摘要:

Proceedingsof the Analytical Division ofThe Chemical Society263264265265273275276278280CONTENTSRegional Advisory Editors of'The Analyst'Reports of MeetingsSummaries of Papers'Original Papers in PharmaceuticalAnalysis''On-line Chemical Analysis''Carbon Atomisers in Atomic-absorption Spectroscopy'Equipment NewsConferences and MeetingsAnalytical Division DiaryVolume 12 No 10 Pages 263-280 October 197PADSDZ 12(10)263-280(1975)ISSN 0306-1 396October 1975PROCEEDINGSOF THEANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof the Chemical SocietyPresidentG. W. C. MilnerHon. SecretaryP. G. W. CobbSecretaryMiss P. E. HutchinsonHon. Treasurer Hon. Assistant SecretariesJ. K. Foreman D.I. Coomber, O.B.E.; D. W. WilsonEditor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members): The Chemical Society, Publications Sales Office, Blackhorse Road, Letch-worth, Herts., SG6 IHN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.@ The Chemical Society 1975Analytical Abstracts-Quinquennial IndexVolumes 11 -1 5 : 1964-1 968To be published Autumn 7975This cumulative index is in two separate parts: the Author section (912 pages) and theSubject section (579 pages). It covers 35800 abstracts of the international literatureon all branches of analytical chemistry. The comprehensive alphabetical subject indexcontains almost I00000 entries and the author index includes titles, as well as the namesof all authors.Clothbound, 9%" x 6&", set of two Volumes €70.00CS Members' price f60.00Decennial Index - Volumes 1-1 0: 1954-1 963The earlier cumulative index, also in two separate parts: author section (1033 pages)and subject section (680 pages), covers 46200 abstracts. It is being offered for alimited period at a special reduced price if ordered with the Quinquennial Index.Decennial and Quinquennial Indexes, set of four Volumes €80.00CS Members' price f65.00Orders should be sent direct, with remittance, or through your usual bookseller to-The Publications Sales Officer, The Chemical Society, Blackhorse Road, Letchworth,Herts, SG6 1 HN

ISSN:0306-1396    

DOI:10.1039/AD97512FX035

出版商:RSC    

年代:1975

数据来源: RSC

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October, 1975 ANALYTICAL DIVISION DIARY 279Analytical Division Diary, continuedNovember, continuedFriday, 14th-3 p.m.: Annual General Meeting.“Thermal Analysis and Everyday Life,” by“Does the Analyst Really Need a Thermo-R. C. Mackenzie.balance ?J’ by D. Dollimore.Saturday, 15th-“Abstract Symbolism in Thermal Analysis,”by J. H. Sharp.“Wider Horizons with Thermal Analysis,”by J. P. Redfern.The remainder of the meeting will be devotedto social activities. All members, theirwives and families will be welcome.The Grosvenor Hotel, Eastgate Street,Chester.Tuesday, 18th, 6.15 p.m. : BirminghamMidlands Region : Annual General Meeting,followed by: “Lasers and their Implica-tions in Analytical Chemistry,” by B.Sharp.The Lecture Theatre, Haworth Building, TheUniversity, Birmingham, 15.Wednesday, 19th, 2.15 p.m.: LondonParticle Size Analysis Group : Annual GeneralMeeting, followed by a meeting on “Applica-tion of Particle Size Analysis to Foodand Drugs.”“The Starch Granule : a Structured Particle,”by J.M. V. Blanshard.“Problems Experienced in the Size Analysisof ‘Intralipid’ Emulsion,” by M. J. Groves.Room N.221, Chemistry Block, ChelseaCollege, University of London, ManresaRoad, London S.W.3.Thursday, 20th, 10.30 a.m. : BirminghamRadiochemical Methods Group : AnnualGeneral Meeting and meeting on “MedicalApplications of Accelerators.”“Medical Applications of Accelerators, byD. Sylvester.“Production of Medically Useful Isotopes bythe Amersham Cvclotron.’’ bv T. D. Wright.“Cyclotron Production of Short-lived Iso-topes for Medical Use,” by J. Clark.“The Preparation of High-purity 1231, and itsClinical Use,” by J. G. Cuninghame, A. L.Nichols, K. E. Britton and H. C . Chang.“Measurement of Pb Distribution in Teeth by3He Activation,” by J. H. Fremlin.“Measurement of Pb in Biological Materialby Proton Induced X-rays,” by N. A.Dyson.“The Determination of Copper and Zinc inBone Ash Using Accelerator ProducedGamma-photons, ’’ by D. R. Williams andJ. S. Hislop.“Activation Analysis in vivo of the HumanBody Using Cyclotron Produced Neutrons,”by D. K. Bewley and D. J. Spinks.“Determination of Whole Body NitrogenThrough the in vivo Production of 11C02 byKnock-on Protons,” by B. Thomas.“Stable Isotope Tracer Measurements UsingAccelerators,” by T.B. Pierce and J. W.McMillan.2.15 p.m. : Annual General Meeting.Department of Physics, The University,Birmingham.Friday, 21st, 7 p.m.: ChepstowWestern Region.Discussion on “Autoanalyzers in Environ-mental Analysis,” to be introduced byG. Jones.George Hotel, Chepstow.Thursday, 27th, 4 p.m. : Glasgow.Sottish Region, jointly with the Glasgow andWest of Scotland Section of the CS and theAndersonian Chemical Society.“Analytical Atomic Spectrometry and theEnvironment,” by J. M. Ottaway.University of Strathclyde, Glasgow.Thursday, 27th, at 6.30 p.m.: LondonBiological Methods Group : Annual GeneralMeeting, followed by a meeting on “Aspectsof Forensic Science.”LondonAnalytical Division DiaryOCTOBERTuesday, 21st, 6 p.m.: NottinghamMidlands Region on “The Analytical Chem-istry of Glass: Its Detection, Identifica-tion and Uses.”“The Quantitative Analysis of Glass Availablein Milligram, Gram and Bulk QuantitiesUsing X-ray Fluorescence,” by D.G.Ashley.“Forensic Examination of Glass,” by R. K.Bramley .The Boots Co. Ltd., Pennyfoot Street,Nottingham.Wednesday, 22nd, 11 a.m.: ColchesterEast Anglia Region, jointly with the EasternRegion of the Industrial Division, on“Applications of Analytical Techniques toIndustrial Effluents.”“Organic Carbon and Oxygen DemandAnalyses and their Relationships in Efflu-ents,” by G. F. Lowden.“The Continuous Monitoring of EffluentsUsing Ion-selective Electrodes,” by M.E.Hofton.“Automated Analysis of Effluents; the Prosand Cons,” by F. J. Whitby.“Studies of Oils and Polycyclic AromaticHydrocarbons (PAH) in Sewage-relatedSystems,” by D. Meek.University of Essex, Wivenhoe Park, Col-Chester.NOVEMBERWednesday, 5th, 2.30 p.m. : LondonAnalytical Division on “Forensic Analysis.”“Forensic Applications of High PressureLiquid Chromatography,” by B. Wheals.“Selective Detectors in Gas Chromatography,”by J. F. Taylor.“The Characterisation of Proteins in Blood,”by P. H. Parkin.“Applications of Electron Probe Instrumentsin Forensic Science,” by R. H. Keeley.The Pharmaceutical Society, 17 BloomsburySquare, London, W.C.l.Friday, 7th, 5 p.m.: GlasgowScottish Region : Annual General Meeting,followed by: “Confessions of a PublicAnalyst,’’ by A.C. Bushnell.University of Strathclyde, Glasgow.Wednesday, 12th, 2 p.m.: LeedsNorth East Region, jointly with the NorthEast and North West Regions of theAssociation of Clinical Biochemists, on“The Work and Training of a ClinicalBiochemist.”“The Training of the Hospital Biochemist,”by C. Toothill and F. E. Harper.“Automation in Clinical Analysis,” byP. M. G. Broughton.The meeting will be followed by a tour of theTeaching Hospital Laboratories.Hugh Garland Gallery, General Infirmary,Great George Street, Leeds, LS1 3EX.Wednesday, 12th, 2.30 p.m. : LondonChromatography and Electrophoresis Group :Annual General Meeting, followed by ameeting on “Pharmaceutical Analysis.”“Electrophoretic Separation of Isoenzymes,”by D. T. Plummer.“Qualitative and Quantitative Aspects of theColumn Chromatography of Aminoglyco-side Antibiotics,” by a member of theAnalytical Chemistry Department, CentralResearch Division, Pfizer Ltd.Chelsea College, University of London,Manresa Road, London, SW3 6LX.Thursday, 13th, 6.30 p.m.: PrestonNorth West Region.“Ion-selective Electrodes,” by C. Neil.Preston.Thursday, 13th: LondonJoint Pharmaceutical Analysis Group on“Standards for Veterinary Medicines.”Speakers to include: S. F. M. Davies andProfessor R. J. Fitzpatrick.Pharmaceutical Society, 17 BloomsburySquare, London W.C.l.Friday to Sunday, 14th to 16th: Chester Thursday, 6th, 6.30 p.m.: ReadingSouth East Region and Education and Train- ’ Debate “That Teachers OfThermal Methods G ~ ~ ~ ~ : Annual GeneralMeeting and 10th Anniversary Meeting on 2%“The Role of Thermal Methods Today.” Analytical Chemistry Have Their Headsin the Clouds.” Proposers : R. F. Colemanand A. Holbrook; Opposers : L. S. Bark andD. W. Wilson.Chemistry Department, The University,Reading. [continued inside back coverPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97512BX037

