ISSN:0003-2654    

DOI:10.1039/AN99318FX009

出版商:RSC    

年代:1993

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN99318BX011

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993, VOL. 118 27N Editorial Any scientific research or investigation must be based on two foundations. 1. Careful observation of a well designed experiment. 2. Truthful reporting of those observations. The intention here is to discuss only the second of these points, taking the first as read. Traditionally, scientific observations are reported in scientific journals such as this one. The editorial management has to walk a tightrope, ensuring that on the one hand all papers containing sound work, which falls within the remit of the journal, are included, and on the other that the size and content of the journal are such as to justify commercial publication. In order to ensure soundness of work, all respectable journals make use of referees. A referee’s task is to vet papers in terms of scientific content and general fitness for publication. N o referee wants to reject a paper unless it fails to come up to standard. Nevertheless some standards must be set.As recent guidelines put it, ‘A referee . . . should judge objectively the quality of the manuscript, of its experimental and theoretical work, of its interpretations and its exposition, with due regard to the maintenance of high scientific and literary standards. A referee should respect the intellectual independence of the authors’. Unfortunately, the increase in higher education and the insistence, whether explicit or implied, that no aspiring postgraduate will receive his or her doctorate without at least one publication, has led to an enormous explosion in papers being submitted for publication.Equally unfortunately, the majority of such papers, however well written, are of little interest to the scientific world at large. The problem is especially pronounced with papers reporting spectrophotome- tric methods for metals and this aspect was discussed by Colin Watson seven years ago.’ This was followed by an Editorial Board decision broadly in line with the aforementioned article, which was communicated to referees but not in its entirety to prospective authors, that such papers should be rejected ‘unless the work constitutes a highly significant develop- ment in the field of analysis’. The problem is, how to cope with such vast numbers of papers within the confines of the publication system, and this poses a considerable problem for the referee.It used to be generally accepted that any piece of sound scientific work that had not been previously reported was acceptable for publication. Indeed I have heard the argument (seriously put) that even negative results should be published in order to avoid other workers wasting their time. Unfortunately, the number of papers submitted has continued to rise and clearly the need to limit the number of such publications is important. As a referee, I am often distressed by the quality of some of the papers offered. Referees like to see good scientific work crowned by a solid, worthwhile publication, yet many a good piece of research is spoilt by the quality of its presentation to the potential publisher. In my view, in order to justify publication the submitted script needs to meet the following criteria.( a ) The work must be novel. One assumes that no one commences bench work without first conducting a thorough literature search. At the same time, a research project which merely substitutes a reagent analogous to, but different from, one in a published paper ought not to be accepted unless there is a substantial gain in analytical performance. (b) The work should either be of fundamental scientific interest or it should be of practical use, filling a clear need. (c) The methodology used should be appropriate and up to date. A ‘new’ reagent for an analyte, for which many other good reagents are already available, or where perhaps most workers would use an alternative technique, is not worth publishing unless there are sound justifications for its use.However, there may be some justification in work on a new reagent for which adequate alternatives exist, if the new reagent has some special merit, e . g . , use in the field in remote or primitive areas, and where there is a genuine need to meet that requirement. This feature of the work should then be made clear in the text. ( d ) The paper should include a full discussion of alternative methods, explaining why this ‘new’ method is being offered. (e) It should include adequate statistical detail, including correlation with at least one, preferably the most commonly used, of the accepted ‘standard’ methods. A paper where the experimental work is minimal and which contains no comparative study of existing methods can not be accept- able. (f) It should be presented logically, clearly and in reason- able English. Of course editors and referees will and do make allowances for authors whose primary language is not English.It follows therefore, that automatic rejection should result from one or more of the following faults (other referees may wish to extend this list): ( a ) ‘Me-tooism’-papers which follow so predictably and logically from previous work that they didn’t need to be written. (6) Papers which claim improvements in method, simplicity, sensitivity or selectivity without producing any evidence of this, or where the claimed ‘improvements’ are vanish- ingly small. (c) Papers which quote no comparison with other, more generally accepted methods. (d) Papers which quote no applications data.( e ) Papers in which a method is developed for the sake of producing a publication, when there is no possibility of the method being used in any other laboratory. Finally, with the exception of methods for use in the field, spectrophotometric methods should only be published if they can be automated, either using specifically built equipment or by utilizing flow injection methodology. Dr. M . A . Russell References 1 2 Ethical Guidelines to Publication of Chemical Research, Anal. Chem., 1992, 64, 109. Watson, C., Analyst, 1986, 111. 1353.28N ANALYST, MARCH 1993, VOL. 118 EIRELEC 1993 Electrochemistry to the year 2000 September 11-15 Adare, Co. Limerick, Ireland Scientific Programme An international conference dealing with recent advances in electrochemical methodology, technology and sensors will be held at the Dun Raven Arms Hotel, Adare, Co.Limerick, Ireland. The programme will consist of plenary, invited and contributed oral papers and posters, and will be organized to allow for maximum discussion of papers. Plenary lectures will be given by: Professor A. Bard (USA) Professor J.O.M. Bockris (USA) Professor J. Wang (USA) A strong programme of invited and contributed lectures is currently being organized. Location Adare is a small, picturesque, historical village located just a short drive from Shannon International Airport (approx. 35 min). The village has been chosen because of the large range of activities it can provide, both cultural and sporting, and ample opportunity will be given to savour the local environment .The conference will be based in the "Olde Worlde" atmosphere of the Dun Raven Arms Hotel; a large range of accommodation is available within and close to Adare, ranging from the world renowned Adare Manor to pleasant bed and breakfast type lodgings. An option has been taken on several family holiday cottages within the town and these will be available to those delegates wishing to be accompanied by their families. Publication We have planned to publish a Special Issue of The Analyst based on the papers and posters that will be presented at this conference, and authors of invited and contributed papers will be encouraged to submit their papers to Professor M.R. Smyth at the address given below before, or at, the meeting. , Those wishing to submit abstracts (1 page A4) or to obtain further details of the meeting should contact I Professor Smyth. The second circular for this meeting will be available in April 1993 and will contain full details of registration fees, accommodation, etc. Contact Address : Professor M.R. Smyth, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland. Tel: +353-1-7045308; Fax: +353-1-7045503

