摘要:

RSC ANALYTICAL DIVISION NORTH WEST REGION A Meeting on SURFACE ANALYSIS will be held at The University of Manchester Institute of Science and Technology on (Tel: 061-236-3311). ~~~~~ September 26th, 1984 For further information and registration forms, contact Dr. R. M. Miller, Department of Instrumentation and Analytical Science, UMIST, P.O. Box 88, Manchester, M60 1 QD ~ ~~ ~ CHALLENGES TO CONTEMPORARY DAIRY ANALYTICAL TECHNIQUES CH A LL€N G€ S TO COPITCMPORW DAIRY Rl'iRLVTlCRL T€CHNIQU€S Softcover 350pp 0 85186 925 4 Price f 16.00 ($29.00) RSC Members f 12.00 Special Publication No. 49 Over many years international organizations, national organizations and private concerns have prepared standardized methods on 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 7 HN, England. RSC members should send their orders to: The Royal Society of Chemistry, Membership Office, 30 Russell Square, London WC7 B 5DT.

ISSN:0144-557X    

DOI:10.1039/AP98421FX025

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

307 ANALYTICAL DIVISION DIARY August, 1984 THINKING OF BUYING A FLAME A TO MIC A BSORPTIO N SPECTROPHOTOMETER? Before committing yourself, read the Analytical Methods Committee’s report on the subject in Analytical Proceedings February, 1984, p. 45 and evaluate the available instruments by using the AMC comparison procedure. If you do not have February Analytical Proceedings, or do not wish to write in the one that you do possess, reprints of the report may be purchased from: Dr. J. F. Tyson, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, LEI I 3TU, price f2.00 ($5.00). SPECIAL ISSUE OF THE ANALYST MARCH 1984 The March 1984 issue of The Analyst contains 46 papers presented at SAC 83 - The 6th International Conference on Analytical Chemistry, held in Edinburgh, 17th-23rd July 1983.The papers presented cover the most important areas of analytical chemistry and provide a valuable overview of the conference. The March issue of The Analyst contains the 4 plenary lectures, as listed below, as well as 42 other papers presented. ~~~ ~~ ~ Plenary Lectures: Recent Developments in Fluorescence and Chemiluminescence Analysis - James N. Miller. Capillary Separation Methods: a Key to High Efficiency and Improved Detection Capabilities - Milos Novotny . Design and Application of Neutral Carrier-based Ion-selective Electrodes - W. Simon, E. Pretsch, W. E. Morf, D. Ammann, U. Oesch and 0. Dinten. Continuum Source Atomic-absorption Spectrometry: Past, Present and Future Prospects - Thomas C. O’Haver. Single Issue Price: RSC Members glO.00 ($18.50). Non-RSC Members S15.00 ($27.50). ORDERING: Non-RSC members should send their orders to: The Royal Society of Chemistry, Distribution Centre, Blackhorse Road, Letchworth, Herts SG6 lHN, England. RSC Members should send their orders to: The Royal Society of Chemistry, Membership Officer, 30 Russell Square, London WClB 5DT. PAYMENT SHOULD ACCOMPANY ORDER. Electronically typeset and printed by Heffers Printers Ltd, Cambridge, England

ISSN:0144-557X    

DOI:10.1039/AP98421BX027

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

ANPRDI 21(8) 279-308 (1984) August 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. Hon. Publicity Secretary Dr. J. F. Tyson, Department of Chemistry, Loughborough University of Technology, Loughborough, Leicestershire, LEI 1 3TU Secretary Miss P. E. Hutchinson Editor, Analyst and Analytical Proceedings P. C. Weston Senior Assistant Editors Assistant Editor Mrs. J. Brew, R . A. Young 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 0144-557x3 is published monthly by The Royal Society of Chemistry, Burlington House, London, WlV 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 1HN. England. 1984 Annual Subscription price if purchased on its own: UK €53.00, Rest of World €56.00, 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. The New President Peter Cobb was born in 1930 at Beeston, Notting- ham, and attended various schools in and around the City.He completed the standard elementary school education, leaving Cottesmore Senior Boys’ School as Head Boy and School Captain in October, 1944. This was his last experience of full time-education and he is grateful for the solid grounding in reading, writing and arithmetic provided which has laid the foundation €or his subsequent career. Along with so many young people in those war years, he had developed a powerful interest in aviation and he hoped to make a career in aeronautical engineering. However, his Headmaster advised him that, as the war drew to its close, there would be a surfeit of engineers and the profession of accountancy would offer better opportunities.At that time a Chartered Accountant friend of the Headmaster was looking for an office junior and Cobb was interviewed and appointed to the post, Although he enjoyed the work, and valued the opportunity to work with top class professionals, he did not feel that his long-term career needs would be satisfied by accountancy because of his interest in science, even though he had received no educa- tion in it. In the course of reading about science, he had developed an interest in forensic science and, upon learning that there was a forensic science laboratory in Nottingham, obtained an interview there with the help of the local police- man (this was before community policing was re-invented). Thus, in May 1946, Peter Cobb began work at the Nottingham laboratory as a Laboratory Attendant and he has spent the whole of his subsequent scientific career in the Home Office Forensic Science Service.He had earlier set about improving his educa- tional qualifications by following a correspon- dence course for London Matriculation, which he completed in 1949 before undertaking his National Service in the Royal Army Medical Corps. He served in Egypt and Jordan, and he was particularly pleased to return to the latter country 30 years later to advise on the organisa- tion of forensic science there. Following National Service, he studied for his “A” levels by evening classes and subsequently was allowed day-release 279280 THE NEW PRESIDENT Anal. Proc., Vol. 21 to study for, and pass, the Associateship of the Royal Institute of Chemistry examination in 1956.He then commenced study for the postgraduate diploma of the RIC (Branch A) in general analytical chemistry, which he obtained in 1960. He feels that satisfying the demands of Drs. Chirnside and Haslam over 5 days of written, oral and practical examinations allowed him to be regarded as a professional analytical chemist. He found it hard to forgive the Royal Institute of Chemistry for not recognising such diploma holders with designatory letters but can now regard with amused cynicism the forms for the RSC remuneration survey which fail even to recognise their very existence! In 1964 he obtained a Diploma in Government Administra- tion from the Local Government Examination Board. Peter Cobb progressed through the ranks of the Forensic Science Service, moving from Notting- ham to the Birmingham Forensic Science Labora- tory in 1954, whence he transferred to the Aldermaston Forensic Science Laboratory in 1972 to become Director.He moved to become Director of the Harrogate Laboratory in 1976, but his prime responsibility there was to set up the amalgamation of that laboratory with the New- castle laboratory at Wetherby in 1977. In 1982 he became Director of the Central Research Estab- lishment (CRE) in order to apply his long operational experience to the management of the research programme. CRE is acknowledged internationally to be the finest of its kind in the world and Cobb is honoured to be its Director. He joined the Society for Analytical Chemistry in 1960 and became a member of the Midlands Section Committee in 1964, at the same time as his Presidential predecessor, Stan Greenfield.They became close friends and their careers within SAC and the Analytical Division followed similar courses. Service as Programmes Secre- tary, Vice-chairman and Chairman of the Mid- lands Region and as an elected member of Council was followed by election to the post of Honorary Secretary of the Division. After serving the statutory 6 years, he became Vice-president and, ultimately, President Elect. He has served on the local committee of the North East Region and on the committees of the Microchemical Methods Group and the Joint Pharmaceutical Analysis Group. He has been Divisional Member of RSC Council for the past two years and was appointed to the Professional Affairs Board last year.He has served on the Council of the Forensic Science Society and is active in the affairs of the International Association of Forensic Toxicolo- gists (TIAFT). He is a member of the organising committee of the VII Triennial Meeting of TIAFT, to be held in September, 1984, with responsibility for the scientific programme. He has acted as external examiner to the University of Strathclyde MSc course in forensic science and as a visiting lecturer at the University at Swansea. He is a member of the chemistry advisory committee of Sheffield City Polytechnic. He has been a member of the Horserace Anti-Doping Committee since 1975. Peter Cobb is married with two sons. His wife, Audrey, is known to many members of the Division through her attendance at SAC Confer- ences and other social events. She was a member of the SAC 77 Social Committee and acted as a courier at SAC 80. Audrey looks forward to meeting many old friends and making new friends whilst accompanying him on his Presidential duties. They take pride and pleasure in the activities of their two sons, the elder being a research scientist in industry and the younger being a Tornado pilot in the RAF. Mr. Cobb sees the coming years as a period of challenge for both the science and the profession of analytical chemistry. He is pleased and proud to be asked by the Division to lead it to meet those challenges and welcomes the support of his many friends within the Division in discharging the responsibilities of office.