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

Vol. 12 No. 10 Proceedings October 1975 of the Analytical Division of the Chemical Society Regional Advisory Editors of The Analyst Recently appointed Regional Advisory Editors for The Analyst are Dr. J . Aggett (University of Auckland, New Zealand), Professor G. Ghersini (Laboratori CISE, Milan, Italy), Dr. I. RubeSka (Geological Survey of Czech- oslovakia, Prague, Czechoslovakia) and Pro- fessor K.Saito (Tohoku University, Sendai, Japan). Biographical notes on Dr. Aggett and Dr. RubeSka are given below; biographies of Professors Ghersini and Saito appeared in the July issue of Proceedings. Dr. J. Aggett John Aggett was born in New Zealand in 1936. He was educated a t the University of Auckland, where he graduated MSc with First Class Honours in Chemistry in 1958.At this time he was awarded the Duffus Lubecki Scholarship and a Postgraduate Research Fellowship. In 1960, he graduated PhD from the University of New Zealand with a thesis on Mechanisms of Reactions of Co-ordination Compounds. Dr. J . Aggett The years 1961-62 were spent as a Research Officer in the Fuel Reprocessing Section of the Australian Atomic Energy Commission’s Research Establishment at Lucas Heights, Sydney.It was here that he was introduced to solvent extraction, an area in which he still maintains an active research interest. In 1963, the offer of a Lectureship in Chemistry brought him back to the University of Auckland, where he has remained and is now an Associate Professor. During the 1960s, he developed under- graduate courses in analytical chemistry for the Chemistry Department curriculum and has been responsible for the teaching of analytical chemistry since these courses were introduced.He was awarded the Nuffield Travelling Fellowship in Science and Humanities and spent 1970 with Professor T. S. West at Imperial College, London, working on the development of carbon filament atomisers for atomic-absorp- tion spectroscopy.This research has been continued since his return to Auckland and he is particularly interested in developing a small versatile atomiser for use where small volume rather than low concentration is the limiting factor. He has been active in the affairs of the New Zealand Institute of Chemistry for a number of years and is currently secretary and organiser of the Auckland Branch of the Analytical Chemistry Groupof the Institute.In 1967 he was elected a Fellow of the New Zealand Institute of Chemistry. Outside chemistry, he is involved with the affairs of a growing family, plays games for the middle-aged such as snooker, darts and kami- kaze chess when time permits, and is very active in promoting the cause of the intellectually handicapped.Dr. 1. Rubegka I. IiubeSka was born in 1931 in Prague, where he received all his primary and secondary schooling. He graduated in Physical Chemistry a t the Charles’ University in 1954 and received his PhD degree from the Technical University of Prague in 1962. After 2 years’ work a t the Central Agricultural Control and Testing Insti- tute in Prague, he joined the Geological Survey of Czechoslovakia in 1956.Currently he is Assistant Head of the Chemistry Department. He has been concerned mainly with the develop- ment of spectroanalytical methods for geological materials (flame spectrometry, emission spectro- graphy and, since 1962, atomic-absorption spectrometry). I n 1968-70 he served as an expert in spectrochemistry with UNESCO in Baghdad. 263264 REPORTS OF MEETINGS Proc.AnaZyt. Div. Chem. SOC. Dr. Rubegka is a member of the Czechoslovak Chemical Society and the Czechoslovak Spectro- scopic Society, currently serving as Scientific Secretary. He is also an Associate Member of Commission V/4 of IUPAC. He was Chairman Dr. I. RubeSka of the Organising Committee of the 1st Inter- national Atomic Absorption Conference, held in Prague in 1967, and is at present the Chairman of the Programme Committee of the XXth Colloquium Spectroscopicum Internationale and the 7th International Conference on Atomic Spectroscopy to be held jointly in Prague in 1977. He is married with one daughter and his leisure activities are divided between tennis, skiing and veteran rowing.

ISSN:0306-1396    

DOI:10.1039/AD9751200263

出版商:RSC    

年代:1975

数据来源: RSC

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264 REPORTS OF MEETINGS Proc. AnaZyt. Div. Chem. SOC. Electrophoretic Analysis,” by P. H. Corran ; “Problems with Polymorphism of Medicinal Compounds,” by A. Clements; “Analysis of Drugs in Forensic Science,” by F. Fish; “Quality Control of Plastics Used in Pharmaceutical Packaging,” by J. E. Pentelow ; “Control of Low Level Cross-contaminants by TLC,” by J . D. Edmond; “Some Assay Methods in the Measurement of Bioavailability of Drugs in Man,” by A.Bye. Reports of Meetings Ordinary Meeting An Ordinary Meeting of the Division, organised by the Scottish Region and in conjunction with the Joint Pharmaceutical Analysis Group, was held on Tuesday and Wednesday, September 16th and 17th, 1975. The subject of the meeting was “Develop- ments in Pharmaceutical Analysis” and the following papers were presented and discussed : “Recent Advances in Pharmaceutical Analysis- Do We Really Need Them ?” by C.A. Johnson; “Quality Assurance Systems in the Pharma- ceutical Industry,” by W. M. Walker; “Enzy- matic Assay Methods for Pharmaceutical Quality Control,” by A. F. Fell and D. R. Stevenson; “Automation in the Analysis of Drugs,” by J . W. Murfin; “The Fluorimetric Analysis of Oestrogens in Oral Contraceptive Preparations,” by J.H. McB. Miller and P. Duguid; “Recent Applications of HPLC in Pharmaceutical Analysis,” by J . H. Knox; “A Review of Applications of Derivative Formation in the Quantitative Gas Chromato- graphic Analysis of Pharmaceuticals,” by J . D. Nicholson; “Recent Developments in CS Autumn Meeting The Division participated in the CS Autumn Meeting on Thursday, September 25th, 1975, at the University of Reading. The subject of the Division’s Symposium, held in conjunction with the Education Division, was “Trends in Education in Analytical Chemistry.” The following papers were presented and discussed : “Teaching of Analytical Chemistry- Past, Present and Future,” by J.A. W. Dalziel; “Sixth Form Chemists and Higher Education,” by J.N. Lazonby; “Attitudes of School Students to the Study of Chemistry,” by B. A. Henman ; “Analytical Chemistry in Schools : the Dying Art,” by M. Vokins; “The Future- Analyst or Technician,” by B. J . Holland; “Putting the Chemistry into Analytical Chem- istry,” by R. A. Chalmers; “Design of Practical Courses in Analytical Chemistry,” by I.L. Marr ; “Recent Trends in the Postgraduate Education of Analytical Chemists,” by Professor D. Thor- burn Burns; “Analytical Chemistry in CNAA Undergraduate and Postgraduate Courses,” by J . A. Sandbach; “Analytical Chemistry for the Iron and Steel Industry,” by T. S. Harrison; “The Future of the RIC Postgraduate Qualification : MChemA,” by R. Sinar ; “Post- graduate Training in Clinical Chemistry,” by D.B. Horn; “Should Albert Woods be Encouraged to Struggle for a PhD in Analytical Chemistry?” by D. Betteridge. The Symposium concluded with a Discussion Panel, at which the Chair was taken by Mr. J . K. Foreman, Honorary Treasurer of the Division. The Discussion was led by R. C. Denney, G. Nickless, J . G. Pritchard and A. Townshend. Microchemical Methods, Atomic Spectroscopy and Radiochemical Methods Groups A Joint Meeting of the Microchemical Methods, Atomic Spectroscopy and Radiochemical Methods Groups was held on Monday and Tuesday, September 22nd and 23rd, 1975, at the British Museum, London, W.C.l.October, 1975 ORIGINAL PAPERS IN PHARMACEUTICAL ANALYSIS 265 The subject of the meeting was “Analysis in Archaeology, Art and Antiquities,” and the following papers were presented and discussed : Plenary Lecture-“ Analysis and Archaeology, ” by J.Musty ; “Thermoluminescence Dating,” by M. J . Aitken; “Mossbauer Spectroscopy in Archaeology,” by N. J. Seeley; “X-rays and Antiquities,” by H. Barker; “Electron Micro- probe Analysis,” by R. E. M. Hedges; “Acti- vation Analysis and Archaeometry,” by G.R. Gilmore ; “Potential Analysis of Museum Objects by ESCA,” by M. Thompson. Microchemical Methods Groups A Meeting of the Elemental Analyser User Forum was held at 2 p.m. on Wednesday, September 17th, 1975, a t the City of London Polytechnic, 100 Minories, London, EC3N 1 JY. The Chair was taken by the Chairman of the Group, Mr. R. Sawyer. A discussion on “The Determination of Oxygen” was introduced by S.Bance and C. J. Howarth. Particle Size Analysis Group An Ordinary Meeting of the Group was held at 2.15 p.m. on Thursday, September llth, 1975, in the University of Technology, Loughborough. The Chair was taken by the Chairman of the Group, Dr. W. Cam. The subject of the meeting was “Photo- extinction and Light Scattering Techniques” and the following papers were presented and dis- cussed : “The Photosedimentation Technique,” by T.Allen; “Aerosol Sizing and Holography,” by T. Bishop. Joint Pharmaceutical Analysis Group An Ordinary Meeting of the Group was held in conjunction with the British Pharmaceutical Conference 1975 a t 2.30 p.m. on Wednesday, September loth, 1975, at the University of East Anglia, Nonvich. The Chair was taken by the Chairman of the Group, Mr. G. F. Phillips. The subject of the meeting was “Bio-analy- tical Techniques Used in Pharmaceutical Analysis” and the following papers were pre- sented and discussed : “Mass Fragmentography,” by I. Midgley ; “Radioimmunoassay,” by A. Sabey ; “Electrophoresis,” by P. H. Corran.

