摘要:

Proceedingsof the Analytical Division ofThe Chemical SocietyPAYCAL39414345454865686969697072CONTENTSSAC Silver MedalsReports of MeetingsFiftieth Anniversary of theNorth West RegionSummaries of Papers'Chemical Aspects of the Drug Scene''Ion-selective Electrodes''Research Topics in ElectroanalyticalChemistry''Recent Developments in the Analysisof Food and Drink'CorrespondenceNoticesPapers Accepted for 'The Analyst'Conferences and MeetingseAnalytical Division DiaryVolume 12 No 2 Pages 39-72 February 197Vol. 12, No. 2 February, 1975PROCEEDINGSANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOF THEOfficers of the Analytical Divisionof the Chemical SocietyPresidentG . W. C. MilnerHon. SecretaryW. H.C. ShawSecretaryMiss P. E. HutchinsonHon. TreasurerJ. K. ForemanHon. Assistant SecretariesD. 1. Coomber, O.B.E.; D. W. WilsonEditor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington HOUSE, London, W1 V OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members): The Chemical Society, Publications Sales Office, Blackhorse Road, Letch-worth, Herts., SG6 1 HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.0 The Chemical Society 1975Analytical Sciences Monograph No. 2The Chemical Analysis of WaterGeneral Principles and Techniquesby A. L. Wilson(Water Research Centre, Medmenham Laboratory)BRIEF CONTENTS:Introduction. Intormation requirements of Sampling and Analysis Programmes. Sampling.The Accuracy and Reporting of Results. Choice and Sources of Analytical Methods.General Precautions in Water-analysis Laboratories. Manual Analytical Techniques.Automatic and On-line Analysis. Data-handling.Pp. viii + 188 f 7.50Clothbound IBSN 0 85990 502 0 CS Members' price f5.75Orders should be sent through your usual bookseller or direct, enclosing remittance, to-The Publications Sales OfficerTHE CHEMICAL SOCIETYBlackhorse Road, Letchworth, Herts. SG6 1 HN, EnglandCS Members must write direct to the above address stating that they are claiming the privilege pric

ISSN:0306-1396    

DOI:10.1039/AD97512FX005

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

February, 1975 CONFERENCES AND MEETINGS 71Analytical Division Diary, continuedMarch, continuedTuesday, 25th : HatfieldEast Anglia Region, jointly with the Mid-Anglia Section of the CS.“Atomic Fluorescence Spectrophotometry andthe Development of Sources of Excitation,”by R. M. Dagnall.The Polytechnic, Hatfield ; 6 p.m.Wednesday, 2 6th : LondonBiological Methods Group.Discussion on “Heparin,” to be introduced byM. Brozovic, V. V. Kakkar and D. P.Thomas.The Pharmaceutical Society of Great Britain,17 Bloomsbury Square, London, W.C.1,2.30 p.m. (N.B. : Change of date).Thursday, 27th : LondonAutomatic Methods Group : This meeting hasbeen cancelledAnalytical Division DiaryFEBRUARYWednesday, 26th : MiddlesbroughAutomatic Methods Group on “Applicationof Computers, Particularly Microprocessors,t o 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.“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 llragonara 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 CS andAberdeen University Chemical Society.“Offshore Corrosion Control,” by M. J. Purcell.The University, Aberdeen; 4.15 p.m.MARCHTuesday, 4th : LoughboroughMidlands Region, jointly with the Lough-borough University of Technology ChemicalSociety.“100 Years of Atomic Spectroscopy,” by D.Room J O O l , Edward Herbert Building, Univer-sity of Technology, Loughborough; 4.15 p.m.Thorburn Burns.Wednesday, 5th : LondonMicrochemical Methods Group : LondonDiscussion Meeting on “Ion Probe Analysis,”to be introduced by J .V. P. Long.Senior Common Room, Imperial College, SouthSide, Princes Gardens, London, S.W.7;6.30 p.m.Wednesday, 12th : DurhamNorth East Region, jointly with the Associa-tion of Public Analysts, on “Spectroscopy andConsumer Protection. ”“Your Money or Your Life,” by 1;. C. Shcnton.“Toxic Metals in Domestic Utensils andToys,” by J . Roburn.“Screening Foods and Other Materials forRiIetallic Contamination,” by J . \V. Itobert-son.The [Jniversity, Durham; 2 p.m.Friday, 14tJt : LondonSAC: Annual General Meeting; 2 p.m.Analytical Division : Annual General Meeting ;2.15 p.m.Special Lecture: “A Composition of SomeDays. . . J” by R. C. Chirnside; 2.45 p.m.Geological Society, Burlington House, Piccadilly,London, W’. 1.Biennial Formal Dinner : Goldsmiths’ Hall,Foster Lane, London, E.C.2; 7 p.m. for7.30 p.m.Friday, 14th : ChepstowWestern Region: Discussion Mecting on“Classical Methods of Analysis in ModernAnalytical Chemistry.”George Hotel, Chepstow ; 6.30 p.m.Monday, 17th : LondonElectroanalytical Group.Professor R. G. Bates.“pH and Ion Activity Standards,” byLecture Theatre 3B20, Kings College, Strand,London, W.C.2; 3 p.m.Tuesday, 18th : LiverfloalNorth West Region, jointly with the LiverpoolSection of the CS.“X-ray Diffraction in Industry,” by M. T. I.Liverpool Polytechnic, Byrom Street, Liverpool ;[continued inside back coverGunbi.7 p.m.Printed by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97512BX007

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

Vol. 12 No. 2 February, 1975 of the Analytical Division of The Chemical Society Society for Analytical Chemistry Silver Medals As announced in the January issue of Proceedings (p. 32), the Second Society for Analytical Chemistry Silver Medal has been awarded t o Dr. John Michael Ottaway and the third Silver Medal to Dr. Alan Townshend. John Ottaway was born in 1939 in New Malden, Surrey. He was educated at Glyn Grammar School, Ewe& and entered the Uni- versity of Exeter in 1957, graduating with First Class Honours from the Department of Chemis- try in 1961.This was followed by post- graduate research at the same University under Mr. (now Professor) E. Bishop, the main effort being concentrated on detailed kinetic and volumetric studies of the analytical reactions of potassium bromate.Papers on this work were read at the SAC Research Topics Meeting held at University College, London, in 1964 and at the first SAC Conference in Nottingham in 1965. Professor Bishop first stimulated his interest in the mechanisms and chemistry of analytical methods and Dr. Ottaway also derived considerable benefit from the teaching and encouragement of his supervisor during these years.In October, 1963, Ottaway was appointed Assistant Lecturer in Analytical Chemistry at the University of Exeter and the PhD Degree was completed in 1965. In September, 1966, Dr. Ottaway was appointed to a Lectureship in the Department of Pure and Applied Chemistry at the University of Strathclyde in Glasgow, where he joined a small Analytical Chemistry Group within the In- organic Section.At Strathclyde his major responsibility has been the organisation of the MSc Course in Instrumental Methods of Analysis. The Analytical Group has now been built up to over 30 postgraduate students, a number which includes students seconded on a part-time basis by local industry. Dr. Ottaway was promoted to Senior Lecturer at the University of Strathclyde in 1973.The main theme of Dr. Ottaway’s research interests lies in the study of the mechanism and chemistry of analytical methods and the applica- tion of such studies in the derivation of new analytical procedures and in the optimisation of existing procedures. In all instances funda- mental studies are closely linked to the practical application of the method under study and he and his co-workers collaborate extensively with colleagues in clinical, industrial and public service laboratories.The original interest in redox reactions in soh tion has been broadened to include studies of reactions of other oxidising agents such as iodate, chlorate, periodate and Dr. J . M . Ottaway hydrogen peroxide, but more particularly now includes the application of such reactions in the catalytic analysis of trace amounts of metals and halides.Detailed kinetic and mechanistic studies of catalysed reactions are carried out in order to identify the chemical properties that give rise to the selectivity in the catalysis of many reactions and ions. The application and automation of such methods are also under 3940 SAC SILVER MEDALS Proc.Analyt. Div. Ckern. SOC. active study in, for example, the determination of chromium in river water and the determina- tion of iron and copper in boiler feed waters. The other main area of research is in the field of atomic spectroscopy. For a number of years, Dr. Ottaway’s research students have carried out detailed studies of chemical interferences and atomisation processes that occur during flame atomisation.Mechanisms of these pro- cesses have been postulated on the basis of measurements of the distribution of atomic, molecular and ionic species in flames and free- energy calculations of reactions that occur in the primary reaction zones of flames. Such studies enable interferences to be overcome and establish the need for careful optimisation of atomic-absorption instrumentation before use in analysis. In recent years, a similar approach has been applied to atomisation using a carbon furnace and this has led to the development of analytical procedures for the determination of trace elements in metals, alloys, biological materials, rocks, effluents and sea water.Dr. Ottaway was an elected member of the SAC and CS Analytical Division Councils from 1971 to 1973 and was recently re-elected for a further term of 2 years.For many years he was Honorary Secretary of the Scottish Region of the SAC and is currently Chairman of the Region. He was also Chairman of the Local Organising Committee of the SAC Symposium held in Glasgow in 1972 in honour of the late Professor C. L. Wilson. He is a member of several CS Committees, including the Analytical Division Programmes Committee, The Analyst Publications Committee and the Analytical Methods Committee. He represents the Analyti- cal Division on the CS Annual Congress Com- mittee and on the CS Primary Journals Committee and represents the AMC on BSI Committee C/44 on Water Quality.John Ottaway lives in Milngavie near Glasgow and is married with two young sons.When time permits, he enjoys hill walking, bird watching, making wine and trying to play golf. Alan Townshend was born in Clydach, near Swansea. He was awarded a State Scholarship to attend Birmingham University, where he obtained a First Class Honours BSc in Chem- istry in 1960. During this period he obtained invaluable analytical experience while working during vacations in the analytical laboratories of the International Nickel Company at Clydach.During the next three years, he studied for his PhD in Professor Belcher’s research school, under the supervision of Dr. W. I. Stephen, investigating aspects of the use of rhodanine derivatives as analytical reagents. In 1963-64, Dr. Townshend was a post- doctoral research fellow at Case Institute of Technology, Cleveland, Ohio, working with (the late) Professor Louis Gordon on aspects of precipitation from homogeneous solution and of metal - oxime complexes.He returned to Birmingham University in 1964 as Assistant Lecturer in Chemistry, becoming Lecturer in 1966. During his time at the University, he has been closely involved in teaching and research in analytical chemistry. He is pleased Dv.A . Townshend to acknowledge the contribution of the fourteen past PhD students and numerous post-doctoral workers to his research work, which has included investigations in polarography, catalytic and enzymic methods of analysis, precipitation phenomena, molecular complexes, atomic- absorption spectrophotometry, polyphosphate analysis and the analytical chemistry of zirconium and hafnium.At present he has a team of thirteen PhD students and research fellows engaged in research in molecular emission cavity analysis (MECA), candoluminescence, insoluble enzymes and environmental problems. He has published nearly 100 papers on his researches, and hasFebruary, 2975 REPORTS OF MEETINGS 41 lectured extensively at international conferences in many parts of the world.Dr. Townshend was awarded his DSc in 1972. He spent a few months in 1974 working with Professor Tolg a t the Max Planck Institut fur Metallforschung, Laboratorium fur Rein- stoffe, Schwabisch Gmund, Germany. Dr. Townshend has taken a great interest in the affairs of the Society for Analytical Chemistry, now the Analytical Division of the Chemical Society.He has served on its Council, and is the Vice-chairman and immediate past Trea- surer of its Midlands Region. He is also a member of TJte Analyst Publications Committee, and of several committees organising the 1977 SAC Conference, which will be held at Bir- mingham. He also served on several Group and Symposia committees. Additionally, he is a member of the Advisory Board of Tuluntu, and is the Recorder of the Midlands Asso- ciation for Qualitative Analysis. With the passage of time, his outside interests have become more sedentary. Having sur- vived numerous rugby seasons intact, and being no longer able to beat all his students a t squash, he spends more time in more relaxing occupations, which include gardening and appreciation of good food and wine. He has, however, so far resisted the temptation to take up golf or politics. He is married, with three sons.