ISSN:0144-557X    

DOI:10.1039/AP9842100279

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

August, 1984 1983 RSC SPONSORED AWARDS 281 Standardization in Particle Sizing The following is a summary of one of the papers presented at a Joint Meeting of the Particle Size Analysis Group and the National Physical Laboratory held on September 28th, 1983, at the National Physical Laboratory, Teddington, Middlesex. Summaries of four other papers presented at the meeting were published in the May issue (p. 159). Direct Inversion Methods for Particle Size Distribution Measurements from Light Scatter in g L. P. Bayvel Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, SW7 2BY Optical methods for the measurement of particle size have significant advantages over conventional sampling. In some situations, where particle clouds are inaccessible because they are physically remote or because they are not amenable to direct sampling, information about the particle size distributions can be obtained only from light scattering measurements.’ The development of instruments based on optical methods is an important problem, and from time to time new methods are proposed and new instruments appear on the market.2-5 Optical techniques for particle measurement can be divided into two broad areas.Single particle counters analyse individual particles traversing a relatively small optical sample volume, and a sequence of particles is sampled in order to build up a discrete size distribution. Ensemble analysing methods are so described because the light scattering or extinction integrated over the contributions for a large number of particles is used to determine particle size distribution.The determination of the particle size distribution from measurements of transmitted or scattered light can be reduced in general to finding a solution for the first kind Fredholm integral equation:282 STANDARDIZATION IN PARTICLE SIZING Anal. Proc., Vol. 21 ce * * (1) I ( ? ) = 1 K ( ? , a ) f ( a ) da . . . . . . . . . . where f(a) is the particle size distribution function, f(a) = AN/(NAa), AN is the number of particles with sizes between a and a + Au, N is the total number of particles, I(?) is light intensity measured as a function of a scattering angle or wavelength and K (?,a) is the kernel defining the general relationship between intensity I(?) scattered or transmitted by a particle size a, known from light scattering theory.The instruments for ensemble analysing are based on two general methods of findingf(a) from equation (1) by direct inversion of the light scattering data. The first method involves representing the kernel with an approximate analytical expression. In most instances the Fraunhofer diffraction theory is used as a theoretical base. According to this theory the intensity of light I ( € ) ) scattered by a particle of a radius a can be found from the Airy equation: where Z, is the intensity of incident light, x = 2 xa/h (h is the wavelength), 0 is the scattering angle andJ1 is the first kind Bessel function. For a particulate system with distribution f ( a ) I0 82 z(e) = - JJ? (xe) d f ( a ) da .. . . . . . . . . Equation (2) is the one which has to be inverted in order to find f ( a ) and its nucleus is an analytical expression J12(x6) a2. In this instance an exact analytical solution of equation (2) can be found.' When the Fraunhofer diffraction theory is applied, it is assumed that the particles are spherical, the size parameter x>>l and the scattering angles 6 are close to 0. In reference 1, it is shown that when the approximate theory is compared with the exact Mie theory the theoretical errors implied in the solution of equation (2) are different for absorbing and non-absorbing particles. For non-absorbing particles the error is greater than 20% if x d 20. If a helium - neon laser is used as a source of light (h = 632.8 nm), this corresponds to a particle diameter DS4 pm.For absorbing particles, the error is greater than 20% if x d 8 (D d 1.6 ym). This means that the smallest particle size that can be measured with reasonable precision by an instrument based on Fraunhofer diffraction is about 4 ym for non-absorbing particles and 1.6 pm for absorbing particles if a helium - neon laser is used. The solution of equation (1) does not depend on the refractive indices of the particles and the surrounding medium. The second method involves expressing the kernel in matrix form using Mie scattering theory. Intensity of light scattered on particles with a size distribution f ( a ) can be found from the following equation: h2 8x2 0 . . . . . . . . I(0) = - I , J- [il(O,x) + i2 ( 0 , x ) ] f ( a ) da * ( 3 ) where il(O,x) and i2(0,x) are non-dimensional Mie scattering intensities with parallel and perpendicular polarisation, respectively.The light extinction coefficient of a particulate system can be expressed by the following equation: . . . . . . . . (4) where Qext is an extinction efficiency known from Mie theory. The particle size distribution function f ( a ) is found from equation (3) or (4) by direct inversion of these quadratures in matrix form. The nucleus of equation (3) or equation (4) is known from Mie theory computations as a numerical function. Several numerical methods for solving equations (3) and (4) are now used.' The terms i l ( 6 , x ) , i 2 ( e , x ) and Qext ( x , h ) depend strongly on the refractive indices of particles and surrounding media and therefore the values of real and imaginary parts of refractive indices have to be known in order to find out the particle size distribution.August, 1984 STANDARDIZATION IN PARTICLE SIZING 283 The Mie theory is valid for spherical particles only and therefore the particles are assumed to be spherical when it is used as a theoretical base for a measuring instrument.Measurements made by all ensemble analysing light scattering instruments are spatial. It is preferable, when using an on-line instrument, for continuous particle size distribution determination to accomplish the measurement in situ, without sampling or diluting the original particle cloud. Particle size measurement based on the methods described above can be performed on-line, without sampling or dilution if the particle concentration is not too large.The restriction on the particle concentration is imposed by the necessity to avoid multiple scattering. Different authors give different criteria for the particle concentration at which multiple scattering takes place. These criteria are expressed sometimes in terms of turbidity (or obscuration). The values of turbidity at which multiple scattering takes place are in the range 0.1-0.7; the corresponding values of obscuration are 10-50%.1.2 The particle size distribution can be obtained by the direct inversion of light scattering data, in principle, without the necessity of pre-supposing a form for the distribution function. Measurements using instruments based on the direct inversion of light scattering data are absolute and do not require an empirical calibration procedure, i.e., the particle size distribution is obtained from data on the light intensity measured at different scattering angles or at different light wavelengths by mathematical means. However, these instruments are based on certain assumptions, which do not always comply with real situations; for example, the particles may not be exactly spherical, the refractive indices of particles may not be known precisely and the particle concentration may be too high. Because of these problems and also because of the possible deterioration in the characteristics of optical and electronics components, it is advisable to perform a periodic check or verification of the performance of the instrument in question by using suitably certified reference materials or photographically produced reticles.By using different known particle sizes the range of the instrument can be covered at a number of points. The agreement between the results produced by the instrument tested and the results obtained by alternative means has to be within the accepted limits for the instrument. It is advisable for a particle size measuring apparatus based on light scattering to contain instrumentation that indicates automatically to the operator that the conditions of the observation will give a satisfactory data output. One such indicator is the obscuration of the light beam caused by a particle cloud which has minimum and maximum acceptable values determined by particle concentration and the path length of the light.Conclusion The methods for particle size distribution measurements based on direct inversion of light scattering data have been discussed. It is shown that measurements obtained from instruments based on these methods are absolute and do not require calibration. The necessity of carrying out a periodic check or verification of the instrument’s performance is substantiated. The state of the art of the method and instruments based on light scattering is now sufficiently advanced to justify consideration as a standard. References 1. 2. 3. 4. 5. . Bayvel, L. P., and Jones, A. R., “Electromagnetic Scattering and its Applications,” Applied Science Swithenbank, J . , Beer, J. M., Taylor, D. S . , Abbot, D., and McGreath, C. C., Prog. Astronaut. Aeronaut., Cornillaut, J . , Appl. Opt., 1973, 11, 265. Muly, E. C., and Frock, H. N., Opt. Eng., 1980, 19, 861. Bayvel, L. P., Eisenklam, P., and Jones, A. R., in “Proceedings of the 2nd International Conference on Publishers, London, and Elsevier, New York, 1981. 1976, 53, 79. Liquid Atomization and Spray Systems, Madison, Wisconsin, USA, June 20-24, 1982,” University of Wisconsin, Madison, WI, USA, 1982, pp. 329-334.

