摘要:

Professor Bishop Symposium The Analytical Division of the Royal Society of Chemistry is organising a Symposium to mark the career of Professor Edmund Bishop in analytical chemistry. The Symposium is to be held at the University of Exeter on Thursday and Friday, April 18th and 19th, 1985. The Symposium will cover electroanalytical chemistry, reagents, reactions and other fields of particular interest to Professor Bishop. Friends and former students of Professor Bishop are invited to submit papers for presentation at the Symposium. Titles and abstracts of about 100 words should be submitted by October 31st, 1984, to Miss P. E. Hutchinson, Analytical Division, Royal Society of Chemistry, Burlington House, London, W1V OBN, UK. The Annual General Meeting of the Analytiql Division will be held on Thursday, April 18th, and there will be a celebration dinner that evening.CHALLENGES TO CONTEMPORARY DAIRY ANALYTICAL TECHNIQUES CHALL€NG€S DAIRY TO COI(T€MPORRRY ANRLY TlCRL I T€CHNlQU€S Softcover 350pp 0 85186 925 4 Price f16.00 ($29.00) RSC Members f 12.00 Special Publication No. 49 Over many years international organizations, national orga izations and private oncern have prepared standardized methods of analysis for food products, including milk and milk products, for purposes of quality control, assessment of nutritive content, enforcement of legal requirements and affirmation of safety. This activity is concerned with identifying the most appropriate current methodology and codifying it in authoritative documents. The object of this book is to appraise the problems that will be faced by analysts of dairy products in the future and examine the means that are likely to be used to solve them. Brief Contents: Collaborative Studies and Reference Materials; Determination of Major Constituents: Automated, Instrumental Methods; Determination of Micro-constituents: Advanced Methods; Determination of Compounds Formed during Processing and Storage (Artefacts) and Contaminants. Non-RSC members should send their orders to: The Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 1 HN, England. RSC members should send their orders to: The Royal Society of Chemistry, Membership Office, 30 Russell Square, London WClB 5DT.

ISSN:0144-557X    

DOI:10.1039/AP98421FX029

出版商:RSC    

年代:1984

数据来源: RSC

ISSN:0144-557X    

DOI:10.1039/AP98421BX031

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANPRDI 21(9) 309-350 (1984) September 1984 Hon. Secretary R. Sawyer Proceedings of the Analytical Division of The Royal Society of Chemistry AD President P. G. W. Cobb Hon. Treasurer D. C. M. Squirrel1 Hon. Assistant Secretary D. I. Coomber, O.B.E. Ho.7. Publicity Secretary Dr. J. F. Tyson, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, LE11 3TU Secretary Miss P. E. Hutchinson Editor, Analyst and Analytical Proceedings P. C. Weston Senior Assistant Editors Mrs. J. Brew, R. A. Young Assistant E ditor Ms. D. Chevin Publication of Analytical Proceedings is the responsi- bility of the Analytical Editorial Board: J. M. Ottaway (Chairman) L. S. Bark L. C. Ebdon A. G. Fogg *P. M. Maitlis A. C. Moffat *Exofficio members B. L. Sharp J.D. R. Thomas A. M. Ure *P. C. Weston All editorial matter should be addressed to: The Editor, Analytical Proceedings, The Royal Society of Chemistry, Burlington House, Piccadilly, London, W1V OBN. Telephone 01-734 9864. Telex 268001. Advertisements: Advertising Department, The Royal Society of Chemistry, Burlington House, Piccadilly, London, W1V OBN. Telephone 01-734 9864. Analytical Proceedings (ISSN 0144-557X) is published monthly by The Royal Society of Chemistry, Burlington House, London, W1V OBN, England. All orders, accompanied by payment, should be sent to The Royal Society of Chemistry, The Distribution Centre, Black- horse Road, Letchworth, Herts., SG6 lHN, England. 1984 Annual Subscription price if purchased on its own: UK f53.00, Rest of World f56.00, US $106.00, including air speeded delivery.Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, N.Y. 11003. USA Postmaster: Send address changes to: Analytical Proceedings, Publications Expediting Inc., 200 Meacham Avenue, Elmont, N.Y. 11003. Second class postage paid at Jamaica, N.Y. 11431. All other despatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe. PRINTED IN THE UK. @The Royal Society of Chemistry, 1984. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers. Editorial Laser Applications It is about 25 years since the first practical lasers were demonstrated, although the principle of Light Amplification by Stimulated Emission of Radiation was postulated by Einstein as long ago as 1917.From the beginning, lasers caught the imagination of the general public and even now they have a certain amount of “Star Wars” mystique about them. Their most public appear- ance is in “laser light shows”-virtually an obliga- tory part of any self-respecting pop concert !-but their technical applications are slowly impinging on everyday life, for example in compact distance-measuring equipment. The laser had a rapid acceptance in analytical chemistry as a powerful tool in the advancement of many branches of spectroscopy. Indeed, it would be difficult to over-emphasise its impor- tance to a technique such as Raman spectroscopy, which has developed, since the introduction of laser sources, from a subject of rather academic interest into an important analytical method applicable to a wide variety of samples.Other techniques, for example multiple photon ionisa- tion, were hardly feasible before the advent of lasers. Even in molecular fluorescence, a tech- nique that has reached an advanced state of development using conventional radiation sources, the effect of lasers can be dramatic. A recent paper by N. J. Dovichi (TrAC, 1984,3,55) described experiments that achieved attogram detection limits (1 ag = 10-18 g) using laser- induced fluorescence. Far from being a case of “sensitivity for sensitivity’s sake,” such an instru- ment as he described could become an important detector for capillary liquid chromatography, which requires extremely low detector cell volumes.A joint Analytical Division - Special Tech- niques Group meeting on Laser Applications will be held at the Scientific Societies’ Lecture Theatre in London on October 24th (see the Diary, p. 348, for registration details). Five speakers will cover a wide range of subjects, from the “mainstream” topic of “Laser Raman Spec- troscopy” by D. L. Gerrard (BP, Sunbury) to the less well-known areas of “Laser Induced Multiple Photon Ionisation” by P. John (Heriot-Watt 309310 BUREAU OF ANALYSED SAMPLES LIMITED Anal. Proc., Vol. 21 University) and “Laser Source Solid State Mass Spectrometry” by P. K. Sanderson (AERE, Harwell). S. R. Holding (RAPRA, Shawbury) will talk on “Low Angle Laser Light Scattering Used in the Measurement of Polymer Molecular Weights,” another technique that was extremely difficult to carry out before the advent of lasers. Professor C. Grey Morgan (University College Swansea) will start the meeting with an overview talk on “Recent Developments in Lasers and their Applications in Analytical Chemistry. ” Although it is impossible to cover more than a small fraction of the applications of lasers in analytical chemistry in a one-day meeting, we can anticipate that this will be a stimulating and instructive selection. A. F. TAYLOR Special Techniques Group

ISSN:0144-557X    

DOI:10.1039/AP9842100309

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

310 BUREAU OF ANALYSED SAMPLES LIMITED Anal. Proc., Vol. 21 Bureau of Analysed Samples Limited: Triennial Meeting of Co-operating Analysts More than seventy senior analysts from indus- trial, research, independent and government laboratories attended the 19th Triennial Meeting of UK Analysts who participate in the certifica- tion analysis of certified reference materials (CRMs) prepared by the Bureau of Analysed Samples Limited (BAS) of Newham Hall, Mid- dlesbrough, Cleveland. This meeting was held in York on May 1. The delegates were welcomed by Mr. B. Bagshawe, Director, who pointed out the difficult industrial and economic conditions which had severely reduced the size of most laboratories’ staff during the past 3 years, and the recognition by BAS of the limited capacity available for internal research and development work.He felt, however, that these restrictions had emphasised the importance of mutual help by participation in outside co-operative analytical projects in the complementary fields of method development and CRM analysis, both nationally and interna- tionally. Furthermore, he indicated that the demand for higher standard of accuracy and precision in industrial control analysis increased the importance of providing industry with reliable reference methods and materials. On behalf of BAS he expressed their appreciation for the goodwill and practical support given by all the co-operating analysts, which had enabled them to help meet the requirements of industry. Mr. P. D. Ridsdale, Managing Director, and Mr. R. P.Meeres, Director, then presented reports on the progress in the preparation of certified reference materials which had been achieved during the past 3 years. Mr. Ridsdale reported that due to the deepen- ing recession during this period there had been some reduction in demand from the UK, but that this had been partly counterbalanced by an increasing demand from developing countries. He also summarised the close co-operation between BAS and a number of national and international research associations and other institutions concerned with the preparation of CRMs and the standardization of methods of analysis. In particular, he referred to the working group on methods of chemical analysis of iron and steel of the European Coal and Steel Community, under whose auspices CRMs for the iron and steel industry, now known as Euronorm-CRMs, are prepared jointly by BAS and organizations in France and Germany.Information was also given regarding publica- tions prepared by the Reference Materials Com- mittee of the International Organization for Standardization, including a world-wide directory of CRMs, which are available from the British Standards Institution. Pr summary of the 75 new and replacement RMs issued during the past three years was then given by Mr. Meeres. The new samples included additional alloy steels, nickel base alloys certified for both alloying and trace elements, and a limestone. Details were also given regarding a number of new projects scheduled for completion during the next triennial period. These included a very low sulphur steel, an electronic flow solder and a ball clay. When the meeting was thrown open for discus- sion the first question concerned the use of X-ray fluorescence as a method for the analysis of CRMs. Mr. H. Bennett, Principal Scientific Officer of the British Ceramic Research Associa- tion, who has developed this technique for the analysis of non-metallic materials, explained that XRF could only be regarded as a primary technique when the sample is taken into solid solution by fusion with a flux and can be calibrated against synthetic standards prepared from pure oxides. Several delegates put forward suggestions for new CRMs, including additional nickel base alloys, steels certified for both acid-soluble and total aluminium content and more CRMs of refractory materials certified for trace elements. At the end of the meeting Mr. Bagshawe thanked the delegates for their attendance and their contribution to the discussion.

