摘要:

of the Analytical Division ofThe Chemical SocietyPAYCALCONTENTS1125 Reports of Meetings8 'Simultaneous Multi-element TraceAmalgamation : A Statement by thePresident of the Analytical DivisionEditorial: The Future of ProceedingsFortieth AGM and Dinner of theScottish RegionAnalysis': Silver Medal AddressChromatography'Analytical Chemistry'SAC Gold and Silver Medals25 'High- performance Liquid313232 SAC Studentships32 'Analytical Abstracts'33 Correspondence34 Obituaries3434 Conferences and Meetings36 Publications Received38 Analytical Division Diary'Research and Development Topics inPapers Accepted for 'The Analyst'Volume 12 No 1 Pages 1-38 January 197Vol. 12, No. 1 January, 1975PROCEEDINGSANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOF THEOfficers of the Analytical Divisionof the Chemical SocietyPresidentG.W. C. MilnerHon. SecretaryW. H . C. ShawHon. TreasurerJ . K. ForemanSecretaryMiss P. E. HutchinsonHon. Assistant SecretariesD. I. Coomber, O.B.E.; D. W. WilsonEdit or, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Pubiications, 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 1 HN.Non-members can be supplied with Proceedings only as part of a combined subscription with The Analystand Analytical Abstracts.@ The Chemical Society 1975Annual Reports on AnalyticalAtomic SpectroscopyVolume 3,1973This comprehensive and critical report of developments in analytica I atomicspectroscopy has been compiled from nearly 1700 reports received fromworld-wide correspondents who are internationally recognised authorities inthe field and who constitute the Editorial Board.In addition to surveyingdevelopments throughout the world published in national or internationaljournals, a particular aim has been to include less widely accessible reportsfrom local, national and international symposia and conferences concernedwith atomic spectroscopy.324 pages Price f6.00 ISBN 0 85990 253 6Obtainable from The Chemical Society, Publications Sales Office,Blackhorse Road, Letchworth, Herts., SG6 1 HNVolumes 1 & 2, covering 1971 & 1972, are still availableMembers of The Chemical Society may buy personal copies at the special price of f3.0

ISSN:0306-1396    

DOI:10.1039/AD97512FX001

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

2 SCOTTISH REGION 4 0 ~ ~ AGM Proc. Analyt. Div. Chem. soc. Fortieth Annual General Meeting and Dinner of the Scottish Region The Scottish Section of the Society of Public Analysts and Other Analytical Chemists was inaugurated in 1935, the opening meeting being held in Glasgow on November 13th. Now the Scottish Region, its fortieth Annual General Meeting was held at Strathclyde University, Glasgow, on November lst, 1974, and the occasion was celebrated with a Regional Dinner in the evening.The Annual General Meeting was reported in the December issue of Proceedings (p. 309). Under “Other Business,” Mr. D. W. Wilson spoke briefly on behalf of the President on the decision made by the members of the SAC to amalgamate with the CS, taken at an Extra- ordinary General Meeting held during the previous week.Dr. D. M. W. Anderson of Edinburgh University, Chairman of the Scottish Region in 1969-70, then gave a lecture entitled “1934-1974: From Lundell to Laitinen.” Dr. Anderson began by hoping that his talk would be controversial and amusing and ap- propriate for what he regarded as a form of birthday party: he therefore invited Mr. D. W.January, 1975 SCOTTISH REGION ~ O T H AGM 3 Wilson (representing the President) and Mr.W. Dunnet (retiring Chairman of the Scottish Region) to celebrate the occasion by accepting a “wee dram.” Dr. J . M . Ottaway (new Chairman of the Scottish Regiort, CENTRE) with Dr. G. R. Jamieson (L) and Dr. D . M . W . Anderson (R). “Married men frequently make very poor husbands” and, somewhat analogously, Dr.Anderson considers that most modern chcmistry graduates make very poor analysts. Whose fault is this ? And why has there been a sad but steady devolution of Lundell’s controversial “analysts” and “determinators”-and even of Mellor and Thompson’s “testers” (1938)-into bevies of blinkered button bashers, baffled be- yond belief by beautiful big black boxes behav- ing badly? Black boxes seem determined to stay ; analysts must be prepared to master them and preferably maintain them, and it seems desirable that they should even be capable of learning how to bash the right button a t the right time.For many, the wrong button at the wrong time appears to be better than no button bashing at all. In the belief that the modern image of analysts and of analytical chemists (and Dr. Anderson asked his audience to take care to distinguish between the two) was some- what tarnished, he invited those present to answer the questions : “What is analytical chemistry ?” and “What should analytical chemists do ?” There never have been universally accepted answers, but to show that some development in thought had occurred over the past 100 years, many of the more interesting, useful or con- troversial attempts at essential definitions by celebrated chemists were considered in turn, starting with C .N. Reilley’s “the only constant feature of science is that of change” and “analytical chemistry is what analytical chem- ists do.” On the basis of Henry Freiser’s “the essence of the science of chemistry must include three main asDects-methods.measurements and models,” a remarkable statement by Maxwell (1871) “the labour of careful measure- ment has been rewarded by the discovery of new fields of research and by the development of new ideas” was taken, together with Ostwald’s “analytical chemistry is the art of recognising different substances and determining their constituents” (1894) as the basis for a discussion of the definitions and statements that have been made by I.M. Kolthoff, F. Feigl, W. H. Rein- muth, I. Shain, J. W. Robinson, D. F. Boltz, H. Liebhafsky, C. Th. J. Alkemade, J . K. Taylor, L. Meites, A. J. P. Martin, W. W. Meinke, H. A. Malissa, H. Kaiser and the Research Directorate of the U.S. National Science Foundation in 1974. More extensive discussion was given to the contribution of G.E. F. Lundell who stressed (1934) the importance of the cost factor, and of A. G. Jones, who envisaged (1973) that “em- ployers are going to want more for their money. ” The importance of Wayne Meinke’s suggestions were emphasised, e.g., his dislike of the word “characterisation” and call for greater attention to be given to the sample itself (1970); his legitimate complaint that tens of thousands of chemists do analytical work but do not appear to care to recognise the fact (1970) ; and his sugges- tion that very few people are really willing to work meaningfully at the 0.1 p.p.m.level al- though a plethora of papers in the literature seem to indicate otherwise (1973). There was also extensive reference to the exhortations and counsel exuded steadily by H.A. Laitinen in recent years. Dr. J . E. Whitley (L) z&h MY. D. W. Dunnet (retiring Chairman). Dr. Anderson associated himself closely with the general tenor of the recent remarks about teaching made by Professor P. W. West (Analyt. Chem., 1974, 46, 784) and also with those made about the employment prospects for analytically trained chemists by Mr.C. Whalley (Proc. SOC. Analvt. Chem.. 1974. 11. 260). In acknow1edg.-4 SCOTTISH REGION 4 0 ~ ~ AGM Proc. Analyt. Div. C1wvz. SOC. ing the personal advice and guidance he had enjoyed since first meeting the late Professor Cecil L. Wilson in 1956, Dr. Anderson con- cluded by saying that, in retrospect, it appeared that his talk might more appropriately have been entitled “from Lundell to West, Whalley and Wilson,” and he wished the student mem- bers of his audience well, because all the easy things in analytical chemistry were done long ago ! Following the meeting, over forty members and guests gathered in the University Staff Club, where an informal reception was held be- fore the Regional Dinner.At the Dinner, the Loyal Toast was proposed by the new Chairman of the Scottish Region, Dr.J . M. Ottaway. He welcomed the repre- sentatives from the SAC in London, and also Dr. Jamieson of the RIC Local Section and Dr. Sherwood of the CS Local Section. Letters of congratulations had been received from Mr. J. Whitehead (Chairman of the North East Region), Mr. C. Whalley and Dr. T. B. Pierce. He spoke of the strong traditions that have developed in the Region, and of its vigorous out- look and cordial relations with the parent Society, and other Regions and organisations.Expressing the intention of the Scottish Region to play a full and active role in the Analytical Division of the CS following amalgamation, he stressed that it was the responsibility of all tnembers to ensure that analytical chemistry continued to flourish in the new organisation.DY. R. A , Clzalnaevs (L) and MY. D . W . Wilson. Dr. R. A. Chalmers, Chairman of the Region in 1963-65, proposed a toast to the Society for Analytical Chemistry. Referring to the well known cartoon that appeared in Punch in September, 1929, reproduced recently in the Society’s History, “The Practising Chemists, ” and depicting the scene at the Society’s Annual Dinner, he suggested that a dinner could be treated as an analytical problem.For example, apparatus-1 table for support, 1 audience, etc. ; reagent-alcohol ; results-can be seen from the tables . . . and so on. Dr. Chalmers then indi- cated that i t was perhaps appropriate that he should propose the toast to the SAC, as he was a supporter of its continuation as an inde- pendent Society.It was sometimes good to look a t the past, and he cited some interesting items that might seem hard to believe today. Volume 1 of The Analyst, for instance, refers to whisky containing 54.5 per cent. w/v of alcohol, and a comparison of prices indicated that The Analyst subscription should now be only just over i4. He also recalled the abstract in The Analyst (1944, 69, 97) which summarised a spoof paper on the toxic effects of “laevorota- tory ice.” Finally, referring to the long and honourable history of the SAC and of the CS, he indicated that the oldest chemical society is, in fact, the Student Chemical Society of Edin- burgh University, which made the CS the second and the SAC the third oldest. He then pro- posed a toast to the SAC and also to its Secre- tary, Miss P.E. Hutchinson, who had recently completed 21 years’ service with the SAC. Mr. D. W. Wilson, an Honorary Assistant Secretary of the SAC/AD, replied on behalf of the President and proposed a toast to the Scot- tish Region. The last 50 years of the SAC’S existence had been a period of rapid growth, due largely to the formation of Sections (now Regions).Much of its strength lay in its Regions and Groups, and Council would con- tinue to foster these activities. During the negotiations with the CS, each side had come to appreciate the difficulties of the other, and this was reflected in the final terms of amalgamation. A small proportion of members had serious reservations and the President and Council ap- preciated that these resulted from a genuine concern for the future. There would certainly be difficulties ahead, and Council would look to the Regions for forbearance and support.In proposing the toast to the Scottish Region, Mr. Wilson pointed out an apparent inconsist- ency in the record of its inception as a Section. The development of the Region has shown a good balance between the interests of industry, education and the various parts of Scotland. He predicted that there would be no diminution of the Regional activities in the future-not just because this was written into an agreement, but because the members and committees had the vigour alid foresight to ensure it and to develop i t in co-operation with the CS.January, 1975 REPORTS OF MEETINGS Mr. W. Dunnet, retiring Chairman of the Scottish Region, replied to the toast to the Scottish Region and thanked Mr. Wilson for the good wishes he had expressed for the Region’s future. 5

ISSN:0306-1396    

DOI:10.1039/AD9751200002

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

January, 1975 PUBLICATIONS RECEIVED 37Analytical Division Diary, continuedbruary, continued“A Data Processing System for QuantitativeNMR,” by P. B. Stockwell, W. Bunting,F. Morley and I. K. O’Neill.“Laboratory Data Collection TechniquesUsing a Time Shared Mini Computer,” byG. B. Fish.“Computer Controlled Monitoring and DataReduction for Multiple Ion SelectiveElectrodes in a Flowing System,’’ by B.Fleet, S. P. Perone and J. H. Zipper.Open Forum and Discussion on “The Use,Problems, etc., of Microprocessors,” intro-duced by J . Stuart.The Dragonara Hotel, Fry Street, Middles-brough; 9.30 a.m.Thursday, 27th : ChesterNorth West Region, jointly with the Chesterand District Branch of the PharmaceuticalSociety of Great Britain.“The Impact of the EEC,” by J.K. Foreman.Venetian Room, Grosvenor Hotel, Chester ;8 p.m.Thursday, 27th : AberdeenScottish Region, jointly with the Aberdeenand North of Scotland Section of the CSand Aberdeen University Chemical Society.“Offshore Corrosion Control,” by M. J.Purcell .The University, Aberdeen ; 4.15 p.mAnalytical Division DiaryJANUARYMonday, 20th : LondonAnalytical Division, jointly with the PesticidesGroup of the SCI on “Residue Determinationof Benzimidazoles.”(For details see December, 1974, issue, p . 343)Society of Chemical Industry, 14 BelgraveSquare, London, S.W.l; 10.15 a.m.Wednesday, 22nd : MiddlesbroughNorth East Region: Annual General Meeting,followed by a lecture to be given by L. S.Bark.Teesside Polytechnic, Middlesbrough ; 7 p.m.Friday, 24th : SalfordNorth West Region: Annual General Meeting,followed by the retiring Chairman’s address.“The Training of an Analytical Chemist-Programming for Inefficiency,” by A.C.Bushnell.Chapman Building, The University, Salford ;6.30 p.m.FEBRUARYWednesday, 5th : LondonAnalytical Division on “The Renaissance ofPolarography . ”“Modern Polarographic Techniques,” by G. C.“Automation of Polarographic Techniques, ”“Voltammetry with Carbon Based Elec-“Some Recent Applications of Polarography“Pulse and A.C. Polarographic TechniquesScientific Societies Lecture Theatre, 23 SavileWednesday, 5th : LondonMicrochemical Methods and Chromato -graphy and Electrophoresis Groups.Discussion on “Data Processing in GLC.”The Polytechnic of the South Bank, London,S.E.1; 6 p.m.Tuesday, 1 l t h : EdinburghScottish Region, jointly with the Edinburghand East of Scotland Section of the CS.“Antibodies as Ultramicroanalytical Reagents(Radioimmunoassay of Steroids),” byE.H. D. Cameron.Mountbatten Conference Theatre, Heriot WattUniversity, Grassmarket, Edinburgh ;4.30 p.m.Barker.by B. Fleet.trodes,” by D. 8. Crow.to Drug Analysis,” by W. F. Smyth.for Trace Analysis,” by R. D. Jee.Row, London, W.l; 3 p.m.Tuesday, 1 l t h : ShefieldSpecial Techniques Group, jointly with theSheffield Metallurgical and EngineeringAssociation.Discussion on “Energy Dispersive X-rayCorporate Development Laboratories, BritishSteel Corporation, Hoyle Street, Sheffield ;2.30 p.m.Fluorescence.”Tuesday, 18th : SwanseaWestern Region, jointly with the South WalesWest Section of the CS.“Science and Crime,” by R. L. Williams.University College, Swansea ; 7.30 p.m.Wednesday, 19th : NewcastleScottish and North East Regions, jointlywith the Society for Water Treatment andExamination.Newcastle upon Tyne; 2 p.m.Wednesday, 19th : CambridgeEast Anglia Region on “The Use of X-raySpillers Ltd., Cambridge; 3 p.m.Techniques in Analytical Chemistry.’’Wednesday, 19th : ManchesterRadiochemical Methods Group on “Prepara-tion and Use of Labelled Compounds.”“Cyclotrons and Labelled Compounds,” byJ. Clark.“Synthesis of Labelled Compounds,” byA. J. Palmer.“Review of Clinical Application of LabelledCompounds, Past, Present and Future,’’by F. Gillespie.“Isotopic Labelling in Studies of Biochemicaland Biological Mechanisms,” by G. R.Barker.“Non-clinical Use of Labelled Isotopes,” byB. Lord.Chemistry Department, The University, Man-Chester M13 9PL; 10.15 a.m.Wednesday, 26th : MiddlesbroughAutomatic Methods Group on “Applicationof Computers, Particularly Microprocessors,to Automatic Analytical Instrumentation.”“Introduction and Definition of Terms,” byJ. Stuart.“A User’s Requirements from a Micro-processor Controlled Analytical Instru-ment,” by D. R. Deans.[continued inside back coverPrinted by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97512BX003