ISSN:0144-557X    

DOI:10.1039/AP984210281b

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

284 LIMITS OF DETECTION Anal. Proc., Vol. 21 Limits of Detection The following is a summary of one of the papers presented at a Joint Meeting of the Electroanalytical and Microchemical Methods Groups held on December 9th, 1983, at the Linnean Society, Burlington House, London, W. 1. Limits of Detection of Ion-selective Electrodes D. Midgley CEGB, Central Electricity Research Laboratories, Kelvin A venue, Leatherhead, Surrey, KT22 7SE A discussion of the limit of detection in potentiometry should start with a practical example, to emphasise that arbitrary definitions of this quantity can be very misleading. The IUPAC recommended definition1 of limit of detection for an ion-selective electrode is obtained, as shown in Fig. 1, by extrapolating the linear portions of the calibration graph until they meet.At 25"C, the limits of detection according to this definition are 530 pg 1-l and 60 pg 1-1 for silver chloride and mercury(1) Concentrationimol I-' Fig. 1. IUPAC limit of detection for an electrode with a 2 X mol 1- * blank. chloride electrodes, respectively. Table I, however, shows the much lower concentrations of chloride that are routinely determined in industry by potentiometry. The recommended definition, therefore, fails a practical test: it actually characterizes not an analytical limit, but the shape of the calibration graph. TABLE I CHLORIDE IN BOILER WATER Targetlpg 1-1 Typical/pg 1-I 2350 psi drum boiler . . . . . . . . Inland 1200} 10-100 Coastal . . . . . . . . 300 Once-through(AGR) . . . . <2 <2 PWR . . . . . .. . . . <200 d 60 In analysis it is normal to consider how all aspects of the procedure affect the precision of the measurements. From the precision and the sensitivity we can estimate how small a concentration can be determined with a specified degree of confidence. This limit of detection, CL, is defined by a multiple of oB, the standard deviation of the blank. The multiple depends on the confidence desired and for 95% confidence CL = 4.65 oB. This definition has been derived by Roo9 and Currie3 and applied to the particular instance of potentiometry , with its log-linear calibration, by Midgley.&6 This statistical definition of limit of detection gives the results shown in Table I1 for chloride-selective electrodes;August, 1984 285 LIMITS OF DETECTION TABLE I1 LIMITS OF DETECTION OF CHLORIDE ELECTRODES Temperature/ Limit/ S.d.1 Electrode "C CLg 1-' mV Hg;?Clz .. 4 1 0.41 . . 25 1 0.08 AgCl . . . . 10 7 0.05 . . 25 15 0.07 these are much lower than the limits given by the other definition. In order to attain such low limits of detection, care must be taken to reduce random error, for which precise control of temperature and the use of a flowing sample are particularly important, as is shownjn Table 111. TABLE 111 STANDARD DEVIATION OF HgS - Hg2C12 ELECTRODE AT 10 pg 1-1 OF CHLORIDE Mode Temperature S.d./pg 1-1 Beaker . . . . Room 15 Beaker . . . . 25°C 8 Flow . . . . 25°C 0.4 At levels near the limit of detection, most of the chloride in solution at the surface of the electrode comes not from the sample but from dissolution of the sparingly soluble chloride salt in the membrane.The effect of this dissolution can be predicted in terms of the limiting slope of the calibration graph and of the limit of detection. The e.m.f.s of silver chloride and mercury(1) chloride electrodes in the region of their limiting calibration slopes are, respectively: k EAgCl = EOAgCl + k In K+ + - K-* C 2 k EHg2C12 = EOHg2C12 + k In (2K)J + - (2Q-3 C 3 where k = RT/zF is the Nernst slope factor (with sign), K the appropriate solubility product and C the analytical chloride concentration. The formulae are fairly simple and their validity is borne out by the wide range of independent results for limiting slopes in Table IV. TABLE IV LIMITING LINEAR SLOPES FOR CHLORIDE ELECTRODES Slope/mV PM- 1 Electrode Medium TPC Obs.Calc. Ref. Ag - AgCl pH 5 acetate 25 0.80 0.80 8 Ag - AgCl 0.01 M KN03 25 0.95 0.91-1.0 7 Ag2S - AgCl 0.1 M HN03 25 0.78 1.26 9 HgS - Hg2Cl2 0.01 M HN03 25 7.9 5.3 10 10 1.25 1.26 The predicted limits of detection for electrodes whose non-Nernstian responses are caused by different combinations of reagent blank, interference and solubility product are given in Table V, but the effect of the different factors is seen more clearly in Fig. 2. All of the calibrations in Fig. 2 coincide at higher concentrations with the extension of the Nernstian line (N) and all give the same IUPAC limit of detection at log C = -5.7. The statistical limits of detection for oB = 1 mV are given by the intersection of line El with the calibration graphs.It can be seen that curve A, which deviates most from the Nernstian line, has the lowest limit of detection and curves B and E, which deviate least, have the highest limits of detection. The curvature in line A is caused only by the presence of an impurity and in lines B and E only by the solubility of the membrane. The other curves represent the effect of solubility combined with either an interference (C) or contamination with the ion being determined (D). Curves C and D each represent one of the infinite number of ways of combining two effects to give the same IUPAC limit of detection; all of the curves would lie between curves A and B, but each would have a unique statistical limit of detection. Another point to note is that improving the precision, e . g ., to (JB = 0.5 mV, as represented by line EQ in Fig. 2, lowers the statistical limit of detection but does not change the IUPAC limit.286 LIMITS OF DETECTION P t Anal. Proc., Vol. 21 15 > > ’c. €10 E ui 5 0 -7.0 -6.5 -6.0 -5.5 Log ( c) Fig. 2. Limits of detection for hypothetical univalent electrodes with non-Nernstian calibrations: A, b = 2 X 10-6 moll-’ (interference or reagent blank determinand, no solubility effect); B, K = 4 x 10-12 moI2 1k2 (solubility effect only); C, 6, = mol 1-1, K = 10-12 mo12 1-2 (solubility effect and interference); D, b, = 1.5 x 10-6 moll- I , K = 10- mo12 1-2 (solubility effect and reagent blank); E, K = 4 X 10-18 mo13 1-3 [non-isovalent (2: 1) solubility effect]; and N , ideal Nernstian response. Lines E , and EL show the statistical limits of detection in e.m.f.terms for standard deviations of 0.5 and 1.0 mV, respectively. Not all types of non-Nernstian response are covered in the above treatment and many types of ion-selective electrodes have not been systematically studied at very low levels. More detailed comments on the performance of individual electrodes are available elsewhere,b but a brief survey will show the main classes of behaviour. Solid-state electrodes for chloride have been discussed above, and similar limiting linear calibration slopes have been obtained for silver bromide, silver iodide and silver azide electrodes.’ Consistent results for lanthanum fluoride electrodes have not been obtained, probably because the response times at low concentrations are so long that an equilibrium treatment is inappropriate.11 Metal sulphide electrodes are of little use outside the Nernstian response region, mainly because of irreversible oxidation of the sulphidp,, either in solution or on the membrane surface itself. Some liquid ion-exchange electrodes have been shown12.13 to have limiting responses governed by a phase distribution of the exchanger. Equations equivalent to those for solid-state electrodes governed by a solubility product can be derived.4.6 In other instances, the limiting response is governed by interferences,l* and an important factor is the purity of the exchanger. Unrecrystallised tetradodecyl- ammonium nitrate exchanger had a large hydroxide interference, which disappeared after the exchanger had been twice recrystallised.14 Commercial nitrate electrodes15J6 have interferences similar to those of the once-crystallised exchanger. TABLE V THEORETICAL LIMITS OF DETECTION FOR ION-SELECTIVE ELECTRODES Limit of detection Factors involved* b = reagent blank + effect of interferences K = solubility product K = solubility product; b = interference K = solubility product; b = reagent blank * In all instances k mV per decade is the Nernst slope factor and L = 4 . 6 5 ~ ~ mV, where oB is the standard deviation of the e.m.f. in the blank solution.August, 1984 IMAGING TECHNIQUES 287 In most studies of liquid ion-exchange electrodes the purity of the exchanger is unknown and the limits are often set by interferences. In view of experience with nitrate electrodes,l4 better performance at low concentrations might be obtained with other electrodes if sufficient care were taken in their preparation.Non-Nernstian calibration graphs have been calculated17 for gas sensing membrane electrodes, but without allowing for diffusion from the bulk of the filling solution of the electrode into the surface film. The calculations, therefore, overestimate the limiting sensitivity. At low concentrations the response time is-very long and few measurements have been reported. With sensors for acidic gases, interference by atmospheric carbon dioxide is a common limiting factor.18 Ion-selective glass electrodes have been used below their IUPAC limits. The ammonium-selective electrode suffers interference from the buffer, as do sodium-selective electrodes when ammonia is used to control the pH.With the use of dialkylamine buffers, however, the range of sodium-selective electrodes can be extended until the e.m.f. is dominated by the dissolution of lithium ions from the glass membrane.19 Published with the permission of the Central Electricity Generating Board. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. References Pure Appl. Chem., 1976, 48, 127. Roos, J . B., Analyst, 1962, 87, 832. Currie, L. A., Anal. Chem., 1968, 40, 586. Midgley, D., Analyst, 1979, 104, 248. Midgley, D., Analyst, 1980, 105, 1002. Midgley, D., Ion-sel. Electrode Rev., 1981, 3, 43. Bardin, V. V., Shartukov, 0. F., and Tolstousov, V. N., Zh. Anal. Khim., 1972, 27, 25. Tomlinson, K., and Torrance, K., Analyst, 1977, 102, 1. Florence, T. M., J. Electroanal. Chem., 1971, 31, 77. Marshall, G . B., and Midgley, D., Analyst, 1979, 104, 55. Hawkings, R. C., Corriveau, L. P. V., Kushneriuk, S. A., and Wong, P. Y.,Anal. Chim. Acta, 1978,102,61. Mathis, D. E., Freeman, R . M., Clark, S. T., and Buck, R. P., J. Membrane Sci., 1979, 5 , 103. Kamo, N., Kobatake, Y . , and Tsuda, K., Talanta, 1980, 27, 205. Nielsen, H. J., and Hansen, E. H . , Anal. Chim. Acta, 1976, 85, 1. Davies, J. E. W., Moody, G. J., and Thomas, J . D. R., Analyst, 1972, 97, 87. Fayad, N. A., and Tyson, J. F., Int. Lab., 1979, 9,49. Bailey, P. L., and Riley, M., Analyst, 1977, 102, 213. Bailey, P. L., and Riley, M., Analyst, 1975, 100, 145. Goodfellow, G. I . , Midgley, D., and Webber, H. M., Analyst, 1976, 101, 848.