ISSN:0306-1396    

DOI:10.1039/AD9751200264

出版商:RSC    

年代:1975

数据来源: RSC

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October, 1975 ORIGINAL PAPERS IN PHARMACEUTICAL ANALYSIS 265 Original Papers in Pharmaceutical Analysis The following are summaries of four of the papers presented at a meeting of the Joint Pharma- ceutical Analysis Group held on June 5th 1975. Determination of Quinine Bisulphate by Non-aqueous Titration G. Carr British Pharmacopoeia Commission, 8 Bulstrode Street, London, W 1M 5FT Quinine salts are still widely used as anti-malarials and as such are featured in many pharmaco- poeias.Monographs for quinine salts have been featured in the British Pharmacopoeia for many years, quinine bisulphate first appearing in the 1932 edition. The current BP mono- graph contains identification tests based on chemical tests for quinine and the sulphate ion, and the blue fluorescence of aqueous solutions.Physical tests include measurements of specific optical rotation and pH. The related impurity test is a thin-layer chromatographic test for other cinchona alkaloids and there is an assay that consists of a non-aqueous titration with perchloric acid. The non-aqueous titration consists of a simple acid - base titration but is carried out in a levelling solvent, e.g. , acetic acid, in order to enhance the basic character of the alkaloid and thereby obtain sharper end-points than are observed in aqueous conditions.In pharmaceuti- cal preparations, the alkaloid ingredients are often present in the form of sulphate or halide salts. As these anions are reasonably basic in acetic acid media, an assay can be conveniently carried out by directly titrating these anions.In the case of a sulphate, it is found that sul- phuric acid is too acidic for the reaction to proceed to completion and it is found that this ion266 Proc. Analyt. Div. Chem. SOC. will only titrate as far as HSO,-, consuming 1 mol of perchloric acid. However, sharp end- points are usually still obtained. This direct method of titration could be criticised on the basis that it is only assaying a counter ion.The species that is the active ingredient in the pharmaceutical preparation is a pro- tonated base and can take no part in the reaction. If the assay is to be thorough, the free alkaloid should first be liberated and then titrated with perchloric acid. In the BP 1973 monograph for quinine bisulphate, the titration is carried out directly on the salt in acetic anhydride.1 This solvent is used because the salt is a heptahydrate and water interferes with the end-point.As both of the nitrogen atoms in quinine are tertiary, there is no risk of acetylation. In the BP 1968, a quinine salt is determined by extraction of the base, which is then determined gravimetrically.2 A sample of quinine bisulphate was recently received at the BP Laboratory that was found to assay at only 94 per cent.by the current BP method. By the BP 1968 method, it gave a satisfactory result and similarly it was satisfactory when the free base was determined by titration with perchloric acid after extraction. The likely explanation was contamination with some free quinine or quinine sulphate, but neither of these explanations could be correct. As the sulphate ion will only titrate to the HSO,- ion, 1 mol of quinine bisulphate is equivalent to 1 mol of perchloric acid.Quinine base, containing two basic nitrogen atoms, will consume 2 mol of perchloric acid and quinine sulphate, consisting of two singly protonated quinine molecules and a sulphate ion, will consume 3 mol. Therefore, any contamination by these species would lead to high assay results.Similarly, contamination with a hydrochloride salt would lead to high results. This species would not be expected to titrate with perchloric acid. Although this is not one of the more commonly encountered quinine salts, it has been known for many years and has been called the tetra~ulphate.~ If our sample of quinine bisulphate were contaminated with 6 per cent.of the tetrasulphate, it would assay at 94 per cent. by the current BP method. If the free base were first extracted, however, a different result would be obtained and in fact the sample would assay only about 1 per cent. low, which was the observed result. In order to confirm this result, the sample was titrated as an acid against sodium hydroxide solution with phenol- phthalein as the indicator. Quinine bisulphate is equivalent to 2 mol of sodium hydroxide as it is doubly protonated.Quinine tetrasulphate is also doubly protonated but the two HS04- ions will titrate to SOZ- so it is equivalent to 4 mol of sodium hydroxide. A sample of bisul- phate containing 6 per cent. of tetrasulphate would be expected to assay at about 104 per cent., which was the observed result.Although the technique of assay of a counter ion was previously criticised, it could be claimed to have identified a bad sample. However, in this monograph there is also a pH requirement and although the allowed limits seem to be very wide (2-8-3.8), it was found that this sample gave a result of 2.61 whereas good samples gave results between 2-94 and 3.03.The validity of this test could be questioned because of the wide pH tolerance and it is sug- gested that a means of dealing with this monograph would be to introduce a double assay. The free base could be liberated with sodium hydroxide and titrated with perchloric acid and then the amount of sodium hydroxide required could be determined by a back-titration with hydrochloric acid.References ORIGINAL PAPERS IN PHARMACEUTICAL ANALYSIS A species that could lead to the low result is the structure Quinine2+.2HS0,-. 1. 2. 3. “British Pharmacopoeia 1973,” H.M. Stationery Office, London, 1973, p. 408. “British Pharmacopoeia 1968,” H.M. Stationery Office, London, 1968, p. 860. Henry, T. A., “The Plant Alkaloids,” Fourth Edition, Churchill, Edinburgh, 1949, p.423. The British Pharmacopoeia Determination of Alcohol A. Islam British Pharmacopoeia Commission, 8 Bulstrode Street, London, W l M 5FT Until 1973 the method of determination of alcohol in galenical preparations prescribed by the British Pharmacopoeia has been a quadruple bulk distillation procedure. In the currentOctober, 1975 ORIGINAL PAPERS I N PHARMACEUTICAL ANALYSIS 267 edition this has been replaced by a gas-chromatographic method, recommended by the appropriate Pharmacopoeia1 committee after due investigation and scrutiny of the literature (notably the paper by Ellis and Wraggl). The gas-chromatographic method was adopted as the official procedure because of its rapidity and simplicity.It was recognised, however, that some might wish to continue using the distillation method, and this they would be at liberty to do, except in instances of dispute, by virtue of the dispensation given in the General Notices to the Pharmacopoeia that alternative methods of assay or test may be used provided that the analyst is satisfied that the method he uses will give a result of equivalent accuracy.Some time after the gas-chromatographic method became official a number of different opinions arose as to the content of alcohol in certain preparations. It was asserted that the gas-chromatographic method gave generally higher values than distillation and for a sample of one preparation it was shown that the content found by use of gas chromatography was higher than could be accounted for by the amount of alcohol used.These differences focused renewed attention on the validity of the gas-chromatographic method and although it was shown that some of the apparently high results were due to the use of a standard alcohol solution that had not been freshly prepared and that was weaker than had been believed some doubts as to the comparability of the distillation and chromatographic methods remained. It was therefore decided to carry out a small collaborative