摘要:

Proceedinas wof the Analytical Division ofThe Chemical Society737477778387889497981001011021031031 04106PAYCALCONTENTSSAC Gold MedalReports of MeetingsSummaries of Papers'One Hundred Years ofMicrochemistry''lon-selective Electrodes''Ternperature- programmedCalorimetry''Instrumental Methods for theExamination of Heterogeneity inInorganic and BiologicalSamples'Spectrometry'Instruments''Newer Aspects of Mass'Evaluation of Automatic Analytical'Treatment and Disposal of Effluents'Correspondence0 bit uariesRank Hilger Spectroscopy PrizeRobert Boyle Essay AwardsConferences and MeetingsPublications ReceivedAnalytical Division DiaryVolume 12 No 3 Pages 73-1 06 March 197Vol. 12, No. 3 March, 1975PROCEEDINGSANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOF THEOfficers of the Analytical Divisionof the Chemical SocietyPresidentG.W. C. MilnerHon. SecretaryW. H. C. ShawHon. TreasurerJ. K. ForemanSecretaryMiss P. E. HutchinsonHon. Assistant SecretariesD. I . Coomber, O.B.E.; D. W. WilsonEditor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, WIV OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members): The Chemical Society, Publications Sales Office, Blackhorse Road, Letch-worth, Herts., SG6 1HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.0 The Chemical Society 1975The Annual MeetingonR and D Topics in Analytical ChemistryLoughborougk University of TechnologyMonday afternoon, July 7th, andTuesday, July 8th, I975will be held atonPapers are invited describing work carried out by postgraduate researchstudents in Universities and Colleges and by young research workers in in-dustrial and other establishments. Contributions are to be presented by thestudent or his industrial counterpart during a 20-minute lecture.Those who wish to offer a paper are asked to send the title and names ofauthors to-Dr. D. I. Coomber, Laboratory of the Government Chemist, Cornwall House,Stamford Street, London, SEI 9NQ.Abstracts (100-150 words) of papers accepted will be required byMay 1st for inclusion in the Notice of the Meeting

ISSN:0306-1396    

DOI:10.1039/AD97512FX009

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

104 PUBLICATIONS RECEIVED Proc. Analyt. Div. Chem. SOC.Analytical Division Diary, continuedAPRILWednesday, 3Oth, 10 a.m.: WiltonNorth East Region, jointly with the NorthEast Region of the Industrial Division, on“Analysis in the Petroleum Based In-dustries-A Critical Evaluation of thePresent Position and Future Developmentin the Primary and Secondary Industries.”“Cracker Analyses,” by G. E. Penketh.“Refinery Analyses,” by F. W. Vaenables.“Plastics Analyses,” by Diana Simpson.“Fibres Analyses and Identification,” by“Analytical Research,’’ by J. Mortimore.Petrochemicals Division, ICI Ltd., Wilton,B. F. Saga.Cleveland. (N.B. : Change of dale)March, 1974 ANALYTICAL DIVISION DIARYAnalytical Division Diary, continuedAPRIL105Thursday, loth, 2.15 p.m.: BradfordParticle Size Analysis Group on “Size Separa-tion Techniques.”“Aerosol Separation by Electrostatic Meth-ods,” by J. I. T. Stenhouse.“The Fritsch Analysette 8 Air Classifier forPreparative Separation and Particle SizeAnalysis,” by A. Taylor.“Experience with the BAHCO CentrifugalDust Classifier,” by L. Svarovsky.“A New Method for the Determination ofDroplet Size in a Liquid -Liquid Dis-persion,” by J. G. Marsland.“Drop Size Measurement in Opaque Liquid -Liquid Systems,” by J. de Carvalho andM. J . Slater.“The Alpine Zig-zag Classifier,” by a repre-sentative of Alpine Machinery Ltd.Department of Chemical Engineering, RoomB227, The University, Bradford, York-shire, BD7 1DP.Monday and Tuesday, 14th and 15th:BirminghamA nalytical Division on “Data Acquisition andProcessing.”Monday, 14th-Survey paper on “Correlation and Deri-vative Spectroscopy,” by D. C.Cham-peney.“Infrared,” by R. P. Young.“Microwave,” by N. L. Owen.“Optical,” by M. L. Butler.“NMR,” by .R. T. Jones.“Mass Spectroscopy-Basic Principles,” byTuesday, 15th-Survey paper on “Unscrambling of Un-“Calibration Curves,” by H. McD. Mc-“GLC Systems,” by P. B. Stockwell.“Nuclear Techniques,” by T. B. Pierce.“Recent Advances in Centrifugal Fast Analy-sers and Methods to Assess their Precision,”by R. W. A. Oliver.“Differential Scanning Calorimetry,” by R. E.Waller.“Coding Chemical Structures by Means ofthe Wiswesser Line Notation,” by M. A.Sim .“13C NMR-IR Applications in Structuraland Quantitative Analysis,” by I.K.O’Neill.‘‘Spectrum Matching in a File (X-ray),”by I. F. Ferguson.“Data Processing as Applied in the Screeningof Biochemical Data,” by Margaret Peters.Lecture Theatre 101, Haworth Building, TheUniversity, Birmingham.resolved Peaks,” by A. B. Littlewood.Geachin.Thursday, 24th, 11.15 a.m.: HuntingdonEast Anglia Region and RadiochemicalMethods Group on “The Use of Radioiso-topes in Metabolic Studies.”Huntingdon Research Centre, Huntingdon.Wednesday, 3Oth, 7 p.m.: CardiffWestern Region, jointly with the Society ofWorks visit to Parke-Davis, Pontypool, 2 p.m.“Industrial Bacteriology,” by J . G. Davis.University Staff Dining Club, Cardiff.Chemical Industry.“X-ray Fluorescence-Matrix Corrections,” “Pharmaceutical Analysis and Safety,” by“Photoelectron Spectroscopy,” by P.Powers. E. R. Squibb & Sons, Moreton, Wirral,“Reaction Rates,” by A. Townshend.by P. Hurley. C. Daglish.CheshirezzzzTuesday, 25th, 6 p.m.: HatfieldAnglia Section of the CS.East Anglia Region, jointly with the Mid-“Atomic Fluorescence Spectrophotometryand the Development of Sources ofExcitation,” by R. M. Dagnall.The Polytechnic, Haffield.Wednesday, %th, 2.30 p.m.: LondonBiological Methods Group.Discussion on “Heparin,k to Ln: introduccti byM. Brozovic, .V. V. Kakkar and L). 1’.Thomas.The Pharmaccutical Society of Great Britain,17 Bloomsbury Square, London, W.C. 1 .Thursday, 27th: LondonAutomatic Methods Group : This meeting hasbeen cancelled.APRILMonday to Friday, 7th to 11th: YorkCS Annual Congress : Wednesday and Thurs-day, 9th and 10th.Fourth Theophilus Redwood Lecture : “Pol-arography in Attacking Practical andTheoretical Problems in Analytical Chem-istry,” by Professor P.Zuman.Symposium on “Analytical Techniques Usedin Industry.”For details of the Congress, see the Februaryissue of Chemistry in Britain, 1975, 11, 72.Monday t o Friday, 7th to 11th: SalfordThermal Methods Group : Fourth ThermalAnalysis School.Monday, 7th-“Thermometric and Enthalpimetric“Thermogravimetry,” by D. Dollimore.“Differential Thermal Analysis,” by F. W.“Differential Scanning Calorimetry,” by K.Methods,” by L. S . Bark.Wilburn.E. J. Barrett.Tuesday, 8th-“Thermomechanical Methods,” by A.Dyer.“Gas Analysis Methods in Thermal Analysis,”by D. L. Griffiths.Analytical Division DiaryPrinted by Heffers Printers Ltd Cambridge England“The Surface Area and Texture of Pow-dered Materials Subjected to Heat Treat-ment,” by D. Dollimore.Practical work in Laboratory.Wednesday, 9th-Practical work in Laboratory.Thursday, 10th-“Applications of Thermal Analysis in Organic“Applications of Thermal Analysis in In-“Applications of Thermal Analysis in Mater-Practical work in Laboratory.Chemistry,” by R. E. Waller.organic Chemistry,” by D. V. Nowell.ials Technology,” by J. H. Sharp.Friday, 1 l€h-Conclusion of practical classes.Thermal Analysis Talk-in; Questions andThe University, Salford.Answers Session.Wednesday and Thursday, 9th and 10th:BathWestern Region, jointly with the WesternBranch of the Institute of Food Scienceand Technology, on “Fruit and Vege-tables-Processing and Analysis.”Wednesday, 9th-Introductory Lecture by A. J. Harrison.“The Use of Ion-selective Electrodes inFruit Analysis,” by J. D. R. Thomas.“GLC Applications in Fruit and Vege-table Analysis,” by G. J. Dickes.“Quality of Canned Fruit Products, ” byV. D. Arthey.“The Processing of Citrus Fruit Drinksand the Significance of Analytical Data,”by Mrs. A. D. Green.“Some Aspects of Fruit Quality,” by A. I.Campbell.Thursday, 10th-‘Vegetable Diseases Affecting Value toProcessor or Loss on Storage,” by R. B.Maude.“The Use of Crop Protection Vegetables forFruit and Vegetable Production,” byM. Sargent.“Pectic Enzymes in Post-harvest Handlingof Plant Commodities,” by R. C. Codnor.The TJniversity, Claverton Down, Bath.[continued inside back cove

ISSN:0306-1396    

DOI:10.1039/AD97512BX011

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

Vo .12, No. 3 March, 1975 of the Analytical Division of the Chemical Society Society for Analytical Chemistry Gold Medal As announced in the January issue of Proceedings (p. 32), the tenth Society for Analytical Chemistry Gold Medal has been awarded to Dr. Robert Lye11 Mitchell. R. L. Mitchell was educated a t Bathgate Academy, whence in 1927 a Newlands Bursary enabled him to study Chemistry a t the Univer- sity of Edinburgh.He graduated BSc with First Class Honours in 1931, having had a sound grounding in analytical chemistry from Sydney Kay and Christina Miller. He then moved to the newly founded Macaulay Institute for Soil Research in Aberdeen where, as a Department of Agriculture for Scotland Research Scholar, he worked on the lime status of Scottish soils, obtaining a PhD of the University of Aberdeen in 1934.This scholarship took him in 1933-34 to the Federal Technical High School in Zurich to study soil science and colloidal chemistry under Georg Wiegner. It was a t the ETH that Mitchell acquired an interest in spectrochemical methods, as the LundegArdh flame-emission technique was being used there by Hans Pallmann. On his return to the Macaulay Institute, he persuaded the Director, W.G. Ogg, now Sir William Ogg, to obtain funds for similar equipment from the Department of Agriculture for Scotland and the Agricultural Research Council. On a research grant and, from 1937, as a member of the Institute staff, he built up a department that has come to be recognised as one of the foremost laboratories concerned with the spectrochemical methods required for the study of soils, plants, and other agricultural, geological and related materials.The flame emission method could not meet the demand for determinations in soils and plants of such trace elements as cobalt, nickel, lead, zinc, molybdenum and copper that were, in the late 1930s, becoming recognised to be essen- tial for or toxic to plants or animals.To meet this requirement, Mitchell and R. 0. Scott by the early 1940s developed a procedure com- bining a concentration method involving pre- cipitation by mixed organic reagents with a variable internal standard cathode layer arc spectrographic technique. The concentration process recovered simultaneously, at the micro- gram level, most of the biologically important elements, while the arc-emission technique gave Dr.R. L. MitcheU a reproducibility of around 5 per cent. for these elements. This method is still used in the Department of Spectrochemistry to provide basic information on trace elements in soils and plants and it has been applied in many labora- tories throughout the world. It and the earlier flame techniques are now supplemented by other arc, spark, porous-cup solution-spark, atomic-absorption and atomic-fluorescence 7374 REPORTS OF MEETINGS Proc.Analyt. Div. Chem. SOC. methods, often involving direct-reading photo- metry and computer assessment, a three-channel flame photometer designed in the course of A.M. Ure’s PhD work having been in use since 1950. In addition, a unit, under V. C. Farmer, dealing with infrared and ultraviolet absorption studies of inorganic and organic constituents of soils is part of the department, which has produccd over 200 papers and now comprises seven research posts and more than twenty support posts.It is interesting to notc that of the nine research workers appointed since 1940 all b u t two are still in the department. The continuity essential for spectrochemical and trace element work has thus been ensured.The major spectrochemical developments for which Mitchell was responsible are described in the 1964 version of his book “The Spectro- chemical Analysis of Soils, Plants and Related Materials.” More than half of his 88 publi- cations have been concernedwith theimplications of trace element findings in soil development, plant growth and animal health.For his part in the advancement of the knowledge of trace element problems he was awarded the Research Medal of the Royal Agricultural Society of England in 1963. He has been invited todescribe various aspects of his work at meetings in the U.S.A., Canada, Australia, New Zealand, U.S.S.R. and many European countries, and has served on spectrographic, soil and trace element committees of numerous organisations in Britain.He was appointed Deputy Director of the Macaulay Institute in 1955 and became Director in 1968, leaving his department in the charge of R. 0. Scott. He has, however, maintained his interest in analytical techniques and was recently instrumental in securing the addition of a spark-source mass spectrometer to the facilities available in Spectrochemistry. R. L. Mitchell is a Fellow of the Royal Insti- tute of Chemistry and of the Royal Society of Eclinburgh and has becn a member of the Society for Analytical Chemistry, now the CS Analytical Division, since 1945. His outside interests include photography and mountain- eering and he is a member, now rather inactive, of the Alpine Club, the Swiss Alpine Club, the Scottish Mountaineering Club and the Cairngorm Club.