ISSN:0144-557X    

DOI:10.1039/AP9842100284

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

August, 1984 IMAGING TECHNIQUES 287 Imaging Techniques The following are summaries of four of the papers presented at a Joint Meeting of the Special Techniques Group, the Computational Physics Group of the Institute of Physics and the Electronic Image Processing Group of the Institute of Electrical Engineers held on February lst, 1984, in Imperial College of Science and Technology, London, S.W. 7 . Image Reconstruction from Partial Information M. A. Fiddy Physics Department, Queen Elizabeth College, Campden Hill Road, Kensington, London, W 8 7AH Introduction We consider the problem of reconstructing the image of an object when only limited sampled noisy data are available in either image or Fourier space. At high frequencies, whether electromagnetic or acoustic radiation is used to probe the object of interest, there is often the additional problem, which we discuss, of missing phase information ( i .e . , measurements are taken from square law detectors). Over-riding these difficulties is the partial information embodied in the physical model adopted to relate the reconstructed image to some intrinsic parameter associated with the object. This is not288 IMAGING TECHNIQUES Anal. Proc., Vol. 21 discussed here in any detail, but it is worth illustrating the point with two examples. In the case of synthetic aperture radar (SAR) imaging, the SAR point spread function can be fairly well described but the image is processed and interpreted on the basis of a simple Kirchhoff (small wavelength) or perturbation theory.’ Even a slightly more sophisticated model for the wave - surface interaction, which includes the known strong dependence of image contrast on depolarisation effects from structures comparable to the wavelength, could provide improved images.2 The second example concerns the reconstruction of the image of an object from measurements of the field it scatters when a plane wave is incident upon it.For wavelengths much smaller than the object detail, as for example in X-ray computer aided tomography, many algorithms prove satisfactory for reconstructing the image from the available projection data. However, as the wavelength increases images from such algorithms become progressively poorer and further “processing” is pointless in the absence of a more appropriate physical model to describe the interaction.This was well illustrated in a recent paper by Devaney,3 which related back projection techniques to so-called back propagation methods for which the first Born or Rytov approximations are valid.4 However, not only is the range of validity of such (weakly scattering) approximations uncertain, but one is also left with the problem of Fourier data on the object being available on a limited set of circular arcs rather than radial lines (central slice theorem), resulting in possible interpolation ambiguities5 Limited Complex Fourier Data Available The restoration or reconstruction of the image of an object from limited discrete data is always a problem in practice, and is known to be an ill-posed problem. However, regularisation theory defines a set of admissible or approximate estimates for the object by imposing constraints on these estimates.6 Even in the absence of noise incomplete sampled data means that there are infinitely many object estimates consistent, say, with the Fourier data and object support, if known.For finite discrete data we take the view that it is always necessary to use models to find an optimum image estimateffor the true object distribution f. Given that an infinite ambiguity occurs using one model, one is forced to adopt some kind of procedure that selects from this infinite choice one estimate, f, which is in some sense “best” or “optimum.” A commonly used and quite successful technique for interpolating and/or extrapolating Fourier data is the iterative procedure of Gerchberg - Papoulis.7 By repeatedly Fourier transforming between object and data spaces and imposing the anticipated object support and measured data values at each iteration, convergence is to a minimum norm solution.The numerical performance of such an algorithm will depend upon the noise but can be regularised and the corresponding error assessed ( e . g . , reference 8). This minimum norm (in this instance minimum energy) reconstruction is a particular case of a more general class of estimation or reconstruction methods in which a suitable Hilbert space of functions is defined, with the anticipated characteristics or features of the actual object ( e . g . , reference 9). For example, if we let p encode the support of the object and, perhaps, some profile information, then one can show that an image reconstruction of the form f = pEa,gi, which minimises Ilf-fllH, is a unique estimate of minimum norm when the a, values a r l found from solving f(ki) = C a,p(ki-km) where denotes Fourier transformation and g, is some known (basis) function.The chosen Hilbert space is a weighted L* space having inner product (f, g)H = Svp-lfg*d31-. For a finite dimensional problem of this kind, one can argue that regularisation is entirely equivalent to enforcing numerical stability as, using this model, there is no doubt about the existence and uniqueness of the solution.6 Examples of the application of this algorithm to limited angle data and its regularisation for noisy data are shown in reference 10. Other reconstruction or estimation procedures, such as maximum entropy, are also widely used (e.g., reference 11).The procedure described above for “polynomial-like” models can be similarly developed for a reciprocal polynomial model of which Burg’s maximum entropy method is seen as a special case when p = 1.12 This class of reconstruction algorithms, or non-linear estimators, modelsf- rather than f as a polynomial and may therefore be expected to be predisposed to higher resolution because of the poles in the model approaching the real plane. For some image reconstruction problems this estimator may be appropriate in that it can give very spiky results. What is not clear, at present, is why MEM is sometimes better than a model of the formpEa,gj with accurate information encoded inp. The useful incorporation of prior knowledge about the object into non-linear methods and the further development of this approach to optimum rational polynomial models in other Hilbert spaces is continuing.mAugust, 1984 IMAGING TECHNIQUES 289 Limited Intensity Fourier Data Available The phase retrieval problem has been the subject of several recent reviews (e.g., reference 13) and can conveniently be divided into one and more than one dimensional problems. It is well known that in one dimension many equally acceptable solutions can occur even with complete and noise-free data; in two or more dimensions this is less likely to be the case. Clearly, with limited data the methods outlined in the previous section can be applied with arbitrary phases assigned to the available intensity data.If, however, a discrete model is adopted for f then the Fourier data represents samples of a polynomial of finite degree, i.e., f(u,v,w) = 2 fjk@vkW’. It has been shown that for the set of multivariable polynomials of finite degree, the set of reducible polynomials is of measure zero.14 This implies that a unique phase can, in general, be associated with If1 because phase ambiguities are associated with the existence of non-self conjugate factors inf.13 In practice, and despite this, iterative algorithms similar to Gerchberg - Papoulis7 and proposed by Fienupls meet with only limited success. Recent work (e.g., reference 16) has concentrated on the incorporation of prior knowledge in the object to ensure that there is no phase ambiguity.Examples include the presence of a suitably positioned (but not necessarily holographic) reference point or an object support shape which results in the “form” off being irreducible. However, ensuring that there is a unique phase in this way does not help us to find it. Current work in this area is concentrating on developing multivariable polynomial factorisation algorithms in order to recover f from If\*. m j , k , l Conclusions It has been argued that good image reconstruction depends primarily on physical information being incorporated into the model. There will then remain a need for the useful incorporation of prior information about the object in order to overcome the inevitable limitations of finite sampled data, perhaps compounded by poor or missing phase information.Some methods for achieving this have been described. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. References McGinn, A., and Sykes, J . , “Microwave Scattering from Natural Targets,” AERE Report 9678, HM Stationery Office, London, 1980. Fung, A. K., in Boerner, W.-M., Editor, “Inverse Methods in Rough Surface Scattering,” NATO Advanced Research Workshop, Inverse Methods in Electromagnetic Imaging, Riedel, Dordrecht, The Netherlands, 1984. Devaney, A. J. “Inverse Scattering as a Form of Computed Tomography,” SPZE, 1982,358, 10. Fiddy, M. A., “Object Reconstruction from Partial Information,” NATO Advanced Research Workshop, Inverse Methods in Electromagnetic Imaging, Riedel, Dordrecht , The Netherlands, 1984; see also Zapalowski, L., Fiddy, M.A., and Leeman, S., “On the Born Rytov Controversy,” “Proceedings of the 1983 IEEE Ultrasonics Symposium, Atlanta,” IEEE, New York, in the press. Pan, S. X., and Kac, A. C. “A Computational Study of Reconstruction Algorithms for Diffraction Tomography: Interpolation versus Backpropagation,” IEEE ASSP-31, 1983, 1262. Bertero, M., De Mol, C., and Viano, G. A., “The Stability of Inverse Problems,” in Baltes, H. P., Editor, “Inverse Scattering Problems in Optics,” Springer Verlag, Berlin, 1980, p. 161. Papoulis, A., “A New Algorithm in Spectral Analysis and Bandlimited Extrapolation,” IEEE CAS-22,1975, 735. Abbiss, J. B., Defrise, M., De Mol, C., and Dhadwal, H. S., “Regularised Iterative and Non-iterative Procedures for Object Restoration in the Presence of Noise,” J.Opt. Soc. Am., 1983, 73, 1470. Hall, T. J., Darling, A. M., and Fiddy, M. A., “Image Compression and Restoration Incorporating Prior Knowledge,” Opt. Lett., 1982, 7, 467. Darling, A. M., Hall, T. J . , and Fiddy, M. A., “Stable, Non-iterative, Object Reconstruction from Incomplete Data Using Prior Knowledge,” J. Opt. Soc. Am., 1983, 73, 1466. Proc. IEEE, 1982, 70(9), 883-1124. Byrne, C. L., Fitzgerald, R. M., Fiddy, M.A., Hall, T. J . , and Darling, A. M., “Image Restoration and Fiddy, M. A., “The Phase Retrieval Problem,” SPZE, 1983, 413, 176. Hayes, M. H., and McClellan, J. H., “Reducible Polynomials in More Than One Variable,” Proc. IEEE, Fienup, J. R., “Reconstruction of an Object from the Modulus of its Fourier Transform,” Opt. Lett., 1978,3, Dainty, J.C., and Fiddy, M. A., “The Essential Role of Prior Knowledge in Phase Retrieval,” Opt. A m , Resolution Enhancement,” J . Opt. Soc. Am., 1983, 73, 1481. 1982, 70, 197. 27. 1984, in the press.290 IMAGING TECHNIQUES Coherent Signal Processing in Scanning Microscopy Ian R. Smith VG Semicon, Imberhorne Lane, East Grinstead, West Sussex, RH19 1 UB Anal. Proc., Vol. 21 Since the introduction of the scanning acoustic microscope by Lemons and Quate in 1973,' the development of scanning microscopes employing coherent radiation has continued apace.2 In confocal scanning optical and acoustic microscopes the coherence confers a modest improvement in resolution while retaining a point spread function similar to that of an incoherent microscope-images do not exhibit speckle-like artifacts. While the majority of imaging has been done using the intensity of radiation detected in these microscopes, coherent phase contrast signal processing has been developed.In the next section the applications for phase microscopy that have resulted in a quantitative means of material characterisa- tion are reviewed. Developments to the phase contrast techniques have lead to differential phase contrast microscopes which are more sensitive and stable. In the second section the developments and applications of these instruments will be reviewed. Phase Contrast Microscopy for Material Characterisation The basic elements of a scanning acoustic microScope are shown in Fig. 1. I To pulse detectoi and image store matching Echo from RF pulse Sapphire Lens specimen Zinc oxide transducer scanned over I Reflective specimen in lens focal plane Fig.1. Schematic diagram of the acoustic microscope lens configuration. A beam of piezoelectrically generated longitudinal sound waves travels down a sapphire buffer rod and is focused in a liquid coupling medium. Energy reflected at a point on the specimen is collected and re-collimated by the same lens and the piezoelectric transducer converts this back into an electronic signal. The intensity of this signal is conventionally used to control the brightness of the display, and the image is formed sequentially by mechanically scanning the acoustic beam over the specimen. The system has two advantages: firstly, image contrast relates to the strength and texture of the specimen; and secondly, images may be formed from beneath the surfaces of opaque materials.These characteristics are particularly useful in the testing of bonds and welds. By use of standard electronic signal processing the reflected signal can be phase compared with the transmitted waveform, so that an image is formed which shows the spatial variation of the phase of the reflection coefficient.3 A parallel reference path is used to compensate for thermal or electrical fluctuations in the imaging apparatus. Digitally controlled microscopes may thus be used to record the complex reflection coefficient of the specimen .4 From the practical viewpoint it is advantageous to record both images as more information may be revealed in one or the other. However, recent developments have shown how the combination of images may be used to obtain quantitative information about the elastic properties of the specimen.August, 1984 IMAGING TECHNIQUES 29 1 Imaging equations for the acoustic microscope have been derived theoretically and are in good agreement with observations5; deviations may be attributed to imprecise characterisation of the acoustic components.Theory shows that image contrast relates to the reflectance spectrum of the specimen, which is in turn related to elastic constants. Two approaches to the inverse problem have been taken. In the first a paraxial formulation is taken6 which shows that, where the specimen is acoustically similar to the coupling fluid, a direct inversion enables the calculation of the density and elasticity of the specimen at each point.Images can be formed showing the spatial variation of these properties and results have been obtained for the mechanical characterisation of diseased and normal human tissue .7.8 In the second approach, restricted inversions of the contrast equations have been p r o p o ~ e d ~ ~ ~ ~ ) by which the reflectance spectrum may be calculated and this can be interpreted to reveal the elastic moduli and density of the specimen, Recently, experimental evidence for a direct, unrestricted inversion has been presented11 which shows promise. The goal of this work is to measure the strength of materials non-destructively and significant progress has already been made. Differential Phase Contrast Microscopy In the conventional phase contrast microscope described above a limitation is in the sensitivity of the apparatus to thermal or electronic fluctuations.The image is associated with the phase response of the specimen, but it actually represents the phase shift undergone by the acoustic beam over its entire path length, typically several hundred wavelengths. Variations to the acoustic path due to microphonic vibration of the specimen or thermal relaxation of the apparatus, as well as changes in the frequency or speed of sound, may all contribute large, time varying phase shifts that obscure fine detail on the specimen. Differential phase contrast microscopy overcomes this problem by forming two images simul- taneously, which are laterally displaced by one resolution cell and then interfered.Because the unwanted variations should be common to adjacent pixels, they cancel in the interference image, which shows detail due to the specimen alone. The system developed by Nomarski is most commonly used in light microscopy,lZ and it achieves a differential phase sensitivity of around five degrees. Althought these microscopes use partially spatially coherent illumination, there is generally no facility for time integration to reduce their noise band width and so the full advantages of differential phase contrast microscopy are not realised. Recent developments in scanning acoustic and optical microscopy have used fully coherent illumination and detection in order to overcome this barrier, with consequent improvements to image sensitivity and stability. In the acoustic microscope two techniques for differential phase contrast microscopy have been demonstrated.In the first13 a split detector is used to phase compare adjacent pixels simultaneously, which is closely analogous with the Nomarski system. In an alternative approach the microscope is operated at two frequencies simultaneously and phase comparison of the two beams yields the image. l4 Because resolution in these microscopes is diffraction limited, the lower frequency image acts as a lower resolution phase reference to the high frequency one. In both instances image artifacts are reduced and so time integration can substantially improve the sensitivity of the microscope. Similar techniques of compensated differential phase contrast microscopy have been used for measuring Rayleigh wave properties, surface topography and residual stress distributions15 via the acousto-elastic effect.In optical microscopy, a recently described system may be of great importance. This system couples a heterodyne Michelson interferometer to a scanning optical microscope. 