test under the auspices of the British Pharmacopoeia Commission.The test and the conclusions drawn from it are now described. The author stresses that he was but one of the participants in the study and that he was simply an instrument to present this work on behalf of all the collaborators, whose names and affiliations are given at the end of this paper and to whom the British Pharmacopoeia Commission is indebted.Each participant was asked to carry out duplicate determinations on three pharmaceutical preparations by use of the two methods. The three preparations were selected in such a way as to require Methods I , I1 and I11 of the distillation procedure given in the British Pharma- copoeia 1968.For the gas-chromatographic method it was noted that certain specific criticisms of the procedure given in Appendix X of the British Pharmacopoeia 1973 had been made (see, for example, reference 2), although in the opinion of some these criticisms resulted more from personal preference than from scientific necessity. To test whether these variations had a significant effect participants were asked to choose the most appropriate conditions for chromatography on the instrument they had available but were requested to use a column of either Porapak Q or Chromosorb 101.Four of the seven laboratories carrying out the chromatographic method used Porapak Q, two used Chromosorb 101 and one used Nonidet P40 on Teflon 6.The column temperatures employed varied from 70 to 175 "C and the sample dilutions used for injection varied from 1 to 10 per cent. To the purist in the art of collabora- tive studies such licence is no doubt disquieting but to the practical scientist, if it could be shown that these variations had no great effect on the result obtained, the flexibility and reliability of the gas-chromatographic method would be established.In each of the tables the contents of alcohol are expressed as per cent. V/V and the values shown are from two individual determinations. The results obtained by gas chromatography were all calcu- lated by measurement of peak areas. In a number of instances results were also calculated by measurement of peak height but this gave less satisfactory reproducibility.In Table I the results are given for a sample of Weak Iodine Solution BP, chosen as representative of Method I of the distillation procedure. The over-all mean results were 87.3 per cent. by gas chromatography, with a coefficient of variation of 0-85 per cent., and 86.7 per cent. by distillation, with a coefficient of variation of 1.43 per cent.With only two results from each laboratory, the within-laboratory variation could not be calculated but this variation appears to be reasonable. The coefficients of variation quoted were calculated using the mean values, thus putting equal weight on each collaborator but disregarding within-laboratory variation. Attention should be drawn, however, to two figures : 83.8 per cent.obtained by laboratory 1 when using the distillation method; and 88.7 per cent. obtained by laboratory 3 when using the gas-chromatographic method. Inspection alone seems to indicate that these results are out of line with those obtained by other laboratories and it will be seen that these two laboratories produced apparently anomalous results by use of distillation and of gas chromatography, respectively, in each of the three instances.Labora- tory 1 admitted to having only a very occasional need to use the distillation method and The results obtained are now presented in condensed form.268 ORIGINAL PAPERS I N PHARMACEUTICAL ANALYSIS Proc. AnaZyt. Div. Chem. soc. TABLE I DETERMINATION OF ALCOHOL I N W E A K IODINE SOLUTION BP Mean alcohol content, per cent.V/V Laboratory Gas chromatography Distillation r A \ 1 87.4, 86.7 83.6, 84.0 2 87.1, 86.4 86.7, 87.0 3 88.5, 88-9 87.0, 87.4, 87.5, 87-1 4 86.8, 86.4 86.8, 87-1 5 87-9, 87.6 87.4, 87-6 6 87.1, 87.3 87-1, 87-1 7 86-7, 86.8 86.4, 86.4 87-7, 87-8 8 - Mean .. .. .. 87.3 86.7 Standard deviation . . .. 0.74 1.24 Coefficient of variation . . 0.85 1-43 Corrected mean . . .. 87.0 87.1 Standard deviation .. .. 0.42 0.43 Coefficient of variation . . 0.48 0.50 then not on a routine basis and laboratory 3, obtaining consistently high results by gas chromatography, was one in which apparently high results had originally been noted. By using Youden’s sum rank limit test3 these laboratories were found to exceed the acceptable limit and hence their results were rejected.The corrected mean values (distillation results from laboratory 1 and chromatographic results from laboratory 3 having been omitted) were determined and the coefficients of variation re-calculated. The alcohol content by gas chrom- atography now becomes 87.0 per cent., with a coefficient of variation of 0.48 per cent., and that by distillation becomes 87.1 per cent., with a coefficient of variation of 0.50 per cent.There is clearly no practical difference between these two mean values or in the precision of the two methods. TABLE I1 DETERMINATION OF ALCOHOL IN CAMPHORATED OPIUM TINCTURE BP Mean alcohol content, per cent. V/V w I Laboratory Gas chromatography Distillation 1 58.1, 58-0 56.6, 56.5 2 57.7, 58-7 58.1, 57.5 3 594, 59.7 58.4, 58.3, 58.3, 58.1 4 58.3, 58-5 58.3, 58.2 5 58.8, 58.8 57.2, 57-6 6 58.8, 59.2 57.2, 57.3 7 58.0, 58.0 57.3, 58.0 8 - 58-3, 58.3 Mean .... .. 58.6 57.7 Standard deviation . . .. 0.57 0.62 Coefficient of variation . . 0.98 1.07 Corrected mean . . .. 58.4 57-9 Standard deviation . . .. 0.41 0.45 Coefficient of variation . . 0.70 0.77 Table I1 shows a summary of the results obtained with Camphorated Opium Tincture BPI a preparation requiring Method I1 of the distillation procedure, and it can be seen that the situation is very similar to that shown in Table I.Again the distillation results from labora- tory 1 and the chromatographic results from laboratory 3 were rejected and the corrected mean results were 58.4 per cent. by gas chromatography, with a coefficient of variation of 0.70 per cent., and 57.9 per cent.by distillation, with a coefficient of variation of 0.77 per cent. Student’s t-test was applied to show that there is no significant difference between the two mean values, although it is recognised that with the limited data available the t-test would be unlikely to reveal a small bias if one should exist. Snedecor’s F-test confirms that the precisions of the two methods are not significantly different.October, 1975 ORIGINAL PAPERS I N PHARMACEUTICAL ANALYSIS 269 Compound Cardamom Tincture BP was chosen as representative of Method I11 of the dis- tillation procedure and the results are presented in Table 111.Again, certain results from the two laboratories previously referred to were rejected after application of Youden’s sum rank limit test and the corrected mean results were found to be 53-7 per cent.by gas chromato- graphy, with a coefficient of variation of 0-76 per cent., and 53-3 per cent. by distillation, with a coefficient of variation of 1.02 per cent. Again, statistical examination shows that there is no significant difference between these mean values or in the precision of the two methods. One cannot help noticing, however, that the coefficient of variation for the two methods (numerically very similar for preparations 1 and 2) is somewhat higher by distillation than by gas chromatography for preparation 3.It would not be surprising if there were a genuine difference in precision for Compound Cardamom Tincture BP, for which the dis- tillation method involves a double distillation and an extraction stage.In this connection it is interesting to note that Ellis and Wraggl reported that losses of alcohol occurred with this method. DETERMINATION OF TABLE I11 ALCOHOL IN COMPOUND CARDAMOM TINCTURE BP Mean alcohol content, per cent. V/V Laboratory 1 2 3 4 5 6 7 8 Mean .. .. Standard deviation . . Gas chromatography 53.9, 53.7 53.1, 53-1 54.7, 54.9 53.7, 54-3 53.9, 53-9 54.0, 54-3 53.5, 53-1 - ..53.9 .. 