ISSN:0306-1396    

DOI:10.1039/AD9751200073

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

74 REPORTS OF MEETINGS Proc. Analyt. Div. Chem. SOC. Reports of Meetings North West Reg ion The fiftieth Annual General Meeting of the Region was at 6.30 pem. On Friday, The University, Salford. The Chair was taken by the Chairman of the Region, Mr. A. C. Bushnell. The following office bearers were elected for the forthcoming year: Chazrman- Thursday, February 27th, 1975, in the Venctian Room, The Grosvenor Hotel, Chester.The Chair was taken by the Chairman of the above Branch of the Pharmaceutical Society. given by J. K. January 24th 1975, in the Chapman Building, A lecture on *‘The Impact of the EEC” was Scottish and North East Regions Dr. L. S. Bark. Vice-Chairman-Mr. J. W. Ogleby. Honorary Secretary-Mr. G. B. Crump, Thornton Research Centre, P.O. Box No. 1, Chester. Honorary Treasurer-Mr.M. McDonnell. Members of Committee-Mr. J. Cottam, Mr. G. Davison, Mr. B. Faulder, Mr. T. Hodson, Mr. G. F. Longman and Mr. M. L. Richardson. Mr. T. Carter and Mr. T. Conchie were appointed as Honorary Auditors. The Annual General Meeting was followed by the address of the retiring Chairman, at which the Chair was taken by the new Chairman of the Region, Dr.L. S. Bark. A lecture on “The Training of an Analytical Chemist-Program- ming for Inefficiency” was given by Mr. A. C. Bushncll. A Joint Meeting of the Scottish and North East Regions with the Society for Water Treatment and Examination was held at 2 p.m. on Wednes- day, February 19th, 1975, in the School of Chemistry, The University, Newcastle upon Tyne. The subject of the meeting was “Pol- lution and Water Chemistry.” At the first session, the Chair was taken by thc Chairman of the Society for Water Treatment and Exami- nation, Mr.F. Bell, and the following papers were presented and discussed : “The Deter- mination of Aluminium in Water,” by J. M. Carter; “Analytical Control of Ion Exchange Systems,’’ by D. Kitchen; “Interference in the Electroanalytical Determination of Copper and Lcad in Water and Wastewater,” by D.Barnes. A Joint Meetingof the Region with the Chester and District Branch of the Pharmaceutical Society of Great Britain was held at 8 p.m. on B. Metters, B. G. Cooksey and C. Metters. At the second session, the Chair was taken by the Chairman of the North East Region, Mr. F. E.March, 1975 REPORTS OF MEETINGS 75 Harper, and the following papers were presented and discussed: “Relationship of Iron and Brown Organic Acids in Moorland Water,” by M.G. Snow ; “Total Oxygen Demand-A Review,” by B. D. Ravenscroft. The vote of thanks was given by the Honorary Secretary of the Scottish Region, Dr. J . E. Whitley. Scottish Region A Joint Meeting of the Region with the Edin- burgh and East of Scotland Section of the CS was heldat 4.30p.m.on Tuesday, February llth, 1975, at the Heriot Watt University, Grass- market, Edinburgh.The Chair was taken by the Chairman of the Scottish Region, Dr. J. M. Ottaway. A lecture on “Antibodies as Ultramicro- analytical Reagents (Radioimmunoassay of Steroids)” was given by E. H. D. Cameron. A Joint Meeting of the Region with the Aberdeen and North of Scotland Section of the CS was held at 4.15 p.m.on Thursday, February 27th, 1975, in the Department of Chemistry, The University, Meston Walk, Old Aberdeen. The Chair was taken by the Vice-chairman of the above Section of the CS, Mr. J. Towler. A lecture on “Corrosion Control Offshore” was given by M. J . Pursell. Western Region The twentieth Annual General Meeting of the Region was held a t 5.45 p.m.on Friday, January 17th, 1975, in the Chemistry Depart- ment, New Building, University of Wales Institute of Science and Technology, Cathays Park, Cardiff. The Chair was taken by the Chairman of the Region, Dr. W. J. Williams. The following office bearers were elected for the forthcoming year: Chairman-Dr. W. J. Williams. Vice-Chairman-Mr.G. J. Dickes. Honorary Secretary-Dr. G. Nickless, School of Chemistry, The University, Bristol8. Honorary Treasurer-Dr. D. Betteridge. Members of Committee-Dr. W. Cule Davies, Mr. M. C. Finniear, Mr. A. G. Hill, Dr. G. V. James, Mr. E. B. Reynolds and Dr. J. D. R. Thomas. Mr. E. A. Hontoir and Mr. E. Minshall were re-appointed as Honorary Auditors. The Annual General Meeting was followed by a Joint Meeting with the South Wales Section of the Society of Chemical Industry, at which the Chair was taken by thechairman of the Western Region, Dr.W. J. Williams. A lecture on “Chemical Analysis and Environ- mental Quality’’ was given by H. Egan. A Joint Meeting of the Region with the South Wales (West) Section of the CS was held at 7.30 p.m. on Tuesday, February 18th, 1975, in the Chemistry Department, University College of Swansea, Singleton Park, Swansea.The Chair was taken by Professor A. Pelter. A lecture on “Science and Crime” was given by R. L. Williams. Midlands Region The Elwell Award Presentation Meeting was held at 6.30 p.m. on Tuesday, January 14th’ 1975, at the Haworth Building, University of Birmingham. The Chair was taken by the Chairman of the Region, Dr.D. Thorburn Bums. Two papers submitted for the Award were read: “A Feasibility Study for the Routine Control of Silica Content in the Pottery Industry by a Radioisotope X-ray Instrument, ” by P. H. Brassington, and “Development of Some Liquid-state Ion-selective Electrodes, ” by A. A. Al-Sibaai. Two other papers were presented at the meeting: “Stability of Flavonoid Com- plexes of Copper(I1) and Flavonoid Antioxidant Activity,” by C .R. Williams, M. Thompson and G. E. P. Elliott, and “The Determination of some Sulphur Anions by MECA,” by D. J. Knowles . Mr. Brassington’s paper was awarded first place by the referees, and he was presented with the trophy and a cheque for L15 by Dr. Elwell. A further cheque for A7 was pre- sented to the winner by Mr.D. M. Evans. Mr. Al-Sibaai’s paper was deemed worthy of the second prize, and he was presented with a cheque for L l O . The other two speakers, Mr. Williams and Dr. Knowles, were presented with book tokens as a memento of the occasion. North East Region The ninth Annual General Meeting of the Regior, was held at 7.30 p.m. on Wednesday, January 22nd, 1975, at the Dragonara Hotel, Fry Street, Middlesbrough.The Chag was taken by the Chairman of the Region, Mr. J. Whitehead. The following office bearers were elected for the forthcoming year: Chairman-Mr. F. E. Harper. Vice-Chairman-To be elected. Honorary Secretary-Mr. D. F. Griffiths, Davy Powergas Ltd., Research & Development Department, Bowesfield Lane, Stockton-on-Tees, Cleveland TS18 3HA.Honorary Treasurer-Mr. G. A. Gray. Members of Committee-Dr. H. Hughes, Dr. A. A. Smales (ex-officio), Mr. L. W. Rell,76 REPORTS OF MEETINGS Proc. Analyt. Div. Chem. SOC. Mr. P. J . Burnill, Dr. L. C. Ebdon, Dr. H. Hughes, Mr. F. C. Shenton, Mr. J. Whitehead and Dr. C. Woodward. Mr. C. N. Bell and Mr. A. E. Heron were re-appointed as Honorary .Auditors. The Annual General Meeting was followed by an Ordinary Meeting of the Region at which the Chair was taken by the new Chairman, Mr.F. E. Harper. A lecture on “The Warmth of Chemistry” was given by L. S. Bark. East Anglia Region An Ordinary Meeting of the Region was held at 3 p.m. on Wednesday, February 19th, 1975, at Spillers Ltd ., Research and Technology Centre, Station Road, Cambridge.The Chair was taken by the Chairman of the Region, Mr. A. W. Hartley. The subject of the meeting was “The Use of X-ray Techniques in Analytical Chemistry” and the following papers were presented and discussed : “X-ray Powder Diffraction-An Analytical Tool, ” by A. Seaman ; “X-ray Fluorescence Analysis-Theory and Appli- cations,” by C. F. Gamage. Microchemical Methods and Chromatography and Electrophoresis Groups A Joint Meeting of the Microchemical Methods and Chromatography and Electrophoresis Groups was held at 6 p-m.on Wednesday, February 5th, 1975, a t the Polytechnic of the South Bank, Borough Road, London, S.E.1. The Chair was taken by Dr. D. F. G. Pusey. A discussion on “Data Processing in GLC,” was introduced by Dr. Austin Woodbridge. Special Techniques Group A Joint Meeting of the Group with the Sheffield Metallurgical and Engineering Association was held at 2.30 p.m.on Tuesday, February llth, 1975, at the Corporate Development Labora- tories, British Steel Corporation, Hoyle Street, Sheffield. The Chair was taken jointly by the Vice-chairman of the Special Techniques Group, Dr. P. B. Smith, and the Chairman of the Sheffield Metallurgical and Engineering Association, Mr.Scattergood. A discussion on “Energy Dispersive X-ray Fluorescence” was introduced by representatives of Nuclear Enterprises Ltd. and Tracor and Ortec Ltd. Automatic Methods Group An Ordinary Meeting of the Group was held at 9.30 a.m. on Wednesday, February 26th, 1975, at the Dragonara Hotel, Fry Street, Middles- brough. The Chair was taken by the Chairman of the Group, Mr.C. L. Denton. The subject of the meeting was “Application of Computers, Particularly Microprocessors, to Automatic Analytical Instrumentation,” and the following papers were presented and discussed : “Introduction and Definition of Terms,” by J. Stuart; “A User’s Requirements from a Micrsprocessor Controlled Analytical Instrument,” by D.A. Deans; “A Data Proces- sing System for Quantitative NMR,” by P. B. Stockwell, W. Bunting, F. Morley and I. K. O’Neill ; “Laboratory Data Collection Tech- niques Using a Time Shared Mini-computer,” by G. B. Fish ; “Computer-controlled Monitoring and Data Reduction for Multiple Ion-selective Electrodes in a Flowing System,” by B. Fleet, S. P. Perone and J. H. Zipper. The meeting concluded with an open forum.Radiochemical Methods Group An Ordinary Meeting of the Group was held at 10.15 a.m. on Wednesday, February 19th, 1975, in the Chemistry Department, The University, Manchester. The Chair was taken by Dr. B. Fox. The subject of the meeting was “Preparation and Use of Labelled Compounds,” and the following papers were presented and discussed : “Cyclotrons and Labelled Compounds,” by J.Clark; “Synthesis of Labelled Compounds,” by A. J . Palmer; “Review of Clinical Application of Labelled Compounds, Past, Present and Future,” by F. Gillespie ; “Isotope Labelling in Studies of Biochemical and Biological Mechanisms,” by G. R. Barker; “Non-clinical Use of Labelled Isotopes,’’ by B. Lord. Joint Pharmaceutical Analysis Group The Annual General Meeting of the Group was held a t 6.30 p.m.on Thursday, January 16th, 1975, at the Pharmaceutical Society of Great Britain, 17 Bloomsbury Square, London, W.C.2. The Chair was taken by the Chairman of the Group, Mr. G. F. Phillips. The following office bearers were elected for the forthcoming year : Chairman-Mr. G. F. Phillips. Honorary Secretary-Mr. J. C. Deavin, William Warner & Co. Ltd., Eastleigh, Hants. Members ofMarch, 1975 ONE HUNDRED YEARS OF MICROCHEMISTRY 77 Committee-Dr. F. J. Bryant (representing the The Annual General Meeting was followed by AD), Dr. J. M. Caldenvood, Mr. B. A. Forder, a discussion on “Pharmaceutical Education Dr. D. C. Garratt, Mr. C. A. Johnson, Mr. S. C. with Special Reference to Pharmaceutical Jolly (representing the Pharmaceutical Society), Analysis,” introduced by F. Hartley. This was Mr. G. F. Meadows, Mr. W. H. C. Shaw and followed by a Cheese and Wine Party. Dr. A. F. Turner.