16 The heterodyne principle enables the elimination of microphonic effects, provided that they fall outside the signal processing band width. In many instances this may be set in the megahertz range, well outside the normal band width of environmental effects, and so the absolute sensitivity of the interferometer can be realised. The embodiment of this apparatus described uses an acousto-optic cell to wobble the optical spot by one pixel and so forms a spatial differential phase contrast image.The sensitivity of this system to topography is approximately 0.1 nm and it is predicted that steps of 10-5 nm may be detected, a factor of lo5 improvement over the Nomarski system. The same system has been used for thermal wave microscopy, which can show thermal properties and subsurface defects." It has also been used for Joule heating microscopy,18 which reveals current density distributions in conductors and can show electron migration effects. The future for this technique seems assured; there is a whole range of electro-optical and magneto-optical effects to be explored, which have so far been undetectable in existing apparatus.292 IMAGING TECHNIQUES Anal. Proc., Vol. 21 Conclusions The use of fully coherent microscopes has been explored over the last decade and unique applications are emerging.As signal processing becomes more sophisticated, the sensitivity of these instruments is improving dramatically and it is expected that many new phenomena will be revealed in an image. 1. 2. 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. References Lemons, R. A., and Quate, C. F., “Acoustic Microscope, Scanning Version,” Appl. Phys. Lett., 1974, 35, Ash, E. A., Editor, “Scanned Image Microscopy,” Academic Press, London, 1980. Wickramasinghe, H. K., and Hall, M., Electron. Lett., 1976, 12, 637. Bennett, S. D., and Ash, E. A., “Differential Imaging with the Acoustic Microscope,” ZEEE Trans. Sonics Wickramasinghe, H. K . , “Contrast in Reflection Acoustic Microscopy,” Electron. Lett., 1978, 14, 305.Bennett, S. D., “Approximate Materials Characterisation by Coherent Acoustic Microscopy,” IEEE Trans. Sonics Ultrason., 1982, 29, 316. Sinclair, D. A., and Smith, I. R., “Tissue Characterisation Using Acoustic Microscopy,” in Ash, E. A., and Hill, C. R., Editors, “Acoustical Imaging,” Volume 12, Plenum Press, New York, 1982. Sinclair, D. A., Smith, I. R., and Bennett, S. D., “Elastic Constants Measurement with a Digital Acoustic Microscope,” IEEE Trans. Sonics Ultrason. , 1984, in the press. Briggs, G. A. D., Illett, C., and Somekh, M. G., in Ash, E. A., and Hill, C. R., Editors, “Acoustical Imaging,” Volume 12, Plenum Press, New York, 1982, pp. 89-99. Hi’ldebrand, J. A., and Lam, L. K., Appl. Phys. Lett., 1983, 42, 413. Liang, K., Khuri-Yakub, B. T., Bennett, S.D., and Kino, G. S . , “Phase Measurements with the Acoustic Normarski, G., J. Phys. Radium, 1955, 16, 9. Smith, I. R., and Wickramasinghe, H. K., “Differential Phase Contrast in the Acoustic Microscope,” Electron. Lett., 1982, 18, 92. Smith, I. R., and Wickramasinghe, H. K., “Dichromatic Differential Phase Contrast Microscopy,” ZEEE J. Sonics Ultrason., 1982, 29, 321. Bennett, S. D., Husson, D., and Kino, G. S., “Measurement of Three-dimensional Stress Variation,” in “Proceedings of the IEEE Ultrasonics Symposium, Chicago, 1981,” IEEE, New York, 1982, pp. 964-968. 385. Ultrason., 1981, 28, 59. Microscope,” Proc. I983 IEEE Ultrason. Symp., 1983. Wickramasinghe, H. K., Ameri, S., and See, C. W., Electron. Lett., 1982, 18, 22. Ameri, S., Ash, E. A., Neuman, V., and Petts, C.R., Electron. Lett., 1981, 17, 337. Wickramasinghe, H. K., Martin, Y., Ball, S., and Ash, E. A., Electron. Lett., 1982, 18, 700. Emission and Transmission Tomography in Non-destructive Analysis Nicholas M. Spyrou Department of Physics, University of Surrey, Guildford, Surrey, GU2 5XH The considerable impact on medicine of computerised tomography (CT) using X-ray transmission measurements, since the introduction of the first commercial CT-scanner by Hounsfield over a decade ago, has provided the impetus for widespread research using various types of ionising radiations, such as gamma-rays, neutrons and heavy charged particles, as well as non-ionising radiations including microwaves, nuclear magnetic resonance and ultrasound, as radiation probes.More recently, as the technique of computerised tomography has become more widely appreciated, the range of applications in non-medical areas, particularly in industrial non-destructive testing, has expanded’ and there has been a development towards more flexible and less expensive scanning systems compared with the commercial CT-scanners, which are optimised for clinical applications. One such example is the prototype scanner that has been designed and constructed for applications to the nuclear industry in a collaboration with AERE, Harwell. It can scan in both emission and transmission modes and employs a variety of detectors €or measuring gamma-rays over a wide range of energies.2~3 Tomographic applications of ionising radiations, only, are discussed with reference to materials analysis.Background Theory It is the aim of tomography to produce an image of a slice through an object that is free from interference arising from underlying and overlying planes. There are various approaches to theAugust, 1984 IMAGING TECHNIQUES 293 solution of the problem that arises from the reconstruction of an object from a set of multiple but finite projections of the object, when for perfect reconstruction an infinite set of all possible projections is required, and the principles of computerised tomography have been clearly explained in the literat~re.~>5 In emission tomography the reconstructed image represents the distribution of the radiation concentration in a plane within the object, provided that the emitted radiation can be detected outside the object, whereas in transmission tomography it is the representation of the physical quantity governing the energy loss, i.e., the stopping power or the attenuation coefficient, in the material when the radiation beam traverses it and is detected on the other side.The magnitude of the photon linear attenuation coefficient depends on the atomic cross-sections of the interaction processes that attenuate the X- or gamma-ray beam, i.e., photoelectric absorption, incoherent (Compton) and coherent (Rayleigh) scattering and pair production, and is a function of the density, p, and atomic number, 2, for a given energy. Therefore, from determination of the linear attenuation coefficient at every point in an object, at a number of photon energies, it is possible to obtain information regarding elemental distribution and density, separately.For example, in the energy range between -400 keV and a few MeV, the attenuation coefficient is largely dependent on Compton scattering and can be written as N,,ZaKNw) P(E)“P A where No is Avogadro’s number, A the relative atomic mass and aKN(E) the Klein - Nishina cross-section per electron for incoherent scattering. Because for all elements, except hydrogen, Z/A is approximately constant, the attenuation coefficient can be considered as a function of density only.5 In tomography, therefore, not only visual representation pertaining to the location of the quantity of interest is provided, but also quantitative information is given on how much of the quantity is present.Problems in Application ( a ) What is the smallest concentration of an element that can be detected by a change in the photon mass attenuation coefficient of the matrix in which it is introduced?6 What is the equivalent “apparent” length that can be detected when a reconstructed image of the matrix is obtained in transmission tomography?7 ( b ) How these minimum quantities of mass and length can be achieved in practical tomography depends on the number of projections taken and their sampling frequency. These, in turn, affect the numer of events to be detected for a particular precision (assuming Poisson statistics) and a given spatial resolution. Thus, the X- or gamma-ray source intensity and the time of counting required are determined. ( c ) It is important to consider the nature of the detected events for a given precision because the photon spectrum consists of both primary and scattered photons, and if the latter are included in the reconstruction of the image, then the image is degraded.How can scattered events, therefore, be reduced and if possible eliminated and what role does the detector energy resolution play? It was shown that the “quality” of the detected events, i e . , the relative magnitudes of the primary and scattered photons used in the reconstruction process, is more critical to image quality than the number of detected events.8 It was also shown to be more important in applications of emission tomography. (d) Useful information can, however, be obtained from scattered photons, both Compton and Rayleigh, if these are measured at an angle to the primary photon beam used for transmission measurements, as it has been shown that the Compton scattering coefficient is a function of density only, whereas the ratio of the coherent to the incoherent counts is a function of 2” and independent of density.9 Compton scattering tomography is therefore proposed as a method of obtaining the density distribution within an object.The possibility of detecting simultaneously characteristic X-rays resulting from absorption in the material, in order to provide additional elemental information, was explored. (e) The case has been made for neutron radiography as a useful complementary method to X- and y-radiography , so why not neutron tomography? Three novel and different methods were suggested, neutron transmission tomography, neutron scattering tomography and neutron induced gamma-ray emission tomography.lome usefulness of the first method was discussed with reference to applications in which neutron absorbing and neutron transparent materials are differentiated, of the second where the distribution of molecules or compounds with high scattering cross-sections (e.g. , water) is determined The following problems were considered and demonstrated with applications.294 IMAGING TECHNIQUES Anal. Proc., Vol. 21 in a body, and of the third where mapping of the elements present in an object is required. All three methods are still at the research stage. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. References Gilboy, W. B., and Foster, J., in Sharpe, R. S ., Editor, “Research Techniques in Non-destructive Testing,” Sanders, J . M., Ph. D. Thesis, University of Surrey, 1982. Sanders, J. M., and Spyrou, N. M., Nucl. Instrum. Meth., 1982, 79. Brooks, R. A., and Di Chiro, Phys. Med. Biol., 1976, 21, 689. Kouris, K . , Spyrou, N. M., and Jackson, D. F., “Imaging with Ionising Radiations,” Surrey University Kouris, K., and Spyrou, N. M., Nucl. Instrum. Meth., 1978, 477. Kouris, K., Spyrou, N. M., and Jackson, D. F., Nucl. Instrum Meth., 1981, 539. Sanders, J . M., and Spyrou, N. M., Nucl. Instrum. Meth., 1984, in the press. Kouris, K., Spyrou, N. M., and Jackson, D. F., in Sharpe, R. S . , Editor, “Research Techniques in Spyrou, N. M., “An Experimental Investigation into the Fundamental Aspects of Neutron Tomography,” Volume VI, Academic Press, London, 1982, pp.255-288. PresdBlackie and Son Ltd., Glasgow, 1982. Non-destructive Testing,” Volume VI, Academic Press, London, 1982, pp. 21 1-253. Annual Report of the Institut Laue-Langevin, Grenoble, France, 1983. Molecular Graphics and Modelling Roy Hubbard David Fincham and John Quinn Department of Chemistry, University of York, Heslington, York, YO1 5DD DAP Support Unit, Queen Mary College, University of London, Mile End Road, London, E l 4NS The images and pictures that are of value in scientific investigations represent various aspects of the object or scene they depict in a form which we can easily appreciate with our visual sense. They have in common the fact that they display, in broad terms, the spatial relationships involved, but they vary very widely in the manner in which they communicate other information about the properties and behaviour of the object portrayed.With molecules, the relationship between object and image is very indirect indeed; what does it mean to talk about a picture of a molecule? A molecule can only be described completely in mathematical terms, and the prime role of graphics in molecular science is to display features of mathematical models in a way that helps us to understand the nature and behaviour of the model, to compare its properties with experimental data and to help us refine it. The Snooker-ball Picture An example of one type of molecular picture is shown in Fig. 1, which is of an insulin dimer. The atomic coordinates were obtained by X-ray crystallography, and so in this sense it is an image of a real molecule.The atoms are represented as if they are solid spheres: let us call this the snooker-ball representation. It is a very simple representation: does it correspond to any physical reality? It does in the sense that we know that if two non-reacting atoms are brought into contact they experience strong repulsive forces as soon as their electronic distributions begin to overlap. In collision such atoms behave to a first approximation like hard spheres. For molecules it is a cruder approximation to represent the electronic distribution by sectors of spheres joined together. Nevertheless, the snooker-ball picture gives a reasonable over-all impression of the shape of the external surface of a macromolecule.The snooker-ball pictures could become much more useful to the chemist as a tool to help him interpret molecular structure and behaviour if they could be produced very rapidly indeed, in fractions of a second rather than in minutes as with present computer systems. First, this would enable moving pictures to be made of dynamic simulations on a regular basis, giving immediate comprehension of complicated dynamic processes. Secondly, it would permit this kind of representa- tion to be incorporated into interactive model building sysems such as are used extensively by protein crystallographers. Fast Picture Generation The evaluation of the snooker-ball picture is slow because of the extensive computation involved in the hidden surface removal and in the shading of the spheres, necessary to give an impression of shape.August, 1984 ANALYSIS OF ANTIBIOTICS 295 Fig. 1. Molecular picture of an insulin dimer. We have managed to reduce the time involved by use of the ICL Distributed Array Processor (DAP) and a technique for the hidden surface removal known as the 2-buffer. The goal is to produce a 512 by 512 array of pixel intensities in the frame-store of the raster graphics terminal. We use 8-bit pixels, with 16 intensity levels for each distinct colour of sphere. We also maintain a 512 by 512 array containing a 2-value (the 2 direction is perpendicular to the plane of the picture) for each pixel; this is the 2-buffer. The atoms are added into the picture one by one. In a separate buffer we create a single shaded sphere for the atom, storing an intensity level and a 2-value for each pixel. (In practice we may pre-compute spheres for each distinct radius of atom that will be present in the picture.) The atom Z-buffer is compared on a pixel by pixel basis with the already existing picture 2-buffer; where the new atom lies in front of the existing picture the atom intensity and 2-value buffers are copied into the picture frame-store and Z-buffer respectively. When this process has been repeated for each atom the final picture results. The 2-buffer technique atuomatically carries out the hidden surface removal and finds the correct intersection between the spheres. The DAP is especially efficient in this process. It consists of an array of 64 x 64 processing elements, so that a block of 64 by 64 pixels can be processed simultaneously. The processing elements can be programmed to perform arithmetic at any precision and work particularly quickly on short word-length fixed-point arithmetic. We take advantage of this by having 2-coordinates as 9-bit integers, giving the same resolutions as in the X and Y directions. We have already achieved a speed of about half a millisecond per atom.