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

January, 1975 REPORTS OF MEETINGS 5 Reports of Meetings North West Region A Joint Meeting of the Region with the Carlett Park Chemical and Physical Society was held a t 7 p.m. on Thursday, December 5th, 1974, in the Tower Block, West Cheshire Central College of Further Education, Carlett Park, Eastham. The Chair was taken by the Chairman of the North West Region, Mr. A. C. Bushnell. A lecture on “Ion-selective Electrodes” was given by J.M. Bather. Scottish Region A Joint Meeting of the Region with the Glasgow and West of Scotland Section of the CS and the Andersonian Chemical Society was held at 4 p.m. on Thursday, December 5th, 1974, at the University of Strathclyde, Cathedral Street, Glasgow. The Chair was taken by the Presi- dent of the Andersonian Chemical Society, Mr.D. Stalker. A lecture on “Analysis of Seawater” was given by Professor D. Dyrssen. Western Region A Joint Meeting of the Region with the South East Wales Section of the CS was held at 6.30 p.m. on Friday, December 6th, 1974, in the University Staff Dining Club, Park Place, Cardiff. The Chair was taken by the Chairman of the Western Region, Dr. W. J. Williams. A lecture on “Atomic Fluorescence and Non-flame Reservoirs” was given by R.M. Dagnall. Midlands Region The twentieth Annual General Meeting of the Region was held a t 6 p.m. on Monday, Novem- ber llth, 1974, at the Strathdon Hotel, Derby Road, Nottingham. The Chair was taken by the Chairman of the Region, Mr. S. Greenfield. The following office bearers were elected for the forthcoming year: Chairman-Dr.D. Thorburn Burns. Vice-Chairman-Dr. A. Tow’nshend. Honorary Secretary-Dr. A. G. Fogg, Chemistry Department, University of Technology, Loughborough, Leics., LE11 3TU. Honorary Treasurer-Dr. J . N. Miller. Mem- bers of Committee-Professor R. Belcher, Mr. D. M. Evans, Dr. B. C. Lewis, Mr. W. M. Lewis, Mr. D. M. Peake, Dr. D. N. Raine, Mr. H. E. Brookes (co-opted) and Mr.S. Greenfield (ex oficio). Mr. W. Harris and Mr. H. Pugh were appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Microchemical Methods Group, at which the Chair was taken by the new Chairman of the Midlands Region, Dr. D. Thorburn Burns. A lecture on “100 Years of Microchemistry” was given by Professor R. Belcher. North East Region A Joint Meeting of the Region with the Modern Methods of Analysis Group of the Sheffield Metallurgical and Engineering Association was held a t 7p.m.on Tuesday, December loth, 1974, at the North Lindsey Technical College, Scunthorpe, Lincs. The Chair was taken by the Chairman of the Modern Methods of Analysis Group of the Sheffield Metallurgical and Engineering Association.A lecture on “Further Applications of Atomic-absorption Spectrophotometry in the Steel Industry” was given by T. S. Harrison. Microchemical Methods Group The thirty-first Annual General Meeting of the Group was held at 6.15 p.m. on Monday, December llth, 1974, a t the Strathdon Hotel, Derby Road, Nottingham. The Chair was taken by the Chairman of the Group, Dr. D. A. Pantony. The following office bearers were elected for the forthcoming year : Chairman- Mr.R. Sawyer. Vice-Chairman-Dr. D. A. Pantony. Honorary Secretary-Mr. P. R. W. Baker, Chemical Research Laboratory, The Wellcome Research Laboratories, Langley Court, Beckenham, Kent. Honorary Treasurer -Mr. A. C. Thomas. Honovavy Assistant Secvetary-Mr. B. T. Saunderson. Members of Committee-Mr. P. G. W.Cobb, Mr. G. C. Dickson, Dr. M. A. Leonard, Mr. D. C. M. Squirrell, Dr. M. Thompson and Mr. C. A. Watson. Mr. H. Childs and Dr. H. I. Shal- gosky were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Midlands Region, at which the Chair was taken by the new Chairman of the Midlands Region, Dr. D. Thorburn Burns. A lecture on “100 Years of Microchemistry” was given by Professor R.Belcher.6 REPORTS OF MEETINGS Proc. Analyt. Div. Clzem. SOC. A London Discussion Meeting of the Group was held a t 6.30 p.m. on Wednesday, December 4th, 1974, a t “The Phoenix,” 14 Palace Street, London, S.W.l. The Chair was taken by the Chairman of the Group, Dr. D. A. Pantony. A discussion on “The Determination of Traces of Selenium and Other Metalloids by Fluorimetry and by Atomic Absorption” was introduced by J.Dixon and J. Warren. Dr. J. H. Hamence were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Discussion Meeting, a t which the Chair was taken by the new Chairman of the Group, Mr. F. W. Webb. A discussion on “Pitfalls in Scientific Communication” was introduced by A.J. Duggan. This was followed by a Cheese and Wine Party. Special Techniques Group The thirtieth Annual General Meeting of the Group was held a t 2 p.m. on Thursday, Novem- ber 7th, 1974, at Imperial College, South Kensington, London, S.W.7. The Chair was Electrophoresis Group Chromatography and taken by the Vice-chairman of the Group, Dr. P. B. Smith. The following office bearers were elected for the forthcoming year: Chair- man-Dr.R. M. Dagnall. Vice-Chairman- Dr. P. B. Smith. Honorary Secretary and Treasurer-Mr. J. T. Davies, Research and Development Department, Metal Box Co., Twyford Abbey Road, Park Royal, London, N.W.lO. Members of Committee-Mr. J . H. Glover, Dr. J. Miller, Dr. T. B. Pierce, Mr. L. H. Ruddle, Mr. P. Scholes and Dr. B. Sharp.Dr. G. Duff and Dr. M. Thompson were appointed as Honorary Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Group, a t which the subject was “Newer Aspects of Mass Spectrometry” and the following papers were presented and discussed : “Chemical Ionisation, ” by R. Craig; “Plasma Sources for Mass Spectro- meters,” by A. Gray; “GC/MS Interfacing Problems,” by A.McCormick ; “Pharmaceutical Applications,” by D. R. Hawkins. Biological Methods Group The thirtieth Annual General Meeting of the Group was held at 6.30 p.m. on Thursday, November 28th, 1974, at “The King’s Arms,” 77 Buckingham Palace Road, London, S.W.l. The Chair was taken by the Chairman of the Group, Dr. L. Singleton. The following office bearers were elected for the forthcoming year : Chairman-Mr.F. W. Webb. Vice-Chairman- Dr. J. A. Holgate. Honorary Secretary-Mr. V. J. Birkinshaw, The Boots Co. Ltd., Pharma- ceutical Research, Pennyfoot Street, Notting- ham, NG2 3AA. Honorary Treasurer-Mr. D. T. N. Hossack Homrary Assistant Secretary- Miss F. N. ,Vulholland. Menzbers of Committee- Dr. L. Singleton, Miss A. Jones, Dr. B. A. Wills and Dr.D. A. Thomas. Dr. M. W. Parkes and The tenth Annual General Meeting of the Group was held at 2 p.m. on Wednesday, November 27th, 1974, in the Research Lecture Theatre, The Boots Co. Ltd. Nottingham. The Chair was taken by the Chairman of the Group, Mr. J. W. Murfin. The following office bearers were elected for the forthcoming year: Chair- man-Mr. J. W. Murfin. Honovary Secretavy and Treasurer-Dr.D. Simpson, Bakelite Xylonite Ltd., Lawford Place, Manningtree, Essex, COll 2NA. J4evtzbers of Committee-- Mr. D. A. Elvidge, Dr. G. H. Jolliffe, Mr. D. L. Southern, Dr. E. V. Truter and Mr. P. F. Wadsworth. Dr. S. J. Purdy and Mr. J. S. Wragg were re-appointed as Honorary Auditors. The Annual General Meeting was held during an all-day meeting on “The Application of Chromatography to Pharmaceutical Analysis” and the following papers were presented and discussed : “The Application of HPLC to Pharmaceutical Analysis,” by J.W. Murfin ; “The Use of Pellicular Ion-exchange Materials for the Separation of Organic Ions,” by E. Davison and P. F. Wadsworth ; “Chromato- graphy in the British Pharmacopoeia,” by Professor E. J. Shellard. Thermal Methods Group The tenth Annual General Meeting of the Group was held at 10 a.m.on Thursday, November 14th, 1974, a t the Royal Astronomical Society, Burlington House, London, W.l. The Chair was taken by the Chairman of the Group, Mr. K. E. J . Barrett. The following office bearers were elected for the forthcoming year: Chairman-Mr. K. E. J. Barrett. Vice- Chairman-Dr. F. W. Wilburn.Honorary7 January, 1975 REPORTS OF MEETINGS Secretary-Mr. C. J. Keattch, Industrial and Laboratory Services, P.O. Box 9, Lyme Regis, Dorset. Honorary Treasurer-Dr. A. A. Hodgson. Members of Committee-Mr. M. Cottrell, Dr. D. Dollimore (co-opted), Mr. I. M. Jackson, Dr. R. C. Mackenzie (co-opted), Dr. L. J . Monkman, Dr. D. V. Nowell, Dr. J . P. Redfern, Dr. R. H. Still and Mr.R. E. Waller (co-opted). Dr. W. Boardman and Mr. P. J. Haines were re-appointed as Honorary Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Group, at which the subject was “Fringe Techniques in Thermal Analysis. ” The following papers were pre- sented and discussed : “Flow Microcalorimetry Applied to Biochemical and Biological Assays,” by H. J.V. Tyrrell; “Some Applications of Thermometric Titrimetry and Direct Injection Enthalpimetry,” by L. S. Bark; “End-point Enhancement in Thermometric Titrimetry,” by G. A. Vaughan; “The Basis of Thermomech- anical Analysis,” by T. Daniels ; “Materials Testing for a Modern Blast Furnace,” by J. Hamilton ; “Applications of Dilatometry and Hot-stage Microscopy in Refractory Tech- nology,” by W.Ford; “Some Applications of Hot-stage Microscopy,” by E. L. Charsley. Particle Size Analysis Group The ninth Annual General Meeting of the Group was held a t 2.15 p.m. on Wednesday, November 20th, 1974, in the Pharmacy Department, Chelsea College, University of London, Manresa Road, London, S.W.3. The Chair was taken by the Chairman of the Group, Dr. M. J . Groves. The following office bearers were elected for the forthcoming year : Chairman- Dr.W. Carr. Vice-Chairman-Mr. B. Scarlett. Honorary Secretary and Treasurer-Mr. M. W. G. Burt, Building B-9C5, Atomic Weapons Research Establishment, Aldermaston, Berks. Honorary Assistant Secretary-Dr. R. Wilson. Members of Committee-Dr. M. J . Groves, Mr. J. E. C. Harris, Mr. J. L. F. Kellie, Mr. R. Lines and Dr.L. Svarovsky. Dr. T. Allen and Mr. P. W. Shallis were re-appointed as Honorary Auditors. The Annual General Meeting was followed by an Ordinary Meeting, at which the Chair was taken by the new Chairman of the Group, Dr. W. Carr. The subject of the meeting was “Characterisation of Particle Surfaces,” and the following papers were presented and discusssed : “The Determination of Some Physical Charac- teristics of Microcrystalline Cellulose,” by K.Marshall and D. Sixsmith; “The Use of Argon and Krypton Adsorption for Surface Area Determination,” by Professor K. S. W. Sing; “The Krypton BET Method,” by M. J. J aycock . Radiochemical Methods Group The eighth Annual General Meeting of the Group was held at 1.45 p.m. on Thursday, November 21st, 1974, at the University of London Reactor Centre, Silwood Park, Sunning- hill, Ascot, Berks.The Chair was taken by the Chairman of the Group, Mr. J. W. McMillan. The following office bearers were elected for the forthcoming year: Chairman-Dr. P. Johnson. Vice-Chairman-Dr. R. Burleigh. Honorary Secretary-Mr. M. A. Crook, Department of Chemistry and Polymer Technology, Poly- technic of the South Bank, Borough Road, London, SEl OAA.Honorary Treasurer-Dr. J. F. C. Tyler. Honorary Assistant Secrefayy- Mr. J. W. McMillan. Members of Commzftee- Dr. H. J. M. Bowen, Dr. D. E. Bowyer, Mr. J . A. Heslop, Dr. G. W. A. Newton and Dr. R. P. Parker. Dr. F. J. Bryant andMr. D. A. Lambie were appointed as Honorary Auditors. The Annual General Meeting was held during an all-day meeting on “Activation Analysis in Biological and Medical Sciences,” and the following papers were presented and discussed : “Whole Body in vivo Activation Analysis,” by R. W. S. Tomlinson; “‘Argon-aut’ and (n,a) Reactions Used to Measure Calcium in vivo,” by D. R. Chettle, E. A. Ozbas, J. Dabek, K. V. Ettinger, J . H. Fremlin, W. V. Prestwich and B. J . Thomas ; “Toxicological Applications of Neutron Activation Analysis,” by J. Cross, I. Dale and H. Smith; “The Study of Trace Elements in Skin Using Neutron Activation Analysis,” by M. Molokhia ; “Biological Analysis with the hTuclear Microprobe,” by J . A. Cookson and G. F. J. Legge. The meeting concluded with a tour of the Reactor.