ISSN:0306-1396    

DOI:10.1039/AD9751200074

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

March, 1975 ONE HUNDRED YEARS OF MICROCHEMISTRY 77 One Hundred Years of M icrochemistry* R. Belcher Department of Chemistry, The Univevsity of Birmingham, P.O. Box 363, Birmingham, B15 2TT Microchemistry is concerned with the identification and determination of amounts of sample that are too small to be analysed by conventional macro-methods. Feigll has objected to the term “microchemistry.” He states, “there is no ‘microchemistry’ as a separate branch.. . A special field of microchemistry would exist if it were concerned with phenomena and modes of behaviour different from those dealt with in ‘macrochemistry.’ However, this is not the case, and the term ‘microchemistry’ is just as erroneous as the familiar term ‘technical chemistry,’ which has now been replaced by ‘chemical technology’.. . Thesituationis different with respect to the term ‘microanalysis,’ which, because of its goal, is actually a special branch of chemical analysis.” Although Feigl’s objection to the use of the word “microchemistry” is logical, the term has been in use for so long that it is now unlikely to be supplanted. Accordingly, this term is used throughout this paper.Although, in the latter, we may be determining the desired constituents at levels equivalent to those in microchemistry, the amount of sample taken is generally in the macro-range. Moreover, the same accuracy is not required, for the amounts are expressed in parts per million, whereas in quantitative microchemistry the amounts are generally expressed in percentages. Between 1935 and 1945, when microchemistry became widely recognised as a general technique, many writers confused the two branches of analysis.Indeed, the terms are sometimes used inter- changeably even today. Some consider it to be Pliny’s2 test for iron sulphate (an adulterant of copper sulphate), in which papyrus soaked in extract of nut-galls was used (1st century A.D.). However, we have no knowledge of the amounts that were involved.Although this was probably the first spot-test, it is doubtful that it would have been applied according to the meticulous methods devised by Feigl. The discovery of the microscope led to some of the earliest methods for identifying small amounts of materials. Probably H ~ o k e , ~ in 1677, was the first to use the microscope in this way.He examined them under the microscope and showed that they were very small particles of flint and of iron, but that the latter predominated. Marggraf4 (1709-1782) examined beet and cane sugar under the microscope and showed them to be the same. He also examined the reactions of platinum under the microscope and was the first to use the flame test to distinguish potassium and sodium (in 1784, De~croizilles~ differentiated sodium and potassium under the microscope as their chloroplatinates). The next investigator to examine compounds under the microscope and to record their crystal forms and other properties, as a basis for their identification, was Tobias Lowitz4 (1757-1804).Lowitz was born in Germany, but went to St. Petersburg and eventually became the Chief Apothecary to the Court.He was the first to separate the alkaline earth metal chlorides by extraction with ethanol. A considerable time elapsed before there was any further reference to the use of the micro- scope in analysis. In 1831 Raspail* recommended that the microscope be used for the identi- It is important that microchemistry be differentiated from trace analysis.It is a little difficult to establish the first microchemical method. He collected sparks from striking flint on steel on a sheet of white paper. *Presented at a joint meeting of the Midlands Region and the Microchemical Methods Group on November Ilth, 1974, at Nottingham.78 Proc. Analyt. Div. C h e w SOC. fication of substances, especially in physiology. He stated that “to work with small amounts of substances is not only economical but involves a new technique.” He examined plant ash and calcium oxalate in plants, the structure of starch granules and the action of iodine on starch. Raspail was a Catholic priest and a Professor of Theology, but he left the Church in order to study natural sciences.He was arrested several times for his political views, but he became very rich in 1840 owing to his invention of the camphorated cigarette, which he patented.In 1853 he was expelled from France, but was able to return in 1871 after the fall of the Empire of Napoleon 111. Some form of spot-testing on paper and on glass slips was used by Reid, for he mentions this technique in a paper delivered to the British Association in 1831L5 Unfortunately, details do not appear to be available.In 1852, Thomas Andrews described what are essentially micro-methods. He detected less than 0.1 pg of sodium in a drop of solution by the depol- arising action of sodium hexachloroplatinate(1V). He also established the composition of “electrolytic gas” by the use of methods which are undoubtedly methods for the microanalysis of gases5 However, these were isolated examples and methods based on the use of the micro- scope were being developed and extended by several investigators.3 These are listed in Table I.TABLE I NOTABLE CONTRIBUTORS TO THE DEVELOPMENT OF CHEMICAL MICROSCOPY IN THE SECOND ONE HUNDRED YEARS OF MICROCHEMISTRY HALF OF THE NINETEENTH CENTURY The dates refer to their main publications.Helvig 1865 Boricky 1877 Hating 1866 Goldschmidt 1883 Wormley 1867 Streng 1883 Sorby 1869 Haushofer 1885 Wormley described the use of the microscope for the identification of poisons. Sorby applied it to the analysis of minerals by examining the products obtained after treatment with the blowpipe. Haushofer (1839-1895), who was Professor at the Technical University in Munich, published his book “Microscopischen Reactionen,” in which he described characteristic reactions for most of the elements.One of the most famous contributors to this field was Theodore Behrens (1843-1905), who was responsible for the development of many microchemical techniques. Behrens tested and selected reliable and reproducible methods. He classified them and published a book “Anleitung zur Mikrochemischen Analyse.’ ’ One volume (1894) described inorganic reactions and other volumes (1895-1898) described organic reactions.In 1874 he was appointed Professor of Mineralogy and Geology at the Technical University of Delft. In 1897 he designed and built there the first microchemical laboratory. His work was continued by his co-author, Kley. This work was to be extended by Schoorl who added tested separation procedures (1907).* Thus the microchemistry practised a hundred years ago was almost exclusively qualitative analysis based on microcrystallographic methods. The most that can be said of that period is that these methods were now widely accepted and widely practised; a few more years were to pass before the basic techniques of quantitative microchemistry were to be developed.The pioneer of quantitative microchemistry was, without doubt, Friedrich Emich of the Technische Hochschule in Graz. In 1889 he began studies in chemical microscopy, but soon changed over to general methods. He developed fibre tests (impregnated with indicators or sulphide) capable of detecting nanogram amounts, and capillary tube operations (crystalli- sation, washing, extraction, sublimation, etc.).He devised a method for the fractional distil- lation of a single drop of liquid and his well known method for boiling-point determination. These techniques were the basis for preparative and purification methods. Emich’s most important contributions were the experiments in quantitative microchemistry. I have not been able to discover exactly when these were initiated, but apparently the first Boricky identified alkali and alkaline earth metals by crystal tests.He also described some new manipulative techniques. *It may be noted that between the Wars, the laboratory of Chamot and Mason at Cornell University was probably the foremost laboratory specialising in microcrystallographic tests.March, 1975 ONE HUNDRED YEARS OF MICROCHEMISTRY 79 published work did not appear until 1909.*3 Emich, with his co-worker Donau, described the determination and separation of several cations using 1Omg or less of sample.Samples were weighed on the Nernst balance, modified by Donau. Donau also developed the filter dish. Methods were described for the determination of sulphur and halogens by the Carius method.Pilch, from Emich’s laboratory, described a micro-Kjeldahl method for the deter- mination of nitrogen, in 1911. The Emich - Donau methods did not find wide acceptance, probably because of the short- comings of the balance, for the operation of which great skill and patience were required. These objections disappeared when the Kuhlmann assay balance was adopted.In 1910, Fritz P ~ - e g l , ~ ~ ~ who was then working at the University of Innsbruck, isolated from bile a degradation product in amounts so small that it could not be analysed by means of normal procedures. Shortly before this period, Pregl had worked at the University of Graz and was aware of the work of Emich. He tried to develop small-scale methods that could be used to analyse these small amounts of material.In 1911 in Berlin, he described, with demonstrations, the determination of carbon, hydrogen, nitrogen, sulphur and the halogens. Pregl adopted the Kuhlmann balance, which he had seen in use in the laboratory of Emich, and he used a special weighing technique that enabled an accuracy of 1-2 pg to be obtained. In 1913 Pregl returned to the University of Graz as Professor of Medical Chemistry.Some of the earlier Pregl methods were empirical and now seem rather unwieldy. In the method for carbon and hydrogen, the products of combustion were collected in a gas holder over mercury and were re-passed through the combustion tube. Carbon dioxide was absorbed in potash bubblers, even though soda-lime had been described by Mulder more than a century bef0re.t The results of the nitrogen determinations were always 10 per cent.high and a correction had to be made. Other methods were developed and refined and when Pregl was completely satisfied they were published (1917). By comparison with present-day methods they seem cumbersome and they certainly demanded a very high skill on the part of the operator, but at that time, and for another two decades, to those who used these methods and had had experience of the macro-methods which preceded them, they seemed to be elegant and refined.In 1923, Pregl was awarded the Nobel prize for his development of micro-methods of organic analysis. Undoubtedly, organic chemistry and biochemistry had advanced at a tremendous pace because of the use of these methods; it was no longer necessary to isolate large amounts of materials for analysis.Nevertheless, many scientists, including Anton Benedetti-Pichler and Herbert Alber, the co-workers of Emich, felt that the pioneering contri- bution of Friedrich Emich had been overlooked and on reflection, it does seem to me that joint recognition would have been a just and fair decision.It will be seen that after the turn of the century, microchemistry, in all its aspects, was developed mainly in Austria.1 The contribution of Donau, one of Emich’s earliest CO- workers, has already been mentioned. Donau was also the first to apply candoluminescence for analytical purpose^.^ Although mentioned briefly by Feig1,l the possibilities of this technique remained unnoticed until recently.’ For some reason, which has never been apparent to me, Donau’s pioneering contributions received little attention and he died in obscurity in 1950.3 Emich’s “Lehrbuch” was published in 1911.*In 1880 Robert Mauselius analysed 67 mg of a sample of Kainosit from Nordmarken for silica. yttrium(II1) oxide, iron, calcium, magnesium, alkali metals and water.6 This is a large amount by present-day standards and would be reckoned a semi-micro sample rather than a micro-sample, but it represented the smallest mass of material that had been analysed quantitatively until that time.tSoda-lime, to be superseded by soda-asbestos (also developed in the last century), had a struggle to replace the potash bubbler. I can recall seeing in the Department of Fuel Technology, Sheffield University, in 1927, potash bubblers being used in the Liebig macro-method.They were replaced by a commercial form of soda-lime in 1929. $Austria appears to be considerably in advance of other countries in the Western World in recognising the achievements of its chemists and particularly its analytical chemists. In 1950, a street in Graz was named the Emichplatz with an appropriate memorial plaque.In 1967, Feigl, then a Brazilian citizen for 27 years, was presented with the Gold Medal of the City of Vienna (equivalent to being made a freeman of a British city). In 1970, a decorated plaquewas attached to Pregl’s house in Graz and in 1974, a special Pregl stamp was issued.80 Proc. Analyt. Div. Chem.SOC. Hans Lieb succeeded Pregl, after the latter’s death in 1931, and maintained the high traditions of the Medical Chemical Institute until his retirement several years after the Second World War. Hans Lieb, now in his 87th year, is still active and was the Treasurer of the International Microchemical Congress held in Graz in 1970. Feigl, working at the University of Vienna, developed spot tests for both inorganic and organic analysis.The success of these tests tended to obscure the contributions that Feigl made to reaction chemistry in general. For example, his masking reactions facilitated the later development of spectrophotometry and EDTA titrations. Feigl began these studies shortly after the First World War and the first edition of his book was published in 1931.Feigl was a frequent visitor to Britain until the Anschluss. He then lost his position at the University of Vienna and after working for a short time in Ghent, he found refuge in Brazil. It is interesting to note that he was offered a position at the University of St. Andrews during this unfortunate part of his life, but was unable to accept because he was already committed to going to Brazil.Ludwig and Adelheid Kofler, while working at the University of Innsbruck in the early 1940’s, developed thermomicroscopic methods. These techniques enabled melting-points and refractive indices to be determined with great accuracy; by the use of eutectic mixtures many compounds could be identified. Many developments of this work are due to Maria Kuhnert-Brandstatter at the same University.* During the 1920s many of the methods for the determination of organic elements were improved, but the determination of iodine by titrimetric methods provided problems because of the high equivalent weight of iodine. In 1929 Leipert described his well known amplifi- cation method, which is still used and has found many other application^.