ISSN:0144-557X    

DOI:10.1039/AP9842100310

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

September, 1984 ADDRESS OF THE RETIRING PRESIDENT 311 Address of the Retiring President This address was delivered after the Annual General Meeting of the Analytical Divison held on June 5th, 1984. Sauces Other than lCPs S. Greenfield Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, LE11 3 TU It was Dr. Johnson who said “Depend upon it, Sir, when a man knows he is to be hanged in a fortnight, it concentrates his mind wonderfully,” and so it was with me, when, not a fortnight but a month or so ago, I suddenly remembered that I was shortly, not to be hanged, but to give this address. I regarded the distinction as academic. With my mind thus concentrated, I did what many of my predecessors may have done: I read most of the addresses of previous Presidents.I have to say that I did not find the inspiration I was seeking. If this be criticism, it is of too slavish an adherence to custom rather than of the illustrious gentlemen who came before me. The early addresses had a strong Public Analyst flavour, as befitted a body which called itself “The Society of Public Analysts and Other Analytical Chemists.” They were annual affairs, typically records of deaths, membership, the number and titles of papers read, complaints about remuneration, status, copyright of papers and similar, the type of material which now finds it way into the Annual Reports of the Division. It was not until 1936 that a change was made, and the President gave only one address and that on his retirement. With this change came a change of content.There was less emphasis on statistics and the Presidents gave discourses on some scientific topic in which they had expertise. Typical titles for these talks were “Trace Metals and their Determination,” “Toxicology of Narcotic Drugs,” “Water and Water Supplies” and “Food.” In 1953, there was another change in title for the association to “The Society for Analytical Chemistry” and with it some change in direction and content of the addresses, although statistical information and scientific small-talk still predominated. It was not until 1961 that it became the practice to give titles to the speeches of the retiring President; a practice that has continued to the present day. This meant that the talks had a central theme and philosophy was the order of the day.One topic, which was first mentioned in 1910 and recurred in every address for the next 18 years, was that of remuneration, or the poorness thereof. In 1916, came a call for Chairs of Analytical Chemistry; I like particularly the preamble to this cri de coeur by Mr. Chapman, the then President: “We are sometimes apt to forget that in the early days of our science, chemistry and analysis were almost synonymous terms, and that it is only in comparatively recent times that a somewhat sharp division into professorial and professional chemists has occurred, chemical analysis being regarded as the special province of the latter class.” He continued “This cleavage was no doubt inevitable, but I cannot help feeling very strongly that much real good would result from the closest intercourse between professorial chemists and their professional colleagues, as well as from the improved teaching of analytical chemistry in our Universities and Colleges.” He went on: “Surely it is time that our petty differences and prejudices should disappear, and that the whole chemical profession should attack with an undivided front the innumerable problems which are not only waiting, but are urgently demanding solution.” This piece of elegant prose was followed at frequent intervals by complaints about lack of status, more calls for chairs, right through to the polemics of recent times.I was quite surprised to find that this bitter argument over money, status and need for analytical chairs had been going on for so long, I had thought it to be a debate of the present.I was mistaken. This caused me to wonder whether, since we apparently have not achieved our objectives after such a long time, our approach to the problem is the correct one. Two quotations came to my mind, one by Ella Wheeler Wilcox “Laugh and the world laughs with you; Weep and you weep alone; For the sad old earth must borrow its mirth, but has trouble enough of its own.” The other by The Bard himself “The lady doth protest too much methinks.” I think we protest too much and do tend to think our troubles are unique. My belief is that a change in direction is required, a more positive approach. If we can’t beat them, and we obviously can’t, then we should join them. Let me explain what I mean. I believe that we should start by improving our status within the Society.To do this we have to have our members active in the Local Sections of the parent body and we need sufficient representation on312 ADDRESS OF THE RETIRING PRESIDENT Anal. Proc., Vol. 21 the RSC Council, and I would remind you that under By-law 28 of the Society, “every member shall have the right: (c) to propose or support the nomination of candidates for election as Officers and National Members of the Council; and (d) to be a candidate for election as a Member of the Council subject to nomination in accordance with the relevant By-law.” Now it is not enough just to have analytical scientists on Council, we need to have them holding office. Furthermore, adequate representation on the RSC Boards and Committees should be sought.I can see no reason why a member of our Division should not become President of the RSC; I am sure we can all think of at least one person of sufficient stature to fill the office. Having said that, I appreciate that I am laying myself open to the charge that saying something should be done is easy, doing it is quite a different matter. That is true, but if we have the resolve and persistence, and we ask as a right not as a suppliant, then we shall achieve our objective. Similar reasoning can be applied to industry. We need analytical chemists in “the official world, the corridors of power”-and power is where the money is, and at the present time this is not in analytical laboratories. It needs to be recognised by teachers of analytical chemistry and through them, by their pupils, that, as in other disciplines, only a few talented and dedicated persons are going to achieve a brilliant career in the subject of their choice: the rest should be encouraged to regard their discipline as a training in logical thought, and motivation should be given to follow their fellows from other disciplines into industry’s key positions-marketing , personnel, management and finance.And if you think this suggestion is difficult of achievement, may I say that I know from personal experience analytical chemists who have entered, and prospered in, each of these fields. Status for our profession in academia is much more difficult to achieve. Chairs are not the problem, they will come if there is a healthy interest in analytical chemistry, which will itself automatically create a demand.A more respectful attitude towards our discipline will only come from the appearance of analytical chemists in the place where decisions are made: it is more Heads of Departments and Vice-Chancellors who are themselves analytical scientists that we need. If we can raise our status within the RSC and in industry, I think eventually academia will accord analytical chemistry equal status with other sciences. But, we shall only achieve this by taking power where we can, and when we can, and we must stop complaining! You may be thinking that I have given lie to my early comment that I gained little inspiration from my predecessor’s speeches. However, the inspiration I was seeking was for an original theme, whereas all I found was some variation on what had gone before, and all to do with chemistry.And so it should be, I can hear some say. I disagree; all work and no play makes for dull people, and I think that as a profession we need to show that we are not dull people; in fact, we are well-rounded people. So, what shall I talk about? I.C.Ps? I think not. No-one can accuse me of not being a well-rounded person! It is a roundness that comes from indulging in my favourite hobby-wining and dining! Now mostly before one eats one has to cook and cooking is another pastime of mine. So it is about cookery that I am going to talk, in particular, the preparation of sauces. In the 17th and 18th centuries in France, cooking was accepted as both an art and a science, and for one brief moment I did consider talking about the preparation and chemistry of sauce making.However, I came to the conclusion that the research that would be necessary to do justice to this topic was far more than I have time to do, so I am leaving a discussion of the chemistry for another day. The word sauce comes from the Latin saltus, possibly through the gascon sauco. The meaning of saltus is “flavoured with salt” and Roman sauces, it is reported, were very salty. There are many extravagant definitions of sauces, and just as many claimants to the authorship of the more lyrical, of which, “Sauces are to cookery what grammar is to language and melody is to music” is fairly typical.Another is “Sauces are the mortar that binds dishes together.” For my taste, too many restaurants take this latter definition literally.I am sure the author was not suggesting sauces were a substitute for Super Glue! A more prosaic definition appears in the “Concise Oxford Dictionary,” which describes a sauce as a “Liquid or soft preparation taken as relish with some article of food.” This indicates that sauces are used to give plain dishes added interest although in all probability, the earliest use of sauces was for moistening, binding and above all masking purposes. I rather like the definition of Raymond Oliver, contained in his book “Classic Sauces and Their Preparation,” “a sauce is a culinary preparation,” a truth which one would find hard to deny. As early as 1739, Franqois Marin’s book “Le Dons de Comus” contained a section on sauces, listing some one hundred of them; the 1961 version of “Larousse Gastonomique” contains over two hundred.“England has many religions but only one sauce,” is a remark attributed to, amongst others, Voltaire, the author, adding for good measure “whereas France has one religion and many sauces.” I feel I should temper this assertion of Gallic pride by pointing out that Italy developed a refined cuisine while the restSeptember, I984 ADDRESS OF THE RETIRING PRESIDENT 313 of Europe was still eating in the medieval fashion, and French cooking-indeed, her eating and manners, owe much to Italian influence. It is over centuries that France, having absorbed this influence, has gradually produced a distinctive cuisine of its own, of which sauce making plays a large part. Although, as I have indicated, there are a large number of sauces, many of these are evolved from three of four “Mkre” or Mother sauces, and there is broad agreement amongst the experts that these are, Espagnole, Bechamel and Veloute. Some authorities would add Tomato sauce to these three.(I must, however, hasten to add here that I am not referring to one of the 57 varieties of a well known company!) With the exception of Bechamel sauce, all these Mother sauces are stock-based. The Espagnole is a brown sauce made from a brown stock with a brown roux: Bechamel is a white sauce made from milk thickened with a white roux: VeloutC is a white sauce made from fish, chicken or veal stock and a white roux. Nowdays, Sauce Espagnole is often replaced by Fond de veau Lie, which is reduced veal stock thickened with arrowroot or cornflour.There is another class of sauces, the emulsified sauces; these are liaisons of eggs with oil, butter or stock. A typical example of an emulsified sauce is Mayonnaise. Then there are simple sauces such as vinaigrettes, butter or bread based sources, vegetable sauces, fruit sauces and sweet sauces exclusively for desserts. Many of these require no cooking, they are simple balances of oils or fats with acid ingredients such as lemon juice or vinegar. So far, I have discussed the derivation of the word sauce, and the definition and classification of sauces. Now I would like to say something about their preparation. I will start with Bechamel sauce, which is attributed to Louis Bechameil, Marquis de Nointel.It is also said to be the creation of Franqois Marin, who dedicated the sauce to the Marquis, which to me seems to be much more likely, although La Varenne, a century earlier, seemed to be the first French cook to have used flour to thicken sauces. Prior to this, sauces were thickened with eggs, or breadcrumbs, or vegetable purees. The manner of making BCchamel has changed over the centuries. It is no longer made by stirring cream into a Veloute sauce, as was the case. Today it is made by pouring milk on to a white roux made by heating butter mixed with flour. The milk may be hot or cold. If hot, it may be optionally infused with onion, peppercorns and bay leaf. It is not good practice to overcook the roux, as not only will the sauce be discoloured, but if the cooking takes place at a high heat, the cells of the flour will be shrivelled and the starch within burnt.Swelling of these cells will not take place, and the flour’s thickening power will be diminished. The cooking time for the sauce varies greatly from Chef to Chef. Generally, if cold milk is used to make the sauce, times of 45 minutes are common; on the other hand, when hot milk is used the time is greatly reduced, two or three minutes or so, although this can vary quite a lot. The general principle is that one cooks the sauce until the taste of uncooked flour is removed. I will illustrate with a few slides the making of Bechamel using cold milk. At this point Professor Greenfield continued his narrative with the assistance of some 70 slides showing the preparation of the Mother sauces and the compound sauces which are made from them. These included Mornay , Crevette, Soubise, Allemande, Supreme, Aurore, Bordelaise and Poivrade. He also spoke briefly on the making of emulsified sauces, illustrating his talk with slides showing the preparation of Bearnaise sauce and a classic custard. He concluded his address as follows. Here I must leave my account of sauce making. I do hope that I have not bored you, that I have not been teaching grandma how to suck eggs and that I have established a precedent for my successors! May I conclude by giving further lie to my early comment and quote from a retiring address given by a certain Mr. Bevan in 1908. “My duties as President are nearly over. If I have achieved any success as President it is due to the cordial and loyal assistance I have had from the Officers and Council and Members generally, and to them I offer my most hearty thanks.’’ I cannot improve on that.

ISSN:0144-557X    

DOI:10.1039/AP9842100311

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

314 SILVER MEDAL LECTURE Anal. Proc., Vol. 21 Silver Medal Lecture The following is the Silver Medal lecture delivered by Dr. R. F. Browner, the tenth SAC Silver Medallist, at the Research and Development Topics in Analytical Chemistry Meeting of the Division, held on March 28th and 29th, 1983, at Loughborough University of Technology. Sample Introduction in Atomic Spectroscopy: the Oldest Problem, the Newest Frontier Richard F. Browner School of Chemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA Atomic spectroscopy is a highly successful instrumental technique. Modern optical design, coupled with sophisticated microprocessor data collection and data processing, provides current instruments with performance that was unattainable even a decade ago. However, the one area where surprisingly little has been accomplished is that of sample introduction.Both in atomic-absorption and in plasma-emission spectroscopy, no major advances have been made over systems that owe their origins to nebulizers developed in the early 19th century, by pioneers of flame spectroscopy. For example, one of the most commonly used nebulizers in ICP spectroscopy today, the concentric all-glass nebulizer, is almost identical in form to the nebulizer described by Gouy in 1879.1 This is not to imply that sample introduction systems as currently used are not effective. On the contrary, especially with atomic-absorption systems, pneumatic nebulizers are both reliable, simple to operate and relatively inexpensive. With inductively coupled plasmas, on the other hand, nebulizers are somewhat less reliable, largely because of limitations imposed by the lower gas flows used with plasma sample injection.Inevitably, the over-all success and sophistication of modern instruments focuses attention on the weakest link in the system, the sample introduction process. Here, quite clearly, serious inadequacies exist. By addressing the problems directly it should be possible to improve analytical performance significantly. One reason why this has not already been accomplished, except on a rather ad hoc empirical basis, is that until recently reliable techniques for characterizing the sample introduction process have not been available. The recent development of improved techniques for taking such mesurements2-7 has opened the way for making systematic studies, which can relate the properties of sample introduction systems to the analytical performance of flame or plasma spectrometers. Now that it is possible to make such measurements, it becomes much simpler to determine what the appropriate properties of sample introduction to optimize analytical performance may be.The first part of this paper will describe the problems and will deal with aspects of both flame and plasma spectroscopy where substantial improvements in measurement capability are needed, which it is hoped to accomplish by improving sample introduction. The second part of this paper will attempt to define the objectives, by discussing current knowledge of the interaction of samples with flames and plasmas, and from there suggesting fruitful lines of approach to making the much needed advances in sample introduction procedures.Identification of Sample Introduction Problems Flame Atomic-absorption Spectroscopy (FAAS) flame atomic-absorption spectroscopy, there are four major aspects. Inefficiency of sample transport with liquid sample introduction Most of the sample introduced to a flame system is sent to waste, and typical transport efficiencies (E,) range from 510% . 3 (Transport efficiency is defined as the percentage of analyte mass reaching the atomizer, compared with the mass of analyte aspirated.) This is an undesirable state of affairs for two reasons. Firstly, precious sample is discarded, resulting in a minimum requirement of 0.5-1.0 ml of solution for a stable signal; secondly, because so much analyte is lost, the analytical signal is much lower than it would be if all of the sample was utilized efficiently.There are several sample introduction areas where major problems are currently experienced. With Sample introduction interferences Flame AAS is relatively free from interferences, especially spectral interferences. However, matrix-induced vaporization interferences (of the Ca*+/P043- type) may still present problems,September, 1984 SILVER MEDAL LECTURE 315 particularly in the air - acetylene flame, although the higher temperature of the nitrous oxide - acetylene flame is generally sufficient for their resolution. These interferences result from the formation in the flame of less volatile species than would otherwise be present when nebulising pure solution.Vaporization of the less volatile species is inhibited, resulting in a lower atom density and hence a reduced signal. Detection limits Flame AAS has inadequate detection limits for many applications. While the use of graphite furnace AAS may improve detection capabilities substantially, at the present state of development it may also cause more severe and less well defined interference problems.* Linear range A further problem with flame AAS is the rather limited linear range available, at least with conventional AAS instruments. This is one of the main limitations of flame AAS as a multi-element technique in comparison with ICP spectroscopy. Additionally, it adds a time-wasting factor when unknown samples must be diluted in order to fall within this limited working range.Such steps are particularly tedious when the element to be determined is present in unknown samples covering a wide concentration range. Inductively Coupled Plasma (ICP) Emission Spectroscopy Inductively coupled plasmas also suffer from sample introduction problems. Although some interferences may not be as severe as with atomic absorption, others may be more substantial. Many of the problems associated with plasma sample introduction are similar to those with flames, but there are some noticeable differences. With the ICP, matrix-induced vaporization interferences are generally less severe , whereas problems of nebulizer salt buildup and particulate induced blockage are often found. Inefficiency of sample transport with liquid sample introduction The transport efficiency with liquid sample introduction for plasmas is generally 5-10 times poorer than for flames.We have tested a wide variety of ICP nebulizers and spraychambers, and found E, values in the range 0.5-2.0% .3,5 Sample introduction interferences Matrix-induced vaporization interferences are a relatively minor problem with the ICP. However, a newly recognised category of sample introduction interference, aerosol ion redistribution (AIR) , can cause problems in certain situations.9 This type of interference results from the actual mechanism of aerosol generation in the nebulizer. When low concentrations of certain cations (e.g., sodium or lithium at <20 yg ml-1) are present with high concentrations of certain matrix species (e.g., calcium or magnesium at >lo00 pg ml-I), the ratio of elemental concentrations in the aerosol can differ from that in the original sample solution.Consequently, the analyte mass transport rate to the plasma is altered, and an interference results. Enhancements are generally observed, and may be as great as 100%. Detection limits Although the detection limits for many elements are lower with the ICP than with flame AAS, they are still inadequate for many direct determinations of great importance in environmental and biological systems. Furthermore, there have been no major improvements in detection limits in the last decade. There is clearly a strong need for improvement in this area. Aerosol Characterization and Transport In order to overcome the deficiencies of liquid sample introduction listed above , an alternative approach to current procedures is called for. Progress in this direction additionally requires a sound base of fundamental knowledge on aerosol transport mechanisms.The interactions taking place between aerosols and the flame or plasma atomizers must also be better understood. All this, of course, presupposes the ability to characterize aerosol properties, such as transport efficiency and drop size distribution, with considerable accuracy.316 SILVER MEDAL LECTURE Anal. Proc., Vol. 21 Transport efficiency and W-parameter Transport efficiency (EJ, as mentioned earlier, is simply the ratio of the mass of analyte reaching the flame or plasma to the mass of analyte aspirated, generally expressed as a percentage.The W-parameter is a mass transport term, and describes the mass of analyte reaching the plasma per second.’ If the drop size distribution of an aerosol produced by a typical pneumatic nebulizer is measured it turns out to be relatively broad, with a median diameter in region of 30 pm. Many of the drops can be as large as 80 pm. It is often found that these large drops create significant vaporization interference problems with flame atomic-absorption spectroscopy and so must be removed from the aerosol. It is possible to divide the aerosol conceptually into two groups, based on drop size, with a dividing line designated by d,,,. .7 The value of d,,,, is the diameter of some hypothetical drop, the contribution of which to the net analytical signal is less than 10%.Drops with diameters less than d,,,, give rise to a useful analytical signal; drops with diameters greater than d,,,. do not. Drops with diameters smaller than also contribute to a useful mass transport term, W,, whereas drops with diameters larger than d,,,, make up the excess mass transport term We. It has been shown that the value of dmax. can be as low as 4 pm, for pure aqueous calcium solutions. Clearly, drops with diameters much in excess of 4 pm contribute no useful signal for calcium, under typical analytical conditions. Furthermore, they may contribute significant interference problems. There are two alternatives for increasing total mass transport of analyte to the atomizer. Either: more total aerosol, irrespective of drop diameter, is allowed to reach the atomizer; or, alternatively, more small-diameter aerosol particles are generated.This would allow a greater analyte mass transport to the atomizer, without any increase in drop size. Of course, the influence of the increased solvent mass loading must be taken into account. This can cause severe atomizer temperature reduction, especially for the ICP. Unfortunately, there are no easy means of generating the “ideal” very fine aerosol for sample introduction, while maintaining high W, values. Drop size and interferences Flame AAS. As an indication of how effective aerosol drop size control can be in reducing interferences, it has recently proved possible to eliminate most vaporization interferences in flame AAS without unduly compromising the analytical conditions.10 This is accomplished by the removal of aerosol drops with diameters greater than approximately 4 pm. Table I summarizes the interferences quoted in the literature. By suitable control of aerosol drop size, it has proved possible to reduce all of these interferences to SWO. The penalty paid for this freedom from interference is a reduction in W,, which leads to a net drop in analytical signal. In atomic absorption, therefore, there appears to be a choice between interference freedom on the one hand, and signal magnitude on the other. TABLE I VAPORIZATION INTERFERENCES REMOVED BY CONTROL OF AEROSOL DROP SIZE Air - C2H2- CaPO, MgIAl Mgmi MgJSi MnIA1 FeISi MnISi NZO - C2H2- Mgmi MgIAI MoJAI AI/Ti AIN CriTi, V, Mn, W, Fe Ni/Ti, V, Cr, Mn, Fe, Co ICP emission spectroscopy.As discussed earlier, the transport efficiencies of ICP nebulizers and spraychambers are very low (typically 0.5-2.0%). The question therefore arises whether it is possible to increase the analyte mass transport term, W, without degrading either the analytical signal or the magnitude of interferences. The options are essentially the same as for atomic-absorption spectroscopy: either more total aerosol is allowed pass to the plasma, or more aerosol with smaller diameter drops must be produced. However, with plasmas, there is no information available on possible d,,,, values, as systematic experiments have not yet been carried out. One difficulty with making such measurements is the near impossibility of changing the analyte loading without simultaneously changing the solvent loading.Plasma signals are extremely sensitive to water loading.” Any increase in total aerosol reaching the plasma will generally be accompanied by a related increase in water loading. The additional solvent will lower the plasma temperature and reduce the emission signal.September, 1984 THE ANALYSIS OF SURFACE COATINGS AND RAW MATERIALS 317 This discussion leads to the fundamental question as to what the ideal aerosol characteristics for an inductively coupled plasma actually are? Properties of importance are drop size, analyte loading and solvent loading. The last factor further breaks down to a consideration of both aerosol and vapour loading. At the present time, we really have relatively little detailed information on truly “ideal” aerosol characteristics for the ICP.One of the serious difficulties facing systematic studies in this area is that it is almost impossible to vary one of these parameters separately. Usually all change simultaneously with any variation in the sample introduction process. Conclusions Currently we have a few answers to the problem of sample introduction for flames and plasmas, but much work remains to be carried out. Nevertheless, it has recently at least proved possible to focus attention on to those areas which give the greatest hope of leading to worthwhile advances in sample introduction procedures. I acknowledge the major contributions made to this work by the many student, postdoctoral and This material is based on work supported by the National Science Foundation under Grant No. visiting scientists who have participated in the research. CHE80- 1 9 9 4 7 . 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Gouy, G. L., Ann. Chim. Phys., 1879, 18, 5. Cresser, M. S., and Browner, R. F., Spectrochim. Acta, Part B , 1980, 35, 73. Smith, D. D., and Browner, R. F., Anal. Chem., 1982, 54, 1411. Cresser, M. S . , and Browner, R. F., Appl. Spctrosc., 1980,34, 364. Whaley, B. S., Snable, K. R., and Browner, R. F., Anal. Chem., 1982, 54, 162. Boorn, A. W., and Browner, R. F., Anal. Chem., 1982, 54, 1402. Browner, R. F., Boorn, A. W., and Smith, D. D., Anal. Chem., 1982, 54, 533. Koirtyohann, S. R., and Kaiser, M. L. Anal. Chem., 1982, 54, 1515A. Borowiec, J . A., Boorn, A. W., Dillard, J . H., Cresser, M. S., Matteson, M. J., and Browner, R. F., Anal. Smith, D. D., and Browner, R. F., Anal. Chem., 1984, in the press. Kull, R., Jr., and Browner, R. F., Spectrochim. Actu, Part B, (Abstracts Supplement), 1983, 38, 51. Chem. 1980, 52, 1054.