ISSN:0003-2654    

DOI:10.1039/AN993180027N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993, VOL. 118 29N Voltammetric Determination of Molecules of Biological Sign if icance By W. Franklin Smyth. Pp. x + 133. Wiley. 1992. Price f35.00. ISBN 0-471-93345-7. This small book covers the application of voltammetric techniques to the determination of biologically important compounds. Intended as a ‘concise practical guide’, the text is divided into eight chapters, in accordance to the nature of the electroactive functionality (following the order nitrogen-, sulfur-, and oxygen-containing molecules, hydrocarbons, halogen-containing and organophosphorus molecules, organo- metallics and inorganic molecules). The versatility and remarkable sensitivity of voltammetric techniques, particu- larly pulse voltammetry, adsorptive stripping voltammetry and amperometric detection for liquid chromatography, for trace measurements of such compounds are illustrated.Modern trends, including biosensors, modified electrodes and immunoassays are also discussed (but in a limited depth). Recent advances in in vivo voltammetry, ultramicroelectrodes or detection for capillary electrophoresis are not covered. Detailed theory is not given and the approach is primarily experimental. The book is clearly written, well organized and full of practical examples. It is illustrated with SO figures, 33 tables and over 300 references (up to l990!). Overall, the book represents a very good source of useful information, and is highly recommended for those using electrochemical tech- niques for measuring biological compounds. Joseph Wung Chemical Analysis in Complex Matrices Edited by Malcolm R.Smyth. Pp. 295. Analytical Chem- istry Series. Ellis Horwood. 1992. Price f50.00. ISBN 0-1 3- 1 2767 1-9. The ‘complex matrices’ given in the title encompass air (for monitoring quality), animal feeds, human foods, the types of components found in brewing, biological fluids (and analyses of these for drugs), adhesives and sealants. The editor provides an interesting introduction to the chapters by other authors in which each stage (or ‘unit process’) of an analytical investigation is identified and some emphasis is placed upon defining objectives in advance, on evolving appropriate methods of sampling, and the prepara- tion of the samples. The subject of the most lengthy chapter is the analysis of drugs in biological fluids; it covers spectroscopic, immunoas- say, chromatographic and voltammetric procedures of various kinds and includes 271 references.As the editor and all of the contributors are at establish- ments in Ireland it could be expected that the chapter about brewing might emanate from a historic company with a harp as its trade mark, and it does. The chapter includes a review of the process and of applications for techniques such as atomic absorption and near infra-red spectroscopy, chromatography, etc., together with the Servo Chem Automatic Beer Analyzer (‘SCABA’), which is capable of analysing 20 samples of beer per hour for alcohol, gravity, colour and pH. The chapter on sealants and adhesives reviews current types and their analysis, with emphasis mainly on nuclear magnetic resonance and chromatography but including differential- pulse anodic stripping voltammetry to obtain a profile of trace metals.In specific examples other techniques are mentioned, and still others, including thermal analysis, in the conclusion. The chapter on analysis of air for quality and pollution includes discussion of different types of emissions, lists the procedures for sampling and methods of analysis for volatile components recommended by NIOSH, and the EPA recom- mendations for methods to determine toxic organic com- pounds in air. (In this connection it should be remembered that the exposure limits cited are not always the current ones for United Kingdom as given in Health and Safety Executive publication EH 40/92 ‘Occupational Exposure Limits 1992’.) The final chapter covers chemical analysis of animal feeds and human foods and it is pleasing to note that once again the importance of sampling is stressed. There is mention of the routine procedures for protein, oil and fat, carbohydrate and fibre and nutritional analysis for amino acids etc., is included. Systems are given for extraction of drugs, pesticides and growth-promoting agents from certain feedstuffs.It is an interesting book and should prove helpful for practitioners in the fields mentioned. Parts of the text are more reviews of existing procedures rather than original matter but the volume contains enough that is original to make it of general interest; in many cases the details of extractions from the matrices should be most helpful.1 would recommend it for purchase by libraries and analysts in the fields concerned. D. Simpson Preparative and Process-Scale Liquid Chromatography Edited by G. Subramanian. Ellis Horwood Series in Chemical Engineering. Pp. 286. Ellis Horwood. 1991. Price f55.00. ISBN 0-1 3-678327-9. The book opens with a chapter that compares preparative with analytical liquid chromatography by considering operational and equipment differences and system operation. This is followed with a very practical chapter on design and control of process-scale systems discussing safety factors, selection of components (e.g. columns, pumps, valves and pipework), automation and validation. A further chapter on the technical structure of liquid chromatography separation plants details differences between those operating with organic solvents and those with aqueous solvents and also considers plant control systems.The next chapter discusses column packings used in preparative chromatography. A1 though the discussion essen- tially considers only straight phase media it addresses ques- tions concerning production routes to preparative silicas and design factors of the media (e.g., particle size, pore volume and size, and particle shape). This is followed by chapters on column technologies, strategies for optimizing process chro- matographic systems and determination of operating para- meters in process systems. The latter chapter discusses selection of stationary and mobile phases, detectors, eluent and gradient elution regimes. A chapter on ion-exchange processes considers selection of different grades of media, factors to consider during scale-up particularly for protein separations and media re-use.This is followed by a chapter on continuous moving bed systems that is far too long, occupying over 20% of the book, and is essentially an advertisement for a particular system. A chapter on large scale purification of bacterial proteins discusses advantages and disadvantages of different packings and some aspects of process design. The following chapter on affinity chromatography argues in favour of this approach for protein separations to reduce the number of purification steps.30N ANALYST, MARCH 1993, VOL. 118 Finally there are two chapters on enantio-separations. The first describes chirality and reviews chiral packings (essentially those available for analytical applications).The second discusses optimization of preparative scale enantio-separa- tions. This book contains a lot of material that should be of interest to analytical chromatographers interested in prepara- tive scale systems and to synthetic chemists considering process chromatography. However, it is this reviewer’s opinion that it has been very poorly edited, contains numerous typographical errors, has poorly presented diagrams in many chapters (in one case half a blank page where a diagram has been omitted), there is too much repetition of topics between chapters and finally that excessive chapter on continuous moving bed systems. For the required price I do not recommend it. G.P. R. Carr Recent Developments in Ion Exchange 2 Edited by P. W. Williams and M. J. Hudson, Pp. x + 366. Elsevier Applied Science. 1990. Price f50.00; US$ 90.00. ISBN 1-85’1 66-520-X. The proceedings of a conference are never exciting reading material, unless the conference concerns a new field in science. Ion exchange is obviously not a new field, hence the collection of papers on recent developments will only appeal to a few readers. A newcomer to the field will not, howcver, receive a balanced picture of what is of concern now in ion exchange from this rather eclectic collection. The various subjects discussed are covered by the headings: Biological Materials, Inorganic Ion Exchangers, Nuclear Industry, Theoretical Aspects and New Advances, New Materials, and Industrial Applications.However, under these headings are hidden several papers concerned with analytical applications (mainly of ion chromatography) with little or no relevance to the subject of the heading. These are the papers by Senior, Laeubli, Humphrey, and Ryder, for instance. Some of the introductory papcrs, such as those of Williams (on biological materials), and Bibler (on nuclear industry, where only 2 out of the 58 references are later than 1983), are more historical surveys than an exposition of recent developments. It is noteworthy that the physical chemistry of ion exchangers and the ion-exchange process appears to be a closed subject, as no new developments in this sub-field are reported (perhaps with the exception of the paper by Watson, that deals with viscous flow in the pores of macroreticular resins).A seemingly novel method, electrochemical ion exchange, is described in the papers by Allen et al. and by Adams and Hudson. This is distinct from electrochemical methods applied to ion transport through or along ion-exchange membranes. The main features of the method have already been established prior to 1987, and its performance is not particularly impressive. Still, the concept of using electric current, as in coulometry, for the sorption and desorption of ions less noble than hydrogen is interesting. Also new and of interest are inorganic exchangers of the pillared or interca- lated type, described in the papers by Dyer and Gallardo, Alberti et al., Ferragina et al., and Hudson et al. These exchangers permit larger ions or molecules to enter them, but do not change their dimensions by swelling excessively, and may have some enhanced selectivity.Pellicular ion exchangers are also relatively new materials, that combine the advantages of low swelling, very rapid kinetics and good selectivity as described in the papers by Cook and by Pohl. The camera-ready format of the papers detracts consider- ably from the appearance of the book. In particular, the editorial modifications were printed in a different type (generally much smaller, sometimes in bold italics) than the main text, producing an unpleasant aspect. Most of the papers have abstracts, but some (those of Cook, Ferragina et al., and McGarvey and Gonzalez) have none. The editorial work on the whole appears not to have been very careful.For the sake of those readers that might need access to the information included in some specific papers, the book should be on the shelves of some central libraries. Most libraries, and certainly individual practitioners of ion exchange, can do without it. Y. Marcus lmmunochemical Assays and Biosensor Technology for the 1990s Edited by Robert M. Nakamura, Yasushi Kasahara, Gary A. Rechnitz. Pp. ix + 41 1. American Society for Microbiol- ogy. 1992. Price US $43.00 (member): US $51.00 (non- member). ISBN 1-55581-040-3. This book is broadly divided into three sections dealing with the concepts of immunochemical assays, the principles of different types of non-isotopic immunoassay and biosensors. The section on concepts is built around chapters dealing with general principles, the choice of labels and antibodies avail- able, together with guidance on the validation of assays.Authors are faced with a major dilemma when preparing texts in the field of immunoassay because of the wealth of knowledge and attendant literature, and it is often difficult to do justice to the breadth of the subject whilst offering a critical viewpoint. Thus, the opening chapter on general principles whilst covering the topic does not focus sufficient attention on some of the important aspects, e.g. reaction kinctics and specificity. The following two chapters deal with labels with a considerable degree of overlap; some useful critical observa- tions are made by Larry Kricka and will be of help to those readers who are new to the field wanting some help through the maze of labels that are available.The chapter on design and production of antibodies is a valuable contribution. This is an area of considerable growth where art is giving way to science and the inherent benefit to the analyst; the authors explore some of the strategies that can be employed to produce antibodies to meet specific analytical goals. The evaluation of these products is then given a rigorous airing; the discussion should give confidence to clinicians who use the results. The second section on non-isotopic assays explores the principles and design of several different immunoassay configurations. However, I was disappointed with the limited amount of consideration given to the principles of light scattering immunoassay .The chapter on homogeneous enzyme immunoassay was also disappointingly brief, particul- arly as there are so many exquisite variations on the theme of modulating catalytic activity. These are becoming ‘black box’ technologies and consequently there is a need to explore them thoroughly by the written word because the routine analyst has little opportunity to do so at the bench. One could make a similar observation about the limited treatment of homogeneous fluoroimmunoassay . One of the major developments in this field is now in the integration of immunoassays into delivery systems. Unfortu- nately this does not receive sufficient coverage; again this is often technology where the literature is not in the public domain. It is important that analysts are aware of design strategies, limitations and potential applications although one accepts that patents can scare off all but the brave or rich.My particular disappointment with this book was the section on biosensors because the title had led me to expect a review of immunoassay technology that would lead the reader logically into the expanding, and often ‘difficult’, literature onANALYST, MARCH 1993, VOL. 118 31N immunosensors. Thus, whilst there was a good chapter on electrochemical detection in immunoassay , which should have appeared in the previous section, there was very little discussion of immunosensor technology (theory or applica- tion). Thus there was nothing on the surface plasmon, total internal reflection, piezoelectric etc. devices, .where it is even more important to explain the basic principles to the reader.Despite some rather negative comments I think that the book is nicely presented and offers some valuable contribu- tions; however, it does not provide the link between immuno- chemistry and sensor technology expected from the title and it is not sufficiently comprehensive in reviewing all of the analytical principles that are going to have an impact in the next few years. C. P. Price Biosensor Principles and Applications Edited by Lo‘ic J. Blum and Pierre R. Coulet. Bioprocess Technology Series 15. Pp. x + 357. Marcel Dekker. 1992. Price US$ 125.00 (US and Canada); US$143.75 (all other countries). ISBN 0-8247-8546-0. This is an excellent text containing a wealth of detailed information of interest not only to the specialist in biosensor research, but to those working in the many biosensor related areas such as fabrication technologies, clinical diagnostics, environmental monitoring, synthetic chemistry and data processing who are looking for ideas or applications. The book consists of 14 chapters written by world leaders in biosensor research. Tt opens with a useful introduction to biosensors by Pierre Coulet that addresses the philosophy and definition of the term ‘biosensor’.This is followed by three chapters dedicated to electrochemical biosensors covering amperometric enzyme electrodes, amperometric enzyme immunoassay biosensors and potentiometric enzyme elec- trodes. The often neglected area of thermally sensitive devices is covered in detail by Hengt Danielsson in a chapter on Enzyme Thermistors. Other chapters cover the use of piezoelectric and field- effect-transistor (FET)-based biosensors, while three chapters address the rapidly growing area of the fibre-optic sensors.These contributions are divided into chemically mcdiatcd, fluorophore and chromophore , and bioluminescence- and chemiluminescence-based biosensors. All the above chapters follow a similar format that includes details on the general principles of the biosensor type, fabrication techniques (with particular emphasis on the problem of immobilization of the bioactive component at the sensor tip), problems and limitations (re-usability is common to most of these, particularly with respect to antibody-antigen systems where the reactions are difficult to reverse without using extreme conditions that damage the sensitive bioactive components in the sensor membrane.The instrumentation required for obtaining and processing the sensor signal is also discussed as is the design of the biosensor itself. Examples of applications are also included. Each chapter finishes with a useful section on research trends and potential developments. Problems and limitations are presented in a way that helps the reader to develop a realistic appraisal of biosensors, rather than to oversell their usefulness, a very laudable attitude given the exaggerated claims that have been all too common in the past. In contrast to the contributions mentioned above, which deal with biosensors in terms of the transduction mechanism, the final four chapters approach the topic of biosensors from a different perspective.Chapters 11 and 12, entitled Immu- nosensors and Microbial Biosensors, respectively, approach the topic from the point of view of the biosensing element. While this does lead to a certain amount of overlap with the content of the previous chapters, it enables the reader to see how a particular approach, such as the use of microbes rather than enzymes or antibodies as the biosensi tive component in the sensor, has been applied across the range of transducers (electrochemical, acoustic, thermal, optical) available. This is very useful as it collates and expands on information that is scattered over the previous chapters. These contributions are followed by a chapter by Vadgama and Desai on in vivo biosensors.The development of inplantable devices for real-time monitoring of important clinical species remains a major challenge to all sensor researchers. The authors have reviewed the progress to date and highlight existing problems and the potential of in vivo biosensors. Interestingly, they adopt the broader definition of the biosensor that focuses on the application rather than the device itself (i.e. a sensor that is directly in contact with a biological matrix or surface but which does not necessarily incorporate a biological component itself). This enables the authors to include devices such as catheter ISEs and oxygen sensors, tissue and transcutaneous oxygen sensors, the Severinghaus C02 electrode, pH ISFETS and optrodes in their review as well as ‘mainstream’ biosensors such as the glucose, lactate and other enzyme-based sensors.This broad view of the term ‘biosensor’ is in contrast to that adopted by the authors of the previous chapters who tend to insist of the presence of a biorecognition element in the sensor transduetion cycle. However, these divergences of opinion are understandable as these authors are clinical users of sensors rather than inventors, and the problems involved with developing in vivo devices are common to all types of sensors. The editors finish up with a chapter discussing the trends and prospects for biosensors. In this chapter, they highlight different areas of research that could make a significant impact on the performance of biosensors. Each chapter is extensively referenced (100-200 references in most cases) with reasonably up-to-date citations (up to 1990), and the book is completed by a detailed index.The authors list includes Guilbault, Arnold, Bannister, Karube, Kaufmann, Kimura, Turner and Wolfbeis and other experts in biosensor research. All in all, this is an excellent addition to the growing literature on biosensors and I recommend it to anyone working or interested in the development or applica- tions of biosensors. Dermot Diamond Gas Chromatographic Enantiomer Separation with Modified Cyclodextrins By Wilfried A. Konig. Chromatographic Methods. Series Editors W. Bertsch, H. Frank, W. G. Jennings and P. Sandra. Pp. viii + 168. Huthig. 