and style. The theoretical discus- sion gets a little bogged-down with formulae in some areas and requires repeated reading.For example, the chapter on NMR techniques, by far the largest in the book, includes detailed discussion of highly specialized experimental techniques suchAnalyst, June 1995, Vol. 120 75N as relaxation measurements. Conversely, the chapter on UVI VIS spectroscopy only provides a very basic treatment of the Beer-Lambert law, no examples of UVNIS spectra are given and derivative techniques and calibration procedures are given only a mention. Nevertheless, there has been a void in the literature for a collective reference work on this subject and this book goes a long way towards filling it. It is generally very well written and contains both extensive reference listings, bibliographies and a concise index. At the front of the book is a strategically placed and useful comprehensive glossary of technical abbre- viations.The figure, diagrams and spectra are reproduced clearly which is important in a work of this nature. It is recommended as a collective reference text for all practising food analysts and food scientists who wish to keep abreast of the latest developments in this area and represents excellent value for money. Michael J. Scotter Ministry of Agriculture, Fisheries and Food CSL Food Science Laboratory Norwich, UK Food Microscopy By Olga Flint. Royal Microscopical Society. Microscopy Handbook 30. Pp. xii + 126. BlOS Scientific Publishers. 1994. Price f 14.50; US$29.00. ISBN 1-872748-04-X. This is an excellent monograph for microscopists with problems to solve, and achieves exactly what it sets out to do, i.e., documenting thoroughly, well tried equipment and techniques for light microscopy in food systems, using commercially available materials and methods. Indeed, because of the careful attention to detail, it is possible that a beginner, with little previous experience in equipment or techniques, could become a proficient microscopist by careful study of this handbook. ‘This will become a classical reference which should probably be part of every food scientist’s library.’ The author adopts a direct and simple approach suggesting ‘that the less is done to the specimen the better’. This is particularly true in foods containing fat where histological methods have been modified to minimize specimen distortion. The chapter on frozen sectioning also describes developments specifically directed towards food materials.Similarly, the value of using iodine vapour to eliminate the problems of starch swelling accompanying the use of aqueous iodine stains is included. Perhaps the only disappointment is that the monochrome figures do not adequately represent the clarity of information that certainly must have been present in the original stained sections, such as those in the Frontispiece. This will become a classical reference which should probably be part of every food scientist’s library. Peter J. Lillford Unilever Research Bedford, UK Analytical Chemistry. 5th Edition By Gary D. Christian. Pp. xx + 812. Wiley. 1994. Price f 18.95. ISBN 0-471-30582-0. This book is designed for undergraduates who are studying chemistry and courses related to Chemistry.The text consists of twenty-two chapters, the first nine dealing with the important basic techniques and principles including: statistics; stoichiometric calculations; acid-base equilibria; complexometric and precipitation titrations. The next four chapters cover electrochemical principles and techniques. These adequately cover potentiometry and ion- selective electrodes and the author has brought this section up- to-date by briefly describing coated-wire electrodes as well as enzyme-coated electrodes (biosensors). However, voltam- metric techniques are given only scant attention with no mention of pulse, square-wave, or stripping voltammetry. There are, however, new sections on ultra-microelectrodes and chemically modified electrodes which briefly introduce the concepts of electrocatalysis and permselectivity .The next chapter covers spectrometry and new topics include, Fourier transform infrared (FTIR) spectrometry, near-infrared instru- ments, diode array spectrometers, and fibre optic sensors. Atomic spectrometric methods are the subject of Chapter 15 and both emission and absorption methods are suitably covered. This is followed by a chapter on solvent extraction which is brought up to date by the inclusion of solid phase and flow injection methods. Chapter 17 covers the area of chromatographic methods and, after a short historical intro- duction, there follows a brief discussion on principles and the different types of chromatography. Two new topics are included in this section namely, supercritical fluid chromato- graphy and capillary electrophoresis.This is followed by a short chapter describing automation in the laboratory. The subject of the next chapter is clinical chemistry and the emphasis is on the practical aspects of analysing some different types of biological material. Included in this chapter is a section on immunoassay which serves as a useful introduction into this area of growing analytical importance. The next chapter, which covers environmental analysis, briefly des- cribes some techniques used to collect and determine air and water pollutants. The final chapter deals with the basic tools and operations of analytical chemistry and includes use of the balance, calibrated glassware, drying ovens and filters. ‘Bearing in mind its modest cost, this text would be a very useful addition to the library in any university where analytical chemistry forms part of the curriculum.’ At the end of each chapter there are a set of questions to test the student’s understanding of the subject, as well as some helpful recommended references.There are also a number of worked examples throughout the text to illustrate the use of important equations. In addition, a total of forty-four experiments are described which involve the application of the techniques previously discussed. Bearing in mind its modest cost, this text would be a very useful addition to the library in any university where analytical chemistry forms part of the curriculum. John Hart University of the West of England Bristol, UK Neural Networks for Chemists. An Introduction By Jure Zupan and Johann Gasteiger.Pp. xix + 306. VCH. 1993. Price DM68.00; f 28.00. ISBN 3-527-28603-9. In recent years there has been an increasing number of publications using artificial neural networks (ANNs) for a broad range of applications including pattern recognition and modelling. However, the study of ANNs and artificial intelligence in general tends to be interdisciplinary, using76N Analyst, June 1995, Vol. 120 terminology and concepts which are likely to be alien to most chemists. With the increasing interest in ANNs there has been an apparent profusion of text-books describing different ANN architectures and training algorithms. This book, however, takes a different approach to the subject by targetting the chemistry audience in an attempt to make ANNs more accessible.It deals initially with the basic principles and terminology underlying ANNs, starting at the scale of the individual neurons then moving to the broader scale of connecting neurons to form networks. The focus then shifts to a range of specific types of networks with a single layer architecture, namely Hopfield, BAM and Kohonen networks. The book then deals with networks having a multi-layer architecture namely the counterpropagation network and the extremely popular feedforward network using back-propagation train- ing. ‘The attractive and clear presentation of this book make it recommendable for the complete novice. However, for those considering using ANNs, it is likely that further reading would be needed before attempting to tackle “realYY problems.’ The last section of the book deals with specific examples of chemical applications of ANNs.These examples tend to be grouped according to the nature of the underlying problem, rather than their relevance to particular chemical sub-disci- plines. This approach reflects an attempt to foster a greater understanding of the types of problems which can be tackled by ANNs. The examples range from classification problems (e.g., the identification of the region of origin of olive oil samples according to their fatty acid composition) to modell- ing problems (e.g., prediction of the effect of mobile phase composition on the separation achieved with a particular HPLC column). The chapters are clearly laid out, each chapter starting with a description of its objectives and finishing with a summary of its major points and equations. The descriptions of the different types of networks appear rather basic.Given the popularity of the back-propagation algorithm for training feedforward networks, a more comprehensive discussion of the practical aspects of using this algorithm would have been desirable. The attractive and clear presentation of this book make it recommendable for the complete novice. It makes the terminology and concepts associated with ANNs less intimi- dating and more accessible for chemists. However, for those considering using ANNs, it is likely that further reading would be needed before attempting to tackle ‘real’ problems. Margaret Hartnett Dublin City University Dublin, Ireland and on computer modelling. The book continues with separate chapters discussing speciation with respect to the atmosphere, freshwaters, soils, biological systems and of radionuclides. It is somewhat suprising that the editors have not included a chapter that specifically discusses chemical speciation in marine or estuarine systems, an important area for research.In my opinion, this a significant omission. The individual chapters provide a sound assessment of each topic area. The chapter on general strategies for speciation reviews briefly the options open to scientists wishing to investigate speciation, paying due attention to the advantages and limitations of each option. This chapter also includes an assessment of electrochemical methods. The techniques for the determination of speciation are divided into a review discussing direct methods, where the species are determined on the sample without preliminary separation methods (e.g., NMR infrared and Raman spectroscopy) and a chapter concerning indirect or hybrid methods for speciation, where a separation step (usually chromatographic) is combined with an on-line, sensitive, element specific detector (e.g., GC- AAS, HPLC-ICP-MS). Each of these sections benefits (as does the whole book) from an up-to-date and informative bibliography.The capabilities of computer models for specia- tion studies are outlined in a user-friendly review that explains clearly the principles behind, and realistic capabilities of, computer-based techniques. ’provides a clear introduction to the need for speciation studies and outlines the full range of techniques available to investigate chemical speciation.’ The reviews of the environmental compartments are generally thorough and provide a solid introduction to the important chemical species and the relevant physical, chemi- cal and biological processes influencing chemical speciation. The final section on trends and developments provides an excellent conclusion to the book in tying together the individual chapters and in filling some of the gaps that may be present in the earlier chapters.In particular it provides some discussion of speciation in marine systems and briefly dis- cusses, along with other elements, the speciation of arsenic, including arsenic metabolism in biota, a topic notable by its omission in the chapter discussing biological systems.Overall, this is a useful book which provides a good summary of the field of chemical speciation. It provides a valuable summary of a rapidly moving subject and will be a valuable addition to the libraries of those wishing to develop expertise in this field and to those wishing to extend their understanding of chemical speciation. S . T. Sparkes Somerset Scientific Services Taunton, UK Chemical Speciation in the Environment Edited by A. M. Ure and C. M. Davidson. Pp. xiii + 408. Blackie. 1995. Price f79.00. ISBN 0-7514-0021-1. Analytical Applications of lmmobilised Enzyme Reactors Edited by S. Lam and G. Malikin. Pp. xii + 276. Blackie Academic and Professional. 1994. Price f65.00. ISBN 0- 7514-0026-2.The authors of this book have made a bold attempt to present an overview of chemical speciation in the environment. The book provides a clear introduction to the need for speciation studies and outlines the full range of techniques available to investigate chemical speciation, with separate chapters on speciation strategies, direct and indirect analytical techniques This volume consists of ten chapters by different international authors. It describes the design and use of immobilized enzyme reactors (IMERs) for use in liquid chromatography systems. These reactors may be used after chromatographic separation in order to produce improved detection charac-Analyst, June 1995, Vol. 120 77N teristics, or before the chromatographic separation to improve the separation process.Often they are employed to produce chromophores or fluorophores from poorly absorbing and non-fluorescing analytes. Many immobilized enzyme reactors utilize dehydrogenases, producing changes in absorption at 340 nm, oxidases producing fluorophores or enzymes that produce electrochemically detectable molecules. The specific- ity of the enzyme is used to improve the selectivity and sensitivity of the molecules of interest in the chromatographic separation. This book will do much to dispel the myth that such systems are inherently difficult to set up and unreliable and unstable in use. ‘Overall, this book presents a very useful and well referenced introduction to the use of IMERs in chromatography.’ The first chapter introduces the topic and gives an outline of the theoretical and preparative background.This is followed by chapters on specific areas of application. Details are given for the analysis of carbohydrates, amino acids, nitrogenous metabolites such as uric acid, hydroxysteroids, bile acids, ethanol, glucuronide and sulfate conjugates, aldehydes and zinc. Generally, the relative advantages of IMERs over other methods of detection are mentioned only briefly, the text concentrating on the IMER applications. In many cases, details of the chromatographic separations (e.g., HPLC) are also given. The use of IMERs to amplify signals by substrate recycling is also covered. Overall, this book presents a very useful and well referen- ced introduction to the use of IMERs in chromatography. It is brimming with references up until about 1992.I recommend it to analysts, or potential analysts, in this field as it should retain its usefulness for several years and it should aid new ideas and provoke further research. It is particularly useful to analysts working in any of the areas mentioned above who are not happy with the sensitivity of their present methods. M . F. Chaplin South Bank University London, UK published a second edition of this book for the benefit of the scientific and technological community. ‘Advances in process development are now treated more completely and emphasis is placed on engineering detail so that the book serves as a handbook for process design.’ The second edition is an impressive text comprising 286 pages and offering an exhaustive coverage of the field of ion exchange.There are now 10 chapters covering the basic fundamentals of ion exchange and providing just enough theoretical detail with sufficient rigour to satisfy the student and the practitioner. Advances in process development are now treated more completely and emphasis is placed on engineering detail so that the book serves as a handbook for process design. I like the idea of specific boxes in the text which describe experiments and demonstrations which can be read separately from the main text. There are many interest- ing examples which can be used as the basis of a teaching exercise or as worked examples. The book is well written in a concise and easy to read style with clear drawings and graphical presentation. I can strongly recommend it to teachers and to academics who need to have a supporting text to stimulate interest in the subject matter.Students will find the book a valuable starting point in their work, especially if they are about to embark on a practical or reasearch project. There is always a temptation to pick up a more advanced text which can be daunting. This book will help to introduce the subject at just the right level for most people in school, university and industry. It is published in paperback at a very competitive price and I strongly recommend it. Michael Streat Department of Chemical Engineering Loughborough University of Technology, UK Ion Exchange: Theory and Practice. Second Edition By C. E. Harland. Pp. xv + 286. Royal Society of Chemistry. 1994. Price f 16.95.ISBN 0-85186-484-8. Ion exchange is a fascinating subject that still attracts considerable research interest and remains an important industrial technology in applications ranging from water treatment to the separation of biopharmaceutical products and the most elegant of chromatographic analyses. The teaching of ion exchange is spasmodic and not always systematic at school or at university. There is a lack of good basic reference books written in a style suitable for the student or practitioner seeking to understand the underlying prin- ciples. In 1975, the Chemical Society published a monograph for teachers by Grimshaw and Harland, which is the first edition of this book. It was then a wonderful little book comprising just 90 pages of basic information designed to help students and teachers grasp the essential principles of ion exchange.I have often recommended this booklet to my students as a first reference to the subject and I know of no other source material that is presented at an appropriate level as a starter text. There has been considerable advance in the last 20 years and I am delighted to find that Harland has now Inspired Characteristic Group Frequencies. Tables and Charts. Second Edition By G. Socrates. Pp. viii + 249. Wiley. 1994. Price €50.00. ISBN 0-471 -94230. This is the second edition of the popular book found in most well equipped spectroscopy laboratories. The main change from the first edition is the inclusion of a section concerning spurious peaks. This is a welcome reminder to users old and new that not everything shown on the trace really belongs to the sample under investigation.Peak arising from both optical and chemical effects are discussed. It could be argued that much more could have been made of these points and in particular something about artefacts arising from spurious use of deconvolution routines and other programs would have been useful. There are, after all, quite a few published spectra based on incorrect application of new technologies. ‘should be present in any serious laboratory dealing with vibrational spectroscopy.’ These points are germane to the very existence of this book, since a new user might be tempted to think ‘why bother with all these correlation charts when a quick computer search gives the best ten matches for my spectrum?’.The author does not address these points directly, but one answer has to be concerned with new compounds that could never be matched78N Analyst, June 1995, Vol. 120 on the library. Another answer is to observe that the question misses the point. Books such as this are meant to illuminate the chemical structure, not merely to match absorbances point-by-point. In computer terms, it is more of an ‘expert- system’ than an alternative to a library search. Now there is an opportunity for the third edition, CD charts and searching. Anyway, returning to the present volume, all the sections have been updated with many more species added. In particular, the section on inorganic compounds and complexes has been extended. The book remains a useful volume and should be present in any serious laboratory dealing with vibrational spectroscopy.J. E. Newbery University of Greenwich London, UK Asphaltene Particles in Fossil Fuel Exploration, Recovery, Refining and Production Processes By Mahendra K. Sharma and Teh Fu Yen. Pp. viii + 244. Plenum. 1994. Price US$75.00. ISBN 0-306-44709-6. This book comprises eighteen selected papers presented at the International Symposium on Asphaltene Particles in Fossil Fuel Exploration, Recovery and Production Processes, spon- sored by the Fine Particle Society (Las Vegas, July 13-17, 1992). The papers are divided into four broad categories: 1, Bitumen and coal-derived asphaltenes; 2, Asphalt and asphal- tene conversion; 3, Surface and colloidal aspects of asphal- tenes; and 4, thermodynamic and molecular aspects of asphaltenes.Whatever the classification may be, the under- lying topic is the well known, but until now unresolved, problem of the flocculation and aggregation of asphaltenes. A great part of the contributions are concerned with colloidal properties, asphaltene-maltene interactions and their implica- tions in asphalt utilization, upgrading and oil recovery processes. Two papers used structural 13C and 1H NMR parameters of asphalts and asphaltenes. Lian et al. suggest, for the classifica- tion of asphalts in sol, gel and sol-gel types, instead of the classical penetration index, the relationship between NMR aromaticity and H/C atomic ratios. The results obtained from only six samples are not convincing, even when compared with 28 other data cited in the literature.In order to correlate the amount of sludge formed during heavy oil conversion (in laboratory tests) to the molecular structure of asphaltene and resins, Storm et al. developed single molecule representations based on elemental composition, and classical NMR paramet- ers. They proposed a function linking the amount of sludge to these data. Colloidal properties of asphaltenes were investigated. The already known relationship between asphaltene concentration and viscosity of bitumen was confirmed by the rheological study by Chakman et al., taking into account the shear rate, the asphaltene concentration and average molecular weight. The self-association of asphaltenes and the interactions between asphaltenes and resins acting as peptizing agents were developed by means of several techniques.By surface tension measurements, Sheu et al. conclude that asphaltenes are surfactant-like components in petroleum and that the classical picture of an asphaltenic core, with a maltene-coated surface, is not necessarily true. The same groups used small- angle neutron and small-angle X-ray scatterings to study the structure, polydispersity , interactions with colloids in organic solvents and solvation of asphaltenes. The diffuse behaviour, studied by Ravi-Kumar et al., confirmed that asphaltenes are polydispersable entities, con- sisting of many components with a broad range of transport coefficients. The nature of the intermolecular forces holding asphaltene molecules together was estimated by solubility parameters by Lin et al., the dispersion forces being the most significant intermolecular force.This study pointed out the conditions of compatibility required for an additive to reduce the aggregation. A molecular thermodynamic model was developed by Kamath et al. to represent asphaltene equilibria and to predict the amount of asphaltene precipitation that would occur from a reservoir oil under the influence of a miscible solvent or immiscible gas. The model had four parameters, which were determined by fitting the model to experimental asphaltene precipitation in oil-solvent mixtures of a given origin. It would be interesting to test the model in other experimental cases. The role of asphaltene precipitation during bitumen mobili- zation with a solvent, in the presence of a bottom-water zone, in thermal enhanced oil recovery, was the subject of a numerical simulation.Carter et al. assumed that this precipita- tion improves bitumen recovery by plugging the bottom-water zone. A new mechanism of fluid flow in solution-gas drive heavy oil reservoirs had been identified through experimental studies and a new mathematical model was proposed in order to describe peculiar pressure-dependent multi-phase flow properties. Islam et al. claimed that asphaltenes and high confinement pressure contribute to the formation of micro- bubbles and higher oil recovery. ‘a great deal of various aspects of the colloidal properties of asphalt and asphaltenes were presented.’ The effects of asphaltenes on natural and accelerated ageing of bitumen were studied by Choquest et al. by monitoring generic composition using classical extraction liquid chro- matography and the ‘spot test’ technique (which is not new as it derives from the norme ASTM D 2781-72). The conditions for laboratory ageing were established and confirmed by a kinetic approach. The fate of asphaltenes in the co-processing reactions of coal and bitumen, in catalytic and non-catalytic conditions was studied by Charma. Unfortu- nately, too many errors make the interpretation of the results doubtful. The same topic of upgrading of petroleum and coal asphaltenes was considered by Ling et al. who showed an enhanced oil recovery by using surfactants and ultrasound, and also the contribution by surfactants to reduce the agglomeration of coal particles and coal-derived asphaltenes in the coal liquefaction process. The production of air blown asphalt within a short time, under ultrasound in the presence of potassium superoxide and of a catalytic amount of ferrous sulfate, was described at a small laboratory scale, by Lian et al. The same authors applied the well known thin layer chroma- tography with flame ionization detector (chromatotron or latroscan) to the fractionation of asphalt. The use of asphalt cement to stabilize contaminants in petroleum hydrocarbon affected contaminated soil (PHAS) was studied by Conca et aE., in order to demonstrate that contaminants, especially metals, will be retained by the asphalted PHAS. In conclusion, a great deal of various aspects of the colloidal properties of asphalt and asphaltenes were presented. Though some subjects are mainly a confirmation of previous results this book affords interesting developments which may be starting points for further studies. D. Cagniant Universite‘ de Metz, France