ISSN:0306-1396    

DOI:10.1039/AD9751200039

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

February, 1975 REPORTS OF MEETINGS 41 Reports of Meetings Joint Meeting A Joint Meeting of the Division with the Pesticides Group of the Society of Chemical Industry was held at 10.15 a.m. on Monday, January 20th, 1975, at the Society of Chemical Industry, 14 Belgrave Square, London, SWlX 8PS. The subject of the meeting was “Residue Determinations of Benzimidazoles” and the following papers were presented and discussed : Opening Remarks by J.M. Winchester; “Trans- formation of Benzimidazole Pesticides,’’ by D. A. M. Watkins ; “Benomyl Residues on Bananas,” by J. R. Cox and J. A. Pinegar; “Extraction of Benzimidazole Fungicides and Studies of their Behaviour in Soils and Potato Tubers by G. G. Briggs and D. J . Austin; “High-pressure Liquid Chromatography of Benzimidazoles,” by D.J. Austin, I. H. Williams and K. A. Lord; “Determination of Thiophanate-methyl and Carbendazim,” by F. Muggleton; “Determin- ation of Carbendazirn in Glasshouse Soil and Tomato Plants,” by C. R. Worthing. Ordinary Meeting An Ordinary meeting of the Division, organised by the Electroanalytical Group, was held a t 2.30 p.m. on Wednesday, February 5th, 1975, at the Scientific Societies Lecture Theatre, 23 Savile Row, London, W.1. The Chair was taken by the President of the Division, Dr. G. W. C. Milner. The subject of the meeting was “The Renais- sance of Polarography” and the following papers were presented and discussed : “Modern Polaro- graphic Techniques,” by G. C. Barker; “Voltam- metry with Carbon Wax-based Electrodes,” by D. R. Crow; “Pulse and A.C.Polarographic Techniques for Trace Analysis,” by R. D. Jee; “Some Recent Applications of Polarography to Drug Analysis,” by W. F. Smyth; “Auto- mation of Polarographic Techniques, ” by B. Fleet. Scottish Region A Meeting of the Region was held at 4 p.m. on Wednesday, January 15th, 1975, in the Chem- istry Department, University of Strathclyde, Glasgow. The Chair was taken by the Chair- man of the Region, Dr.J. M. Ottaway. A lecture on “Some Interferences in Flame Spectroscopy,” was given by I. RubeSka. Atomic Spectroscopy ,Group and ARAAS The Second Annual Reports on Analytical Atomic Spectroscopy Symposium was held at 11.30 a.m. on Thursday, January 9th, 1975. in Ranmoor House, The University, Sheffield. The Chair at the first session was taken by Dr.J. B. Dawson,\Chairman of the ARAAS Board, and the following lecture was given: “Atomisation in Graphite-furnace Atomic- absorption Spectroscopy : Peak Height Method zwsm Integration Method of Measuring the Absorbance Signals,” by R. E. Sturgeon, C. L. Chakrabarti, I. S. Maines and P. C. Bertells. The Chair at the second session was taken by Dr. G. F. Kirkbright, and the following lecture was given : “Atomic Spectroscopy in Geology: Some Problems and Solutions,” by I.RubeSka. The meeting concluded with a discussion on “Standards and Standardisation in Analytical Atomic Spectroscopy,” under the Chairmanship of Mr. D. Hobbs.42 REPORTS OF MEETINGS PYOC. Analyt. Div. Chem. SOG. Atomic Spectroscopy Group The tenth Annual General Meeting of the Group was held at 2.30 p.m.on Tuesday, December 3rd, 1974, in the Chemistry Department, Thames Polytechnic, Woolwich, London, S.E. 18. The Chair was taken by the Chairman of the Group, Dr. G. F. Kirkbright. The following office bearers were elected for the forthcoming year : Chairman-Dr. R. Smith. Vice-Chairman- Mr. C. P. Cole. Honorary Secretary-Mr. D. J. Willis, Rank Hilger Ltd., Westwood Industrial Estate, Ramsgate Road, Margate, Kent.Honor- ary Treasurer-Dr. G. B. Marshall. Honorary Assistant Secretary-Dr. W. J. Price. Members of Committee-Dr. R. F. Browner, Dr. H. Hughes, Dr. L. Ranson (co-opted), Dr. B. Sharp, Dr. A. E. Smith, Mr. C. A. Watson and Mr. J. F. Woolley. Mr. D. Moore and Mr. R. White were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Education and Training Group, at which the Chair was taken by the Vice-chairman of the Atomic Spectro- scopy Group, Mr.C. P. Cole. The subject of the meeting was “Teaching Atomic Spectro- scopy,” and the speakers were J. Mendham, W. J. Price and R. Smith. Automatic Methods Group The ninth Annual General Meeting of the Group was held at 2.30 p.m.on Thursday, December 5th, 1974, in the Chemistry Department, Imperial College, London, S.W.7. The Chair was taken by the Chairman of the Group, Mr. C. L. Denton. The following office bearers were elected for the forthcoming year: Chair- man-Mr. C. L. Denton. Vice-chairman- Mr. D. C. M. Squirrell. Honorary Secretary- Dr. P. B. Stockwell, Laboratory of the Govern- ment Chemist, Cornwall House, Stamford Street, London, SE 1 9NQ.Honorary Treasurer- Mr. K. H. Wall. Honorary Assistant Secretary -Mr. R. M. Cooper. Members of Committee- Dr. B. Fleet, Mr. J. L. Martin, Mr. D. G. Porter, Dr. J. M. Skinner, Mr. K. Swann and Mr. F. Trowell. Dr. J. E. Page and Mr. W. H. C. Shaw were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Electroanalytical Group, a t which the Chair was taken for the first session by the Chairman of the Automatic Methods Group, Mr.C. L. Denton, and for the second session by the Chairman of the Electro- analytical Group, Mr. A. Bottom. The subject of the meeting was “On-line Electrochemical Analysis” and the following papers were presented and discussed : “Design and Some Applications of Phase Boundary Detection,” by P.B. Stockwell; “An Automatic Digestion System for the Determination of Trace Metals in Foodstuffs by the Use of a Glass pH Electrode to Control the Neutralisation Stage,’’ by J. Jackson ; “On-line Measurement Techniques Using Ion-selective Electrodes,” by B. Fleet; “The Determination of Surfactants Using Ion-selective Electrodes : Application to Continuous Monitoring,” by B.J. Birch. Electroanalytical Group The fifth Annual General Meeting of the Group was held at 2.15 p.m. on Thursday, December 5th, 1974, in the Chemistry Depart- ment, Imperial College, London, S.W.7. The Chair was taken by the Chairman of the Group, Dr. B. Fleet. The following office bearers were elected for the forthcoming year : Chairman- Mr.A. Bottom. Vice-Chairman-Dr. W. F. Smyth. Honorary Secretary-Dr. B. J. Birch, Unilever Research Laboratory, Port Sunlight, Cheshire, L62 4XN. Honorary Treasurer-Dr . R. D. Jee. Honorary Assistant Secretary-Dr. A. G. Fogg. Members of Committee-Dr. D. Brand (co-opted), Dr. P. 0. Kane, Dr. B. Fleet, Dr. D. Parker (co-opted), Dr. M. Riley, Dr. T.Ryan and Dr. H. Thompson. Dr. J. A. W. Dalziel and Mr. J. H. Glover were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Automatic Methods Group (for details see above). Education and Training Group The fourth Annual General Meeting of the Group was held at 2.45 p.m. on Tuesday, December 3rd, 1974, at Thames Polytechnic, Woolwich, London, S.E.18.The Chair was taken by the Vice- Chairman of the Group, Dr. J. B. Headridge. The following office bearers were elected for the forthcoming year : Chairman-Dr. J. B. Head- ridge. Vice-Chairman-Dr. D. Thorburn Burns. Honorary Secretary-Dr. N. T. Crosby, Labora- tory of the Government Chemist, Cornwall House, Stamford Street, London, SE1 9NQ. Honorary Treasurer-Dr. J . G. Pritchard. Members of Committee-Mrs. M. I. Arnold, Mr. W. B. Chapman, Dr. J. Parsonage, Dr. D. A. Spratt, Mr. J. D. Wheatley and Dr. W. J. Williams. Mr. J. Bassett and Dr. J. A. W. Dalziel were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the Atomic Spectroscopy Group (for details see above).February, 1975 FIFTIETH ANNIVERSARY OF THE NORTH WEST REGION 43 17 Bloomsbury Square, London, W.C.Z. The Chair was taken by the Chairman of the Group, Joint Pharmaceutical Analysis Group An Ordinary Meeting of the Group was held at 2.30 p.m. on Thursday, December 12th, 1974, at the Pharmaceutical Society of Great Britain, Mr. G. F. Phillips. Quality Control.” The subject of the meeting was “Hospital

ISSN:0306-1396    

DOI:10.1039/AD9751200041

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

February, 1975 FIFTIETH ANNIVERSARY OF THE NORTH WEST REGION 43 Fiftieth Anniversary of the North West Region The notices which advertised the one-day preserve an equivalent broad spectrum of topics meeting which celebrated both the 50th in the lecture programme. The advertised Anniversary of the founding of the North of choice had been between “Some Aspects of England Section of the Society for Analytical Food Poisoning,” “The Science in Shakespeare” and “Chemical Aspects of the Drug Scene.” Unfortunately, the Preston pathologist who would have spoken about food poisoning was taken ill, and rather more people experienced a taste of “liberal studies” than had been intended.In the late afternoon there was a showing of a collection of films which had been made a t North of England Summer Meetings of ten to twenty years ago, and Mr.C. H. Manley, the longest serving member of the Region, spoke briefly about some of the young-looking faces which had just been seen in them. A vote of MY. A . C . Bushnell with Dr. Ann E . Robinson. Chemistry and the 21st Anniversary of the founding of the Association of Public Analysts had borne the title “The Stuff of Life-Reflec- tions at 50.” The event took place on November 8th, 1974, but it must have been an odd kind of life whose stuff was assembled that day. The chemists visited the purpose-built N. W. Forensic Science Laboratories, their wives saw a demonstration of Christmas cooking at Blackpool Catering College and those who preferred not to be parted from one another were conducted around the Lion Brewery, where all the processes are still open and visible in their modern stainless-steel vats, and therefore are more instructive than the closed Quatermass fermenters of more modem lager synthesisers.The intention of the planners had been to Mrs. W . Winn and Miss J . D. Peden. thanks was afterwards given by a runner-up in long service, Mr. A. Leather, and a letter of apology for absence by the oldest member,44 FIFTIETH ANNIVERSARY OF THE NORTH WEST REGION PYOC.AnaZyt. Div. Chem. SOC. (L-R) Mrs. C. Whalley. MY. C . Whalley, Mvs. J . Clegg, Mr. J . Clegg (Vice- Chairman, Lancashire Public Protection Committee), Mrs. A . C. Bushnell, MY. A . C. Bushnell, Mvs. W . Winn (Chairman, Lancashire Public Protection Committee), Miss J .D. Pedevl (President, Association of Public Andysts) and MY. P . Inman (Chief Executive, Lancashire County Council). Mr. Gordon Cary, now 89 years old, was read. In the evening, Lancashire County Council acted as hosts at a dinner at which Mrs. W. Winn, Chairman of the Public Protection Committee and acting on behalf of IMr. Leonard Broughton, Chairman of Lancashire County Council, repre- sented the local authority. Mr.A. C. Bushnell, Chairman of the North West Region of the SAC/AD, explained who everybody was and how each had helped with the celebration; and MI. C. Whalley (immediate Past-President of the SAC, speaking in Dr. Milner’s unavoidable absence) and Miss Joan Peden (President of the APA) responded for the guests on behalf of both rcspective celebrating bodies, and Mr, \\%alley presented a copy of the SAC‘S History.“The Practising Chemists,” to Mrs. Winn. The meeting had been based on Lancashire County Council’s Management Centre at Heskin Hall, where a display prepared by the County Architects Department and which made use of photographs provided by Dr. D. W. Kent- Jones and Mr. T. McLachlan was on view, and where overnight guests hoped to meet the sixteen year old lady ghost who is said to haunt the spacious bedrooms.A free booklet which gave a history of the North of England Section and which had been compiled by Mr. George Delegates at the hT. TV. Forensic Science Laboratovies.February, I975 CHEMICAL ASPECTS OF THE DRUG SCENE 45 Longman, past Honorary Secretary and past Chairman, was available to all participants, as were souvenir bookmarks on which the insignia of both participating Societies were shown.The North of England Section has always had a great deal of support from Public Analysts, indeed, in the period 1955-60 there was a little gentle pressure put upon the Hon. Secretaries of the time to break that dominance, but even at the jubilee there were no fewer than twenty- two among the seventy-six participants who were Public Analysts or past Public Analysts who had been associated with the Section.In her remarks at the Celebration Dinner, Mrs. W. Winn reminded those who were present of the large proportion of office holders in the Section who had been employed by Lancashire County Council, and she drew attention to the fact that the floral decorations a t the tables and the colours in the ice-cream gateaux which had formed part of the meal, had reflected the colours in the armorial bearings of the Societies.In the afternoon, at the Chorley Little Theatre, Mr. H. W. Payne spoke on “The Science in Shakespeare,” and told how passages in Shakespeare reflected the stage that science had reached in the early 1600s.Following Mr. Sinar’s showing of Mr. F. Clark’s films, the talk by Mr. C. H. Manley, a founder member of the Section and its Chairman in 1947-48, probably struck the right note for a 50th Anniversary celebration. He recalled his early associations with some of the first honorary officers of the Section, including Professor W. H. Roberts, the Liverpool City Analyst, who was the first Chairman, and H.J. Lea, J. R. Stubbs and A. Lees, who acted as Honorary Secretaries during the period 1925-54. G. D. Elsdon, Chairman in 1930, had shown the usefulness of the Hortvet freezing-point method for distinguishing naturally poor milk from watered milks and had worked on the deter- mination of butter in margarine and drawn up sugar analysis tables. John Evans, the Sheffield City Analyst who was Chairman in 1932-33 and later became President of the Society, published a paper in The Analyst in 1929 that paved the way for the present methods for the determination of alcohol in urine.In 1951, the Section’s Summer Meeting was held at Llandudno, and the deliberations there of a group of Public Analysts ultimately led to the formation of the SAC and APA as separate bodies. He then went on to refer to the part played by Public Analysts in exposing worthless food substitutes during World War I1 (e.g., a coloured baking powder an ounce of which was claimed to be equivalent to six eggs), and finally paid tribute to some of the past Chairmen and notable members of the North of England Section and North West Region. Also during the afternoon, Dr. Ann E. Robinson of the London Hospital Medical College gave the Plenary Lecture entitled “Chemical Aspects of the Drug Scene,” and an extended summary of her paper follows this report.