ISSN:0144-557X    

DOI:10.1039/AP9842100314

出版商:RSC    

年代:1984

数据来源: RSC

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September, 1984 THE ANALYSIS OF SURFACE COATINGS AND RAW MATERIALS 317 The Analysis of Surface Coatings and Raw Materials The following was one of the papers presented at a Joint Meeting of the Analytical Division and the OCCA held at the Scientific Societies Lecture Theatre, Savile Row, London, W.l, on February 8th, 1984. Summaries of two other papers presented at this meeting were published in the July, 1984, issue (p. 255). Techniques Used in the Analysis of Titanium(1V) Oxide Pigments R. C. Hutton Tioxide UK Limited, Central Laboratories, Portrack Lane, Stockton-on-Tees, Cleveland, TS18 2NQ The complex chemistry and physics behind the pigmentary performance of titanium(1V) oxide (Ti02) are not widely appreciated within the general scientific community. To many it is a white powder added to paints.There are, however, a vast number of other commercial products which incorporate Ti02 into the formulation, as is shown in Table I. For these reasons, a wide range of analytical techniques is necessary to measure the many important variables which influence the performance in these applications. The techniques used in the analysis of titanium(1V) oxide pigments are X-ray fluorescence, X-ray diffraction, atomic-absorption spectrometry, ICP emission spectrometry, spark-source mass spectro- graphy , gas chromatography, infrared spectrometry, electron microscopy, thermal analysis and autotitrimetry. All of these are very sophisticated techniques and each one provides information which can be used to build up an over-all picture of the pigment.318 THE ANALYSIS OF SURFACE COATINGS AND RAW MATERIALS Anal.Proc., Vol. 21 TABLE I INDUSTRIAL PRODUCTS THAT INCORPORATE Ti02 Pigmentary- Non -pigmen tary- Paints-il based, water based, coloured and white Plastics Electronic components Printing inks Welding rods Textiles Catalysts and supports Paper Organic titanates Packaging materials Cosmetics Food materials, drugs Vitreous enamels Synthetic sapphires and rubies Ti02 gains its prominance as a pigment primarily because of its ability to scatter light. The high refractive indices (2.75 for rutile, 2.55 for anatase) are amongst the highest known and impart a high degree of opacity to any media into which they are incorporated. A typical pigment is composed of 8&99% of Ti02, the remainder being made up of impurity elements and elements added as deliberate additions in order to improve performance in some particular application.For instance, a pigment may consist of 8549% of Ti02 together with inorganic coatings (A1203, Si02, ZnO), organic coatings (silicones, glycols, etc.), processing impurities (Fe, Nb2O5, Zr02, Sn, etc.) and trace inorganics (Pb, Mn, Cr, Cu, etc.). XRF Spectrometry The majority of pigment analyses are carried out by XRF. At Tioxide a 14-channel simultaneous instrument is used to determine the most important elements in the pigment.' From this analysis, information regarding the nature of the pigment can be obtained. A1203 and Si02 are determined in order to monitor the added inorganic coating levels on the pigment, Nb2O5 and Zr02 analyses to provide information on the raw material used, whilst impurity elements from the process such as Fe, Sb, Pb and Sn are also determined.The XRF spectrometer is interfaced to a minicomputer which performs a grade identification from a reference library of known pigment analyses. This facility is of use not only when checking that our own pigments are within specification but also to confirm the grade, and hence the manufacturer, of pigments used in any samples of paints, plastics, etc., under investigation. The facilities are also available to perform pigment grade identification by using a microcomputer for instances where samples are not analysed by XRF spectrometry. This may be the case when samples originate from unusual sources, e.g., paper bags, nuts and bolts, and also small paint flakes.In these instances, the sample size prohibits the use of XRF and chemical digestion techniques in conjunction with ICP - OES must then be used to determine the important elements in the pigment. Samples as small as 5-10 mg can be taken for analysis in this way with a high degree of confidence that an identification of the pigment grade is possible. Organic Analysis Small amounts of organic materials such as silicones, amines and polyols are often added to the pigments to aid compatibility in different applications. The number of different materials used varies from manufacturer to manufacturer and the levels at which these materials are added to pigment are so low as to make analysis difficult. The techniques are not commercially available, which would allow rapid evaluation of these coatings.Typically, chemical extraction schemes employing large amounts of sample are necessary. However, a dedicated pyrolysis gas chromatograph has been developed in-house, which allows finger-print identification (and some quantification) of these organics. This device consists of a resistively heated tantalum filament, which heats up rapidly to 500 "C. At this temperature the organic coatings thermally decompose to give characteristic and reproducible breakdown products, which are separated on a conventional column chromatograph. The amount of sample used may be 10-1O00 mg, which allows for great flexibility. The technique is more rapid than chemical extraction and/or chemical derivitization schemes and is simple enough to be used by relatively inexperienced staff.Many of the products into which Ti02 is incorporated are organic in nature. These include paints, polymers, fabrics, inks, etc. It is often necessary to examine the matrix as well as the pigment in order to gain information as to how that pigment performs in a certain application. Paints are often evaluated for solvent and resin systems, whilst polymers may be analysed for type, surface impurities,September, 1984 THE ANALYSIS OF SURFACE COATINGS AND RAW MATERIALS 3 19 anti-oxidants and slip agents. These requirements mean that the analyst must have considerable- expertise in handling a very broad range of products. The techniques used include gas - liquid chromatography, infrared spectrometric analysis and microchemical analysis.Trace Element Analysis The levels of trace elements in Ti02 are very important. Certain trace transition elements markedly affect the pigment colour. A pink or brown colour may be obtained from traces of manganese or iron, whilst a grey tone can be a result of small amounts of nickel. There are also certain applications, e.g., those covered by food contact legislation, where traces of toxic metals such as lead, arsenic, antimony and mercury must be below certain well defined levels. A full trace element profile of a pigment can be obtained from a spark source mass spectrometry scan. This includes all elements from mass number 12 to 238. It is, however, only semi-quantitative and the accuracy of the technique is not good enough to satisfy the demands of the criteria mentioned previously.For such analysis, AA spectrometry using electrothermal atomization (ETA) is the preferred technique. However, because of the low levels typically determined, i.e., <O. 1-5 pg g-1, difficulties arise with contamination, sample heterogeneity, technique sensitivity and precision and blank levels. All of these factors seriously influence the reliability of the results. The first rule of thumb in trace analysis must always be “keep it simple.” The fewer steps involved in sample preparation the better. One way of minimising sample preparation time and steps is to prepare the sample as an aqueous slurry. As Ti02 is incorporated into emulsion paints, which may be regarded essentially as aqueous slurries, this seems a logical step forward.These slurries are of a gel consistency and are stable for several days. They require minimal sample prepation, viz., grinding to less than 10 pm, dispersion in Viscalex,* addition of ammonia solution to pH 7 and dilution to volume, and this stabilized slurry does not require constant agitation in order to maintain suspension. As such, this means that these slurries can be used on commercial autosamplers of electrothermal atomizers. The small particle size of the pigments allows the use of aqueous calibration standards, with no loss of accuracy.2J Table I1 indicates the typical detection limit capabilities of the slurry system for solid pigment analysis. The technique is faster and much less contamination prone than conventional sample preparation techniques and is ideally suited for use not only in high throughput laboratories, but also where high accuracy trace elemental analysis is required. TABLE I1 DETECTION LIMITS ON Ti02 PIGMENTS USING ETA - AAS Trace element c o Cr Cu Fe Mn Mo Ni V Zn Detection limit/p.g g - 1 0.1 0.1 0.2 1.0 0.1 0.1 0.2 0.1 0.1 The author thanks the Directors of Tioxide UK Limited for permission to present this lecture and to publish this work. References 1. Denton, C. L., Himsworth, G., and Whitehead, J., Analyst, 1972, 97, 461. 2. Fuller, C. W., Analyst, 1976, 101, 961. 3. Fuller, C. W., Hutton, R. C., and Preston, B., Analyst, 1981, 106, 913. * Viscalex HV30 is a polyacrylate thixotropic thickening agent supplied by Allied Colloids Ltd., Bradford.