^ This method has generally been ascribed to winkle^-,^ around the turn of the century, and to later Hungarian chemist^.^ However, the method for the amplification of iodine is much older and appears to have been described first by Friedrich Mohr in 1853.4 It is surprising that this method, so admirably suited for microchemical analysis, was overlooked for so long.In the 1930s various modifications and improvements were described, but the organic analysts of that time were to prove as conservative as their predecessors, as will be remarked later.In Pregl’s method for the determination of carbon and hydrogen, a duplicate scaveng- ing train was used so that the absorption tubes could be swept out with air before the final weighing. This practice had certainly been abandoned in the Pregl Institute by 1937, yet several years later many British and American microanalysts were demanding the manufacture of this out-dated assembly.However, the advent of the Second World War brought many forced changes. British microanalysts depended on Continental sources for much of their equipment and reagents. The steps that were taken to overcome these problems have been described else- where and need not be repeated here,5 except to say that one outcome was the use of external absorbents for nitrogen oxides and another, the development of simpler packings for the combustion tube.l o Shortly before the war, Schuetze had described a new direct method for the determination of oxygen; such a method had been the dream of organic chemists for more than a century.Immediately after the war, when investigating teams visited Germany, they were astonished to find the direct method for oxygen, adapted to the micro-scale, in general routine use. All combustion methods were semi-automated in some way and a number of improvements had been made in other directions.ll In the period immediately after the war the empty-tube method became widely used in Britain12 until it was superseded after about twenty years by automatic methods.The method still finds occasional use for the analysis of difficult compounds. The analysis of compounds that contain fluorine received a great deal of attention as did the determination of fluorine itself. Various highly active catalysts and oxygen donors were developed, including mixtures of old and new tube-fillings.Two of the more popular tube-fillings were cobalt(I1) - cobalt(II1) oxide (CO,O,)~~ and a mixture of manganese(1V) oxide and silver produced by the decomposition of silver permanganate.12 There is no doubt that these materials are more effective than the conventional copper(I1) oxide filling, and both fillings have their particular adherents.The oxygen-flask method, developed in the last century by Hempel and examined at intervals by various investigators,13 remained almost unknown until Mikl and Pech reduced ONE HUNDRED YEARS OF MICROCHEMISTRY There were, however, to be developments outside the schools of Emich and Pregl.March, 1975 ONE HUNDRED YEARS OF MICROCHEMISTRY 81 it to the semi-micro scale and used it for the determination of halogens and sulphur.Even then, analysts remained unenthusiastic or sceptical and it was not until Schoeniger reduced the method to the micro-scale and extended its application that it became widely ad0pted.1~ This is still the most widely used method for the determination of organic elements other than carbon, hydrogen and nitrogen. In the early part of the 1960s fully automated commercial apparatus of various kinds and using different principles began to be used.Some of them are now well established and each has its particular adherents. In most forms of this kind of apparatus, nitrogen is determined with carbon and hydrogen. The materials used for the fillings are extremely vaned and are generally sold by the manufacturers of the equipment.Most microanalysts prefer to buy this material because although exorbitant in price, it is uniform and reliable and thus the analyst can be independent of technicians. Automated equipment has taken much of the drudgery (and skill) out of routine operations, but there are still certain types of compound that require special treatment; hence it is still advisable to keep some of the manually operated equipment available for particular compounds or in the event of emergency.Probably the largest routine microanalytical laboratory in the world is that of the BASF in Ludwigshafen and the organisation of this laboratory and its data processing have been described in a recent article by Merz.14 The methods used in this laboratory are typical of advanced present-day practice and are probably indicative of the type of method to be used for several years to come.Post-war Developments in Other Branches of Microanalysis I have emphasised developments in organic microanalysis because this is probably now the most important branch. It will be noted that for routine purposes micro-methods for the analysis of organic compounds have completely superseded macro- and semi-micro methods, although the latter may occasionally be used in special circumstances.Methods of inorganic microanalysis were still widely used in the early post-war years, but have become obsolete owing to the development of accurate spectrophotometric methods. Nevertheless, some of the elegant equipment still finds occasional application.Shortly before the Second World War, Anton Benedetti-Pichler, a former pupil of Emich, began developing sub-micro methods for inorganic analysis. These methods were extended by other investigators and proved invaluable in studying the chemistry of the trans-uranic elements. The techniques were further developed by a number of other inve~tigatorsl~ and similarly, sub-micro methods for organic analysis were developed.These methods were for analysis at the 100-500 pg,16 15-50 pg17 and 5-10 pgl8 levels. As with sub-micro methods for inorganic analysis, these methods were not developed for routine purposes, but for special cases where only minute amounts of sample were available. The “Might Have Beens” One cannot help but feel that organic analysts have been very conservative, at least until recent times. Thus, in the days before microanalysis was developed, analysts used almost exclusively the Liebig method for the determination of carbon and hydrogen, even though the simpler, elegant Dennstedt method had been available since the turn of the century.In the latter method a platinum contact catalyst was used with suitable boat fillings to remove interfering acid gases.A primary and secondary supply of oxygen was used, but this did not complicate the apparatus unduly. There cannot be many people living today who have actually determined carbon and hydrogen by the macro-method of Liebig, but those who have will remember that it probably took two days to prepare the reagents and to pack the tube and then some days to burn off the tube and reduce the blank to reasonable proportions. And even then if everything went well, it was possible to make only two determinations in a single day.In 1911 Kurtenackerlg had indicated that cobalt oxide (Co30,) was more efficient than copper(I1) oxide or other oxides and yet this compound was not recommended again until 1958. During the 1920s Ter Meulenm developed many new methods for elemental analysis.He used manganese(1V) oxide as an oxygen donor in the determination of carbon and hydro- gen. It is obvious from his published work that this was a more effcient agent than those in general use at that time. In effect, the Ter Meulen packing was virtually the same as that No packing was necessary.82 Proc. Analyt. Div.Chem. SOC. recommended many years later as the “decomposition product of silver permanganate,” for this product is essentially a mixture of manganese(1V) oxide and silver metal. The advantages of the latter over manganese(1V) oxide are only marginal. The oxygen flask was first recommended in 1892 by HempeP3 and was studied at regular intervals by other workers for the next half century.But it was not until Schoeniger (see above) reduced the flask size to 250 ml, applied it in microanalysis and extended its uses, that it became widely used, as was stated earlier. For more than one hundred years the organic analysts attempted to develop a satis- factory method for the direct determination of oxygen and many different processes were investigated. It was not until a few months before the outbreak of the Second World War that such a method was described,13 yet the principle of this method had been described in 1904 by Markert,21 a pupil of Hempel, and the method was referred to in Hempel’s book in 1913. 22 Although one now has the advantage of hindsight, it would seem that organic analysts have generally used the hardest and most cumbersome methods when simpler and more efficient processes were available.23 One cannot help feeling that even Pregl himself could have used simpler methods.At least, he would have saved himself a great deal of trouble if he had modelled his method for carbon and hydrogen on that of Dennstedt rather than on that of Liebig, as Friedrich12 was to do later (1931). ONE HUNDRED YEARS OF MICROCHEMISTRY Other Methods In a paper of this type it has been necessary to concentrate on inorganic and organic microanalysis and in the most general way.Other methods, of course, were developed simul- taneously, e.g., electrometric and spectrophotometric methods ; particularly, new separation methods were developed e.g., chromatography in all its aspects. It is impossible to describe the development of these techniques in a short paper of this type.However, it may be mentioned that the development of refined separation techniques would have been of little use but for the existence of methods of organic microanalysis. Generally speaking, as instruments improve in accuracy and versatility, the more compli- cated and expensive they become; however, there is one exception to this rule, the ring-oven, which is very cheap to make and is simple in operation.24 It was originally developed for qualitative and semi-quantitative analysis but it has developed into one of the most accurate instruments available for the analysis of trace amounts of materials.Conclusions Although qualitative methods of microchemistry were known over one hundred years ago, it was only during the first decade of the present century that quantitative methods of inor- ganic and organic microanalysis were developed.For the analysis of organic compounds micro-methods are now used almost exclusively. Most laboratories use fully automated equipment for the determination of carbon, hydrogen and nitrogen, and the oxygen flask is widely used for the determination of most other elements.Apart from further developments in data processing, there is little likelihood of great changes taking place during the next decade or so. Although a good deal of conservatism existed amongst organic analysts for about two generations, when the simpler and more efficient methods that were available tended to be overlooked, the present state of organic analysis could not have been reached much earlier, because it is dependent on newer methods of measurement and the availability of commercial instruments.It would seem that equipment of this type was put into use almost as soon as it became available. The elegant equipment developed for inorganic microchemistry is no longer necessary because of the great advances in accurate spectrophotometric methods ; nevertheless this equipment is still of use in special circumstances.The amounts that can be determined have been extended to levels undreamt of half a century ago. Thus it is possible to determine any organic element or functional group in samples of the order of 20-50 pg. A more limited analysis can be carried out on amounts as low as 5 pg.Such methods, of course, are applied only when the amount of sample is extremely small, for they require far more skill and care than routine micro-methods. There are now various rival techniques available for the establishment of the structure ofMarch, 1975 ION-SELECTIVE ELECTRODES 83 organic compounds; thus, many of the micro-methods for the determination of functional groups are obsolescent.However, organic chemists still appear to find it comforting to know the elemental analysis of their compounds, so it is unlikely that organic microanalysis will be displaced from its current pre-eminent position for the next two decades. Probably the greatest advances are to be expected in the development of simultaneous multi-element determinations.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. References Feigl, F., “Spot Tests in Inorganic Analysis,” Elsevier, Amsterdam, 1958. Plinius, C. S., Naturalis Historiae Libra, 34, 26. Lieb, H., “Microchemical Techniques,” Interscience Publishers, New York, 1961, p. 7. Szabadvary, F., “History of Analytical Chemistry,” Pergamon Press, Oxford, 1966.Belcher, R., in “Proceedings of the International Symposium on Microchemistry, 1958,” Pergamon Alber, H. K., “Mikrokemi Fyra Foredrag av Herbert Alber,” P. A. Norstedt and Soners Forlag, Belcher, R., Bogdanski, S., and Townshend, A., Talanta, 1972, 19, 1049. Kuhnert-Brandstatter, M., “International Symposium on Microchemical Techniques, 1965,” Butter- worths, London, 1965, p. 133; “Thermomicroscopy in the Analysis of Pharmaceuticals,” Pergamon Belcher, R., Talanta, 1968, 15, 357. Belcher, R., “Microchemistry and its Applications,” R.I.C. Monograph, Royal Institute of Chemistry, B.I.O.S. Report 715, 1946; B.I.O.S. Report 1606, 1948. Ingram, G., “Organic Elemental Analysis,” Chapman and Hall, London, 1962. Macdonald, A. M. G., Analyst, 1961, 86, 3. Merz, W., Talanta, 1974, 21, 481. Alimarin, I., and Petrikova N., “Inorganic Ultramicroanalysis,” Pergamon Press, Oxford, 1964. Kirsten, W., and Hozumi, K., Mikrochim. A cta, 1962, 777; Mikroanalyslaboratoriet Uppsala Belcher, R., “Submicro Methods of Organic Analysis,” Elsevier, Amsterdam, 1966. Tolg, G., “Ultramicro Elemental Analysis,” Wiley-Interscience, New York, 1970. Kurtenacker, A., 2. Analyt. Chem., 1911, 50, 548. Ter Meulen, H., and Heslinga, J., “New Methods of Organic Chemical Analysis,” Dunod, Paris, 1932. Markert, F., Inaugural Thesis, Dresden Technical University, 1904. Hempel, W., “Gasanalytische Methoden,” Verlag Friedr. Wiegweg u. Sohn, Braunschweig, 1913, Elving, P. J ., “Microchemical Techniques,” Butterworths, London, 1965, p. 68. Weisz, H., “Microanalysis by the Ring-oven Technique,” Second Edition, Pergamon Press, Oxford, Press, Oxford, 1959, p. 558. Stockholm, 1933, p. 9. Press, Oxford, 1971. London, 1946. Universitets Publikationer, 1944-64. p. 364. 1970.