ISSN:0306-1396    

DOI:10.1039/AD9751200005

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

8 SILVER MEDAL ADDRESS Pvoc. Analyt. Div. Chem. SOC. Simultaneous Multi-element Trace Analysis The following is the Silver Medal Address delivered by Dr. G. F. Kirkbright, the first Society for Analytical Chemistry Silver Medallist, at a meeting of the SAC/AD held on November 6th, 1974, and reported in the November issue of Proceedings (p. 284). At the beginning of the meeting the President, Dr.G. W. C. Milner, presented the Silver Medal and a cheque for LlOO to Dr. Kirkbright. It is expected that the other two papers presented at the meeting will appear in a later issue of Proceedings. Dr. G . F . Kirkbright (R) receiving the Silver Medal and cheque from The President, Dr. G . W . C . Milner. Optical Density - Its Rewards and Penalties G. F. Kirkbright Department of Chemistry, Imperial College, London, SW7 2A Y When thinking of a suitable theme for this paper I wished to avoid a simple catalogue for- mat that comprehensively described the results of the activities of my research group during the past few years.The subject of simultaneous multi-element analysis in atomic spectros- copy, and multi-component analysis in molecular absorption and emission spectrometry, has become of increasing importance during the past decade.A number of effects associated with the techniques that might be used to accomplish these analyses, but which conspire against their use in the simultaneous multi-channel mode, have been of Interest to us during this period. These effects are most frequently related to the fundamental processes of absorption of radiation in real sample cells.For the theme of this paper, therefore, I have chosen “optical density” (rather than absorbance) ; I hope to illustrate, from our own research work and that of other workers, the rewards and penalties of its utilisation, particularly in the context of simultaneous multi-species analysis. Introduction Techniques that depend on the absorption or emission of electromagnetic radiation by atoms or molecules are well known to provide sensitive, and frequently highly selective, analytical methods for their determination. The rewards that occur from the utilisation of these phenomena have become widely recognised in the examination of matrices where the analyte species is a major component and, more particularly, when the analyte species is present in trace concentration.The advantages for these purposes of techniques such as ultraviolet - visible and infrared absorption spectrometry, solution spectrofluorimetry and phosphorimetry, X-ray fluorescence, arc and spark emission spectrometry and atomic- absorption and atomic-fluorescence spectrometry have been repeatedly demonstrated. InJanuary, 1975 SILVER MEDAL ADDRESS 9 each of these techniques, the species to be determined is contained within a “cell” whose geometry is known either very accurately (in techniques such as ultraviolet absorption spectrometry in solution) or is reasonably well defined (as in a flame or arc).The analyte absorption or emission signal observed from the cell is related to the optical thickness and particle density.In the general case, we may define “optical density’’ as the product of the absorption coefficient for the analyte species at the wavelength of measurement, Kv, and the effective path length of the cell, L. The magnitude of the absorption coefficient, Kv, will depend on the particular transition and the nature of the energy states involved in the absorption process and will also be proportional to the particle density (Le., concentration) of the absorbing species.This well known relationship, expressed for all techniques of absorption spectrometry via the Beer - Lambert law, permits quantitative analysis and relates the observed signal strength to the particular characteristics of the analyte species. In order to achieve high sensitivity in absorption spectrometry, appreciable optical density (absorbance) should be attainable with low concentrations of analyte in the sample “cell.” This results from the difficulty associated with the precise measurement of extremely small optical densities, i.e., where the intensities of the incident and transmitted radiation from the source are similar. In most absorption techniques, difficulties in making precise optical density measurements begin when less than about 2-3 per cent.of the incident radiation is absorbed by the analyte at the wavelength of measurement. Consequently, as mentioned above, in the development of improved methods utilising absorption spectrometry, an attempt is usually made to produce the highest optical density possible for low analyte concentrations.In fluorescence techniques, where the emission of radiation must be pre- ceded by its absorption, similar considerations apply. While this approach is beneficial when the determination of only one species at a time is required for a particular sample, it is difficult to apply when simultaneous multi-element analysis is required. In this context, it may be preferable deliberately to create low optical density conditions, and to improve the techniques by which the low particle densities associated with these low optical densities are measured, rather than to strive for greater optical density from the components of a par- ticular sample.This approach may be generally applicable in spectrometry but at present it seems that the best methods available for achieving precise monitoring in optically thin cells involve the measurement of emission or fluorescence rather than absorption. I would like to elaborate upon and illustrate these considerations by reference to scme recent work in my own laboratory and elsewhere where techniques utilising this approach have proved successful in simultaneous multi-component analysis for both molecular and atomic species.Molecular Fluorescence Spectrometry It is well known that the detection and determination of both inorganic and organic species by spectrofluorimetry and spectrophosphorimetry may provide considerably higher sensitivity than molecular absorption spectrometry. This usually results from the relative ease with which the luminescence emission from the species determined is monitored at concentrations in the sample cell that produce only low optical density.The conventional “right-angle” illumination and viewing of the sample cell most fre- quently employed in solution luminescence studies is shown in Fig. 1; the radiant power of the luminescence can be obtained from the expression Pp = light absorbed x quantum efficiency = (Po - Pol0-ecZ)+ = Po(l - 10-ec’)+ where = quantum efficiency of the luminescence process for the analyte molecule; = the effective path length of the incident beam through the solution that is accepted = molar absorptivity of the analyte species; = concentration of the analyte species.Po = incident radiant power from the source; I e c at the detector; Equation (1) expresses the total luminescence radiant power.Only a fraction of this It is clear, however, that the luminescence radiant power is collected by the detector optics.10 SILVER MEDAL ADDRESS Proc. Analyt. Div. Chem. SOC. power, PF, can be directly proportional to the analyte concentration, c, for dilute solutions only when the higher terms involved in the expansion of the light absorption factor can be neglected. Under these conditions, equation (1) reduces to Pp = P,,ec+ It is therefore necessary to retain low optical density conditions in the sample cell in order to obtain linear analytical working curves over a wide concentration range. This may be achieved by working with solutions of low concentration and utilising powerful sources (PpccpO) and sensitive detection techniques such as photon counting to detect the weak luminescence signals which result, or by minimising the path length, 1.A method by which this can be accomplished is the adoption of the “front-surface” rather than the “right-angle” method of illumination and viewing (see Fig. 1). -I- PF Fig. 1. Right-angle (a) and frontal (b) viewing in fluorescence measurements.An additional spectrometry is factor that affects the analytical working curves for molecular luminescence the type of “inner-filter” iffect in which radiation emitted by the analyte species at its wavelength of maximum fluorescence intensity is absorbed before it can leave the cell. The absorption may result from “self-absorption” due to pronounced overlap of the absorption spectrum of the analyte with its luminescence spectrum, or may be caused by the presence of other species in the sample that absorb at this wavelength.Again, it is preferable to use low optical density conditions in these circumstances ; additionally, these “inner-filter” effects can be minimised by attempting to decrease the absorption and emission band-widths in order to decrease their overlap.The above considerations can be illustrated by recent studies in our laboratory concerned with the determination of polynuclear aromatic hydrocarbons (PAH) by luminescence techniques1 Although the detection and determination of these compounds can frequently be made with high sensitivity by conventional fluorimetry at room temperature in organic solvents , the broad absorption and emission spectra obtained under these conditions make their determination unselective.Thus, when samples contain complex mixtures of PAH compounds, their spectra overlap; it is necessary to resort to gas or liquid chromatography or other separation procedures before their identification and determination by solution spectrofluorimetry. If the Shpol’skii effect2 is utilised, however, this disadvantage is mini- mised and the presence or absence of individual PAH compounds in relatively complex mixtures can be confirmed.Using this effect, PAH compounds are included into the cry- stalline matrix formed at 77 K or below by selected n-paraffin solvents; extremely well resolved fine structure is then observed in their luminescence emission spectra. The obser- vation under these conditions of line-like structure, in which these individual lines may be less than 0.1 nm in half-width, can be explained by the postulate that the solute analyte molecules become embedded in the crystalline solvent lattice formed on cooling.In contrast to the case that applies in solvents that form transparent glasses at low temperature, where the glass does not show short range order and the electronic transitions are very sensitive to variation in the molecular field, in the crystalline solid solutions produced for PAH com- pounds in n-paraffin solvents the solute molecules experience a well defined molecular field that gives rise to sharp-line (quasi-linear) electronic spectra.Our early studies with this technique indicate that utilisation of these spectra should provide for the sensitive and extremely selective detection and determination of these compounds.January, 1975 SILVER MEDAL ADDRESS 11 Wavelengthhm Fig.2. Fluorescence emission spectrum of a M solution of 3,4- benzpyrene in n-octane at 77 K. To place our work on low-temperature luminescence spectrometry using the Shpol’skii effect into the context of the theme of this paper, a number of advantages in its application can be quoted.The spectra in Figs. 2 and 3 show the improved resolution obtained for 3,4- benzpyrene when the quasi-linear luminescence emission spectrum is produced in n-octane rather than its luminescence emission spectrum at 77 K in EPA (diethyl ether - isopentane - ethanol, 5+5+2), the solvent used frequently for low-temperature fluorimetry.The use of “front-surface” illumination of the crystalline matrix formed from n-octane results in a linear calibration graph over a concentration range of about 103-fold. The problems associated with overlapping excitation and emission spectra are minimised by the well resolved nature of the spectra. Indeed, it appears that the excitation spectra are also quasi-linear in many instances and it is probable that in the future selective excitation of quasi-linear luminescence using a narrow band-width tunable dye laser will result in virtually specific analyses even in complex mixtures.With this type of narrow-line excitation of a narrow “line-like” luminescence, a technique for analysis of molecular species analogous in its operation to the techniques of atomic-absorption and -fluorescence may be visualised.Wavelengthhm Fig. 3. Fluorescence emission spectrum of a M solution of 3,4-benzpyrene in EPA at 77 K. Atomic-absorption Spectrometry Fig. 4 shows the manner in which the absorption or emission line-width for an atomic For an atom cell of given geometry, it can be species varies with increasing optical density.12 SILVER MEDAL ADDRESS PYOC.Analyt. Div. Chem. SOC. expected that at low optical densities the absorption half-width is independent of atomic concentration. At high values, when the absorption (or emission) factor begins to approach unity ( i t ? . , the equivalent at the central wavelength for a black body at the same temperature), little further increase is possible at the central wavelength. The absorption (or emission) factor at the wings of the line can continue to increase, however, and line broadening occurs.When a line source (i.e., a hollow-cathode lamp) of spectral width smaller than the absorption line width of the analyte is employed for atomic-absorption spectrometry in a particular atom cell, this behaviour imposes an upper concentration limit for the analyte element beyond which there is progressive deviation from linearity; eventually, at very high optical density, there is no further dependence of absorbance upon Concentration.Similarly, when a con- tinuum source (e.g., a xenon arc lamp), the spectral band width selected from which is wider than the absorption line width, is employed a linear growth curve with a slope of unity is obtained until the half-width of the absorption line begins to increase; at higher optical density, a growth curve with a slope of Q is obtained (see Fig.5). For both line and continuum sources, this behaviour is predicted from evaluation of the expression for the total absorption factor, AT, for high and low optical density conditions (e.g., see ref.4). As mentioned earlier, the lower limit of optical density at which precise atomic-absorption measurements can be made depends on the instrumentation employed and the signal to noise ratios obtained at these low values. In general, however, difficulties with these measurements would begin when less than 1-2 per cent. absorption is to be measured. These two factors at high and low optical density serve to restrict the linear working range over which precise and accurate measurements can be made in atomic-absorption spectrometry.E -12 -8 -4 0 4 8 12 w 2(X - Xo)/A 1, Fig. 4. Variation of atomic line-width at different values of optical density (K,Z) for line characterised by dispersion profile. Adapted from ref.3. The above considerations of