ISSN:0306-1396    

DOI:10.1039/AD9751200043

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

February, I975 CHEMICAL ASPECTS OF THE DRUG SCENE 45 Chemical Aspects of the Drug Scene Ann E. Robinson The London Hospital Medical College, Turner Street, London, E l 2AD One of the less desirable features of contemporary society during the last decade has been the marked increase in the non-medical use of drugs, some but not all of the drugs being those which induce dependence if used on a chronic basis and the purpose of this paper is to outline some of the chemical aspects and to introduce some facts into the wealth of fiction and hearsay that surround the subject.By 1965, there was a disturbing rise in the incidence of addiction to heroin and cocaine, especially among young people, the main source of supply being over-prescribing, and there was evidence of increasing abuse of stimulants by teenagers, often as an adjunct to their wakefulness during all-night parties and notably at weekends.This trend in the non- medical use of drugs by the young should not be confused with the inappropriate use of drugs by other age groups-the use of “purple hearts” by those suffering from the “tired housewife syndrome” or the chronic (and increasing) use of barbiturates for insomnia-the drugs in the latter cases were obtained licitly and on prescription, whereas the adolescents were mostly obtaining the drugs from others and rarely on prescription.Soon afterwards, the escalating use of heroin was causing concern and deaths due to intravenous narcotism were beginning to be reported in the U.S.A. Deaths following acute reaction to the injection occurred, often a syringe needle being left in situ in a vein at death,46 CHEMICAL ASPECTS OF THE DRUG SCENE PYOC.Autalyt. Div. Chem. SOC. and others died of hanging, strangulation, electrocution, etc. Although these deaths had been examined in detail on a pathological basis, there was a striking lack of chemical data even to confirm that a drug was present at autopsy, let alone that it was present in an excessive amount ; there was and still is considerable doubt as to whether even some of the heroin deaths are due to over-dosage rather than to an acute physiological response to foreign particles or impurities. Consideration of the chemical problem rapidly produced the conclusion that nothing much was known about heroin, or even morphine, in man because sufficiently sensitive analytical methods were not available.In order to make a useful study of drugs in the body, whether one is considering the living or the dead, it is necessary to review (a) the known metabolic pathways for each drug and (b) analytical methods appropriate for the detection and measure- ment of the unchanged drug and its known metabolites in biological specimens.Note that the concentrations that may be found are likely to be very small in comparison, for example, with the concentration of a drug in an injection solution. Fol- lowing administration, it is hydrolysed by blood enzymes and is excreted via the kidney mostly as morphine and its conjugate with glucuronic acid. There are other pathways of metabolism, e.g., N-demethylation, conjugation with sulphate, but these are minor quantitatively in com- parison.Thus morphine is the substance to look for in specimens taken from persons sus- pected of having taken heroin-chemically it is not possible to discover whether any morphine found in blood, urine, etc., was derived from administration of heroin or of morphine. Although opium, which of course contains morphine, is one of the oldest drugs known to man, comparatively little was known about its human distribution because no suitable analy- tical methods were available.Animal distribution studies were limited and mostly performed with radioactively labelled drug samples. Colorimetric methods for morphine depended either on complex formation with methyl orange (or other indicators) or a reaction for the phenolic hydroxy group, e.g., with Folin - Ciocalteu reagent.Thus the detection methods were non- specific and the results obtained were only as selective for morphine as the preliminary separa- tion and concentration procedure allowed. After some preliminary efforts using a differential spectrophotometric method, we turned our attention to gas chromatography.Morphine tails badly in many systems and requires high column temperatures. Heroin usually decomposes and gives two peaks, for heroin and monoacetylmorphine, i.e., there is no point in acetylating morphine-containing extracts for gas chromatography. Silylation, however, proved satisfactory and this is still the method that we use. Others have found that a fluorimetric assay for morphine is suitable and this involves oxidation with hexacyanoferrate( 111) under alkaline conditions to convert morphine into its highly fluorescent dimer, pseudomorphine.Recovery of morphine from biological specimens is achieved by solvent extraction, usually with a halogenated solvent such as chloroform or dichloroethane; addition of a proportion of a higher alcohol often improves recoveries by redhcing losses due to adsorption on glass. Also, the pH of the aqueous phase is critical, and must be between 8.5 and 9.Methadone was a drug that was introduced into the treatment of heroin dependence and for which analytical methods suitable for use with biological specimens were non-existent in 1967. Indeed, the identification of methadone in some fatalities reported in 1955 depended partly on chemical tests and partly on the Straub test in mice.A qualitative method for methadone, however, was more readily established as it can be recovered by solvent extraction under alkaline conditions. Gas chromatography of the extract allows assay of methadone and its metabolites if care is taken with the conditions. The metabolism of methadone is more complex than that of morphine.The major pathway involves monodemethylation of the dimethylamino group followed by ring closure with dehydration, and in a minor metabolite, formed by rearrangement, the unsaturation is endocyclic. Other pathways of human metabolism have been elucidated but as most of the metabolites have been identified from data obtained by gas chromatography - mass spectro- metry and pure compounds are not available, it has not yet proved possible to establish assay methods.From the end of 1966 we began to study in detail every drug addict death that was autopsied for the Coroner in the areas for which the Department pathologists work. The immediate cause of death was not necessarily acute intoxication. The analytical study in Heroin, the popular name for diamorphine, is the diacetyl derivative of morphine.February, 1975 CHEMICAL ASPECTS OF THE DRUG SCENE 47 each case is qualitative in the first instance to establish the nature of the drugs present and quantitative analysis is then undertaken to establish the concentration of the drug or drugs present so that the pathologist may advise the Coroner of the cause of death.At first, the cases analysed were mostly those of known users of heroin and cocaine, with barbiturates sometimes used as a hypnotic and taken orally. However, within a comparatively short time, methadone was introduced as a means of treating heroin dependence and methyl- amphetamine, which was available as a solution for injection as well as in tablets for oral use, found favour as an alternative stimulant to cocaine.Methylamphetamine was available on prescription and many doctors prescribed it for their patients, probably unaware of the risk and the problems that were to ensue. It soon became obvious that there was a need for psychiatrists to have laboratory evidence in support of the diagnosis of a drug-related syndrome or condition.We had already estab- lished a qualitative testing procedure as a preliminary examination of post mortem specimens and it was a simple matter to apply this to urine specimens from the living. The screening procedures involve simple liquid - liquid extractions from pH-adjusted urine specimens. Solvent extracts are concentrated and subjected to thin-layer chromatography for morphine, methadone and barbiturates and gas - liquid chromatography for amphetamine and related compounds.Other drugs may be detected incidentally in the routine procedure but the scheme is not comprehensive. The results of screening tests on urine specimens of patients suspected of drug use were shown and the influence of legislation and the timely action of a drug company were illustrated.Since 1969-70, the indiscriminate use of mixtures of drugs has become apparent, sometimes including alcohol. There was a vogue during 1970-71 for injection of barbiturates (prepared from capsule contents); the phase passed but re-appears at intervals, usually when there is a shortage of heroin cr methadone. Our autopsy work continued and we accumulated data for the human distribution of various drugs and began to interpret the qualitative data in general terms : were the results consistent with fatal overdosage? ; were the results consistent with intoxication, so that the deceased suffered the consequences of some hazardous activity (e.g., crossing the road)?; were the results indicative of “therapeutic dosage” ? ; was there evidence of previous or chronic dosage of a drug or drugs?; etc.To illustrate this, the data for methadone and its major metabolite in autopsy specimens for five cases were presented and discussed. As an example, a case involving a mixture of drugs was considered, involving a 20 year old male found collapsed in a house and dead on arrival at hospital. He was a known addict with a 4- or 5-year history of drug use and many old injection sites on both arms.Quantitative analysis showed the presence of measurable amounts of methadone and morphine in the specimens. An intermediate-acting barbiturate was found in the urine, was not detectable in the blood (less than 0.05 mg per 100 ml) but was present in tissue from an injection site and in a syringe needle. Swabs from the hands showed positive evidence of (contact traces of) cannabis constituents.The immediate cause of death appeared to be an acute reaction to a recent injection of barbiturate and morphine or heroin. Other cases have shown combinations of methadone or morphine with other drugs including amphetamine, codeine, methaqualone and diphenhydramine, diazepam, nitrazepam, diphenylhydantoin, etc.The use of drugs in addition to heroin and/or methadone now usually appears to be indiscriminate and to reflect supply and demand, but the only reliable data of the drugs actually used are obtained by chemical analysis; hearsay and survey data can be mis- leading in this regard. Little mention has been made of cannabis and hallucinogens, not because they are not encountered but because they are not yet detectable in blood or urine on a routine basis.It is, however, only a matter of time before this detection will be possible, as cannabinoids can now be detected and measured in the blood of man by mass fragmentographic methods and an immunochemical method has also been described. Similarly with lysergide, an immuno- chemical method has been reported to be suitable for measurement of serum levels.These methods, however, require more detailed evaluation before they can be considered for routine use. Cannabis constituents, however, can more easily be demonstrated in contact traces-hands, lips and mouths following handling or smoking and also in the atmosphere of woms in which the drug has been smoked. Sensitive methods of detection are available for demonstration48 ION-SELECTIVE ELECTRODES PYOG.Analyt. Div. Clzem. SOC. of cannabis constituents but, without a mass spectrometer connected to the gas chromatograph, one has to depend on comparative chromatographic methods that may not provide unequivocal evidence of identity. Analysis of samples of drugs found near a dead addict or from other relevant sources provide further objective evidence concerning the drugs in circulation. Although many drugs, such as the barbiturates, are usually recognisable as the manufactured tablets or capsules, white powders may be pure heroin or talc, flour or even sodium hydrogen carbonate. Some “illicit” products may be crudely made, while others may be manufactured to resemble a popular product although devoid of its usual active constituents, e.g., blue tablets containing caffeine have been seen that resemble in size, colour and shape a proprietary preparation containing dexamphetamine and amylobarbitone. In analysing any such “drugs,” it is as well to keep an open mind and to consider results critically rather than to start with pre-conceived ideas and jump to conclusions. But, then, this is what forensic toxicology is all about.