ISSN:0306-1396    

DOI:10.1039/AD9751200077

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

March, 1975 ION-SELECTIVE ELECTRODES 83 Ion-selective Electrodes The following is a summary of one 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). Summaries of five other papers presented at the meeting appeared in the February issue of Proceedings (p.48). The Effect of Methanol and Ethanol on Solid-state Ion-selective Electrodes in Direct Potentiometry A. M. Elbakai, G. J. Kakabadse, M. N. Khayat and D. Tyas Department of Chemistry, University of Manchester Institute of Science and Technology, Manchester, M60 1QD The aims of this study were threefold: (i) to apply electrochemical techniques to organic reactions, (ii) to extend the lower limit of detection of an electrode as an aid to trace analysis and (iii) to establish the dependence of electrode potential on solvent concentration.Organic Reactions An example is the reaction of diphenyl disulphide with sodium sulphide in methanolic84 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem.Soc. potassium hydroxide solution : Cleavage of the S-S bond can be monitored by the decrease of sulphide ion concentration by using a sulphide electrode. At pH*(S)l 116, a systematic increase in potential over a period of time indicated that reaction (1) was more than 99 per cent. complete.2 Reaction time varied with the concentration of the reactants from approximately 30 min to over 2 h in 10-3 and 10-4 M diphenyl disulphide solutions, respectively.Under identical conditions, calibration of the electrode against sodium sulphide standard solutions gave a Nernstian response (slope about 30 mV per decade) down to 2 X lo-, M sodium sulphide solution. Measurements were conducted in an enclosed system under hydrogen. Lower Limit of Detection As the lower limit of detection of a solid-state electrode is a function of membrane solubility, addition of alcohol decreases this limit as expected.Tables 1-111 show the slopes of the electrode response and the lower limits of detection for chloride, bromide and iodide electrodes in methanol - water mixtures over the range 0-80 per cent. of methanol. In general, the TABLE I AND LOWER LIMIT OF DETECTION OF AN ORION SILVER CHLORIDE ELECTRODE EFFECT OF METHANOL CONCENTRATION ON THE SLOPE OF THE ELECTRODE RESPONSE Concentration of methanol, Slope/ Lower detection per cent.V / V -mV per decade limit/mol dm-3 0 52.9 4-5 x 10-5 10 53.4 2.3-3 x 10-5 20 53-2 2.5 x 10-5 30 55-1 2.5 x 10-5 80 53-1 1.5 x 10-5 effect of the alcohol is appreciable. It is greatest for the bromide electrode, the detection limit of which is extended by 0.9 of a decade, whereas the corresponding change in 0-80 per cent. ethanol is only 0.5 of a decade.The iodide electrode (Table 111) shows the least syste- matic behaviour; there is an improvement in the lower limit of detection with concentrations of methanol up to 60 per cent. but the limit rises again when 80 per cent. methanol is used.TABLE I1 EFFECT OF METHANOL CONCENTRATION ON THE SLOPE OF THE ELECTRODE RESPONSE AND LOWER LIMIT OF DETECTION OF A CORNING SILVER BROMIDE ELECTRODE IN THE PRESENCE OF 0.1 M POTASSIUM NITRATE SOLUTION I Concentration of methanol, Slope/ Lower detection per cent. V / V -mV per decade limit/mol dm-s 0 57.7 5 x 10-6 20 58.0 3 x 10-6 40 59.0 3 x 10-6 60 57.5 2 x 10-6 80 58.0 4 x 10-7 Dependence of Electrode Potential on Solvent Concentration For a given concentration of X (X = F-, C1-, Br- or 1-1, the observed electrode potential shifts to more negative values with an increase in methanol (ethanol) concentration, whereas for X = Ag+ the reverse trend is observed. For a given solvent, e.g., methanol (Table IV), the magnitude of potential change, for the electrodes decreases in the order : chloride > bromide > iodide.For a given electrode, e.g., bromide (Table V), the decrease in AEobs follows the sequence ethanol > methanol, in agreement with the lower dielectric constant of ethanol. In both solvents the values of &Fobs for the fluoride electrode are greater than those for the other halide electrodes3March, I975 ION-SELECTIVE ELECTRODES TABLE I11 85 EFFECT OF METHANOL CONCENTRATION ON THE SLOPE OF THE ELECTRODE RESPONSE AND LOWER LIMIT OF DETECTION OF AN ORION SILVER IODIDE ELECTRODE IN THE PRESENCE OF 0.1 M POTASSIUM NITRATE SOLUTION Concentration of methanol, Slope/ Lower detection per cent.V / V -mV per decade limit/mol dm-8 0 61.8 1 x 10-6 20 62.0 1 x - 8 x 40 62.0 4 x 10-7 60 60.0 2 x 10-7 80 60.5 3-4 x 10-7 The value of AEobs in zero per cent.methanol is taken arbitrarily as zero (Tables IV and V) and those values in higher concentrations of methanol are adjusted relative to this. For a given concentration of X, the systematic change of electrode potential with variation in methanol (ethanol) concentration provides a new method for a rapid determination of these organic solvents in methanol - water or ethanol - water mixtures.In practice, the mixtures are submitted to direct potentiometry in the presence of a known amount of MX (e.g., NaC1) and the percentage concentration of methanol (ethanol) is read from a calibration graph pre- pared from standard mixtures having an identical MX content. TABLE IV COMPARISON OF OBSERVED POTENTIAL CHANGES (AEobs) FOR HALIDE ELECTRODES IN M HALIDE SOLUTIONS WITH VARYING METHANOL CONCENTRATIONS IN THE PRESENCE OF 0.1 M POTASSIUM NITRATE SOLUTION Concentration of - bEobs/mV per cent.V / V -mide methanol, Iodide ' 0 0.0 0.0 0.0 20 15.3 13.1 6.4 40 32-2 24.4 10.7 60 51-6 37.2 17-3 80 83-6 55.5 36.5 For a given electrode, concentration of X and temperature, the observed change in potential, AEobs, with change in methanol (ethanol) concentration, may be related to several contributory potential terms: AE,, which corresponds to changes in molar activity coefficientsl; AEj, the change in liquid-junction potential at the reference electrode*; and AE,,l, which corresponds to the change in membrane solubility of the indicator electrode.Calculated values of AE,19596 for 10-4-10-2 M sodium chloride solutions in methanol - water mixtures are presented in TableVI.In 0.1 M potassium nitrate solution, the values of AE, for individual halides are practically identical.' In ethanol - water mixtures, AE, values are approximately 40 per cent. higher than those in methanol - water mixture^.^ TABLE V OBSERVED POTENTIAL CHANGES (AEobs) FOR A CORNING SILVER BROMIDE ELECTRODE IN M POTASSIUM BROMIDE SOLUTION AND 0.1 M POTASSIUM NITRATE SOLUTION WITH VARYING METHANOL AND ETHANOL CONCENTRATIONS Concentration of - AEob8 jmV alcohol, (-*--, per cent.V / V Methanol Ethanol AAEobs 0 0.0 0.0 0.0 20 13.1 12.3 - 0.8 40 24.4 25.8 1.4 60 37.2 42-1 4.9 80 55-5 64-3 8.886 ION-SELECTIVE ELECTRODES Proc. Analyt. Div. Chem.SOC. TABLE VI CALCULATED POTENTIAL CHANGE (AE,) CORRESPONDING TO A CHANGE IN MOLAR ACTIVITY COEFFICIENTS OF CHLORIDE IN lo:*, 10-3 AND 10-ZM SODIUM CHLORIDE SOLUTION, AND IN 10-3 M SODIUM CHLORIDE SOLUTION IN THE PRESENCE OF 0.1 M POTASSIUM NITRATE SOLUTION I N METHANOL - WATER MIXTURES Concentration of Chloride concentration/mol dm4 methanol, A \ per cent. V/V lo-* 10-3 + 0.1 M potasium nitrate 0 0.00 0.00 0.00 0.00 20 0.03 0.11 0.34 0-76 40 0-09 0.28 0.81 1.94 60 0-19 0.59 1.66 4.04 80 0.36 1.10 3-14 7.50 The presence of a liquid junction (between the solution inside the reference electrode and the test solution) of variable potential gives rise to some uncertainty in measurements of p~tential.~ An attempt was made to evaluate experimentallys the change in liquid-junction potential (Le., AEj) with a change in methanol (ethanol) concentration by using the following cell, comprising two Orion double-junction reference electrodes where RE(1) RE(1) = Ag I AgCl 11 Inner reference solution 11 0.1 M KNO, (outer chamber) ; and RE(I1) = Ag I AgCl 11 Inner reference solution + 0.1 M KNO, + (&80%)MeOHII 0.1 M KNO, + (O-80~o)MeOH (outer chamber) While RE(1) was kept constant throughout, the inner and outer filling solutions of RE(I1) were varied systematically, in order to match the test solution.The observed potential changes, AE(d) (representing AEj), are shown in Table VII. In the instance of AE(e), chloride was absent from the test solution. Analogous measurements in ethanol - water mixtures gave AEJ values that were approximately 20 per cent.higher.' M X + 0.1 M KNO, + (O-80~o)MeOH i RE(I1) TABLE VII DIFFERENCE IN ELECTRODE POTENTIAL ARISING FROM MODIFICATION OF THE INNER AND OUTER FILLING SOLUTIONS OF A DOUBLE- JUNCTION REFERENCE ELECTRODE Concentration of methanol, per cent. V / V AE(d) /mV AE(e) /mV 0 20 40 60 80 0.0 0.0 8.7 8-3 17.8 16.9 24-6 25-7 34.7 33.2 Potential shifts due to change in membrane solubility, AEsol, can be calculated from known solubility datagtlo for silver halides in alcohol - water mixtures using the relation AESo1 = 59 A (-log&,) (at 25 "C), where Ksp is the solubility product of the silver halide in water and the mixed solvent.For example, in 80 per cent. methanol, values of AEsol for silver chloride, silver bromide and silver iodide are 126.9, 98.5 and 67.9 mV, respectively.' Dr.A. K. Covington's advice is gratefully acknowledged. References 1. Bates, R. G., Analyt. Chem., 1968, 40, 28A. 2. Kakabadse, G. J., and Tyas, D., unpublished results. 3. Elbakai, A. M., and Kakabadse, G. J., unpublished results.March, 1975 TEMPERATURE-PROGRAMMED CALORIMETRY 87 4. Covington, A. K., SFec. Publs Natn. Bur. Stand., 1969, No. 314, p. 127 5. Bates, R. G., and Robinson, R. A., in Conway, B. E., and Barradas, R. G., Editors, “Chemical Physics of Ionic Solutions,” John Wiley & Sons, New York, 1966, p. 211. 6. Covington, A. K., and Dickinson, T., Editors, “Physical Chemistry of Organic Solvent Systems,” Plenum Press, New York, 1973, p. 138. 7. Kakabadse, G. J., and Khayat, M. N., unpublished results. 8. Covington, A. K., personal communication. 9. Parton, H. N.,.Davis, D. J., Hurst, F., Gemmel, G. D., and Perrin, D. D., Trans. Faraduy Soc., 10. Kazarjan, N. A., and Pungor, E., Analytica Chim. Actu, 1970, 51, 213. 1945, 41, 575 and 579.