restrictions of the linear working range in atomic-absorption spectrometry become of primary importance when an attempt is made to undertake simul- taneous multi-element analysis rather than single-channel work. Problems arise when the simultaneous determination of a number of elements is required using a single set of flame conditions and a single sample solution.Fig. 6 shows the atomic-absorption calibration graphs that might be obtained for two elements, A and B, when the determination of element A can be made with greater sensitivity than that of B. If the linear working range for each falls between, for example, 3 and 70 per cent. absorption at the wavelengths chosen, then it is apparent that if both elements are to be determined simultaneously in the same sample solu- tion, the ratio of the concentration of B in the solution to that of A must lie within a relatively narrow fixed range.It is therefore not possible to determine simultaneously both elements by atomic-absorption spectrometry when they may be present in samples over a wide range of concentration ratios. This situation naturally becomes of increasing complexity as the number of elements whose simultaneous determination is required increases.Attempts to resolve this difficulty by introduction of the sample solution into the cell at several dilutions result only in slow sequential analysis. It is also not possible to obtain a satisfactory solution to the prob- lem by resorting to the use of atomic lines of different oscillator strength; this procedure simply exchanges the necessity for the concentration of a particular element in the sample toJanuary, 1975 SILVER MEDAL ADDRESS 13 lie within one concentration range if one of its resonance lines is used, for the necessity for its concentration to lie in a different range at an alternative wavelength.In order to ensure that the concentration of an element lies in the linear analytical range at the wavelength chosen, at least some knowledge of its concentration level in the sample is pre-supposed.The problem of simultaneous multi-element analysis by atomic-absorption spectrometry using either flame or non-flame atom cells is further complicated by the fact that different elements may require different atomisation conditions in the cell.Thus, the flame stoicheiometry required for the efficient atomisation of A may be different from that required for element B in the same sample, particularly when the need to minimise interference effects is taken into account. Concentration of A or B Fig. 6. Calibration graphs in atomic- 0.1 1 -0 10 100 and B whose determination is of widely Nfthh cm- different sensitivity (for 1 per cent.absorption) using a single set of conditions in a given atom cell. 0.001. I I I I absorption spectrometry for elements A Fig. 5. Growth curves calculated for atomic absorption with continuum and narrow line sources. Adapted from ref. 4, where the calculation refers to the magnesium 285.2-nm line and a cell tempera- ture of 2400 K. Low optical density High optical density Line source .. Continuum source The situation may be even more difficult if non-flame atomisation is to be employed in the simultaneous multi-element mode. In non-flame cells, such as the graphite filament or furn- ace atomiser, high sensitivity is usually obtained by the deliberate formation of a short- duration optically dense atom population; attempts to control atomisation conditions so as to retain a worthwhile range of concentration ratios in the sample over which simultaneous determinations of a number of elements may be made, while minimising interference effects, will give rise to difliculties.Thus, while a number of workers have reported instrumental systems in which ingenious techniques have been described to facilitate simultaneous multi- element atomic-absorption spectrometry by the use of a number of spectral line sources and detectors with a single atom cell (e.g., see refs.5-49, the fundamental limitation to the general utility of all of these systems lies in the atom cell itself as described above. This is not to say that these systems will not fulfil a need for certain well specified tasks, where a small number of elements must always be determined in a particular sample type whose composition does not vary very.greatly from sample to sample, and where the best compromise conditions can be established carefully for the simultaneous determination of these elements at a single dilution. In view of the difficulties involved in the general application of atomic-absorption spectrometry to simultaneous multi-element work, where each user requires the determination of a different combination of elements at widely different concentrations in samples of different types, it is perhaps not surprising that no commercial multi-element instrumentation based on atomic- absorption spectrometry has appeared.A technique that we have employed, which may assist the application of flame sources in multi-element analysis by atomic-absorption spectrometry, involves the use of a special type14 SILVER MEDAL ADDRESS Proc.Artalyt. Div. Chew. SOC. of capillary burner system shown in Fig. 7. In this burner, the pre-mixed fuel and oxidant carry the nebulised sample to form a stable flame on the longer set of capillaries.The second, shorter capillaries interspaced between those carrying the pre-mixed gases and sample aerosol can be supplied with an ineft gas such as nitrogen or argon without affecting the flame stability. The provision of these auxiliary capillaries enables the flame gases above the primary reaction zones to be diluted with inert gas. Thus, in a situation where two elements, A and B, are to be determined in a single sample solution at one dilution and, for example as in Fig.6, element A gives greater sensitivity than B and is present at a concentration that produces very high absorbance at the resonance line chosen, the auxiliary inert gas supply can be employed to lower the optical density obtained for B to a value that ensures that it is measurable within its linear working range.Thus, as shown in Fig. 8, the absorbance for A is measured within its linear working range without the use of the auxiliary gas and the “off-scale” value for B is ignored. The auxiliary gas is then switched on automatically at a pre-set flow-rate and the absorbance for B is measured within its working range while the very low value for the absorbance of A is ignored.By this technique, which can readily be operated automatically, the particle density in the flame cell is lowered by dilution of the flame rather than by dilution of the sample solution. A subsidiary advantage of the burner system is that when air is used in the auxiliary capillary system, the flame stoicheiometry above the primary reaction zone can be varied so as to provide alternatively fuel-rich and fuel-lean conditions for the atomisa- tion of different elements.Diluent - t Flame gases + sample Fig. 7. Capillary burner with provision for dilution of flame with inert gas. 0 Fig. 8. Time + Use of capillary burner (see Fig. 7) with different diluent gas flows for the determination of two elements A and B in a single sample solution. The above approach, however, produces only a partial solution to the problems described earlier in the use of atomic-absorption spectrometry for multi-element analysis and produces sequential rather than simultaneous analysis.It may find application, however, for a number of specific problems. As mentioned in the introduction, a more general solution to these problems may be to “dilute out” the effects and deliberately create very low optical density conditions simultane- ously for all elements to be determined in a single sample.Thus, low particle densities and/or path length should be used. Naturally, this will produce conditions where only very small absorbance values are to be measured. With the type of absorption measurement system available at present, it is *cult to make these measurements with high precision.Probably the best available alternative is to monitor the absorption indirectly, via that fraction re- emitted as atomic fluorescence, or to abandon absorption and return to the measurement of the thermal emission from atoms at low particle density in a hot source. Thus, it seems that the detection of the low light signals associated with atomic emission from optically thin sources may be more suitable than atomic-absorption spectrometry for the precise measurement of low particle densities. I shall now consider the use of these techniques for simultaneous multi- element analysis, via the use of atomic-emission spectrometry with an inductively coupledJanuary, 1975 SILVER MEDAL ADDRESS 15 high-frequency plasma source and atomic-fluorescence spectrometry with pulsed spectral sources.Radiofrequency Plasma Emission Spectrometry Fig. 9 shows a schematic representation of a plasma emission spectrometer system that we have described earlier.l03l1 The 36-MHz plasma torch system is similar to that described by other w0rkers12-l~; aqueous sample solutions can be introduced into the plasma without the requirement of desolvation of the aerosol.Our early studies confirmed reports from other ,;Q Grating mo nochromator PMT EHT =I4 r Lock- i n - amplifier Recorder laboratories that high detection sensitivity in emission could be obtained with this source for a wide range of elements and that the linear working concentration range attainable was fre- quently considerably greater than that attainable in atomic-absorption spectrometry or flame- emission spectrometry.In a recent study, we predicted the comparative performances of the nitrous oxide - acetylene flame and high-frequency plasma atom cell as emission sources for simultaneous multi-element analysis by the use of simple mathematical models of both cellsu In these models of flame and plasma, reasonable assumptions are made concerning the tem- perature, velocity and flow conditions of the hot gases. A summary of the characteristics of the two atom cells is shown in Table I. - TABLE I TYPICAL OPERATING CONDITIONS FOR THE RADIOFREQUENCY INDUCTION-COUPLED PLASMA AND PRE-MIXED NITROGEN SHIELDED NITROUS OXIDE - ACETYLENE FLAME Parameter Fuel gas flow-rate Injector gas flow-rate Oxidant gas flow-rate Coolant gas flow-rate Shield gas flow-rate Sample uptake rate, QLI Nebuliser efficiency, i+h Path length of cell, L Width of burner, b Height of reaction zone, ht Height of viewing zone Surface area of core Volume of core Mean gas density, p Mean specific heat of gas, Cp Flame expansion factor Ambient temperature, To Flame temperature, T Maximum temperature, Tmax.Plasma Flame 3.3 dm3 min-1 3.0 dm3 min-1 6.6 dm3 min-1 15 dm3 min-I 1.6 cm3 min-l 0.01 20 mm 25 mm 10 mm 22 cm2 8 cma 1.78 g dm” 0.524 J g-l K-l 1.0 300 K 8260 K 9000 K 15 dm3 min-l 4.2 cm3 min-l 0.1 50 mm 0.4 mm 0.1 mm 10 mm 50 mme 2 mm3 0-96 g dm-3 1.35 J g-l K-l 1.667 300 K 2800 K 3000 K16 SILVER MEDAL ADDRESS Proc. Analyt. Div. Chem. SOC. It is instructive to compare the particle density obtained for analyte elements introduced into the atom cells and the effect of the particle density on the degree of self-absorption and the working curves produced.The particle density, NA, of an analyte element in either cell can be calculated from where Qs is the volume of flame or plasma gas entering the atom cell per second at an ambient temperature To, C$ is the nebuliser efficiency, A is Avogadro's number, Qs is the sample uptake rate, MA is the relative atomic mass of the analyte element, T is the mean flame temperature, y is the molar flame expansion factor and CA is the concentration of analyte element A in aqueous solution.For the purpose of comparison of the two atom cells, the line emission observed for the calcium atom and ion at 422.67 and 393.37 nm, respectively, zinc at 213.86 nm and copper at 327.40 nm will be considered.The particle densities of elements calculated from equation (3) give the total particle density of all species of that element, so that in order to determine the particle densities of the indi- vidual species, the free atom fraction and the degree of ionisation must be measured or calcu- lated.Few data are available concerning the free atom fraction of these species in the radio- frequency plasma, although consideration of the dissociation energies of their oxide and hydroxide species suggests that the assumption of a value of unity for the free atom fraction is realistic. With values of the dissociation energy of calcium hydroxide, copper(I1) oxide and zinc oxide of 104, 95 and 65 kcal mol-l, respectively, we calculate a value of unity for the free atom fraction of each element assuming a partial pressure of low6 atm for the oxide species and a temperature of 8000 K.We cannot assume a value of unity for the free atom fractions of these elements in the nitrous oxide - acetylene flame, however, as lower values have been found by several workers.For the purposes of our calculations, we have assumed values of 0.33, 0.33 and 0.50 for the free atom fractions of calcium, copper and zinc, respectively.1Q-" In the radiofrequency plasma, the degrees of ionisation of calcium and zinc were measured to be 0-75 and 0-1, respectively, from the observed intensities of the atom and ion lines, assuming a temperatnre of 8250 K.The calculated degree of ionisation of copper using the Saha equa- tion under these conditions is 0-5. In the plasma, the high free electron density (about 10aom--3) is so much greater than the analyte particle density that the degree of ionisation remains virtually constant at all concentrations of the analyte considered. In the nitrous oxide - acetylene flame, the degree of ionisation of calcium has been calculated to be 0.43 using the Saha equation and assuming a partial pressure of 10" atm for the analyte atoms.The measured degree of ionisation of calcium in this flame has been reported to be 0.43 (ref. 22) and 0.38 (ref. 23) and for this calculation we have assumed a value of 0.4. The calculated degree of ionisation of zinc in this flame is less than 0.01 and can be neglected, while that of copper is only about 0.03, and has also been neglected in this calculation.The degree of ionisation for each element in the flame refers to that for a 1 p.p.m. solution; no allowance has been made for any variation in the degree of ionisation with analyte concentration. TABLE I1 PARTICLE DENSITIES OF ANALYTE ATOMS IN THE PLASMA AND FLAME ATOM CELLS AND THE DOPPLER HALF-WIDTH AND OSCILLATOR STRENGTH OF THE LINES OF THE ATOM CONSIDERED Particle den~itylm-~ Doppler hdf-width/nm t 3 r- Species A/cm M A f Plasma Flame Plasma Flame Ca I 422.67 40-1 1-75 6.8 x 1015 8-2 x 1015 0.0043 0.0025 Ca I1 393.97 40.1 0.69 2.1 x 1015 5.4 x 1015 0-0040 0-0024 Cn I 327.40 63.5 0.16 8.6 x 1 0 x 4 8.6 x 1015 0.0027 0.00 16 Zn I 213-86 65-4 1.2 1.6 x 1015 1.3 x 10ls 0-0017 0~0010 A Table I1 shows the calculated particle densities of these species when a solution containing 1 p.p.m.of