0.56 1 Distillation 52.1, 52.2 53.7, 53.7 53.9, 53-5, 53-8, 53-5 53.7, 53.7 52-5, 52-6 52.4, 52.6 53.4, 53.4 534, 53.7 53.2 0-65 Coefficient of variation . . 1.04 1-22 Corrected mean . . .. 53.7 Standard deviation . . .. 0.41 Coefficient of variation . . 0.76 53.3 0.54 1.02 In conclusion, it is considered that this small collaborative test has demonstrated that a method based on gas chromatography is capable of yielding results for the alcohol content of galenical preparations that are comparable with those which can be obtained by the long established distillation methods. On the basis of these findings the British Pharmacopoeia Commission has decided to retain a gas-chromatographic method of determination as its official procedure for the determination of alcohol but it recognises that improvements in the description of the method as currently set down might be possible.The fact, however, that diverse conditions used in the present study have given such good concordance suggests that amendments to the basic conditions proposed are not essential but that additional detail might be needed.The Commission would welcome suggestions from any quarter as to how the method might be improved. Collaborators in this study were: Mr. J. B. Cooper (Evans Medical Ltd.); Mr. M. J. de Faubert Maunder (Laboratory of the Government Chemist); Mr. B. Evans (Department of Trade and Industry); Mr. J. F. Fernie (ICI Pharmaceuticals Division); Dr.D. C. Garratt (Pharmaceutical Society of Great Britain) ; Professor W. G. Overend (Department of Chemis- try, Birkbeck College); Mr. M. Ransom (William Ransom & Sons Ltd.); Mr. A. N. Sherlock (Bush Boake Allen Ltd.) ; Mr. F. H. Tresadern (Bush Boake Allen Ltd.) ; and Mr. J. S. Wragg (Research Department, The Boots Co. Ltd.). References 1. 2. 3. Ellis, J. R., and Wragg, J. S., Analyst, 1970, 95, 16.Couldry, S. P., and Greenwood, N. D., Pharm. J., 1974, 212, 4. Youden, W. J., “Statistical Techniques for Collaborative Tests,” Association of Official Analytical Chemists, Washington, D.C., 1969, pp. 27-29.270 Determination of Sodium Valproate and Sulthiame in Plasma by Gas - Liquid Chromatography and the Study of Their Interaction with Diphenyl hydantoin ORIGINAL PAPERS IN PHARMACEUTICAL ANALYSIS Proc.AnaZyt. Div. Chem. SOC. P. N. Patsalos, V. D. Goldberg and P. T. Lascelles Department of Chemical Pathology, Institute of Neurology, The National Hospital, Queen Square, London, W C l N 3BG As many epileptic patients receive multiple-drug therapy, it is important to know the degree of interaction that occurs between certain anticonvulsant drugs.By using the Perkin-Elmer F30 gas - liquid chromatograph it is possible to determine the plasma concentrations of sodium valproate and sulthiame, and to study the interactions of these anticonvulsants with diphenylhydantoin (DPH) in humans and experimental animals. Sodium valproate can be determined quickly and conveniently by the method of Toseland,l which involves a single extraction with diethyl ether of plasma acidified with 2 N orthophos- phoric acid, with the addition of hexanoic acid as internal standard.Plasma proteins present in the ether extract are precipitated with ammonium sulphate, the precipitate is discarded and the drug is converted into its potassium salt by addition of potassium hydr- oxide. The extract is then evaporated to dryness under oxygen-free nitrogen.After acidi- fication with formic acid, 1-p1 portions of the extract are injected into a 3-ft column packed with 2 per cent. WG-11 on Chromosorb W (HP), 80-100 mesh, or Gas-Chrom Q. Nitrogen is used as carrier gas and the peaks are resolved at a flow-rate of 50 ml min-l and an oven temper- ature of 112 "C. This method has been adapted in this laboratory for the determination of sodium valproate in rat brain.Brain tissue is first homogenised with acidified diethyl ether in a tissue extractor in the presence of internal standard; sodium sulphate is used as the protein precipitant instead of ammonium sulphate because it is also a drying agent. Our method for the quantitative determination of sulthiame differs from the conventional methods involving multiple-step extraction, which have so far proved unsuitable for sulthiame.The method involves asingle extraction with chloroformof untreated plasma to which 5-((p-tolyl)- 5-phenylhydantoin is added as internal standard. The chloroform extract is evaporated to dryness under oxygen-free nitrogen at room temperature and is then methylated with tetra- methylammonium hydroxide.Aliquots (1-p1) of the extract are injected, 10-20 min later, into a 6-ft column packed with 3 per cent. OV-1 on Chromosorb W(HP), 80-100 mesh. Nitro- gen is used as carrier gas and the peaks are resolved at a flow-rate of 50 ml min-l at an oven temperature of 195 "C. Under these conditions, sulthiame appears as two symmetrical peaks on the gas - liquid chromatogram.Standard graphs can be constructed by using either or both of these peaks. In man, the major urinary metabolite of DPH is 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) 2,3 with small amounts of 5-(m-hydroxyphenyl)-5-phenylhydantoin (m-HPPH). Dihydroxyphenyl-5-phenylhydantoin (di-HPPH) was also detectable. In the rat, the m-HPPH and the di-HPPH metabolites are more prominent, with relatively small amounts of the (p-HPPH metabolite.After hydrolysis with concentrated hydrochloric acid in order to release the metabolites from their conjugated form with glucuronic acid they can be deter- mined easily by the method of To~eland.~ . Urine samples taken from patients on DPH and other anticonvulsants before and after commencement of treatment with sodium valproate in addition to these drugs were analysed.No inhibition of hydroxylation in these already highly induced patients was produced by sodium valproate, as assessed by measurement of the (p-HPPH to DPH ratio. In rats injected intraperitoneally with DPH for 7 d and with DPH and sodium valproate for a further 6 d, 24-h urine samples also showed no inhibition. These results should be considered in conjunc- tion with those of experiments performed with rats by Sapeika and Kaplan,5 who demonstrated that sodium valproate caused no significant induction of liver microsomal cytochrome P450.By contrast, we found that when rats were injected with DPH for 7 d and with DPH and sulthiame for a further 6 d, a pronounced decrease in the (p-HPPH to DPH ratio was observed, which implies that DPH metabolism is inhibited by sulthiame. If this is so, a rise in blood DPH levels would be expected and this, in fact, was observed.Further, an increase in both the concentration and the 24-h total excretion of unmetabolised DPH in rat urine was observed.October, 1975 ORIGINAL PAPERS I N PHARMACEUTICAL ANALYSIS 271 These results, together with those of Houghton and Richens,6 suggest that sulthiame or one of its metabolites inhibits the para-hydroxylation of DPH, as originally proposed by Hansen et nZ.7 References 1.Toseland, P. A., personal communication, 1974. 2. Butler, T. C., J . Pharmac. Exp. Ther. 3. Chung, T., and Glazko, A. T., in Woodbury, D. M., Kiffin Penry, D. J., and Schmidt, R. P., Editors, 4. Toseland, P.A., personal communication. 5. Sapeika, N., and Kaplan, E. R., Res. Commun. Chem. Path. Pharmac., 1975, 10, 767. 6. Houghton, G. W., and Richens, A., Br. J . Clin. Pharmac., 1974, 1, 59. 7. Hansen, J. M., Kristensen, M., and Skovsted, L., Epilepsia, 1968, 9, 17. 