ISSN:0306-1396    

DOI:10.1039/AD9751200083

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

March, 1975 TEMPERATURE-PROGRAMMED CALORIMETRY 87 Temperature-programmed Calorimetry The following are summaries of two of the papers presented at a meeting of the Thermal Methods Group held on November 22nd, 1973, and reported in the January, 1974, issue of Proceedings (p. 3). Design Considerations in Advanced Systems for Differential Scanning Calorimetry M. Cottrell Perkin-Elmer Ltd., Beaconsfield, Bucks.A direct power measuring differential scanning calorimeter, such as the Perkin-Elmer DSC-2, has both unique capabilities and unique design problems. The juxtaposition of heating and sensing elements in a low thermal mass sample holder puts particular strain on the temperature programmer. Programming noise and fluctuations are not thermally filtered or smoothed by large furnace systems as in conventional designs.Also, for rapid programmed cooling experiments and quick turn-round times, it is desirable that the immediate environment of the sample holders be maintained at low temperature. Consequently, large temperature gradients can exist between sample holders and surroundings which can affect base line reproducibility and linearity. Further, the benefits of direct power measurements are realisable only through a considerably more complex sample holder construction than typical AT measuring systems.This paper outlined a variety of design improvements that led to a differential scanning calorimeter capable of operating from near liquid nitrogen temperatures to 725 "C with superior base line linearity repeatability and with substantially greater temperature linearity and accuracy than previously achieved.A novel filter network in a digital programming system has removed the scanning rate dependence of sample holder temperature calibration and allows nearly instantaneous programming changes without the usual thermal transients and lags. These features combined with highly automated programming and positive en- vironmental control permit the extension of direct power measuring differential scanning calorimetry into more demanding areas of application with relative ease. Differential Scanning Calorimetry of Elemental Sulphur B.R. Currell and A. J. Williams Department of Chemislry, The Polytechnic of North London, Holloway, London, N7 8DB The DTA curve for a single crystal of 6N sulphur, i.e., orthorhombic sulphur (S,) hasendotherms at 112 "C (melting of S,) and 173 "C (formation of polymeric sulphur).No evidence of the enantiotropic transition S,+ Sp was observed for single crystals, even when heated under88 INSTRUMENTAL EXAMINATION OF HETEROGENEITY PYOC. Analyt. Div. Chem SOC. isothermal conditions for 1 h at 100 "C. Presumably the presence of a seed is essential for the S,+ Sp conversion to occur, the endotherm for which (at 100 "C) is seen, together with those at 112 and 173 "C, in the DTA curve of microcrystalline S,.The DTA curve of monoclinic sulphur (Sp) has endotherms at 119 "C (Sp melting) and at 173 "C (formation of polymeric sulphur). Pure polymeric sulphur gives a DTA curve with a single broad endotherm at 104 "C, due to melting of the polymer. The area under the peak representing the transition Sa+ Sp can be used to give the mass of Sapresent in the sample.Similarly, the Sp fusion peak is proportional to the mass S, + Sp present in the original sample. Note that any S a present in the original sample is converted into Sp before fusion. Ten determinations of crystalline sulphur (S, + Sp) were carried out on a mixture of sulphur and polymeric polysulphides. An average value of 64-3 per cent. with a standard deviation of 2.15 was obtained. The authors gratefully acknowledge financial assistance from The Sulphur Institute.

ISSN:0306-1396    

DOI:10.1039/AD9751200087

出版商:RSC    

年代:1975

数据来源: RSC

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88 INSTRUMENTAL EXAMINATION OF HETEROGENEITY PYOC. Analyt. Div. Chem SOC. Instrumental Methods for the Examination of Heterogeneity in Inorganic and Biological Samples The following are summaries of four of the papers presented at a Joint Meeting of the Micro- chemical Methods and Radiochemical Methods Groups and the Southern, Midlands and North- ern Microanalyser User Groups held on September 19th and 20th, 1974, and reported in the October issue of Proceedings (p.258). Summaries of two of the other papers have already been published in connection with other meetings: that by J. D. Garnish in the May, 1974, issue (p. 121), and that by T. B. Pierce in the December, 1974, issue (p. 333). Statistical Limitations in the Analysis of Heterogeneity W. Johnson British Steel Corporation, Swinden Laboratories, Rotherham, Yorkshire Underlying Statistical Theory In order to overcome problems in microanalysis that arise from instrumental errors, sampling errors and heterogeneity, it is necessary to make sufficient measurements to know the probability function associated with the sampling and measuring techniques.It is then possible to make a statement of the type, "there is a 95 per cent.chance that the result lies within & x per cent. of the mean result." Random errors arise in measurements from a number of sources and have equal probability of being either positive or negative. Systematic errors have an unequal probability and are more likely to be of the same sign for each separate measurement. The binomial distribution (9 + q)" represents the distribution function of errors.As n becomes large, the binomial distribution becomes smoother and approximates to the normal or Gaussian distribution, i.e., the probability of x successes in n trials, f(x), is given by the mean p = np and the standard deviation 0 = .\/* Poisson distribution, ie., If n is large and p very small so that np<n, the binomial distribution approximates to the f(x) = C(ut,x) p~ qn-" (np).e-""/x!March, 1975 INSTRUMENTAL EXAMINATION OF HETEROGENEITY If p is large, the Poisson distribution approximates to the normal distribution, i.e., 89 (origin moved for curve to be symmetrical about p). For the Poisson distribution, o2 = p. Addition of Errors Errors are additive according to the sum of their variances and therefore there is little point in attempting to reduce other errors below the largest irreducible error for the given system of measurement.Sources of Heterogeneity Heterogeneity arises both chemically and physically. Physical mechanisms include mechanical mixing and de-mixing, sedimentation, condensation and volatilisation and produce sharp discontinuities in composition.Chemical segregation in solidification and sub-solidus reactions can produce concentration gradients (e.g., coring in dendrites) or sharp discontinui- ties as in eutectoid reactions. Diffusion reactions also produce concentration gradients across single-phase regions. Most examples of heterogeneity in metallurgy, ceramics and igneous petrology are covered by these mechanisms.Effect of the Volume of Material on Changes in Concentration The method of analysis always involves a finite volume of material and this smears out to some extent changes in composition by producing an average composition. In order to ob- tain true measurements on gradients or discontinuities, it is necessary to know the magnitude of the smearing effect and attempts to determine this with the aid of metallic couples were described. Definition of Homogeneity There is a marked relationship between the size of the volume analysed and the ability to detect heterogeneity.For example, neutron activation using 14-MeV y-rays to detect oxygen in steel is not capable of revealing segregation within a single sample. Similarly, analysis of a paint by chemical analysis would reveal it to be very homogeneous compared with an electron microscope assessment, which would reveal the separate pigment particles. Even a single- phase alloy would appear to be heterogeneous when analysed atom by atom on an atom probe device that uses a field ion tip and time-of-flight mass spectrometer to monitor individual atoms.Thus, heterogeneity is very much a function of the method of measurement and the volume of material examined. It is possible t o define a homogeneous material as one in which for a given method, the Probability of detection of a component (atom, phase, crystal form, etc.) i s the same for all samples.A heterogeneous material is one where this probability varies amongst samples and therefore with position in a larger sample or with time.Statistical Effects in Sampling For a homogeneous sample consisting of small grains containing an over-all concentration, c, of an element, the probability of selecting the element would be p = c and of not detecting it q = 1 - c. If the sample to be analysed contains n atoms or particles, then the probability function, f(x), is given by which is the probability of the sample of n particles or atoms containing exactly x particles or atoms of the element in question.np = en and the standard deviation f(x) = C(n,x) en qn-" The mean value of the function is dqq = dnc(1- c ) giving a coefficient of variation of 100l/nc(lc)/nc = (l/lFic/dG) x 100 per cent.90 INSTRUMENTAL EXAMINATION OF HETEROGENEITY Proc. Analyt. Div. Chem. SOC.If n is large, this leads to a relatively small error, but, for example, with n = 1000, a 1 per cent. error (with 95 per cent. confidence limits) occurs for a concentration level of 30 per cent. If within this sample only a minute fraction of atoms is actually detected, then the prob- ability of detection is extremely small and Poisson statistics will apply, giving a standard deviation of d g o n the n signals recorded.The relative sizes of the sampling error variance and the analysis error variance is given by the between-sample variance minus n and n itself. For a heterogeneous sample, the between-sample variance represents a combination of heterogeneity variance and sampling variance and it is necessary to reduce the latter to a low level in order to expose the heterogeneity variance.When this is done, it is possible to express heterogeneity as a density map showing the most probable concentration varying with position or with time in the case of a time series of measurements. Examples of Heterogeneity The following three examples of heterogeneity problems were discussed. Inclusions in Steel Because of the low concentrations involved and the small volume of material examined by optical metallographic or electron microprobe scanning methods, very large numbers of measurements are necessary in order to obtain meaningful results.Automatic quantitative metallography offers some hope but as yet little correlation exists between this and other methods, such as ultrasonics. Analysis of individual oxides and sulphides has, of course, given invaluable information on the chemistry of steelmaking processes and ways of controlling inclusion composition.Detection of Quartz and Cristobalite in Airborne Dusts In this analysis, X-ray diffraction is used to measure the concentration of silica in airborne dusts collected on filters. Calibration is difficult but can be achieved satisfactorily by prepar- ing filters from liquid suspensions of known concentration.Because of the small number of particles involved, sampling problems are severe, but, un- like X-ray fluorescence methods, it is possible to improve the sampling statistics by rotating the specimen in its own plane and giving each crystal the chance to diffract X-rays into the detector, thereby increasing the number of crystals examined.Standards for Microprobe Analysis The problems associated with producing standards other than pure elements were discussed and included coring in cast materials, second phase particles and the effect of the scale of these relative to the probe size. Analytical Transmission Electron Microscopy G. W. Lorimer Department of Metallurgy, Faculty of Science, University of Munchester, Manchester, M13 9PL The technique of analytical electron microscopy enables quantitative chemical analyses to be carried out on thin foil samples from areas less than 0.1 pm in diameter.The possibility of obtaining, within the same instrument, a high-resolution image (about 0.7 nm), electron diffraction patterns from areas less than 1pm in diameter and chemical information from volumes of approximately 10-15 cm3, is a major advance over conventional microprobe analysis.The use of a thin foil sample results in low counting rates, and hence a deterioration in accuracy of analysis. The use of a thin sample also means that X-ray absorption and fluores- cence can be ignored, thus the simple expression where Il and I , are the measured X-ray intensities, Cl and C2 are the mass fractions of the two elements concerned and k is a constant that must be determined from the specimen itself or from thin standards, can be used to carry out quantitative analyses.ls2March, 1975 INSTRUMENTAL EXAMINATION OF HETEROGENEITY 91 The energy-dispersive X-ray detector is sufficiently stable that a given specimen will yield exactly the same “fingerprint” from one analysis to another, even if these analyses are carried out days or weeks apart and by different operators (but, of course, on the same instrument at the same accelerating voltage).The combination of a stable X-ray detector and a thin specimen (no absorption or fluorescence) enables the observed characteristic X-ray intensity ratios from any two elements in the sample to be converted into mass fraction ratios.Once this operation has been carried out for a series of thin specimens of known composition, quantitative analysis can be carried out without referring to standards at the time of analy~is.