ISSN:0306-1396    

DOI:10.1039/AD9751200045

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

48 ION-SELECTIVE ELECTRODES PYOG. Analyt. Div. Clzem. SOC. Ion-selective Electrodes The following are summaries of five of the papers presented at the SAC/AD Symposium on Ion-selective Electrodes which formed part of the CS Autumn Meeting on September 24th, 1974, held at the University of Leicester, and reported in the October, 1974, issue of Proceedings (p. 257). Ion-selective Electrodes: Contribution to Chemistry and Biochemistry J.D. R. Thomas and G. J. Moody Chemisfyy Department, UWIST, Cardig, CF1 3NU, Wales Apart from stimulating interest in the solid-state chemistry of glass and crystals and in the specificity for metal ions by synthetic and natural organic complexing agents, the new genera- tion of ion-selective electrodes have contributed handsomely to progress in many areas of chemistry and bi0chemistry.l For the purpose of this brief survey, these contributions are summarised in terms of the activities of ions, complexation and reaction rate studies, the study of biomedical phenomena, enzyme reactions, environmental and industrial monitoring, general analysis and non-aqueous media studies.Activities and Activity Coefficients The response of ion-selective electrodes reflects the activities of single ionic species so that their development has created renewed interest in single ionic activity coefficients and par- ticularly in means of obtaining reference standards for calibration.Although the calibration of an electrode selective to a particular counter ion is frequently (but not always, because of complexation and other phenomena) independent of the nature of the co-ion, it has been recommended2 that cation-responsive electrodes be standardised in solutions of the corres- ponding completely dissociated chloride salts and that mion-responsive electrodes be stan- dardised in solutions of the completely dissociated sodium salts. Among the exceptions k the recommended calibration3 of fluoride ion-selective electrodes with potassium fluoride rather than with sodium fluoride, which is likely to become associated in moderately con- centrated solutions.The practical matter of choosing an arbitrary “conventional” means of evaluating the activity of an individual ionic species that cannot be exactly defined may be discussed from the standpoint of dilute solutions, concentrated solutions and mixtures of electrolytes.lA In dilute solutions, multiple pathways to the activity coefficients (7) of single unassociated ions exist and as can be seen from Table I the values of pM and pX obtained by various simple conventions do not differ greatly at an ionic strength of 0.1.In concentrated solutions, the matter of choosing the most suitable pathway increases in importance.Further, when the cation is hydrated in solution, the activity coefficient frequently passes through a minimum in the molality range 0-5 to 1.0 mol kg-1 and there- after rapidly becomes greater than unity.( To counter the greater problems at higher ionic strengths, Bates et d6 used the Robinson - Stokes hydration theory as the basis of a con- vention for single ionic activities.This means that individual variations in ionic activityFebruary, 1975 ION-SELECTIVE ELECTRODES TABLE I COMPARISON OF PM AND px VALUES BASED ON DIFFERENT CONVENTIONS Data are taken from Reference 4 and refer to I = 0.1 and t = 25 O C . Debye - Huckel convention MacInnes convention pH convention --- Salt PM PX PM PX PM PX KCl 1.1 14 1.114 1,114 1.1 14 1-118 1.110 NaCl 1-1 10 1.110 1.106 1-114 1.108 1.110 NaF 1-116 1.116 1.106 1.126 1.108 1.124 NaC10, 1.111 1.111 1-106 1-116 1.108 1-114 CaCl, 1.898 1.282 1.880 1-291 1.887 1.286 49 at a given ionic strength are accounted for in terms of individual ionic hydration numbers (h), assigned on the assumption that the chloride ion has zero hydration number.Thus, by applying the thermodynamics of electrolyte solutions, equations have been d e v e l ~ p e d ~ ~ ~ for splitting mean activity coefficients into the contributions of the individual ions and which satisfy the conditions4 of (i) being consistent with the MacInnes, Debye - Huckel and pH conventions at ionic strengths of less than 0.1; (ii) allowing for specific differences in the properties of ions in concentrated solutions; and (iii) recognising that the activity coefficient of a given ion is not dependent solely upon ionic strength but varies with the composition of the solution.For a univalent - univalent ele~trolyte~-~ MX : and where # is the water activity (osmotic coefficient) and m the molality. In practice, one of the attractive features of ion-selective electrodes is their ability to respond to the activity of one particular ion in the presence of other ions in mixed electrolyte systems, so that a knowledge of ion activities in mixtures is of some importance.The problems have been assessed and illustrated by Bates,* but it is also interesting to recall the conclusion of Bags regarding sodium chloride and calcium chloride mixtures , which , of course, form the basis of mixed electrolytes of biological importance.Thus, within experi- mental error, the mean activity coefficient of calcium chloride in many mixed solutions up t o an ionic strength of 0.3 M are equal to those which would hold for pure calcium chloride solutions of the same ionic strength.g In using ion-selective electrodes, it must be remembered that electrodes standardised in a dilute solution of a single electrolyte may display rather large residual liquid junction errors when used in solutions of great range of ionic strength or in solutions containing two ionised ~ o l ~ t e ~ .2 ~ 4 For this reason, it is desirable to standardise the electrode assembly in a mixture similar to that of “unknowns.” The Study of Complexes The ability of ion-selective electrodes to measure the activity of unassociated ions has For been put to advantage in the study of complexes and especially of fluoride Complexes.example, the equilibria .. .. H+ + F- s HF HF + F- + HF? (3) may be studied by monitoring the decreasing activity of free fluoride ions with increasing acidity, monitored with a pH glass electrode. Although claimed to be less sensitive than the indirect determination of free fluoride with an iron(II1) - iron(I1) redox couple in studying strong fluoride complexes, the fluoride electrode is said to be superior in convenience, sen- sitivity and accuracy for studying weak complexes.Such studies have recently been re- viewed’ and the /I values obtained range from less than 1 for the fluoride complex of barium to about 50 for that of lead.In the dental and mineralised tissue field, the calcium ion-selective electrode study of the complexation of calcium ions with various inorganic phosphates is of special interest, while50 ION-SELECTIVE ELECTRODES Proc. AnaZyt. Div. Chem. Soc. in the wider biological context ion-selective electrode studies have led to both controversial association constants’ and to an indication8 of the existence of a hitherto unknown calcium adenosine triphosphate complex (Ca,ATP) .The association constants of KATPS- and NaATP3- were obtained from measurements with valinomycin potassium-sensitive and glass sodium-sensitive electrodes, respectively, and at just over 2 x lo2 1 mol-1 are about fifteen times greater than values previously obtained from indirect measurements.7 Biomedical Studies Just a short step on from complexation, it is as well to remember than many biological phenomena are fundamentally related to solution ionic activities rather than concentrations.For example, only the ionised fraction of calcium is physiologically active so that the calcium liquid ion-exchanger based sensor for ion-selective electrodes represents a major breakthrough in studying electrolyte metabolism.Also, the electrolyte composition of body fluids (Table 11) illustrates a wider role for these new techniques. TABLE I1 INORGANIC ELECTROLYTE COMPOSITION M) OF CERTAIN BODY FLUIDS Adapted from Moore, E. W., in G. Eisenman, Editor, “Glass Electrodes for Hydrogen and Other Cations: Principles and Practice,” Marcel Dekker, New York, 1966.Ion Na+ K+ Csz+ Mg*+ c1- HC0,- HP0,’- SO,’- Plasma 153 5 2.6 1 110 28 1.5 0-5 Cell fluid Erythrocyte (muscle) fluid 10 15 148 150 - - 20 1.5 74 8 27 67 - - The calcium ion contents of serum and plasma have received much attention (Table 111) and Moore9 has examined many parameters of the ion-selective electrode determination including technique, selectivity, calibration, freezing and pH.Regarding calibration , uncertainties in ionic activity coefficients and liquid junctions are best overcome by cali- brating the electrode with calcium chloride standards (0*5-2 mM in 0.150 M sodium chloride solution). The results for total calcium in serum and plasma shown in Table I11 were obtained by spectroscopic methods and it should be noted that although just less than half of this is ionised, non-diffusible protein-bound and diffusible complexed forms can represent 30-55 per cent.and 5-15 per cent., respectively. The calcium ion-selective electrode has also been applied to saliva, cerebrospinal fluid, gastric juice and urine. Of these, urine presents difficulties because of variations in pH, sodium ion concentration and ionic strength.In an approach to overcome these difficultiesm by the use of standards mimicing urine, it was shown that ionised calcium represented 50 per cent. of the total with the remainder being accountable by various soluble, citrate, phos- phate, sulphate and oxalate complexes. Among the specific problems studied with the calcium-selective electrode are membrane alkalisation in mitochondria,21 mito~is,~~,*~ rate of cell division2* and chelation of the protein polysaccharides of cartilage.25 Potassium ion-selective electrode studies (valinomycin and liquid ion-exchange types) confirm the 4-5 mmoll-l range of potassium ions in blood serum.In a special study,*6 the i.n sitzl use of a microcapillary version of the liquid ion-exchanger type of electrode showed that the mean tubular fluid to plasma potassium ion concentration falls significantly from 0.89 for the first convolution to 0.81 for the last convolution of the proximal tubule of a rat kidney.The sodium glass and chloride crystal membrane ion-selective electrodes have shown their mettle in the screening and diagnosis of cystic fibrosis.While the sodium electrode parotid saliva test can be applied only after the fourth or fifth month of life, the chloride electrode can be applied2’ at birth and depends on the elevated chloride ion levels in patients’ sweat (about 100 m) compared with a “normal” level of about 25 mM.Febraary, 1975 ION-SELECTIVE ELECTRODES TABLE I11 TOTAL AND IONIC CALCIUM IN HUMAN SERUM, PLASMA AND BLOOD Ionic levels determined with calcium ion selective electrode.51 Sample Serum Plasma Whole blood Total calcium/mM Ionised calcium/mM r- Mean (& 2 S.D.) Mean (& 2 S.D.) Range Range 2-41 2.45 2.39 2.41 2-48 3-04 2-64 2-29 2-44 2-43 2.65 2-71 - 2-72 1.42 2.45 2.60 0.56 0.24 0-15 0.10 0.29 0.42 0.24 0.08 0-1 1 0.4 1 0-06 - - 0.03 0.05 0-04 0.04 1.18 0.99 1.24 1.10 1-14 1.39 1.21 1.22 1-25 1.00 1.16 1-31 1.08 (estimate) 1.34 1.11 1.09 1.24 0.3 1 0.08 0.09 0.06 0.13 0.25 0.09 0.03 0.06 0.22 0.02 - - 0.02 0.02 0-02 0.02 x 100 Ionised Total 49.2 40.5 50.8 45.6 45.8 45-7 45.6 63.4 51-24 41.2 43.8 48.2 49.2 45.7 44.4 47-7 No.of subjects for ionised calcium 17 23 21 22 52 2 20 22 50 8 6 8 13 7 23 Reference 10 11 12 13 14 15 16 17 18 33 19 16 14 19 19(adults) 19 (children) 19(newborns) Reaction Rate Studies Equilibrium measurements in the study of complexation and solubility have been extended to the study of reaction kinetics.For example, the reaction of aluminium(II1) with fluoride ions has, on the evidence of data obtained with the fluoride electrode, been suggested= to involve the following mechanisms, with reaction (5) being rate-limiting at high acidities : .. * - (5) AP+ + HF-+AlF2+ + H+ .. .. .. Al(H,O)3+ + F-+AlOH2+ + HI; The development of fast-flow reaction systems permits the study of reactions with second- order rate constants of up to 106-107 1 mol-l s-l with liquid membrane electrode monitorsB and 108 1 mol-l s-l with crystal membrane electrodes.30 Enzyme Systems Enzyme-based reactions illustrate an extension of ion-selective electrode monitoring.The principle of an enzyme or substrate-soaked matrix between the sample solution and a sensor electrode which detects one of the enzymatic products has far-reaching possibilities. These include the determination of blood and urine ureas based on the ammonium ion produced in the enzymatic reaction.31 Other examples of the role of ion-selective electrodes in enzyme reactions include use of the fluoride electrode to monitor directly the fluoride ion released during the inactivation of chpotrypsin by diphenylcarbamyl fluoride,32 and of the iodide electrode to follow the fall in iodide ion concentration arising from catalytic oxidation by hydrogen peroxide produced in the enzymatic conversion of /3-D-glUCOSe to D-gluconic acid with glucose o x i d a ~ e .~ ~ Environmental and Industrial Monitoring In the environmental scene, ion-selective electrodes have provided additional means of surveillance and their applications extend to plants, foods, animal feeds, fertilisers, rock, soils, sewage and effluents, natural waters, sea water, smoke and air.l The procedures52 ION-SELECTIVE ELECTRODES Proc.Analyt. Div. Chem. SOC. usually involve end-determination following conventional methods of bringing materials into solution, and have recently been reviewed.1 There are, however, interesting examples of more sophisticated work, such as the intricate differential potentiometric determination of nanogram per litre amounts of chloride ion in boiler feed water using two solid-state Orion 9 6 1 7 chloride electrodes.