ISSN:0144-557X    

DOI:10.1039/AP9842100317

出版商:RSC    

年代:1984

数据来源: RSC

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320 APPLICATIONS IN ION CHROMATOGRAPHY Anal. Proc., Vol. 21 Recent Developments and Applications in Ion Chromatography The following are summaries of three of the papers presented at a Meeting of the North West Region held on February 22nd, 1984, at the Lord Daresbury Hotel, Warrington. Industrial Applications of Ion Chromatography A. Westwel I ICI Organics Division, Blackley, Manchester So far most published applications of ion chromatography have been concerned with the monitoring of aqueous environments and the analysis of relatively high purity water, e.g., in electric power generation. Ionic species at low levels are often important in chemical manufacturing and analyses for these ions must be performed in more complex matrices with greater potential interferences than are usually encountered in water analysis.Ion chromatography, particularly of anions, provides an elegant solution to these analytical problems. For low level cations, spectroscopic methods are generally preferred. As a broad generalisation chromatographic separation has enabled the analyst to work with relatively simple detection and measuring techniques whilst avoiding the problems of interferences and lack of specificity. Thanks to the initial work of Small and co-workers in 1975, ion chromatography now enables the scope of well established chromatographic methods to be applied to ionic species. These advances in ion chromatography would not have been possible without the development of the hardware for HPLC, such as loop injection valves, high pressure pumps, detectors and column fittings.Recent developments have further blurred the boundaries between the analytical applications of HPLC and ion chromatography (IC). Water analysis itself is, of course, important in the manufacture of chemicals. As an example, ion chromatography is used to monitor boiler water composition with special reference to the use of phosphate to control scale formation and sulphite as an oxygen scavenger. Sulphite is determined from the difference in sulphate levels before and after oxidation with hydrogen peroxide. The use of a chemical reaction in conjunction with ion chromatography is a useful aid to peak identification. An example of this is the determination of chlorate, which has an identical retention time to nitrate; reduction with sulphur dioxide eliminates the chlorate peak, with a corresponding increase in the chloride peak.Combustion methods in elemental analysis often require the determination of an anion to complete the analysis. Typical elements are chlorine and sulphur. Ion chromatography can provide a more convenient and rapid finish to elemental analyses, and is especially useful when the sample contains more than one halide. The analysis of mixtures of common anions and organic acids is sometimes required to control manufacturing processes and the quality of the final product. Changes in eluent composition from the usual sodium carbonate - sodium hydrogen carbonate mixtures in suppressor column type chromato- graphy can often resolve such mixtures. The analysis of mixtures of the fluoroacetic acids, including measurements of sulphate, chloride and fluoride, affords an indication of the scope of this approach.Organic dyestuffs usually contain inorganic salts, either as deliberate additives or as residues from the manufacturing process. Chloride and sulphate are typically present and the determination of sulphate is troublesome by gravimetric procedures, etc., if the dye contains sulphonic acid groups which result in the formation of insoluble barium salts. Phosphate is added to certain water soluble dyes as a stabiliser and its determination by the usual Molybdenum Blue method requires removal of the dye by wet oxidation. Much time can be saved by the use of ion chromatography in these analyses, even though there are problems caused by irreversible attachment of the dye to the IC column.A similar approach can be used in the manufacture of certain dyes for acrylic fibres. In this instance the excess methosulphate ion, after quaternisation of an intermediate with dimethylsulphate, is determined by ion chromatography. The ratio of nitrite to nitrate was thought to be important in the manufacture of aniline by the catalytic reduction of nitrobenzene. The direct measurement of this ratio is possible by ion chromatography and almost impossible by any other method. An aqueous extract of the reaction mixture is injected directly into the ion chromatograph. Another difficult analysis for nitrite is inSeptember, I984 APPLICATIONS IN ION CHROMATOGRAPHY 321 cutting oil emulsions where it is added as a corrosion inhibitor.By using a guard column to protect the analytical column, the sample can be analysed for nitrite directly, after dilution, without any need to break the emulsion. Ion Chromatography M. Cooke School of Chemistry, University of Bristol, Cantock’s Close, Bristol, BS8 1TS Interest in ion chromatography has increased considerably in recent years. This development can be traced directly to the relative ease with which ion chromatography can be performed using standard HPLC equipment. The introduction of fixed site ion exchange packing materials based on 5 pm silica permits the preparation of very efficient columns. Indirect photometric detection has also contributed greatly to the ease with which non-ultraviolet absorbing species, such as C1- and NO3-, can be detected with high sensitivity. For indirect photometric detection to operate successfully the eluting ion must absorb ultraviolet light.The most commonly used eluting ion is phthalate, but benzoate, p-hydroxybenzoate, salicylate and trimesate have all been used successfully for anion chromatography. Of the column packing materials available today probably the most widely used is Partisil 10 SAX. This is a packing material of moderate capacity and is particularly suited to the separation of inorganic ions such as C1-, NO3- and SO4*-. For this kind of separation a phthalate concentration of 1 X M is used. If separation of nitrite from chloride is required then 5 x 10-4 M phthalate in de-ionised water is a suitable mobile phase. Acetate elutes quite quickly under these conditions but other organic acids such as lactate, pyruvate and 3-hydroxybutyrate, which have great significance in clinical diagnosis, can be chromatographed easily.Ions such as iodide are relatively strongly retained and may be chromato- graphed successfully is a stronger eluent is used (with an appropriate change in detector wavelength) or if an organic modifier is added to the mobile phase. In indirect photometric detection the concentration of phthalate ion emerging from the column is monitored at a suitable wavelength. This concentration varies as the various non-absorbing ions elute 0 2 4 6 8 10 12 1416 Tirne/rn in Fig. 1. Separation of chloride (C), nitrate (N) and sulphate (S) on a Partisil 10 SAX column using 1 X M potassium hydrogen phthalate solution in de-ionised water as the mobile phase.Detection was at 264 nm. 0 2 4 6 8 1 0 1 2 1 4 Tirnehin Fig. 2. A river water sample chromatographed under similar conditions to Fig. 1. *, possibly H2P04-.322 APPLICATIONS IN ION CHROMATOGRAPHY Anal. Proc., Vol. 21 and so they are detected by increased transmission rather than increased absorbance. Detection in this mode is as sensitive as conductivity detection and can easily take place in the low nanogram range. The areas of application of this form of ion chromatography are many, but one of particular relevance is its use to study the extent of pollution of water by chloride, nitrate and sulphate caused by “acid rain”. A typical separation of these ions is shown in Fig. 1. A chromatogram of a river water sample is shown in Fig.2 and a tapwater sample in Fig. 3. The large peak which elutes before choride is thought to be HZP04- (the pH of the mobile phase is about 4.1 for 1 x 10-3 M phthalate). 1 , 1 1 1 , 1 , 1 1 1 1 4 R 12 Time/min F I I I I I 0 4 8 12 16 Time/min Fig. 4. Separation of chloride (l), nitrite (2), nitrate ( 3 ) and sulphate (4) on a v-Bondapak ODS column using TBA and PHP in the mobile phase. Fig. 3 . A tap water sample chromatographed under similar conditions to Fig. 1. Peaks represent: 1, 17 p.p.m. C1-; 2,15 p.p.m. NO,-; 3 , 27 p.p.m. SO,*-; *, phosphate. More recently, conventional ODS column packing materials have been used for the chromatography of ions. Ion-exchange character is generated by establishing an equilibrium loading of a compound such as tetra-n-butylammonium hydroxide (TBA).Hence, the mobile phase for use with ODS columns might consist of both TBA and phthalate in equal concentrations. The hydrophobic nature of the butyl groups on the TBA permits partition into the ODs, converting the column into one which demonstrates ion exchange character provided that the TBA concentration is maintained. Columns produced in this way have lower capacity than fixed site ion-exchange materials and thus allow shorter analysis times. A typical example of the separation that can be achieved on this type of column is shown in Fig. 4. The Latest Developments in Ion Chromatography M. B. Masters Dionex Ltd., Eelmoor Road, Farnborough, Hampshire, GU14 7QN Dionex Ion Chromatography has developed from the early days (1975), when the capabilities extended to only a few strong acid anions detected conductimetically, to todays multi-separation/multi-detection modes.The species which can be analysed on the Dionex system can be summarised as follows. Anions There are currently seven different anion separator columns, which have been designed for particular specialist applications. The columns are all based on a pellicular styrene - divinylbenzene base, which gives excellent chemical stability throughout the full pH range.September, 1984 APPLICATIONS IN ION CHROMATOGRAPHY 323 The base material is surface sulphonated, and a polystyrene latex with quaternary ammonium functionality is grafted on to the SO3- sites. The variations in column capabilities are brought about by variations in such features as the degree of cross-link on the styrene latex, the quaternary ammonium functional groups and the particle size. For the analysis of strong acid anions (with pk, < 7) (Fig.1) the optimum mode of detection is chemically suppressed conductivity. This technique involves the conversion of the eluent ions (e.g. , Na2C03) to a very low conductivity form (e.g., H2CO3) in a device known as a fibre suppressor. The fibre suppressor provides an exchange membrane for the removal of cations which not only dramatically reduces the background conductivity, but also removes the interference of cationic species from the sample matrix. The device only requires a gravity fed supply of dilute sulphuric acid to become operational and is rapidly equilibrated from start-up each day.Start-up times are as short as 15 min before reproducible analytical capabilities for p.p. b. levels of anions are available. Chemical suppression provides the advantage of greater sensitivity and wider linear dynamic range for the detection of most anions. For ions such as CN- and S2- with pk, > 7, amperometric detection is used. If the analysis of strong and weak acid anions is required simultaneously the conductivity and amperometric detectors can be run in series to give a full anion profile. Standard anion analysis is carried out on separators s1-S~ and the choice of column is very much dependent on the matrix, which can range from ultra-pure water (where p.p. t. detection capabilities are required), to percentage concentrations of strong acids or brines, where trace contaminant levels are of interest. Carbohydrates are not normally considered to be anions, yet their pk, values are between 12 and 14, and by use of sodium hydroxide as eluent they can be ionised and separated on an anion-exchange column (HPIC AS6).Detection is carried out by using a specially designed pulsed amperometric detector. A pulse sequence is required to clean and recondition the gold electrode after the oxidation and detection has taken place. High carbohydrates of up to 1&12 polymer units can be separated and detected on the same separation/detection system. The analysis of polyvalent anions, in particular polyphosphates and sequestering agents such as EDTA and polyphosphates, has always been difficult.The AS 7 column, with nitric acid as eluent, is 0 ' 4 a Timelmin Fig. 1. Ion chromatography of strong acid anions. Li+ T 1 0.3 pS Rb+ h cs+ , JN 0 4 8 12 16 20 Time/m in Fig. 2. Ion chromatography of alkali and alkaline earth metal cations. Cation fumtional fibre membrane suppressor in use, regenerated with 0.02 M tetramethylammonium hydroxide solution.324 APPLICATIONS IN ION CHROMATOGRAPHY Anal. Proc., Vol. 21 capable of giving such separations directly from soap powder and detergent liquid matrices. Detection is via post-column derivatisation and ultraviolet - visible measurement of the complexes at 330 nm, Cations Styrene - divinylbenzene based sulphonated resins are again used for the separations. The detection mode for alkali (plus ammonia) (Fig.2) and alkaline earth metals is again chemically suppressed conductivity. The cation functional fibre membrane converts the eluent, e.g., HCl, into H20 and virtually eliminates the background conductivity. The current separations require two different eluents for the separation of alkali and alkaline earth metals. A latex based resin is under development, which will enable the two sets of cations to be analysed in one single run. Chromatographic analysis of transition metals (Fig. 3) has been carried out in a variety of different ways. Dionex have found that to obtain the desired selectivity, it is necessary to involve complex formation in the separation process. Eluents containing organic acids, such as oxalate, tartrate and citrate, are used to promote the formation of anionic complexes. These complexes have different k values and this feature provides the basis for separation.If a cation-exchange column is used, the metals which form the more stable complexes will elute more quickly and vice versa. In this instance the control of pH has a significant effect on the stability of the complexes and hence on the retention times. By changing to an anion-exchange column the order of elution is, as expected, approximately reversed. Detection is again via post-column derivatisation and ultraviolet - visible measurement at a suitable wavelength. The introduction of a new membrane reactor has significantly improved the signal to noise ratio and, therefore, improved the detection limits for transition metals. Acids and Alcohols Exclusion chromatography is traditionally used for the separation of small molecule carboxylic acids (Fig. 4).Until recently, detection on a Dionex system has involved packed bed suppression with :u2+ 2+ rc + Fe2+ 0 4 8 12 16 20 Tirne/rnin Fig. 3. Ion chromatography of a transition metal standard. pH value of the standard, 1.47; pH value of the eluent, 4.33. 0 3 6 9 1 2 1 5 Ti me/rnin Fig. 4. Ion chromatography of carboxylic acid standard. Concentrations are 10 p.p.m. of sulphate, 10 p.p.m. of maleic acid, 10 p.p.m. of malonic acid, 20 p.p.m. of lactic acid, 10 p.p.m. of formic acid, 20 p.p.m. of acetic acid and 20 p.p.m. of propionic acid.September, 1984 DIAS AT UMIST. PART I1 325 conductivity detection. The packed bed suppressor used in this situation was a silver-form resin, which required replacement when exhausted. A new membrane suppressor, known as AFS-2, has been developed which, in conjunction with strong organic acid eluents (such as octanesulphonic acid or tridecafluoroheptanoic acid), provides the advantages of chemical suppression on a continuous basis. Amino acids and alcohols can also be separated on the exclusion system. Detection for both species is achieved by use of the pulsed amperometric detector (PAD). MPIC (Mobile Phase Ion Chromatography) MPIC utilises neutral styrene - divinylbenzene resin packings, which act as separation sites for the ion pairs formed between the analyte ion and eluent ion. After separation, the eluent ion pair is removed in a suppressor unit and the ion is detected conductimetrically. Until recently the packed bed suppressors, which were used in the system, required periodic regeneration. The new AFS-2 membrane suppressor can be used in the MPIC mode for hydrophobic anion analysis and provides continuous suppression. The membrane can withstand 90% acetonitrile without loss of integrity. MPIC is used for analysis of a wide variety of hydrophobic anionic and cationic species including surfactants, metal complexes, amines and quaternary ammonium compounds.