analyte element is nebulised into both the plasma and flame operated under the conditions shown in Table I, the wavelength of the line of the species considered, the oscillator strength of these lines and the Doppler half-widths of these lines calculated assuming a plasma temperature of 8250 K and a flame temperature of 2800 K.January, 1975 SILVER MEDAL ADDRESS 17 The absorption coefficient at the line centre, Kv, of the analyte element at the line considered can be calculated from the following equation: In equation (a), e is the electronic charge, m is the mass of the electron, c is the velocity of light, A&, is the Doppler half-width, f i s the oscillator strength, E,, is the permittivity of free space and No is the particle density in the ground state.The values of Kv and KvL calculated for the plasma and flame at the particle densities obtained from equation (4) and assuming that the radiation is viewed from the centre of the atom cell are shown in Table 111.TABLE I11 ABSORPTION COEFFICIENTS OF ANALYTE ATOMS IN THE Plasma PLASMA AND FLAME ATOM CELLS Flame r 1 Species h/nm Kv/rn-l KvL Ca I 422.67 0.408 0.00408 cu I 327.40 0,046 0.00046 Zn I 213.86 0.406 0.00406 Ca I1 393.37 0.460 0.00450 f 1 Kv/m-l K,L 8-41 0.210 2-06 0.051 0-79 0-020 5.80 0-145 From the values of KVL obtained for these lines, it is possible to construct theoretical calibra- tion graphs using the relationship where I,, is defined by the Einstein - Boltzmann equation: where u is the partition function of the atom or ion, h is Planck's constant, gk is the statistical weighting factor of the upper state involved in the transition, Ek is the energy of the upper state and k is the Boltzmann constant.Curves obtained for the four lines considered are shown in Fig.10. The intensity represented for the plasma is the intensity emitted per unit volume relative to the intensity emitted per unit volume in a flame taken as unity at the limit where the absorption coefficient, Kv, becomes equal to that of a black body at the wavelength concerned. It is apparent from these curves that the radiofrequency plasma exhibits an extended linear working range at high solution concentration compared with that attainable with the flame.In the plasma, the linearity of the Ca I line at 422.67 nm, the Ca I1 line at 393.37 nm and the Zn I line at 213.86 nm are predicted to be almost identical, as the value of KvL for each line is similar. Also, as the absolute emitted intensity at any line is very much greater in the plasma than in a flame, the potential sensitivity of the technique is much higher and the linear range should also be extended to lower optical densities (Le., concentra- tions).A second advantage of the plasma system is that as the absolute emitted intensity is very much higher than that obtained with a flame, it is possible to reduce the sample uptake rate of the nebuliser system and maintain adequate signal intensity, which reduces the value of K,.This technique, therefore, offers a very simple means of extending the linear range obtained at high concentrations in the plasma with minimal sacrifice in sensitivity. One of the advantages claimed for the radiofrequency plasma system is that the residence time of an analyte particle in the discharge and tail-flame is long compared with that in a flame or arc excitation cell.For the plasma system employed in the present work, it can be assumed that the linear velocities of analyte particles and carrier gas atoms are the same; the residence time of analyte particles will therefore be the same as that for the gas atoms or molecules. The linear velocity of gas through the entrance port into the plasma is given by the equation VO = 4QG/vLa (7)18 SILVER MEDAL ADDRESS Proc.Artalyt. Div. Chem. SOC. where L is the path length of the cell (Le., the diameter of the tail-flame), Qa is the flow-rate of the gas at ambient temperature and vo is the linear velocity of the gas up the plasma tube. The corresponding equation for the flame is vo = Qa/bL (8) where L is the burner slot length and b the burner slot width.Solving these equations for the operating conditions of Table I gives a linear velocity of gas into the plasma of 0.16 m s-1 and into the flame of 8.25 m s-l. After passing into the plasma core or primary reaction zone of the flame, a volume expansion takes place. Thus the linear velocity of gases after leaving the reaction zone is given by where y is the molar flame expansion factor.respectively. equation where ht is the thickness of the reaction zone and vBV is the average linear velocity through the reaction zone. For the plasma, it is assumed that the average velocity through the plasma core is 4.4 m s-l and for the flame it is assumed that the average velocity through the primary reaction zone is 70 m s-l.The calculated residence times are 5.7 ms for the plasma and 1.5 ps for the flame. VT = voy T/To (9) Solving this equation for the plasma and flame gives linear velocities of 4.4 and 130 m s-1, The residence time of analyte particles in the reaction zone can be calculated from the tr = h t / L ( 10) 0.1 1 10 100 1000 Concentration, p.p.rn. Fig. 10. Calculated growth curves for plasma and long flame cells for elements considered: (A) calcium a t 422-67nm; (B) calcium at 393-37nm; (C) zinc at 213-86 nm; and (D) copper at 327-40 nm.If it is assumed that the emission intensity is viewed over a length of 10 mm above the top of the plasma core or primary reaction zone, the residence time of analyte in the viewing zone can be calculated from the equation The residence time for an analyte particle in the plasma tail-flame is therefore 3.3 ms com- pared with 77 ps in the flame.t, = l/lOoV, (11)January, 1975 SILVER MEDAL ADDRESS 19 The plasma system can readily be seen to retain the analyte atom in the volume viewed for a much longer period than the flame. It can therefore undergo many more collisions to effect excitation during its residence compared with the number experienced in the flame. As the lifetime of the excited atom is typically a few nanoseconds, it is apparent that the atom can be excited and may emit about thirty times in the plasma tail-flame compared with once in the flame.The additional advantage of the longer residence time is that for samples whose rate of vaporisation is low, complete vaporisation may be possible during their residence in the plasma, whereas complete vaporisation cannot be attained in the nitrous oxide - acetylene flame.Fig. 11 shows the effect of variation in the sample uptake rate in the radiofrequency plasma upon the calibration graphs obtained for calcium at 422.67 nm. At low sample uptake rates, the particle density, and hence optical density, is low, and the linear range is therefore extended to higher solution concentration compared with the range obtained with high sample uptake rates. The observed emitted intensity at each line is, of course, reduced at low uptake rates as the particle density is lower.The detection limit does not deteriorate at low sample uptake rates to the same extent as the signal attenuation predicted from the reduction of particle density.This is probably due to the fact that less solvent is transferred to the dis- charge at low sample uptake rates so that there is less impedence mismatch between the resonance circuit of the oscillator valve and the plasma discharge. Also, it is to be expected that the plasma temperature will increase at low sample uptake rates as there is less solvent in the discharge to absorb the applied power.0.001 I I I 1 I I 2 20 200 2000 20 ooo Concentration, p.p.m. Fig. 11. Effects of sample uptake rate on calibration graphs in the R.F. plasma for calcium at 393-37 nm. Uptake rates: A, 4-5; B, 3.2; C, 1-5; and D, 0.8 ml min-'. In the nitrous oxide - acetylene flame, a similar effect of longer linear range at low sample uptake rates i s observed for the calibration graphs, but even at low uptake rates the linear range is still small.The advantage of the radiofrequency plasma is that the observed linear range of the calibra- tion graphs can be made to extend for about five to six orders of magnitude, while for the flame under the conditions employed the maximum observed was three orders of magnitude.Analysis of Aluminium Alloys In order to compare the application of flame emission and plasma emission spectrometry, the determination of six minor elements in aluminium alloys was examined. The plasma and flame were operated under the conditions shown in Table I. Solutions of BCS aluminium samples and standard solutions were introduced into the plasma at a sample uptake rate of 1.5 cms min-l and were determined sequentially from the same solution without dilution for different elements.Titanium was determined at 365.35 nm, iron at 371.97 nm, manganese at 403.07 nm, zinc at 213436 nm, copper at 327.40 nm and magnesium at 285.21 nm. A slit width of 25 pm [a spectral band pass of 0-08 nm] was employed throughout. The acetylene gas flow-rate to the nitrous oxide - acetylene flame was adjusted so as to maximise the signal obtained for titanium.The solutions were introduced directly into the flame and analysed for titanium, manganese and iron at the same lines as those employed for the plasma.20 SILVER MEDAL ADDRESS Proc. Analyt. Div. Chem. SOC. Because of the non-linearity of the calibration graphs for magnesium and copper at these lines, appropriate dilutions were made before these metals were determined.Insufficient sensitivity was obtained for zinc in the flame to allow its detection in three of the aluminium samples and zinc was detectable but could not be determined with adequate precision in the fourth sample. The results of these analyses are shown in Table IV.Each value shown is the mean of six results obtained by each technique; the values are compared with the BCS certificate values in each instance. There appears to be no significant discrepancy between the results except where dilutions of the stock solution were necessary (for magnesium and copper) due to re- stricted linear range when the nitrous oxide - acetylene flame was employed. The results obtained for titanium by flame emission spectrometry are somewhat high; this may be due to the fact that no ionisation suppressant was added to the standard titanium solutions or to the aluminium samples.TABLE IV ANALYSIS OF ALUMINIUM ALLOYS BY PLASMA AND FLAME EMISSION All analyses were performed on a solution containing 1 g of alloy in 100 cm3 of solution by plasma emission These solutions were also used for flame emission spectrometry except for: (a) 0-1 g of alloy spectrometry.per 100 cm3 of solution; (b) 0.01 g of alloy per 100 cm3 of solution. Alloy Element BCS 216/2 BCS 26311 BCS 300 BCS 181/1 cu Mg Fe Mn Ti Zn cu Fe M g Mn Ti Zn c u Fe :: 2 Ti Zn cu Fe Ti Zn Certificate value, per cent. 3.99 f 0.02 0-36 f 0.01 1.42 f 0.03 0.10 & 0.01 0.14 f 0.01 0.02 f 0.01 4.66 f 0.01 0-28 f 0.01 0.75 f 0-01 0.71 f 0.01 0.037 f 0.001 0.20 f 0.01 0.09 f 0.01 0.35 f 0.01 4-92 f 0.05 0.36 f 0.01 0.038 f 0.001 0.05 f 0.01 1-28 f 0.02 0.30 f 0.01 2-76 f 0.03 0.41 f 0.01 0.16 f 0.01 5.98 f 0.04 Plasma value, per cent.3.97 & 0.08 0.36 f 0.01 1.41 f 0.04 0.10 f 0.01 0.14 f 0.01 0.02 f 0.01 4.54 f 0.10 0-28 f 0.01 0.75 f 0.03 0.70 f 0.01 0.03'7 f 0.003 0.20 f 0.02 0-10 f 0.01 0-33 f 0-02 4-94 f 0.11 0-36 f 0.01 0-037 f 0.004 0.05 & 0.01 1-27 f 0.04 0.30 f 0.01 2-78 f 0.09 0.41 f.0-01 0.16 f 0.01 5-94 f 0.15 Flame value, per cent. 3.8 & 0-4(a) 0-34 f 0.04 1-4 f O-l(b) 0.09 f 0.01 0.18 f 0.04 -* 4-3 f 0.3(a) 0.27 f 0.03 0.90 f 0*04(b) 0.71 f 0-04 0.04 f 0-02 0.10 f 0.02 0.34 f 0-03 4.6 f 0-3(b) 0.35 -& 0.05 0.04 & 0-02 1.4 f O.l(a) 0.29 f 0.02 2.9 f O-l(b) 0.41 f 0.02 0-18 f 0-06 -t -* -* * Not detected.t Not determined. The results shown for the analysis of aluminium alloy samples by both plasma and flame emission spectrometry demonstrate the utility of the wide concentration ranges for each ele- ment over which linear calibration is obtained with the high-frequency plasma source.Thus, whereas all of the analytical results shown in Table IV for plasma emission spectrometry were obtained at a single dilution (1 g of alloy per 100 cm3) , in the corresponding analysis by flame emission spectrometry several dilutions were required for each sample in order to effect the determination of five elements. Atomic-fluorescence Spectrometry Atomic-fluorescence spectrometry has been shown by a number of workers to provide for high sensitivity in the determination of a range of elements using either flame or non-flame atomisers.As radiation from a spectral line or continuum source must be absorbed by the analyte atomic population before it can be re-emitted as atomic fluorescence, these effects which influence the total absorption factor, AT, and its variation with the analyte concentra-January, 1975 SILVER MEDAL ADDRESS 21 tion, as described earlier for atomic-absorption spectrometry, also affect the working curves obtained in atomic-fluorescence spectrometry (e.g., see ref.24). The working curves that result in atomic-fluorescence spectrometry with atomic line sources are illustrated in Fig.12. The ideal fluorescence intensity curves are similar to those obtained in atomic-absorption spectrometry owing to the direct proportionality between the integrated fluorescence intensity, IF, and the total absorption factor, AT, through the expression where I0 is the radiant flux that excites the fluorescence under consideration, W is the width of the exciting beam of radiation, i2 is the solid angle over which the excited fluorescence is detected and measured (47r is the total radius over which fluorescence is emitted from the cell) and 4 is the fluorescence yield (the fraction of the absorbed photons that is re-emitted as fluorescence).Log N Fig. 12. Hypothetical growth curve in atomic- fluorescence spectrometry with a narrow line source. IF is intensity of fluorescence signal and N the con- centration of ground-state analyte atoms in cell.Broken lines indicate effect of increasing extent of incomplete illumination and viewing of atoms in cell. In practical atom cells, the assumptions made in the derivation of the simple expressions for AT and Ip are usually not adhered to. Thus, with flames, it is not often that the entire fluorescence cell is within the solid angle excited by the source and viewed by the detector, and where a cell has an appreciable path length some fluorescence emission is invariably lost by re- absorption.These effects become most serious for resonance fluorescence effects and high optical densities (as illustrated in Fig. 12) and provide the high concentration limit to the linearity of the working curves.For non-resonance fluorescence processes, such as in direct- line fluorescence, re-absorption of fluorescence radiation may be less severe because the popula- tion of the intermediate level is small; under these conditions, a longer linear working range may be achieved. At low optical densities, however, the linear relationship between fluores- cence intensity and analyte concentration is easily preserved in most atom cells.As seen from equation (12), the intensity of fluorescence, IF, is directly proportional to the source intensity, Io. It is therefore possible to make measurements in atomic fluorescence when the total absorption factor, AT, (or optical density) is very low, by the use of an intense spectral source and sensitive detection systems.Such measurements are possible at optical densities that would be too low to monitor directly by atornic-absorption spectrometry. It is this factor which accounts for much of the gain in sensitivity attainable by atomic-fluorescence spectrometry compared with atomic-absorption spectrometry for a number of elements. This factor also results in extension of the available linear working range by provision o1 a method of measurement of lower optical densities even though the upper limit to the working range may be similar.The greater available linear working range attainable, together with the minor advantage that it is frequently easier to arrange a number of sources and a single detector around the atom cell employed in atomic-fluorescence spectrometry than in atomic-absorption spectrometry, results in the justification of the use of atomic-fluorescence22 SILVER MEDAL ADDRESS PYOC.Analyt. Div. Ckem. SOC. spectrometry rather than atomic-absorption spectrometry for simultaneous multi- element analysis. Fig. 13 shows the working curves for chromium, zinc and calcium in an air - acetylene flame using pulsed hollow-cathode lamp sources and an atomic-fluorescence spectrometer capable of rapid sequential operation25; the instrumental system employed was based on the multi-channel atomic-fluorescence spectrometer described by Mitchell and Johansson.