% Response tirne~1,~5,36, of ion-selective electrodes indicate an important role for monitoring process streams, but attention must be paid to problems of open circuits created by trapped air bubbles and of static charges resulting from fast-moving streams rubbing against the plastic walls of electrodes.Nevertheless, there exists a whole variety of situations where ion- selective electrodes are used successfully in automatic process control, including autoanalysers.A classic example in process monitoring is the use3’ of the sulphide electrode in the paper and pulp industry to monitor the sulphide ion level during the purging with air of spent “black liquor. ’ ’ General Analysis Apart from the instances already cited, the normal contribution of ion-selective electrodes in general, organic and pharmaceutical analysis is to provide alternative direct or potentio- metric titration end-determination methods in elemental analysis.The preliminary stages are conventional ; for example, hot-flask combustion, oxygen-flask combustion and fluorine release with sodium biphenyl reagent have each been used to prepare samples of organic compounds for fiuorine analysis.l The subsequent stages involve pH adjustment with TISAB (total ionic strength adjustment buffer) or otherwise, regardless of whether the final de- termination is direct or by potentiometric titration.There are also many instances of ion-selective electrodes providing alternative indirect analytical procedures where no selective electrodes exist.For example, this auxiliary role may be taken by fluoride and cyanide electrodes in the direct determination of aluminium and nickel(II), respectively, while in the potentiometric location of titration end-points, the lead ion-selective electrode can be employed for sulphate, oxalate and phosphate determina- tion in conjunction with lead perchlorate titrant.Ion-selective Electrodes and Non-aqueous Media Finally, this brief survey would not be complete without mentioning that ion-selective electrodes, especially the crystal membrane types, are functional in mixed solvent media and can frequently be used to advantage. Thus, 50 per cent. dioxan is claimed to improve the potentiometric titration of sodium sulphate with lead nitrate using a lead electrode.% More fundamental recent developments in the mixed solvent area concern the use of ion- selective electrodes for determining free energies of transfer of halide and alkali metal ions from water to mixed solvents.39 1.2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. References Moody, G. J., and Thomas, J. D.R., Sel. A . Rev. Analyt. Sci., 1973, 3, 59. Bates, R. G., and Alfrenaar, M., in Durst, R. A., Editor, “Ion-Selective Electrodes,” Special hblica- Robinson, R. A., Duer, W. C., and Bates, R. G., Analyt. Chem., 1971, 43, 1862. Bates, R. G., Pure Afipl. Chem., 1973, 36, 407. Bates, R. G., Staples. B. R., and Robinson, R. A., Analyt. Chem., 1970, 42, 867. Bagg, J., Ausf. J. Chem., 1969, 22, 2467.Mohan, M. S., and Rechnitz, G. A., J . Amev. Chem. SOC., 1970, 92, 6839. Mohan, M. S., and Rechnitz, G. A., J. Amer. Chem. SOL, 1972, 94, 1714. Moore, E. W., J. Clin. Invest., 1970, 49. 318. Raman, A., Biochem. Med., 1970, 3, 369. Hattner, R. S., Johnson, J. W., Bernstein, D. S., Wachman, A., and Brackman, J., Clin. Chim. Ada, Robertson, W. G., and Peacock, M., Clin.Chim. Acta, 1968, 20, 315. Sachs, Ch., Bourdean, A.-M., and Balsan, S.. Ann. B i d . Clin., 1969,27,487. Moore, E. W.. J. Clan. Iwest., 1970, 49, 318. Moody, G. J., Oke, R. B., and Thomas, J. D. R., unpublished results, 1970. Oreskes, I., Hirsch, C., Douglas, K. S., and Kupfer, S., Clin. Chim. Acta, 1968, 21, 303. Li, T.-K.. and Piechocki, J. T., Clin. Chem., 1971, 17, 411. Fuchs, C., and Paschen.K., Dt. Med. Wochenschv., 1972, 97, 23. Radde, I. C., HBffken, B., Parkinson, D. K., Sheepers, J., and Luckham, A., Clin. Chem., 1971, 17, Robertson, W. G., Clin. Chim. Ada, 1969, 24, 149. tion No. 314, National Bureau of Standards, Washington, D.C., 1969. 1970, 28, 67. 1002.53 February, 19 7’5 ION-SELECTIVE ELECTRODES 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.32. 33. 34. 35. 36. 37. 38. 39. Chance, B., and Yoshioka, T., Biochemistry, 1966, 5, 3224. Perris, A. D., and Whitfield, J. F., Nature, Lond., 1967, 216, 1350. Perris, A. D., Whitfield. J. F., and Rixon, R. H., Radiat. Res., 1967, 32, 550. Perris, A. D., Whitfield. J. F., and Tiilg, P. K., Nature, Lond., 1968, 219, 527. Woodward, C., and Davidson, E. A., Biochemistry, 1968, 60, 201. Khuli, R.N., Agulian, S. K., and Wise, W. M., Pfliigevs Arch. Ges. Physiol., 1971, 322, 39. Hansen, L., Buechele, M., Koroshec, J., and Warwick, W. J., Amer. J . Clan. Path., 1968, 49, 834. Srinivasan, K., and Rechnitz, G. A., Anulyt. Chem., 1968, 40, 1818. Fleet, B., and Rechnitz, G. A., Analyf. Chem., 1970, 42, 690. Thompson, H. I., and Rechnitz, G. A., Analyt. Chem., 1972, 44, 300. Guilbault, G.G., and Hdbankova, E., Andyticu Chim. Acta, 1970, 52, 287. Erlanger, B. F., and Sack, R. A., Analyf. Biockm., 1970, 33, 318. Llenado, R. A., and Rechnitz, G. A., Analyt. Chem.. 1973, 45, 2166. Florence, T. M., J. EkctroumzZyf. Ckm., 1971, 31, 77. Fleet, B., Ryan, T. H., and Brand, M. J. D., Anulyt. Chem., 1974, 46, 12. Moody, G. J., and Thomas, J. D. R., Lab.Pruct., 1974, 23, 475. Swartz, J. L., and Light, T. S., TAPPI, 1970, 53, 90. Mascini, M., and Liberti. A., Analylicu Chim. Acfu, 1972, 60, 405. Covington, A. K., and Thain, J. M., International Symposium on Selective Ion-sensitive Electrodes, UWIST, Cardiff, 1973, Paper 59. Response Times of Ion-selective Electrodes: Their Measurement and Interpretation T. H. Ryan* and B.Fleet Chemistry Department, Imperial College, London, S W7 7 UR The finite time required for an ion-selective electrode to come to a new equilibrium potential after it has been placed in a solution or after the activity of ions has been changed in a solution is usually regarded in an analytical context as merely an inconvenient delay-a waste of time. This is not the case, however, when one is interested in interpreting the operation of these devices or understanding their mechanism.The shape of the potential - time profile is very indicative of the performance of the electrode and can be interpreted to give a great deal of useful information both about the electrode and about the solutions in which it is operating. A potential - time measurement is a kinetic measurement and, as such, may be related to some or all of the kinetic parameters determining the electrode potential, e.g., ion-exchange rates, mass transport across the membrane - solution interface and electron transfer rates.Apart from these theoretical considerations, a study of electrode response times will enable limits to be set to the practical application of ion-selective electrodes in real analytical situ- ations. Electrode Response Time A problem that has hampered this area of discussion has been that of precise quantifi- cation of electrode response time.The qualitative concept is relatively straightforward but arriving at an exact, reproducible time interval characteristic of a particular electrode under particular conditions is not easy.The parabolic nature of the potential - time profile is the main reason for this uncertainty and we have proposed a new response time parameter, Tss, which has been shown to be reproducible and characteristic under well defined circumstances1 The definition is illustrated in the upper trace of Fig. 1 and can be stated as follows: Ts5 is the time taken by an electrode to come to 95 per cent.of its new equilibrium potential when subjected to a step-change in the activity of the ion to which it is responding. The direction and magnitude (usually 1 decade) of the activity change must be specified. Some advantages of this approach to response times are as follows: (a) the response time is independent of the slope of the electrode response; (b) the slope of the potential - time profile at 95 per cent.of equilibrium is still appreciable and so the time abscissa can easily be measured; * Present address: EDT Research Ltd., 5 Epirus Road, London, SW6 7UR.54 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem. SOC. (c) the value of Tg5 is a real, practicable measure of response time which can be used in the application of ion-selective electrodes to analytical systems, especially in continuous- flow techniques .Some characteristic values of TQ5 for a variety of electrodes are given in Table I. TABLE I RESPONSE TIMES OF DIFFERENT ION-SELECTIVE ELECTRODES Electrode Chloride Bromide Iodide Calcium Pot assi um Calcium Potassium Type Response time ( Tg5) Solid membrane 350 f 20 ms 200 f 20 ms 50 f 5ms 2.2 & 0.2 s 3.2 f 0.2 s 1.4 f 0.2 s 9-2 f 0.7 s Liquid membrane PVC membrane Factors Affecting Response Times selective electrode.There are three main factors determining the magnitude of the response time of an ion- (i) The type of membrane naturally determines the nature of the response mechanism and hence the response speed. The general order of response is solid-state membranes > PVC membranes > liquid membranes.Other factors that contribute to response speed but are related to the nature of the membrane are the electrical reversibility of the reaction mechanism at the membrane surface, the presence ofpolymers and whether the site species in the membrane are charged or uncharged, associated or dissociated. (ii) The rate of change of ion activity. The activity change should approximate to a step- change when compared with the electrode response.The method of activity change can also affect response time; hence the response time when the electrode is either first placed in a solution or rapidly transferred from one solution to the other is larger than if the same activity change is brought about with the electrode continuously immersed in the same solution. The former is known as the “static” response time while the latter is the “dynamic” response time.The probable reasons for the difference are such factors as the disruption and re-establishment of the electrical double layer and concentration profiles. (iii) The presence of interferents has long been known to have a drastic effect on electrode response times.z Fig.1 shows the effect of various other alkaline earth elements on the response time of the calcium electrode. From an examination of the effects of a number of interfering species on the response of the calcium electrode (Table 11), and considering also their conventional selectivity ratios, it was possible to distinguish three groups of interferents : (1) ions whose effects on response time were negligible and whose selectivity ratios were very small, e.g., Na+ and N(Bu),+; (2) ions whose selectivity ratios were large but whose effects on response times were very small, e.g., Pb, Cd and Cu; (3) ions whose selectivity ratios were intermediate but whose effects on response times were very large, e.g., Ba, Sr, Zn and Mg.The interpretation placed on these results, based on further experimental work,3 was that in the presence of an interfering ion a site - interferent complex is formed within the membrane and it is the lability or otherwise of this species that determines the response speed.February, 1975 ION-SELECTIVE ELECTRODES 55 No interferent I I I I I I I I I I I I I I I Tirne/s Fig.1. profile of the calcium electrode.Effect of interferents on the response Thus in the ions of group (l), the selectivity is so low that almost no interferent - site complex is formed and no effect is felt. In group (2), the complex is readily formed, as shown by the high selectivity ratios, but the lability is high and in the presence of an increase in calcium the calcium - site species are readily re-formed.The response time is thus not much affected. The ions of group (3), however, form moderately strong non-labile complexes with the site species and the advent of further calcium ions in the membrane causes a slow re-distribution of sites (slow because of the non-lability of the interferent - site complexes) and a considerable extention of Tg5 is observed. TABLE I1 RESPONSE TIMES OF THE CALCIUM ELECTRODE IN THE PRESENCE OF A SELECTION OF INTERFERING IONS Interfering ion Selectivity ratio T95b Na+ 0.001 N(Me)4+ 04006 H+ 2 x 104 Pb2+ Cd2+ cua+ Mg2+ Ba2+ Zn2+ SP+' 1.8 1.7 0.13 0.040 0.026 0.009 0403 3-0 2.3 2.2 3.2 3.0 2.2 4-0 8.5 224 9.6 None - 2.2 The practical implications of electrode response time measurements are wide, especially in the area of continuous flow analysis using ion-selective electrodes, effluent monitoring and process control where the sensor is part of a servo loop or alarm system and in automatic titrators.In these circumstances, the factors described above, especially the unexpected presence of interfering species, can lead to very large increases in the response time of the sensor (the primary element in such a system), giving spurious results that cannot easily be explained .Hence, far from being an inconvenient feature of the operation of ion-selective electrodes, a constructive interpretation of their response times can lead to useful information on the performance and mechanism of these most useful sensors.56 ION-SELECTIVE ELECTRODES References Proc. Analyt. Div. Chem. Soc.1. 2. 