ISSN:0144-557X    

DOI:10.1039/AP9842100320

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

September, 1984 DIAS AT UMIST. PART I1 325 Analytical Chemistry in UK Universities, Polytechnics and Colleges This series of articles began in 1978 with an article on analytical work within the Queen’s University of Belfast (August issue, p. 248). Two more articles appeared, on UWIST (May, 1979, p. 169), and Wolverhampton Polytechnic (July, 1979, p. 215). We now present the second part of a two-part article on DIAS at UMIST. As many readers will know, the senior author, Professor Gordon Kirkbright, tragically died in July. These comprehensive articles will serve to demonstrate the great breadth of his activities and illustrate how sorely he will be missed in the analytical community. Anyone wishing to write an article describing analytical science in their department is invited to send it to the Editor of Analytical Proceedings, who will also be pleased to advise on the general content of the articles.DIAS at UMIST Themes and Images. Part II* M. A. Browne and (the late) G. F. Kirkbright Department of Instrumentation and Analytical Science, University of Manchester Institute of Science and Technology, P. 0. Box 88, Manchester, M60 1QD Introduction Part I of this article described some of the research programmes that are currently in progress in the Department of Instrumentation and Analytical Science at UMIST. The theme in the first section of this review was “imaging”; in this second part we hope to illustrate themes of sensor and systems research in the areas of measurement science in which the Department is concerned. Thus, present research systems concerned with fibre optic devices for the sensing of physical and chemical parameters, optical and ultrasonic cross-correlation sensors, microwave spectroscopy and plasma emission spectroscopy are considered.Fibre Optic Devices and Systems Research concerned with fibre optic sensors forms an important and expanding interest within the Department of Instrumentation and Analytical Science at UMIST. Present activity and interests relate to both analogue and digital optical sensors, multiplexed passive fibre optic systems, mainly using non-coherent light, multimode fibres and intensity/wavelength variation; displacement inputs and bulk-sensitive devices are of particular interest. Quantities of interest for measurement range from the * For Part I, see Analytical Proceedings, 1984,21,261.326 DIAS AT UMIST.PART I1 Anal. Proc., Vol. 21 parameters of pressure, temperature, flow and level to chemical quantities such as pH, and gas sensing as required by the process industries. The emphasis is on the development of simple, reliable systems for these industries and also for biomedical sensing. New developments include opto-fluidic converters and control-by-light systems. Principles Using optical fibre sensors, variations in the measured parameter are employed to modulate the source radiation by its change in intensity, phase, wavelength or polarisation. Techniques of intensity modulation and the means of detection may be quite simple; two approaches will be outlined: (i) a shutter modulator using parallel gratings and (ii) a pressure sensor using a diaphragm and a self-reference reflection technique. Because of the adventitious effects on light intensity in such a measuring system caused by source and optical link changes and owing to variations in detector responsivity it is essential for intensity-modulated sensors to have a means of referencing in order to nullify unwanted variation of the output of the instrumental system.This can be achieved partly in both the shutter modulator and the reflection sensor system; other means of referencing for intensity modulated optical sensor instrumentation are under investigation. The Shutter Modulator The shutter modulator under development consists of a pair of superposed parallel gratings, each of which is coarsely ruled with transparent spaces and opaque bars, which may or may not be of equal width.The width of a space and bar pair measured perpendicularly to the rulings is known as the grating pitch, w . This pitch is normally the same for each grating. If the first grating is illuminated with normally incident white light and the second is traversed across this in a direction perpendicular to the grating lines, the transmitted light will vary periodically; its intensity will be at a maximum when the spaces coincide and at a minimum when they are directly out of phase; one complete output cycle then corresponds to a relative movement between gratings of one grating pitch. The intensity of the transmitted light is thus a function of the relative positions of the gratings, x , the grating pitch, w , and the separation between the gratings, g, along the optical axis.For gratings of fine pitch it is necessary to consider diffraction effects but for coarser gratings (for example less than 25 lines mm-1) diffraction is less significant. Under these conditions the second grating may be considered to be in the geometrical “shadow” of the first. The output intensity will then vary with displacement of one of the gratings in a saw-toothed fashion provided that the light sourcp, is collimated and that the grating axial separation is small. If the relative movement of the gratings is limited to a single leg of the serrisoid generated, the transmitted light intensity can be used to measure displacement in an unambiguous fashion. If the serrisoid was perfect a linear displacement characteristic would result over a displacement of w/2.As the grating separation is increased the output intensity profile moves from serrisoidal to sinusoidal and the contrast is reduced. At a grating separation of g = w/4@, where $ equals the half-angle divergence of the light source, the contrast falls to zero. Thus, if the pitch of the grating is reduced the sensitivity of the system is increased although its linearity and contrast may be reduced. The experimental modulator configuration under development is shown in Fig. 1 in schematic form. Radiation in the infrared region of the spectrum (820 nm) from a light-emitting diode (LED) is coupled to a 300-pm core diameter step index optical fibre link of CQ. 1 m in length.This radiation is led to the modulator and returned via a second similar link to a PIN diode operated at zero bias to reduce noise. The light intensity of the source is square-wave modulated at a frequency of 700 Hz and the output from the photodiode is amplified and demodulated by phase-sensitive detection to enable high signal to noise ratios to be achieved and to effect discrimination against ambient radiation. Sapphire spheres (4 mm in diameter) are employed to obtain a collimated beam of light in the modulator; the sphere separation is 12 mm. The sensor, which consists of two parallel gratings about 5 X 10 mm, is interposed between the sapphire spheres. One grating is fixed relative to the input fibre and the other, mounted on a pair of spring flexures to enable parallel motion and to provide a restoring force, is traversed across the fixed grating in a direction perpendicular to the grating lines.The output/displacement characteristic of the modulator, I @ ) , is affected not only by movement of the grating but by other adventitious intensity changes. To reduce these effects the light input level to the modulator is stabilised by taking part of the input radiation to the modulator and returning this via a reference fibre and a hybrid photodiode/ amplifier as a feedback signal to the source current driver.September, 1984 DIAS AT UMIST. PART I1 Moving grating 327 Output fibre / Displacement input / Y Input fibre Reference fibre Fig. 1. Schematic diagram of fibre-optic shutter modulator device. The characteristics of this type of shutter modulator device for monitoring of small displacements for process control applications are at present under investigation; its operation in hostile environments and for remote sensing of small pressure, temperature and level changes will be apparent.Reflective Pressure Sensor A fibre optic pressure sensor has been developed1 in the Department in which the movement of a reflective diaphragm under applied pressure is used to modulate the amount of light returned from the sensor to the control station electronics. If two adjacent fibres face a reflective diaphragm and one of these fibres carries light from the control station to the sensor, then radiation leaving the end of this fibre will be reflected from the diaphragm and some enters the core of the second fibre to be returned to the detection electronics. The intensity of this returned radiation is a function of the relative positions of the fibre ends and the diaphragm.If the distance between the ends of the fibre and the diaphragm is zero then no light is returned. If this distance is increased, the intensity of the returned light increases in linear fashion until the whole of the return fibre core is illuminated; the increase then flattens off. If the distance is increased still further, the returned intensity decreases as the inverse square of the separation. It is the initial steep, linear region that is chiefly of interest for sensing purposes. The simple sensor outlined above suffers from a common problem with light intensity sensors that repeatability is subject to random changes in light intensity. A system that partly alleviates these problems is shown in Fig.2. Two LEDs, switched at different frequencies, supply light to two input Reflector Light-emitting diodes II 1 1 2 kHz Oscillator 1 \rn 62 H z Oscillator 2 W - l (3) 2 kHz Detector/amplifier Band pass Precision Smoothing Analogue Displav Liquid filters rectifiers to digital driver crystal d i s p I a y Block diagram of prototype three-fibre sensor. converter Fig. 2.328 DIAS AT UMIST. PART I1 Anal. Proc., Vol. 21 fibres. These are terminated at the sensors together with a single return fibre in a probe where they form two reflective sensors of the type described above, but with a common return fibre. The ends of the fibres are positioned so that one sensor works on the steep linear part of its characteristic and the second sensor on the flat top section of the response curve.The two signals are separated electrically after detection at the control station electronics and give outputs corresponding to lines A and B in Fig. 3. The ratio of these outputs (shown as line C) is an indication of pressure and is insensitive to changes in detection sensitivity, return fibre attenuation and diaphragm reflectivity. The two LEDs and the input fibres are not included in the referencing system, but it is envisaged that these would form a servo-controlled “ring-main” serving many such sensors via Y-couplers whereby the over-all light level would be maintained electrically. 1.2 - m ~ 0. tu 0.14 & 1.0 h E ..0.8 a 0.10 - r a u) 0.12 - .- c 0.6 - 0.08 ‘ I 1 I I 0 40 80 120 160 200 Pressure vs. coupled power for the reflective sensors and the ratio of output (high-sensitivity Pressureim bar Fig. 3. sensor output/low-sensitivity sensor output). The experimental prototype operates over a pressure range of 0-200 mbar, has a linearity of +1.5% of range and a projected repeatability of +0.2% of range when the source/detection unit is about 250 m from the sensor and is connected to it using silica glass multimode fibre. The sensitivity of the sensors can be expressed as the change in optical power out of the probe for a given pressure change and has a value of 5 Pi x 10-6 pW mbar-1, where Pi is the optical power led to the probe. Hysteresis effects are low, typically less than +0.05% of range, and the simple design allows for ease of assembly and high durability.Chemically Sensitive Fibre Optics The concept of immobilising an indicator dyestuff, whose colour change might be employed to observe variation in pH, dates back at least to the use of litmus paper. The integration of this principle with fibre optic techniques represents an important extension of pH measurement which can complement and improve on conventional potentiometric methods. The results obtained in the early studies clearly demonstrate the feasibility of this approach. The probe itself is of rugged construction, intrinsically safe and capable of remote operation and miniaturisation. It is ideally suited for use where the fragility of glass electrodes would present severe limitations. Current devices are 2.0 mm in over-all diameter, and the sensing head may be only 10 mm in length.Miniaturisation of these devices has not yet been attempted but should be possible and thus present the opportunity for use in clinical and other biomedical applications. The pH probe utilises a polymer fibre bundle, transparent in the visible region of the electromagnetic spectrum. At the end of this is fabricated a tip, which consists of a styrene - divinylbenzene copolymer on to which indicator dyestuff is adsorbed; the copolymer is retained in position at the end of the fibre bundle using a membrane of polytetrafluoroethylene (PTFE). Changes in pH in the vicinity of the tip thus cause a variation in the attenuation of specific reflectance bands.2 Instrumentation A schematic diagram of the experimental instrumentation system employed is shown in Fig.4.September, 1984 I Y T I I I I 1 A1 DIAS AT UMIST. PART I1 Chart Detector Analogue Reservoir 329 Fig. 4. Schematic diagram of instrumentation employed with the flow cell. Initial experiments were conducted using a tungsten - halogen bulb (f2 V, 55 W). The filament was focused at the fibre optic entrance aperture using a glass lens. The light path was periodically interrupted by a rotating sector to provide a signal source capable of modulation in the range 10-800 Hz. The amplifier employed to enhance the signal from the photomultiplier tube was synchronised to the modulation frequency of the source to provide discrimination against ambient light.The radiation reflected from the sensitive tip of the probe was taken to a grating monochromator before being detected by the photomultiplier tube. Results and discussion Tests on the pH probe and evaluation of its response characteristics were made using an open glass reservoir. A laboratory pH meter fitted with a combination electrode was used independently to monitor the pH. The pH was varied by the addition of aliquots of 0.1 M hydrochloric acid. The total ionic strength of test solutions was maintained using 0.1 M sodium chloride solution. The measured response of the pH probes corresponds to the attenuation of the reflected radiation at specific wavelengths in the visible region of the spectrum selected by the grating monochromator. This response is frequently presented as the normalised reflected radiation intensity, RN, and is expressed by R - &in Rmax - Rmin RN = where R,,, and Rmin define the upper and lower limits to R , respectively; these are measured as the maximum and minimum reflected intensities in arbitrary units.The results presented are those obtained for an immobilised bromothymol blue pH probe. Radiation attenuation was measured at 593 nm to provide the optimum signal dynamic range with respect to pH. The wavelength was selected after comparison of the reflectance spectra obtained for the probe in excess acid and base shown in Fig. 5. The reflectance spectrum of the probe without adsorbed indicator is also presented; this demonstrates the wavelength response of the optical system separately to that of the absorption bands of the supported indicator.330 DIAS AT UMIST.PART I1 Anal. Proc., Vol. 21 Probe response in clear and turbid solutions As shown in Fig. 6, a slight difference in response of the probe in clear and turbid solutions was detected. The turbid solution was simulated by the addition of 5 g of pulverised graphite (Fluka A.9) to the reservoir solution (1.5 1) and this was maintained as a suspension by vigorous stirring. As the solution was opaque the response difference could be attributed to either ambient light reduction at the sensitive tip or absorption of scattered radiation at the membrane - solution interface. 350 800 Wavelengthlnm Fig. 5. Reflectance spectra from a bromothymol blue pH probe: A, with the indicator predominantly in the base form; B, with approximately equal concentrations of each conjugate form of the indicator; C, with the indicator in the acid form; and D, without indicator present.8 9 10 PH Fig. 6. Probe responses to pH as a function of solution turbidity: A, from pH 10.5 to 8.0 in a turbid solution (see text); and B, from pH 8.0 to 10.5 in a clear solution. Probe response time characteristics Response times have been recorded for a probe between pH 7 and 12, in incremental steps of 1 pH unit, and for transitions from acid to base, and base to acid, as shown in Fig. 7. The pH range examined was thus greater than the linear response range of the probe. In each experiment a stable response ~ 0 5 10 15 Time/min Fig. 7. Probe response time characteristics: (a) from pH 12 to 7 in steps of 1 pH unit; and (b) from pH 7 to 12 in steps of 1 pH unit.September, 1984 DIAS AT UMIST.PART I1 331 (corresponds to greater than 99% of change in pH recorded independently) was observed within 5 min. If an exponential response function is assumed the characteristic response time to reach 63% (lie) of the final corresponds to 65 s for the electrode employed. The results obtained indicate that the response time is a complex function of the difference between the initial and final pH values of test solutions employed, e.g., when the probe is subjected to a large abrupt step change (pH 7 to 12) only 50 s are required to achieve a stable response. An important contributing factor to the response time is the rate of diffusion of solvent and ions across the hydrophobic PTFE membrane of the probe.The probe and its dimensions are illustrated in Fig. 8. Fig. 8. The fibre-optic based reflective pH probe. Flow Measurement Research Another of the research and teaching themes in the Department is flow measurement. This ranges from ultrasound Doppler blood flow measurement to industrial applications of cross-correlation flow measurement of multiphase fluids. Major programmes involving the development of cross-correlation flow measurement techniques are in progress; the following describes the basic ideas involved in the technique and some applications. The Concept Cross-correlation flow meters measure the transit time of a tagging signal (turbulence, clumps of particles, etc.) in the flow between two axially spaced sensors.The technique has only recently become a realistic proposition for routine industrial application because of the reducing cost of large-scale integrated circuits and microprocessors from which the correlator may be realised. Fig. 9 illustrates the principle of cross-correlation flow measurement.3 The cross-correlation function is defined to be It can be shown that this function has a maximum value when the cross-correlation lag T is equal to the transit time z* of the tagging signals. Hence the flow velocity u is given by u = Lit* where L is the spacing of the sensors A and B. R,,(t) = Sxct - ‘dly(t)dt332 Tagging markers take time t” to travel from A to B DIAS AT UMIST. PART I1 Sensing Cross-correlator