= The concentration range over which linear working curves can be obtained is typically as great as lo4 or lo6.This may be exploited, in a manner similar to that described above for the high-frequency inductively coupled plasma source, in the simultaneous detennin- ation of a number of elements by atomic-fluorescence spectrometry at a single dilution in samples where widely different concentration range ratios of one element to another are expected in the sample.This has been confirmed for multi-channel atomic-fluorescence spectrometry in the simultaneous determination of six elements in sea water,m lubricating oils28 and aluminium alloys. g9 0901 001 0.1 1 10 100 1000 Concentration, p.p.m.Fig. 13. Atomic-fluorescence spectro- metric working curves for chromium, calcium and zinc obtained with an air- acetylene flame and pulsed hollow-cathode lamp sources. Adapted from ref. 25.Before leaving consideration of the technique of atomic-fluorescence spectrometry , the recent advances in this technique using pulsed laser sources of high intensity should be rnen- tioned. As described above, any method whereby source power delivery to the atom cell used for atomic-fluorescence spectrometry may be increased has a beneficial effect on sensitivity in atomic-fluorescence spectrometry.As pointed out by Fraser and Winefordner,m the use of a stable, repetitively pulsed source of excitation with a small duty cycle, i e . , a small ratio of on- to-off time, might permit an increase in the fluorescence signal to noise ratio owing primarily to decreased noise; during the short on-time, the signal may be of the same magnitude as the average signal obtained using a continuously operated source, whereas the noise would be small because of the small number of random photo-detector pulses from dark current, flame background emission, etc.Thus, the high peak power output from a repetitively pulsed, tunable laser should provide for high power delivery to an analytical atom cell and permit the attainment of high detection sensitivity.This type of system should in most respects be the ideal source for analytical atom$-fluorescence spectrometry. Fraser and W i n e f ~ r d n e r ~ , ~ ~ have reported the use of a fast repetition rate pulsed system utilising a nitrogen laser-pumped tunable dye laser for excitation of atomic fluorescence from a wide range of elements in air - hydrogen, air - acetylene and nitrous oxide - acetylene flames.The peak power output of the dye laser over a spectral band width of 0-1-1 nm is about 10 kW, the average power output of the dye laser is about 0.001 W, the pulse half-width is 2-8 ns and the repetition rate is 1-30Hz depending on the dye used. Ten dyestuffs were used, each covering a spectral range of about 30 nm in order to provide a system tunable over the range 360-650 nm.As the output of the tunable dye laser can be varied over a range of 10-30 nm, depending on the dye, it is possible to wavelength scan the output of the dye laser. This pro- vides a convenient means of correction for any background scatter signals and obtaining spectral information by the use of a fast response photomultiplier tube and a boxcar integrator capable of aperture gate widths of the order of 10 ns.With this laser technique, therefore, atomic fluorescence is effectively excited with a wide-line source with a power output ofJanuary, 1975 SILVER MEDAL ADDRESS 23 10 kW, i.e., during the laser “on-time” fluorescence is excited with a source having an effective black body temperature of 75 OOO K at 400 nm and during the “off-time” no signal or noise is being measured.With a duty cycle of about IO-’, i.e., with the laser “on” for only 1 part in l o 7 parts, random noise effects from flame flicker, electronic measurement, noise and fluctua- tions in sample introduction are negligible at most concentrations. The resonance fluores- cence signal to noise ratio at high concentrations is dependent on shot noise in the signal owing to the randomness in the emission of photons, pulse-to-pulse amplitude variations in the dye laser output and also scatter noise.At low concentrations, i.e., near the limit of detection, the resonance fluorescence signal to noise ratio is primarily dependent on scatter noise from particles and optical inhomogeneities in the flame gases. Linear analytical fluorescence calibration graphs were constructed by Fraser and Wine- f ordner for fluorescence of aluminium, calcium, cobalt, chromium, gallium, indium, iron, manganese, molybdenum, nickel, strontium, titanium and thallium over three or four orders of magnitude concentration range.Resonance and non-resonance fluorescence effects were utilised. A limitation of the present dye laser excitation systems is the lower useful wave- length limit of 360 nm, which precludes the possibility of excitation of intense fluorescence of many elements.In flame atomic-absorption and atomic-fluorescence spectrometry with continuum sources and with dilute atomic vapours, the integral of the atomic-absorption coefficient, AT, is generally dependent only on the wavelength and the optical density of the absorber.This is strictly correct, however, only in the limit of zero incident light flux, i.e., when the incident radiation does not cause significant population of the excited state relative to the ground state. This is a good approximation only for low incident light fluxes available from conven- tional sources such as hollow-cathode or electrodeless discharge lamps.When the source flux is very high, however, as in laser excitation, this expression does not provide an accurate description of the attenuation of the light beam. Under these conditions the absorptiort coeficient becomes also a function of the incident radiant flux density (non-linear absorption) .53 The intense radiation may then induce in the sample a state of near-saturation of the energy levels in which the excited state population becomes substantially equal to that of the ground state.Winefordner and co-workers93 and PiepmeierW have described the theoretical and practical consequences of the occurrence of saturation in atomic-fluorescence spectrometry for a broad-band laser excitation source and a monochromatic laser excitation source, respectively.The reader is referred to the publications of these authors for a comprehensive treatment of the theoretical consequences of working near to saturation conditions. In the context of this paper, however, the effect of working close to saturation conditions, and the important observa- tion that under these conditions the radiated fluorescence flux is influenced very little by collisional quenching, have several consequences of great importance from a practical analytical point of view: (1) The fluorescence signal is not greatly influenced by the source stability.The satura- tion effect above a certain value of the source power ensures that any pulse-to-pulse variation in the source irradiance does not affect the stability of the fluorescence signal. (2) The linearity of the fluorescence working curve is extended to higher concentrations. At saturation, the medium becomes transparent at the wavelength of the transition because the excited and ground-state populations are similar and further absorption in the irradiated volume cannot occur.If the irradiance of the source is such that the atomic system can be kept at saturation for any value of analyte atom concentration, the fluorescence flux will be linearly related to this and the calibration graphs will have a slope of unity even at high apical densities.If the medium is transparent, self-absorp- tion cannot take place, and also the source irradiance is no longer a function of the length along the absorption path. Obviously, this consideration of transparency under saturation conditions applies only for the irradiated volume; the factors of self-absorp- tion and self-reversal must still be considered for the post-filter effect produced in any unilluminated volume between the fluorescing volume and the detector.(3) The proportional dependence of fluorescence signal on the quantum efficiency which is observed at low irradiance is removed under saturation conditiorts.Thus, provided that the atomisation efficiency does not change, the magnitude of the saturated fluores- cence signal would not be expected to be greater in the oxygen - argon - hydrogen flame than in a hydrocarbon flame containing nitrogen in spite of the large difference in24 SILVER MEDAL ADDRESS Proc. Analyt. Div.Chem. SOC. quantum yield for these flames. Thus, the nitrous oxide - acetylene flame is just as effective as other flames from this viewpoint and can be used in atomic-fluorescence spectrometry to maximise atomisation efficiency and minimise chemical interferences without the penalty of lower quantum yield experienced under low irradiance condi- tions. Obviously, the first consequence has a direct bearing on the detection limits obtained in atomic-fluorescence spectrometry using a low source.The extension of the linear range of the analytical working curves is of direct relevance in the context of multi-element analysis as is also the benefit of independence of the fluorescence signal on the flame type employed. Thus, a single flame type and stoicheiometry may be suitable for the determination of a large number of elements; we may expect the successful use of linear working curves over a very wide range of concentrations due to the improved signal to noise ratios at low optical densities and the extension of the upper limit of linearity obtained when working close to saturation conditions.I hope that I have been able to illustrate some of the problems for multi-component analysis that result from the very process, the absorption of electromagnetic radiation by atoms and molecules, which makes the techniques of spectroscopic analysis possible.I also hope I have shown the results of some recent work, both in our own laboratory and elsewhere, directed to- wards solution to these problems. It is a pleasure to thank the students who have worked with me during the past years in our research in analytical atomic and molecular spectroscopy.For our own studies reported in this paper I wish to thank Mr. C. de Lima, Dr. L. Ranson and Dr. A. F. Ward. I wish again to express my thanks to the Council of the Society in honouring me with the award of the first Society for Analytical Chemistry Silver Medal. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. SO. 31. 32. 33. 34. References Kirkbright, G. F., and de Lima, C. G., ANaZyst, 1974, 99, 338. Shpol’skii, E. V., Zh. Prikl. Spektrosk., 1967, 7 , 492. Hooymayers, H. P., Ph.D. Thesis, Utrecht, 1966. Zeegers,P. J. T., Smith, R., and Winefordner, J. D., Analyt. Chem., 1968, 40, 26A. Walsh, A., in Kirkbright, G. F., and Dagnall, R. M., Editors, “Atomic Absorption Spectrophotometry,” Mavrodineanu, R., and Hughes, R. C., Appl. Opt., 1968, 7, 1281. Aldous, K. M., Mitchell, D. G., and Jackson, K. W., PYOC. 4th Int. Conf. Atom. Spectrosc., Toronto, Rawson, R. A. G., Proc. 4th Int. Conf. Atom. Spectrosc., Toronto, 1973. Kirkbright, G. F., and Ranson, L., unpublished work. Kirkbright, G. F., Ward, A. F., and West, T. S.. Analytica Chim. Acta, 1972, 62, 241. Kirkbright, G. F., Ward, A. F., and West, T. S., Andytica Chim. Acta, 1973, 64, 363. Greenfield, S., Jones, I. C.. and Berry, C. T., Analyst, 1964, 89, 713. Wendt, R. H., and Fassel, V. A., Analyt. Chem., 1965, 37, 920. Wendt, R. H., and Fassel, V. A., Analyt. Chem., 1966, 38, 337. Dickinson. G. W., and Fassel, V. A., Analyt. Chem., 1968, 40, 247. Hoare. H. C., and Mostyn, R. A,, Analyt. Chem.. 1967, 39, 1153. Ekmmans, P. W. J. M., and de Boer, F. J.. Spectrochim. Acta, 1972, 27B. 391. Kirkbright, G. F., and Ward, A. F., Talanta, 1974, 21, 1145. Willis, J. B., Spectrochim. Acta, 1970, 25B, 487. Koirtyohann, S. R., and Pickett, E. E., Paper presented a t the XIIIth Colloquium Spectroscopicum de Galan, L., and Samaey, G. F., Spectrochim. Acta, 1970. 25B, 245. Amos, M. D., and Willis, J. B., Spectrochim. Acta, 1966, 22, 1325 and 2128. Manning, D. C., and Capacho-Delgado, L., Analylica Chim. Acta, 1966, 36, 312. Kirkbright, G. F., and West, T. S . . Chemy Britain, 1972, 8, 428. Mitchell, D., “Proceedings of Technicon International Symposium, New York, 1970,” Halos Associ- Mitchell, D. G., and Johansson, A., Spectrochim. Ada, 1971, 26B, 677. Jones, M., Kirkbright, G. F., Ranson, L., and West, T. S., Ancxlytica Chim. Acta. 1073, 63, 210. Gardels, M., Demers, D., and Mitchell, D., “Proceedings of Technicon International Symposium, Dagnall, R. M., Kirkbright, G. F., West, T. S., and Wood, R., Analyst, 1972, 97, 246. Fraser, L. M., and Winefordner, J. D., Analyt. Chem., 1971, 43, 1693. Fraser, L. M., %nd Winefordner, J. D., Analyt. Chem., 1972, 44, 1444. Omenetto, N., Hatch, N. N,, Fraser, L. M., and Winefordner, J. D., AnaZyt. Chem., 1973, 45. 196. Omenetto, N., Benetti, P., Hart, L. P., Winefordner, J. D., and Alkemade, C. Th. J.. Spectrochim. Piepmeier, E. H., Spectrochim. Acta, 1972, 27B, 431 and 445. Butterworths, London, 1970, p. 1. 1973. Internationale, Ottawa, June, 1967. ates, Miami, 1970. New York, 1970,” Halos Associates, Miami, 1970. Acta, 1973,28B, 289.