1957, 119, 1. “Anti-epileptic Drugs,” Raven Press, New York, 1972, p. 149. A Single Thin-layer Chromatography System for Foreign Alkaloids in Morphine, Codeine and Papaverine P.C. Barrett Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ Certain opiates have been widely used in medicine as analgesics. Opium contains about 20 alkaloids, which constitute about 25 per cent. of its total weight. The approximate pro- portions of the five major opiates are morphine, 10-16; codeine, 2; papaverine, 2; noscapine, 4-9; and thebaine, 1 per cent.Opium is used as a source of the first three opiates, which are readily extractable. However, in order to satisfy demand, codeine is usually prepared semi- synthetically by the methylation of natural morphine, but this reaction also yields some dimethylmorphine. As in all preparations of natural products, there is a need to monitor related substances and the speed and experimental simplicity of thin-layer chromatography render it a very convenient method when limit tests rather than precise content are required.A number of solvent systems for thin-layer chromatography have been variously recommended for the different opiates : (i) benzene - ethyl acetate - diethylamine (80 + 20 + 5) (ii) chloroform - ethanol - acetone - ammonia (25 + 10 + 10 + 1) (iii) chloroform - benzene - methanol - ammonia (20 + 20 + 5 + 1) (iv) chloroform - acetone - ammonia (25 + 20 + 1) (v) toluene - ethyl acetate - diethylamine (70 + 20 + 10) In all of the systems studied, thin-layer plates of commercially pre-coated silica gel incor- porating a fluorescent indicator were used.Table I shows the RF values of the alkaloids in the various systems.TABLE I MEAN R F x 100 VALUES OF ALKALOIDS UNDER STUDY Solvent system r 1 Alkaloid 0) (ii) (iii) (iv) (v) 61 Noscapine 48 73 59 - Papaverine 33 73 55 - 46 Thebaine 32 54 37 27 45 Dimethylmorphine - 51 - 22 41 Codeine 9 35 13 7 21 Morphine 1 15 5 2 3272 Proc. Analyt. Div. Chem. SOC. System (i), which has been used in this Laboratory to determine the alkaloid composition of papavereturn injections, with1 and without2 added hyoscine, and adulterated diamorphine,l was found to give a good opiate spread.However, papaverine remained unresolved from the- baine, benzene is considered to be a health hazard and the mobile phase was found to discolour rapidly. In system (ii), which is recommended3 for morphine congeners, the alkaloids were found to have much higher RF values than in system (i), although in this instance papaverine and noscapine were unresolved.There have also been reports4 of explosions in waste solvent reservoirs containing this mixture. System (iii), which has been used for papaverine impurities, was found to have no advantages over systems (i) and (ii).System (iv) was specifically recommended3 for the determination of dimethylmorphine impurities in semi-synthetic codeine. It was confirmed that dimethylmorphine runs suffi- ciently far in front of the codeine to permit its determination. However, codeine masks any slower running morphine and it has been reported that the codeine loading alters the size of the dime t h ylmorphine spots.System (v), in which toluene replaces benzene in another BPC ~ y s t e m , ~ was recommended6 for morphine impurities. The mobile phase was usable for at least 1 d after initial mixing. Thebaine and papaverine were not completely resolved but while dimethylmorphine and codeine had the same relative positions as in system (iv), they both had much higher RF values and codeine was well separated from morphine.System (v) appears to be useful for determining the major opiates in the presence of excess of morphine as papaverine and thebaine are adequately separated, provided that the loading of either is not excessive. Any of the major opiates present in papaverine could also be determined, except for thebaine, which could be readily made visible by running a separate plate in system (ii).It was concluded that, of the systems studied, (v) had the most universal application for determining impurities in morphine, codeine and papaverine preparations. The limits of visual detection of the alkaloids as cited in Table I1 were determined by using system (v) and development with (a) short-wavelength ultraviolet radiation, (b) acidified iodoplatinate spray and (c) Dragendorff reagent spray.ORIGINAL PAPERS IN PHARMACEUTICAL ANALYSIS TABLE I1 VISUAL DETECTION LIMITS OF THE MAJOR OPIATES Detection limit/pg r 1 Alkaloid UV (254 nm) Acidified iodoplatinate Dragendorff Morphine 0.5 1.0 - Noscapine 1.25 1.0 3 Dimethylmorphine 1-25 0.5 2 Papaverine 0.5 0.5 0.5 Thebaine 1.0 0.8 1 Codeine 0.8 0.6 2-5 It is assumed that a laboratory that regularly checks foreign alkaloids present in morphine, codeine or papaverine will have available or can readily acquire reference samples of the other opiates. However, for other laboratories, and certainly in tests that might be officially adopted, it is desirable to minimise the number of official authentic specimens that need to be circulated, especially the controlled drugs thebaine and dimethylmorphine.Hence, it would be preferable to determine the nature and approximate content of a foreign alkaloid by measuring its RF value and its intensity in comparison with a reference marker. The following reference solutions were used : (a) a solution of noscapine hydrochloride, thebaine and dimethylmorphine with each free (b) a solution of morphine hydrochloride, papaverine hydrochloride and codeine phosphate (c, d, e) solutions individually containing 100 pg pl-l of codeine, morphine and papaverine, base concentration equivalent to 1 pg pl-l; with each free base concentration being 0.5 pg pl-1; respectively.October, 1975 ON-LINE CHEMICAL ANALI‘SIS 273 Separate 5-pl additions were made of c, d and e to a silica plate and each spot was carefully overspotted with 5 p l of a.The plate was developed in system (v) and the “impurity” alkaloids a t the 1 per cent. level were readily made visible, except for the thebaine in the main papaverine chromatogram. The 5-pg spots were compared visually with those on a separate plate, prepared by 1-10-p1 serial additions of b. The amounts of 5 pg of minor alkaloid that were matched by markers codeine and papaverine are shown in Table 111.There was no evidence of codeine altering the size of the dimethylmorphine spots although the heavy codeine loading modified the RF value of dimethylmorphine slightly (0.44 instead of 0.42). TABLE I11 MICROGRAMS OF MARKER APPARENTLY EQUIVALENT TO 5 pg OF NAMED ALKALOID (AS BASE) UV (254 nm) Acidified iodoplatinate Dragendorff -vw Alkaloid Papaverine Codeine Papaverme Codeine Papaverme Codeine - 1 Noscapine 1.5 4.5 2.5 - Thebaine 1.7 4.8 - 2.5 4 5 - Dimethylmorphine 1.2 3.8 - 4.0 3 - System (v) was used to study various nominally pure samples of morphine, codeine and papaverine. A morphine sulphate sample was estimated to contain 1.8 per cent. of codeine and a codeine hydrochloride specimen 0.5 per cent. of dimethylmorphine. No foreign alka- loids were detected in a papaverine specimen when chromatographed in systems (v) and (ii). I t is concluded that system (v) should be recommended as a uniform limit test for impurities in morphine, natural and synthetic codeine and, with a slight modification, papaverine. It is also of use for more complex mixtures such as papaveretum injections. Both manufacturing quality control and public laboratories could find the system useful as it is rapid, sensitive and inexpensive. This investigation formed part of a continuing programme giving technical advice and support to British and European Pharmacopoeia Commissions. This paper is published with the permission of the Government Chemist and of the British PharmacopDeia Commission. 1. 2. 3. 4. 5. 6. References “Report of Government Chemist 1971,” H.M. Stationery Office, London, 1972, p. 16. “British Pharmaceutical Codex 1973,” Pharmaceutical Press, London, 1973, Appendix 5B : TLC Ritchie, D., personal communication. King, H. K. Cherny Ind., 1970, 55. “British Pharmaceutical Codex 1973,” Pharmaceutical Press, London, 1973, Appendix 5B : TLC The Laboratories of the Boots Company-, personal communication. System B. System A.