~ Fig. 1 is a plot of characteristic X-ray energy Zteims k = (Cz/Csi) (Isi/Iz) for a number of thin film standards, as obtained for our analytical electron microscope (EMMA-4) operating at 100 kV.This curve shows that for elements lighter than silicon, to convert the observed characteristic X-ray intensity ratio into a mass fraction ratio, it must be multiplied by a factor greater than unity in order to compensate for the low efficiency of X-ray production and pre- ferential X-ray absorption in the window.For heavier elements, the observed characteristic X-ray intensity ratio must again be scaled upwards because of the increased transparency of the silicon detector to high energy X-rays. < O i 2 3 4 5 6 7 keV Fig. 1. Calibration graph for 11 < 2 < 28 of k versus X-ray energy (keV) a t 100 kV. The simple technique of quantitative analysis described above has been used by the author and his colleagues to study the distribution of alloying elements in steels,4,5 the distribution of zinc near grain boundaries in aluminium - zinc - magnesium alloys,6 the solute distribution in orthopyroxenes7 and to determine the chemical composition of small fibres of the mineral tacharanite for the first time.8 References 1.Lorimer, G. W.. Nasir, M. J., Nicholson, R.B., Nuttall, K., Ward, D. E., and Webb, J. R., “Pro- ceedings of the Fifth International Materials Symposium, Berkeley, California,” University Press, Berkeley, 1972, p. 222. Cliff, G., and Lorimer, G. W., “Proceedings of the Fifth European Congress on Electron Microscopy, Manchester,” Institute of Physics, London, 1972, p. 140. Cliff, G., and Lorimer, G. W., J. Microsc., in the press.Lorimer, G. W., Razik, N. A., and Cliff, G., J. Microsc., 1973, 99, 153. Razik, N. A., Lorimer, G. W., and Ridley, N., Acta Metall., 1974, 22, 1249. Ward, D. E., and Lorimer, G. W., in “The Microstructure and Design of Alloys,” Institute of Metals, Lorimer, G. W., and Champness, P. E., Amer. Miner., 1973, 58, 243. Cliff, G., Gard, J. A., Lorimer, G. W., and Taylor, H.F. W., submitted for publication. 2. 3. 4. 5. 6. 7. 8. London, 1973, p. 606.92 INSTRUMENTAL EXAMINATION OF HETEROGENEITY Proc. Analyt. DiV. Chem. SOC. An Improved Technique for Scanning X-ray Microprobe Displays of Particles and Concentration Differences A. P. Skeats and E. W. Ward Post Ofice Research Station, Dollis Hill, London, N W2 7DT Improvement in the image quality of X-ray microanalysis element distribution photographs is obtained without any increase in exposure time, by using a variable speed line scan systeni1r2 in which the line scan spEed through areas of interest is modulated by the localised X-ray count rate.Regions of no interest are scanned rapidly (100 ms per line), while those of interest, such as pax ticles, inclusions or regions of increased concentration of the chosen element, are scanned more slowly as their count rate increases.The exposure time is therefore more usefully allo- cated, with a consequent improvement in the signal to noise ratio compared with the normal scan system. The modulation scan system is of most use for specimens in which the areas of interest occupy a small proportion of the total area scanned, e.g., grain boundary precipitates and inclusions; it offers no advantage where the element is present in large concentrations over the whole area.The system can be used with crystal spectrometer or energy-dispersive X-ray detectors, and is particularly advantageous for the latter as the maximum count rate is usually less than 1000 per second. It is possible to obtain better quality pictures in 200s than can be achieved with standard scanning for much longer times.Basic System This consists of a 1000-line stepped frame generator, triggered by line flyback pulses from a modulation line scan generator, and can be plugged directly into the external scan input of a Stereoscan 2A or S4/10 instrument. The modulation line scan generator provides a line scan sp:ed (on the cathode-ray tube) of 0.02-1*0 mm ms-l.In the absence of pulses, the fast speed is retained; each incoming X-ray pulse reduces the speed to the slow value, where it is held for a dwell time t D , then increases exponentially in a time tE back to the fast speed, When an area of high pulse rate is traversed, the interval between pulses is less than tDSE, so that the fast spzed is not regained until the area is vacated.A much longer time is therefore spent on this area and a bright image is recorded on the photograph, the brightness increasing with the count rate as the mean spot velocity decreases; the relationship is not linear, however, and when desired the sensitivity to changes in element concentration can be greatly enhanced.The optimum settings of tD and tE depend on the maximum and minimum count rates on the specimen, and are usually determined by observing a stationary line through areas of interest. This manually positioned line is also very useful for ascertaining which particles, etc., contain the element of interest, as they appear as bright segments on the line. When required, an attenuated electron image can be superimposed on the X-ray display.This happens automatically with the Stereoscan 2A instrument, etc., if the video-amplifier is set for a normal electron picture. The attenuated electron picture is produced during the fast scan periods by x-modulation of the cathode-ray tube spot, while the X-ray image is formed during the reduced speed periods. This facility is very useful in locating particles of interest in a complicated structure containing several elements.Background Blanking A valuable addition to the basic system is a cathode-ray tube blanking module, which feeds a blanking signal to the Stereoscan valve V302. This can give considerable improvements in picture quality by rejecting from the display any pulses due to background “white” radiation and low concentration level general distribution of the chosen element, when the time interval since the previous pulse exceeds a pre-set value.The spot length can also be reduced, e.g., by blanking out the variable speed portion, and the cathode-ray tube can be blanked completely between pulses to give an improved black level. References 1. 2 , Ward, E. W., and Weeks, R., EZectronics Lett., 1972, 8, 619.Ward, E. W., “Scanning Electron Microscopy: Systems and Applications,” Institute of Physics Conference Series, No. 18, November 1973.March, 1975 INSTRUMENTAL EXAMINATION OF HETEROGENEITY Ion - pro be M ic roa na I ysis 93 S. J. B. Reed Department of Minevalogy and Petvology, Univevsity of Cambridge, Downing Place, Cambridge, C B 2 3E W In secondary ion mass spectrometry (SIMS), primary ions of several keV energy impinge on the sample and produce sputtered secondary ions, which are analysed by a mass spectrometer.The depth distribution of elements of interest can be plotted while the surface is eroded away by sputtering. The best means of doing this is to scan a focused beam in a rectangular raster and use the signal from the flat central area only, in order to avoid edge effects.Effective depth resolution better than 5 nm is possible. This technique has been applied successfully to semiconductors used in electronic devices, and to corrosion layers, for example. Surface monolayers can be analysed in a quasi-static mode, using a low primary ion current, which gives a very low erosion rate, but if contamination effects are to be avoided very good vacuum is required (with normal currents the erosion rate is sufficient to keep the surface clean).In the ion microprobe, the primary ion beam is focused to a fine (typically 1 pm) spot. The instrument thus has lateral resolution similar to that of the electron microprobe, to which it is closely analogous. By scanning the primary beam, as in the electron microprobe, element (or isotope) distribution images may be produced, and all elements down to hydrogen can be imaged. The high cost of the ion probe (about LlOO 000) has to be justified on the basis of what it can do that the electron microprobe cannot.In addition to surface analysis, depth profiling and “light” element analysis, its principal advantages are lower detection limits (typically 1 p.p.m., or 10-l8 g absolute) on account of the low background level in the mass spectrum, and the ability to discriminate between isotopes.In geology, isotopic analysis on a micrometre scale opens up interesting possibilities as yet hardly touched upon. Another application of isotope analysis is for determining self-diffusion coefficients using an isotope tracer.Isotope ratio measurements would appear to be relatively straightforward, provided the mass spectrometer has the high resolving power (10 000 is desirable) needed to separate interfering peaks (e.g., hydrocarbons and polyatomic ions). Mass resolution is important in trace element analysis for the same reason, but here con- siderable additional complications in converting the measured intensities into concentrations are encountered.Ionisation efficiencies for different elements vary by three orders of magni- tude, being strongly dependent on the ionisation potential, among other things. Thus, the convenient first approximation in electron microprobe analysis, namely that the intensity is approximately proportional to concentration, is completely inapplicable.An important step towards successful quantitative analysis was the recognition of the ad- vantage of using oxygen as the bombarding species. The presence of an abundance of oxygen in the sputtering region increases the positive ion yield due to the affinity of oxygen for electrons. The yield is not only higher but also more stable than if argon, for example, is used, in which event the surface state of the sample has a marked effect. With oxygen bombardment, quantitative analysis is possible, using a theoretical model in which the sputtering region is treated as a dense plasma in local thermal equi1ibrium.l For major and minor elements in silicates, -&lo per cent. accuracy is obtainable, but arbitrary correction factors are required for certain elements (phosphorus, molybdenum, zirconium, niobium, rare earths, thorium and uranium), while for others (e.g., palladium, cadmium, mercury and osmium) the results are unreliable at present. Andersen and Hinthorne indicated’ that the model should at least give a result within a factor of two of the true concentration for almost any trace element in any solid matrix, with a minimum of knowledge about the sample. Practical applications of quantitative ion probe analysis include trace element distributions among different phases in lunar rocks, in some instances at concentration levels well below those accessible to the electron microprobe. Reference 1. Andersen, C. A., and Hinthorne, J . R., Analyt. Chem., 1973, 45, 1421.