ISSN:0003-2654    

DOI:10.1039/AN995200073N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Analyst, June 1995, Vol. I20 79N Conference Diary Date 1995 July 2-6 2-7 9-13 9-14 9-15 10-13 30-518 Conference VII International Congress of Toxicology 12th International NMR Meeting 3rd International Symposium on Applied Mass Spectrometry in Health Sciences and 3rd European Tandem Mass Spectrometry Conference 13th Australian Symposium on Analytical Chemistry/4th Environmental Chemistry Conference SAC 95 Vth COMTOX Symposium on Toxicology and Clinical Chemistry of Metals XXIInd International Conference on Phenomena in Ionized Gases August 5-10 6-1 1 13-17 14-16 20-25 27-219 Location Seattle, USA Manchester , UK Barcelona, Spain Darwin, Australia Hull, UK Vancouver, Canada Hoboken, USA 1995 International Symposium on Soil and Plant Analysis The Netherlands Wageningen, NIR '95-The Future Waves Montreal, Canada ICFIA '95,7th International Conference on Flow Injection Analysis and JAFIA, Japanese Seattle, Association for Flow Injection Analysis USA 41st International Conference on Analytical Science and Spectroscopy Canada Windsor, 12th International Symposium on Plasma Chemistry Minneapolis, USA CSI XXIX: Colloquium Spectroscopicum Leipzig, Internationale Germany Contact Jada Hill, The Sterling Group, 9393 W, 110th Street, Suite, Overland Park, KS 66210, USA Tel: +1913 345 2228.Fax: +1913 345 0893 Dr. J. E. Gibson, Royal Society of Chemistry, Burlington House, Piccadilly , London, UK W1V OBN Tel: +44 (0)171437 8656. Fax: +44 (0)171 734 1227 Professor Emilio Gelpi, Palau de Congressos, Departamento de COnvencions, Avda, Reina Ma Christina, O8004 Barcelona, Spain 13AC/4EC, Symposium Secretariat, Convention Catalyst International, G.P.O.Box 2541, Darwin "I' 0801, Australia Tel: +6189 811 875. Fax: +6189 411 639 Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 (01171 437 8656. Fax: +44 (0)171 734 1227 F. William Sunderman, Jr., M.D., Departments of Laboratory Medicine and Pharmacology, University of Connecticut Medical School, P.O. Box 1292, Farmington, CT 06034-1292, USA Tel: +1203 679 2328. Fax: +1203 679 2154 E. E. Kunhardt, Physics Department, Stevens Institute of Technology, Hoboken, NJ 07030 USA Tel: +1201216 5099. Fax: +1201216 5638 Soil and Plant Analysis Council,, Georgia University Station, P.O. Box 2007, Athens, GA Tel: + 1 706 546 0425.Fax: + 1 706 548 4891 NIR '95, The Canadian Grain Commission, Grain Research Laboratory, 1403-303 Main Street, Winnipeg, Manitoba, Canada R3C 3G8 30612-2007, USA Gary D. Christian, Department of Chemistry, BG-10, University of Washington, Seattle, WA 98195, USA Tel: + 1 206 685 3478. Fax: + 1 206 543 5340. E-Mail: christia@chem.washington.edu William E. Jones, Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada N9B 3P4 L. Graven, 315 Pillsbury Drive, SE, University of Minnesota, Minneapolis, MN 55455-0139, USA Tel: +1 612 625 9023. Fax: +1 612 626 1623 GDCh-Geschiiftsstelle, Abt. Tagungen, Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358. Fax: +49 69 791 747580N Analyst, June 1995, Vol.120 Date Conference Location Contact 27-119 46th Annual Meeting of the International Xiamen, Secretariat, XLVIth ISE Annual Meeting, Society of Electrochemistry (ISE46) China P.O. Box 1995, Xiamen University, Xiamen 361005, China Tel: +86 592 208 5349. Fax: +86 592 208 8054 Resonance Microscopy Germany Wurzburg, Am Hubland, D-97074 Wiirzburg, 27-119 Third International Conference on Magnetic Wiirzburg, Dr. A. Haas, Physikalisches Institute, Universitat Germany EUROTOX '95, P.O. Box 88, Sokolska 31,120 26, Prague 2, Czech Republic Tel: +42 2 24 915195. Fax: +42 2 24 216836 27-30 EUROTOX Prague, Czech Czech Medical Association J. E. PurkynC, Republic September 1-4 3-6 3-8 5-8 6-8 6-9 10-14 12-15 12-16 17-20 17-21 24-28 CSI XXIX, Post-symposium ICP-MS and 11th German ICP-MS Users Meeting Wernigerode, Germany Third International Meeting on Recent Louvain la Advances in Magnetic Resonance Application Neuve, to Porous Media Belgium 6th European Conference on the Villeneuve Spectroscopy of Biological Molecules d' Ascq , France RSC Autumn Meeting.Analytical and Sheffield, Faraday Symposium: Ions in Solution UK 5th Symposium on Chemistry and Fate of Modern Pesticides France Paris, Joint Meeting of the Royal Society of Chemistry Fast Reactions in Solution Discussion Group and the Molecular Spectroscopy Group on Ultrafast Processes in Laser Spectroscopy Ion-Ex '95, The Fourth International Conference and Industrial Exhibition on Ion Exchange Processes Nonvich, UK Wrexham, UK 5th International Symposium on Drug Leuven, Analysis Belgium European Symposium on BiOS Europe '95: The European Biomedical Optics Symposium Week Barcelona, Spain 6th Surrey Conference on Plasma Source Spectrometry UK Jersey, 109th AOAC International Annual Meeting and Exposition USA Tennessee, 11th Asilomar Conference on Mass Spectrometry-Molecular Structure USA Determination: Activation, Mass Analysis and Detection Pacific Grove, Professor Lieselotte Moenke, Department of Chemistry, Martin-Luther University, Halle- Wittenberg, Institute of Analytical and Environmental Chemistry, Weinbergweg 16, D-06120 Halle, Germany Professor J.M. Dereppe, Universite de Louvain, Place Louis Pasteur 1, B-1348, Louvain la Neuve, Belgium Professor J. C. Merlin, ECSBM '95, LASIR, UST Lille BBt.C5, 59655 Villeneuve d'Ascq Cedex , France Dr. J. F. Gibson, The Royal Society of Chemistry, Burlington House , Piccadilly , London, UK W1V OBN Tel: +44 (0)171 437 8656. Fax: +44 (0)171734 1227 Mrs. Frei-Hausler, IAEAC Office, Postfach 46, CH-4123 Allschuril2, Switzerland Fax: +4161482 08 05 Professor B. H. Robinson, School of Chemical Sciences, University of East Anglia, Nonvich, UK NR4 7TJ Ion-Ex '95 Conference Secretariat, Faculty of Science, The North East Wales Institute, Connah's Quay, Deeside, Clwyd, UK CH5 4BR Fax: +44 (0)1244 814305 Professor J. Hoogmartens, Institute of Pharmaceutical Sciences, Van Evenstraat 4, B-3000 Leuven, Belgium Tel: +32 16 32 34 40. Fax: +32 16 32 34 48 Ms. Karin Burger, BiOS Europe '95, EUROPTO Series, c/o Direct Communications GmbH, Xantener Strasse 22, D-10707 Berlin, Germany Tel: +49 30 881 50 47.Fax: +49 30 881 50 40 E-Mail: Burger, 100140.321 l@compuserve .com Dr. Kym Jarvis, NERC ICP-MS Facility, CARE, Imperial College, Silwood Park, Ascot, Berkshire, UK SL5 7TE Tel: +44 (0)1344 294517/6. Fax: +44 (0)1344 873997 Meetings and Education Department, AOAC International, 2200 Wilson Boulevard, Suite 400, Arlington, Virginia, 22201-3301, USA Tel: + 1 703 522 3032. Professor R. Graham Cooks, Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette, IN 47907, USAAnalyst, June 1995, Vol. 120 81N Date Conference Location Contact 25-28 5th Symposium on 'Kinetics in Analytical Moscow, Dr. I. F. Dolmanova, Analytical Chemistry Moscow State University, 119899 Moscow, Russia Tel: +7 095 939 3346.Fax: +7 095 93982579 Chemistry' (KAC '95) Russia Division , Chemical Department, Lomonosov October 1-5 9-13 15-20 16-18 19-20 23-25 24-27 26-27 21st World Congress of the International Society for Fat Research (ISF) The Hague, The Netherlands Mrs. J. Wills, ISF Secretariat, P.O. Box 3489, Champaign, IL 61826-3489, USA Tel: +1217 359 2344. Fax: +1217 351 8091 EPEL-ECASIA 95, Department des Materiaud LMCH, CH-1015 Lausanne, Switzerland Fax: +41 21 693 3946 Joseph A. Caruso, FACSS National Office, 198 Thomas Johnson Dr., Suite S-2, Frederick, MD 21702, USA Tel: +1301 694 8122. Fax: +1 301 694 6860 Mr. Ben Keddy, Cambridge Healthtech Institute, 1037, Chestnut Street, Newton Upper Falls, MA 02164, USA Tel: +1617 487 7989. Mrs. Gestiana Munteanu, Biotechnos S.A., Str.Dumbrava Rosie, nr. 18, Bucuresti 70254, Romania Tel: +40 1 210 20 15. Fax: +40 1 210 97 05 Mr. Ben Keddy, Cambridge Healthtech Institute, 1037, Chestnut Street, Newton Upper Falls, MA 02164, USA Tel: +1 617 487 7989. General Service Office, The International Sixth BCEIA, Room 585, Chinese Academy of Science Room, San Li He, Xi Jiao, P.O. Box 2143, Beijing 100045, China Dr. D. Diamond, School of Chemical Sciences, Dublin City University, Glasnevin, Dublin, Ireland Tel: +353 1 704 5308. Fax: +353 1 704 5503 ECASIA '95 Montreux, Switzerland 22nd Annual Conference of the Federation of Analytical Chemistry and Spectroscopy Societies Cincinnati, USA Image Enhancement and Analysis Washington DC, USA Biotechnology Now and Tomorrow Bucharest, Romania 2nd Annual Blood Safety and Screening Washington DC, USA BCEIA '95-The International Sixth Beijing Conference and Exhibition on Instrumental Analysis Beijing, China Sensors and Signals County Dublin, Ireland November 5-10 1st Mediterranean Basin Conference on Analytical Chemistry Cordoba, Spain Professor Alfredo Sanz-Medel, Depart men t of Physical and Analytical Chemistry, Faculty of Chemistry, University of Oviedo, C/Julian Claveria, no.8 33006 Oviedo, Spain Tel: +34 85 10 34 74. Fax: +34 85 10 31 25 Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC 20036-1023, USA Tel: +1202 223 9034. Fax: +1202 416 6100 Ms. Helen Phipps, Institute of Food Research, Nonvich Laboratory, Nonvich Research Park, Colney, Nonvich, UK NR4 7UA Tel: +44 (0) 1603 255219.Fax: +44 (0) 1603 255168 Dr. M. P. Coward, Chemistry Department, UMIST, P.O. Box 88, Manchester, UK M60 1QD Tel: +44 (0)161 200 4491. Fax: +44 (0)161 228 1250 Dr. Matti Elomaa, Laboratory of Polymer Chemistry, P.O. Box 55, FIN-00014 University of Helsinki Tel: +358 0 191 40338. Fax: +358 0 191 40330 5-10 OPTCON '95 San Jose, USA 8-9 Biological Applications of Inorganic Mass Spectrometry Nonvich, UK 14-15 International Conference for Chemical Information Users Manchester, UK 14-16 Nordic Polymer Meeting Helsinki, Fin1 and82N Analyst, June 1995, Vol. 120 Date Conference 14-16 KEMIA95 Locat ion Helsinki, Finland December 13-14 BMSS 2nd LC-MS Symposium Cambridge, UK 17-22 International Symposium on Environmental Hawaii, Biomonitoring and Specimen Banking USA 1996 January 8-13 1996 Winter Conference on Plasma Florida, Spectrometry USA 21-25 VIth Latin American Congress on Caracas, Chromatography Venezuela February 4-7 The Fifth International Congress on Trace Meribel, Elements in Medicine and Biololgy: Therapeutic Uses of Trace Elements France 6-9 Fourth International Symposium on Bruges, Hyphenated Techniques in Chromatography Belgium (HTC 4); Hyphenated Chromatographic Analysers March 17-21 47th Pittsburgh Conference on Analytical Chicago, Chemistry and Applied Spectroscopy USA 25-29 ESEAC '96,6th European Conference on Durham, ElectroAnal ysis UK 3 1 4 4 7th International Symposium on Supercritical Indianapolis, Fluid Chromatography and Extraction USA April 9-12 26th International Symposium on Vienna, Environmental Analytical Chemistry Austria 23-26 Analytica Conference '96 Munich, Germany Contact Ms.Ritva Becker, Exhibition Manager, P.O. Box 21, FIN-00521 Helsinki, Finland Tel: +358 0 150 9211. Fax: +358 0 142 358 Dr. J. Oxford, Glaxo Research and Development Ltd., Park Road, Ware, Hertfordshire, UK SG12 ODJ K. S. Subramanian, Environmental Health Directorate, Health Canada, Tunney's Pasture, Ottawa, Ontario, Canada K1A OL2 Tel: +1613 957 1874. Fax: +1613 941 4545 R. Barnes, Department of Chemistry, Lederle GRC Tower, University of Massachusettes, P.O. Box 34510, Amherst, MA 01003-4510, USA Tel: +1413 545 2294. Fax: +1413 545 4490 Irene Romero, Interep SA, P.O. Box 76343, Caracas 1070-A, Venezuela Arlette Alcaraz, Chrug Hapita1 A. Michallon, Biochimie C, BP 217, F-38043 Grenoble Cedex 9, France Tel: +33 767 65484.Fax: +33 767 65664 Dr. R. Smits, Royal Flemish Chemical Society (KVCV), Working Party on Chromatography, BASF Antwerpen N.V., Central Laboratory, Haven 725, Scheldelaan 600, B-2040 Antwerp, Belgium Tel: +32 3 561 2831. Fax: +32 3 561 3250 The Pittsburgh Conference, 300 Penn Center Boulevard, Suite 332, Pittsburgh, PA 15235-5503 USA Tel: +1 412 825 3220. Fax: +1412 825 3224 Dr. A. G. Fogg, Loughborough University of Technology, Loughborough, Leicestershire, UK LE113TU Tel: +44 (0) 1509 263171. Fax: +44 (0) 1509 233163 Mrs. Janet Cunningham, Ban Enterprises, 10120 Kelly Road, P.O. Box 279, Walkersville, MD 21793 USA Tel: +1301898 3772. Fax: +1301 898 5596 Professor Dr. M. Grasserbauer, Institute for Analytical Chemistry, Vienna University of Technology, Getreidemarkt 91151, A-1060 Wien, Austria Fax: +43 1 5867813 Congress Center, Messegelande , D-80325 Miinchen, Germany Tel: +49 89 5107 159.Fax: +49 89 5107 180Analyst, June 1995, Vol. I20 83N Date Conference May 17-19 VIIth International Symposium on Luminescence Spectrometry in Biomedical Analysis-Detection Techniques and Applications in Chromatography and Capillary Electrophoresis 18th International Symposium on Capillary Chromatography 20-24 Location Contact 23-25 XIIIth National Conference on Analytical Chemistry Sophia Antipolis, France Professor Way R. G. Baeyens, University of Ghent , Pharmaceutical Institute, Department of Pharmaceutical Analysis, Harelbekestraat 72, B-9000 Ghent, Belgium Tel: +32 9 221 8951. Fax: +32 9 221 4175 Professor D.P. Sandra, IOPMS, Kennedypark Tel: +32 56 204960. Fax: +32 56 204859 Romanian Society of Analytical Chemistry, 13 Boulevard Republicii, Sector 3,70346 Bucharest, Romania Tel: +40 1 631 00 60. Fax: +40 1 631 00 60 Riva del Garda, Italy 20, B-8500 Kortrijk, Belgium Craiova, Romania June 16-21 HPLC '96: 20th International Symposium on California, Mrs. Janet Cunningham, Barr Enterprises, 10120 High Performance Liquid Phase Separations and Related Techniques 21793, USA USA Kelly Road, P.O. Box 279, Walkersville, MD Tel: +1301898 3772. Fax: +1301898 5596 July 8-12 XVI International Congress of Clinical London, Mrs. Pat Nielsen, XVIth International Congress Chemistry UK of Clinical Chemistry, P.O. Box 227, Buckingham, UK MK18 5PN Fax: +44 (0)1280 6487 17-19 8th Biennial National Atomic Spectroscopy Norwich, Dr. S. J. Haswell, School of Chemistry, Symposium (BNASS) UK University of Hull, Hull, UK HU6 7RX Tel: +44 (0)1482 465469. Fax: +44 (0)1482 466410 August 20-23 7th International Symposium on Osaka, Pharmaceutical and Biomedical Analysis Japan (PBA '96) September 1-7 Euroanalysis IX 15-20 21st International Symposium on Chromatography Professor Susumu Honda, Faculty of Pharmaceutical Sciences, Kinki University, Kowakae 3-4-1, Higashi Osaka 577, Japan Fax: +816 721 2353 Bologna, Italy Professor Luigia Sabbatini, Euroanalysis IX, Dipartimento di Chimica, Universita di Bari, Via Orabona, 4, 70126 Bari, Italy Tel: +39 80 242020. Fax: +39 80 242026 Varrentrappestr. 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 791 7358. Fax: +49 69 791 7475 Stuttgart, GDCh-Geschiiftsstelle, Abt. Tagungen, Germany 1997 April 14-19 Genes and Gene Families in Medical, Texas, Mrs. Janet Cunningham, Barr Enterprises, 10120 Agricultural and Biological Research: 9th International Congress on Isozymcs USA Kelly Road, P.O. Box 279, Walkersville, MD 21793, USA Tel: +1 301 898 3772. Fax: +1301898 5596