ISSN:0306-1396    

DOI:10.1039/AD9751200265

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

October, 1975 ON-LINE CHEMICAL ANALI'SIS 273 On-line Chemical Analysis The following is a summary of one of the papers presented at a Joint Meeting of the Automatic Methods and Electroanalytical Groups held on December 5th, 1974, and reported in the February, 1975, issue of Proceedings (p. 42). Application of Phase Boundary Detectors to Automatic Chemical Ana I ysis P. B. Stockwell Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ It is often necessary to sense phase boundaries, for example in the reading of a burette or the operation of a separating funnel.Achieving this function automatically is useful in the274 ON-LINE CHEMICAL ANALYSIS Proc. Annlyt. Div. Chew. soc. control of automatic analytical systems or for actuating an alarm or safety device when a control parameter exceeds defined limits.There is often a significant difference in one or more of the physical characteristics of the phases. Sensors must have a rapid response and be reliable, economic and simple to operate. They must not react with any of the materials that surround them or introduce any components into the system that might give erroneous analytical results.For preference, the sensor should be situated external to the containing vessel but this places constraints on the vessel construction and the size of the sensor itself. Methods of Phase Boundary Detection Changes in conductivity can be used to control a valve and retain the upper phase in the vessel, which is the basis of an automatic solvent extraction system developed at AWRE.l This method has been used in a number of applications involving automatic separations by solvent extraction.A problem experienced with this type of sensing device is corrosion, which subsequently leads to failure. Corrosion can be overcome either by mounting the electrodes in a removable fashion or by introducing a cleaning cycle into the procedure.An additional problem associated with such devices is the potential explosion hazard with highly volatile solvents. This hazard can be avoided by the use of solvent with a high flash point,3 or a different sensing device. Another form of sensor, marketed by Fisons Ltd., is based on electrical capacitance. It is small and compact and can be used to sense temperature, level, flow, pressure and position.The sensing head incorporates a clip that will fit most types of thermometer and that can easily be modified for attachment to the side of larger vessels. The efficiency of the detector depends on the difference in dielectric constants of the two phases; for air and mercury it is ideal, but when the difference is very small the sensor must be adjusted.At high sensitivity, the sensor will respond too readily to external influences unless adequate screening is provided, giving an unacceptable increase in the size of the detector. When dealing with two phases of widely differing colour, a sensor based on transmission would be suitable, but this is not generally possible. The difference in refractive index has been used by Porter et aL4 Light is transmitted via a light guide to one face of the rectangular tube and passes through the liquid to a second light guide, which carries the refracted beam on to a small silicon solar cell. The second light guide is adjusted with one phase in the cell to produce the maximum response and with the second phase in the cell only scattered light is directed on to the solar cell.Care must be taken to keep the tube clean, as failure to do so will cause a drift in the background response. A pH electrode can be used as a sensing device provided that there is a difference in pH between the two phases measured against a reference electrode. It is both slow to respond and of limited application, particularly when organic solvents are used. Ion-selective electrodes can be considered in a similar fashion.Thermistor probes carrying a small current dissipate heat at a rate that is dependent on the surrounding medium. A change of surrounding medium causes a change in current flowing through the thermistor. The response is also a function of flow-rate of the medium over the thermistor, which restricts its applications. If an ultrasonic probe is placed in one side of a tube containing liquid, sound waves are reflected from the opposite wall.Pulsing the transducer allows the reflected wave to be monitored. Industrial Applications The systems discussed above are designed for use in an analytical environment but it is worthwhile to consider some industrial designs and their applications. Conductivity varies with depth and applications abound in the milk, water and sewage industries. Probes at different depths are used in order to control the flow of liquid between them.A system using sonic energy, designed by Wesmar Industrial Systems Division to measure the level of stored materials, is marketed by Davies Electronics. The sound waves are directed in a narrow beam to the surface of the stored material, which reflects them back to the sensor.The energy of the returned signal is proportional to the distance between the sensor and the stored material. Radioactive materials as a source of radiation are useful in many applications where the sensor cannot be placed inside the container. A narrow collimated beam of gamma-radiation penetrates the container and the emergent beam is sensed by a detector aligned in the field of collimated radiation.The change in detector current is used to actuate an electronic relay,October, 1975 CARBON ATOMISERS IN AAS 275 which operates alarms or control valves. Changes in level are relatively large or sudden and a simple Geiger - Muller tube detector is suitable. Systems based on these principles are available from Landis and Gyr, A.M. Lock and Co., Endress and Hauser, Nuclear Enterprises and Davies Electronics. Recently , microwave systems have been developed as level and indicator controls ; one, the “Barrier Link,” has been developed by James Scott (Engineering) Ltd. Basically, it consists of two units, a transmitter and a receiver, fitted with microwave transparent windows and sealed in aluminium cases so as to prevent ingress of dust, air or moisture.The system is aligned on opposite walls of a container vessel and attenuation of the signal occurs when any dielectric or metallic substance is introduced into the beam. Two other systems are worth mentioning, one available from Adwell Industries Ltd. , which uses radiofrequency principles and the other a fluidic control device available from Hunt and Co. (Bournemouth) Ltd. Conclusions The choice of a phase-sensing system for application is not simple. A sound knowledge of the chemistry involved, both of the reactions taking place and the effects on the materials of construction in the sensor itself, are extremely important. I thank Mr. F. Trowel1 of AWRE, Aldermaston, for very helpful contributions to this paper. References 1. Trowell, F., Lab. Pruct., 1969, 18, 44. 2. Sawyer, R., Stockwell, P. B., and Tucker, K. B. E., Analyst, 1970, 95, 879. 3. Tucker, K. B. E., Sawyer, R., and Stockwell, P. B., Analyst, 1970, 95, 730. 4. Porter, D. G., Jackson, C. J . , and Bunting, W., Lab. Pract., 1974, 23, 111.

ISSN:0306-1396    

DOI:10.1039/AD9751200273

出版商:RSC    

年代:1975

数据来源: RSC

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October, 1975 CARBON ATOMISERS I N AAS 275 Carbon Atomisers in Atomic-absorption Spectroscopy The following is a summary of the paper presented at a Meeting of the Midlands Region held on July lst, 1975, and reported in the August issue of Proceedings (p. 216). Carbon Atomisers in Atomic-absorption Spectroscopy J. W. Robinson Department of Chemistry, Louisiana State University, Baton Rouge, La.70803, USA The total amount of absorption experienced in atomic-absorption spectroscopy is given by the equation ne2 mc sK,dv = - Nf where JK,dv = total absorption; N = number of free atoms; f = oscillator strength; T, e, m, c = usual physical meaning and constants. I t can be seen that most of the components of this equation are constants and that the principal variable is the number of ground-state atoms in the system.In commercial carbon atomkers, the normal atomisation process involves firstly, a heating step to remove excess of solvent; secondly, a second heating step to ash the sample; and thirdly, a heating step to atomise and vaporise the sample. It can be shown that metals, particularly volatile metals such as cadmium and mercury, can be readily lost from the sample during the evaporation and276 EQUIPMENT NEWS Proc.Analyt. Div. Chem. SOC. ashing step. It can also be understood that the release of free atoms generated during the atomisation step is very fast and time dependent. In commercial equipment, it can be seen that factors that affect chemical interference when flame atomisers are used also affect the rate of formation of free atoms in the vicinity of the carbon atomiser and thus directly affect the absorption signal generated by the system.In practice, therefore, commercial carbon atomisers suffer from two major sources of error, viz., chemical interferences and a high molecular background absorption. The latter can be partially corrected by using a background corrector if the molecular absorption is low.However, this is not always the case and in some instances high and variable molecular background can contribute to inaccuracy in the signal generated. The use of calibration techniques involving rigidly controlled heating processes (both tempera- ture and time) alleviates the problem to some extent, but is ineffective if there is significant1 variation in the types of sample analysed. The problem has been overcome to a large extent by using the carbon hollow T atomiser.In this system, the atomisation takes place in the stem of the atomiser and the products of atomisation are drawn at a relatively slow rate into the cross-piece, where absorption measure- ments are made. The whole process takes several seconds to complete, but this time period is sufficient to permit complete destruction of the solvent and to complete, as far as possible, the atomisation of the sample.Under these conditions, molecular backgrounds are greatly reduced as only free hydrogen now remains to cause a correctable background. Also, chemical inter- ferences are greatly reduced as the sample has sufficient time to come to equilibrium and is not controlled by the dynamic equilibrium between the chemical form of the sample and the free atomic form desirable for measurement.Application of the system has been made to the detection and determination of lead in the atmosphere. The sensitivity of the system is extremely high and permits real-time analyses to be carried out on samples of air as low as 200 ml.In addition to measuring total lead in the atmosphere, it has been found possible by the use of a highly efficient carbon filter (pore size 0.01 pm) to filter out particulate material and to measure the non-filterable or vaporised lead compounds in the atmosphere. The filtered-out particulates can also be measured on the same system. By using this technique, measurement can be made of molecular lead and particulate lead from the same sample of air. The results have indicated that there is a significant amount of vaporised molecular lead compounds in the atmosphere. Some speculation on the health effects of these lead compounds was made but no conclusions were drawn.