1992. Price DM 138.00. ISBN 3-7785-2026-1. The past decade has witnessed a remarkable increase in research on chiral separations for analysis, due partly to the greater demands of regulatory authorities for high quality characterization of drugs, pesticides and food additives, but also to an increasing interest in the problems of chiral discrimination per se.Many of these analytical methods have been based on the successful development of enantioselective stationary phases for HPLC. Thus the present book by Professor Konig is all the more welcome for bringing a well-balanced focus on recent developments in enantioselec- tive GC, which until now has been something of a cinderella in the field. This monograph largely summarizes the contribu- tions of the Konig group in developing practicable GC phases for enantioseparation based on substituted cyclodextrins (CDs), but does so with a helpful perspective on the valuable Contributions of others in the field, including Schurig and Armstrong.The book consists of two principal sections, a32N ANALYST, MARCH 1993, VOL. 118 general introduction to the historical and synthetic develop- ment of modified CDs, and an extensive collection of applications based primarily (but not exclusively) on the well characterized phases developed by the Konig group. Two very short chapters give an initial treatment on the putative mechanism of host-guest interactions with modified CDs, together with a summary of some recent studies with high-field 1H NMR. A brief but valuable discussion of the historical develop- ment of enantioselective GC methods, based partly on an earlier monograph by the same author in 1987, concludes with the prophetic statement by Szejtli in 1987 predicting the ‘successful utilization of derivatized CDs in capillary GC for the excellent chiral recognition and resolution of many racemates’.That this should have been so quickly demon- strated independently by Schurig (actually in 1987) and by Konig in 1988, leading to the renaissance of enantioselective GC, is in itself remarkable. The general introduction gives an authoritative account of the synthesis and fundamental properties of a range of derivatized CDs, limited necessarily to those developed by the author, or well known in the literature. Apart from some obvious typographical errors and a few inconsistencies in the author’s own use of his valuable scheme of abbreviations for the CD derivatives [e.g., in Table 6 heptakis-(3-O-butyryl-2,6-di-O-pentyl)-cd is incorrectly des- cribed as the y-CD derivative], this is a valuable introduction to the essential reactivity and chemistry of a, p- and y-CDs.Although the detailed description of synthetic routes (all of them published) can be regarded as peripheral in a monograph on chromatographic methods, they do afford a useful insight into the difficulties involved and the care required to characterize the products adequately, illustrating the use of Gray’s reductive depolymerization method, quantitative GC, GC-MS and NMR. The description of the author’s so-called ‘inversely substituted’ derivatives is particularly valuable, whereby the secondary hydroxyl at C2 and the much less reactive hydroxyl at C3, located on the wider end of the CD torus, are substituted by pentyl groups, while the primary C6 hydroxyl at the narrower end of the torus is selectively substituted by various alkyl groups, to give the 6-0-alkyl-2,3- 0-pentyl CD derivative (by contrast with the more easily formed 2,6-0-pentyl-3-0-alkyl CDs previously described).This chapter also gives useful practical data on the preparation and testing of Pyrex glass and fused silica capillary columns. This monograph has an excellent collection of applications, all the more remarkable for its diversity considering the relatively short time since the development of these new phases. The author has wisely chosen to group the applica- tions for ease of reference by classes of compound, ranging from alkanes and cycloalkanes, through epoxy alcohols, carbohydrates, and ketones to amino acids.There is a particularly useful discussion on the problems of racemization of amino acids and some new techniques for the analysis of all amino acids involved in protein synthesis. Most of the major fields of application are covered in this extensive chapter, including the assignment of absolute configuration to natural compounds (pheromones, flavours, peptide antibiotics), determination of enantiomeric excess in asymmetric synthesis (with a nice discussion of the Sharpless asymmetric epoxida- tion procedure), in chiral synthons, auxiliaries and catalysts and in several pharmaceuticals. A small sub-chapter on the analysis of chiral drugs is the only section devoted to a specific application area, illustrated by reference to barbiturates and similar heterocyclic systems.It would have been helpful to have included a table cross-referencing the many other drugs described under the individual chemical classes, e.g., antibiot- ics, ibuprofen (non-steroidal anti-inflammatory), anaesthetics and CNS agents. However, this is a minor criticism, given the comprehensive index provided. Moreover, some advances in techniques are presented, including the use of two-dimen- sional GC, where the peak is ‘heart-cut’ from the first-column for resolution on a chiral column. It would have been useful to have referred to recent applications in SFC, notably by Schurig in 1991. The monograph concludes with brief reference to the putative mechanisms of supramolecular host-guest interac- tions, and some preliminary data on high-field lH NMR studies of model systems. The book is strongly recommended as an introduction to the new field of chiral GC on modified CD phases, for which this monograph will serve as an excellent guide both to newcomers and experienced researchers alike.As a source book of applications the author has succeeded in condensing work from some 270 citations into a readable and useful format. This book should serve as a valuable stimulus to further research in the field and will be invaluable to those wishing to gain an informed insight into the present state-of-the-art of chiral GC based on modified CD phases. Anthony F. Fell Coal Quality and Combustion Performance.An Interna- t io na l Perspective Edited by J. F. Unsworth, D. J. Barratt and P. T. Roberts. Coal Science and Technology 19. Series Editor Larry L. Anderson. Pp. x + 638. Elsevier. 1992. Price US$223.00; Df 1435.00. ISBN 0-444-88703-2. This book emphasizes the challenge the fuel technologist has in designing combustion and heat-exchange systems for a material so diverse in composition and physical characteristics as coal. T particularly like the efforts of the authors to validate the analytical methods by establishing international round- robin exercises for sampling and analysis of coal. They have then utilized their analytical and fuel oil combustion experience to produce a text giving help and a fundamental understanding of the qualities of international coals and their influences on combustion plant efficiency and related processes. T agree with the authors whole-heartedly in their suggestion that the volume will earn its rightful place alongside the works of other distinguished authors in the field.It certainly will sit on my own bookshelves alongside the works of Lowry. The text of the book is easy to read and flows logically from chapter to chapter. The three main sections, described briefly later, are all prefaced, which I found particularly helpful in establishing the scene for the following chapters. Figures and illustrations are also clear and well thought out. However, the reproduction of the plates, particularly the scanning electron micrographs, is a little disappointing in relation to the other very high qualities of the book.To give a flavour of this exceptional book, I will briefly comment on the contents of its chapters. The book sets the scene for the later chapters nicely by describing in the introduction the international scene in coal trade and the fundamental approach to research, i.e., coal constitution, laboratory assessment of combustion behaviour, burning trials in pilot scale plant and finally usage, as in power station combustion. The first part of the book, Part A, Coal Characteristics, continues with descriptive chapters on coal quality and analysis, organic structure of coal with two very interesting sections on rank and maceral composition. Finally, in this section of the book the last chapter deals with specific inorganic heteroatom influences on coal combustion, i.e., sulfur and nitrogen and also the effect of other mineral matter. Part B of the book details chapters on the influence of organic components on combustion performances.Particular emphasis is given to pulverization, pyrolysis, char-oxidation, with a very useful chapter on maceral influences on high temperature oxidation temperature. Carbon burn-out isANALYST, MARCH 1993, VOL. 118 33N discussed in some detail with full scale validation of burn-out calculation models. Finally, in Part B, the development of a model for flame stability is discussed and the influence of rank demonstrated. The authors clearly state the assumptions made in their model predictions and the limitations in their calculations. The final section, Part C , of the book deals with the influence of heteroatom and inorganic components on com- bustion performance. Chapter 10, in this section, deals with coal quality effects on boiler operation and pollutant emissions and clearly demon- strates the inadequacy of the conventional, and much used, ‘slagging and fouling indices’, to predict boiler performance.The authors rightly conclude that such indices should not be taken as generally applicable to all coal-fired boiler systems. The atmospheric emission section of this chapter discusses particulates, oxides of nitrogen, sulfur and carbon, and trace elements, in the light of current international legislative limits. The final three chapters of the book deal with the prediction of ash deposition by combustion limits and suggested practical methods for prevention and removal, the evaluation of ultra-fine coal as an option for industrial fired boilers and finally the fates of fly ash, nitrogen and sulfur during combustion.I consider I have been privileged to be asked to review a book of such high quality and fuel technologists world-wide, I am sure, will recognize its worth and add it to their own bookshelves. W. C. Pearce ~ ~~~ HPLC Methods on Drug Analysis By Mantu K. Ghosh. Pp. xvi + 586. Springer-Verlag. 1992. Price DM 198.00. ISBN 3-540-53824-0; 0-387-53824-0. The book reviews HPLC methods of analysis for over 230 different drugs. Methods are presented for the analysis of drug substances, formulated products and for the measurement of drugs in biological matrices such as plasma and urine.Literature references from over 50 journals and publications are used, with the majority coming from the established chromatography and pharmaceutical publications such as Journal of Chromatography (including Biomedical applica- tions), Journal of Chromatographic Science, Journal of Pharmaceutical and Biomedical Analysis and Clinical Chem- istry. Each drug entry is arranged alphabetically and contains information on the compound, such as the Chemical Abstracts Service number, chemical name, empirical formula, mole- cular mass, proprietary names, clinical use, solubility and light absorption. This is followed generally by several HPLC methods covering a variety of applications. Within each method, details are given of type of sample, extraction procedures, equipment used, column, mobile phase, flow rate, internal standard, injection size, method of detection and recording, and the reference publication.A particularly valuable section in each entry includes data on retention times of related substances such as metabolites, degradation products and co-prescribed or similar drugs. Other useful information contained in the book are tables of HPLC separation system characteristics, descriptive guides to sorbent selection and a solvent miscibility table. Of lesser value are tables of elemental atomic weights and unit conversion factors. A list of abbreviations and glossary of terms used in the text are also included. Overall, the book contains a comprehensive survey of HPLC methods for the drugs listed and will be a valuable addition to the literature of any practising analytical chemist in the areas of pharmaceutical chemistry, dosage form analysis, bioanalysis and clinical chemistry.Some important modern drugs are omitted from the book, presumably because of their omission from the general current literature. Chiral chromatography is mentioned for some drugs, but is not covered in specific detail. The book will be a good practical guide to analysts wishing to set up methods, not only for those drugs listed, but also for compounds with similar structures and properties. The author has clearly undertaken a painstaking and thorough review of the recent literature on HPLC methods for drug analysis, and his book can be recommended for general use by analysts in the pharmaceutical field.I . E. Davidson Mass Spectrometry in the Biological Sciences: A Tutorial Edited by Michael L. Gross. Pp. xxi + 461. NATO AS/ Series. Series C: Mathematical and Physical Sciences. Volume 353. Kluwer Academic. 1991. Price Df1255.00; US$146.00; f87.00. ISBN 0-7923-1 539-1. The spectacular advances in the science of mass spectrometry since 1975 formed the subject for the NATO Advanced Study Institute on Mass Spectrometry in the Molecular Sciences held in Italy in June 1990. At that Institute, the senior lecturers decided, wisely, against publishing a series of short articles in mass spectrometry as a record of the meeting and instead came up with the idea of a tutorial-type review. Divided into three parts on instrumentation (140 pages), methods (180 pages), and applications to biomolecules (130 pages), the volume is designed to serve as a tutorial on the current status of biological mass spectrometry. It is said to be appropriate for newcomers and graduate chemists. There are 29 contributions from a group of 52 internationally respected authors. The instrumental topics include the theory of electric and magnetic sectors, hybrid tandem mass spectrometry, triple quadrupole systems, ion traps, Fourier transform mass spectrometers, time-of-flight analysers and ion detectors. The section on methods covers the major in-vogue ionization techniques such as electrospray and matrix assisted laser desorption, as well as more established methods such as plasma desorption, continuous-flow fast atom bombardment, liquid chromatography-mass spectrometry, semi-empirical molecular orbital theory, and neutralization-reionization mass spectrometry.Reflecting current trends in the literature, the majority of the applications concern peptides, glycopep- tides and proteins, but nucleic acid components and lipids are also covered to some extent. Each contribution is accom- panied by a list of references, predominantly citing papers published from 1985 to 1990. The book ends with a subject index. So, what makes this book different from other collections of reports‘? It is called a tutorial. Presumably this title implies a didactic approach, maybe even an interactive text with self-assessment questions, and writing that is somewhat less passive or formal than in a standard textbook. The reader may even expect practical hints that do not often appear in conventional reviews. Unfortunately, none of these expecta- tions is realized.This reviewer could not distinguish the contributions from conventional reviews (apart from some of the chapters on applications which have much the same format as conventional papers). Hence, the book’s sub-title is misleading. Many of the reviews arc clear and enjoyable expositions but are not gentle enough for newcomers to mass spectrometry. I would only recommend this book to those with a grasp of the basics and a background in the traditional aspects (electron ionization, gas chromatography-mass spectrometry, and so on). Such readers could use this ‘tutorial’ to update and extend their knowledge to modern methods.34N ANALYST, MARCH 1993, VOL.118 One set of authors was brave enough to notc that their field is developing so rapidly ‘that this picture may well be out of date by the time this chapter is in print’. However, the book succeeds in reflecting the status of biological mass spec- trometry in 1990. In fact, the volume covers a wider range of mass spectrometry than might be expected. Overall, there is a lot of useful information in this book but beware, the information is not as accessible as the title suggests. M . E. Rose Analytical Artifacts: GC, MS, HPLC, TLC and PC By Brian S. Middleditch. Journal of Chromatography Library. Volume 44. Pp. xxiv + 1034. Elsevier. 1992. Price US$241.50. Dfl. 495.00. ISBN 0-444-971 59-6. How often as an analyst have you tried to fit the odd peak and perplexing mass spectrum to the problem in hand, only to discover that the compound in question was a contaminant? Indeed in these days when detection limits are going to much lower levels, whilst the range of analytes are becoming far more complex, the problem of the formation of artifacts and general contamination is a serious one.This latest book from Brian Middleditch should be on every Analyst’s shelf. Based on a format originally used with his earlier work on ‘Priority Pollutants’ this latest book has expanded on the mass spectra shown there and includes details of chromatography and other analytical procedures used. Each entry is headed by thc common name, empirical formula and molecular mass based on the most abundant isotope (e.g., C1 = 35, not 35.5). This is followed by the mass spectrum, all EI at 70 eV. Next a structure, CAS number, Merck Index and synonyms. The bulk of the cntry is an abstract describing the re.ported appearance of the artifact complete with description of its origin, spectra of any derivatives formed and a reference. To help with the interpretation there are 8-peak style tables laid out with details of the mass spectra. A comprehensive index of references and authors is also given. This is the moment when the book becomes a real joy to read. When first opened I was intrigued by an entry ‘Pink Beards and Black Spots’. The entry describes work by A. J . P. Martin in the early days of chromatography when purple spots due to amino acids appeared to grow a pink beard. Eventually the cause was traced to the fan used to dry the paper after the first direction which had a badly sparking commutator. This deposited black spots of copper on the paper and the pink beards were due to complexes of the amino acids with copper. Well the book has many tales like that and the author addresses this in his preface. ‘This book . . . is dedicated to the innumerable scientists who made mistakes, used impure chemicals and solvents, suffered the consequences of unantici- pated side-reactions, and were otherwise exposed to mayhem yet were not too embarrassed to publish their findings. Contributions to a sequel will be gratefully received.’ Lest this review suggest that the book only comprises such tales it should be stressed that the bulk of the entries describe the artifacts most of us are familiar with such as plasticizers, TLC binders, decomposition products in stale blood, artifacts from stationary phases and more. These are listed as that, so there is a section on TLC artifacts with cross references to the individual entries where the artifact is described in detail. In conclusion this is a book to be recommended for every laboratory carrying out analytical work using TLC, GC and mass spectrometry. I am looking forward to the sequel; indeed I may have an embarrassing tale or two of my own to tell. N . J . Haskins