measures time for system I tagging markers to travel from A to B Velocity :1 I -1- Adjustable x(r-t) - 4 Anal.Proc., Vol. 21 Cross-sectional area A t Cross correlation R x y ( t ) = J ~ ( t - ~ ) y ( t ) d t measure time delay T” of cross-correlation peak Transit time t* 1 Flow Q Fig. 9. Cross-correlation flow meter: basic principles of operation. The volume flow-rate is the product of the velocity, the cross-sectional area, A, of the pipe, and a calibration factor, k, which allows for the measured velocity to be related to the mean velocity in the pipe. The volume flow-rate, Q, is obtained from the equation kLA ’c* Q = - Referring again to Fig. 9, we see that simple computing blocks can calculate the cross-correlation function R,(‘c), determine the transit time t* of the fluid and calculate the flow rate, Q.Although the calculations are simple, a large computer capacity has in the past been required, because the sensor output data x ( t ) and y ( t ) have a fairly wide band width (say 10 kHz) and the transit time t* must be resolved to a high precision (say 99.8%) over a wide range of flows (typically a range of ten to one). In practice, most digital computers and currently available microprocessors are unable to do the calculations shown in Fig. 9 sufficiently quickly and this difficulty required a solution in order to make the use of cross-correlation flow meters a realistic proposition. Cross-correlation Tagging Signals The tagging signals that are fundamental to cross-correlation are generated by the fluid turbulence. These turbulent eddies can be detected, for example, by the modulation they superimpose (by Doppler effect) on an ultrasonic beam perpendicular to the direction of flow.Alternatively, particles can become entrained in the turbulent eddies to form clouds (just as puffy white “cotton wool” clouds are formed in the atmosphere by the effects of atmospheric turbulence on the water droplets). These “clouds” can form the tagging signal and they may be detected by ultrasonic or optical beams, electrical conductivity or electrical capacitance effects. An “observer” moving at the same velocity as the flowing fluid would note that the eddies at position A in Fig. 9 gradually changed their shape as they moved down the pipe. However, provided that the downstream sensing point B is reasonably close to A (say less than five pipe diameters distant), the eddies are sufficiently similar to be recognised by the correlator to enable the transit time to be measured.The turbulent eddies have a wide range of sizes and hence they can present a wide range of frequencies to the sensors. The spectrum is band-limited white noise with its upper frequency dependent on viscous damping of the turbulent eddies, caused by the shearing effect of layers of the fluid. Typically the upper frequency limit may be as high as 10 kHz. Ideally, the flow sensors in the cross-correlation flow meter should respond to the whole range of these turbulent frequencies. Unfortunately, this wide band width is only possible when using point-sensing devices such as laser probes or hot wires, which are much too delicate for use in industrial environments.Sensors for jSeptember, I984 DIAS AT UMIST. PART I1 333 industrial use, such as ultrasonic beams and capacitance- and conductivity-sensing plates, average over a substantially sized volume of the flow, and hence they will not respond to the higher frequency turbulent eddies. A prime need in system design has been to minimise the averaging effects of the sensors used, otherwise this would limit the information on bandwidth to the cross-correlator and thus limit the accuracy and response time of the system. The sensors used to detect the tagging signal may fall into three broad categories, viz., those monitoring modulation of radiation by the flowing fluid, emission of radiation by the flowing fluid or the electrical and thermal properties of the fluid.The final practical choice is based principally on reliability and the cost of the sensing devices. The gain stability of the sensors is not important as the cross-correlator simply measures the time delay of signals between the sensor and this time delay is not dependent on the gain of the sensors. Optical and ultrasonic sensors The sensors can sometimes even be remote from the measured flow, as in the system made for use by volcanologists who wish to measure the flow velocity of volcanic jets. An optical cross-correlation flow meter has been used on Mt. Etna in Sicily and on Mt. Eibus in the Antarctic. It can be located safely away from the lava “bombs” and intense heat of the volcanic jet. A flow meter similar in principle to the volcano system has been used for some time in a number of British Steel plants to measure the gas flow-rate from basic oxygen steelmaking vessels and electric arc furnaces.It has been found to be extremely reliable. Another form of the optical cross-correlation flow meter is used by the Water Research Centre to measure the flow in underground sewers. In this instance the instrument is mounted in a manhole above the sewer pipe and measures both the speed and depth of the fluid so that the total flow-rate in the open channel may be determined. For flow measurement in closed pipes that may contain fluids at high pressure, the ultrasonic cross-correlation flow meter, which clips to the outside of the pipe, seems the ideal instrument. This flow meter is now at the production test stage and is made commercially under licence from BTG.The following advantages in cross-correlation flow meter techniques are being realised: (i) the technique is based on an absolute measure of transit time using a digital cross-correlator, which can be time-shared between a number of sensing heads to reduce the cost; (ii) sensors are now available for a large variety of flows; (iii) in most applications, the cost does not increase as the size of the pipe increases; and (iv) the sensors are simple and require practically no maintenance. Variations in the gain of the sensors do not affect the accuracy of flow measurement. Recent surveys have emphasised the need for better measurement instrumentation to improve the quality of process control and increase productivity in the process industries. The need for better flow measurement has been particularly highlighted. Better instrumentation inherently must require reduced maintenance; cross-correlation flow meters, using sensors requiring no calibration and all-digital systems for data handling, ideally match this need.Microwave Spectrometry Microwave spectrometry is being used in several research projects in DIAS. Microwave rotational spectroscopy is being employed in multi-component gas analysis and for the determination of water in crude oil flowing through pipelines. The following gives an outline of microwave rotational spectroscopy, spectrometers and some details of their use in analysis of gaseous mixtures. Microwave Rotational Spectroscopy (MRS) Molecules can absorb energy from electromagnetic radiation in the microwave region of the spectrum, resulting in an increase in their rotational potential energy.In some instances the energy is coupled into an inversion resonance, when an atom oscillates between two symmetric positions as, for example, the nitrogen atom with respect to the plane through the three hydrogen atoms of the pyramidal NH3 molecule. The energy levels are quantised and the characteristic absorption frequencies are dictated by the shape, moment of inertia, molecular mass and size of the molecules rather than by any particular chemical grouping. The microwave spectrum of a molecule is, thus, rather individual, and the technique of MRS is able to distinguish between positional isomers and isotopic isomers of the same chemical formula and functionality. The resonance frequency changes when the molecules are exposed to an electric field.the Stark effect. A resonance line may have a linear (first-order) or quadratic (second-order) Stark effect,334 DIAS AT UMIST. PART I1 Anal. Proc., Vol. 21 depending on the molecule and the quantum numbers involved in the transition giving the resonance line. In the linear Stark effect, a line splits into two lines on each side of the original line, the shift being proportional to the applied field and is ca. 20-100 V cm-1 MHz-l. In the quadratic Stark effect, the line is shifted only in one direction independent of the sign of the applied Stark effect. Microwave Spectrometers The simplest microwave spectrometer consists, just as does a spectrometer for shorter wavelengths, of a source, an absorption cell and a detector.4The absorption cell is a waveguide, for practical reasons not longer than about 1 m, and the detector is a diode. The attenuation in the absorption cell due to an absorbing line is small: a strong line, having an attenuation coefficient of 10-4 cm-1, will be attenuated 1% in a 1-m cell when the gas is at resonance.This small change in attenuation when the gas resonates cannot be detected accurately. The microwave frequency could be swept around the gas resonance frequency, but frequency-dependent transmission in the rest of the microwave system will tend to “blur” the changes due to gas absorption. Instead, the microwave frequency is kept constant and the frequency of the gas resonance is swept by means of a Stark field, which is generated by putting a voltage on an electrode in the middle of the waveguide. The microwave properties of the absorption cell will not be changed significantly by the electrode because it is perpendicular to the electrical field of the microwaves.When the microwave frequency and line frequency coincide, maximum attenuation occurs. A periodic varying voltage is applied to the Stark electrode and the line frequency is displaced so that the gas has no absorption at the constant microwave frequency. At the detector a periodically varying output voltage is obtained and its a.c. component is amplified and detected by a lock-in amplifier. The sensitivity of a Stark spectrometer is proportional to the electrical length of the absorption cell.One can increase the sensitivity by using a resonant cavity of high quality factor which has an apparent path length much greater than the physical length, for example a cavity of the type shown in Fig. 10. The improved sensitivity of a cavity spectrometer is obtained at the cost of use of a more complicated apparatus. Cavity frequency and oscillator frequency must always coincide. This can be achieved when the oscillator frequency is determined by the absorption cavity, and the oscillator amplitude is influenced by the gas absorption. The change in oscillator amplitude due to a certain absorption will be higher with decreasing amplitude; hence the oscillator amplitude should be small and in this state is called a “marginal oscillator.” Small amplitudes are also required in order to avoid saturation of the gas.The change in amplitude can be measured by a detecting diode, or the oscillator itself can also be used as a detector because the oscillator amplitude influences the supply current. In this instance, a detector diode is not necessary, and the apparatus is extremely simple, although a slightly higher noise level results when self-detection is used. Analysis by MRS The presence of a gas in a mixture can be checked by measuring the absorption at one or more of the resonances of the gas. Tables giving many of the resonance lines for gases are available. The line frequencies needed for identification must be known with a relative accuracy of 10-6, which can only be achieved by either a microwave frequency counter or a microwave frequency synthesiser.Although the lines are narrow, it is difficult to ensure that an absorption at a certain frequency identifies the gas unambiguously. A statistical investigation has been made by other workers5 of the probabilities of making a mistake in identifying a gas. The study assumed a mixture of 33 different gases having 10 000 lines in the frequency range 26-40 GHz. The average distance between the lines is then 1.4 MHz. With a resolution of 0.2 MHz, there is a probability of 0.44 that two lines from different molecules will overlap at any one frequency; the probability of overlap between lines of these two species at two different frequencies reduces to 0.02, so there is little chance of making a mistake in identification.The high degree of specificity attainable with MRS is one of its most attractive features for gas analysis, both qualitative and quantitative. Analysis by Microwave Spectrometry The sources in microwave spectrometry are generally monochromatic line sources of band width less than 100 kHz. As such they can be used directly for spectrophotometry or spectrometry if theSeptember, 1984 DIAS AT UMIST. PART I1 335 absorption band width of the analyte species is broad. It is this factor that renders possible the analysis of hydrocarbon mixtures (of low dielectric constant) (about 3) and loss for water which, at 22 GHz, has a broad absorption band and has a high dielectric constant (about 30) and loss. Fig. 10.Microwave spectrometer assembly. A 22-GHz microwave absorption spectrometric system has been developed in DIAS for the determination of water in crude oil in the condensed phase using this technique. Good sensitivity and near linearity over the range 0.5-12% of water make this an attractive technique. The gradual decrease in the real cost of microwave equipment should lead to a much wider use of these techniques, especially in rotational spectroscopic measurements, where the analytical rewards are high, but also in remote detection and measurement of chemical and physical parameters for on-line automatic analysis in production control and remote sensing of the presence of dielectric materials. Plasma Emission Spectroscopy Analytical optical emission spectrometry for a wide variety of applications in environmental, industrial and biomedical disciplines forms an important part of the activities of the Department.The emphasis of research, however, lies in the development and application of “novel” instrumentation, particularly regarding the manner in which samples may be introduced into plasma discharges-both inductively coupled plasmas (ICP) and microwave-induced plasmas (MIP). Inductively Coupled Plasma Instrumentation Recent publications from this laboratory6.7 have described studies of a novel system in which small volumes and masses of liquid and solid samples, respectively, may be applied to a graphite rod for direct axial insertion of the rod into a continuously operating low power (<1.5 kW) inductively coupled argon plasma.With this technique some volatile elements have been determined by optical emission spectrometry at the sub-nanogram level with adequate precision and high powers of detection. The use of argon - 0.1% Freon 23 injector gas has been shown to permit efficient volatilisation of refractory oxide- and carbide-forming elements with this system. A microprocessor-controlled graphite rod direct sample insertion device has now been developed. The insertion of the rod into the plasma is effected by336 DIAS AT UMIST. PART I1 Anal. Proc., Vol. 21 using a microprocessor-controlled stepper motor assembly. The software design enables the plasma to be used for the desolvation and ashing of samples solutions and for their vaporisation. Present research is concerned with optimising the heating rate of the graphite rod vaporisation process in the plasma via modification of the rod configuration.8 As described below, for the microwave-induced plasma, work is also in progress with the use of a mini-hydride generator for the direct introduction of those elements which form volatile hydrides into the inductively coupled plasma.This work shows promise and the system developed should be capable of automatic operation. Microwave-induced Plasma Emission Spectrometry Several projects are in progress within the Department concerned with the use of 2450-MHz microwave-induced plasma discharges for analytical purposes. These programmes are concerned firstly with the use of the mini-hydride generator for routine analysis for arsenic, selenium and other elements which form volatile hydrides.This particular type of hydride generation system as shown in Fig. 11 has the advantage that large volumes of hydrogen are not generated and therefore cause minimum perturbation to the plasma discharge at the low powers at which these microwave systems operate. Secondly, they are also concerned with the development of an efficient system whereby gas chromatographic separation of volatile organometallic compounds can be combined with efficient excitation of the metal (or metalloid) species in the microwave plasma. Thus an active programme at present is concerned with the determination of organo-lead, -tin and -mercury compounds in plants and industrial atmospheres. The studies undertaken to date indicate the possibility of a rugged and reliable instrumentation system, possibly used with an optical multi-channel analyser arrangement , for this purpose.TMolo cavity Activated ch a rcoa I Fig. 11. sources. diethyl ether Mini-hydride system for generation of volatile hydrides into ICP and microwave plasma Other Topics It has been possible in these two articles to outline only a limited number of the research projects that are now in progress in the new and thriving Department of Instrumentation and Analytical Science at UMIST. We have therefore necessarily omitted much work concerned with high-performance liquid chromatography using micellar systems, an exciting project concerned with the development of suitable instrumentation for on-line mass spectrometry and sampling of liquid streams and the manner in which we are at the moment employing laser-excited correlation techniques for thermal wave imaging. We apologise to colleagues within our Department but have hoped to create an awareness within the analytical chemistry community of the diversity of our interests in instrumentation and measurement and can only suggest to anybody interested in exploring further the interests of our Department in relation to their needs and requirements, “Pay us a visit!’’September, 1984 EQUIPMENT NEWS 337 We thank all members of the Department of Instrumentation and Analytical Science at UMIST for allowing us to borrow heavily on their research and published papers. Special thanks go to academic colleagues, Professors Peter Payne and Maurice Beck and Drs. Barry Jones, Fred Alder and Richard Miller, each of whom has extensive interests in the activities described in this article. 1. 2. 3. 4. 5. 6. 7. 8. References Jones, B. E., Spooncer, R. C., Cox, E. R . , and Philp, G. S., Proc. Transducer - Tempcon, 1983. Kirkbright, G. F., Narayanaswamy, R., and Welti, N. A., Analyst, 1984, 109, 15 and 1025. Beck, M. S., NRDC Bull., No. 52, 1980. Alder, J. F., Brennan, M. F., Clegg, I. M., Drew, P. K. P., andThirup, G., Trans. Znst. Meas. Control, 1983, Jones, C. E., and Beers, E. T., Anal. Chem., 1971,43, 656. Kirkbright, G. F., and Walton, S. J., Analyst, 1982, 107,276. Kirkbright, G. F., and Li-Xing, Z . , Analyst, 1982, 107, 617. Li-Xing, Z . , Kirkbright, G. F., Cope, M. J . , and Watson, J . M., Appl. Spectrosc., 1983, 37, 250. 5, No. 2.