ISSN:0306-1396    

DOI:10.1039/AD9751200008

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

January, 1975 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY 25 High-performance Liquid Chromatography (HPLC) The following are summaries of three of the papers presented at a meeting of the Midlands and East Anglia Regions and the Special Techniques and Chromatography and Electro- phoresis Groups held on May 23rd, 1974, and reported in the June issue of Proceedings (p. 137). Developments in H ig h-performance Liquid Chromatography Packings and Columns R.E. Majors The renaissance in liquid chromatography (LC) is due, in part, to developments in column packing materials. Classical column chromatography utilised large-diameter porous packings such as silica gel or alumina, with particle diameters of 100 pm or greater. These particles are undesirable for high-performance liquid chromatography, particularly at high flow- rates, because of band broadening due to slow mass transfer of sample components, which is caused by the deep pores and convective mixing within interparticle channels.On the other hand, these porous particles, due to their high surface area, typically 200 to 400 me g-1, have large sample capacity. Sample capacity is particularly important for preparative chromatography or when larger samples are required for detectors of low sensitivity.Theoreticians predicted that there were at least two ways to reduce these band broadening phenomena. One way was to use the so-called porous layer beads (PLB) developed in the late 1960s. These packings consist of a solid non-porous core (usually glass) of approxi- mately 40pm and a thin porous outer shell approximately 1 to 2 pm thick.The outer layer usually consists of silica gel, alumina or an ion-exchange resin (referred to as a pellicular). Owing to the thin coating, solute mass transfer in the stationary phase is improved and high flow-rates can be used with little loss in efficiency. Most important, the thin coating also means that relative to the totally porous packings, sample capacity is reduced.An alternative way to reduce band broadening due to long diffusion paths and convective mixing is to reduce the particle diameter of the packing. This fact had been known for some time but techniques of sizing and packing such small particles were unavailable. During the last 2 years, these problems have been overcome and a renewed interest in porous particles has taken place.When properly packed, small porous particles (SPP) not only exhibit high efficiency but still retain the advantage of the large porous particles-large sample capacity. A large number of both PLB and small porous particles, with diameters of less than 15 pm, have become commercially available. Comparative performance of small porous particles and PLB has both theoretical and practical interest.Table I compares the relative efficiency (HETP) for various packings at a linear velocity of 1 cm s-l. Although not an exact comparison, the data indicate that, for best efficiency, columns packed with the Varian A ssociates Limited, Russell House, Molesey Road, Walton-on-Thames, Surrey, KT12 3P J EFFICIENCY Packing Durapak-OPN Merckosorb Si-60 Corasil I (1% BOP) Corasil I1 Zipax (0.6% BOP) Spherisorb silica Merckosorb Si-60 TABLE I AS A FUNCTION OF PARTICLE SIZE* Average particle P 55 3.30 P 45 2.50 PLB 44 1.40 PLB 44 0.80 PLB 30 0.66 P 20 0-66 P 6 0.07 T v e t diameter/ pm HETP/mm Packing technique Dry or slurry, Dry Dry Dry Dry b.d.+, Dry or slurry.Slurry, b.d. b.d. * For test solute, capacity factor (R') = 1 to 2, and linear velocity (V) = 1 cm s-l.P = porous; PLB = porous layer bead. b.d. = balanced density.26 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY Proc. Analyt. Div. Chem. SOC. smallest diameter porous packing should be used. However, as the particle size is decreased, the back-pressure increases. Then, the pressure output of the LC pump and/or system may become the limiting factor.Roughly speaking, for a given column length and set of con- ditions, if the particle diameter is reduced by one half, the pressure drop across the column is raised by a factor of 4. However, due to the greatly increased efficiency of SPP, short columns may generate many theoretical plates. These short columns require only moderate pressures. For example, at normal flow-rates (2 ml min-l) a 15-cm column of 10-pm silica gel may generate one thousand or more theoretical plates but require a pressure of only several hundred pounds per square inch for low-viscosity mobile phases.Thus, to accomplish the same separation in the same analysis time, SPP may require lower pressures than PLB.1 However, for difficult separations requiring thousands of theoretical plates, long columns packed with small particles (5 pm) and high pressures may still be required.Table I1 compares PLB and SPP on the basis of several general criteria. Column efficiency is shown as the best values obtainable at reasonable flow velocities. The capacity of PLB is lower than that of SPP on a milligram of solute per gram of packing basis but when compared on a column volume basis (PLB are more dense than porous packings) the difference is reduced.Pressure requirements are compared for columns of equal diameter and length operated under the same conditions (i.e., the same linear velocity, mobile phase, etc.). The performance factorg compares columns in terms of their effective plates normalised for pressure drop and separation time.In other words, if we compare effective plates per unit pressure drop for the same analysis time, SPP give higher values than PLB. On a practical basis, PLB can be successfully dry-packed using packing techniques not unlike those used for gas-chromatographic columns. On the other hand, SPP, especially those below 20 pm, require special packing procedures. Slurry packing procedures are the easiest to use but dry packing can be mastered by those with patience and/or a “soft touch.” On a cost basis, SPP purchased in bulk are generally less expensive.Prices for pre-packed columns of both types are in the same range. However, due to the higher number of plates for an SPP column, more than one PLB column may be required to equal a single SPP column.COMPARISON OF Factor Efficiency (best values) Capacity TABLE I1 POROUS LAYER BEADS AND SMALL PARTICLE SIZE POROUS PACKINGS Pressure (50 cm x 2.2 mm column) Performance factor (N/ AP) Packing ability Cost : Packing Prepacked columns Fig. 1 presents the results of Porous layer beads (40 pm) Reasonable (H = 0.2 to 0.3 mm) Low (0.1 mg g-1) Low (300 to 500 lb i r S ) 10 to 1s Easy, dry pack Difficult (slurry pack or pre- High: L2 to 3/g flS0 to 90 Small porous packings (5 to 10 pm) High (H = 0-01 to 0.03 mm) High (5 mg g-l) Higher (greater than 2000 lb in-2) 50 to 100 packed columns) Lower: fl0-5 to l.O/g L60 to 110 a separation run under comparable conditions on a PLB (40-im) column and an SPP (5-pmj silica gel column.Although selectivity (relative re- tention) for the two columns is slightly different, a number of useful comparisons can be made.To achieve base-line separation of all four components on the PLB column, a I-m column was required. A better separation was achieved on a 15-cm column of 5-pm silica. This improved separation was a result of both increased efficiency (lower HETP) and increased selectivity. For N-ethyl-9-phenylazoaniline, an impurity was resolved, which remained unresolved on the PLB column.With the SPP column, analysis time could have been shortened considerably by (a) increasing the flow-rate but at the expense of pressure; (b) increasing the mobile phase strength; and/or (c) decreasing the column length. For the PLB column, the pressure drop was only 180 Ib in-2 compared to 1350 Ib in-2 for the 5-pm SPP.Through the chemical bonding of stable siloxane (5-0-Si) phases on to both PLB and SPP, unique separation selectivity may be obtained. These phases do not “bleed,” are stable in aqueous and non-aqueous media and, most important, may be used with solvent programming (gradient elution). Bonded phases on SPP have the advantage of higherJanuary, I975 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY la) e N = N e N E t 2 I I I I I I 1 I I I 0 2 4 6 8 1 Time/mi nutes 27 JYmpurity I I 3.8 4.8 ! 3 0.5 1 1 *5 1 -8 Time/minu tes Fig.1. Comparative separation of azo compounds on porous layer beads and on small porous particles. (a) Column dimensions, 1000 mm x 2-2 mm; average particle diameter of porous layer beads, 37 to 50 pm; pressure drop, 180 lb in-2; linear velocity, 1 cm s-l; mobile phase, 1 per cent.methylene chloride in hexane. (b) Column dimensions, 150 mm x 2-2 mm; average particle diameter of porous silica, 5 pm; pressure drop, 1350 lb i r 2 ; linear velocity, 1 cm s-l; mobile phase, 10 per cent. methylene chloride in hexane. 3 loading than the PLB ones. Both non-polar phases, such as those containing octadecylsilane groups, and polar phases, such as alkylnitrile and alkylamine, have been permanently bonded to 10-pm silica gel.3 Compared with silica gel, which has partially acidic hydroxyl groups on its surface, the -NH, phase has basic properties and, in acidic media, may function as a weak anion exchanger.Owing to their obvious advantages such bonded phase packings should eventually replace conventionally coated liquid - liquid chromatographic materials.28 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY R o c .Artalyt. Div. Chem. SOC. References 1. 2 . 3. Majors, R. E., and MacDonald, F. R., J . Chromat., 1973, 83, 169. Snyder, L. R., in Stock, R., and Perry, S. G.. Editors, “Gas Chromatography 1970,” Institute of Majors, R. E., in Grushka, E., Editor, “Bonded Stationary Phases in Chromatography,’’ Ann Petroleum, London, 1971, pp.81 to 111. Arbor Science Publishers, Ann Arbor, Michigan, 1974, Chapter 8, pp. 139-172. Large-scale Moving- bed Liquid Chromatography P. J. Carr Unilever Research, Port Sunlight Laboratories, Wirral, Cheshire, L62 4XN In recent years resurgence of interest in liquid chromatography in columns has led to the optimisation of materials and operating parameters, giving vast improvements in speed and resolution.As a research technique, high-performance liquid chromatography has narrowed the gap considerably, between itself and gas chromatography in terms of speed, resolution and convenience of operation. The coupling of liquid chromatography with highly sensitive spectroscopic methods has meant that individual components can be isolated from admixtures in microgram to milligram amounts for subsequent identification by spectroscopic methods such as infrared spectroscopy, mass spectrometry and nuclear magnetic resonance spectroscopy. However, we have found that this type of chromatographic service has, by itself, been unable to satisfy completely the demands of many research workers in product development chemistry.There is now a growing need for the isolation of preparative amounts of pure compounds, or narrow fractions from commercial and reaction products in order to evaluate their behaviour in user property tests. Preparative amounts are normally defined as any level of material that is isolated for subsequent testing; this paper deals with tens of grams amounts sufficient for the testing of user properties, e.g., which component in a mixture gives improved deter- gency or foaming.We have found that simple scale-up of conventional columns has enabled us to achieve separations of up to 0-5 to 1.0 g of material into narrow fractions (or values covering the range 1.05 to 1.50) on l-inch diameter columns without any loss of resolution; with 2-inch columns a marked loss in resolution occurred.However, the demand for increased scale- up persuaded us to look at the area of moving-bed continuous chromatography by means of an instrument known as a sequential separator. The instrument is now manufactured by Precision Engineering Produds (Suffolk) Ltd.* There are two basic approaches to moving- bed chromatography : (i) A free-falling system in which the adsorbent is allowed to fall freely down a vertical column up which the mobile phase containing the feed is passed; (ii) A closed-column system in which a number of columns are flow programmed to operate in sequence as (a), a series of independent columns or (b), a continuous column.The liquid sequential separator is based on the second of these concepts and can be used to operate under overload conditions or as a continuous analytical instrument. Principle Sequential separation is a form of moving-bed chromatography which can be used to separate continuously or to concentrate a feed solution.Up to twenty independently controlled chromatographic columns may be used. When the columns are set to operate in sequence the mobile phase and sample are programmed to move along the bed in a pre- determined manner ; take-off points for separated components are similarly programmed.The process of sequential separation is made possible by means of a multi-port rotary valve that consists of a “stator” (which is fixed and into which sample and solvents are fed and individual components are eluted from the system), a graphite-loaded PTFE programmable disc and a “rotor” (which can move and from which all the columns are suspended). When the rotor is moved between positions (indexed) the columns are moved opposite to the mobile phase flow.Thus, slow-moving components are moved counter-current to the mobile phase * Atlas Works, Cullum Road, Bury St. Edmunds, Suffolk.January, 1975 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY 29 flow (upstream) while faster moving components leave the downstream end of the system, together with the mobile phase.Also, by matching the index time to the rate of movement of one component in a mixture, it is possible to concentrate that component at or near the central feed-point. Applications The equipment is capable of separating up to 100 g h-l of complex synthetic and natural organic mixtures into as many as twelve fractions.By using solvents of increasing strength around the system, separations can be achieved (via stepwise gradient elution) which are comparable in resolution to medium-resolution liquid chromatography. The separations obtained on 1 x 50 cm columns packed with 60-pm silica gel include: (i) separation of isooctane and toluene from admixture at a sample throughput rate of 100 g h-l; (ii) separation of an organic reaction product into hydrocarbon, monomer and dimer fractions at a sample throughput rate of 5 g h-l; (iii) fractionation of ethoxylated non-ionic compounds into thirteen narrow-cut fractions using a multi-step solvent gradient system; a sample throughput rate of 2 g h-l was obtained; (iv) isolation of a single ethoxylated non-ionic compound in high purity (greater than 98 per cent.) from a wide distribution mix at a sample throughput rate of approxi- mately 2 g h-l.The technique has also been applied to the separation of dyes and drugs and to the con- centration of trace components. SUMMARY AND CONCLUSIONS Organic reaction products have been separated by means of a sequential separator into individual components or narrow cuts at sample throughput rates of lOOg h-l on 1 x 50 cm columns; high resolution can be obtained when sample throughput is sacrificed (e.g., 2 g h-1 throughput).The instrument has obvious applications in the purification of fine chemicals and polymers and in the enrichment of trace components in pollution studies.Practical High-performance Liquid Chromatography Using Small Size Particles Brian H. Freeman James A . Jobling G- Co. Ltd., Laboratory Division, Stone, Staffordshire The survival of classical liquid chromatography has been due, to a great extent, to its great versatility in comparison with other forms of chromatography.In comparison with the inert gas generally used in gas chromatography, the mobile phase in liquid chromatography can play a central role in the separation process by selective interactions within the mobile phase. The recent advances in liquid column chromatography have been caused in part by im- proved packing materials. Both pellicular and microparticular materials are used to solve the problems caused by the slow rate of diffusion in liquids.Under pressure, high flow-rates can be obtained and resolution of compounds can take place in a few minutes. In order to obtain the efficiency necessary for high-performance liquid chromatography these particles must be packed into regular and homogeneous columns. The two methods of packing most uni- versally accepted are the Kirkland modified tap - fill methodl of dry packing and the high- pressure slurry packing method.2 Pellicular particles consist of a non-porous sphere coated with a thin layer of adsorbent material approximately 1 pm in thickness.They are generally 30 to 40 pm in diameter and can be adequately packed by the dry-packing procedure. They give reasonable efficiency but have low sample capacity and are relatively expensive.Microparticles are totally porous small size particles normally 5 to 10 pm in diameter. They are more difficult to pack, usually requiring a high-pressure slurry method, but they do have a high sample capacity, can give very high efficiencies and are relatively cheap. Unfortunately, at the moment, there is no universally accepted criterion by which the performance of different columns can be easily compared.Work on the packing of micro-30 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY Proc. Anatyt. Div. Chem. SOC. particles has shown that the efficiency of a column, expressed as the height of a theoretical plate, can vary with the flow-rate and the retention time of the solute. Another important variable is the pressure drop across the column.To compare fairly the performance of different types of packing both the flow-rate and the capacity factor should be virtually constant. A number of nicroparticulate silicas have been packed by the high-pressure slurry method at 6OOO lb in-2 in glass-lined stainless-steel columns (300 mm x 1.8 mm id.) and their performances compared (Table I). TABLE I PERFORMANCE OF MICROPARTICULATE SILICA COLUMNS Particle diameter/ Clm Sorbsil-0520 5-20 Merckosorb S 1-60 10 Partisil- 10 11 Partisil-5 7 Spherisorb Slow 10 Linear velocity/ cm s-l 0.26 0.30 0.30 0.32 0-24 Capacity factor Pressure HETP, (k‘) drop (AP) H/mm 2.0 800 0.16 1.7 280 0.07 1.6 260 0.09 1.7 210 0.12 1.9 800 0-04 The system consisted of a Jobling LD711 Eluent Delivery Unit using hexane modified with 1 per cent.of acetonitrile as solvent. A specially designed syringe injection head allowed introduction of the sample, which was a mixture of standard solutions of pentane (unretained), benzene, phenetole, ethyl benzoate, nitrobenzene and benzophenone dissolved in the eluting solvent. Detection was effected by the Jobling LD1205 Ultraviolet detector operating at 254 nm.At similar flow-rates and capacity factors the efficiency obtained must be viewed in conjunction with the pressure drop across the column. The irregularly shaped silicas in this study, both with narrow particle diameter ranges, namely Merckosorb S1-60 and Partisil-10, both gave good, efficient columns with a reasonable pressure drop across the column. Partisil- 5 gave an improvement in efficiency but also a large pressure increase.Sorbsil-0520, with its wide range of particle size, gave only moderate efficiency and a high pressure drop and so fares very badly in this comparison. Spherisorb, although giving the lowest pressure drop, as expected from its narrow particle diameter range and its spherical shape, was gene- rally disappointing and is probably better packed by other methods.Extra-column effects become very much more important with microparticulate materials, the high efficiency obtained meaning that fairly short columns are used. Thus, design of injection head, detector and connectors are critical for good performance. The injection of sample should be as near on-column as practical aspects allow, connectors between the column and detector should be of minimum dead volume and the detector cell should be as small as practicable and have good flow characteristics.On-column injection quickly destroys the top of the column packing and gives rise to rapid deterioration of column performance so, in practice, it is necessary to have some kind of porous inlet filter at the top of the column although this can reduce efficiency by a factor of 2 to 3.3 Large variations in efficiency can be obtained with microparticulate packings, depending on the capacity factor of a particular solute.Efficiency is usually at a maximum when k‘w2 and the optimum range occurs when the solutes in question have capacity factors between about 1.5 and 4. For all types of column packings an increase in flow-rate decreases the time of analysis but also decreases the efficiency of the column and a higher pressure is required.For a particular analysis a compromise must be made between these conflicting effects. With the larger size pellicular particles longer columns are generally used and extra-column effects become less important. This means that less care is needed to optimise conditions for routine operation and the pellicular columns are very useful for “scouting” for conditions.Dry-packing procedures are generally accepted for particles of more than 20 pm, with the modified tap - fill method being the most generally used. However, dry-packing pro- cedures are difficult to reproduce with respect to column performance and are time consuming and tedious.High-pressure slurry packing is the method of choice for particles of less than 20 pm. It is comparatively reproducible but does require high-pressure apparatus. The slurryJanuary, 1975 R AND D TOPICS IN ANALYTICAL CHEMISTRY 31 can be prepared as a balanced-density or an ammonia-stabilised suspension; both give good results. Ultrasonic mixing is not essential provided the suspension is well shaken. The Suspension is then packed into a column at a high flow-rate and at 5000 lb in-2, to give regular and homogeneous packing. Some small size particles have been packed by dry-packing procedures, notably by tamping between additions and in published cases4 this method can give good results. How- ever, it remains tedious and lacks reproducibility. Spherisorb is normally packed using vibration and is reported to give very good results. However, in this case, the prepared column suffers badly from peak asymmetry, probably caused by flow-path inequalities due to disturbed packing at the column walls. When difficult separations are required, or very small amounts of solute need to be detected, the high-efficiency columns of microparticles are very useful. Examples include the concentration of aflatoxins in groundnuts, the separation of acetoxycholanates and the analysis of vitamins in foodstuffs. References Lower pressures do not give such good results. 1. 2. 3. 4. Kirkland, J. J., J . Chromat. Sci., 1972, 10, 129. Majors, R. E., Analyt. Chem., 1972, 44, 1722. Kirkland, J. J., J . Chronzat., 1973, 83, 149. Huber, J. F. K., Chirnia, Aarau, Supplement, 1970, 24.

ISSN:0306-1396    

DOI:10.1039/AD9751200025

出版商:RSC    

年代:1975

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January, 1975 R AND D TOPICS IN ANALYTICAL CHEMISTRY 31 Research and Development Topics in Analytical Chemistry The following is a summary of one of the papers presented at the annual Research and Development Topics in Analytical Chemistry meeting of the SAC/Analytical Division held at Jesus College, University of Cambridge, on March 26th and 27th, 1974, and reported in the May, 1974, issue of Proceedings (p.105). Summaries of nine other papers presented at the meeting appeared in the July (p. 161) and October (p. 264), 1974, issues of Proceedings. Application of Photoelectron Spectroscopy to the Analysis of Pigment Surfaces D. Betteridge and D. Jones Department of Chemistry, University College of Swansea, Swansea, SA2 8PP Phthalocyanines are commercially important compounds because of the fact that some of them are excellent pigments.Many methods, including X-ray diffraction, particle size reflectance and gas adsorption techniques, have been used to try to develop an understanding of processes occurring at treated (and untreated) pigment surfaces that lead to wide variations in the pigment performance in various formulated products. Preliminary results have shown that photoelectron spectroscopy, an experimental technique for measuring the binding energies of electrons in particular atomic and molecular orbitals,l could provide an important contribution towards an understanding of these processes.The photoelectron spectrum of a compound offers characteristic peak positions correspond- ing to different atomic and molecular orbitals. Shifts in these characteristic peak positions provide information about differences in molecular environments, for example, before and after a given interaction between different species, or differences arising due to changes in the substitution pattern of molecules.The ultraviolet photoelectron spectrum of copper phthalocyanine (CuPc) in the vapour phase showed characteristic peak positions corresponding to the uppermost filled molecular orbital levels in the CuPc molecule.It was also shown that CuPc pigments that had under- gone different finishing treatments gave characteristically different spectra. The X-ray photoelectron spectrum of a sample that had been subjected to a “salt-grinding” treatment showed peaks whose positions were characteristic of silicon (2s and 2p orbitals), sulphur (2p orbital) and sodium (2s orbital), corresponding to those elements which were present in the materials used for processing the pigment.32 PYOC.Analyt. Div. Chem. SOC. The X-ray photoelectron spectra of samples of pure sublimed CuPc and of treated CuPc showed the presence of only one type of molecular environment for carbon and nitrogen (Is orbitals) in the sublimed sample and the presence of two types of molecular environment for carbon and nitrogen in the treated form. Future study of the uppermost filled molecular orbital levels in the pigment molecules using the ultraviolet technique promises to elicit much more detailed information on the nature of interactions at pigment surfaces. Reference R AND D TOPICS IN ANALYTICAL CHEMISTRY 1 . Baker, A. D., and Betteridge, D., “Photoelectron Spectroscopy-Chemical and Analytical Aspects,” Pergamon Press, Oxford, 1972.