3. Fleet, B., Ryan, T. €I., and Brand, M. J. D., Anafyt. Chem., 1974, 46, 12. Rechnitz, G. A., and Lin, Z. F , Analyt. Chern., 1968, 40, 696. Ryan, T. H., and Fleet, B., in preparation. Applications of Ion-selective Electrodes in the Development of a Chemical Model for Sea Water Michael Whitfield Marine Biologicad Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth, PL 1 2PB Sea water is the most abundant electrolyte solution on this planet, covering 70 per cent.of the earth's surface to a mean depth of 4OOO m. The world ocean is an active chemical system whose composition is apparently controlled by an intricate network of interactions involving also the lithosphere, the atmosphere and the biosphere. In order to unravel this underlying pattern of chemical reactions, we need to have some concept of the nature of sea water itself, i.c., we need a chemical model to describe the consequences of interactions between the various dissolved constituents.In thermodynamic terms, this model will define the chemical poten- tials of the solution components. These chemical potentials will in turn enable us to make quantitative predictions about the ultimate progress of transport processes and spontaneous reactions within the sea and about the chemical composition of the system at equilibrium and will help to define a clear framework against which to view the intricacies of the real ocean.Sea water is a complex electrolyte mixture (Table I) with a mean ionic strength of 0.7 M, a mean volume temperature of about 3 "C and a mean volume pressure of approximately 250 atm.These conditions have tended to isolate marine chemistry from the mainstream of solution chemistry, pre-occupied as it has been with dilute solutions at 25 "C and 1 atm total pressure. Consequently, progress in the development of a suitably flexible chemical model has been rather slow. Over the past few years, a number of general procedures have TABLE I IONIC SEA WATER COMPONENTS THAT MAY BECOME AMENABLE TO DIRECT ANALYSIS BY ION-SELECTIVE ELECTRODES Components Concentration (molal) * Notest Major- c1- Na+ Mgl+ c a 2 + Ii+ so,2- Mznov- HC0,- Br- B(OH)*- cosg- Sr4+ F- HPO,%- NO,- 0.552 a.c 0.470 a, c 0.054 a, d 0.028 a, (4 0.010 a, (b), d 0.010 a. c 1.8 x 10-3 4.3 x 1 0 - 4 3 X.10-4 8.5 x 10-o 9.7 x 10-6 7.4 x 10-5 2.3 x 1 x 10-8 * At an ionic strength of 0.7 M. t a Maintains nearly constant concentration ratio to chloride. b Actively involved in biological cycles. c Suitably selective electrode available for direct measurement. d Electrodes available for studies on simplified systems. (Notes indicated in parentheses apply only in restricted circumstances.)February, 1975 ION-SELECTIVE ELECTRODES 57 been introduced for calculating the chemical potentials of constituents in electrolyte mixtures.l These rely mainly on the assumption that interactions between ions of opposite charge sign are dominant and they enable the properties of complex electrolyte mixtures to be deduced from the properties of the component single electrolyte solutions.Such models can be used to calculate either mean-ion or conventional single-ion activity coefficients. These theoretical advances can be augmented and tested by direct measurements of solute activity coefficients using ion-selective electrodes. Major Sea Water Components In a representative sample of oceanic water (Table I), six components (Na+, K+, Mg2+, Caa+, C1- and SO,2-) make up more than 99.5 per cent.of the dissolved material and form a background electrolyte that influences the chemistry of all of the minor components. A remarkable feature is that these constituents are present in an almost constant concentration ratio throughout the world's oceans. With the exception of calcium, they remain unaffected by the biological activity within the sea.The most direct and unequivocal way of testing the theoretical sea water models for these constituents is to measure the mean-ion activity coefficients of the constituent salts in sea water using electrodes that respond selectively to the anion and cation in question. Un- fortunately, selectivity considerations have restricted the experimental measurements to relatively few salts.In instances that have been investigated (Table 11) , the experimental and theoretical estimates of y+ are in reasonably good agreement with one another.lS2 A calcium electrode is now available with good selectivity characteristics with respect to sodiumS and so the corresponding measurements for calcium chloride should soon be made. It is to be hoped that both the experimental and theoretical approaches will eventually break their ties with the physico-chemical norm of 25 "C and 1 atm pressure and that corres- ponding data will become available for more realistic oceanographic conditions.TABLE I1 MEAN-ION ACTIVITY COEFFICIENT MEASUREMENTS IN SEA WATER (IONIC STRENGTH 0.7 M, 25 "c, 1 ATM PRESSURE) EMPLOYING ION-SELECTIVE ELECTRODES* Y& (talc.) r A 1 - Cluster integral Cation-selective Anion-selective Ion-pair Specific inter- expansion Salt electrode electrode Y+ (obs-) model actien model model 0.669 NaCl Na (amalgam) Ag - AgCl 0.668 rfi.0.003 0.666 Na (glass) Ag - AgCl 0-672 f 0.007) o*666 KCl K (valinomycin) Ag - AgCl 0-645 f 0.008 0.627 0-649 0.648 Na,SO, Na (amalgam) Pb(Hg) - PbSO, 0.378 f 0.016 0.323 0-378 0-366 K,SO, K (valinomycin) Pb(Hg) - PbSO, 0.352 f 0.013 0.299 0.365 0.345 *Taken from ref.1, where full details will be found. The availability of electrodes, selective to individual ionic components, has also awakened marine scientists to the possibility of defining useful single-ion activity coefficients. A brief survey of some experimental estimates (Table 111) indicates the variety of approaches that have been made to the conventional definition of these coefficients in sea water.A re- assessment of these experimental values on a uniform and clearly defined basis is sorely needed. The procedures described by Bagg and RechnitzS present a promising avenue of approach. Despite the disparate conventions employed, the experimental single-ion activity coefficients are in reasonable agreement with the theoretical values calculated from different view-points (Table 111).Once a uniform conventional approach has been decided upon, those single-ion measurements, too, will have to be extended to cover a more realistic range of temperature, pressure and ionic strength. A considerable advance in our understanding of ionic interactions in sea water would be made if electrodes were available with selectivities suitable for the direct measurement of magnesium or sulphate activities.The lead amalgam - lead sulphate electrode that has58 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem. SOC. been used so far for sulphate measurements is very sluggish and unreliable at low tempera- tures and can be used only in artificial sea waters, as carbon dioxide must be excluded. Theoretical models describing interactions between the major electrolyte components can now make accurate predictions of solution properties using only data for the component single electrolyte solutions.1*2 Conse,quently, measurements of the mean-ion activity co- efficients of any of the sea salt components over a range of temperature and pressure would find immediate application.Ion Ka+ I<+ MgZ + CaZ+ TABLE I11 CONVENTIONAL SINGLE-ION ACTIVITY COEFFICIENTS ESTIMATED FROM ION-SELECTIVE ELECTRODE MEASUREMENTS’S~ Working electrode* Na (amalgam) I< (glass) Orion water hardness electrode Orion calcium liquid ion exchanger yi ( C B I C ) -L---7 Ionic inter- Ion-association action Calibration assumptiont Reference yi (obs.) model model UfNaCl = ma+.4 0.67 0.10 0.65 Calibrate in pure NaCl at same ionic strength as sea water. Calibrate in dilute solution 5 where YE+ can be calculated from extended Debye - Huckel equations. Calibrate concentration 6 response in CaCl,, MgCI,, NaCl mixture similar to sea water. Assume y values of free ions are only affected by the ionic strength and that the electrode only responds to the free ion in sea water.As above. 7 0-60 0.26 0.63 0.62 0.26 0.23 0.2 1 0.34 0-20 *All use a calomel - saturated KC1 reference electrode. t All assume liquid junction poteii tial negligible. Minor Components Once chemical models have been used to establish some measure of understanding of the interactions between the major ionic components, these ideas can be extended to explain the influence of the major salt components on the chemistry of the minor constituents that are of greater biological and geological interest.Only in a very few instances (e.g., the carbon dioxide system, the hydrolysis of ammonium ions) has the theoretical approach been de- veloped to this extent. As many of these minor constituents are directly involved in biolo- gical processes (Table I), their chemistry is very labile and direct measurement in the field is imperative.The main emphasis of electrode measurements in studying these components has consequently been on the development of in situ techniques9 Efforts so far have been concentrated on the i n situ measurement of pH, not least because a reliable and perfectly selective electrode has been available for more than 50 years.Two sea water pH scales are currently in use sJO; one is based on the dilute NBS buffers and con- tains an unknown liquid junction contribution (“apparent” pH scale) and the other is based on a series of clearly defined sea water buffers (thermodynamic pH scale). The former scale has been widely used in oceanography for a third of a century, whereas the latter has been available €or only 1 year.There is naturally considerable controversy between oceano- graphers about the relative merits of the two scales. Several electrode designs have success- fully overcome the problem of equilibrating the pressure on either side of the glass membrane.9 Silver - silver chloride reference electrodes are generally used and the reference solution is maintained under a slight positive pressure so as to ensure the development of a stable andFebruary, 1975 ION-SELECTIVE ELECTRODES 59 reproducible liquid junction potential.The most sophisticated probes11 incorporate data logging systems so that the pH readings can be recorded in situ with the minimum of distortion to the electrode signal.It is also possible to use the pH cell to carry out in sit^ experiments at several thousand meters depth in the oceans. For example, the degree of saturation of sea water with respect to calcium carbonate can be assessed by following the pH changes that occur when sea water is allowed to equilibrate with a coarsely ground sample of the solid carbonate.12 The pumping and equilibration cycles and the sequence of electrode readings are controlled by the data logger and no outside signals or power sources are required.The relative constancy of proportions of the major electrolytes suggests the possibility of using an electrode selective to one of these ions as a reference. For example, it is possible to measure accurately changes in pH in oceanic waters using the sodium-selective glass electrode as a reference.1, This concept has not yet received any extensive field application. A similar technique has been used to see whether the concentrations of fluoride and chloride ions are in a constant ratio in the 0~eans.l~ Pressure-compensated solid-state fluoride and chloride electrodes were mounted side-by-side protruding from a pressure-tight glass sphere that contained the measuring circuitry.The results of the measurements were not very conclusive because hysteresis effects distorted the cell potential. Of the other ion-selective electrodes now available, only the sulphide electrode has sufficient selectivity for in situ measurement. Although it is potentially useful in modelling anoxic systems,15 it has been used only infrequently in the field.Electrodes with adequate selec- vity for the determination of nitrate, monohydrogen phosphate , hydrogen carbonate, car- bonate and strontium ions in sea water are eagerly awaited by oceanographers. Much useful information, pertinent to the development of chemical models, can still be obtained with the electrodes we already have at our disposal.For example, the mean-ion activity coefficients of the following component salts would provide important extensions of the available models : CuCI,, CuBr,, CuI,, MgCO,, K,CO, and MgF,. The application of recently developed potentiometric gas sensors should also provide some very useful information on the activity coefficients of the volatile non-electrolytes in sea water, particularly ammonium and sulphur dioxide.There are no adequate means at present for estimating these values theoretically. The precision of the measurements is h0.02 pH unit. Conclusion For the major electrolyte components, we now have a wealth of theoretical models but a dearth of good thermodynamic data. Consequently, we are unable to decide which model gives the more accurate picture of the properties of sea water.Ion-selective electrodes, even at their present state of development, are capable of providing much valuable infor- mation on the variation of mean-ion activity coefficients in sea water, particularly over the oceanographic pressure and temperature range. A unif o m conventional approach to the definition of single-ion activity coefficients in sea water is urgently required so that experi- mental and theoretical single-ion activity coefficients can be compared in a realistic manner.Few detailed theoretical studies have been made of the minor components in sea water and the emphasis is still placed on the accumulation of accurate observations. pH measure- ments in the ocean have reached a high degree of sophistication and the electronic hardware is now available to take full advantage of any future developments in electrode technology.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Whitfield, M., in Riley, J. P., and Skirrow, G., Editors, “Chemical Oceanography,” Second Edition, Whitfield, M., Mar. Chem., 1973, 1, 251. Ruzicka, J., Hansen, E. H., and Tjell, J.C., AnaZytica Chim. Actu, 1973, 67, 155.Platford, R. F., J . Fish. Res. Bd Can., 1965, 22, 885. Garrels, R. M., and Thompson, M. E., Amer. J . Sci., 1962, 260, 57. Thompson, M. E., Scielzce, N . Y . , 1966, 153, 866. Thompson, M. E., and Ross, J. W., Science, N.Y., 1966, 154, 1643. Bagg, J., and Rechnitz, G. A., Analyt. Chem.. 1973, 45, 1069. Whitfield, M., in Riley, J. P., and Skirrow, G., Editors, “Chemical Oceanography,” Second Edition Hansson, I., Deep-sea Res., 1973, 20, 479.Ben-Yaakov, S., and Kaplan, I. R., Mar. Tech. SOC. J., 1971, 5, 41. Academic Press, London, 1974, Volume 1, Chapter 2. Academic Press, London, 1974, Volume 2, Chapter 20.60 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem. SOC. 12. 13. 14. 15. Ben-Yaakov, S., and Kaplan, I. R., J. Geophys. Res., 1971, 76, 722.Wilde, P., and Rogers. P. W., Rev. Sci. Instvum., 1970, 41, 356. Brewer, P. G., and Spencer, D. W., Woods Hole Oceanographic Institution, Mass., U.S.A., Tech. Berner, R. A., Geochim. Cosmochim. Acta, 1963, 27, 563. Rep. No. 70-21, 1970. Studies on the Role of t h e Solvent on the Selectivity of the Calcium Liquid Membrane Electrode K. Garbett Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey, KT22 7SE Liquid ion-exchange electrodes that have a cation response are formed from liquid membranes composed of the salt of a hydrophobic anion (the exchanger) dissolved in a water-immiscible solvent.It has been shown1 that the nature of the hydrophobic anion can affect the selectivity and other properties of these electrodes, but the inlluence of the solvent has not been well established. It is known: however, that an electrode prepared from calcium bis(di-n- decylphosphate) with decan-1-01 as the solvent, as in the commercial water hardness electrode, has little divalent cation selectivity, whereas with di-n-octyl phenyl phosphonate as the solvent it has a pronounced calcium ion selectivity. A detailed study has been made of the role played by the solvent on the selectivity and other properties of electrodes.In all instances these electrodes were prepared in an Orion electrode body with liquid membranes formed from solutions containing 0.1 per cent. m/m of calcium bis(di-n-decylphosphate) dissolved in various solvents saturated with water. Using a flow cell with a saturated calomel reference half-cell, the performance of these electrodes was then characterised by measuring the e.m.f.s of solutions containing various activities of either calcium, magnesium, nickel, copper or sodium.From the results, the lower limit of Nernstian response to calcium was determined (i.e., the lowest calcium activity at which the electrode responded according to the Nernst equation) and selectivity constants were calculated by the separate solution method described by Moody and Thomas2 Preliminary experiments demonstrated that satisfactory electrodes could be prepared using alcohols, phosphate esters or phosphonate esters as solvents, but not from other solvents such as toluene, nitrobenzene, n-decane, diisobutyl ketone, di-n-butyl ether or n-butyl propionate. The failure with these solvents was due in most instances to the low solubility (g0.1 per cent.) of the exchanger, but with toluene, where the solubility is relatively high (>I per cent.), it was probably due to the presence of highly polymeric solute specie^.