ISSN:0144-557X    

DOI:10.1039/AP9842100325

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

September, 1984 EQUIPMENT NEWS 337 Equipment News Fourier Transform Infrared Spectrometer System With Digilab’s Micro/IR systems, infrared trans- mittance and reflectance spectra of samples as small as 20 pm in diameter can be measured. Also available are a computer controlled X-Y stage for Spectral Data and the National Bureau of Stan- dards’ National Institute of Health - Environmen- tal protection Agency (NIH - EPA) Database. It offers direct access to more than 80 000 spectra of some 68 OOO compounds. It is available from the Nicolet Instrument Corporation as an optional part of their mass spectrometry instrument pack- age, through Hewlett-Packard for the HP5987 GC - MS system and on magnetic tape direct from the maker. John Wiley & Sons Inc., 605 Third Avenue, New York, NY 10158, USA.Automated Hydride Generator The generator, to be coupled to the Spectraspan range of plasma emission spectrometers, is espe- cially suited for selenium and arsenic investiga- tions and provides a method for the rapid analysis of arsenic, bismuth, tin, antimony, selenium, tellurium, germanium and lead at a rate of 40-50 samples h-1 with detection levels in the region of 0.1 p.p.b. Beckman-RIIC Ltd., Progress Road, Sands Industrial Estate, High Wycombe, Buckingham- shire. sample mapping and the Digilab 3250 data system. Polaron Equipment Ltd., 21 Greenhill Cres- cent, Holywell Industrial Estate, Watford, Hert- fordshire, WD1 8XG. Mass Spectral Database The Wiley - NBS Mass Spectral Database com- bines information from Wiley’s Registry of Mass Inductively Coupled Plasma Spectrometer The new simultaneous instrument from Jobin- Yvon is aimed at the foundry market.It uses two polychromators: a 0.5-m unit employing a master holographic grating and a flat field type. A Silex or Apple I1 computer uses PASCAL software for spectrometer management. EDT Research, 14 Trading Estate Road, London, NWlO 7LU.338 EQUIPMENT NEWS Anal. Proc., Vol. 21 Portable Spectrometer The Jobin-Yvon Q500 offers in situ identification of metal stocks. A spark generator is connected to an electrode in a hand-held gun. Microprocessor controlled data manipulation gives rapid indica- tion of “in” or “ou~” of tolerance. EDT Research, 14 Trading Estate Road, London, NWlO 7LU. Modular Raman System The Jobin-Yvon Ramanor UlOOO system was developed for the molecular identification and localisation, on a macroscopic or microscopic scale , of organic, inorganic and biological com- pounds.Its modular design allows the user to assemble a system tailored to particular needs. EDT Research, 14 Trading Estate Road, London, NWlO 7LU. Atomic Absorption Spectrophotometer The SB 902, from GBC Scientific Equipment Pty Ltd. of Australia, features an alphanumeric display that guides the user with simple cues. It can resolve graphite furnace peaks of lead in 1% sodium chloride solution without background correction. Accessories include a hydride genera- tor, graphite furnace and data station. EDT Research, 14 Trading Estate Road, London, NWlO 7LU. Gas Chromatography Development: Total Transfer A new development in the live circuit of the Sichromat-2 enables substance groups to be transferred from the packed separating column to the capillary separating column.Thus, of the entire sample injected on to the preliminary column, only the components under investigation are passed to the high-performance separating column. Siemens Ltd., Siemens House, Windmill Road, Sunbury-on-Thames, Middlesex, TW16 7HS. Hydrogen Safety System This device monitors the actual hydrogen concen- tration in gas chromatographs and switches off the gas flow and oven heating at a pre-set concentration. The main parts of the safety system are continuously checked for faults by an electronic circuit. Chrompack UK Ltd., 61 Shrubbery Road, London, SW16. Autosamplers Two samplers are announced: Model I, with a tray capacity for 25 samples; and Model 11, which will accommodate 125 samples.Both combine with all types of liquid chromatographs. The interfacing of data systems and system controllers can be carried out in either master or slave mode. Chrompack UK Ltd., 61 Shrubbery Road, London, SW16. HPLC Pre-packed Columns Two ranges are available: the “Premium” range, offering 3 and 5 pm materials with efficiency up to 100 000 plates, and the “General Purpose” range, with 10 pm materials and up to 30 000 plates. The columns are of stainless steel, with Parker Hanifin female end fittings of 4.6mm i.d. J. Bibby Science Products Ltd., Stone, Staf- fordshire, ST15 OSA. HPLC Detector The Shimadzu SPD-M1A is a photodiode array detector, which gives a three-dimensional spec- trochromatogram across the entire ultraviolet - visible wavelength range.Dyson Instruments Ltd., Sunderland House, Station Road, Hetton, Houghton-le-Spring, Tyne and Wear, DH5 OAT. Chromatography Integrator - Data System Interfacing the Spectra-Physics SP 4270 integra- tor to the ACT Apricot personal computer provides a large disc capability for storage and retrieval of method files, results, raw chromato- grams and BASIC programs. A second channel is available for the SP 4270, and multiple units can be networked into a multi-channel system. Severn Analytical, 36 Brunswick Road, Gloucester, GL1 1JJ. Data and Chromatography Control Station The Waters 840 control station incorporates the Digital Professional 350 computer with the mak- er’s Expert chromatography software.It allows the user to employ direct Quick-set commands for setting up methods and running analyses. Millipore (UK) Ltd. , Waters Associates Divi- sion, Millipore House, 11-15 Peterborough Road, Harrow, Middlesex, HA1 2YH. Clinical Packing for Drug Screening The 3% CP Sil 34 - Chromosorb GHP 100-200 mesh coated gas - liquid chromatography packing was developed for the analysis of antiepileptic drugs and their metabolites without prior derivat- ization. The analysis of commonly used anti- epileptic drugs is possible in less than 15 min. The maximum temperature that can be used is 260-275 “C. Chrompack UK Ltd., 61 Shrubbery Road, London, SW16. Columns for Capillary Chromatography Large 0.53mm i.d. vitreous silica columns are announced. Two bonded phases are available,September, 1984 EQUIPMENT NEWS 339 with a choice begween 1.0 and 3.8pm film thickness: BP-1, a crosslinked methylsiloxane, and BP-10, a crosslinked 7% cyanopropyl - 7% methylsiloxane. Scientific Glass Engineering (UK) Ltd., 1 Potters Lane, Kiln Farm, Milton Keynes, MKll3LA.Input Selector and Digital Thermometer The selector has rotary switch selection of 12 inputs and is suitable for type K or J thermo- couples. The H1000-IS digital thermometer has a range from -20 to +lOOO"C. Hale Instruments Ltd., Manor House, Manor Road, Altrincham, Cheshire, WA15 9QX. Thermometer Probe A fast response probe, Model H12, suitable for use with the maker's H66 and H66D thermomet- ers, is designed for measurements by immersion in liquids, gases, dough, etc.Hale Instruments Ltd., Manor House, Manor Road, Altrincham, Cheshire, WA15 9QX. Portable Digital Thermometer The Temp Stick has a platinum resistance sensor covering the range from -100 to +199.9"C with an accuracy of +0.2"C. The sensor can be adjusted to point either up or downward. Gallenkamp, P.O. Box 290, Technic0 House, Christopher Street, London, EC2P 2ER. pH and mV Meter The Jenway Model 6071 is a hand-held instru- ment offering measurement ranges of &14 pH to a resolution of 0.01pH and 0 to 1999mV to a resolution of 1 .O mV. Lenton Thermal Designs Ltd., 12/14 Fairfield Road, Market Harborough, Leicestershire, LE16 9QQ. i s available for measuring. samples af. Im ionic strength, such as pure water and acid rain. Beckman-RIIC Ltd., Progress Road, Sands Industrial Estate, High Wycombe, Buckingham- shire.Closed Loop Stripping Analysis (CLSA) System The Tekmar Model CLS-1 is a semi-automatic system for the analysis of trace organic com- pounds in water. Complementing the purge and trap procedure, the CLSA technique involves recirculation of the headspace gas through the sampler - trap - pump system. The purged organics are trapped on charcoal, eluted and analysed by gas chromatography. Analysis Automation Ltd., Southfield House, Eynsham, Oxford, OX8 1JD. Gas Analysers Two analysers are available for standard applica- tions, such as flue gas, hot house and generator gas monitoring and the quality control of natural gas. The Ultramat-21 can measure only one pH - Specific Ion Meter The HNU Model 74 is microprocessor controlled and offers a direct readout of concentration, a standard addition method and the entry of exponentially expressed data.Also announced is the digital conductivity meter Model 63, which has six automatically switched ranges covering 0-99 900 pS cm-1. The dedicated dissolved oxy- gen meter, Model 60, gives a digital readout from 0-20.0p.p.m. Analysis Automation Ltd., Southfield House, Eynsham, Oxford, OX8 1JD. pH Electrodes The Futura range of eleven electrodes includes glass, reference k d combination electrodes. One ~ , component; the Ultramat-22 can measure two. Both are single-beam devices with optopneumatic double-layer detectors operating on the principle of non-dispersive absorption of infrared light. Siemens Ltd., Siemens House, Windmill Road, Sunburv-on-Thames .Middlesex. TW 16 7HS.340 EQUIPMENT NEWS Anal. Proc., Vol. 21 Sulphur Dioxide Analyser The CSI - Meloy Model SA700 ambient level sulphur dioxide analyser is built for direct moni- toring, using a continuous ultraviolet source of intermediate intensity and high stability. It has a standard response time of 90 s or less to 95% of a step change and is within EPA noise, precision and span requirements. Techmation Ltd., 58 Edgware Way, Edgware, Middlesex, HA8 8JP. Non-methane Hydrocarbon Analyser The CSI - Meloy HC500-2C monitors ambient concentrations of non-methane hydrocarbons, total hydrocarbons and methane without the need for hydrocarbon-free air. It has separate recorder outputs for each of three channels. Concentra- tions are read out in ranges of 10-1000 p.p.m.full scale with a minimum sensitivity of 0.1 p.p.m. Techmation Ltd., 58 Edgware Way, Edgware, (CH,). Middlesex, HA8 8JP. Air Monitoring System The Sigma 115 system, designed for continuous monitoring of the workplace atmosphere, deliv- ers samples to a gas chromatograph from mul- tiple, remote locations. Substances that may be hazardous to health, e.g., ethylene oxide, vinyl chloride, benzene and acrylonitrile, can be deter- mined. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Buckinghamshire, HP9 1QA. Xylene Detector The 200th variety of the maker's vapour detection tubes is announced; it is for xylene. Draeger Safety, Draeger House, Sunnyside Road, Chesham, Buckinghamshire, HP5 2AR. Oxygen Monitors The Oxyalarm D is a pocket-sized instrument designed as a personal oxygen monitor.It measures oxygen concentrations over the range from 0 to 100% by volume at normal atmospheric pressure. Alarm levels are adjustable but are normally set between 19 and 23% of oxygen. The Oxyalarm 100R measures oxygen concentrations between zero and 99.9% in 0.1% increments. It has a remote sensing head which, with the standard cable supplied, can be used up to 10m from the main instrument. Both instruments are BASEEFA approved. Draeger Safety, Draeger House, Sunnyside Road, Chesham, Buckinghamshire, HP5 2AR. Counting Scales Two precision counting scales incorporate a memory feature that allows the count value to be stored and accumulated up to 200000 com- ponents at a time, thus facilitating regular stock- taking of lightweight components.The PBC 200 can weigh up to 200 g with 1 mg resolution; the PBC 2000 weighs up to 2000 g with 10 mg resolu- tion. Salter Industrial Measurement Ltd., George Street, West Bromwich, B70 6AD. Cooling Baths A range of cooling baths, circulation pumps and accessories, together with full service support, is announced. It includes open and circulation cooling baths operating at temperatures down to -80 "C. Additional models have shaking and magnetic stirring facilities. A variety of combina- tions is offered. Paar Scientific Ltd., 594 Kingston Road, Raynes Park, London, SW20. X-Ray Diffractometer The 1840 benchtop model features a solid-state detector with a self-adjusting divergence slit. Because of the detector's low leakage current at ambient temperatures, there is no need for liquid nitrogen cooling.The 1840 can be retrofitted to any of the maker's generators that is fitted with a suitable X-ray tube shield. Philips Analytical X-Ray Group, 85 McKee Drive, Mahwah, NJ 07430, USA. Spectrophotometer Two new ultraviolet - visible instruments covering the 325-900nm range are announced, the PU 8650 and PU 8660. They complement the original PU 8600 and the life-science orientated PU 8610, which cover the complete 195-900 nm spectrum. They provide the benefits of the PU 8600 series for those users who do not require full ultraviolet capability . Pye Unicam Ltd., York Street, Cambridge, CB12PX. Spectrophotometer The Lambda 9 is a double-monochromator, double-beam, ratio recording ultraviolet - visible instrument capable of scanning the range from 185 nm up to 3200 nm in the near infrared.It can be used in such applications as the characterising of industrial glasses and optical filters and the determination of water in biological samples and organic solvents. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Buckinghamshire, HP9 1RA. Computer Linking System for Nuclear Spectroscopy The 918 multi-channel buffer (MCB) for linking nuclear spectroscopy inputs to computer systemsSeptember, I984 EQUIPMENT NEWS 341 is packaged in a two-wide NIM module and contains a 10-p~ conversion time successive approximation ADC, an 8000 channel data memory, a Z-80A microprocessor and a FIFO buffer. RS232C and optional IEEE 488 interfaces are provided for linking to the computer systems.EG & G Instruments Ltd., Doncastle House, Doncastle Road, Bracknell, Berkshire, RG12 4PG. Automatic Liquid Injection System for Gas Chromatography The AS 550 is for cold, septumless, on-column injections. It is compatible with existing 2000, 4000 and Mega series gas chromatographs. Benef- its claimed include the elimination of ghost peaks and of discrimination between materials of low and high relative molecular mass. Low temperat- ure operation avoids thermal degradation of the sample. Erba Science (UK) Ltd., Headlands Trading Estate, Swindon, Wiltshire, SN2 6JQ. Chromatographic Analysis of Alcoholic Beverages An 80-120 Carbopack B AW - 5% Carbowax 20M column separates the major components of whisky, brandy, rum, vodka and other spirits.For the minor components and for analysis of beer, wine or other fermentation products, 80-120 Carbopack B AW - 6.6% Carbowax 20M is effective. Supelchem UK (R. B. Radley & Co. Ltd.), London Road, Sawbridgeworth, Hertfordshire, CM21 9JH. Glass HPLC Columns A cartridge system is announced. The internal diameter of the columns is 3.0mm and they are available filled with CP Spher Si, C8 and CI8. Chrompack (UK) Ltd., Unit 4, Indescon Court, Millharbour, London, El4 9TN. Fixed Wavelength Detector for Liquid Chromatography The LC-1SB ultraviolet detector gives a maxi- mum noise of k1 x 10-5 absorbance units and drift of less than 2 x 10-4 absorbance units at the standard 254-nm wavelength. Range settings down to 0.0001 AUFS are included. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Buckinghamshire, HP9 10A.Amino Acid Analysis by HPLC The Spherogel amino acid column is an ion- exchange column designed for amino acid analysis. The Model 230 post-column reactor is designed for o-phthalaldehyde derivatization of primary amines. The Model 157 fluorescence detector extends the capability of the maker’s 6300 amino acid analyser. Beckman RIIC Ltd., Progress Road, Sands Industrial Estate, High Wycombe, Buckingham- shire. HPLC Purification of Monoclonal Antibodies The Bakerbond MAb column can, for example, purify an IgG monoclonal antibody from mouse ascites fluid (centrifuged and dialysed) in less than 30min with a recovery greater than 90%. The isolated monoclonal antibody is also free of transferrin contamination. A US patent is pend- ing.J. T. Baker Chemicals B.V., P.O. Box 1,7400 AA Deventer, Holland. Computing Integrator for Chromatography The Shimadzu C-R1B has a built-in printer - plotter providing the chromatogram and the analysis parameters and data on the same chart. Peak detection sensitivity is determined auto- matically, and tangential - trapezoidal correction of base line drift allows the separation of unresol- ved peaks and the skimming of peaks on tails to be processed automatically. Dyson Instruments Ltd., Sunderland House, Station Road, Hetton, Houghton-le-Spring , Tyne and Wear, DH5 OAT. Light Absorbance Detectors The uvMonitor 1255 is a fixed wavelength detec- tor, which continuously and quantitatively moni- tors the absorbance of one liquid stream or the differential absorbance between two streams.It exhibits noise of 1 x 10-4 AU peak to peak and a base-line drift of 2 x 10-4 AU h-1. The Spectro- Monitor D variable wavelength detector now has autozero as a standard feature. This is push- button operated and will compensate for k0.7 AU of background. Laboratory Data Control (UK) Ltd., Milton Roy House, High Street, Stone, Staffordshire, ST15 8AR.342 EQUIPMENT NEWS Anal. Proc., Vol. 21 D@tal/Ambgue Meter-k Gas Adysers The Harmony meter is being fitted to the Ana- lytical Development Company’s RF series of gas analysers. Where a digital readout is the primary requirement, the analogue tsend bar is helpful in assessing fast moving trends. The digital meter is claimed to be less susceptible to vibration than a moving coil meter.Sifam Ltd., Woodland Way, Torquay, Devon, TQ2 7AY. Oxygen Analyser The 756A low concentration oxygen analyser incorporates a zirconium(1V) oxide sensor and is available in six switched ranges. It features single-point calibration , linear analogue meter indication and a range of linearised voltage/ current outputs. Options include a remote sensor, dual level oxygen alarm and bench mounting. Servomex Ltd. , Crowborough, Sussex, TN6 3DU. Gas Detector A Binos visible - ultraviolet analysis system has been developed for flue gas monitoring. Designed to detect sulphur dioxide and other gases, it features freedom from interference due to the presence of NO, H20, C02 and CO. Leybold-Heraeus Ltd., 16 Endeavour Way, Durnsford, London, SWlG 8UH. Macrodual Zoom System Available for use with the maker’s Polyvar-Met macroscopic examination apparatus, when mac- roscopic examination of large specimens is required, the system is suitable for use with semi-automatic image analysis systems.The mac- rodual zoom image can be seen in the binocular tube, the camera system and a TV camera, if connected. Reichert-Jung UK, 820 Yeovil Road, Slough, SL14JB. Pressure Transducer An addition to the maker’s P102 range is announ- ced: the 4-20mA version, designed for applica- tions in which transmission signals have to be passed over long distances. M a p o d Instruments Ltd., Ranking Road, Daneshill West Industrial Estate, Basingstoke, Hampshire, RG24 OPP. Pressure Transmitters The Mini-series instruments cover pressure ranges from 0-1 bar to W O O bar.A 3-15 lb in-2 VG pressure to current converter is available as standard. The intrinsically safe BHL-4411 and flameproof BHL-4412 are BASEEFA approved. The BHL-4410 is for general industrial use, and the BHL-4413 and BHL-4414 can be immersed in up to 200m of water. CEC Instrumentation, Lennox Road, Basing- stoke, Hampshire, RG22 4AW. Carbon-14 Measurement System A multi-sample carbon-14 measurement and dat- ing system developed by AERE Harwell for archaeological, biochemical and environmental research is to be made commercially available. Measurements can be obtained from samples containing as little as 10 mg of carbon, and up to 16 samples can be measured simultaneously. John Caunt Scientific Ltd. , Oakfield Industrial Estate, Stanton Harcourt Road, Eynsham, Oxfordshire, OX8 1JA.Literature A new version of “Guide to Techniques and Applications of Atomic Spectroscopy” is avail- able. This brochure lists detection limits for both atomic-emission and -absorption spectroscopy, and it includes a bibliography of application articles, all of which are available free as reprints. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Buckinghamshire, HP9 10A. Literature describes the Response ultraviolet - visible spectrophotometer. This instrument offers an autoranging photometric system that monitors a full 4A response over the ultraviolet - visible range. Wavelength scanning, time scanning, kin- etics, multi-wavelength analysis and curve rou- tines are standard features. Corning Medical and Scientific, Corning Ltd., Halstead, Essex, C09 2DX. A brochure describes a network of gas- chromatographic equipment controlled by the Model 439 gas chromatograph or a stand-alone operating station that can be equipped for bi- directional transmission to an external computer. Up to 12 satellite gas chromatographs can be included in the network. Packard Instruments Ltd. , 13-17 Church Road, Caversham, Berkshire, RG4 7AA.September, 1984 EQUIPMENT NEWS 343 A data sheet gives details on the series 150LC production-scale HPLC system. This is a pilot- plant scale unit for processing and separating mixtures. Chromatelf, B.P.22, F-39360 St. Symphorien d’Ozon, France. A technical guide details the advantages, proper selection and applications of Bakerbond wide- pore HPLC columns in protein and other bio- polymer separations.J. T. Baker Chemicals B.V., P.O. Box 1, Deventer, Holland. Brochure No. 60 describes Heliflex Affordable Capillaries, which are available with three phases and two internal diameters. Of fused silica, they are 30m long and have a film thickness of 0.25 pm. Alltech Associates, Applied Science Ltd., 9A New Street, Carnforth, Lancashire, LA5 9BX. A preliminary data sheet describes the Model 3700 portable triple gas detector for the protec- tion of personnel working underground or in confined areas. The Model 3700 gives audible and visual alarms of hazardous conditions due to oxygen deficiency or the build-up of flammable gases or hydrogen sulphide. MDA Scientific (UK) Ltd., Ferndown Indus- trial Estate, Unit 6 , l Haviland Road, Wimborne, Dorset, BH21 7RZ.An application note is available on digital storage oscilloscopes, comparing them with other classes of waveform-storage instruments. It also dis- cusses the effects of resolution and sampling on waveform capture. Gould Instruments Ltd., Roebuck Road, Hai- nault, Ilford, Essex, IG6 3UE. A brochure presents the P96M range of micro- processor based digital display controllers. Kent Industrial Measurements Ltd., Industrial Instruments, Howard Road, Eaton Socon, St. Neots, Huntingdon, Cambridgeshire, PE19 3EU. A 20-page brochure, “Auriema Hire Instru- ments,,’ gives details of specialised instruments from the Company’s instrument hire division. Equipment is available for the measurement of moisture, humidity, pH, conductivity, oxygen and combustibles, dissolved oxygen, flow, tem- perature, mass, force, light, colour and level.Data loggers and electrical demand monitors are also available. Auriema Ltd., 442 Bath Road, Slough, SL1 6BB. A twice monthly newsletter, The Analytical Instrument Industry Report, is being launched to provide information concerning the industry to analytical instrument manufacturers, distributors and agents. P.O. Box 61, Crawley, West Sussex, RHlO 4FA. A leaflet gives information on the Anion Fiber Suppressor-2, a continuous eluent suppression system, providing improved analytical reproduci- bility for weak acids separated by ion exclusion chromatography using the maker’s Series 2000i ion chromatograph. Dionex (UK) Ltd., Eelmoor Road, Farnbor- ough, Hampshire, GU14 7QN.An application bulletin describes the use of the CSI 740 hand-held XRF analyser in rapid field screening of hazardous waste materials. Elements such as arsenic, selenium, cadmium, lead, chro- mium, mercury and silica are measured in situ. Columbia Scientific Industries Corporation, P.O. Box 9908, Austin, Texas 78766, USA. A 12-page leaflet describes the Nova Biomedical range of electrolyte analysers. Nine models for the analysis of combinations of sodium, potas- sium, chloride, total carbon dioxide and ionized calcium are briefly described. Clandon Scientific Ltd., Lysons Avenue, Ash Vale, Aldershot, Hampshire, GU12 5RQ. A technical guide details the advantages, proper selection and applications of Bakerbond Wide- Pore HPLC columns in protein and other bio- polymer separations. Linton Products, Hysol, Harlow, Essex, CM18 6QZ. A brochure describes the D470 titration kit for connecting titration equipment to a Hewlett- Packard HP-85 personal computer. The kit includes all interface connections and fully documented software to convert the HP-85 to a titrator. Radiometer AIS, Emdrupvej 72, DK-2400, Copenhagen NV, Denmark. A brochure describes the Soxtec HT2 multi- purpose extraction system for the determination of soluble materials in food, feeds, soil, petro- chemicals, detergents, paper pulp, fibres, phar- maceuticals, etc. Tecator AB, Box 70, S-263 01 Hoganas, Sweden.344 ANALAR JUBILEE LECTURE AND GOLD MEDAL A brochure describes two series of electronic balances: the EB series, accurate up to one part in 5000, and the PB series, accurate up to one part in 200 000. Salter Industrial Measurement Ltd., George Street, West Bromwich, B70 6AD. A leaflet gives details of a new magnetic stirrer and stirrer - hotplates. Gallenkamp, P.O. Box 290, Technic0 House, Christopher Street, London, EC2P 2ER. Anal. Proc., Vol. 21

ISSN:0144-557X    

DOI:10.1039/AP9842100337

出版商:RSC    

年代:1984

数据来源: RSC