ISSN:0003-2654    

DOI:10.1039/AN995200079N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

84N Analyst, June 1995, Vol. 120 Courses Date Conference Location Contact 1995 July 3 Fourier Transform Infrared Spectroscopy 17-19 Techniques Workshop (Chemometrics) September 4-5 4-8 5-8 6-8 17-22 Short Course on Sample Handling of Pesticides in the Aquatic Environment Workshop in Liquid Scintillation Counting The Leeds Course in Clinical Nutrition 5th Workshop on Chemistry and Fate of Modern Pesticides 1995 European Workshop in Chemometrics December 11-12 BMSS LC-MS Course 18-19 LC-MS Training Course 5-6 The Next Step in Capillary Gas Chromatography for Trace Analysis 1996 February 5-6 Pre- and Post-column Techniques in HPLC for Improved Analyte Isolation, Derivatization, Clean-up, Separation and Detection 5-6 Isotopically Labelled Compounds in Hyphenated GC-techniques Manchester, UK Hull, UK Paris , France Loughborough, UK Leeds, UK Paris , France Bristol, UK Cambridge, UK Cambridge , UK Bruges, Belgium Dr.M. P. Coward, Chemistry Department, UMIST, P.O. Box 88, Manchester, UK M60 1QD Dr. M. J. Adams, School of Applied Sciences, University of Wolverhampton, Wulfruna Street, Wolverhampton, UK WV1 1SB Tel: +44 (0)1902 322141. Fax: +44 (0)1902 322680 Mrs. Frei-Hausler, IAEAC Office, Postfach 46, CH-4123 Allschuril2, Switzerland Fax: +4161482 08 05 Dr. P. Warwick, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, UK LE11 3TU Tel: +44 (0)1509 222585. Mrs. Hilary L. Thackray, Department of Continuing Professional Education, Continuing Education Building, Springfield Mount, Leeds, UK LS2 9NG Tel: +44 (0)113 233 3233.Professor M.-C. Hennion, ESPCI, Laboratoire Chimie Analytique, 10 Rue Vauquelin, 75005 Paris, France Mrs. C. Hutcheon, School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS Tel: +44 (0)1179 287645 ext. 4421. Fax: +44 (0)1179 251295 Dr. J. Oxford, Glaxo Research and Development, Park Road, Ware, Hertfordshire, UK SG12 ODJ Dr. J. Oxford, Glaxo Research and Development, Park Road, Ware, Hertfordshire, UK SG12 ODJ Congress Secretariat, Ordibo bvba, L. Hennincksraat 18, B-2610 Wilrijk, Antwerpen, Belgium Tel: +32 38 28 89 61. Bruges, Belgium Congress Secretariat, Ordibo bvba, L. Hennickstraat 18, B-2610 Wilrijk, Antwerpen, Belgium Tel: +32 38 28 89 61. Congress Secretariat, Ordibo bvba, L. Henninckstraat 18, B-2610 Wilrijk, Antwerpen, Belgium Tel: + 32 38 28 89 61. Bruges , BelgiumAnalyst, June 1995, Vol. 120 85N Date Conference Location Contact 5-6 Analytical Tools for GC-MS (Advanced Bruges, Congress Secretariat, Ordibo bvba, L. Modes of Ion-trap Mass Spectrometry) Belgium Henninckstraat 18, B-2610 Wilrijk, Antwerpen, Be lgi um Tel: +32 38 28 89 61. Henninckstraat 18, B-2610 Wilrijk, Antwerpen, Belgium Tel: + 32 38 28 89 61. 5-6 Biomedical Applications of GC-MS Bruges, Congress Secretariat, Ordibo bvba, L. Belgium Entries in the above listing are included at the discretion of the Editor and are free of charge. If you wish to publicize a forthcoming meeting please send full details to: The Analyst Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF. Tel: +44 (0)1223 420066. Fax: +44 (0)1223 420247. E-mail:Analyst@RSC.ORG.