^ All of the solvents used were immiscible with water.Although they did not necessarily have low mutual solubilities with water, an excessive solubility was found to cause rapid electrode failure. The solubility of water in the solvents varied appreciably, but with each homologous series it decreased rapidly, as expected, as the series was ascended (for example, tri-n-propyl phosphate, 16.1 per cent.m/m; tri-n-decyl phosphate, 0.95 per cent. m/m; pentan-l-ol,7.76 per cent. m/m; decan-1-01, 3.60 per cent. m/m).For more systematic studies, three solvent groups were selected, homologues of the n- alcohols (C, to C8, Clo) and tri-n-alkyl phosphates (C3 to Cg, el,,) and ten isomeric octanols. The restrictions on the range of the homologous series were determined by their miscibility with or solubility in water at the lower end and their melting-points or viscosity at the upper end.Representative response curves for the electrodes prepared are shown in Fig. 1, from which two characteristics are apparent: (a) major variations in the response to cations other than calcium with different solvent types and between the two tri-n-alkyl phosphates, and (b) a variation in the extent of Nernstian response to calcium ions. In the electrodes studied, the deviation from Nernstian response at low calcium activities can be explained by considering the over-all equilibrium that exists between the exchanger, calcium bis(di-n-decylphosphate), and its dissociated ions in the aqueous solution, namely Ca2+ (aqueous) + 2s- (aqueous) + CaS, (liquid membrane) .* (1)Febrzlary, 1975 ION-SELECTIVE ELECTRODES 61 where S is the di-n-decylphosphate anion.At low calcium activities in the aqueous solution, calcium will be extracted from the liquid membrane into the aqueous solution, thus increasing the calcium activity, at least in the region of the liquid membrane interface. A greater e.m.f. is therefore generated than is predicted on the basis of the original calcium activity, which results in a deviation from Nernstian response.The calcium activities at which this effect becomes apparent depend on the value of the distribution coefficient for equation (l), with the region of Nernstian response being extended to lower calcium activities as the distribution coefficient increases. The variati +80 n-Pentanol 4-Methyl-4-heptanol > E E Tri-n-propyl phosphate Tri-ndecyl phosphate 4-40 - 0 - -40 - - 80 I I I -5.0 -3.0 -1.0 -5.0 -3.0 -1 Log a M I Fig 1.Response curves for electrodes containing 0-1 per cent. of calcium bis(di-n-decylphosphate) dissolved in various solvents : x, calcium ; 0, copper; A, nickel; 0, magnesium; and 0, sodium. n in the range of Nernstian response found showed that the distributi n co- efficient was, as expected, solvent dependent. Invariably, the tri-n-alkyl phosphates produced electrodes that had lower limits of Nernstian response (i-e., a greater distribution coefficient) than did the corresponding n-alcohols.In addition,octan-1-01 gave a lower limit of Nernstian response than the branched-chain isomers of octanol. The effects with the two homologous series are illustrated in Fig. 2. In each series, there is a progressive extension in the lower limit of Nernstian response to calcium as each series is ascended, indicating a progressive increase in the distribution coefficient.This increase probably reflects the decrease in the bulk dielectric constant of the solvent that occurs as each series is ascended (owing to the decrease in the dielectric constant of the solvent and the decrease in the contribution from dissolved water as each series is ascended).In addition, it was noted that the noise levels of an elec- trode due to pressure pulses and to static charges generated in the flow system invariably increased as the bulk dielectric constant of the liquid membrane solvent decreased, presumably due to an increase in the liquid membrane resistance.62 ION-SELECTIVE ELECTRODES Proc.AmaZyt. Div. Chem. SOC. -4.8 * 3 4 5 6 7 8 9 1 0 Alkyl chain length Fig. 2. Lower limit of Nernstian response for electrodes prepared from members of the homolo- gous series of n-alcohols (A) and tn-n-alkyl phosphates (0). A parameter of great importance is the response to interferent ions, characterised in the electrodes studied by the selectivity constant, K$&. An interferent cation can participate in the generation of an e.m.f.by participating in a cation-exchange equilibrium with the ex- hanger,^ the over-all equilibrium being written as AG3M M2+ (aqueous) + CaS, (liquid membrane) e , M S 2 (liquid membrane) + Ca2+ (aqueous) (2) where M2+ is a divalent interferent cation and ACaM is the ion-exchange equilibrium constant. The over-all equilibrium can be broken down into four equilibria, the distribution equilibria for the dissociated cations between the phases (constants kc, and kM) and the equilibria for the formation of the associated species between the cations and the di-n-decylphosphate anions in the liquid membrane (constants K O and KMs).The ion-exchange equilibrium constant can then be expressed as The expression, together with mobility terms, appears in the theoretical expressions put forward by Morf et aL4 for the selectivity constant, K z .It is apparent that any process which can alter the values of the terms in equation (3) by stabilising the species of one cation relative to another will also alter the selectivity constant. The results summarised in Fig. 3 illustrate the degree to which the solvents used in this study affect the selectivity constants.The electrodes can be separated into three major classes, depending on their divalent cation selectivities : (i) K g = Cu > Ni GS Mg > Ca All n-alcohols, octan-2-01 and also 2-methylheptan-2-01 (ii) Kg; = Cu > Ca > Ni w Mg . . .. Octan-3-01, octan-4-01 and the methylheptanols with hydroxyl groups on carbon atoms 3 or 4 .. . . (iii) KEA = Ca > Cu > Ni Mg . . . . All tri-n-alkyl phosphates In addition to this broad classification, trends can also be seen within the two homologous series examined. For the n-alcohols there is a progressive separation in the selectivity con-February, 1975 ION-SELE CTIVE ELECTRODES 63 stants as the series is ascended, while for the tri-n-alkyl phosphates there is a rapid increase in calcium selectivity.In general, the electrodes are less selective to sodium than to the divalent cations, with the values of its selectivity constants following the same trends as divalent cation selectivities within each homologous series. The effect of the solvent on the selectivities can be understood in part by proposing that a direct solvent interaction, in which steric interactions play a significant role, occurs with the cations, in either their dissociated or associated forms.These effects will be minimised for those cations where the spatial separation of the co-ordinated solvents is greatest, i.e., in calcium with its greater ionic radius and to some extent in copper with its distorted octahedral symmetry.These cations may then be expected to be stabilised relative to cations such as nickel or magnesium. If we assume that the order of stability constant found for ligands such as orthophosphate or pyrophosphate in ~ a t e r , ~ i.e., Cu > Ni > Mg > Ca, is similar to that for the di-n-decylphosphate anion, then a progressive steric effect favouring calcium should produce the orders Cu > Ca > Ni > Mg and eventually Ca > Cu > Ni > Mg with concomitant changes in the orders of selectivity constants.n-Alcohols 1 .o -1.0 - -2.0 - - I some ri c lJC1 5 6 7 8 10 Alkyl chain length 1 2 3 4 Hydroxyl group position t Tri-n-alkyl phosphates 3 4 5 6 7 8 10 Alkyl chain length Fig. 3. Selectivity constants for electrodes containing 0.1 per cent.of calcium bis(di-n-decylphosphate) dissolved in members of the homologous series of n-alcohols or tri-n-alkyl phosphates and in isomeric octanols (octan-1-01 to octan-4-01). This effect is essentially in accord with the known solvent interactions found in solvent extraction studies.s With water-immiscible alcohols, the cations retain their co-ordinated water and the alcohol only interacts via the outer co-ordination shell.The n-alcohols should not, therefore, produce significant steric interactions although the branched-chain alcohols, because of their shape, may do so to some extent. Although changes in selectivity are apparent with the n-alcohols, this may reflect changes in other solvent properties such as the dielectric constant or the intermolecular hydrogen bonded structure of the solvent in the presence of variable amounts of dissolved water.The tri-n-alkyl phosphates, however, co-ordinate directly to the extracted cations, displacing water, even though the latter is present in solution to an appreciable extent. With such bulky solvents, large steric interactions can occur, which could account for the high selectivity for calcium found in electrodes having the larger tri-n-alkyl phosphates as solvents.This work was carried out at the Central Electricity Research Laboratories and is published by permission of the Central Electricity Generating Board.64 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem. SOC. References 1. 2. 3. 4. 5. 6. Ross, J. W., in Durst, R. A., Editor, “Ion Selective Electrodes,” National Bureau of Standards Moody, G.J., and Thomas, J. D. R., “Selective Ion Sensitive Electrodes,” Merrow Publishing Co., Healy, T. V., and Kennedy, J., J. Inorg. Nucl. Chem., 1959, 10, 128. Morf, W. E., Ammann, D., Pretsch, E., and Simon, W., Pure Appl. Chem., 1973, 36, 421. Martell, A. E., and Sillen, L. G., Editors, “Stability Constants of Metal Ion Complexes, Supplement Marcus, Y., and Kertes, A.S., “Ion Exchange and Solvent Extraction of Metal Complexes,” John Special Publication No. 314, Washington, D.C., 1969, p. 57. Watford, 1971. No. 1,” The Chemical Society, Special Publication No. 25, London, 1971. Wiley & Sons, London, 1969, pp. 617-716. Ion Permeability Studies on PVC Matrix Membranes Containing Calcium Liquid Ion Exchanger A.Craggs, G. J. Moody and J. D. R. Thomas Chemistry Department, UWIST, Cardifl, CFl 3NU, Wales Radiactive tracer studies with 45Ca2+ and 3%l- demonstrate that PVC matrix membranes with trapped Orion 92-20-02 liquid calcium ion exchanger are permselective to counter cations. The diffusion coefficient for 45Ca2+ ion permeation through a membrane based on 0.40 g of the exchanger in 0.17 g of PVC and interposed between M calcium chloride solutions is 11 x 109cm2 s-l. Such a low order of magnitude can be attributed to per- meation through a very viscous medium. Increasing the concentration of calcium ions in the solutions on each side of the membrane to 10-2 M causes an increase in the diffusion coefficient to 15 x lo9 cm2 s-l, while a decrease in the solution calcium ion level reduces the diffusion coefficient to 0-4 x lo9 cm2s-l. These changes with concentration are related to the rate of attainment of radioactive tracer equili- brium being relatively less at both the and M concentration levels compared with the 10-3 M level. This may arise from flux restrictions imposed by the exchange - transport sites in the membrane. Thus, it is suggested that the 1 0 - 2 ~ case arises from the inability of the exchange - transport sites to increase their output in proportion to the increase in solution concentration. The M case, on the other hand, is more difficult to explain, for here the effect appears to be related to an actual reduction in the exchange - transport sites by processes such as leaching, which can well be magnified in the membrane surface layers. However, apart from the effect of reduced membrane thickness, halving the amount of ion exchanger in the PVC matrix leads to further substantial reductions in the diffusion coefficients at each of the solution concentrations of and M studied. Such an effect is not surprising in view of the fewer exchange - transport sites in a more viscous PVC medium compared with the corresponding controls. While it has not been possible to calculate diffusion coefficients for the permeation of 45Ca2+ ions through the membranes from calcium chloride solution to Group I1 metal chloride solution, relative permeation studies with 45Ca2+ indicate that magnesium, strontium, barium and beryllium ions inhibit permeability through the membrane. In the case of magnesium, strontium and barium, it is suggested that these, as indicated by solvent extraction and elec- trode selectivity coefficient data, have low affinity for the membrane exchange - transport sites; hence, there is little incentive for calcium ions to pass into the solution on the other side of the membrane. In the case of beryllium, however, it is suggested in the light of solvent extraction and electrode selectivity coefficient data that beryllium ions have a strong affinity for the dialkylphosphate sites. There is a possible consequent blockage of the mem- brane exchange - transport sites hindering the passage of calcium ions to the solution on the other side of the membrane. As expected, the diffusion coefficient is proportional to membrane thickness. The authors thank the Science Research Council for financial support.