ISSN:0003-2654    

DOI:10.1039/AN993180029N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993. VOL. 118 35N Conference Diary Date Conference March 30-114 April 3-4 4-8 5-7 5-9 5-8 6-7 13-17 18-21 19-2 1 19-22 19-23 19-22 20-23 20-23 25-29 Location 12th Pharmaceutical Technology Conference Elsinore, Denmark VDI-Meeting on Progress in Thermic, Catalytic and Sorptive Exhaust Cleaning Mannheim, Germany XIIIth World Congress on Occupational Safety New Delhi, and Health India 3rd International Conference on Ion-Beam and Namur , Surface Specific Analysis Techniques Belgium 4th International Meeting on Trace Elements in Chamonix, Medicine and Biology France Annual Chemical Congress, ‘New Materials: New Toxicology’ UK Southampton, BTS Colloquium (of the British Toxicology Society) on Early Markers of Carcinogenesis Canterbury, Kent, UK International Meeting on the Effects of War Zadar, Activities in the Environment Croatia Fourth International Symposium on Pharmaceutical and Biomedical Analysis USA Baltimore, MD, ANAKON ’93 Baden-Baden, Germany Annual Physics Congress: Spectroscopy, The Changing Face of Physics UK Brighton, Focus ’93: The Association of Clinical Biochemists Annual National Scientific UK Meeting and Exhibition ECIO ’93: European Conference on Integrated Neuchatel, Optics Switzerland Birmingham, International Symposium on Electroanalysis in Loughborough, Biomedical, Environmental and Industrial Leicestershire, Sciences UK 5th European Congress on Biopharmaceutics Brussels, and Pharmacokinetics Belgium Eurolab 93, 12th SFBC National Meetingloth Nice, IFCC European Congress of Clinical France Chemistry Contact The 12th Pharmaceutical Technology Conference, 24 Menlove Gardens North, Liverpool, UK L18 2EJ VDI, Verein Deutscher Ingenieure (Kommission Reinhaltung der Luft), Graf Recke-Strasse 84, P.O.Box 1139, D-W-4000 Dusseldorf 1, Germany National Safety Council, P.O. Box 26754, Siom, Bombay 400022, India Professor G. Demortier, Facultes Universitaires, N-D de la Paix, 22 rue Muzet, B-5000 Namur, Belgium A. Favier, Laboratoire de Biochimie C., Hopital A. Michallon, B .P. 217X, F-38943 Grenoble Cedex 09, France Tel: +33 76 76 54 07. Fax: +33 76 42 66 44 Mervyn Richardson, BASIC, 6 Birch Drive, Maple Cross, Rickmansworth, Hertfordshire, UK WD3 2UL Tel: +44 923 774187. Fax: +44 494 714516 Dr. E. S. Harpur, Sterling Winthrop Research Centre, Willowburn Avenue, Alnwick, North Cumberland, UK NE66 2JH Mervyn Richardson, BASIC, 6 Birch Drive, Maple Cross, Rickmansworth, Hertfordshire, UK WD3 2UL Tel: +44 923 774187.Fax: +44 494 714516 Shirley E. Schlessinger (Symposium Manager), PBA ’93, Suite 1015, 400 East Randolph Drive, Chicago, IL 60601, USA Tel: + 1 312 527 2011. Gesellschaft Deutscher Chemiker, Abteilung Tagungen, Varrentrappstrasse 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 79 17 366. Fax: +49 69 79 17 475 Spectroscopy, The Changing Face of Physics, The Conference Department, The Institute of Physics, 47 Belgrave Square, London, UK SWlX SQX Tel: +44 71 235 6111. Fax: +44 71 259 6002 Pat Nielsen, Pipers, Main Street, Akeley, Buckingham, UK MK18 5HW 0. Parriaux, Conference Chair, Centre Suisse D’Electronique et de Microtechnique, Maladiere 71, Case Postale 41, CH-2007, Neuchatel, Switzerland Tel: +41 38 205 111.Fax: +41 38 205 630 Dr. Arnold Fogg, Electroanalysis Conference, Chemistry Department, Loughborough University of Technology, Loughborough, Leicestershire, UK LEll3TU Mrs. F. Rey, 3/17 Avenue de I’Observatoire, B-1180 Brussels, Belgium Tel: +31 2 375 1648. Fax: +31 2 375 3299 Groupe SEPFI, Technoexpo, 8 rue de la Michodiitre, 75002 Paris, France Tel: +33 1 47 42 92 56. Fax: +33 1 42 66 14 2836N ANALYST, MARCH 1993, VOL. 118 Date 25-29 26-115 27 May 2-7 3-5 3-5 4 4-5 4-6 4-6 6-12 9-14 9-13 10-13 11-15 20-2 1 23-28 24-26 Conference Location 84th AOCS Annual Meeting & Expo: A joint meeting with the Japan Oil Chemists’ Society ‘Wasser’, Berlin’93 Berlin, Germany Anaheim, CA, USA Validating Multicomponent Analysis London, UK CLEO/QELS ’93, The Thirteenth Conference on Lasers and Electro-Optics concurrently with the Quantum Electronics and Laser Science Conference EuroResidue 11: Residues of Veterinary Drugs Veldhoven , in Food The Netherlands Baltimore , MD , USA Fifth Symposium on the Analysis of Steroids Szombathely , Hungary Capillary Chromatography: the Spring Greenford, Symposium and Annual General Meeting of the Middlesex, Chromatographic Society UK ASTM Symposium On Quality And Statistics: Total Quality Management USA Deauville Conference and Symposium on Analytical Sciences-SAS 93 France Atlanta, GA, Deauville, 9th Optical Fibre Sensors Conference Florence, Italy Interpack’93 (Environmentally Justified Diisseldorf, Packaging) Germany HPLC ’93, 17th International Symposium on Column Liquid Chromatography Germany Hamburg, EMAS ’93-Modern Developments and Applications in Microbeam Analysis Italy International Environment ’93 and Analysis ’93 UK Rimini , London, IV Encontro de Usuarios de RMN Rio de Janeiro, Brazil 4th International Meeting on Scnning Laser Ophthalmoscopy , Tomography and Germany Microscopy Heidelberg, 41st ASMS Conference on Mass Spectroscopy Las Vegas, NV, USA 11th Dechema Annual Meeting on Biotechnology Germany Frankfurt , Con tact American Oil Chemists’ Society, P.O.Box 3489, Champaign, IL 61826-3489, USA Cornelia Wolff, v.d. Sahl, AMK Berlin, Ausstellungs-, Messe- und Kongress-GmbH, Postfach 19 17 40, D-1000 Berlin 19, Germany Mr.T. Frost, The Wellcome Foundation, Dartford, UK DAZ 5AH Meetings Department, Optical Society of America, 2010 Massachusetts Avenue, NW, Washington, DC Tel: + 1 202 223 9034. Fax: + 1 202 416 6100 Dr. N. Haagsma, Department of the Science of Food of Animal Origin, Faculty of Veterinary Medicine, University of Utrecht, P.O. Box 80.175, NL-3508 TD Utrecht , The Netherlands Tel: +31 30 535 365. Fax: +31 30 532 365 Professor S. Gorog, c/o Chemical Works of Gedeon Richter Ltd., P.O. Box 27, H-1475 Budapest, Hungary Tel: +36 1 157 4566. Fax: +36 1 157 1578 The Executive Secretary, The Chromatographic Society, Suite 4, Clarendon Chambers, 32 Clarendon Street, Nottingham, UK NG14BU Tel: +44 602 500596. Fax: +44 602 500614 Scott Orthey, ASTM, 1916 Race Street, Philadelphia, PA 19103, 215/299-5507, USA Sabine Lauras, Nicko & Cri Associks, 7 rue d’Argout.F-75002 Paris, France Tel: +33 1 42 33 47 66. Fax: +33 1 40 41 92 41 Annamaria Scheggi, Instituto di Ricerce, Sulle Onde Elettromagnetiche , del Consiglio Nazionale delle Ricerche , Via Pancialichi , 64, Florence, Italy Tel: +39 55 43 78 512. Fax: +39 55 41 08 93 Dusseldorfer Messegesellschaft mbH ‘NOWEA’, P.O. Box 32 02 03, Stockumer Kirchstrasse 61, D-W-4000 Diisseldorf 30, Germany Gesellschaft Deutscher Chemiker, Abteilung Tagungen, Varrentrappstrasse 40-42, Postfach 90 04 40, D-6000 Frankfurt am Main 90, Germany Tel: +49 69 79 17 360. Fax: +49 69 79 17 475 Abraham Boekestein, Mansholtlaan 12, Postbus 356, D-6700 Wageningen, Germany Eileen Davies, IE ’93,12 Alban Park, Hatfield Road, St Albans, Hertfordshire, UK AL4 OJJ Tel: +44 727 855574.Fax: +44 727 841694 The Associacao de Usuarios de Ressonancia Magnetica Nuclear (Auremn), A/C Sonia Maria Cabral de Menezes, Petrobras/Cempes/Diquim, Radial 2, Quadra 7,21910.240 Cidade Universitaria, Ilha Do Fundao, Rio de Janeiro, RJ, Brazil Reinhard Burk or H. E. Volcker, Augenklinik, Ruprecht-Karles-Universitat Heidelberg, Im Neunheimer Feld 400, 6900 Heidelberg, Germany Tel: +49 6221 56 66999. Fax: +49 6221 56 5422 American Society for Mass Spectrometry, P.O. Box 1508, East Lansing, MI 48826, USA Tel: +1 517 337 2548. Dechema, P.O. Box970146, D-W-6000 Frankfurt am Main 97, Germany 20036- 1023 , USAANALYST, MARCH 1993, VOL. 118 37N Date 24-27 24-29 25-27 25-27 27-28 27-28 June 2-4 3 3-4 7-9 8-1 1 13-17 13-17 14-16 14-20 16 17-18 Conference Location Contact 15th International Symposium on Capillary Chromatography (ISCC) Riva del Garda, Italy Professor Dr.P. Sandra, IOPMS, Kennedypark 20, B-8500 Kortrijk, Belgium Tel: +32 56 204960. Fax: +32 56 204859 Dr. V. N. Makatun, Organizing Committee of the Mendeleev Congress, Presidium of Byelorussian Academy of Sciences, 66, F. Scorina Avenue, Minsk, Byelorussia Professor Dr. Willy R. G. Baeyens, University of Ghent, Pharmaceutical Institute, Harelbekestraat 72, B-9000 Ghent, Belgium Stephen Ward, Enterprise Public Relations, 165 Kensington High Street, London, UK W8 6SH Professor Dr. P. Sandra, IOPMS, Kennedypark 20, B-8500 Kortrijk, Belgium Tel: +32 56 204960. Fax: +32 56 204859 Dr. V.M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5V7 Tel: + 1 613 932 7702. XV Mendeleev Congress on General and Applied Chemistry Minsk, Byelorussia Vth International Symposium on Quantitative Luminescence Spectrometry in Biomedical Sciences Control and Instrumentation Exhibition ’93 Ghent , Belgium Birmingham, UK Riva del Garda, Italy 2nd European Symposium on Analytical Supercritical Fluid Chromatography and Extraction (ESASF) European Conference on Environmental Pollution, Aquatic and Atmospheric Environment, Airmater Quality, Hazardous Wastes and Hydrology Helsinski, Finland International Symposium on Analysis of Peptides Stockholm, Sweden The Swedish Academy of Pharmaceutical Sciences Symposium on ‘Analysis of Peptides’, P.0. Box 1136, S-111 81 Stockholm, Sweden Tel: +46 8 24 50 85. Fax: +46 8 20 55 11 Professor J. Mattinen, Abo Akademi, Institution for Organisk Kemi, Akademig 1, SF-20500 Abo 50, Finland Dr. V. M. Bhatnagar, Alena Chemicals of Canada, P.O. Box 1779, Cornwall, Ontario, Canada K6H 5v7 Tel: +1 613 932 7702. G. Lachenal, Laboratoire d’Etudes des Matkriaux Plastiques et des Biomateriaux, Universitk Claude Bernard, Lyon 1, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne Ckdex, France Tel: +33 72 43 12 11. Fax: +33 78 89 25 83 The Conference Registrar, 18 Portway Drive, West Wycombe, Buckinghamshire, UK HP12 4AU Tel: +44 494 448048. Fax: +44 494 448154 Congress Secretariat, c/o Professor Laura Frontali, Department of Cell and Developmental Biology, University of Rome ‘La Sapienze’, P.le Aldo Moro 5 , 00185 Rome, Italy Tel: +39 6 445 3950. Fax: +39 6 499 12351 SSC3 Secretariat, Department of Chemical Technology, Danish Technological Institute, Teknologiparken, DK-8000 Arhus C, Denmark Telt 1+45 86 14 24 00. Fax: +45 86 14 74 45 Ms. Janet Cunningham, Barr Enterprises, P.O. Box 279, Walkersville, MD 21793, USA Tel: t-1301 898 3772. Fax: +1 301 898 5596 Mrs. Tarja Jalasto, Finnish Society for Quality Control, Laaksolahdentie 41, P.O. Box 1, SF-02730 Espoo, Suomi-Finland Dr. Paul Illing, Health and Safety Executive, R425 Magdalen House, Stanley Precinct, Bootle, UK L20 3QZ Tel: +44 51 951 3420. Fax: +44 51 922 7918 Dr. V. M. Bhatnagar, Alena Chemicals of Canada; P.O. Box 1779, Cornwall, Ontario, Canada K6H 5v7 Tel: +1 613 932 7702.NMR Symposium Turku, Finland European Conference on Analytical Chemistry, Chromatography and Spectroscopy and Thermal Analysis Brno, Czechoslovakia ESIS ’93: European Seminar on Infrared Spectroscopy Egham, Surrey, UK The Seventh International LIMS Conference 6th European Congress on Biotechnology Firenze , Italy 3rd Scandinavian Symposium on Chemometrics Arhus, Denmark PREP-93, 10th International Symposium on Preparative Chromatography Arlington, VA, USA European Organization for Quality Control Helsinki, Suomi-Finland Substances and Processes Dangerous to the Environment Preston, Lancashire , UK International Conference on Analytical Chemistry & Applied Chromatography/ Spectroscopy Toronto, Canada38N ANALYST, MARCH 1993, VOL. 118 Date 27-117 29-417 July 4-7 4-8 4-9 11-14 11-15 12-14 19-21 19-23 25-29 Conference Fullerenes '93, 1st International Interdisciplinary Colloquium on the Science and Technology of the Fullerenes XXVIII Colloquium Spectroscopicum Internationale XXVIII CSI Post-Symposium: Graphite Atomizer Techniques in Analytical Spectroscopy 6th International Conference on Indoor Air Quality and Climate, Indoor Air'93 22nd Meeting of the Federation of European Biochemical Societies International Symposium on Polymer Analysis and Characterization Chemometrics 111, 3rd Czechoslovak Chemometric Conference R & D Topics Meeting 1993 6th Symposium on Handling of Environmental and Biological Samples in Chromatography 12th International Symposium on Nuclear Quadrupole Interactions 107th AOAC Annual International Meeting and Exposition August 9-11 3rd Soil and Sediment Residue Analysis Workshop 9-13 Asianalysis 11: Second Asian Conference on Analytical Chemistry 9-13 ILC '93: International Conference on Luminescence and Optical Spectroscopy on Condensed Matter Location Santa Barbara, CA, USA York, UK Durham, UK Helsinki, Suomi-Finland Stockholm, Sweden Crete Brno, Czechoslovakia Bradford, W.Yorkshire, UK Guildford, Surrey, UK Zurich , Switzerland Washington, DC, USA Contact Gill Spear, Pergamon Seminars, c/o Elsevier Advanced Technology, Mayfield House, 256 Banbury Road, Oxford, UK OX2 7DH; Tel: +44 865 512242. Fax: +44 865 310981 or for North America, Kim Cavellero, Pergamon Seminars, 660 White Plains Rd., Tarrytown, NY 10591-5153, USA Tel: +44 865 512242.Fax: +44 865 310981 Dr. B. L. Sharp, Loughborough University of Technology, Department of Chemistry, Loughborough, Leicestershire, UK L E l l 3TU XXVIII CSI Post-Symposium, Department of Chemistry, (CSI Secretariat) , Loughborough University of Technology, Loughborough, Leicestershire, UK LE 1 1 3TU Tel: +44 509 22575. Fax: +44 509 233163 Professor Olli Seppanen, SF-02150 Espoo, Finland Dr. Stefan Nordlund, FEBS '93, Department of Biochemistry, Arrhenius Laboratories, Stockholm University, S-10691 Stockholm, Sweden Judith A. Sjoberg, Professional Association Management, 815 Don Gaspar, Sante Fe, NM, USA Dr. Josef Havel, Department of Analytical Chemistry, Masaryk University, Kotlarska 2, CS- 61137 Brno, Czechoslovakia Tel: +42 5 712984. Fax: +42 5 740108 Miss P.Hutchinson, Analytical Division, The Royal Society of Chemistry, Burlington House, Piccadilly, London, UK W1V OBN Tel: +44 71 437 8656. Fax: +44 71 734 1227 M. Frei-Hausler, IAEAC Secretariat, Postfach 46, CH-4123 Allschwil2, Switzerland Tel: +4161632789. Fax: +41 61 4820805 Professor D. Brinkmann, Physik-Institut, University of Zurich, Schonberggasse 9, CH-8001 Zurich, Switzerland Margaret Ridgell, AOAC, 2200 Wilson Boulevard, Suite 400, Arlington, VA 22201-3301, USA Winnipeg, Manitoba, Canada Dr. G. R. Barrie Webster, Pesticide Research Laboratory, Department of Soil Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2. Tel: +1204 474 6039. Fax: + 1 204 275 6019; or Professor Dr. Joseph Tarradellas, IGE, Federal Technical Institute EPF-L, CH-1015 Lausanne Ecublens, Switzerland Professor Erkang Wang, Asianalysis 11, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, P. 0. Box 1022, Changchun, Jilin 130022, China Tel: +86 431 682 801 (ext. 562). Fax: +86 431 685 653 Professor Douglas Hamilton, Physics Department, 2152 Hillside Road, University of Connecticut, Storrs, CT 06269-3046, USA Changchun, China Storrs, CT, USA Entries in the above listing are at the discretion of the Editor and are free of charge. If you wish to publicize a forthcoming meeting please send full details to: The Analyst Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK CB4 4WF. Tel: +44 (0)223 420066. Fax: +44 (0)223 420247.