ISSN:0144-557X    

DOI:10.1039/AP9842100287

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

August, 1984 ANALYSIS OF ANTIBIOTICS 295 Analysis of Antibiotics The following is a summary of the paper presented at a Meeting of the North West Region held on February 9th, 1984, at Moreton, Merseyside. A Novel Approach to the Analysis of Antibiotics R. F. Cosgrove The Syuibb Institute for Medical Research, Reeds Lane, Moreton, Merseyside, L46 1 Q W Quantitative microbiological assays are relative and not absolute methods of analysis. Responses of an organism are compared with responses to standard preparations of known composition and concentration. The two principal methods of bio-assay are agar diffusion and turbidimetric methods and these are described in detail elsewhere.’ There is general concern as to the precision of microbiological assays and, as stated by Kavanagh,’ all too often the real “biological variation” probably has a macro- and not microbiological origin.An assay can be no better than the sample preparation and the assay procedure employed. In other words, the quality of an assay is related to the understanding by the analyst of the pitfalls of the assay. One of the most important factors in bioassays296 ANALYSIS OF ANTIBIOTICS Anal. Proc., Vol. 21 is replication, or lack of it, and the effect of this has recently been highlighted by Hewitt.2 In 1968, Arret and Eckert stated3 that the 95% confidence range of an average microbiological assay should be f10%. By 1973 the British Pharmacopoeia requirement was +5% and currently any result within this range is considered normal variation while any result outside the range is considered significantly different.The main contributory causes of this "biological" variation are variations in the inoculum, in the method of preparation of standard solutions of the antibiotic and also in available media (for example, see Freeman et aZ.4). Improvements in the reproducibility of nystatin agar diffusion assays have been achieved by the use of inocula stored in liquid nitrogen and deep frozen standard stock solutions. The over-all percentage variability of the assay has been reduced from over 5% with daily prepared standards and inocula to around 1% with a frozen inoculum and to 0.6% with a combination of frozen inoculum and standards.5 However, long periods of incubation are required for organisms to produce growth sufficient for the measurement of zones of inhibition in agar or turbidity in broth.Polyene antibiotics, such as nystatin and amphotericin B, cause leakage of cytoplasmic constituents, particularly of monovalent catons,6?7 from susceptible micro-organisms. A correlation between polyene concentration and potassium efflux was found to exist, but the measurement of K+ leakage was thought unsuitable for an assay system, because of the distinct possibility of natural contamination by K+ ions. An alternative ion, which could be introduced into the yeast cells without affecting their viability or membrane function but which had a very low level of natural occurrence, was sought. To reproduce as closely as possible the characteristics of K+ ion leakage across the nystatin-impaired yeast cell membrane, it was necessary to find an ion of like charge and ionic radius.K+ ions exist in solution in a hydrated form, and the hydrated ionic radii of K+ (0.232 nm) and Rb+ (0.228 nm) are very similar, as are the ionic mobilities of these two ions. Rubidium ions are known to be well tolerated by erythrocytes and there are a number of reports in the literature concerning the uptake of Rb+ ions by the yeast Saccharomyces cerevisiae.s-10 Rubidium can also be determined at low levels with precision by atomic-absorption spectrophotometry . It was therefore decided to examine the feasibility of using Rb+ uptake and its subsequent release from yeast cells by the action of nystatin and amphotericin B as a bioassay system. Preliminary experiments showed that the amount of Rb+ incorporated into the yeast cells was dependent, up to a concentration of 50 mM, upon the amount present in the growth medium.As the cellular rubidium concentration increased, the cellular potassium level decreased, and a total concentration of K+ plus Rb+ ions was maintained, although the ratio of one to the other varied. The rates of growth of the yeast in the presence and absence of potassium and/or rubidium were compared, and apart from a slightly increased lag phase in the absence of potassium no significant differences were apparent. A 90% recovery of both cell types was achieved following storage in liquid nitrogen, but there was an immediate loss of about 60% of monovalent cations from both normal and rubidium loaded cells. This was not unexpected from the known effects of sub-zero temperature on yeast and knowledge of the use of various cryoprotectives to reduce the leakage of cellular constituents, particularly monovalent cations, reported in the literature." As some of these agents could help in maintaining the Rb+ ion content of the cells, various freezing menstra and various rates of cooling and thawing were examined.Some success was achieved, but if the cells were left to stand at room temperature, the ion loss would continue until an approximate 60% loss was reached. Unfrozen cells suspended in Tris buffer lost monovalent cations to the same level, the rate of loss varying with the temperature at which the cells were stored. At room temperature the loss occurred over a period of about 48 h; at 4 "C the rate of loss was slower and at 37 "C faster.Nevertheless, the concentration of monovalent ions lost from the cells was consistent and corresponded with that resulting from cryogenic storage. Thus, there appears to be an equilibrium concentration for monovalent cations in this organism below which no further cation release occurs under the storage conditions described. This finding is of cardinal importance in the assay system, as the cells being used at equilibrium only release ions when exposed to nystatin. Thus, the Rb+ measured is that caused solely by the action of the polyene and is not a compounded result of Rb+ released by nystatin and that released naturally. Therefore, any assay interference caused by a continually changing background level of rubidium is removed.For an assay to be precise and accurate the dose-response is critical, and therefore the factors influencing the curve are most important. Once initiated, the release of Rb+ ions from the cells is a continuous process until all of the Rb+ is depleted. Not only is the release of the ions time dependent, but it is also temperature dependent, and 30 min at 37 "C have been found to be the optimum conditions for a satisfactory dose response. Nystatin samples of various potencies and nystatin formulated intoAugust, I984 EQUIPMENT NEWS 297 various dosage forms were assayed by the conventional agar diffusion assay and the Rb+ efflux assay.12 The results showed a good correlation, with results on 15 samples being within +5% by the two methods.The Rb+ assay was shown to be stability indicating, again by using the two methods to assay nystatin that was heat degraded at 85 “C for various time intervals. Atomic-absorption spectrophotometry suffers from two main disadvantages: the necessity of removing the treated cells from the suspension before analysis, and the consumption of the sample during analysis. It was felt that a rubidium ion-selective elctrode would overcome these disadvantages. Unfortunately, such an electrode was not available commercially but a commercially available potassium electrode was modified to give a sufficiently high selectivity coefficient for rubidium over potassium to be used in the Rb+ assay.13 The electrode exhibited Nernstian behaviour for Rb+ concentrations between 10-1 and 10-5 M and the selectivity of the electrode for Rb+ over K+, assessed by the separate-solutions method,14 was found to be 1.6 x 10-1, and for the mixed-solutions method14 2 X 10-1 with 10-4 M K+ and 7 x 10-1 with 10-5 M K+.The efflux of Rb+ ions from yeast cells subjected to a range of nystatin concentrations was monitored continuously over a 15-min period at 50 “C. If the electrode potential after 10 min incubation was plotted against the logarithm of the nystatin concentration, this being the normal bioassay relationship, a straight line was obtained within a narrow concentration range. Thus, the electrode could be used as an alternative to atomic-absorption spectrophotometry and would lend itself more readily to automation. However, the sensitivity of the electrode was such that the rnV range between the highest and lowest concentrations of nystatin on the linear section of the dose-response curve was small, and thus very small errors in sample readings could cause considerable changes in potency values.Thus, although the electrode will satisfactorily measure Rb+ ion concentrations, for routine use the preferred detection system is the atomic-absorption spectrophotometer. The obvious advantages of the Rb+ assay are speed, simplicity and economy. Allowing for assay preparation (weighing, diluting, etc.) and final calculations, results can be obtained within 90 min. The cost savings of the system over the conventional diffusion assay are also considerable. In routine use for the assay of 1712 samples it was found that there was a saving of 46% in assay time and a monetary saving of some 60%.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Kavanagh, F., “Analytical Microbiology 11,” Academic Press, London, 1972. Hewitt, W., Pharm. Int., 1982,3, 370. Arret, B . , and Eckert, J . , J . Pharm. Sci., 1968, 57, 871. Freeman, K. A . , Johnson, D. P., and Garth, M. A . , J. Assoc. Off. Anal. Chem., 1977, 60, 1261. Cosgrove, R. F., Beezer, A . E . , and Miles, R. J . , J . Pharm. Pharmacol., 1979,31, 83. Marini, F., Arnow, P . , and Lampen, J . O., J. Gen. Microbiol., 1961, 24, 51. Sutton, D. D., Arnow, P. M., and Lampen, J . O., Proc. SOC. Exp. Biol. Med., 1961, 108, 170. Azoulay, L., and Borst-Pauwels, G. W. F. H., Acta Bof. Need., 1974, 23, 505. Borst-Pauwels, G. W. F. H . , Schnetkamp, P., and van Well, P., Biochim. Biophys. Acta, 1973,291,274. Borst-Pauwels, G. W. F. H., Wolters, G. H. J . , and Henricks, J. J . , Biochim. Biophys. Acfa, 1971,225,269. MacCleod, R. A . , and Calcott, P. H . , SOC. Gen. Microbiol. Symp., 1976, 26, 81. Cosgrove, R. F . , J . Appl. Bact., 1978, 44, 199. Cosgrove, R. F . , and Beezer, A. E . , Anal. Chim. Acta, 1979, 105, 77. Moody, G. J., and Thomas, J. D. R., “Selective Ion Sensitive Electrodes,” Merrow, London, 1971.