ISSN:0306-1396    

DOI:10.1039/AD9751200048

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

Febrzcary, 1975 RESEARCH TOPICS IN ELECTROANALYTICAL CHEMISTRY 65 Research Topics in Electroanalytical Chemistry The following is a summary of one of the papers presented at a meeting of the Electro- analytical Group held on November 6th, 1974, and reported in the December issue of Proceedings (p. 310). Development of Some Liquid-state Ion-selective Electrodes A. A. Al-Sibaai Chemistry Depavtment, University of Technology, Loughborough, Leicestershire, LEI 1 3 U Since the introduction of liquid membrane electrodes selective to calcium in 1967,l many new electrodes of this type with selective response to both cations and anions have become available.Evaluative studies2-6 of these electrodes have demonstrated the Nernstian re- sponse and dynamic range of these electrodes, but also revealed their gradual loss of selectivity and general deterioration with time under extended use.The relation of salt solvent extraction (partition) equilibria to the selectivities of liquid membrane electrodes has received attention recently. An extensive review of partition coefficients has been compiled by Leo et aZ.7 The role of solvent extraction parameters has been discussed and applied.*-10 Buck and Sandiferll treated theoretically and by digital simulation the response of mixed valence electrolytes.Time response has been studied for anion-responsive membranes12 as well as their general electrochemical behavi0~r.l~ The dependence of the selectivity factor on the organic salt concentration has been studied.l* In general, the selectivity of liquid membrane electrodes for the ion of primary interest with respect to common interfering ions is only moderate.lb Nevertheless, the electrodes have been successfully employed analytically for direct potentiometry or potentiometric titration under suitable conditions where interfering ions are absent or present in low con- centrations.One should not stress the advantages of liquid-state membrane electrodes over solid-state membrane electrodes or vice versa; the two types complement each other.The liquid-state membrane electrodes can be applied when no solid membrane is available. In the recent literature, 73 publications concerning liquid-state membrane electrodes occur, compared with 108 publications concerning solid-state non-glass membrane electrodes of different types. There were 15 publications concerning Ca2+ liquid-state membrane elec- trodes and their application in measuring calcium in serum and plasma, in water analysis and other branches of industry, while only a few publications were concerned with calcium solid-state membrane electrodes.Applications concerning the nitrate electrode are re- stricted to the liquid-state membrane.Further examples including application of liquid- state membrane electrodes in industry can be found in recent reviews.16J7 Ion-selective electrodes differ in the details of the process by which the ion to be determined moves across the membrane and by which other ions are forbidden access to the membrane phase. It is useful to separate the transport process of an ion in the membrane into two steps: the movement of the ion within the membrane phase and the process by which the ion enters the membrane.It is necessary that the ion to which the membrane is selective should be able to enter the membrane and to move within it. Rejection by the membrane of other ions can be achieved by blocking either the movement or the ability to pass the mem- brane - solution interface or both.Eisenman18 illustrated that solid ion exchangers are highly selective for univalent cations but considerably less so for divalent cations. This limitation is not due to poor ion-exchange affinity for divalent versus monovalent cations but it appears to be the result of a low mobility of divalent cations within the solid exchanger. In this respect, liquid membranes appear to offer a fundamental advantage over solid membranes.Their principal difference results from the fact that the ion-exchange sites, which are fixed in the solid membrane, are free to move in liquid systems. This means that undissociated ion pairs between the site ion and the deter- mined ion, which are immobilised in the solid, contribute to the movement of the species in the liquid exchanger.The several drawbacks associated with liquid membrane electrodes are :66 RESEARCH TOPICS IN ELECTROANALYTICAL CHEMISTRY Proc. Analyt. Div. Chem. SOC. (i) the theoretical treatment is more complicated for liquid membrane electrodes as a consequence of the sites not being fixed; (ii) unlike solid-state electrodes, they cannot be used in organic solvents; (iii) owing to the manner of construction of liquid-state electrodes, air bubbles tend to become trapped between the test sample and the membrane ; (iv) no combination electrodes analogous to the solid-state series are available; (v) liquid-state electrodes tend to have a shorter life-time.The present work is based on basic dye salts that have been used for the last few years in colorimetric work.Selectivity may be obtained by careful choice of complexing agent, basic dye and solvent. The data from colorimetric work have provided the best conditions for successful extraction of the basic dye salts. These conditions have been found to be the conditions in which the electrodes function best. Basic dye salt electrodes were developed by Entwistle and HayeslD for the determination of uranium, and by Fogg, et aL20 for the determination of zinc.Basic dyes for the determi- nation of Sb(V), Sb(II1) and TI(II1) are the concern of the present work. The electrode body was fabricated20 from PTFE tubing (gin internal diameter, 14 in external diameter). A 8-in section was cut from the end of the tube and threads were cut into the parts so that they could be screwed together and hold a rubber membrane of $-in diameter.Electrical contact with the back of the membrane was made with a &-in diameter carbon rod, which just fitted the tube and which was held firmly in place by a narrow nylon screw passing through the main body of the electrode. Solutions of SbC16- were prepared by oxidising a 5 per cent.solution of antimony(II1) potass- ium tartrate in 5 M hydrochloric acid with a 10 per cent. solution of sodium nitrite. The excess of the nitrite was reduced with urea. These solutions were used to precipitate the appropriate hexachloroantimonate salt from 0.5 per cent. m/V solutions of Sevron red L, Sevron red GL and flavinduline. The pre- cipitates were left in the solution for a few minutes and then filtered off on filter-paper and washed with 2 M hydrochloric acid.Saturated solutions of each antimony dye salt in o-dichlorobenzene were prepared by dissolving less than 100 mg of the dye salt in 25 ml of dichlorobenzene. Lightly cross-linked natural rubber sheeting (0.18 cm thick) was found to absorb the organic basic dye solution. Swelling was complete within 2 h for the lightly cross-linked natural rubber and within 1 d for more highly cross-linked natural rubber.The basic dye salts were found to be distributed more uniformly through the lightly cross-linked rubber. There were clear signs of adsorption of the dye salt on to the surface of the more highly cross- linked natural rubber, which detracted from the reproducibility of the electrode response.The electrodes gave responses of 61aOmV per decade change of concentration of Sb(V) in 2 M hydrochloric acid between 10-3 and M, 57 mV from to M and 47 mV from Pre-soaking is needed for at least 2 h in M Sb(V) in 2 M hydro- chloric acid for electrodes made from lightly cross-linked rubber. The electrode gave a steady response within 3 min when it was moved from a more concentrated solution to a more dilute solution and less than 2 min for a move from the dilute solution to the more concentrated solution.The electrode has to be kept in 10-3 M Sb(V) in 2 M hydrochloric acid when it is not in use. Keeping the electrode in distilled water shortened the life of the electrode. The electrode needed to be re-soaked in the antimony solution for about 4 h before use, after it had been left overnight in distilled water.The electrode needed at least 2 h pre-soaking in the antimony solution before use when it was kept overnight in contact with a saturated solution of the dye salt in dichlorobenzene. The electrode potential drifts in one particular direction and the extent of the drift depends on the dye salt used and on the rubber.The drift is most marked after 1 d of preparation than for the following 4 weeks. For this reason, it is desirable to leave the electrode in contact with Sb(V) in Z M hydrochloric acid overnight before use. In any event, on one particular day the reproducibility is good, i.e., within 1 mV. Flavinduline showed an over-all shift of 60 mV after 1 d of preparation, 74 mV after 10 d and 84 mV after 15 d, while Sevron red L showed a 2 mV shift after 5 d and no further shift in the following 20 d.Sevron red GL showed a 4 mV shift after 1 d and 13 mV after 7 d. Each salt was dried at 70 "C. to lo4 M.February, 1975 RESEARCH TOPICS IN ELECTROANALYTICAL CHEMISTRY 67 For this reason and because the lifetime of the Sevron red L electrode was longer than the others, as it has been used for 4 weeks with satisfactory results, Sevron red L is recommended for general use.Additions of M Cu2+, Hg2+, Pb2+, Ni2+ and 10-1 M Fe3+ caused little or no interference on the response of M Sb(V) in 2 M hydrochloric acid. The change in the potential for these ions was between 0 and -2 mV. Thallium(III), which also forms an anionic complex in 2 M hydrochloric acid, interferes in the determination of antimony.The antimony electrode responds slowly to Tl(II1) in 2 M hydrochloric acid; full response to thallium can be obtained by soaking the antimony electrode in M Tl(II1) in 2 M hydrochloric acid for 2 h. The electrode then gives a res- ponse of 57 mV per decade change of the concentration from to 104 M of TI(II1) in 2 M hydrochloric acid.Thallium(II1) salts of Sevron red L, Sevron red GL, flavinduline and phenzinduline were also prepared. The preparations were similar to those mentioned for antimony. The electrodes made from these salts showed a similar response to Tl(II1) to that described earlier for antimony. The electrode responds fully to antimony(V) after 2 h soaking in 10-3 M Sb(V) in 2 M hydrochloric acid.After observing these results, an electrode was prepared from phenzinduline zinc chloride. The electrode gives full response to Sb(V) or Tl(II1) after soaking it in the solution of 2~ hydrochloric acid of the ion to be determined. The results were as good as the results ob- observed with the Sevron red L electrode. The lifetime of the electrode was more than 4 weeks.The potential shift for Tl(II1) was less than 1 mV after 4 d and about 1 mV for Sb(V) after 10d. Another interesting observation was made that the electrode responded to Sb(II1) in 2 M hydrochloric acid after soaking the Sevron red L or phenzinduline electrode in M Sb(II1) in 2 M hydrochloric acid for 2 h with 57 mV change from M and 42 mV from 10-4 to 10-8 M.Tl(1) does not interfere at the M level as it does not form a chloride com- plex and at higher concentrations it precipitates as TlCl, which is insoluble in water. The advantages of liquid-state electrodes of the type described above are: (i) they are inexpensive, (ii) very little dye salt is required and (iii) they are easy to prepare. to 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.13. 14. 15. 16. 17. 18. 19. 20. References Ross, J. W., Science, N.Y., 1967, 156, 1387. Shatkay, A., Analyt. Chem., 1967, 39, 1056. Rechnitz, G. A., and Lin, 2. F., Analyt. Lett., 1967, 1(1), 23. Potterton, S. S., and Shults, W. D., Analyt. Lett., 1967, 1(2), 11. Hseu. T. M., and Rechnitz, G. A., Analyt. Lett., 1968, 1(10), 629. Carlson, R. M., and Paul, J. L., Analyt. Chem., 1968, 40, 1292.Leo, A., Hansch, C., and Elkins, D., Chem. Rev., 1971, 71, 524. James, H. J.. Carmack, G. P., and Freiser, H., Analyt. Chem., 1972, 44, 853. Back, S., and Sandblom, J., Analyt. Chem., 1973, 45, 1680. Baum, G. J.. J. Phys. Chem., 1972, 76, 1872. Buck, R. P., and Sandifer, J. R., J. Phys. Cbem., 1973, 77, 2122. Reinsfelder, R. E., and Schultz, F. A., Analytica Ckim. Acta, 1973, 65, 525. Danesi, P. R., Salvemini, F., Scibbona, G., and Scuppa, B., J. Phys. Chem., 1971, 75, 554. Danesi. P. R., Scibbona, G., and Scuppa, B., Analyt. Cham., 1971, 43, 1892. Srinivasan, K., and Rechnitz, G. A., Analyt. Chem., 1969, 41, 1203. Buck, R. P., Analyt. Chem., 1974, 46, R28. Covington, A. K., Crit. Rev. Analyt. Chem., 1974, 3, 355. Eisenman, G., Editor, “Glass Electrodes for Hydrogen and Other Cations : Principles and Practice, Entwistle, J. R., and Hayes, T. J., Abstracts of Papers, IUPAC International Symposium on Fogg, A. G., Duzinkewycz, M., and Pathan, A. S., Analyt. Lett., 1973, 6, 1101. Marcel Dekker, New York, 1967. Selective Ion-sensitive Electrodes, Cardiff, April, 1973.

ISSN:0306-1396    

DOI:10.1039/AD9751200065

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

68 ANALYSIS OF FOOD AND DRINK Proc. Analyt. Div. Chem. SOC. Recent Developments in the Analysis of Food and Drink The following is a summary of one of the papers presented at a joint meeting of the Scottish Region with the Scottish Branch of the Institute of Food Science and Technology held on September 18th, 1974, and reported in the October issue of Proceedings (p. 257). Standardisation of Methods of Analysis for Potable Spirits W.Dunnet” and R. E. B. Duncan? Distillers Company Limited, Menstrie, Clackmannanshive A Committee was formed in 1966 under the chairmanship of the Government Chemist to develop and publish acceptable analytical methods for the determination of ethanol and congeners in potable spirits.l Prior to that date, there had been no published evidence based on collaborative tests within the UK of the reliability of the analytical methods being used.In the work that the Committee has since carried out, it has been a major consideration that a method to be evaluated should not be one requiring specialised apparatus. Thus, the most exotic piece of equipment likely to be required is a modest gas chromatograph. Even so, a colorimetric method has always been evaluated as well.For all normal day-to-day purposes, this is done using a hydrometer system. The Sikes hydro- meter as used in the UK gives a measure of ethanol content in discreet steps which, at the usual spirit strength of 70” proof, amount to 0.4” proof or approximately 0.2 per cent. V/V. Various pycnometer methods were tested by the Committee and it was shown that two analysts should be able to produce results within 0.1 per cent.V/V of each other.2 Quantitatively, the most important congeners in potable spirits are the higher alcohols, n- propanol, isobutanol and “isoamyl alcohol,’’ the last term referring to a mixture of 2-and 3- methylbutanols. The AOAC colorimetric method using 4-hydroxybenzaldehyde-3-sulphonic acid and a number of gas chromatographic methods have been tested.l The determination of methanol by using a colorimetric method based on chromotropic acid and by using gas chromatography has also been e~amined.~ Volatile acidity, total aldehydes and total esters, all as measured by the AOAC pro~edures,~ complete the list of congener methods that the Committee have so far scrutinised.It is hoped that the information contained in the Committee’s reports will prove of value both to analysts familiar with spirit analysis and to those who may carry out only the occas- ional analysis of a potable spirit.The most important quantity to be measured in a potable spirit is the ethanol content. The authors would like to record their appreciation of Dr. H. Egan, Government Chemist, who supported the presentation of this paper. References 1. 2. 3. 4. J . Assoc. Publ. Analysts, 1970, 8, 81. J . Assoc. Publ. Analysts, 1974, 12, 45. J . Assoc. Publ. Analysts, 1912, 10, 49. J . Assoc. Publ. Analysts, 1974, 12, 40. * Glenochil Technical Centre. t Glenochil Research Station.

ISSN:0306-1396    

DOI:10.1039/AD9751200068

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

February, 1975 CORRESPONDENCE 69 Papers Accepted for Publication in The Andyst The following papers have been accepted for publication in The Analyst and are expected to appear in the near future. “Voltammetric Determinaton of Ascorbic Acid by Use of a Carbon Paste Electrode,” by J. Lindquist. “Voltammetric Determination of Pyridoxine by Use of a Carbon Paste Electrode,” by P. Soderhjelm and J.Lindquist. “Application of Differential Pulse Polaro- graphy to the Assay of Vitamins,” by J. Lindquist and S. M. Farroha. “Mass Spectroscopic Analysis of Solutions Using an Atmospheric Pressure Ion Source,” by A. L. Gray. “The Determination of Lead and Cadmium in Paints by Atomic-absorption Spectro- photometry Utilising the Delves Micro- sampling Technique,” by 0. W. Lau and K. L.Li. “An Investigation into the Interferences on the Determination of Elements Forming Volatile Hydrides with Sodium Boro- hydride Using Atomic-absorption Spectro- photometry and the Argon - Hydrogen Flame,” by A. E. Smith. “The Determination of 2-( 1-Cyano-1-methyl- ethylamino) -4-ethylamino- 6-methylthio- 1 , 3,5-triazine (Cyanatryn) Residues in Water by High-pressure Liquid Chromato- graphy,” by T.H. Byast. “Determination of Polycyclic Hydrocarbons in Yeast,” by J. Archibald and A. L. Cochrane.70 CONFERENCES “A Semi-automated Procedure for the Deter- mination of Iodine in Plant Tissue and Soil Extracts,” by H. van Vliet, W. D. Basson and R. G. Bohmer. “Application of Data Processing Techniques to Amino-acid Analysis,” by W. Bunting, F. MorIey, I. Telford and P. B. Stockwell. AND MEETINGS Proc. Analyt. Div. Chem. SOC. This course effects a unique opportunity for engineers and other technologists active in the field to make themselves acquainted with the very latest developments in the theory and practice of comminution and air classification. Application forms can be obtained from The Secretary, School of Powder Technology, Uni- versity of Bradford, Bradford, BD7 IDP.

ISSN:0306-1396    

DOI:10.1039/AD975120069c

出版商:RSC    

年代:1975

数据来源: RSC