ISSN:0003-2654    

DOI:10.1039/AN995200084N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Analyst, June 1995, Vol. 120 85N Future Issues will lnclude- Comparison of Two Microdiffusion Methods Used to Measure Ionizable Fluoride in Cows’ Milk-R. W. Kimarua, D. N. Kariuki and L. W. Njenga Determination of Brodifacoum in Commercial Rodenticides by High-performance Liquid Chromatography With Fluores- cence Detection-Mantai 2. Mesmer and R. Duane Satzger Approaches to Predicting Stability Constants-P. Warwick, Paul W. Dimmock and R. A. Robbins Analysis of Amoxycillin in Capsules and Oral Suspensions by High-performance Liquid Chromatography-R. B. Taylor, 0. Shakoor and R. R. Moody Estimation and Determination of Steroid Solubility in Super- critical Carbon Dioxide-John R. Dean, Mark Kane, s. Khundker, Chris J. Dowle, Roy L. Tranter and P. Jones Simultaneous Determination of Pseudo-uridine, Neopterine and Creatinine in Urine by Ion-pair High-performance Liquid Chromatography With In-series Ultraviolet and Fluorescence Detection-F.Palmisano, Taddeo Rotunno, M. La Sorsa, C. G. Zambonin and I. Abate Novel Extraction Method for the Determination of Avoparcin in Animal Feedingstuffs-Niall P. Fagan, John D. G. McEvoy, L. Lynas, J. Noel Campbell and W. John McCaughey Ferrocene-modified Horseradish Peroxidase Enzyme Elec- trode for the Determination of Hydrogen Peroxide and Linoleic Hydroperoxide-Antony E. G. Cass and W. C. Tsai Simultaneous Determination of Hydroquinone Ethers in Cosmetics by Preconcentration at a Carbon Paste Electrode- Lai-Hao Wang Effect of Temperature on a Multicomponent Ultraviolet Spectrometric Determination and the Development of a Temperature-independent Assay Procedure-Christopher Burgess and Robert Bourne Determination of Ninhydrin Positive Substances in Sea-water and Hemolymph-Stephen J.Haswell, Saloua Sadok and Roger Uglow A Sensitive Gas Chromatographic-High Resolution Mass Spectrometric Method for the Determination of Methyl- malonic Acid in Bovine Plasma-Paul B. Young, W. John Blanchflower, S. Armstrong Hewitt, John Price and D. Glenn Kennedy Determination of Lasalocid Sodium in Poultry Feeds and Premixes-Analytical Methods Committee Fermentation Monitoring Using a Glucose Biosensor Based on an Electrocatalytically Bulk-modified Epoxy-Graphite Biocomposite, Integrated in a Flow System-Salvador Alegret, F. Cespedes, F. Valedro, Esteve Martinez-Fabregas and Jordi Bartroli COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (0)171-437 8656. Fax: +44 (0)171-287 9798. Telecom Gold 84: BUR210. Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society’s Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge.

ISSN:0003-2654    

DOI:10.1039/AN995200085N

出版商:RSC    

年代:1995

数据来源: RSC

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Technical Abbreviations and Acronyms The presence of an abbreviation or acronym in this list should NOT be read as a recommendation for its use. However those defined here, need not be defined in the text of your manuscript. AAS ac A/D ADC ANOVA AOAC ASTM bP BSA BSI CEN CPm CMOS c.m.c. CRM CVAAS C.W. CZE dc DRIFT dPm DELFIA DNA EDTA ELISA emf ETAAS EXAFS EPA FAAS FAB FAO-WHO FIR FT FPLC FPD GC GLC HGAAS HPLC ICP id INAA IR ISFET iv im IGFET ISE LC LED LOD atomic absorption spectrometry alternating current analogue-to-digital analogue-to-digital converter analysis of variance Association of Official Analytical Chemists American Society for Testing and Materials boiling point bovine serum albumin British Standards Institution European Committee for Standardization counts per minute complementary metal oxide silicon critical micellization concentration certified reference material cold vapour atomic absorption spectrometry continuous wave capillary zone electrophoresis direct current disintegrations per minute diffuse reflectance infrared Fourier transform spectroscopy dissociation enhanced lanthanide fluorescence immunoassay deoxyribose nucleic acid ethylenediaminetetraacetic acid enzyme linked immunosorbent electromotive force electrothermal atomic absorption spectrometry extended X-ray absorption fine structure spectroscopy Environmental Protection Agency flame atomic absorption fast atom bombardment Food and Agriculture Organization, far-infrared Fourier transform fast protein liquid chromatography flame photometric detector gas chromatography gas-liquid chromatography hydride generation atomic absorption spectroscopy high-performance liquid chroma tograp h y inductively coupled plasma internal diameter instrumental neutron activation infrared ion-selective field effect transistor intravenous intramuscular insulated gate field effect transistor ion-selective electrode liquid chromatography light emitting diode limit of determination assay spectrometry World Health Organization analysis LOQ mP MRL mRNA MS NIR NMR NIST od OES PBS PCB PAH PGE PIXE PPt PPb PPm PTFE PVC PDVB QC QA REE rf RIMS rms rPm RNA SCE SE SEM SIMS SIMCA SRM STM STP TIMS TLC TOF TGA TMS tris TRIS uv UV/VIS VDU XRD XRF YAG Commonly Used Symbols M Mr r 3 U limit of quantification melting point maximum residue limit messenger ribonucleic acid mass spectrometry near-infrared nuclear magnetic resonance National Institute of Standards and Technology outer diameter optical emission spectrometry phosphate buffered saline polychlorinated biphenyl polycyclic aromatic hydrocarbon platinum group element particle/proton-induced X-ray parts per trillion (1012; pg g-'1 parts per billion (109; ng g-'] parts per million (106; pg g- ) poly (te trafluoroe thylene) poly(viny1 chloride) pol y (divinyl benzene) quality control quality assurance rare earth element radiofrequency resonance-ionization mass spectrometry root mean square revolutions per minute ribonucleic acid saturated calomel (reference) electrode standard error scanningkurface (reflection) secondary-ion mass spectrometry soft independent modelling of class analogy, statistical isolinear multicategory analysis Standard Reference Material scanning tunnelling (electron) standard temperature and pressure thermal ionization mass thin-layer chromatography time-of-flight thermogravimetric analysis trime t h y lsilane 2-amino-2-( hydroxymethy1)- tris( hydroxymethy1)methylamine ultraviolet ultraviolet-visible visual display unit X-ray diffraction X-ray fluorescence yttrium aluminium garnet emission electron microscopy microscopy spectrometry propane-l,3-diol molecular mass relative molecular mass correlation coefficient standard deviation atomic mass