ISSN:0306-1396    

DOI:10.1039/AD9751200088

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

94 MASS SPECTROMETRY PYOC. Analyt. Div. Chem. SOC. AL Newer Aspects of Mass Spectrometry The following are summaries of two of the papers presented at a meeting of the Special Techniques Group held on November 7th, 1974, and reported in the January issue of Pro- ceedings (p. 6). A Plasma Ion Source for Trace Analysis of Solutions A. L. Gray Applied Research Laboratories Ltd., Wingate Road, Luton, Bedfordshire, L U4 8PU The use of an atmospheric pressure plasma as a source of ions was described in an earlier paper delivered to a Joint Meeting of the North East Region and the Atomic Spectroscopy Group at Leeds on April 24th, 1974, a summary of which appeared in the July, 1974, issue of Pro- ceedings (p.182). In this further paper, the basis of the technique was described and some consideration given to the sensitivity of the technique and its definitions. A small d.c.plasma in argon is used to ionise the samples which are introduced to it as a mist produced directly by an ultrasonic or pneumatic nebuliser from the unknown solution. Ions are extracted from the plasma through a small orifice into a vacuum enclosure and are formed into a beam suitable for introduction into a quadrupole mass spectrometer.Improvements in the ion optics have enabled the background levels for many elements on blank solutions to be reduced to a few counts per second. Signal levels obtained for a number of elements are shown in Table I, where it can be seen that for elements with an ionisation potential less than 8 V the count rate for a 1 pg ml-l solution varies from about 17 x 103 counts s-l for silver to 230 X lo3 counts s-l for magnesium. At signal levels of this magnitude and blank levels of a few counts per second for elements not normally present in the blank, the low noise and interference background obtained lead to figures for detection limits SO low as to seem unrealistic under normal laboratory conditions.The sensitivity used in Table I is suggested as a convenient measure of system performance where the background is low.The use of the limit of detection based on background standard deviation might then be most usefully reserved for particular analytical situations where it can be meaningfully applied, for example where the true elemental background is at least an order of magnitude greater than that due to noise.An illustration of the low background obtainable is shown in Fig. 1, where the characteristic 23Na h2 m/e Fig. 1. Spectrum showing magnesium at about the 0.001 pg ml-l level,March, 1975 MASS SPECTROMETRY 95 TABLE I ELEMENTAL SENSITIVITY FOR A 1 pg ml-1 SOLUTION Sensitivity1 Isotope Ionisation los counts s-1 measurement potential/V per pg ml-1 56Fe 7.87 182 5 8 C ~ 7.86 68 e4Mg 7-64 232 107Ag 7.57 17 eo*Pb 7.42 34 mass spectrum of the three isotopes =Mg, 25Mg and 2sMg can be clearly seen following the much larger 23Na peak.The blank level of the 24Mg peak was about 50 counts s-l, roughly the same as the blank 27Al peak seen here, and in order to obtain this trace 5 p1 of 1 pg ml-1 magnesium solution were added to 5 ml of water in the sample cup, giving a concentration of approximately 1 ng ml-l, The background between peaks is a few counts per second.Pharmaceutical Applications of Mass Spectroscopy D. R. Hawkins Huntingdon Research Centre, Huntingdon, PE 18 6ES Mass spectroscopy has now become a widely used technique in biochemical and biomedical research, and this great increase in applications has been seen especially in the pharmaceutical industry.The two most important areas of application are concerned with the biological aspects of drug research and development, namely in the field of drug metabolism and asso- ciated topics, which include clinical drug development. These aspects of research have assumed greater importance owing to the requirements of licensing authorities on safety evaluation and therapeutic efficacy. The use of mass spectroscopy in these areas can be separated into qualitative and quan- titative applications.The qualitative aspects are confined to the identification of drugs and metabolites in biological extracts. The quantitative application is important especially during clinical evaluation in the development of sensitive and specific methods for the measure- ment of concentrations of drugs and metabolites in biological samples such as plasma.The techniques for mass spectral analysis of drug metabolites are either by direct insertion into the instrument after prior isolation and at least partial purification or by using a combined gas chromatography - mass spectrometry system. Unfortunately, metabolism tends to produce metabolites of greater polarity than the parent drug.With very polar metabolites, there may be severe problems in isolation and separation, and elution on gas chromatography without thermal degradation. It is very seldom that one can obtain the mass spectrum of metabolites uncontaminated with biological components and consequently it is not always easy to recognise a recorded spectrum as belonging to a metabolite.In some instances where there is a very characteristic frag- mentation pattern for the drug, which also occurs in the metabolites, this problem is alleviated. The recognition of metabolites is also helped if compounds contain bromine or chlorine. Owing to the natural-abundance isotopes 59Br : 81Br (1 : 1) and 35Cl: 37Cl (3: 1), the molecular ions of metabolites and any fragments that contain these atoms will be present as characteristic doublets in the mass spectra.Consequently, as there are very few endogenous chlorine- or bromine-containing components, it is much easier to recognise spectra derived from meta- bolites. For compounds that do not contain these natural-abundance isotopes, artificial isotopic doublets can be produced by mixing unlabelled and stable isotope-labelled drugs.The stable isotope label may be deuterium, nitrogen-15, carbon-13 or oxygen-18. As an example, a dideuterium nitrogen-15 labelled form of nortriptyline has been synthesised and used in a study of the human urinary and biliary metabolites of this drug.l An equimolar mixture of unlabelled and labelled nortriptyline was administered and the parent drug and any metabolites that retained the label were readily identified by the presence of M, M+3 doublets.Recent developments in alternative ionisation methods are also having a wide application in96 MASS SPECTROMETRY Proc. Analyt. Div. Chem. SOC. drug metabolism. An increasing number of drugs, and especially the more polar metabolites, do not give molecular ions in the mass spectra, either due to a very rapid fragmentation induced by the excess energy supplied from electron impact or due to thermal degradation during heated vaporisation of the metabolite.These problems have been partly overcome by the development of milder ionisation processes such as chemical ionisation and field ionisation or field desorption.Chemical ionisation invariably produces quasi-molecular ions (M+ - 1 or M+ + 1) from compounds that give either very weak or no molecular ions in their electron impact spectra. The spectra obtained are frequently simpler as a result of less fragmentation, which, when dealing with impure samples of metabolites, can be an advantage as the background inter- ference from impurities is also simplified. Field desorption ionisation has the advantage that ionisation takes place before the sample is vaporised and with the minimum of thermal stress.The technique has particular use for the examination of very polar metabolites such as conjugates of glucuronic acid. A field desorption spectrum of estriol-16a-glucuronide has been obtained2 where the most abundant ion is due to MNa+ + 1.Quantitative analysis by mass spectroscopy is rapidly becoming a major analytical tech- nique owing to the high sensitivity obtainable and the specificity of the method. Basically, the mass spectrometer is used as a detector for a gas chromatograph. The specificity is achieved by selecting two or more characterisitic ions in the mass spectrum of the compound for analysis and adjusting the mass spectrometer for continued and rapid focusing on these ions during elution of the compound from the gas chromatograph.This technique, called multiple ion detection or mass fragmentography, can be used to identify metabolites during a gas-chromatographic run when they are present in very small amounts or are eluting together with impurities.The ions selected are those of highest abundance and generally in the higher mass range in order to increase the specificity of the detection. By incorporating an internal standard into the isolation and analysis stages of the drug, this technique can be used as an extremely sensitive assay. The use of an internal standard is to compensate for losses during extraction, derivatisation and from adsorption on columns, and consequently these standards should behave in an identical manner to the drug.The types of compounds used as internal standards are either very closely related chemical structures or isotopically labelled derivatives. The latter type are almost ideal as internal standards and are usually labelled with carbon-13, nitrogen-15 or oxygen-18.The drug and labelled internal standard can be detected and measured by monitoring the isotopic fragment ions. Calibration graphs are constructed by multiple ion detection and peak height or peak area measurements on known mixtures of drug and internal standards after isolation from the appropriate biological sample. It is important that the multiple ion detection is continued throughout the complete elution of a gas-chromatographic peak as it is possible for the isotopically labelled standard to have a retention time slightly different to that of the parent drug.It is very useful that with this technique it is not necessary for the drug to be separated from endogenous impurities, provided that there is no interference in the mass spectrum at the mass numbers being monitored.The specificity of the technique is given by the retention time, the appearance of two or more characteristic fragment ions and the characteristic ratio of intensities of these ions. The sensitivity is at the picogram level (10-l2 g) , which is equivalent to that of an electron-capture detector, but the technique is obviously applicable to a much wider range of compounds. The sensitivity can be increased further by using chemical ionisa- tion, where a larger percentage of the total ion current is concentrated in a single ion, the quasi-molecular ion. Some examples of the use of quantitative multiple ion detection with sensitivity are methaqualone3 (200 pg), amphetamine4 (100 pg) and carbamezephine5 (1 ng) . References 1. Knapp, D. R., Gaffney, T. E., McMahon, R. E., and Kiplinger, G., J . Pharmac. Exp. Ther., 1972, 2. Adlercreutz, H., Soltman, B. and Tikkanen, M. J., J . Steroid Biochem., 1974, 5, 163. 3. Alvan, G., Lindgren, J.-E., Bogentoft, C., and Ericsson, O., Europ. J . Clin. Pharmac.. 1973, 6, 187. 4. Cho, A. K., Hodshon, B. J., Lindeke, B., andMiwa, G. T., J . Pharm. Sci.. 1973, 62, 1491. 5. Palmer, L., Bertilsson, L., Collste, P., and Rawlins, M., Clin. Pharmac. Ther., 1973, 14, 827. 180, 784.

ISSN:0306-1396    

DOI:10.1039/AD9751200094

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

March, 1975 AUTOMATIC ANALYTICAL INSTRUMENTS 97 Evaluation of Automatic Analytical Instruments The following is a summary of one of the papers presented at a Joint Meeting of the Automatic Methods Group with the Association of Clinical Biochemists held on September 24th, 1974, and reported in the October issue of Proceedings (p. 258). Test Procedures for Ana lytica I lnst rument Evaluation S.W. J. Hopkins Sira Institute Limited, South Hill, Chislehurst, Kent, BR7 5EH Automatic control in the process industries depends to such an extent upon reliable instru- mentation that the need for evaluation before purchase and installation is obvious. The cost resulting from shut-down of plant could amount to several thousands of pounds per day, although the cost of the instrumentation may be only a small fraction of the total.The cost of a comprehensive evaluation is also small compared with these potential losses. Evaluation may be described as a thorough investigation into the performance of an instrument by means of a series of tests carried out under a wide range of controlled conditions in order to form an assessment of its capability to perform its required function when intro- duced on-line.In general, the test programme applied to a process analytical instrument is similar to those for other types of instrument except that the calibration check is more complex, and additional tests, for example to investigate any effects of interfering chemical components, may be necessary. In a Sira evaluation, the tests are carried out in accordance with a test programme, pre- agreed by the sponsor and the instrument manufacturer. Major references for the work are the manufacturer's specification, any international or national standards in existence and the sponsor's specification. The results are presented in an Evaluation Report, which is first issued as a draft, normally to the sponsor and the manufacturer of the subject instrument, and later as a final version after both have had the opportunity to make comments.In the first instance, a number of basic tests are carried out in order to check the performance of the instrument under reference conditions, normally defined as an ambient temperature of 20 & 2 "C and a relative humidity less than 60 per cent., with the instrument powered by a supply at the recommended nominal voltage and frequency.Hence, a pre-requisite for subsequent tests is a knowledge of the warm-up time, which may be a few seconds for a purely electronic instrument or 1 h or more in an analytical instrument including a reaction chamber maintained at an elevated temperature. The stabilisation period having been established, the next important test is the basic accuracy of the instrument.This is checked several times at a number of points on the span in order to determine the mean value at each point, the repeatability, linearity and hysteresis. For the purpose of measuring accuracy, it is desirable to have reference methods with discrimination an order of magnitude better than that of the instrument under test and an accuracy four times better than that of the instrument.Such reference methods for physicochemical or analytical instruments are generally not readily available. Calibration methods for instruments used to determine the composition of liquid mixtures are usually straightforward, and suitable gravimetric samples for checking the accuracy can be readily prepared. While acknowledging the known difficulties in preparing samples for calibration of gas analysers, nevertheless, their preparation is a basic requirement of an evaluation laboratory and a number of techniques have been adapted or developed for this purpose.In making the choice of techniques, it is necessary to take into consideration the specified accuracy of the instrument under evaluation, For example, for checking the basic performance of flammable gas detectors in the range 0-100 per cent.LEL (lower explosive limit), it is satisfactory to use certified mixtures provided by the usual suppliers of bottled gases. A number of methods are also available for preparing gas mixtures directly in the laboratory. Ratio mixing pumps (e.g. , the Wosthoff pumps) are capable of high accuracy and discrimination and, if supplied with pistons of the appropriate alloy, can even be used to prepare mixtures that contain highly corrosive gases.Such mixtures can also be prepared by other dynamic blending methods in which the composition is determined by the relative flow-rates. Constitutents required in low concentrations can be introduced into a stream of98 TREATMENT OF EFFLUENTS Proc.Amlyt. Div. Chem. SOC. carrier gas by means of a syringe, the plunger of which is driven at low speed by a variable speed motor. Low concentrations of some gases can also be introduced by diffusion through an inert, permeable membrane. This method is particularly applicable to gases the critical temperature of which is above normal ambient temperatures. The vapour above such a liquid sealed in a PTFE tube diffuses through the walls of the tube under the influence of its own vapour pressure.The permeation rate at constant temperature is then determined gravi- metrically. By measuring the flow-rate of diluent gas over the permeation tube, and that of a by-pass flow (which is then mixed with the permeation gas in a second dilution stage), the final low concentration of the minor sample gas constituent is calculated. A further method, and perhaps the most reliable, is to introduce the minor constituent through a septum into a pre-evacuated gas cylinder.The major constituent is then intro- duced under pressure and weighed. This method is applicable to gas mixtures which are stable and in which no component is adsorbed significantly on the cylinder walls.Having established the performance of the instrument under reference conditions, it is necessary to investigate a number of other basic performance parameters, such as the dead zone, the response time to step changes in composition, satisfactory function of any temperature compensation, effects of changes in ambient atmospheric pressure and interference effects of other chemical species that could be present in the sample gas or liquid.As the instrument may be installed under conditions where long-term or transient changes in the power supply may be experienced, it is necessary to conduct a number of electrical tests. These tests include mains voltage and frequency variations in combination, power supply interruptions and depressions over short time periods, effects of transient over-voltages, and series and common mode interference effects.In some situations, the instrument may also be exposed to magnetic field effects and therefore an appropriate British Standard test is often applied. Instruments installed on-line may be required to operate under adverse environmental conditions and therefore a number of environmental tests are carried out.These are selected from the following: effects of high and low ambient temperatures, high humidity at elevated temperatures, effects of vibration and shock, dust test and salt mist test. The results of all of these tests are compiled in a comprehensive report, the format of which is designed to provide the major findings at a glance and to give greater detail in later sections for the reader who requires a fuller knowledge of the instrument and of the tests to which it has been subjected.Evaluation can be carried out on behalf of users or manufacturers in confidence. Alter- natively, evaluation costs to a user can be greatly reduced if the work is carried out under multi-client sponsorship.Such a scheme is in operation at the Sira Institute, where evalua- tions are carried out on behalf of a panel of instrument users. Each member of the Sira Evaluation Panel (SIREP) can nominate instruments of his choice for evaluation and the reports provided under the scheme are released to all members of the panel. Another user group, the Working Group on Instrument Behaviour (WIB), centred in the Netherlands, sponsors evaluations at appropriate institutes and reports are exchanged between SIREP and WIB on an equal basis. The evaluation reports provided under the two schemes therefore have wide international circulation. While these evaluation schemes have been mainly concerned with process instrumentation, the same approach could be adopted for laboratory instrumentation, although it is anticipated that an evaluation programme for laboratory instruments need not be so detailed.

ISSN:0306-1396    

DOI:10.1039/AD9751200097

出版商:RSC    

年代:1975

数据来源: RSC