ISSN:0003-2654    

DOI:10.1039/AN993180035N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993, VOL. 118 39N Conference Report 19th International Symposium on Chromatography: September 13-1 8, 1992, Aix-en-Provence, France Although there are now a number of series of specialized conferences in various areas of separation science, the 19th meeting in the more wide-ranging series of ‘International Symposia on Chromatography, attracted a large number of delegates. Analysts clearly perceive a need to keep informed of progress in a broadly based set of topics in chromatography and related areas. The lively and informative meeting lived up to expectations. The Symposium began with the award of the Martin and Jubilee Medals of the Chromatographic Society to Professors J. Jorgenson (North Carolina) and K. Markides (Uppsala), respectively. Plenary Lectures were then presented describing the state-of-the-art in: chiral separation (D.W. Armstrong); field-flow fractionation (J. C. Giddings); capillary electro- phoresis in bio-analysis (B. L. Karger); and isoelectric focusing (P. G. Rhighetti). These were followed by 62 oral presentations, some in parallel sessions, spread over five days. A necessarily subjective list of highlights includes: application of capillary GC with atomic emission detection (P. Sandra); narrow-bore capillary GC (V. Packova); analysis of polar substances by SFC (M. B. Evans and T. A. Berger); packed-bed hydrodynamic chromatography (J. C. Kraak); synthesis of functionalized polysiloxane stationary phases (H. Frank); chromatofocusing in protein analysis (C. Horvath); sample introduction in micellar electrokinetic chromato- graphy (J.Vindevogel) ; biosensor and immunospecific detec- tors in liquid chromatography (G. Marko-Varga and F. E. Regnier) ; and coupled solid-phase extraction-GC-ECD in environmental analysis (R. A. Baumann). An increasing emphasis on microcolumn chromatography was evident from lectures by J. F. Chervet and 0. I. Voroshilova. Advances across the chromatographic range were described in over 300 posters. Here, applications dominated, especially in the analysis of environmental, biomedical, food and fuel samples; but practical and instrumental developments were also well to the fore, with new GC and HPLC phases, especially for chiral separations, detectors, coupled methods and chemometrics all strongly represented. Much attention was paid to sample preparation, particularly by supercritical fluid extraction.A poster by F. I. Onuska on microwave- assisted extraction attracted much interest. The conference ended with a comprehensive Plenary Lecture by H. Mandery summarizing and contrasting the application areas of the various chromatographic techniques. Clearly chromatography continues to develop on several fronts and maintains its pre-eminent place in analytical laboratories. The meeting was accompanied by a large exhibition of chromatographic instrumentation and accessories. Notable among these was the launch by Hewlett-Packard of a new instrument for supercritical fluid chromatography. This per- mits simultaneous programming of mobile phase composition, density and temperature. Operation in gas, liquid or super- critical mode is hence possible-the concept of ‘borderless’ chromatography. The 20th International Symposium on Chromatography will be held in Bournemouth, UK, in September 1994. K. D. Bartle School of Chemistry, University of Leeds, Leeds, UK LS2 9JT Chirality Medal Nominations are invited for the Chirality Medal to be awarded in 1993 at the 4th International Symposium on Chiral Discrimination in Montreal, Quebec, Canada. The Chirality Medal was instituted by the Italian Chemical Society in connection with the International Symposium on Chiral Discrimination in Rome in 199 1. This Medal is awarded to recognize distinguished achievement in any aspect of the field of Chiral Discrimination. Nominations, together with a short supporting statement, should be sent before April 30, 1993, to: Professor A.F. Fell, Secretary, Chirality Medal IIonours Committee, Pharmaceutical Chemistry, University of Bradford, Bradford, UK BD7 IDP.

ISSN:0003-2654    

DOI:10.1039/AN993180039N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

40N ANALYST, MARCH 1993, VOL. 118 Future Issues will Include- Determination of Trace Amounts of Phosphorus by Laser Excited Time-resolved Fluorimetry-Ronghua Li and Zhauro Zhou Determination of Aluminium in Different Tissues of the Rat by Atomic Absorption Spectrometry With Electrothermal Atomization-Aleksandar Radunovic, Michael W. B. Brad- bury and H. Trevor Delves Determination of Ascorbic Acid by Flow Injection Analysis With Chemiluminescence Detection-Abdulrahman A. Alwarthan Palladium-Magnesium Nitrate as a Chemical Modifier for the Determination of Lead in Mussel Slurries by Electrothermal Atomic Absorption Spectrometry-P. Bermejo-Barrera, M. Aboal-Somoza, Rosa Maria Soto-Ferreiro and R. Dominguez- Gonzalez Immobilization of Glutamate Oxidase on Non-porous Glass Beads.Automated Flow Injection System for the Assay of Glutamic Acid in Food Samples and Pharmaceuticals-Stella M. Tzouwara-Karayanni, Constantine D. Stalikas and Mil- tiades I. Karayannis Novel Instrumentation and Biomedical Applications of Very Near Infrared Fluorescence-M. B. Brown, Tony E. Edmonds, James N. Miller, D. P. Riley and Nichola J. Seare Enzymes for Amperometric Detection of Herbicides in Aquatic Environments-Fiona A. McArdle and Krishna C. Persaud Incorporation of Hydroxamic Acid Ligands Into Nafion Film Electrodes-Damien W. M. Arrigan, Brian Deasy, Jeremy D. Glennon, Brian Johnson and Gyula Svehla Determination of Zirconium and Molybdenum With 4 3 - Dihydroxybenzene-l,3-disulfonic Acid Disodium Salt by Ion- pair Reversed-phase High-performance Liquid Chromato- graphy-hh- Jen Jane, Tsai and Hsiao-Tzu Yan Molecular Recognition Using Conducting Polymers: Basis of a New Electrochemical Sensing Technology-G.G. Wallace and P. R. Teasdale Determination of Iodide Ion in Impregnated Charcoals by Flow Injection-Colin G. Taylor, Cheryl D. Monks and Duangjai Nacapricha Recovery of Sulphadimidine from Pig Feeds-Peter Warwick, Neil T. Crosby and Ian M. Barwick An Account of Kinetic Determinations and Other Kinetic Aspects of Analytical Chemistry: from C6rdoba to Erlangen -Horacio A. Mottola Separation and Determination of Thiosulfate, Sulfite and Sulfide in Mixtures-Tomozo Koh, Katsuaki Okabe and Yasuyuki Miura Poly(pyrro1e) Based Amperometric Sensors: Theory and Characterization-Michael E. G. Lyons, Cormac H. Lyons, Catherine Fitzgerald and Thomas Bannon Multi-layer Conducting Polymer Gas Sensor Arrays for Olfactory Sensing-Jonathan M.Slater, J. Paynter and Esther J. Watt Evaluation of Coating Materials Used On Piezoelectric Crystals for the Detection of Dimethylsulfide in Liquefied Petroleum Gas-K. Hawkesworth and John F. Alder Monitoring of Sulfur Dioxide Using a Piezoelectric Crystal Based Controller-John J. McCallum, F. Benmakroha, T. Boudjerda, R. Boufenar, H. Allag and F. Djerboua Present State of Fabrication of Chemically Sensitive Field Effect Transistors-Karel Domanskf , Jiii Janata, Mira Josowicz and Danuta Petelenz Biosensor System Employing Acoustic Impulses in Thin Polymer Films-P. W. Walton, P. M. Gibney, M. P. Roe, M. J. Lang and W. J. Andrews Sodium-selective Membrane Electrode Based on p-tert-Butyl- calix[4]arene Methoxyethylester-K. Cunningham, S. J. Har- ris, M. A. McKervey and Gyula Svehla Development of Interdigitated Acoustic Wave Transducers for Biosensor Applications-D. Zhang, G. M. Crean, T. Flaherty and A. Shallow Novel Approach to the Development of Alkalinity and Acidity Detectors-0. Lev and M. Tsionsky Laboratory of the Government Chemist, Past and Future- Richard D. Worswick 2nd National Symposium on Planar Chromatography: Modern Thin-Layer Chromatography Co-Chairmen: Professor Harold M . McNair and Professor Colin F. Poole September 19-22, 1993 Research Triangle Park, North Carolina,USA Further information may be obtained from: Janet E . Cunningham, Barr Enterprises, P . O . Box 279, Walkersville, MD 21793 USA Phone: (301) 898-3772 - Fax: (301) 898-5596