ISSN:0003-2654    

DOI:10.1039/AN995200086N

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Analyst, June 1995, Vol. 120 1617 Solid-state Instruments for Optical Fibre Chemical Sensors A Review Mohd N. Taib and Ramaier Narayanaswamy Department of Instrumentation and Analytical Science, UMIST, Sackville Street, Manchester, UK M60 1QD Summary of Contents Introduction Principle of Measurement Instrumentation Systems Conventional Systems All Solid-state Systems LED-based Instruments Measurement Techniques Direct measurement Referencing technique Multichannels and multiparameters Discussion Future Trends References Keywords: Optical fibre chemical sensor; optoelectronic; instrumentation; digital; light emitting diode; review Introduction The application of optical fibres to sensing and measurement is not new. Initial work, exploiting the use of optical fibres in telecommunications, was reported as early as the 1970s and the amount of work published has grown rapidly since.'-2 Advances in the design and manufacturing technology of optical fibres, optoelectronics and semiconductor components has further promoted and intensified research in the optical fibre sensor (OFS) field.3-8 Many other factors, including industrial requirements,+lI support from government and higher market demands12-19 have inspired a rapid advance- ment of OFS technology.Current development of OFSs can be found in almost all areas of sensing and rnea~urement.3.7.13.20,21 For example, in the chemical field, OFSs have been established for measuring pH,Z22-24 oxygen ,2427 glucose ,28 temperat~re~23.29 vapour of polar organic solvents,30 narcotics,25 organochlorine com- pounds,31 ammonia,32 nitrogen dioxide,33 moisture34 and copper.35 Various other successful optical fibre chemical sensors (OFCSs) are reported in the literature.6,8921 Initial designs of OFSs employed optical fibres as light guides in a modified conventional optical system such that measurement can be carried out directly at the reaction point.This immediately expanded the use of optical fibres for sensor applications, in place of the traditional optical methods and at the same time took advantage of the numerous optical methods which were already established.4-5J6 The application of modern integrated electronic signal processing techniques also played a major role in this success. Optical sensor methodologies are based on the changes of^ optical properties through measurement of reflection, dispey- sion, scattering, interference, absorption, refraction and diffraction.When one or more of these phenomena takes place, the changes in the optical properties will be reflected in the modulation of either one or more of the following properties: wavelength (colour) , amplitude, phase, or polari- zation.37-40 Amplitude and colour modulation techniques are the most popular. However, they suffer from effects such as light source fluctuations, optical signal losses in connectors and optical couplings, fibre bending and photobleaching of indicator dyes. On the other hand, phase and time delay (or polarization) techniques, which can be found mainly in interferometric sensor applications, are immune to fibre bending and photobleaching effects.In comparison to conventional electrodes and physical transducers, OFSs offer many benefits which have been treated comprehensively in the literature .6,41 Some of these advantages include immunity to hazardous chemical environ- ments, freedom from electrical noise, intrinsic safety due to no electrical power being employed in the fibre (in the case of a monolithic sensor, a very low voltage and current is used), very small sensor size and low cost. These characteris- tics plus the intrinsic properties of an optical fibre539~39~42-46 allow for great flexibility in the ways in which OFSs can be applied, e. g . , in trusivehvasive or non-intrusivehon- OFCS technology is a product of adapting optical fibres and optoelectronics for chemical sensors.Various papers in the literature have focused on optical fibres,s.gJ9,42-46 OFCSs.3J5721951-53 This paper will focus on the particular type of instruments that can be employed in conjunction with OFCSs. The development of instrumentation for OFCSs has had much less attention until recently. With the widespread availability of high-quality and low-cost optoelectronics, digital components and high-performance light emitting diodes (LEDs) and laser diodes (LDs) covering a wider range of peak wavelengths, together with the current rising demands for low-cost portable and rugged instruments for OFCSs,39,54 the design and development of suitable instruments has become more attractive commercially. This paper reviews some of the techniques published in the literature, focusing on LED-based instruments. A discussion of future trends in OFCS instrumentation, including application of smart sensors and intelligent digital signal processing techniques, is also presented.invasive. 14-16,23,29,49 OFSs,5,6,8,11,13,23,48,49 chemical sensors15,21,41 S O and Principle of Measurement In general, OFSs can be divided into two main cate- goTies,2,6,8,23,45,51,55-57 i. e., intrinsic sensors where the measu- rand directly interacts with the light in the optical fibre; and extrinsic sensors where the measurand affects the light properties through a medium external to the fibre whilst the fibre only acts as a waveguide to transmit light to and from the sensing device. Most of the examples cited earlier are of the1618 Analyst, June 1995, Vol.120 latter type. The intrinsic type is less popular but is receiving more attention lately. Its design is more difficult and c0mplex.~>5~ Some of the more popular methods of intrinsic sensor can be found in fibre optic immunoassay systems, where the evanescent field of light travelling in the fibre interacts with a recognition-layer matrix bound directly to the fibre optic surface,S~58,59 interferometric sensors,5,38,54,57,62 where changes in optical time delay or phase lag is measured as a function of concentration of target chemical species, and polymer swelling63.64 which is based on non-spectroscopic parameters. Examples of successfully fabricated intrinsic sensors include those for hydrocarbon gas ,65 pH,63764,66 micro- organism detection,67 bile reflux,66 phenolic contaminant68 and uranium;41 further examples are presented in Table 1.The measurement principle for a chemical sensor is based on a chemical variable causing a change in the optical properties of the sensor, intrinsically, as a result of interaction between electromagnetic radiation and the sensing material. By properly measuring and quantifying the optical changes, the corresponding chemical changes can be calibrated on a suitable indicator or plotted on a chart recorder for visual inspection and analysis. Full treatment of chemical trans- duction systems and their respective optical techniques have been discussed in the literature.3.39.41.69~70 Instrumentation System The instrumentation used for OFCSs is usually a modified conventional optical system where connectors are attached at the light source and at the detector slits to allow for connection to optical fibres.39,71,72 Generally, OFCS instrumentation comprises five main parts: (1) a light source; (2) one or more optical fibres as the light guides; (3) a transducer to translate the concentration of the target chemical species into measur- able modulated light component; (4) a signal processing unit; and (5) a display or output unit.Fig. 1 shows the block diagram of a basic OFCS instrument system. Light from the source is launched into the optical fibre and directed to the sensing region where the optical property will be affected. The returned modified light is then collected by the same or another optical fibre and directed to a signal processing unit.Both the light source and the signal processing unit can be of a single integrated instrument or several instruments interconnected through suitable electrical and optical connectors. Optical couplers may be used to couple light to/from the optical fibres. Most OFCS instruments utilize source modulation to provide a method of discriminating the ambient light and a means of synchronization. The modulation pulse is provided via a square-wave electronic oscillator. This technique elimi- nates the requirement to put the transducer and the chemical species in a light-proof container to avoid the influence of the ambient light. The optical transducer varies in design depending upon the chemical species to be measured and the associated signal processing.The most popular technique is to immobilize an indicator dye on a support polymer membrane affixed to the tip of an optical fibre. The signal processing unit then simply measures any variation in reflected light intensity correspond- ing to any changes in the concentration of the target chemical species. Various other methods are employed which can be found in the literature. When the measured light is received from the transducer it is converted to an equivalent electrical current by a photo- detector. This current is processed by signal processing circuitry which provides a conditioned electrical currenthol- tage suitable for display on an electrical meter or recording on a chart recordedmagnetic disk of a computer connected to the system. The instrumentation system available today can be cat- egorized into two main groups, viz., the conventional system and the all solid-state system.Conventional Systems The term conventional used here is actually arbitrary and it refers to the traditional optical systems employed for 0FCS~~73-75 as mentioned earlier. The system constitutes the main apparatus for optical fibre reflectance/absorbance measurement used in laboratories and research centres since the 1970s. A commercial instrument based on a tungsten lamp became available in 1973 (as reported by Anfalt et al.76). The conventional system is characterized by its large size, high electrical power requirement and consists of several packages. It mainly consists of first-generation optical devices40 and may Fig. 1 OFCS Instrumentation. Table 1 Examples of extrinsic and intrinsic OFCSs Measurement Absorption Absorption Absorption Absorption Absorption Absorption Absorption Fluorescence Transmittance Absorption Absorption Absorption Transmittance Absorption Absorption Analyte NO2 cu2+ Water Alcohols Bilirubin D20 in blood Spectra Gas Humidity Methane Ammonia Humidity pHlammonia pHltemperature pfl6, UF6, F2 Wavelength, hpeakInm 496 2541365 820 1900 110011600 458 4000 574 5601660 940 3392 560 690 580 675 Light spectrum VIS uv NIR IR NIR VIS IR VIS VIS NIR IR VIS VIS VIS VIS Sensor tY Pe Extrinsic Extrinsic Extrinsic Extrinsic Extrinsic Extrinsic Extrinsic Extrinsic Intrinsic Intrinsic Intrinsic Intrinsic Intrinsic Intrinsic Intrinsic Application Environmental Environmental Environmental Environmental Environmental Biomedical Biomedical Chemical Environmental Automotive Environmental Environmental Environmental Environmental Environmental Ref.no. 45 45 45 45 45 45 45 45 53 53 53 53 53 53 53Analyst, June 1995, Vol. 120 1619 combine the use of discrete semiconductor components. The above characteristics of the system rendered it usable only for sensor development work and in non-portable applications. The light sources employed are incandescent lamps such as tungsten, tungsten-halogen, xenon and quartz-halogen lamps. These lamps have a short life span but they emit a broad-band continuous spectrum of optical radiation suitable for use as sources of ultraviolet and visible light in short-range OFSs. They are relatively bulky, require a high amount of very stable electrical power supply, produce heat and are generally not very stable. Mechanical beam choppers are used for the light source modulation.The schematic of the modulator is shown in Fig. 2. In a typical measurement set-up, an electronically con- trolled, small sized electric motor rotates a thin metal chopper wheel at a set frequency. Fig. 3 shows a typical signal from a modulated light source and its possible response after returning from an optical transducer. Normally, the modula- tion frequency is set at a value different from the main power supply frequency or its harmonics to avoid their influence in the electronic signal processing employed in the instrument. The mechanical choppers may contribute to some measure- ment errors arising from small variations in the modulation pulses due to drift in the motor frequency and also uneven holes cut in the chopper wheel.This requires a precision lock- in amplifier as part of signal processing. The light source is focused onto an optical fibre using a lens. A similar lens is used to couple the optical fibre onto a photodetector. A monochromator or an optical interference filter is used to select the desired peak wavelength where the response of the transducer is optimum. But these devices lead to significant coupling losses of light intensity. A photomultipler tube (PMT) is usually used for detection together with current and lock-in amplifiers. The current amplifier magnifies the weak photocurrent from the PMT and feeds this to the lock-in amplifier which provides synchroniza- tion with the light source modulation.The synchronization effectively removes the ambient light effect but does not account for light source deterioration or fibre bending effects. Further processing