ISSN:0306-1396    

DOI:10.1039/AD9751200275

出版商:RSC    

年代:1975

数据来源: RSC

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276 EQUIPMENT NEWS Proc. Analyt. Div. Chem. SOC. Equipment News Fluorescence Analysis Two new accessories for the Baird-A tornic Fluoripoint and Fluoricord spectrofluorimeters facilitate the application of fluorimetry in chromatography and enzymology. The TLC Plate Scanner can focus the output from the excitation monochromator on to the TLC plate and the resultant fluorescence into the emission monochromator and then scan the plate a t a constant speed of 10 or 20 mm min-l.Alternatively, qualitative measurements can be made on individual spots by automatic scanning of fluorescence and emission wave- lengths. Improved precision and convenience are claimed, e.g., Baird-Atomic have measured 2 x 10-10 g of benzo[a]pyrene extracted from an air sample. The Temperature-Controlled Turret is custom- built for analysts engaged in reaction-rate enzyme studies by fluorescence.Up to four samples erature studied can be maintained at a constant temp- (usually 37 "C) and enzyme activity over any desired time interval. The minimum volume of sample required per cell is 0.5 ml. Further information from Baird-Atomic Ltd., East Street, Braintree, Essex. Measurement of Moisture in Solids Du Pont ( U K ) Lid.have announced the 902 Moisture Evolution Analyser (MEA), claimed to be maintenance free and easy to apply to such solids as thermoplastic and thermosetting resins, dry chemicals, pharmaceuticals and foodstuffs. It is based on the electrolytic cell principle and is specific for water, which it can measure with an accuracy of f 2 per cent.moisture, data being displayed digitally in the range 0.1- 99 999.9 pg. The Model 902 can operate fromOctober, 1975 EQUIPMENT NEWS 277 ambient temperature to 300 "C and the 902H For further information, write to Du Pont (UK) Ltd., Instrumentation Products Division, Wilbury House, Wilbury Way, Hitchin, Herts. , SG4 OUR. up to 1000 "C. Infrared Measurements An infrared process instrument by Techmation for the continuous monitoring of trans-iso- merisation of fats by attenuated total reflect- ance spectroscopy (ATR) is now available in the UK.The Wilks MIRAN I1 Hydrogenation Monitor has a flow-through cell and can observe changes continuously. Unfiltered oil direct from the hydrogenator is circulated through the heated ATR cell, there is no interference from the catalyst and the usual steps of weighing and diluting the sample are eliminated.A unique two-wavelength filter system and advan- ced electronics give long-term stability and an excellent signal to noise ratio. Output can be presented as analogue data using the built-in meter and accessory strip chart recorder or in discrete form by using an auxiliary digital display instrument.Techmation also has recently introduced a 120-m gas cell that can be adapted for use with a number of commercial infrared spectrophoto- meters. The Wilks Scientific Corp. three- mirror, multiple reflection cell has an externally adjustable path length from 4 to 132 m in 8-m steps. It is fitted with KBr windows and can be pressurised to 10 atm for increased sensitivity or maintain a vacuum of 10-5 torr.Particularly useful applications are the study of atmospheric pollution, industrial plant environments and gas-phase reactions. The cell can be modified for use with highly corrosive fluoride gases. Further details from Techmation Ltd., 58 Edgware Way, Edgware, Middlesex, HA8 8 JP. Analysis of Water The sensitive Hach 1720A continuous recording turbidimeter for monitoring water quality is designed for municipal and industrial water treatment plant applications.It is based on photocell measurement of the amount of light scattered at right-angles by the turbidity par- ticles, and is suitable for the measurement of turbidities in the range 30-0-04 Nephelometric Turbidity Units (NTUs) . The instrument is said to be easy to install and almost maintenance free.Also from Hach, a new bacterial incubator for use with both total coliform (incubation at 35 f 0-5 "C) or faecal coliform testing (incuba- tion at 44.5 f 0.2 "C) can accommodate 5 sets of 5 coliform tubes of the standard 10-ml test vial size. Test media and necessary supplies for the multiple tube fermentation technique of coliform testing are available.For further information, write to Hach Chemical Co., PO Box 907, Ames, Iowa 50010, USA or Hach Europe SA/NV, BP 51, 5000 Namur 1, Belgium. X-ray Fluorescence Ortec Ltd. are introducing a new energy- dispersive X-ray fluorescence system designed for the analysis of multi-element materials. The Ortec 6110 Tube Excited Fluorescence Analyzer (TEFA) provides non-destructive analysis of material containing up to 82 elements from Na to U plus transuranium elements.All measurements are made simultaneously and the TEFA is able to detect and measure the elements over a broad range of concentrationsfrom p.p.m. to 100 per cent. The spectrum obtained of the number of X-rays emitted versus X-ray energies is then processed by a built-in on-line computer, which produces an analytical report giving the required data.For further information, write to Ortec Ltd., Dalroad Industrial Estate, Dallow Road, Luton, Beds., LUl ISU. Automatic Analysis An automatic sampler suitable for use with a continuous flow analytical system is available from ChevnLab Instruments Ltd. The CS40 includes a unique probe system which improves the wash pattern.The fibre-glass sample case is resistant to most laboratory reagents. Controls include facilities for independent sample and wash times (from 0 to 120 s) and a fully tempera- ture-compensated solid-state electronic timer gives excellent reproducibility. Also included is an audible and visual alarm to indicate "end of run" and a switch for continuous operation. The sampler can also give a signal to a data printer unit or computer.Further details can be obtained from ChemLab Instruments Ltd., 602 High Road, Ilford, Essex, IG3 8BT. Laboratory Centrifuges Two Damon/IEC floor-model centrifuges, the CRU-5000 Refrigerated and the CU-5000 General Purpose, are offered by Searle Instru- ments and include electronic control of all aspects of operation. A dual-range timer selects run times in 0-5-min increments to278 EQUIPMENT NEWS 15 min and in 5-min increments from 15 to 105 min.Once speed, temperature (CRU model only), time and braking mode have been selected, the full centrifugation cycle is automatic and reproducible. Further details from Baird and Tatlock, PO Box 1, Romford, Essex, RM1 1HA. Airborne Particle Counters Wessex Electronics Ltd., the UK representatives of Climet Instruments, announce the availability in the UK of their range of particle counters.Some of these instruments are based on light scattering, the sample of air being passed through a bright light, any particles present causing scatter which is converted into elec- trical pulses. The larger the particle, the larger is the pulse, and both particle count and particle diameter are measured immediately.The CI-208 model can count concentrations of particles up to lo7 per cubic foot and size down to 0-5 pm. I t is designed for continuous long-term measure- ment of air-borne particulates and the results are displayed numerically. Special options and accessories are also available. The CI-250 is a rugged portable model suitable for con- tinuous measurements in the field.It also can operate at concentrations of lo7 particles per cubic foot. Further information can be obtained from Wessex Electronics Ltd., Stover Trading Estate, Yate, Bristol, BS17 5QP. Chart Recorder for Remote Duties A new, battery-wound chart-recorder mecha- nism for use on sites remote from electricity mains is available from A rkon Instruments Ltd.In the mechanism, which can be left unattended for at least 6 weeks, a standard 14-V U2 dry cell re-winds the clockwork spring at regular intervals and then switches itself off. This minimises drain on the battery but ensures that the clockwork mechanism remains active. The new mechanism can be supplied only for the standard Arkon chart speed of Q in h-l. Further details from Arkon Instruments Ltd., Whaddon Works, Cromwell Road, Cheltenham, GL52 5EP. Liquid Chromatography A new catalogue is now available from Waters Associates giving information on their packing materials, including selection, loadability and compatibility with solvents. For a free copy, request “LC Column Packing Materials and Packed Columns,” DS 013, from Waters Associates (Inst.) Ltd., Greg Street, South Reddish, Stockport, Cheshire, SK5 7BR. PYOC. Analyt. Div. Chem. SOC.

ISSN:0306-1396    

DOI:10.1039/AD9751200276

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

278 EQUIPMENT NEWS PYOC. Analyt. Div. Chem. SOC. Conferences and Meetings Debate : “That Teachers of Analytical Chemistry Have Their Heads in the Clouds” Novevnbev 6, 1975, Reading The Analytical Division South East Region is holding a joint evening debate with the Education and Training Group in the Chemistry Department of Reading University at 6.30 p.m. on Thursday, November 6th. Light refresh- ments and bar will be available from 6.15 p.m.Proposers of the motion “That teachers of analytical chemistry have their heads in the clouds” are Dr. R. F. Coleman (Laboratory of the Government Chemist) and Mr. A. Holbrook (ICI Pharmaceuticals Division), and the Opposers are Dr. L. S. Bark (University of Salford) and Mr. D. W. Wilson (City of London Polytechnic). Further information can be obtained from Dr.J. Warren, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, SE19NQ (Tel. : 01-928-7900, Ext. 643). Postgraduate School on Drug Metabolism in Man March. 29-ApriZ 2, 1976, London This School is to be held at the Department of Pharmacy, Chelsea College, London and is being organised jointly by that Department and the Pharmaceutical Society of Great Britain.There will be a programme of lectures and discussions and a supporting programme of practical work and demonstrations. Lecture titles include : “The Use of Chromato- graphic Methods in the Study of Drug Metabo- lism in Man,” by Dr. M. Mitchard (The Medical School, Birmingham) ; “Physical Methods in Elucidating Metabolite Structure-Mass Spectrometry,” by Dr. H. Drafen (Inveresk Research) ; “Physical Methods in Elucidating Metabolite Structure,’’ by Dr. D. Case (Imperial Chemical Industries Ltd.) ; and“1sotopic Methods in Drug Metabolism Studies in Man,” by Dr. S. Curry (The London Hospital Medical College, London). Application forms can be obtained from Mr. R. E. Marshall, Department of Pharmaceutical Sciences, The Pharmaceutical Society of Great Britain, 17 Bloomsbury Square, London, WClA 2”.

ISSN:0306-1396    

DOI:10.1039/AD9751200278

出版商:RSC    

年代:1975

数据来源: RSC