ISSN:0144-557X    

DOI:10.1039/AP9842100295

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

August, 1984 EQUIPMENT NEWS 297 Equipment News Spectrophotometer The Shimadzu UV-260 ultraviolet - visible record- ing double-beam instrument features a visual display screen with graphic function that allows the display and manipulation of data. The data can also be recorded by means of a built-in graphic printer - plotter. Data processing options include the peak-pick program, which allows peak or trough wavelength detection within user selectable limits, and an area calculation mode, which allows calculations of total or partial areas under the curve and area ratio calculations. V. A. Howe & Co. Ltd., 12-14 S t . Ann’s Crescent, London, SW18 2LS. Spectrophotometer The Spectracomp 602 double-beam micropro- cessor controlled instrument replaces the Model298 EQUIPMENT NEWS Anal.Proc., Vol. 21 601. Major features are a double optic with holographic blazed grating and an RS 232/C interface for external computing. It will be supplied with analytical programs for absorbance, transmittance and Concentration measurements. Erba Science (UK) Ltd., Headlands Trading Estate, Swindon, Wiltshire, SN2 6JQ. Printer - Plotter for DU-7 Spectrophotometer A new printer uses fan-fold paper, which is less costly than thermal paper and does not fade. Fully labelled printouts of graphical and tabulated data are obtained for wavelength scans, concentration measurements, multi-component analysis and kine tic determinations. Beckman-RIIC Ltd., Progress Road, Sands Industrial Estate, High Wycombe, Buckingham- shire. Gas Chromatographs The 4300 series includes an analytical oven with base bodies for ionisation and/or thermal conduc- tivity detectors.The oven top is designed to accept two vaporising injectors, which may be for holds 100 sample vials. There are three modes of operation: manual, automatic and remote. Perkin-Elmer Ltd., Post Office Lane, Beacons- field, Buckinghamshire, HP9 1 QA. Capillary Interface The Tekmar Model 1000 interfaces purge and trap or dynamic headspace concentrators to gas chromatographs using capillary columns. It freezes the desorbed sample from the concentra- tor into a narrow band on a fused silica pre- column. The focused sample is then flash heated and injected into the gas chromatograph. Analysis Automation Ltd., Southfield House, Eynsham, Oxford, OX8 1JD. Column Pressure Switching System The system upgrades dual detector gas chromato- graphs (packed or capillary) for multi- dimensional chromatography.Techniques such as heart-cutting, back and fore-flushing, variable splitting and cold trapping can all be performed. Scientific Glass Engineering (UK) Ltd., 1 Potters Lane, Kiln Farm, Milton Keynes, MKll3LA. Chromatography Accessories A 20-ml vial is available for headspace analysis. A range of specialist seals is also announced. They are in 11 and 8 mm sizes and can be used with crimp caps or screw caps. Chromacol Ltd., Glen Ross House, Summers Row, London, N12 OLD. Computer The IBM CS-9000 scientific 16-bit microcomputer is being introduced with multi-channel chromato- graphy software. Additional capabilities include packed or capillary operation. The 4300 can be used in conjunction with many of the data systems developed for the maker’s Mega series of gas chromatographs.Erba Science (UK) Ltd., Headlands Trading Estate, Swindon, Wiltshire, SW2 6JQ. Autosampler for Gas Chromatography The AS-300 is a programmable system for use with the maker’s Model 8300 or any of their Sigma range of gas chromatographs. The sample trayAugust, 1984 EQUIPMENT NEWS 299 instrument control, data acquisition, data analy- sis, graphics, multi-colour plotting, extensive data storage and general programming. Kemtronix (UK) Ltd., High Street, Compton, Berkshire, RG16 ONL. HPLC Gradient Program A program is available which enables the pumps of a binary gradient chromatograph to be con- trolled by an Apple I1 computer.Gradient flow profiles of up to 110 steps can be produced. Laboratory Data Control (UK) Ltd., Milton Roy House, High Street, Stone, Staffordshire, ST15 8AR. Compact Materials Analyser The Model 740 provides readouts of up to 32 elements in one measurement. The element range is from atomic number 13 (aluminium) to number 92 (uranium), inclusive. The instrument, which is portable, carries out non-destructive testing with- out sample preparation in as little as 15 s. Columbia Scientific Industries Corporation, P.O. Box 9908, Austin, Texas 78766, USA. Control Analysis System The Amica system consists of an autosampler, a liquid processor, a microcomputer, a printer and either a spectrophotometer or a pH meter, depending upon the type of measurement to be taken.Modular hardware and the software enable simple adaptation of the system to a wide range of methodologies. V. A. Howe & Co. Ltd., 12-14 St. Ann's Crescent, London, SW18 2LS. Ion Titration System The Radiometer IMS 885 system for ion analysis and titration consists of the Ion 85, a micropro- cessor controlled pH/ion meter, and the ABU 80 autoburette module. V. A. Howe & Co. Ltd., 12-14 St. Ann's Crescent, London, SW18 2LS. pH/Temperature Meter The Jenway PHM 9 hand-held instrument offers a pH measurement range of 0-14 to a resolution of 0.1, and a direct temperature measurement range from -40 to +150 "C with a resolution of 1 .O "C. Automatic temperature compensation is standard. Lenton Thermal Designs Ltd., 12-14 Fairfield Road, Market Harborough, Leicestershire, LE16 9QQ.Karl Fischer Turbo Titrator An instrument is available for measuring water content in solids and other samples that resist mixing. It features a 6000 rev min-1 homogeniser. The water content in mg is calculated electronic- ally. The sensitivity is to 2 p.p.m. of water in a 50-g sample with an accuracy of k 1.2% at 10 mg and 50.3% above 50 mg. GCA Corporation, 209 Burlington Road, Bedford, Massachusetts, USA. Dissolved Oxygen MetedThermometer The POM 2 hand-held instrument measures oxygen in percentage saturation from 0-25% and 0-200%, and in p.p.m. from 0-19.9. Automatic temperature compensation is a standard feature. The temperature measurement range is 0-50 "C to a resolution of 1.0 "C. Jenway Ltd., Gransmore Green, Felsted, Dunmow, Essex, CM6 3LB.Conductance Meter The YSI Model 34 gives a direct digital display of temperature compensated values for conductance or resistance. An analog output is provided for recording, monitoring, controlling and data- logging and for applications such as conducti- metric titrations. Clandon Scientific Ltd., Lysons Avenue, Ash Vale, Aldershot, Hampshire, GU12 5RQ. Refractive Index Detector The HP1037A can detect nanogram amounts of compounds. It compares the refractive index of a pure reference solvent with that of the reference solvent plus the sample.300 EQUIPMENT NEWS Anal. Proc., Vol. 21 Hewlett-Packard Ltd., Nine Mile Ride, East- hampstead, Wokingham, Berkshire, RGll 3LL. Oxygen Analyser The 790E instrument is primarily intended for use on small industrial and commercial boilers with maximum flue gas temperatures of 350 “C.Servomex Ltd., Crowborough, Sussex, TN6 3DU. Gas Alarm The System 320 instrument has been designed for industrial and offshore instdllations where toxic and flammable gases must be monitored. Sensors are available for combustible gas and toxic hazards such as carbon monoxide, hydrogen sulphide, chlorine, oxygen or hydrogen cyanide. A poison resistant flammable gas sensor has been developed to cope with contaminants such as sulphur and lead. MSA (Britain) Ltd., East Shawhead, Coat- bridge, ML5 4TD. Temperature Sensors A range of mineral-insulated, metal-sheathed thermocouples offers sensors in K, J, T, E, R and S calibrations to international standards with insulated, grounded or exposed junctions.TC Ltd., P.O. Box 130, Uxbridge, Middlesex, UB8 1AD. Blood Analyser The Model S880 offers the standard eight parameters, including whole blood platelet count. Triplicate analysis is performed in sequence on a dual aperture system. The instrument is micro- processor controlled and has a liquid crystal display. Coulter Electronics Ltd., Northwell Drive, Luton, Bedfordshire, LU3 3RH. PTFE Rotary Operated Valves The T-series valves for flow switching and sample injection are suitable for flow-injection analysis and conventional continuous flow analysis. The basic 6-port valve is available in two configura- tions: as a changeover valve and complete with sample loop for plug injection. PS Analytical Ltd., 2 Eagles Drive, Tatsfield, Westerham, Kent. Freeze Driers A range of seven standard models is available, together with a selection of accessories, including vacuum pumps, vacuum connection kits and filters.Paar Scientific Ltd., 594 Kingston Road, Raynes Park, London, SW20. Literature A brochure gives details of matched reagent, calibrator and control systems for haematology. It includes information on two diluent and reagent systems and the maker’s 4C whole blood controls, thrombocyte controls and new calibrators. Coulter Electronics Ltd. , Northwell Drive, Luton, Bedfordshire, LU3 3RH. A leaflet describes the SpectroMonitor D ultra- violet - visible variable wavelength detector, which features a digital display with full diagnos- tics and a 0.001-2.0 a.u.f.s. sensitivity range. Laboratory Data Control (UK) Ltd., Milton Roy House, High Street, Stone, Staffordshire, ST15 8AR. A document provides details of fume cupboard specifications and options designed to help users and engineers. It commences with an introduction to the specifications based on BS DD80:1982. A. R. Hoare & Co. Ltd., 42 Croydon Road, Penge, London, SE20. Brochures give full details on the 0700 laboratory X-ray fluorescence spectrometer and the Micro- analyst 8000 full signal microanalysis system. Also available are a brochure describing the Analyst 6700 analysis system and a booklet, “Digital Imaging with the Electron Microscope-Basic Principles. ” Kevex Corporation (UK), 2 The Howard Estate, Chilton Road, Chesham, Buckingham- shire, HP5 2AU. Professor Alan Townshend We are pleased to announce that Dr. Alan Townshend has been appointed to a personal Chair of Analytical Chemistry at the University of Hull. Obituaries Dr. H. Egan and Professor G. F. Kirkbright We deeply regret to announce the deaths of Dr. H. Egan, the former Government Chemist, and Professor G. F. Kirkbright, Head of the Department of Instrumentation and Analytical Science at the University of Manchester Institute of Science and Technology.