includes ac to dc conversion and scaling of the output signal. The conventional system is invaluable for much early development work of OFCSs such as design, characterization and evaluation. In some cases, results from experiments using the conventional system are used as a basis for comparison Fig. 2 Light source modulation. Fig. 3 Synchronizedpulse lock-in measurement. with those of a compact solid-state instrument .2233,75?77,78 Designs and applications of OFCSs using this system are numerous and are considered beyond the scope of this paper.All Solid-state Systems Instruments in this group operate using the same principle as the conventional system, except that LDs and LEDs form the main light sources, and the signal processing units are fully electronic systems. In comparison with the conventional sources, the semiconductor sources offer advantages such as lower power consumption, high stability and reliability, small size, robustness, and generally do not require optical couplers or monochromators. Much recent work has emphasized the tendency towards the exploitation of these sources .79 At present, various types of LEDs and LDs are available offering a range of wavelengths from UV to IR regions. Laser diodes require a much higher and stable electrical source than LEDs. They are more costly and often suffer from inherent optical feedback and degradation of performance with increasing temperature.80 An advantage of LDs is their highly intense and coherent intensity (bandwidth of less than 5 nm) which allows for remote sensing via very long optical fibres.Excellent treatments of both LDs and LEDs can be found in the literature.39.81-83 In many OFCS instruments, similar signal processing techniques are employed for both type of sources, but there are a lot of different characteristics which are unique to each of the sources and sometimes these are reflected in the imple- mentation of the instruments. In the following sections, we attempt to review only those OFCS instruments that use LEDs as their main light source. Many of these instruments have already been fabricated in the form of portable systems or incorporated in large-scale electronic integration to form microsensors. LED-based Instruments The LED is an inexpensive semiconductor light source and has been widely used for industrial instrumentation as well as for household appliances.There are two basic types of LED that are commonly used for fibre optic sensors: the surface emitting diode and the edge emitting diode.80 The surface emitting diode radiates in an essentially isotropic fashion, and light is captured by butt coupling a fibre in close proximity to the emitting surface. Typically these devices are used in associa- tion with large-core multimode fibres. The edge-emitting LEDs confine light to a waveguide region. In general, each LED produces a narrow-band continuous spectrum with a bandwidth of 20-80 nm.79 In the early days when optical fibres were used for telecommunications, the optical fibres and LEDs were designed to cover the wavelengths 780-900 nm,84 But today, various different coloured LEDs and different types of optical fibres which cover much of the visible and some NIR wavelengths, are readily available.Some characteristics of LEDs that are of interest to fibre optic sensors include a very low coherence length (often the result of very broad spectral output), very low sensitivity to back reflection, very low power and very high reliability,Ss often with projected mean time between failure (MTBF) of the order of 100 000 h. LEDs are amenable to direct electronic modulation, and can be easily and efficiently coupled to optical fibres.8637 The application of LEDs in optical instrumentation for analytical chemistry commenced as early as the 1970s. For example, Flaschka et a1.a used the combination of an LED and a phototransistor for a spectrophotometric instrument. In 1976, Anfalt et al.76 constructed a spectrophotometric titration instrument using an LED (peak wavelength, hpeak = 560 nm).1620 Analyst, June 1995, Vol. 120 The reference beam was obtained by optical splitting. By employing electronic modulation of the source, it was reported that the influence of the ambient light had been considerably reduced, and a precision of 0.35% was obtained for determination of the total alkalinity in sea-water. Measurement Techniques Several later works that utilize LEDs in OFCS instruments are listed in Table 2.There are a variety of techniques used by the instruments shown here. The optical modulation techniques employed are fluorescence, absorption, reflectance, refractive index and colour. There are three prevailing electronic signal processing techniques used: full analogue systems, mixed analogue and digital systems, and computer-assisted analogue or analogue/digital systems. The methods used to derive the required signal include direct measurement, direct referenc- ing, and lock-in or pulsed referencing. Single or multiple wavelengths may be used, depending on the measurement technique. Some LED-based instruments will be considered later, categorized by their measurement techniques and appropriate signal processing.Direct measuremen2 The direct measurement technique is the simplest and cheapest method to implement in a compact and portable instrument, but care must be taken to avoid temperature drift of the LEDs and also fibre bending. In the direct measurement method, the final signal is obtained directly, either from optical modulation of continuous source or integration of pulses from optical modulation of modulated sources. The latter method automatically eliminates effects from ambient light. Wolfbeis et al.89 constructed a very simple instrument for monitoring acid-base titration. A blue LED (peak wave- length, beak = 465 nm) was used to excite an added indicator. A photodetector and a signal amplifier monitor fluorescence changes of the indicator and display the state of the titration process on a meter.The set-up allows titration of minute sample volume and an error of less than 1% was achieved when 0.001 mol 1-1 solutions of acid-base were titrated. The instrument demonstrated a strong immunity against inter- ference from surface potentials and was of very low cost compared to an electrode system. A disadvantage of the system is that the titration must be carried out in a fully light- proof container to avoid ambient light effects. Hauser and Tan86 also used a blue LED for a fluorescence- based OFCS. The LED and a photodiode were coupled directly to optical fibres. Electronic modulation at 362 Hz and a four-stage electronic signal processing were employed. The photocurrent produced by the photodiode was amplified by an operational amplifier, then demodulated via a balanced demodulator which fed its output to a low-pass (LP) filter.Finally, the signal was amplified once more and displayed on a five-digit multimeter. The performance of the system com- pared well with conventional methods, with response time of 1 min and an accuracy of 0.5% of oxygen concentration. The electronic system was reported to exhibit a 0.25% h-l drift and a precision with a standard deviation of <0.05%. The ambient effect detected was generally three to four orders of Table 2 LED-based instruments LED colour Red IR IR Yellow reference LED 2 Green 2 Red 2 Yellow Orange Blue Blue Blue Red Green Green Red Blue Green Yellow Amber Red Red Red IR Red 2 x IR Measurement Peak h/ nm 635 820 860 580 * * * * * * 480 * * 565 570 * 480 555 570 605 635 660 700 935 660 820 Optical Reflectance Refractive index Absorption Colour Fluorescence Fluorescence Absorption Reflectance Colour and reflectance Reflectance Ref.no. 22 29 30 36 86 89 90 91 94 99 Chemical Technique Comment Digital Analogue processing meter Temperature Referencing Computer assisted Vapour Referencing Full analogue concentration 2 detectors PH Gases or Bar-graph Computer- liquid display on controlled mixtures oscilloscope Oxygen nitrate pH. pH (titration) pH (titration) PH 8 Channel spectrophoto- meter Lock-in Direct Referencing with 2 detect. Computer display Referencing Uses modulation No No modulation modulation Analogue processing 1 detector controlled with 2 detectors Computer- Blood oxygen * Low power hematocrit and voltage * Not indicated in original paper.Analyst, June 1995, Vol.120 1621 magnitude higher than the signal of interest but the demodula- tion technique employed here provides good discrimination against it. Referencing technique This technique is used by most of the instruments presented in Table 1. In principle, this technique employs at least two sources, which can be from one or more LED. One source is used for the measurement and the other is guided directly to the detector as a reference. In the case of a single light source, an optical fibre splitting technique is used to split the light from the source. Fig. 4 shows the schematic of a simple referencing technique. If the sources are not electronically pulsed, then the instruments may employ either a single LED with two detectors or multiple LEDs with at least one detector.For the latter case, filters must be employed to separate the measure- ments and the reference signals. Brenci et a1.29,66,78 employed a single light source coupled onto an optical fibre connected through a four-way optical fibre coupler such that the light source intensity (reference signal) and optical signal from a temperature sensor could be monitored simultaneously. Two photodiodes were used here. Two of these instruments29.66 are all solid-state and micro- processor-based, while the other78 is based on a conventional system. The light source was pulsed and the output was computed from the ratio of the measured and reference signals. The ambient light effect and the dark current of the photodiode were not considered in this case.However, a precision of 0.1 "C (for temperature ranges 30-50,* 30-7029 and 25-50 "C78) and a stability error of approximately f 0 . 3 "C over 12 h were achieved. used a single green LED (Ape& = 565 nm) in an optical fibre pH sensor. Optical fibre bundles were used to direct the light source to the sensor and to a reference photodiode detector. Another photodiode was used for measuring the sensor signal. Output was calculated by an analogue circuit from the ratio of the sensor signal to the reference signal. A digital voltmeter was used to display the output. A stability error of less than 0.5% h-l and a pH resolution of k0.05 with excellent reproducibility in the pH range 6.8-9.7, was reported.The temporal response, which was in the sub-microsecond region, was better than that of a conventional glass electrode system. The referencing tech- nique used in this instrument only discriminates the effect of source fluctuations but not fibre bending, and, since no source modulation was employed, the analyte needed to be covered in an opaque layer in order to avoid ambient light effects. If the sources are electronically pulsed, normally using an electronic timer such as a 555 timer or a microprocessor controlled J-K flip-flop, then a more flexible system may be used for the OFCS instruments. Single or multiple detectors could be used with single or multiple LEDs. For example, Baccii et al.91 used a green LED (Apeak = 570 nm, centred on Benaim et Fig.4 Referencing technique. the peak absorption of immobilized Phenol Red) for the measurement of pH, and a red LED as a reference. A single photodiode was used to detect both signals with electronic filters separating the two signals. Further processing of the signals was carried out by a computer. Falciai et a1.77 used a blue (hpeak = 480 nm) and an IR (hpeak = 860 nm) LED as signal and reference sources, respectively, in a compact and easily transportable instrument for use in vivo enterogastric reflux detection. A trifurcated optical fibre bundle was used for directing both sources to the sensor and for returning the optical signal to a photodiode. The ratio between the sum and difference of both signals was used for output. Analogue narrow-band filters and circuitry were utilized for signal processing.The results show good agree- ment with those of a pH electrode and the instrument also succeeded in detecting the reflux when pH electrode measure- ments failed. The above system was improved by incorporat- ing a double-channel system92 in which two LEDs were used for signal and referencing in each channel. Each channel measures a different pH range (pH 1-3 and 3-8) and the reported result showed a precision of S0.05 with response time of less than 15 s. The instrument was battery operated and fully portable. Grattan et ~ 1 . ~ ~ employed a green (hpeak = 565 nm) and an IR (Ape& = 810 nm) LED as signal and references sources, respectively, in a simple optical pH sensor system. Both LEDs were pulsed and driven from a single constant-current source so as to eliminate power source fluctuations. A single photodiode (built-in integral amplifier) was employed for detection.Ambient and photodiode effects were eliminated by measuring the photodiode current when both LEDs were switched off, and then subtracted from the signal and reference measurements. The final output signal was com- puted from eqn. (1): signal - background reference - background (1) output = The result presented shows an accuracy of k0.04, in the range pH 6-9, with response time of less than 100 ms and temperature