ISSN:0003-2654    

DOI:10.1039/AN993180040N

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993, VOL. 118 235 Efficacy of Robust Analysis of Variance for the Interpretation of Data From Collaborative Trials Michael Thompson, Bart Mertens and Margalith Kessler Department of Chemistry, Birkbeck College, Gordon House, 29 Gordon Square, London, UK WC7H OPP Tom Fearn Department of Statistical Science, University College London, Gower Street, London, UK WC? E 6BT The Analytical Methods Committee (AMC) robust analysis of variance method has been compared with the Harmonized Protocol for the interpretation of data from collaborative trials. Many data sets, representing the extremes of concentration and precision, have been selected from published studies and subjected t o the two methods for calculating estimates of the mean and the variances of repeatability and reproducibility.In addition the variabilities of the statistics have been investigated by the bootstrap method. The conclusion is that the AMC robust procedure is considerably more reliable than the Harmonized Protocol. Although the two methods give quite close results generally, the variability of the estimates produced by the Harmonized Protocol is considerably greater because of the masking of outliers. Even the robust method gives estimates that are more variable than expectations based on normal distribution theory. Keywords: Collaborative trial; Harmonized Protocol; robust statistics; outlier; analysis of variance; bootstrap The collaborative trial has long been recognized as an essential step in validating an analytical method and establishing its performance characteristics prior to its recognition as a standard method.The collaborative trial is nominally a randomized replicated experiment, although in practice the participating laboratories are rarely selected on a random basis. Analysis of variance (ANOVA) is the obvious method of interpreting the results of collaborative trials, in terms of a grand mean, p, a between-laboratory effect with variance, oL2, and a within-laboratory variance, or*. These parameters are conventionally regarded as properties of the analytical method. In recent times o,2 has been called the variance of repeatability and oR* = oL* + 0,2 called the variance of reproducibility. A knowledge of (J, for an analytical system permits the prediction of differences between the results obtained in one laboratory, while oK provides corresponding information for results obtained from two different labora- tories.The corresponding relative standard deviations, RSD, and RSDR, are also in common use. A number of variant approaches to the interpretation of data from collaborative trials have been proposed’-7 and various bodiess-10 including the International Organization for Standardization ([SO)’ I have issued protocols for conduct- ing and interpreting them. By far the greatest controversy surrounds the question of the treatment of outlying results. Recent international activity by ISO, the International Union of Pure and Applied Chemistry (IUPAC) and the Association of Official Analytical Chemists (AOAC) has resulted in the adoption of the Harmonized Protocol,I2 which inter alia prescribes the exclusion of outliers by Grubb’s and Cochrane’s tests.Despite this, outlier exclusion is not universally accepted within the analytical community.7 A modern approach to the treatment of data containing outliers is called robust statistics.13-14 Robust statistics are applied to data that are essentially normally distributed, but are contaminated with a minor proportion of outliers, or with ‘heavy tails’. These features are typical of analytical data, where the accumulation of numerous, small independent errors in the various stages of the analytical procedure tends to give rise to a normal distribution, but the occasional large errors (perhaps due to contamination, mistakes in procedure or transcription errors) give rise to outliers.Therefore, robust methods seem to be ideally suited to the treatment of analytical data. Robust statistics such as means and variances are estimated by accommodating, rather than by excluding, outlying results and, therefore, no tests of significance are required as part of the estimation procedure. The estimates are descriptors of the ‘good’ part of the data. The most effective of the robust estimators have to be calculated by the iterative application of an algorithm. Although the procedure is not difficult, a computer is needed for this task because the convergence is inconveniently slow for manual calculation. The use of robust ANOVA for the interpretation of collaborative trial data has been proposed by Lischerls and the Analytical Methods Committee (AMC).16 The AMC paper provides a FORTRAN program for executing robust ANOVA on collaborative trial data. The properties of a particular method of robust ANOVA are inherent in the algorithm, but can also be explored by simulation or by the bootstrap method.17 In simulation tests the AMC program gives good results and can eliminate the effect of reasonable proportions of both analytical outliers (i. e., discordant replicates within a laboratory) and outlying laboratories. However, reassuring as simulation results are there is always some fear that ‘real’ data sets, with all of their peculiarities, may cause complex problems that give rise to incorrect information. In this paper the statistics produced by the AMC program are compared with those produced by the Harmonized Protocol approach, making use of a substantial amount of representative ‘real data’.The data were taken from the reports of two trials and were selected to represent the extremes of analyte concentration range. Data for crude protein determined by the Kjeldahl method represented the upper concentration ranges (10-100% m/m) and good preci- sion (RSDR = 2% and RSD, = 1.5%). Data for aflatoxins represented the lowest concentrations for which trial data were available (0-12 ppb) and poor precisions (RSDR = 40% and RSD, = 2070, typically). Experimental Data Sources Kanelx described a double collaborative trial in which 26 animal feedstuffs and related materials were analysed for Kjeldahl protein in duplicate in 22 laboratories by two variants of the procedure.The results of one procedure (using a copper sulfate catalyst) are used here. A collaborative trial of a method for the determination of aflatoxinsly was also used. The results obtained at each individual level of analyte in both236 ANALYST, MARCH 1993, VOL. 118 of these trials were subjected to separate comparison of the statistical met hods. Basic Statistics Data were entered manually from the original papers into a statistical spreadsheet on a personal computer and subjected to a number of tests for reliable transcription. The data sets were then subjected to classical one-way ANOVA, to the Harmonized Protocol, and to robust one-way ANOVA in their original states. Calculations were performed with an authentic copy of the FORTRAN program provided by the AMC.16 Bootstrap Method The variability of the results from the three methods was assessed using bootstrap samples drawn from the Kjeldahl protein data sets. The calculations were programmed in GAUSS (Aptech Systems, Maple Valley, WA 98038, USA). The GAUSS routine was used to calculate the robust estimates and the results were compared with those obtained with the AMC FORTRAN program, and found to give iden tical results (apart from round-off errors). The bootstrap is a useful and established method of obtaining the standard errors and distributions of complex statistics, such as robust estimates, that cannot be calculated analytically. In the context of collaborative trials, the boot- strap method reveals the likely outcome of repeating the trial a large number of times (often about 1000 times), with random selection each time from an infinite population of laboratories of comparable ability.While the bootstrap method can occasionally give aberrant results due to an atypical original data set, the conclusions in this paper are based on data from 46 separate examples, and so can safely be regarded as typical of collaborative trials. Results and Discussion Basic Statistics Kjeldahl protein Estimates of the grand mean F, the standard deviation of repeatability (6,) and the standard deviation of reproducibility ( 6 K ) were produced by classical ANOVA (no outliers removed), by the robust procedure (Rob) and by the Harmonized Protocol (HP) and are presented in Table 1. Where no outliers are removed the HP gives the same result as classical ANOVA.Generally the robust method gave similar results to HP, but there are some noticeable differences. The standard deviation of repeatability estimates (6,) are compared in Fig. 1. When no outliers were excluded by the HP, the robust method tended to give the slightly lower value, with an average value of 6,(HP)/b,(Rob) of 1.3. This effect was smaller when one or more outliers were excluded by the HP, giving an average value of 6,(HP)/b,(Rob) of 1.1. The difference between the results of the two methods is largely attributed to the conservative nature of the outlier tests used in HP, which use the 1% point for rejection of a laboratory’s results. The robust method accommodates any marginal outliers that the HP ignores. However, when outliers are removed by the HP, thc two methods give results that agree more closely.The standard deviation of reproducibility estimates (6,) show a similar pattern (Fig. 2), although the deviation between them is smaller. The ratio bR(HP)/bR(Rob) had an average value of 1.1 when no outliers were rejected by the HP and 1.0 when one or more were rejected. Again the slightly high tendency of the HP is due to its conservatism in treating marginal outliers. The grand mean estimates (p) produced by the robust method and the HP are very similar. Fig. 3 shows the relative difference between the estimates [ (@(HP)-fi( Rob))/@( Rob)] plotted against the analyte concentration [@(Rob)]. The mean relative difference is not significantly different form zero (p = Table 1 The statistics 6,, eR, and P for 26 materials analysed for Kjeldahl protein (% m/m) in a collaborative trial using 22 laboratories.The statistics were produced by the Harmonized Protocol (HP) classical ANOVA (Clas) and the AMC robust ANOVA (Rob); H is the number of laboratories rejected by the Harmonized Protocol 6, 6 R P HP Clas Rob 0.79 0.79 0.62 1.13 1.13 0.76 0.57 0.99 0.61 0.62 3.00 0.87 0.47 1.14 0.48 0.69 0.68 0.40 0.53 0.52 0.44 0.80 0.80 0.63 0.75 1.23 0:57 0.44 1.02 0.49 0.82 0.82 0.89 0.93 0.93 0.55 0.30 0.30 0.29 0.26 0.39 0.23 0.22 0.40 0.20 0.32 0.78 0.20 0.43 0.43 0.23 0.22 0.35 0.22 0.31 0.70 0.22 0.29 0.44 0.22 0.17 0.46 0.21 0.29 0.29 0.20 0.34 0.48 0.31 0.18 0.35 0.17 0.19 0.19 0.21 0.14 0.51 0.17 HP Clas Rob 1.47 1.47 1.22 1.42 1.42 1.37 1.21 1.35 1.08 1.02 3.11 1.43 0.97 1.55 1.07 1.39 2.41 1.08 0.68 0.89 0.65 0.93 0.93 0.79 0.78 1.23 0.75 0.44 1.02 0.59 1.17 1.17 0.92 0.96 0.96 0.69 0.56 0.56 0.51 0.39 0.54 0.36 0.43 0.48 0.33 0.46 0.80 0.46 0.48 0.48 0.44 0.24 0.39 0.30 0.39 0.75 0.33 0.33 0.45 0.33 0.25 0.46 0.30 0.36 0.36 0.31 0.34 0.48 0.32 0.29 0.38 0.26 0.19 0.34 0.24 0.25 0.51 0.25 HP 90.17 85.79 87.85 85.80 84.82 80.63 54.26 53.90 44.46 44.08 40.54 39.42 29.79 29.26 28.15 27.00 18.71 17.93 17.76 17.76 17.02 16.86 16.25 15.71 13.37 10.16 Clas 90.17 88.79 87.91 85.65 84.93 81 .05 54.13 53.90 44.52 44.12 40.54 39.42 29.79 29.33 28.15 26.91 18.71 17.96 17.86 17.81 17.01 16.86 16.16 15.74 13.37 10.24 Rob 90.21 88.81 87.92 85.84 84.84 80.73 54.22 53.93 44.51 44.08 40.52 39.40 29.76 29.31 28.17 26.97 18.72 17.95 17.80 17.78 17.02 16.86 16.20 15.73 13.38 10.20 H 0 0 1 4 3 1 1 0 1 4 0 0 0 1 1 1 0 3 1 1 2 0 3 1 0 3ANALYST, MARCH 1993, VOL.118 237 0.09). The median absolute difference from zero is 0.0005 in instances where no outliers were removed by the HP and 0.0011 where one or more outliers were removed. Overall, for these data, the AMC robust ANOVA gave similar basic statistics to those of the HP and both methods coped well with the data sets. The tendency of the HP to produce higher estimates of the standard deviation is due to its failure to reject marginal outliers. Aflatoxin data The estimates p, 6r and eR produced by classical ANOVA, robust ANOVA and by the Harmonized protocol are presen- ted in Table 2. Again, the results produced by the HP were similar to thosc produced by robust ANOVA.The 6, values are compared in Fig. 4. There is a tendency for the HP estimates to be slightly higher and, with an average value of 6,(HP)/6,(Rob) of 1.1, no obvious distinction based on the number of outliers removed. The eR values are compared in Fig. 5. The robust estimates are similar to the HP estimates when no outliers were rejected, with an average value of 6R(HP)/6R(Rob) of 1 .O. In instances when one or more laboratories were rejected as outliers by the HP, the average was smaller at 0.8. The grand mean estimates are compared in Fig. 6, which 1.2 E 1.0 2 8 0.8 - -0 5 0.6 a 0.4 I E 6 0.2 0 0 0.2 0.4 0.6 0.8 1 .o ir,, Robust method (% m/m) Fig. 1 Standard deviation of repeatability estimated by robust ANOVA and the Harmonized Protocol for the determination of Kjeldahl protein (% m/m).The number of laboratories rejected by the Harmonized Protocol are shown as zero (a), one ( X ) or two or more (+). The line represents equality between the methods shows the difference between the estimates [ @(HP)-@(Rob)] plotted against the analyte concentration [ p(Rob)]. The mean difference is not significantly different from zero. The median absolute difference from zero is 0.02 ng g-1 for instances where all laboratories were included by the HP and 0.20 ng g-1 where one or more laboratories were rejected. 0 0.4 0.8 1.2 1.6 6~ Robust method (% m/m) Fig. 2 Standard deviation of reproducibility estimated by robust ANOVA and the Harmonized Protocol for the determination of Kjeldahl protcin (YO m/m).The number of laboratories rejected by the Harmonized Protocol are shown as zero (a), one ( X ) or two or more (+I 0.004 7 I x a, 0.002 1 0 m I X X t, - X I $ -0.002 X X X -0.004 I I I I I 0 20 40 60 80 100 Fig. 3 Relative differences between the grand mean estimated by robust ANOVA and the Harmonized Protocol, for the determination of Kjeldahl protein (% m/m). The number of laboratories rejected by the Harmonized Protocol are shown as: zero (0) or one or more ( X ) Concentration (% m/m) Table 2 The statistics 8,, bR and @ for 20 peanut butters analysed for aflatoxins (ng g-1) in a collaborative trial. The statistics were produced by the Harmonized Protocol (HP), classica1,ANOVA (Clas) and the AMC robust ANOVA (Rob). L is the numbcr of laboratories in the trial and H is the number of laboratories rejected by the Harmonized Protocol 6, 6 R P HP Clas Rob HP Clas Rob HP Clas Rob L H 5.77 5.77 6.36 2.59 4.58 2.22 0.54 2.55 0.62 0.79 1.95 0.70 1.67 1.67 1.38 0.83 0.83 0.80 1.50 1.50 1.20 0.71 0.71 0.81 0.50 1.39 0.62 0.56 1.21 0.32 0.44 0.44 0.49 0.32 0.32 0.36 0.73 0.73 0.53 0.26 3.56 0.36 0.58 0.58 0.61 0.44 0.44 0.29 0.35 0.35 0.20 0.26 0.26 0.24 0.12 3.05 0.13 0.08 0.20 0.14 11.61 5.30 3.53 3.80 2.16 3.04 1.68 1.63 I .90 1.66 1.07 1.14 0.94 0.75 1.01 0.51 0.38 0.40 0.21 0.06 11.61 13.10 5.83 5.66 4.03 4.11 2.16 2.27 3.04 3.37 1.68 2.70 1.63 1.59 2.16 2.18 1.78 1.78 1.07 1.16 1.14 1.26 0.94 0.93 3.56 1.03 0.69 1.07 0.51 0.46 0.38 0.29 0.40 0.42 3.07 0.27 0.23 0.14 3.89 4.15 25.84 11.42 8.53 7.14 5.99 5.89 5.34 4.84 4.22 3.8.5 2.88 2.62 2.59 1.89 1.98 0.94 0.58 0.54 0.26 0.03 25.84 11.67 8.29 6.96 5.99 5.89 5.34 4.84 4.42 3.78 2.88 2.62 2.59 2.62 1.98 0.94 0.58 0.54 0.84 1 .05 25.81 I I .70 8.29 6.96 5.99 5.92 5.34 4.96 4.44 3.78 2.90 2.64 2.58 2.16 1.95 0.96 0.56 0.54 0.29 0.05 12 0 13 1 12 2 12 1 13 0 12 0 13 0 12 0 12 1 12 1 13 0 12 0 13 0 13 2 13 0 12 0 13 0 13 0 13 1 13 2238 X X ANALYST, MARCH 1993, VOL.118 0 1 2 3 ir,, Robust rnethodlng g Fig. 4 Standard deviation of repeatability estimated by robust ANOVA and thc Harmonized Protocol, for the determination of aflatoxins (ng g-I). The number of laboratories rejected by the Harmonized Protocol arc shown as: zero (0) or one or more ( X ) . Thc line represents equality between the methods 0 2 4 GR, Robust methodlng g- 6 Fig.5 Standard dcviation of rcproducibility cstimatcd by robust ANOVA and the Harmonized Protocol, for the detcrmination of aflatoxins (ng g-I). The number of laboratories rejected by the Harmonized Protocol arc shown as: zero (0) or one or more ( X ) . The line represents equality between the methods . a, C F a, !E -0.1 - 0 -0.2 1 Variability of Estimates To compare the variability of the estimates from the three methods a bootstrap exercise was performed using the 26 Kjeldahl protein data sets. Bootstrap samplesl7 were gener- ated from a given data set as follows: generate 22 laboratory means by sampling, randomly with replacement, from the 22 Table 3 Crude protein data used for detailed illustration of the bootstrap methods results. The corresponding statistics arc in row 17 of Table 1 Duplicate Laboratory results (% m/m) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1s 16 17 18 19 20 21 22 22.63 26.86 26.50 26.89 26.01 27.39 27.33 27.03 26.69 27.29 26.72 27.13 25.99 26.85 27.16 27.74 27.28 27.00 26.68 26.72 27.40 26.92 27.36 26.88 26.93 27.18 26.81 27.42 27.16 27.14 26.50 27.38 26.79 26.25 26.17 26.95 27.07 27.85 27.42 27.76 26.63 28.03 27.30 26.84 observed means; generate 22 differences between duplicates by sampling, randomly with replacement, from the 22 observed differences; pair means and differences in the order drawn to construct a data set of the same structure as the original.This procedure was repeated 1500 times for each of the 26 data sets and p, 6, and ciR were calculated by each of the three methods for each bootstrap sample.The variability of the estimates over the generated samples is a natural estimate of their variability over repetitions of the trial that produced the original data. This approach was preferred to the alternative of simulation because it avoids possibly inappro- priate distributional assumptions; the bootstrap samples look like real data because they are drawn directly from real data. The method of drawing the bootstrap samples merits some discussion. In drawing means and differences independently, it fails to preserve any tendency in the original data for outlying laboratory means and large differences between duplicates to occur in the same laboratory. This may adversely affect the performance of the ‘Harmonized Protocol which benefits from any such tendency.However, the obvious alternative approach, which is t o sample 22 laboratories with replacement and use the original duplicates for these labora- tories as the bootstrap sample, may also be criticized on the grounds that it under-represents the variability. On balance the method described first was preferred. As a check, part of the bootstrap excercise was repeated using the alternative sampling method. The results obtained were quantitatively but not qualitatively different. Figs. 7-9 show the results of the bootstrap method for one of the 26 data sets (Table 3). These three sets of histograms show the distribution over the 1500 bootstrap samples of ci,, ciR and F produced by the three ANOVA methods and the results are typical of the data as a whole.The three histograms for the mean (Fig. 9) are quite similar, but those for the two standard deviations (6, and 3,) reveal marked differences between the methods. Consider the repeatability, 6, (Fig. 7). The first laboratory produced a very large difference between its duplicate observations. In the bootstrap samples this difference, if it is present at all, may occur more than once. The five clumps of values in the histogram for the classical method correspond (left to right) to 0, 1, 2, 3 and 4 occurrences. An example of more than twoANALYST, MARCH 1993, VOL. 118 239 30° 250 - (c) 0 0.5 1 .o 1.5 Standard deviation of repeatability (% m/m) Fig. 7 Distribution over 1500 bootstrap samples from a single protein data set of the estimate of repeatability obtained by (u) the robust procedure, ( h ) the Harmoniied Protocol and ( c ) the classical procedure 50t I 2 50 200 0 150 100 50 n c 2 3 150 100 50 n 0.5 1 .o 1.5 Standard deviation of reproducibility (% m/m) Fig.8 Distribution over 1500 bootstrap samples from a single protein data set of the estimate of reproducibility obtained by ( a ) the robust procedure, ( b ) the Harmonized Protocol and (c) the classical procedure occurrences is a rare event, but has a considerable impact on the estimate of repeatability when it happens. The Harmo- nized Protocol rejects a single outlier when it is present, thus merging the second clump into the first and sometimes, but not always, rejects both of two outliers. It cannot cope with more than two, the problem of multiple outliers masking each 150 100 50 0 150 > c U ; 100 2 u- 50 0 26.4 26.6 26.8 27.0 27.2 27.4 Grand mean (% m/m) Fig.9 Distribution over 1500 bootstrap samples from a single protein data set of the estimate of grand mean obtained by ( u ) the robust procedure, ( b ) the Harmonized Protocol and (c) the classical procedure 0 50 100 150 200 Scaled standard deviation of 6, (%) Fig. 10 Plots of the RSD of the 6, estimated by the three methods (r, robust analysis; h, Harmonized Protocol; and c, classical analysis) for 26 data sets. The RSDs are calculated as 1 0 0 ~ (standard deviation of 6,. over 1500 bootstrap samples)/(robust estimate of or from original data set) other being well known. The reason why the two histograms do not match exactly on the right hand side, despite being based on the same bootstrap sample, is that the Harmonized Protocol also rejects laboratories with outlying means.Thus the same three outlying differences may represent a larger proportion of the total data for the Harmonized Protocol estimate of (J, than for the classical estimate. The robust procedure is able to accommodate even four outliers and produces a histogram with a long right-hand tail but no detached clumps of values. The histograms obtained for the standard deviation of reproducibility (c?~) tell a similar story (Fig. 8), with the Harmonized Protocol only partly coping with outliers and the robust procedure successfully accommodating even multiple outliers. The situation is now more complicated because outlying laboratory means also affect 6R and various combina- tions of outlying means and differences are possible.Figs. 1&12 summarize the variability of the estimates for all 26 sets of protein data. The plots are based on the standard deviations, calculated over 1500 bootstrap samples, of p, 6, and GR. To make these standard deviations comparable240 ANALYST, MARCH 1993, VOL. 118 0 20 40 60 80 100 Scaled standard deviation of 6~ (%) Fig. 11 Plots of the RSD of the iTR estimated by the three methods (r, robust analysis; h, Harrnonizcd Protocol; and c, classical analysis) for 26 data sets. The RSDs arc calculated as 1OOX (standard deviation of iTR over 1.500 bootstrap samples)/(robust estimate of oR from original data set) h h M f h W i h h h h H? h h h h h Scaled standard deviation of (%) Fig.12 Plots of the RSD of thc @ estimated by the three methods (r, robust analysis; h , Harmonized Protocol; and c. classical analysis) for 26 data sets. The RSDs are calculatcd as lOOX (standard deviation of @ over 1500 bootstrap samples)/(robust estimate of p from original data set) between data sets they have been scaled by dividing by the corresponding (robust) parameter estimate from the original data set and multiplying by 100. The points plotted may thus be interpreted as the RSD of the statistic in question. Two features deserve comment. Firstly, the Harmonized Protocol gives estimates at least as variable as the classical method, whereas those from the robust procedure are far less variable. Secondly, most of the RSDs are alarmingly large.This is not an artifact of the bootstrap procedure: a bootstrap exercise with data generated from the normal theory model underlying the classical ANOVA produced RSDs of 11 and 10% for er and ijR respectively, in agreement with theoretical values. The large RSDs are a consequence of the non- normality of the real data used to generate the bootstrap samples. Conclusions The AMC robust ANOVA gave values of @, 6, and GR that were close to those provided by the Harmonized Protocol (in comparison with the likely standard errors) and the method could be used with equal facility. On those grounds alone the robust method must be regarded as a powerful alternative for interpreting collaborative trials. However, there are further reasons, based on the standard errors of the precision estimates, that show the robust method to be clearly prefer- able.The bootstrap method showed that the standard deviations of the robust estimates of or and oR are smaller than those of the Harmonized Protocol by an average factor of about two. The individual studies (e.g., Figs. 7-9) show the distribution of the HP estimate to be strongly skewed to high values, which in practice would result in a substantial proportion of collabora- tive trials giving unrepresentatively high results. This is due to the limitations of outlier rejection procedures. The bootstrap procedure also revealed that the AMC robust ANOVA has larger standard errors for 6, and 6R than those calculated from classical normal theory. Individual estimates of or and oR must therefore be interpreted with some caution.Analytical chemists must be aware of the substantial con- fidence interval that must be placed around these estimates. In practice this variability of individual results is mitigated somewhat by the fact that collaborative trials involve studies on six or more separate materials. However, the results suggest that the number of laboratories and materials used in a collaborative trial could, with advantage, be increased beyond the minimum number currently recommended ( i . ~ . , eight and five respectively). With a view towards possible revision of the Harmonized Protocol, it is recommended that the results from AMC robust ANOVA should be reported alongside those of the Harmo- nized Protocol in future published reports of collaborative trials.This will provide further information for comparison purposes and any discrepancies would alert users to the possibility of an inappropriate result from the Harmonized Protocol. The authors acknowledge financial support for this project from the Ministry of Agriculture, Fisheries and Food. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 References Youden, W. J . , Statistical Techniques for Collaborative Tests, Association of Official Analytical Chemists. Washington, DC, 1969. Zaalberg, J., J . Assoc. Off. Anal. Chem., 1989, 72, 34. Kelly, P. C., J . Assoc. Off. Anal. Chem.. 1990, 73, 58. Malanoski, A. J., J. Assoc. Off. Anal. Chem., 1990, 73, 231. Malanoski, A. J., J . Assoc. Off Anal. Chem., 1990, 73, 23.5. Malanoski, A. J., J . Assoc. Off. Anal. Chem., 1990, 73, 411. Mandel, J.. Chemom. Intell. Lab. Syst., 1991, 11, 109. Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method. AS'I'M E691-87. American Society for Testing and Materials, Philadelphia, PA, 3988. Determination and Application of Precision Data in Relation to Methods of Test for Petroleum Products. IP 367184 in Institute of Petroleum Standard Methods for the Analysis and Testing of Petroleum and Related Products, Wiley, Bognor Regis, 1992. Guidelines for the Development of Standard Methods by Collaborative Study, Laboratory of the Government Chemist, London, 4th edn., 1988. Precision of Test Methods-Determination of Repeatability and Reproducibility for a Standard Test Method by Interlaboratory Tests. I S 0 57251986, International Organization for Standard- ization, Geneva, 1986. Honvitz. W., Pure Appl. Chem., 1988. 60, 855. Analytical Methods Committee, Analyst, 1989, 114, 1693. Rousseeuw, P. J., J. Chemom., 1991, 5 , 1. Lischer, P . , Lebensm. Wiss. Technol., 1987, 20, 167. Analytical Methods Committee, Analyst, 1989, 114, 1699. Efron, B., and Tibshirani, R., Stat. Sci., 1986, 1, 54. Kane, P. F., J. Assoc. Off. Anal. Chem., 1984, 67, 869. Patey, A. L., Sharman, M.. and Gilbert, J . , J . Assoc. Off. Anal. Chem., 1991,74. 76. Paper 2104246 K Received August 6, 1992 Accepted October 20, 1992