ISSN:0144-557X    

DOI:10.1039/AP9842100297

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

August, I984 F. E. BEAMISH LECTURES 301 RSC Endowed Medals and Prizes Nominations for the following medals and prizes should reach the Local Affairs Officer, Royal Society of Chemistry, Burlington House, Pic- cadilly, London, W1V OBN, by December 31st, 1984. The Corday-Morgan Medal and Prize The Council of the Society makes annually up to three awards in different branches of che- mistry. These awards, each consisting of a silver medal and a monetary prize of 250 guineas, are made to the British chemists of either sex who, in the judgement of the Council of the Society, shall have published during the year in question and in the immediately preceding five years, the most meritorious contribution to experimental che- mistry and who shall not have attained the age of 37 years by December 31st of the year of the award (in this instance 1983).The Meldola Medal and Prize This award is the gift of the Society of Macca- baeans and commemorates Raphael Meldola, who was President of that Society and the then Institute of Chemistry. The award, consisting of a bronze medal and a monetary prize of f100, is given to British chemists under 30 years of age at December 31st of the year of the award, for showing the most promise as indicated by pub- lished chemical work, which may have been conducted anywhere in the world. Nominations are invited for the 1984 prize. The Beilby Medal and Prize This annual award, administered jointly by The Royal Society of Chemistry, the Society of Chemical Industry and the Metals Society, was founded in 1924 as a memorial to Sir George Beilby, President of all three bodies or their predecessors. The award, consisting of a silver gilt medal and a monetary prize of &500, is given for “Advancement in Science and Practice.” The awards are made to British scientists, normally under the age of 40, in recognition of original work of exceptional merit which has lead to advances of practical significance. The work should have been carried out continuously over a period of years and should have involved the development and application of scientific prin- ciples in any field related to the special interests of Sir George Beilby, i.e., in chemical engineering, fuel technology or metallurgy.Nominations are invited for the 1985 prize. The Harrison Memorial Prize This Prize was created in 1922 to commemorate the devoted services of the late Colonel Edward Frank Harrison, formerly Deputy Controller of the Chemical Warfare Department, for the protection of the British Forces from poison gas in the first world war. It is jointly administered by The Royal Society of Chemistry, the Society of Chemical Industry and the Pharmaceutical Society. The Prize, of one hundred guineas and a bronze plaque, is awarded, normally at intervals of three years, to a British chemist of either sex who, in the opinion of the Selection Committee, shall, during the year in question, and in the imme- diately preceding four years, have conducted the most meritorious and promising original investi- gations in chemistry and shall have published the results of those investigations in scientific period- icals. Candidates shall not have attained the age of 30 years by December 1st of the year of the award (in this instance 1984).

ISSN:0144-557X    

DOI:10.1039/AP984210301b

出版商:RSC    

年代:1984

数据来源: RSC

摘要:

302 ANALYTICAL DIVISION DISTINGUISHED SERVICE AWARD Anal. Proc., Vol. 21 Publications Received Chromatography of Antibiotics. Second, Com- pletely Revised Edition. Gerald H. Wagman and Marvin J. Weinstein. Journal of Chromatography Library, Volume 26. Pp. xviii + 504. Elsevier. 1984. Price $113.50 (USA & Canada); Dfl295 (Rest of World). ISBN 0 444 42007 X. Developments in Food Analysis Techniques-3. Edited by R. D. King. Developments Series. Pp. x + 217. Elsevier Applied Science. 1984. Price f26. ISBN 0 85334 262 8. Analytical Pyrolysis. Techniques and Applica- tions. Edited by Kent J. Voorhees. Pp. x + 486. Butterworths. 1984. Price E35. ISBN 0 408 01417 2. The Eight Peak Index of Mass Spectra. Third Edition. Mass Spectrometry Data Centre. 1983. Price f595; $1130.50. The Eight Peak Index of Mass Spectra is a unique index designed for the identification of unknown compounds by comparison of their mass spectral data with the equivalent data in the Index.Published by The Mass Spectrometry Data Centre (MSDC) in collaboration with Imperial Chemical Industries (Organics Division), the Eight Peak Index contains the eight most abun- dant ions in 66720 mass spectra (covering 52332 compounds) indexed by relative molecular mass, elemental composition and the eight most abun- dant ions. The 3rd edition, published late in 1983, has been produced in response to user demand for an update of the very successful 2nd edition published in 1975 (31 101 spectra). It is worth noting that the new Eight Peak Index is up to four times less expensive than other collections of similar size.Since 1967, the MSDC has acted as a centre for collecting and cataloguing mass spectra on a world-wide basis. The staff of the MSDC are in regular contact with some of the leading experts in mass spectrometry and routinely monitor the published mass spectral literature. The Eight Peak Index includes spectra drawn from the collections of other organisations, from published literature and from the MSDC’s own collection. The Eight Peak Index includes Chemical Abstracts Registry Numbers wherever possible. These are arbitrarily assigned by CAS to each unique compound and provide a convenient point of entry to other mass spectral collections and to mass spectral information appearing in the scien- tific literature. They can also be used to access related information in many other manual and computer-readable files. The 3rd edition of the Eight Peak Index of Mass Spectra will be an invaluable publication to many scientists working in the field of mass spec- trometry.Full details are available from the MSDC, The Royal Society of Chemistry, The University, Nottingham, NG7 2RD. Teoria y Practica de la Extracion Liquido - Liquido. M. Valcarcel and M. Silva. Pp. xii + 376. Alhambra, Madrid. 1984. ISBN 84 205 10130.August, 1984 PUBLICATIONS RECEIVED 303 Karl-Fischer-Titration. Methoden zur Wasser- bestimmung Eugen Scholz. Anleitungen fur die Chemische Laboratorium- spraxis, Band X X . Pp. x + 136. Springer-Verlag. 1984. Price DM84; $32.60. JSBN 3 540 12846 8. Chemistry and Crime. From Sherlock Holmes to Today’s Courtroom.Edited by Samuel M. Gerber. Pp. xiv + 135. American Chemical Society. 1984. Price $19.95 (USA & Canada); $23.95 (Export). ISBN 0 8412 0784 4. New Approaches in Liquid Chromatography. Proceedings of the 2nd Annual American-Eastern European Symposium on Advances in Liquid Chromatography, Szeged, Hungary, June 1618, 1982. Edited by H. Kalasz. Analytical Chemistry Symposia Series, Volume 16. Pp. x + 291. Elsevier. 1984. Price $67.25; Dfl175. ISBN 0 444 99642 7 (Volume 16); 0 444 41786 9 (Series). Topics covered are HPLC (4 papers), displace- ment chromatography (2 papers), characterisa- tion of stationary phases (2 papers), optimisation (3 papers), TLC (2 papers), analysis of amino acids (4 papers) and analytical and preparative separation of peptides and proteins (6 papers).Analytical Spectroscopy. Proceedings of the 26th Conference on Analytical Chemistry in Energy Technology, Knoxville, TN, October 11-13,1983, Edited by W. S. Lyon. Analytical Chemistry Symposia Series, Volume 19. Pp. xiv + 394. Elsevier. 1984. Price $75; Dfl195. ISBN 0 444 42312 5 (Volume 19); 0 444 41786 9 (Series). Topics covered are lasers (15 papers), mass spectrometry (14 papers), plasmas (8 papers), nuclear methods (11 papers) and other spectro- scopic techniques (16 papers). Gas Chromatography - Mass Spectrometry. Applications in Microbiology. Edited by Goran Odham, Lennart Larsson and Per-Anders Mirdh. Pp. xvi + 444. Plenum. Price $59.50. ISBN 0 306 41314 0. Topics in Forensic and Analytical Toxicology.Proceedings of the Annual European Meeting of the International Association of Forensic Toxicolo- gists, Munich, August 21-25, 1983. Edited by R. A. A. Maes. Analytical Chemistry Symposia Series, Volume 20. Pp. x + 214. Elsevier. 1984. Price $57.75; Dfl150. ISBN 0 444 42313 3 (Volume 20); 0 444 41786 9 (Series). Chapters in this book are as follows: 1, Gas Chromatography; 2, Mass Spectrometry; 3, Fatty Acids and Complex Lipids; 4, Carbohydrates; 5 , Amino Acids and Peptides; 6, Analysis of Vola- tile Metabolites in Identification of Microbes and Diagnosis of Infectious Diseases; Head-Space/ Gas - Liquid Chromatography in Clinical Micro- biology with Special Reference to the Laboratory Diagnosis of Urinary Tract Infections; 8, Analysis of Cellular Components in Bacterial Classifica- tion and Diagnosis; 9, Quantitative Mass Spec- trometry and Its Application in Microbiology; 10, Analytical Pyrolysis in Clinical and Pharmaceut- ical Microbiology; 11, Volatile CI-Cs Com- pounds in Marine Sediments; and 12, Mass Spectrometry of Nitrogen Compounds in Ecolog- ical Microbiology.Electron Deficient Aromatic- And Heteroaromatic-Base Interactions. The Chemistry of Anionic Sigma Complexes. E. Bungel, M. R. Crampton, M. J. Strauss and F. Terrier. Studies in Organic Chemistry, Volume 14. Pp. viii + 499. Elsevier. 1984. Price $115.50; Dfl300. ISBN 0 444 42305 2. Advances in Materials Characterization. Edited by David R. Rossington, Robert A. Condrate and Robert L. Snyder. Materials Science Research, Volume 15. Pp. xii + 680. Plenum. 1984.Price $89.50. ISBN 0 306 41347 7. Topics covered are surface spectroscopy ( 5 chap- ters), surface techniques (4 chapters), vibrational spectroscopic techniques (7 chapters), electron optical methods (10 chapters), acoustic and mechanical properties (5 chapters), general crystallographic techniques (8 chapters) and general glass characterisation studies (8 chapt- ers). The Jahn - Teller Effect. A Bibliographic Review. 1. B. Bersuker. Pp. x + 589. IFI/Plenum. 1984. Price $85. ISBN 0 306 65206 4. The Jahn - Teller Effect and Vibronic Inter- actions in Modern Chemistry. I. B. Bersuker. Modern Inorganic Chemistry. Pp. xiv + 319. Plenum. 1984. Price $45. ISBN 0 306 41319 1. Challenges to Contemporary Dairy Analytical Techniques. Special Publication No. 49. Pp. xii 4 337. Royal Society of Chemistry. 1984. Price f16. ISBN 0 85186 925 4.304 CONFERENCES AND MEETINGS Advances in Infrared and Raman Spectroscopy, Volume 11. Edited by R. J. H. Clark and R. E. Hester. Pp. xx + 383. John Wiley. 1984. Price f49.50. ISBN 0 471 26267 6. A History of Platinum and its Allied Metals. Donald McDonald and Leslie B. Hunt. Pp. xii + 450. Johnson Matthey. 1982. ISBN 0 905118 83 9. Plasma Chromatography . Edited by Timothy W. Carr. Pp. xiv + 259. Plenum. 1984. Price $37.50. ISBN 0 306 41432 5. Mammalian Semiochemistry . The Investigation of Chemical Signals Between Mammals. Eric S. Albone. Pp. xii + 360. John Wiley. 1984. Price f29.50. ISBN 0 471 10253 9. Anal. Proc., Vol. 21

ISSN:0144-557X    

DOI:10.1039/AP984210302b

出版商:RSC    

年代:1984

数据来源: RSC