ISSN:0306-1396    

DOI:10.1039/AD9751200031

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年代:1975

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32 R AND D TOPICS I N ANALYTICAL CHEMISTRY PYOC. Analyt. Div. Chem. soc. The Studentships awarded in 1973 to Mr. K. P. Ranjitkar at Birmingham University and Mr. C. McLeod at Imperial College, London, have been continued for a further year. Society for Analytical Chemistry Studentships The Trustees of the Analytical Chemistry Trust Fund have awarded Studentships to Mr. A. A. L. King at Imperial College, London, and to Mr. P. David at the University College of Swansea.

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DOI:10.1039/AD975120032a

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年代:1975

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Janzlary, 1975 CORRESPONDENCE 33 Correspondence Correspondence is accepted on all matters of interest to analytical chemists. Letters should be addressed to The Editor, Proceedings of the Analytical Division, The Chemical Society, Burlington House, London, W1 V OBN. Analytical Chemistry in the Polytechnics Sir, In a recent Editoria1,l Dr. J. M. Ottaway described the present level of activity in the undergraduate teaching of analytical chemistry within the Universities. He drew attention to an excessive orientation towards the training of pure chemists specialising in organic, inorganic, physical or theoretical chemistry and the need for a better balance between analytical chemi- stry and these subjects.Chemistry degree courses in the Polytechnics present a different picture. The Polytechnics inherited a commitment to a tradition of vocational orientation, resulting in the emer- gence of a large number of applied degrees within higher education.In addition to the sandwich structure of many of these courses, i t may well be that analytical chemistry is also one of the vehicles of vocational relevance. Of the thirty designated Polytechnics, nineteen now offer undergraduate degree courses in chemistry or applied chemistry and, of these, seventeen offer courses that contain an option, specialisation or module in analytical chemistry.The report of a survey by the Education and Training Committee of the SAC2 did not, unfortunately, give specific figures for the numbers of academic Polytechnic staff whose major teaching function was concerned with analytical chemistry.In this department, there are three full-time analytxal chemists out of a total of twenty chemistry staff. In addition, the general interest in analytical chemistry may be reflected by the fact that about five other staff also teach some aspects of the subject to varying extents at both BSc and MSc levels. While in this case the pro- portion of analytical staff is 15 per cent.this is probably above the average for Polytechnics, and we would estimate the true figure to be in the region of 10 per cent. Why were so many of the Polytechnics’ chemistry degree courses designed with an analytical flavour? Was it partly the com- bined forces of Polytechnic vocational tra- ditions, an obvious lack of undergraduate analytical chemistry in the Universities, and the desire to offer new, different and relevant courses? Whatever the answer, we have, along with many other Polytechnics, experienced a small but significant increase in student interest in our applied chemistry degree courses over the last few years.The resulting graduates have apparently not found employment so difficult to come by as have the “pure” chemistry graduates of the Universities, but of course the latter are in the majority (chemistry degree enrolments 1972-73 in Universities totalled 2300 and in Polytechnics 400). It would seem that there is a reasonable and growing provision for undergraduate analytical chemistry.However, as pointed out in the SAC report,l the separation of the high level of analytical research activity in the Universities from the high level of analy- tical teaching activity in the Polytechnics is regrettable and causes speculation about how this situation may change over the next few years.We think it fairly safe to assume that the higher education sector will comprise two distinct types of institution (Polytechnics and Universities) for many years to come, and therefore that any change that may occur should come from a growth of research activity in the Polytechnics.Unfortunately, it may well take several years for such growth to become significant. This is due to a number of factors, any one of which can discourage research but in combination very often pre- vents or seriously curtails it. During the next few years the rate of change occurring within the Polytechnics is likely to remain a t the present high level and to continue to consume large amounts of staff time through committees, planning and teaching on new courses.This situation is aggravated by the relatively high teaching and administrative load carried by the Polytechnic lecturer and which shows no sign of decreasing. Nevertheless, many Poly- technics are actively seeking to increase their research activity. We believe that if this ex- pansion is to be successful, then it must be accompanied by close liaison and co-operation with industry.It is early days for much of industry to have learned to accept that the34 CONFERENCES AND MEETINGS Proc. Analyt. Div. Chem. SOC. Polytechnics are institutions in higher edu- cation alongside the Universities and to under- stand that they can and should play an im- portant role in helping to shape the indi- viduality and character of these developing institutions.We look fonvard optimistically to increasing activity in Polytechnic analytical research and on the industrial collaboration that must accompany it. References 1. Ottaway, J. M., “Analytical Chemistry in the Universities,” Proc. Sac. Analyt. Chem., 1974, 11, 73. “Education and Training in Analytical Chem- istry a t Educational Establishments,” a Report by the Education and Training Committee of the Society for Analytical Chemistry, Proc. SOC. Analyt. Chem., 1972, 9, 173. 2. Yours faithfully , N. A. Bell D. J. Mowthorpe Shefield Polytechnic Obituaries We regret to announce the deaths of Mr. C. J. House, Chairman of the North of England Section of the SAC in 1963-64, and Dr. D. P. Hubbard, recently appointed as a Regional Advisory Editor of The Analyst.

ISSN:0306-1396    

DOI:10.1039/AD9751200033

出版商:RSC    

年代:1975

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34 CONFERENCES AND MEETINGS Proc. Analyt. Div. Chem. SOC. Conferences and Meetings ’ Recent Trends in Inorganic Analysis March 19-21, 1975, Sart-Tilman, Belgium The Bulletin des SociCtCs Chimiques Belges is sponsoring an International Symposium on Recent Trends in Inorganic Analysis at the University of Liege, Sart-Tilman, Belgium, organised by the Analytical Sections of the Vlaamse Chemische Vereniging and the SociCtC Chimique de Belge.The following ten Plenary Lectures will be given : G. Blaise (UniversitC Paris-Sud) : “Surface Analysis by Secondary Ionic Emission. ” J. L. de Vries (Philips, Eindhoven): “X-ray Absorption and Emission.’’ G. G. Guilbault (Technical University of Denmark) : “Ion-selective Electrodes. ” J. Hoste (Instituut voor Nucleaire Weten- schappen, Gent) : “Some Modern Aspects of Neutron Activation Analysis.” A.S. Kertes (Hebrew University of Jerusa- lem) : “Chemistry of Solvent Extraction Processes : Analytical Applications.” . lJanuary, 1975 CONFERENCES AND MEETINGS 35 I. M. Kolthoff (University of Minnesota) : “Effect of Hydrogen Bonding on Acid - Base Equilibria in Non-aqueous Solvents.” K. Laqua (Inst. fur Spektrochemie und Angew.Spektroskopie, Dortmund) : “Optical Emission Spectrochemical Analy- sis. ” G. H. Morrison (Cornell University) : “Spark Source Mass Spectrometry. R. A. Osteryoung (Colorado State University) : “Analytical Electrochemistry.” T. S. West (Imperial College, London): “Atomic Spectrometry for Chemical Analy- sis (ASCA).” Research papers on related topics are in- vited.Additional information can be obtained from H. Thun, Laboratory for Analytical Chemistry, J. Plateaustraat 22, B-9000 Gent, Belgium. Original Papers in Pharmaceutical Analysis June, 1975 It is proposed to hold a meeting of the Joint Pharmaceutical Analysis Group for presen- tation of short original papers on pharmaceu- tical analysis in early June, 1975 (probably on Thursday, June 5th) a t a venue to be decided.Members are asked to indicate their intention to participate with a contribution as soon as possible so that the meeting can be confirmed in the light of the response. It would be helpful if a brief summary of the contribution to be read were sent to: The Secretariat Office, Joint Pharmaceutical Analysis Group, 17 Bloomsbury Square, London, WClA 2NN, not later than March 30th, 1975.ASTM Symposium on Flameless and Cold Vapour Atomic Absorption June 22-28, 1975, Montreal, Canada This Symposium will be held during the 78th Annual Meeting of the ASTM in Montreal and is sponsored by the ASTM Committees E-3 on Chemical Analysis of Metals, E-2 on Emission Spectroscopy and E-16 on Sampling and Analysis of Metal Bearing Ores and Related Materials.Papers are invited and should relate to experiences with or specific applications of flameless atomic absorption in the ultra-trace determination of elements in the analysis of raw materials, in metal production or in environmental studies. Further details can be obtained from Om P. Bhargava, The Steel Company of Canada Ltd., Chemical Laboratory, Wilcox Street, Hamilton, Ontario, Canada.NMR Spectroscopy July 6-11, 1975, St. Andrews, Scotland An International Meeting on NMR Spectro- scopy is being organised by The Chemical Society, and six consecutive symposia will cover: (1) Recent applications of lSC and other nuclei studies to chemical problems; (2) NMR studies of oriented molecules; (3) NMR studies of solids; (4) Correlation and Fourier spectroscopy; (5) Applications of NMR to biological ’systems; (6) Theoretical aspects of NMR.Contributed papers are invited, and titles +25-word synopses should be sent to Prof. E. W. Randall, Chemistry Department, Queen Mary College, Mile End Road, London, El 4NS, not later than February 1st. Further details can be obtained from Dr. J. F. Gibson, The Chemical Society, Burlington House, London, W1V OBN.Fifth International Conference on Atomic Spectroscopy August 25-29, 1975, Melbourne, Australia This Conference will be held at Monash Uni- versity, Clayton, Melbourne, and the fields covered will include atomic emission, absorption and fluorescence spectroscopy, with particular emphasis on the application of these techniques to analytical chemistry.There will be an exhibition of scientific equipment of interest to atomic spectroscopists and technical visits to the CSIRO Division of Chemical Physics and to Varian Techtron Pty. Ltd . The following Plenary Lectures will be presented : “Spectroscopic studies on the state of equilibrium in flame gases,” by A. G. Gaydon (U.K.) ; “The line-profile factor in atomic- absorption spectroscopy,” by P.Hannaford (Australia) ; “Atom formation processes in analytical flames,” by G. M. Hieftje (U.S.A.); “Glow discharges-a means to complete and universal spedtrochemical analysis,” by K. Laqua (German Federal Republic) ; “The possi- bility of local sensing of physical parameters in flames,” by N. Omenetto (Italy) ; “Flameless atomic spectroscopy-a quantum jump in investigating the environment,” by D.A. Segar (U.K./U.S.A.) ; “The emission of optical radi- ation arising from low-energy ion - atom and36 CONFERENCES AND MEETINGS Proc. Analyt. Div. Chem. SOC. ion - surface collisions,” by N. H. Tolk (U.S.A.) ; and “Application of the Zeeman effect to atomic-absorption spectroscopy,” by K. Yasuda Further details can be obtained from Dr. J.B. Willis, Secretary, Fifth International Conference on Atomic Spectroscopy, Box 160, Clayton, Victoria, Australia 3168. Those definitely planning to attend the Conference should contact Cadogan Travel Ltd., 159 Sloane Street, London, S.W.l., directly in order to make the necessary travel arrange- ments. (Japan) - Determination of Halogens in Organic Compounds September, 1975 The Microchemical Methods Group is planning a meeting, to be held in London, probably in September, 1975, on the above subject, possibly in the form of an extended Discussion Meeting.Contributions, both long (30 min) and short (5-10 min), are invited from analysts who have developed new or modified methods, who have overcome problems, or who have en- countered insurmountable problems.Correspondence should be addressed to the Honorary Secretary of the Group, Mr. P. R. W. Baker, Chemical Research Laboratory, Well- come Research Laboratories, Langley Court, Beckenham, Kent. Liquid Scintillation Counting Sefitember 16-19, 1975, The Assembly Rooms, Bath The Radiochemical Methods Group is organising an International Symposium on Liquid Scin- tillation Counting, to be held in Bath in Sep- tember. Conference Themes .- The principal themes will be devoted to : Scintillation Processes ; Recent Advances in Sample Preparation ; Radio- immunoassay ; Errors in Liquid Scintillation Counting.The meeting will be preceded by a “Teach-in” given by Dr. Ayrey, Queen Elizabeth College, and Mr. Sutton of the Ministry of Agriculture, Fisheries and Food.Exhibition .- As on previous occasions, the meeting will be supported by an extensive exhibition of liquid scintillation counters and related equipment. Accommodation .- Accommodation will be available a t Bath University. Special trans- port arrangements have been made between the University and the Bath Assembly Rooms. Lunch, tea and coffee will be available at the Assembly Rooms.A full Ladies and Social Programme has been arranged, including Receptions and Conference Dinner. If you wish to be kept informed of arrange- ments and to receive application forms please write to : The Secretary, Analytical Division, The Chemical Society, 9/10 Savile Row, London, W1X IAF. Analytical Chemistry: A Means to Environ- mental Quality Management November 30-December 5, 1975, Mexico City The Analytical Chemistry Division of The Chemical Institute of Canada, the Analytical Chemistry and Environmental Chemistry Divisions of the American Chemical Society and the Analytical Chemistry Division of the Mexican Chemical Society are jointly co- sponsoring a session at the First North Ameri- can Chemical Conference devoted to the theme “Analytical Chemistry : A Means to Environ- mental Quality Management.” Original contributions are invited in the fields of analytical organic chemistry, inorganic chemistry, biochemistry, biology and the related environmental chemistry and instru- mentation.The closing date for abstracts of 200 words or less is May 15th, 1975. Com- plete manuscripts will be required by October 15th. For information and special forms for sub- mission of abstracts, write to: Dr. s. Barabas, Canada Centre for Inland Waters, P.O. Box 5050, Burlington, Ontario, Canada, L7R 4A6.

ISSN:0306-1396    

DOI:10.1039/AD975120034b

出版商:RSC    

年代:1975

数据来源: RSC