ISSN:0003-2654    

DOI:10.1039/AN9931800235

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993. VOL. 118 24 1 Detection of Aluminium(iii) Binding to Citrate in Human Blood Plasma by Proton Nuclear Magnetic Resonance Spectroscopy Jimmy D. Bell NMR Unit, Hammersmith Hospital, Du Cane Road, London, UK W12 OHS Gina Kubal, Stojan Radulovic, Peter J. Sadler" and Alan Tucker Department of Chemistry, Birkbeck College, University of London, Gordon House and Christopher lngold Laboratories, 29 Gordon Square, London, UK WCIH OPP Reactions of AP+ (50-500 pmol 1-1) with intact blood plasma and its low relative molecular mass ultrafiltrate (<5 kDa) have been studied by proton nuclear magnetic resonance spectroscopy. Binding t o citrate was detected and was reversed by addition of desferrioxamine. The use of combined exponential and sine-bell functions for the resolution enhancement of spectra of plasma is illustrated.Keywords: Proton nuclear magnetic resonance spectroscopy; aluminium; citrate; desferrioxamine; blood plasma There is a great deal of current interest in the speciation of AF+ in the body. Aluminium is not thought to be an essential element for mammals, and has only toxic effects.',* The speciation of AF+ determines its biological availability,3 and there is a need to understand the processes by which Al3+ is absorbed into the blood stream and either excreted, or, when the kidneys do not function efficiently, is deposited in the brain." The main carriers of AP+ in blood plasma are thought to be citrate , transferrin and possibly albumin.5-10 Calculations of the distributions of AP+ species are usually based on thermodynamic stability constants and do not take kinetic factors into account. 1 1 Speciation via the separation and isolation of complexes can be complicated by changes in the equilibria during the separation process.We have there- fore used nuclear magnetic resonance (NMR) spectroscopic methods to study AF+ complexation as intact blood plasma can be studied, and kinetic measurements can be made. Blood plasma is a complicated heterogeneous mixture of fat particles (the lipoproteins) , proteins (such as immunoglobu- lins, albumin and transferrin), and small molecules and ions.12 The lipoproteins are organized particles consisting of triacylgl ycerols, phospholipids, free and esterified cholesterol and proteins; some of the lipids are relatively mobile within the core of the particles.The smallest and densest particle HDL (high density lipoprotein) contains the highest protein and phospholipid content. Several plasma proteins are in- volved in binding functions. For example, albumin (66 kDa), the major plasma protein (concentration approximately 0.65 mmol 1-I), binds fatty acids, metal ions such as Zn2+ and Ca", hormones and various drugs,l3 and transferrin (an 80 kDa glycoprotein) transports iron as FeT+ along with carbo- nate anions.14 The details of many of these biologically- important binding processes, including the mechanisms of metal ion and small molecule uptake and release by plasma proteins, are currently poorly understood. Proton (1H) NMR spectra of blood plasma consist of a complicated mixture of broad and sharp resonances, and normal single-pulse spectra are often difficult to interpret.Previously the broad resonances have been filtered out using Hahn or CPMG (Carr-Purcell-Meiboom-Gill) spin- echo seque'nces. This leaves the resonances from the mobile small molecules and a few highly mobile parts of macromole- cules.12.1"16 We have assigned resonances for the N-acetyl groups of mobile glycan chains of acute-phase plasma proteins,17 and resonances for the mobile parts of chylo- microns, very low density lipoproteins (VLDL) , low density * To whom correspondence should be addrcssed. lipoproteins (LDL) and HDL.18 It is even possible to distinguish between these various classes of lipoproteins. I n some situations the peaks for these mobile protons are relatively intense and can be used, for example, to monitor disease states such as diabetes or lipidaemia,ly and to investigate the binding of paramagnetic Cu2+ ions.") In this paper the reactions of AP+ with intact blood plasma and a low relative molecular mass ( M , ) ultrafiltrate, and the reversal of the binding processes with the clinically-used chelating agent desferrioxamine, are studied.The use of combined exponential and sine-bell functions for resolution enhancement of 1H NMR spectra is illustrated and discussed. Experimental Materials Blood plasma samples were prepared from freshly drawn heparinized venous blood taken from normal healthy volun- teers. Cells were removed by centrifugation at 277 K. Sodium hydrogen carbonate (25 mmol 1-1) was added to maintain the pH at 7.4.Protein-free low M , ultrafiltrates (<5 kDa) were prepared using Amicon Centrifree filtration devices, which had been thoroughly washed with water ( 5 ~ ) to remove preservatives, and centrifugation for 1 h at 277 K. Aluminium was added in microlitre aliquots of an aqueous stock solution of AIC13 (Fluka). Desferrioxamine (Desferral) was obtained from Ciba-Geigy and trisodium citrate was purchased from Aldrich. NMR Spectroscopy The 'H NMR spectra were recorded on Bruker AM500 and JEOL GSX500 instruments at 500 MHz, using 0.55 ml of solution in a 5 mm tube, ambient temperature, 128 transients, 45" pulses, relaxation delay 1.6 s, 16 k data points (zero-filled to 32 k), 6 kHz spectral width, and gated or continuous secondary irradiation of HOD.For Hahn spin-echo spectra a 90"-~-180"-~-collect free induction decay (FTD) (typically T = 60 ms) sequence was used." Exponential functions equivalent to a line-broadening of 0.5-2 Hz were used for processing where necessary. For resolution enhancement, FTDs were typically processed using exponential functions equivalent to line-broadenings of 1-2 Hz combined with unshifted sine-bell functions. Data processing was carried out on a Bruker Aspect 1000, or SUN SPARC2 (Varian VNMR software), or Silicon Graphics personal IRIS 4D35TG using FELIX software (D. Hare).242 ANALYST, MARCH 1993, VOL. 118 The effect of enhancement functions on peak heights was investigated using the PANIC simulation program (Bruker Spectrospin). Spectra containing single lines of different widths at half height were simulated followed by inverse Fourier transformation to produce the FIDs.Results and Discussion In Fig. 1, 500 MHz 1H NMR spectra of the methyl and methylene regions of heparinized human blood plasma are compared. In the normal, single-pulse spectrum [Fig. l(A)], some sharper resonances superimposed on a broad envelope of resonances can just be discerned. The broad peaks arise predominantly from fatty acids (triacylglycerols and phospho- lipids) and the major protein albumin. Two methods of filtering out the broad peaks are shown. First, the Hahn NAc I :i" A W I ! 'HB 3.0 Fig. 1 Aliphatic region of 500 MHz 1H NMR spectra of human blood plasma. A, Single-pulse spectrum: FID multiplied by an exponential function (equivalent to a line broadening of 1 Hz) prior to Fourier transformation. B.Resolution-enhanced single-pulse spectrum: FID multiplicd by an cxponcntial function (equivalent to a line broadening of 2 Hz) followed by an unshifted sine-bell function prior to Fourier transformation. C, Hahn spin-echo spectrum: T = 60 ms, FID multiplied by an exponential function (equivalent to a line broadening of 2 Hz) prior to Fourier transformation. NAc = N-acetyls of glycoproteins; Gln = glutamine; Val = valine; HB = hydroxybuty- rate; and Lac = lactate. P = lipoprotein pcaks: PI, HDL and LDL CH,; P,, VLDL and chylomicron CH,; P3, HDL and LDL CH,; and P4, VLDL and chylomicron CH2 spin-echo spectrum Fig. 1(C). With this procedure the contribution of magnetic field inhomogeneity to linewidths is removed, but linewidths are not otherwise reduced.Broad resonances are filtered out because the magnetization asso- ciated with them decays before acquisition begins (spin-spin relaxation times, T2, short compared with the total delay 2 X T). Intensities are also reduced by diffusion in local inho- mogeneous fields in the sample during the delay,22 and by phase modulation of the multiplets.23 The choice of t is a compromise between removing sufficient of the broad signals to achieve the simplification required, and retaining interpret- able phase modulation.16 With t = 60 ms, most of the doublets are inverted (T = 1/2 J ) . The largest peaks (P) are those for the CH3 (P2) and CH2 (P4) groups of chylomicrons and VLDL,18 and the N-acetyl groups of the glycan chains of acute-phase glycoproteins such as al-acid glycoprotein.17 Well-resolved sharp multiplets include those for valine, hydroxybutyrate, lactate, alanine and citrate. Secondly, a normal spectrum is shown after enhancement using combined exponential and sine-bell functions. The over-all appearance of this is similar to the spin-echo spectrum, except that there is no phase modulation, and partly as a result of this, some peaks are enhanced in intensity, e.g., P1 and P3. The peaks for glutamine are now interpretable, whereas in the spin-echo spectrum they are severely distorted. The advantage of resolution enhance- ment is that it can be carried out after the single-pulse spectrum has been acquired, and does not require acquisition of further experimental data. Resolution enhancement is a well-known procedure in NMR spectroscopy,24.2~ but the combined application of exponential and sine-bell functions, although proposed ,26,27 has been little used in the past.The sine-bell function26 is a commonly uscd window function, especially for studies of proteins. In the simplest use of this function, the FID is multiplied by a half cycle of a sine function with a period of twice the acquisition time. However, the improvement in resolution obtained with this function is often accompanied by an excessive degradation of the signal-to-noise ratio and distortion of baselines. We have countered this problem by pre-multiplication of the FID by a line-broadening exponen- tial function, a procedure that we have found useful for the study of the large plasma proteins albumin and trans- ferrin .28-30 The function begins at zero (ensuring suppression of the broadest lines), rises to a maximum, which might be at an earlier point in the time domain than for the sine-bell (depending on the exponential function used), and then decays smoothly to zero.Mathematically the sine-bell func- tion produces an FID that, after Fourier transformation, is equivalent to the discrete differential of the dispersion spectrum ,27 yielding a spectrum with inherently narrower lines, but with a poorer signal-to-noise ratio than the absorption spectrum. The introduction of either a phase-shift of the sine-bell function or pre-multiplication by an exponen- tial function effectively adds a fraction of the absorption spectrum to the dispersion differential, improving the signal- to-noise ratio and broadening the lines slightly.The phase- shifted sine-bell does not begin at zero and is not as effective in suppression of broad resonances. We investigated the effect of sine-bell and exponential sine- bell resolutim enhancements on the intensity of resonances using simulated spectra. The FIDs for Lorentzian lines of varying widths at half height (2-30 Hz) were simulated and transformed with and without pre-multiplication with en- hancement functions. The reduction of pcak heights in enhanced spectra resulting from linewidth changes was determined. The curve for exponential sine-bell enhancement was much shallower than that for sine-bell, i.e., enhanced spectra are less affected by linewidth changes.For example, if a spectrum is enhanced using the sine-bell function, then an increase in peak width from 2 to 5 Hz leads to a 45% reduction in peak intensity, and an increase from 2 to 10 Hz to a 71%ANALYST, MARCH 1993. VOL. 118 243 DFO I 1 I 1 I I I I 1 1 I I I I II I I II II II I I I I I I I1 II II Citrate 3.0 2.0 1 .o h (PPm) Fig. 2 Aliphatic region of resolution-enhanced 500 MHz 1H NMR spectra of human blood plasma. A. Control; B. after addition of AF+ (SO pmol 1-1); and C, after further addition of desferrioxamine (100 pmoll-l). Exponential functions (equivalent to a line broadening of 2 Hz) followed by unshifted sine-bell functions were applied to the FIDs prior to Fourier transformation. DFO = desferrioxamine reduction, whereas the corresponding reductions i n peak intensity are 28% (increase in linewidth from 2 to 5 Hz) and 56% (from 2 to 10 Hz), respectively, as a result of using exponential sine-bell enhancement. The choice of acquisition time greatly affects the enhancement procedure when sine- bell functions arc used, as the period of the function is normally set to twice that of the acquisition time, i.e., the maximum of the function is at half the acquisition time.Hence the choice of acquisition time determines the portion of the FID that is maximally enhanced. The effect of AP+ on the resolution-enhanced spectrum of blood plasma i s shown in Fig. 2. After addition of 50 pmol 1-1 AP+ the intensities of the peaks forming the AB quartet for citrate near 2.6 ppm, present at a concentration of 0.11 mmol 1-1 in this sample of plasma (i.e., within the normal range), markedly and selectively decrease intensity [Fig.2(B)]. No further change was observed in the spectrum for the next 24 h. The citrate peaks disappear from the spectrum completely after addition of 200 pmol 1-1 AP+, and no other resonances were affected up to a concentration of 500 pmol l-1 t - m lz m m .- I I 1 I I I I I I I I I I I B I Fig. 3 Aliphatic region of 500 MHz 'H NMR spectra of a low M , ultrafiltrate (<5 kDa) of human blood plasma. A , Control; B, after addition of 50 pmol I-' A13+; and C, after further addition of desferrioxamine (100 vmol 1- I ) . Most of the multiplets between 3.2 and 3.9 ppm are assignable to glucose Al3+ (data not shown). Addition of dcsferrioxamine to the plasma sample containing 50 pmol 1-1 A P + led to the rapid (minutes) reappearance of citrate peaks, Fig.2(C), although in a slightly broader form than they were originally. Addition of desferrioxamine alone to plasma had no effect on the peaks for plasma components. Single-pulse IH NMR spectra of the low M , (<5 kDa) ultrafiltrate of blood plasma are shown in Fig. 3. Now there are no broad peaks in the spectrum because the high M , macromolecules have been separated out. It can be seen that addition of Al3+ (50-300 pmol 1-1) causes a specific decrease in intensity of the citrate peaks, whilst there is little effect on peaks for other small molecules such as lactate and alanine. Addition of desferrioxamine restored the intensity of the citrate peaks again, Fig.3(C). The 1H NMR spectra of model systems containing A13+ and citrate were studied. The spectrum of a 0.75 + 1.0 mixture of Al3+ and citrate at pH* 6.6 (pH* = pH meter reading in D20 solution; adjusted with NaDC03) for example, gave rise to about 20 quartets covering the range 2.2-3.5 ppm. Evidently244 ANALYST, MARCH 1993, VOL. 118 there are a large number of different coordination modes for citrate in AP+-citrate complexes. This conclusion has already been drawn by others from 13C NMR work,31 and from X-ray crystallography of isolated complexes,32 and appears to explain why new peaks for an aluminium citrate complex are not readily observable in spectra of plasma or its ultrafiltrate. The crystalline trinuclear complex [AI3(H- ,Cit),(OH)- (H20)]+ isolated from 1 + 1 mixtures of AP+ and citrate (Cit) in the pH range 7-9,32 contains three similar but distinct six-coordinate AP+ ions bridged by tetradentate citrate anions; the hydroxyl and carboxyl groups are deprotonated.Curiously, the 1H NMR spectrum of this 1 + 1 cluster was reported to consist of a single multiplet at 4.71 ppm (i.e. , very close to the water resonance). As the citrate ligands are magnetically-inequivalent, a total of six quartets arising from four magnetically-inequivalent protons per citrate might have been expected. Desferrioxamine is known to bind AF+ more strongly than citrate o r transferrin, and is used in the clinic for decreasing plasma aluminium levels after exposure to toxic levels .33 These 'H NMR data suggest that AP+ added to heparinized blood plasma (or plasma ultrafiltrate) in vitro initially binds to citrate.Citrate, which has three ionized carboxylate groups at neutral pH (pK values = 2.87,4.35 and 5.69),34 is known to be a strong ligand for A13+,11 and probably plays a role in promoting the absorption of aluminium from food into the blood stream. Here much of the AP+ at the lowest dose studied (SO pmol 1-1) could have been transferred to trans- ferrin, which is normally present at a concentration of 30-40 pmol l-1 in plasma and usually has only about one third of the Fe3+ sites (two per protein molecule) occupied. 14 This would leave about 4&53 pmol l-I of vacant sites available for binding Ali+. Perhaps citrate to transferrin transfer is very slow under the conditions used.There is good evidence that transferrin is the ultimate binding agent for AP+ in vivo,s.~ and AP+ is known to bind strongly to transferrin in vitro.h.7 An alterna- tive, and less likely, explanation for our results is that AP+ binding to transferrin (or another protein) induces a confor- mational change that in turn leads to citrate binding to the protein and broadening of resonances because of slow tumbling. This is difficult to rule out at the moment but might be clarificd when experiments on AF+ binding to transferrin in the presence of citrate are studied by NMR spectroscopy. So far our own attempts,35 and those of othcrs,'h to detect Al?+ binding to transferrin by 27Al NMR have not been successful, presumably due to quadrupolar broadening. The IH NMR methods such as those described here should be useful for investigating the effectiveness of potential thera- peutic chelating agents designed to remove aluminium from blood plasma.We thank the MRC, SERC, Wellcome Trust, Wolfson Foundation and ULlRS for their support for this work. We also thank Dr. M. C. Grootveld (London Hospital Medical School) and Dr. R. W. Evans (Guy's Hospital) for stimulating discussions. This paper is based on work presented at the XXVII-CSI Post-Symposium in Loen, Norway, June 16-18, 1991. References 1 Aluminum in Chemistry, Biology and Medicine, eds. Nicolini, M., Zatta, P. F., and Corain, B . , Cortina International. Verona. 1991. 2 Aluminium in Biology and Medicine, eds. Chadwick. D., and Whelm, J., CIBA Foundation Symposium 169, Wiley, New York. 1992.Daydk, S . , Filella, M., and Berthon, G., J . Inorg. Riochem., 1991,38,241. Candy, J . M., Oakley, A. E., Klinowski, J . , Carpenter, T. A., Perry, R. H., Atack, J . R., Perry, E. K., Blcsed, G.. Fairbairn, A , , and Edwardson, J. A., Lancet, 1986, i , 354. Martin. R. B., Clin. Chem. ( Winston-Salem N.C.), 1986, 32, 1797. Harris, W. R.. and Sheldon, J . , Inorg. Chem., 1990, 29, 119. Fatemi, S. J . A . , Kadir, F. H. A., and Moorc. G. R., Biodzem. J . , 1991, 280, 527. Day, J. P., Barker. J.. Evans, I . J. A . , Perk\, J . , Seabright, P. J . , Ackrill, P., Lilley, J . S . , Drumm. P. V., and Newton, G. W. A.. Lancet, 1991, 337, 1345. 9 Venturini, M., and Berthon, G.. J . Inorg. Bioclzem., 1989, 37, 69. 10 Fatemi, S. J . A., Williamson, D. J., and Moore.G. R., J . Inorg. Riochem., 1992, 46, 35. 11 Martin, R. B., in Aluminum in Ciicwzistry, Biology und Medicine, eds. Nicolini, M., Zatta, P. F., and Corain, B., Cortina International, Verona, 1991, pp. 3-20. 12 Bcll, J. D., Brown, J . C . C., and Sadlcr, P. J.. Chem. Br. 1988, 24, 1021. 13 Peters, T., Jr., Adv. Prolein Chem., 1985, 37, 161. 14 Crichton, R. R., Inorgunic Biochc~mistry of Iron Metubolism, Ellis Horwood, Chichester, 1991. 15 Nicholson. .J. K., Buckingham, M. J., and Sadler. P. J., Biochem. J., 1983, 211, 605. 16 Bell, J. D., Brown, J . C. C., and Sadler, P. J . , NMK Biomed., 1989. 2, 246. 17 Bcll, J . D.. Brown, J . C. C . , Nicholson, J . K., and Sadlcr, P. J . , FEBS Lctt., 1987. 215, 311. 18 Bell, J . D . , Sadler, P. .I.. Macleod, A. F., Turner, P.R.. and LaVille, A., FEBS Lett., 1987, 219, 239. 19 Nicholson, K. K., O'Flynn, M. P.. Sadler, P. J . , Macleod, A. F., Juul, S. M . , and Stinksen, P. H., Biochem. J . , 1984,217, 365. 20 Bligh, S. W. A., Boyle. H . A., McEwen, A. B., Sadler, P. J . , and Woodham, R. H., Biocliem. Phurm., 1992, 43. 137. 21 Hahn, E. L., Piiys. Rev., 1950, 80, 580. 22 Brown. F. F., and Campbell, I . D., Proc. R. Soc. London Ser. R, 1980, 289, 395. 23 Rabenstein, D. L., and Naka\hima, T. T., Anal. Chem., 1979, 51, 1465. 24 Lindon, J. C., and Ferrige, A . G., Prog. NMR Spectrosc'., 1981, 14, 27. 25 Sanders, J . K. M., and Hunter. B. K., Modern NMR-Spectro- scopy. A Guide for Chemists, Oxford University Press, Oxford, 1987. 26 De Marco. A., and Wuthrich, K., J . Magn. Reson., 1976, 24, 201. 27 Gudron, M., J . Magn. Reson., 1978, 30, 515. 28 Kubal, G., Sadler, P. J . , and Evans, R., J . Am. Chem. Soc., 1992, 114, 1117. 29 Kubal, G., Mason, A. B., Sadler, P. J., Tucker, A . , and Woodworth, R. C., Biochem. J . , 1992, 285, 71 1. 30 Sadler, P. J.. and Tucker, A., Eur. J. Riochem., 1992,205,631. 31 Fatemi, S. J . A., Kadir, F. H. A., Williamson, D. J., and Moore, G. R., Adv. Inorg. Chem., 1991, 35, 409. 32 Freng, T. I>.. Gurian, P. L., Healy, D., and Barron, R., Znorg. Chem., 1990, 29, 408. 33 Leung, F. Y . , Hodsman. A. B., Muirhcad, N., and Henderson, A. R., Clin. Chem. ( Winston-Salem N. C.), 1985. 31, 20. 34 Martell, A. E., and Smith, R. M., Critical Sfahifity Constants. Plenum, New York, 1977, vol. 3, p. 161. 35 Kubal, G., Kiang, W., and Sadler, P. J . , unpublished work. 36 Fatemi, S. J . A., Williamson, D. J . , and Moore, G. R., J . lnorg. Biochem., 1992, 46, 35. 3 4 5 6 7 8 Puper 2/03] 47G Received June 16, I992 Accepted October 28, 1992

ISSN:0003-2654    

DOI:10.1039/AN9931800241

出版商:RSC    

年代:1993

数据来源: RSC

摘要:

ANALYST, MARCH 1993, VOL. 118 245 Determination of Total Phosphate in Waste Waters by On-line Microwave Digestion Incorporating Colorimetric Detection Kathleen E. Williams and Stephen J. Haswell" School of Chemistry, University of Hull, Hull, UK HU6 7RX David A. Barclay CEM Microwave Technology Ltd., 2 Middle Slade, Buckingham Industrial Park, Buckingham, UK MK18 1 WA Gaynor Preston Severn Trent Laboratories, 156-1 70 Newhall Street, Birmingham, UK B3 ISE A flow injection (FI) system for on-line microwave digestion of waste water samples with determination of total phosphate by means of colorimetric detection is described. Acidified samples are introduced into a water carrier stream and digested under continuous-flow conditions in thin-bore tubing. Following digestion, the samples are cooled on-line and then combined with further reagent streams for subsequent colorimetric detection based on the reduction of heteromolybdophosphoric acid to Molybdenum Blue as an FI peak at 690 nm.Signals from the flow-through detector are recorded as peak height on a chart recorder. Optimization of parameters such as digestion tube length, digestion tube diameter and reagent concentrations is discussed. Calibration was found to be linear up to 20 ppm of phosphate with a limit of detection of 0.10 ppm. Samples of waste water can be analysed at a rate of approximately 2 min per sample with typical sample relative standard deviations of <5% being achieved. Results for a range of samples were found to agree with those obtained by a conventional 'block' digestion autoanalyser method.The pre-treatment of samples with pyrophosphate phosphohydrolase ensured that the determination of total phosphate as orthophosphate could be achieved for samples containing pyrophosphate species. Keywords: Microwave digestion; on-line digestion; colorimetric detection; waste water; phosphate determination Waste water samples, which often contain high levels of suspended organic solids, are routinely analysed by the water industry for phosphate concentration. 1 This form of routine analysis requires rapid, simple and robust methodology in order to handle the large numbers and varying concentrations of phosphate species found in such samples. Most procedures for the determination of trace elements require the digestion of sample prior to instrumental analysis.2 Commonly, this preliminary step proves to be both laborious and time consuming, particularly when using traditional digestion methods such as wet and dry ashing.3 However, the develop- ment of microwave sample dissolution has proved to be of great advantage in that it dramatically reduces digestion time, and reduces both volatile analyte loss and sample contamina- tion from the atmosphere.4 The development of an on-line microwave digestion method would offer a more attractive approach to sample preparation over the discrete open or bomb digcstion of samples.There have been a limited number of reports in the literature of systems for flow injection (FI) based methodologies5 that will accommodate on-line sample preparation.&' 1 This paper describes the development of an FI system with on-line microwave digestion and subsequent colorimetric detection of phosphate in waste water samples.Experimental Reagents All chemicals were of analytical-reagent grade, and distilled, de-ionized water was used throughout. Ammonium heptamolybdate (0.005 mol 1-1) (BDH, Poole, Dorset, U K ) in 0.4 moll-' nitric acid (Fisons, Loughborough, Leicestershire, U K ) . * To whom correspondence should be addressed. Ascorbic acid (2% mlv) (Aldrich, Gillinghum, Dorset, U K ) in 1 1 distilled water with 10 ml of glycerol [May & Raker (now Rhone-Youlenc), Dagenham, Essex, UK]. A few drops of Triton X-100 (Sigma, Poole, Dorset, UK) were added to each of the above reagents. Phosphate stock standard solution, 100 ppm.Prepared from potassium dihydrogen orthophosphate (KH2P04) (BDH) in 5% vlv nitric acid. Nitric acid (5% vlv) in distilled water. Stock solution o f sodium tetrametuphosphate [(Na- Stock solution of anhydrous trisodium trimetaphosphate Inorganic enzyme pyrophosphatase (pyrophosphate phos- P02)4-4H20] (100 ppm) (Albright & Wilson, London, U K ) . C(NaP~li)liI (100 PPm) (Sigma). phohydrolase; EC 3.6.2.1.) (Sigma). Apparatus The on-line system is illustrated in Fig. 1 and consisted of the following: a water carrier stream in 0.5 mm i.d. poly- (tetrafluoroethylene) (PTFE) tubing; an Tsmatec MV-Z pump (Glattbrugg, Zurich, Switzerland); a Rheodyne injection valvc (Model 5020 Anachem, Luton, Bedfordshire, UK) with a 1 ml sample loop; a Model MDS81 microwave oven (CEM, Buckingham, UK) containing 7.2 m of 0.5 mm i.d.PTFE tubing wrapped around a PTFE box; a 7 m cooling loop in an anti-freeze bath cooled by Peltier devices (M11069T-O3AC, Marlow Industries, Tadworth, Surrey, UK); a Rheodyne injection valve (Anachem 5020) with an on-line back-flush filter (made in-house) fitted instead of a sample loop; a CEM pressure sensor; a 516.75 kPa (75 psi) back-pressure regulator (Anachem P736); and a de-bubbler fitted to the outlet from the back-pressure regulator. The outlet from the back-pressure regulator was coupled to a colorimetric detection system consisting of: two colorimetric reagent streams for molyhdate and ascorbic acid reagents; two Gilson Minipuls 2 peristaltic pumps (Anachem); a 100 cm mixing coil; a 4 m reaction coil in a thermostatically controlled246 Carrier ANALYST, MARCH 1993, VOL.118 11.8 I Cooler Pressure sensor Back-pressure regulator V Waste 150 cm mi coil Reaction Xing coil I ( 4 m ) Waste Fig. 1 Schematic diagram of the on-line digestion FI system water-bath; a Cecil spectrophotometer (S & M Products, Didsbury, Greater Manchester, UK); and a Kipp & Zonen (Delft, Holland) BD112 flat-bed chart recorder. Poly(tetrafluoroethy1ene) tubing of 0.5 mm i.d. was used throughout the whole system. Procedure Standards covering the range 0-20 ppm were prepared by taking appropriate dilutions of the stock standard phosphate solution and making up to volume in 5% v/v nitric acid. A 0.5 mi aliquot of concentrated nitric acid was added to 10 ml of waste water sample, resulting in a 5% v/v acidic solution.Standards and samples were analysed by injecting 2 ml aliquots into the system. Absorbance signals were recorded on a chart recorder and peak height measurements taken. Total analysis time for each sample was approximately 2 min. Replicate measurements were performed for each standard and sample. Study on phosphate species present in samples Samples and standards were prepared as described in the above procedure but without acidification. Sufficient units of enzyme activity were added to ensure hydrolysis of all pyrophosphate present in the standards and samples to orthophosphate. [Note: 1 U of enzyme activity will liberate 0.1 ppm min-1 of orthophosphate at pH 7.5 and 25"C.I For example, 100 U of enzyme activity (500-700 U mg-I) were added to 10 ml of a 10 ppm standard and the solution was left to stand at room temperature for 1 min before being acidified and analysed as detailed above.Results and Discussion Optimization of Digestion Conditions It has been previously determined that the optimum micro- wave power and acid strength for sample digestion are 90 and 5% v/v, respectively.:! The remaining variables controlling the _ _ 3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.2 Carrier flow rate/ml min Effect of carrier flow rate through the FI system on Fig. 2 response 2o I 18 16 . c-' L .: 14 JZ - / signal 10 "y 8 1 I I I 0.5 1.5 2.5 3.5 Effect of sample injcction volume on signal response Sample injection volume/mI Fig. 3 rate of digestion of sample in the microwave cavity are, therefore, flow rate, sample volume tube length and internal tube diameter. Signal sensitivity was evaluated by comparing the absorbance response for a standard 5 pprn phosphate solution in 5% v/v nitric acid.Having already selected a tube length of 7.2 m and an internal tube diameter of 0.5 mrn,lO the effect of flow rate on signal response was investigated. The colorimetric reagent flow rate was kept constant throughout this experiment. Fig. 2 shows a plot of absorbance (measured as peak height) as a function of carrier flow rate through the F1 system. At lower flow rates, dispersion will tend to increase with the sample slug being observed as a broad peak. However, as the carrier flow rate increases, the peaks become narrower while maintaining the same peak area; hence an increase in peak height is observed.It can be observed from the graph that an optimum signal response occurs when the carrier flow rate is set at 4.5 ml min-1, indicating that on reaching the colorimetric reagents, an optimum reaction time and hence colour development has been achieved. At the higher flow rates (4.5-6 ml min-1) there is insufficient reaction time to achieve optimum colour development and so the peak response rapidly begins to tail off. Fig. 3 illustrates the effect of sample injection volume on signal response and clearly indicates that an optimum peak height for absorbance is achieved when a sample injection volume of 2 ml or more is used. Hence an optimum carrier flow rate of 4.5 ml min-1 and an injection volume of 2 ml were used. Optimization of Phosphate Detection by FI In order to obtain optimum signal sensitivity in the detection system it was necessary to minimize the dispersion of the sample slug as it passed through the detector.The degree of dispersion of the sample slug as it passed through the detectorANALYST, MARCH 1993. VOL. 118 L i - - - I I 1 I I 1 247 11.1 I I I I 0 0.008 0.016 0.024 0.032 Effect of molybdate concentration on signal response Moly bda t e co ncen t rat ionim o I I 1 Fig. 4 1 - 10 I 5 4 - A 0 2 4 Ascorbic acid concentration (% m/v) Fig. 5 Effcct of ascorbic acid conccntration on signal response was controlled in effect by the flow rate, and the intensity of colour produced was found to be dependent on reagent concentration. Therefore, the two variables that most affect the signal sensivity were flow rate and reagent concentration.Signal sensitivity was evaluated by observing the absorbance response as peak height while holding the sample carrier flow rate constant at the pre-determined optimum. Figs. 4 and 5 show the effect of molybdate concentration and ascorbic acid concentration on signal response, respectively. Although the graph in Fig. 4 shows an optimum molybdate concentration being approached at 0.03 mol 1-1, it was found to be more practical to operate at a concentration of 0.015 mol 1-1 molybdate, as solutions above this concentration were found to be unstable and began to change colour and re-precipitate after several hours. Fig. 5 simply shows that an optimum signal response is achieved at an ascorbic acid concentration of 2.5% m/v .Hence the optimum reagent concentrations were chosen as 0.015 mol 1-1 molybdate and 2.5% m/v ascorbic acid. A study of the effect of reagent flow rate on peak height was carried out and the results are summarized in Fig. 6. As the flow rate increases, an increase in peak height is observed owing to a reduction in dispersion while maintaining sufficient reaction time for colour development to occur. At high flow rates, a reduction in peak response is attributed to inadequate time for reaction and colour development to occur. Hence an optimum peak response is observed at a flow rate of 2.4 ml min-1. The graph shown in Fig. 7 illustrates the effect of changing the reaction coil length for colour development on signal response. As the coil length increases, the time allowed for colour development increases and reaches an optimum at approximately 3 m, at which point the peak response begins to decrease owing to an increase of dispersion in the longer coils.Hence it can be concluded that at reagent concentrations of 0.015 rnol 1-1 (molybdate) and 2.5% m/v (ascorbic acid), a flow rate of 2.4 ml min-1 and a coil length of 3 rn, an optimum 7 6 E g 5 0, c Y a .- 0 4 3 3 2 1 Fig. 6 Effcct of reagent flow rate on signal response 11.9 11.8 A I! 11.2 11.3 1 \ b- 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 Reaction coil length/m Effect of changing reaction coil length for colour development Fig. 7 on signal response signal response was obtained in the FI detection system for a given fixed carrier flow rate of 4.5 ml min- 1 .Calibration Calibration using standards over the range 0-20 ppm phos- phate in 5% v/v nitric acid was carried out and proved to be linear up to 20 ppm with relative standard deviations (RSDs) 4% ( n = 10). The equation lor the linear calibration graph was: y = 1854~ - 0.152 (Y = 0.9983). A limit of detection of 0.1 ppm was obtained with a samplc throughput time of 30 h-1. Analysis of Samples Table 1 shows a comparison of results for the determination of total phosphate in waste waters by a conventional 'block' batch digestion method with those obtained by the proposed FI methodology. The results, in general, were in good agreement with those obtained with the standard 'block' method and analysis was completed much more rapidly. The FI method was found to have a precision (RSD) of 1.4% (n = 10) at the 5 pprn level and a sampling rate of 25 h-1 (including sample preparation). No precision data (RSDs) were avail- able for the batch method but they were expected from performance data to be in the range 1-5%.No particulates were observed in the flow system on leaving the microwave, indicating that complete digestion of suspended solids in the sample had taken place. The above results indicate that the proposed FI method represents a rapid and effective analytical methodology comparable in total phosphate recoveries to the traditional batch technique. Phosphate Species Study Previous studies have shown that only three classes of phosphate are stable to any extent in aqueous solution:" (i) orthophosphate (monophosphate); (ii) straight-chain poly- phosphates (including pyro- and tripolyphosphate); and (iii) ring met aphospha tes.248 ANALYST.MARCH 1993, VOL. 118 Table 1 Analysis of waste water samples by batch and FI methods for the determination of total phosphate Sample number 1 2 3 4 5 6 7 8 9 10 11 Total phosphatc Total phosphatc by batch method by on-line FI (PPm) method (PPm) 10.7 10.5 14.9 14.4 17.0 16.0 11.1 11.8 2.2 2.4 4.2 4.4 5.8 6.3 20.9 21.1 14.3 15.6 6.4 6.0 31.7 30.5 Total analysis time: 3 h 25 min Precision ( n = 10) 1.4 1.9 4.8 1.4 1.6 1.8 2.9 2.3 3.1 2.6 1.4 (RSD) (%) Several studies have also shown that after complete hydrolysis, all of the ring and chain phosphates are converted into orthophosphate. 13 It was considered important to determine whether or not all forms of phosphates present in waste water samples are converted into orthophosphate prior to detection and hence the total phosphate content is determined.Hence, several inorganic phosphates were chosen to be analysed and their percentage recoveries determined as orthophosphate. The phosphates analysed were as follows: tetrasodium pyrophos- phate (Na4P407- 10H,O); sodium tetrametaphosphate [(Na- P02)4.4Hz0]; and trisodium trimetaphosphate [(NaPO&] (anhydrous). By using the system and methodology described previously the results showed that good recoveries were obtained for the tetra- (101%) and trimetaphosphate (99%) but a fairly poor rccovery was observed for the pyrophosphate (67%). This low percentage recovery is attributed to the rate of hydrolysis of pyrophosphate to orthophosphate.The three main factors affecting the rate of hydrolytic degradation of ring and chain phosphates in aqueous solution are temperature, pH and enzymes.13 As the system was already operating at optimum temperature and pH (strong acid), it was necessary to examine the effects of enzymes on the rate of hydrolysis of pyrophos- phate. The inorganic enzyme pyrophosphatase (pyrophosphate phosphohydrolase; EC 3.6.1.1) was considered to be a suitable enzyme for this experiment. Standard solutions were analysed using the methodology described and the results are reported in Table 2. Good recoveries were observed for ortho-, trimeta- and tetrameta- phosphate, but a reduction of signal was found for the pyrophosphate standard. However, after treatment of the standard with the inorganic enzyme pyrophosphate phos- phohydrolase, a recovery of 99.1% was achieved.On analys- ing waste water samples, the same reduction in signal was observed as before; however, the addition of enzyme en- hanced the signal to give a spiked recovery of 99%. It can, therefore, be concluded that pre-treatment of samples with enzyme prior to acidification and analysis results in good percentage recoveries of total phosphate in samples where pyrophosphate might be present. Although pyrophosphates were not thought be be present in the waste water samples analysed, the proposed method is recommended where the form of phosphate in a sample is not known. Table 2 Pcrcentage recovery of samples and standards for the determination of phosphate using the proposcd FI method Rccovcry (as orthophosphate) Sample ("/.I RSD ( Y o ) Orthophosphatc (10 ppm standard) 100 3.4 Trimetaphosphate (10 ppm standard) 101 2.4 Tctrametaphosphate (10 ppm standard) 99.3 3.I Tctrapyrophosphate (10 ppm standard) 66.4 4.6 Pyrophosphatc (10 ppm standard) + enzyme 99.1 2.7 Waste water sample + Wastc water sample + 2 ppm pyrophosphate spike (2 ppm) 68.1 3.1 pyrophosphate spike + enzyme 99.5 2.8 Conclusion The proposed on-line sample digestion method with colori- metric detection was found to have a limit of detection of 0.1 ppm, a precision (RSD) of <5% ( n = 10) and a sample throughput rate of 25 h- 1 (including sample enzyme prepara- tion). No particulates were observed in the flow system on leaving the microwave, indicating that complete digestion of suspended solids in the samples had taken place.Results for a range of waste water samples agreed with those obtained by a conventional 'block' digestion autoanalyser method. The pre-treatment of samples with the inorganic enzyme pyro- phosphatase ensured that the determination of total phos- phate as orthophosphate could be achieved for samples containing pyrophosphate species. 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 References Total Nitrogen and Total Phosphorus in Sewage Sludge. Section C. Methods for the Examination of Waters and Associafed Materials, HM Stationery Office, London, 1985. Matusiewicz, H., and Sturgeon, R. E., frog. Anal. At. Spectrosc., 1989, 12, 21. Minczewski, J., Chwastowska. J., and Dybezynski, R., Separa- tion and Preconcentration Method3 in Inorganic Trace Analysis , Halsted Press, Chichester, 1983. Gorsuch, T. T., The Destruction of Organic Matter, Pcrgamon Press, Oxford, 1970. RfiiiCka, J . , and Hansen, E. H., Flow Injection AnalyJis, Wiley, New York, 2nd edn.. 1988. Burguera, M., Burguera, J . L.. and Alarcon, 0. M., Anal. Chim. Acta, 1086, 179. 351. Petersen, C., New Sci., 1989, September, 44. Burgucra, J. L., de la Guardia, M., and Salvador, A . , 1. Flow Inject. Anal., 1988, 5 , 121. Haswell, S. J., and Barclay, D., Analyst, 1992, 117, 117. Williams, K. E., M.Sc. Thesis, University of Hull, 1991. Hinkamp, S., and Schwedt, G.. Anal. Chim. Acta, 1990, 236. 34s. van Wazer, J. R., in Encyclopedia of Chemicul Technology, eds. Kirk, R. C., and Othmcr, D . F . , Interscience, New York, 1953, van Wazer, J. R., Anal. Chem., 1954, 26, 1755. van Wazer, J. R., Phosphorus and its Compounds. Volume I . Chemistry, Wiley-Interscience, New York, 1958. V O ~ . X, pp. 403-510. Paper 210551 7A Received October 15, 1992 Accepted November 3, 1992

ISSN:0003-2654    

DOI:10.1039/AN9931800245

出版商:RSC    

年代:1993

数据来源: RSC