drift of about 0.004 K-l for temperature variations in 21-50 "C range. Another very similar set-up22 reported an improved performance with 0.01 resolution in the linear region of the same pH range. Besar et ~1.93 employed an interesting connection for LEDs (he& = 565 nm and 930 nm for signal and reference, respectively) in a dynamic fibre optic pH spectrophotometric cell system for use in clinical applications.The two LEDs were connected in parallel but with reversed polarity such that a square-wave pulse switched odoff each LED in turn. Elec- tronic signal processing separated the two signals and calcu- lated the ratio of signal from sensor to reference signal as an output which was sampled by a computer via an ADC. The transient time for steady-state measurement was reported to be 4 min, which was better than that which could be achieved using an electrode system. Jawad and Alder75 demonstrated the use of a different ratioing technique in an automatic detection system for hydrogen cyanide.Colour changes of a green LED (Ape& = 560 nm) associated with a reaction of cyanogen chloride with 4-picoline-barbituric acid reagent was monitored. A red LED (hpeak = 635 nm) was used for referencing. The LEDs were pulsed alternately and two detectors were used for simul- taneous measurement of signal and reference. An integrated analogue signal processor computed the output [eqn. (2)]:1622 Analyst, June 1995, Vol. 120 The ambient light effect was not considered in this case and the instrument was successfully used in a simulated study but no system performance result was presented. Multichannels and multiparameters When two or more LEDs, each with a different peak emission spectrum, are utilized then the instruments could be capable of carrying out multichannel and multiparameter measure- ments.36.94,95 Fig.5 shows the block diagram of such a multichannel system. Kopola et aZ.94 constructed an eight-channel electronic spectrophotometer for continuous reflectance measurements in industrial application. The instrument utilized eight elec- tronically modulated LEDs, with peak emission spectra at 480 (blue), 555 (green), 570 (yellow), 605 (amber), 635 (red), 660 (red), 700 (red) and 935 nm (IR). The LEDs were time- multiplexed and two photodiodes were used for simultaneous measurements of sensor signal and LED reference signal in a sampling duration of 640 ps. Background effects were also sampled, but for only 60 ps, in between the LED pulses. The system employed a full analogue signal processing unit with a microprocessor as a controller.A temperature controller was included for the LEDs and photodiodes in order to minimize temperature fluctuations. Absolute reflectance measurements (R,) were evaluated using eqn. (3) where Mpx = average signal pulses, Mbx = average signal- background, R,, = average reference pulses, RbX = average reference background, x = channel used, s = specimen under test, and c = calibration specimen (manganese oxide). Relative reflectance measurements were also provided by comparing the reading with that of any channel which has the highest value of absolute reflectance. In the result presented, the blue LED was not used since its intensity was too low. The stability of the instrument was in the range 0.1-0.3% (in terms of absolute reflectance) and an accuracy of 1% was achieved for colour test measurement. Another system was set up to detect and identify constitu- ents of gaseous or liquid mixtures.36 Eight LEDs in an array were sequentially pulsed and guided through eight optical waveguides, coated with a thin film that is known to react specifically with one or more analyte components in the sample mixture.Optical fibre bundles were used to couple the individual waveguide outputs to a single photodetector. The LEDs were synchronized with the detector using a microcom- puter. The output was displayed as a bar-graph on an oscilloscope. Fig. 5 Block diagram of a multichanncl system. In an instrument utilized for flow injection,96 two measure- ment LEDs (hpeak = 605 nm) and two reference LEDs (hpeak = 950 nm) have been used.A 80386 PC was used to control the instrument and produce a 40 Hz pulse to drive the LEDs. The LEDs were divided into two groups of emitters, and a pair of bifurcated optical fibre bundles were used to guide the light to two groups of photodetectors (two for the signal and two for reference). A four-channel ADC was used for sampling the output of the photodiodes directly into the computer. The instrument exhibited an absolute error of <3.7% in measuring micromolar concentrations of Bromothymol Blue in samples containing up to 1.5% whole milk and 60% ethanol. Discussion It has been shown above that a variety of LED-based OFCS instruments have been successfully produced for both moni- toring and analytical purposes in a wide-ranging area of applications.The use of LEDs has been proved to be the cheapest method to implement OFCS instruments which can be of low power, compact in size and portable. Many challenges and problems39.52 encountered with earlier LED- based instruments have now been overcome. The versatility and flexibility achievable using these instruments are reflected by the instruments discussed above. From a measurement point of view, many LED-based OFCS instruments can perform better than the conventional systems; their precision is normally better and, in certain cases, owing to the small size of OFCS, they can be used for measurements which are not possible with conventional systems. By combining several LEDs (of different peak wavelengths), it has been possible to set up an instrument which constitutes a high light throughput alternative to the continuous sources employed in conventional systems, but with the advantage of a very simple detection system.The measurement range has also been expanded by utilizing multichannel or multisensor systems. Current methods used have also advanced from the use of intensity modulation to other more sophisticated techniques such as fluorescence with self-referencing, polarization and a variety of interferometric techniques. Another highly encouraging factor, is the relative ease of coupling of LEDs to optical fibres. The most popular method used by many of the instruments discussed in this paper, is the part machining of the plastic lens of the LED and then coupling the optical fibre almost directly to the transmitting element of the LED.A more complicated method utilizes micromachining and silicon wafer technology ,87 where LEDs and associated optoelectronics components can be integrated and miniaturized. This technique could not be achieved with LDs at this stage. The inexpensiveness and ease of manipulation of a variety of suitable optical fibres have also helped in the development of OFCS instruments. These fibres allow for easy coupling to LEDs and detectors. Table 3 presents the various methods of optical fibre coupling for light guides between the sources, transducers and detectors, and the typical fibre length employed by LED-based instruments. The length of optical fibres that are used effectively has increased from a typical 2 or 3 m.In our work,97 12 m of porous polymer optical fibres were successfully used for remote pH sensing. The maximum length cited here is 300 m, which was used for remote gas and water pressure sensors. However, this still lags behind laser-based instruments with which remote applications using fibre length of over 1 km have been reported.11>41 Future Trends In general, the advances in OFCS instruments are very much in parallel with advances in semiconductor technology,Analyst, June 1995, Vol. 120 1623 including integrated electronics, microprocessors and very large scale integration (VLSI) techniques. This technology equips OFCSs with state-of-the-art measurement and signal processing components providing increased accuracy and sensitivity, rapid response, and higher reliability.Further- more , instruments with microprocessors are capable of handling and processing a tremendous amount of sensory information, thus producing a far more intelligent interpreta- tion of measurement data.40798 Miniaturization of OFCSs has been achieved through silicon wafer technology, producing monolithic sensors which are suitable for in vivo applications .7399-101 The incorporation of intelligent VLSI electronics with the miniaturized OFCSs has produced a new breed of sensors, known as the smart or hybrid sensor77,13,19,51,102 combining the benefits of optical fibre and electronic systems which can improve performance by; local processing, small physical size, high reliability, multifunction sensing and a readily computer compatible data bus.14 The concept of a multisensor for simultaneous detection of concentration of several chemical species has recently received a lot of attention.41 Since the reaction of the analyte species with the chemical transduction system is often accompanied by a change in temperature, pressure or volume (which can be measured optically), instruments with multi- channeVmultiparameter capability could easily monitor these parameters or other related properties simultaneously. An example of a multiparameter probe is the sensor for the measurement of pH, oxygen and carbon dioxide.49J00 Another method which has attracted a lot of application ~~ ~~~~~~~~~~~ ~~ Table 3 Optical fibre applications for LED-based OFCSs Measurement (analyte) Optical encoding Intensity Absorption (pressure) (temperature) (PW Absorption (pH) Absorption (temperature) Fluorescence Fluorescence (titration) Absorption (PW (PHI Reflectance (pH) Optical fibre Type/Size pm* PCS/16-core 200 PCS/200 PCS/600 signal LED, 200 reference LED and 4 x 600 to detector PCS/600 scs/600 glass/50 t PCS/2 X 600 signal LED, 200 reference detector and 4 x 600 signal detector porous polymer/1000 Coupling method bundle four-way coupler bundle/ bifurcation trifurcation four-way coupler bifurcation bundle/ bifurcation bifurcation twidbundle * Diameter of effective end surface area; PCS, Plastic clad silica; SCS, Silicone clad silica.t Not indicated in original paper. Ref. Length/m no. 300 51 5-7 66 2 74 t 77 t 78 t 86 1.5 89 2 90 12 97 Multisensing multichannel intelligent microsensor I I Fig.6 Technologies associated with OFCS: current and future trends.1624 Analyst, June 1995, Vol. 120 especially in spectroscopic analysis is a multichannel system which can provide a spectral scan for pattern recognition. By using multichannel and multiparameter sensing, OFCSs which are connected directly to microprocessors can carry out direct parallel digital processing under software control, hence exploit the capabilities of pattern recognition74 and know- ledge-based system such as artificial neural networks (ANNs)l03 or fuzzy logic. For example, ANNs have been applied to qualitative identification of fuels and oils based on fluorescence spectra,lo4 vapour recognition105.106 and IR spectroscopy,107-109 and fuzzy logic has been used for intel- ligen t interpretation of spectroscopic data .110,111 Computerized and microprocessor-based instruments may enable the application of an inference engine.In certain cases, chemical sensors may often be sensitive to chemical species other than the one of interest. This would permit the measurement of other parameters, via an inference engine,2 using the measurement of the known species. An analogy to this technique is the fact that of our five senses, one is dedicated to gas analysis, one is dedicated to liquid analysis and two of the remainder are frequently employed for inferring composition.15 For example , in biotechnology pro- cess control such as fermentation, parameters measured include substrate feed rate, temperature, pH, oxygen and carbon dioxide. These measurements are used to deduce information about the physiological parameters affecting productivity, i.e. , biomass, growth rate, respiratory activity and product concentration. 112 Another major factor which is revolutionizing OFCSs is the inherent characteristic of multimode optical fibres. This property allows multicomponent lightwave modulation to be transmitted along a single optical fibre. Thus an array of sensors, each measuring different independent parameters, can be multiplexed and connected to a single fibre attached to a remote instrument. Several OFSs have been implemented Two very recent developments in optical instrumentation are making a big impact in OFS systems. These are the application of charged coupled devices (CCDs) and integrated optics system.CCDs are being used to replace conventional and other semiconductor detectors. They have high quantum efficiency, long lifetime, very low noise, and have been shown to produce a rapid and superior spectrum scan enabling simultaneous multichannel measurements.2~~'17-1~9 On the other hand, integrated optics has produced optical com- ponents such as in-line tunable filters which can be fabricated directly onto an optical fibre providing fast and precise wavelength selection and simplifying the detection system. In addition to those that have been mentioned previously, both of these can also be envisaged tc greatly influence the direction of OFCSs and other systems in the future. These technologies and their interrelationships are schematized in Fig.6. 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ISSN:0003-2654    

DOI:10.1039/AN9952001617

出版商:RSC    

年代:1995

数据来源: RSC