摘要:

Proceedinas m - - -of the Analytical Division ofThe Chemical Society343344346347349349354358359360361362364CONTENTSNew Members of CouncilThe Analytical Work of GeorgePearson MD, FRS (1751-1828)Analytical Chemistry Trust FundEighth Theophilus RedwoodSummaries of PapersLecture'Why Teach Electroanalytical'Recent Developments in HPLCChemistry ?'Stationary Phase Technology andApplication to AnalyticalChemistry'New British StandardsCorrespondencePublications ReceivedConferences and MeetingsCoursesAnalytical Division DiaryVolume 16 No 12 Pages 343-364 December 197PADSDZ 16(12) 343-364 (1979)I SSN 0306-1 396PROCEEDINGSDecember 1979OF THEANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof The Chemical SocietyPresidentR.BelcherHon. SecretaryP. G . W. CobbHon. Treasurer Hon. Assistant SecretariesJ. K. Foreman D. I . Coomber, O.B.E.; D. C. M. Squirrel1Secretary Hon. Publicity and Public Relations Officer Editor, ProceedingsDr. A. Townshend, Department of Chemistry.University of Birmingham. Birmingham, B15 2TTMiss P. E. Hutchinson P. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864. Telex 268001.Subscriptions (non-members) : The Chemical Society, Distribution Centre, Blackhorse Road,Letchworth, Hens., SG6 1 HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analystand Analytical Abstracts.@ The Chemical Society 1979ANALYTICAL D IVI SI ON M I D LAN D S REG I0 NWEST MIDLAND REGION OF THE ASSOCIATION OFCLI N I CAL B I0 C H EM I STSPractical Immunoassay-The Present Stateof the ArtThe University of Aston in BirminghamJanuary 24, 1980A Joint Meeting onto be held atThe papers given at the meeting will be: "An Overview of Immunoassay"by V.Marks; "Techniques of lodination" by W. R. Butt; "Fluorescence-linkedI m m u n oa ssa y " by J . N . M i I I er ; " C hem i I u m i n esc e n ce - I inked I m m u no assay "by J. S. Woodhead; "Enzyme-linked Immunoassay" by M. J. O'Sullivan;and "Turbidimetry, Nephelometry and Centrifugal Analysis with Referenceto the Quality Control of Antisera" by I. Deverill. The registration fee (f10)will include lunch and refreshments.For details of the meeting contact either the Honorary Secretary of theMidlands Region, 35 Dunster Road, West Bridgford, Nottinghamshire,IVG2 6JE, or the Secretary of the West Midland Region of the Associationof Clinical Biochemists (Mr. P. W. Lewis), Clinical Chemistry Department,General Hospital, Birmingham B4 6NH

ISSN:0306-1396    

DOI:10.1039/AD97916FX042

出版商:RSC    

年代:1979

数据来源: RSC

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Analytical Division DiaryDECEMBERWednesday, 19th, 6 p.m.: LondonEducation and Tvaining G ~ o u p : AnnualGeneral Meeting, followed by a DiscussionMeeting.A discussion on “Educating Chemists for anAnalytical Problem Solving Laboratory-Industry’s Needs and Expectations,”introduced by S. Greenfield.Room N25, Chemistry Department, ChelseaCollege, Manresa Road, London, S.W.3.JANUARYTuesday, 15th, 6 p.m.: LondonSouth East Region and Micvochemical L’2fetliodsGmup : Annual General Meetings, followedby a joint meeting.“Problems of a Gas Man,” by J . G. Firth.13ritish Academy Meeting Room, BurlingtonHouse, Piccadilly, London, W. 1 .Thursday, 17th, 12 noon: LondonJoint Phamtaceutical Analysis Gvoup : AnnualGeneral Meeting, followed by a meeting on“Aspects of Microbial Control.”l’harmaceutical Society of Great Britain,I Lambeth High Street, London, SE1 7 JN.Friday, 18th, 6.30 p.m.: SalfordNovth West Region : Annual General Meeting,“Analyst-On and Off the Hails,” by M.Hdl.The University, Salford.followed by an Ordinary Meeting.Friday, 18th, 6 p.m.: ChepstowWestem Region : Annual General Meeting,“Sampling,” by G. V. James.Two Rivers Hotel, Newport Road, Cliepstow.followed by an Ordinary Meeting.Tuesday, 22nd, 4 p.m.: BelfastNovthevn Ireland Sub-Committec.“Scanning Electron Microscopy and ElectronProbe Micro Analysis in Forensic Science, ”by V. L. Beavis.Chemistry Department, The Queen’s Univer-sity, Belfast.Pleasc note change of date.Wednesday, 23rd, 7.15 p.m.: DarlingtonNovth East Region : Annual General Meeting,followed by a Discussion Meeting. A dis-cussion on “Safety Aspects of HazardousMaterials,” will be introduced by D. TV.Butcher.Europa Lodge Hotel, Darlington, CountyIJ urh am.Thursday, 24th, 10.30 a.m. : BirminghamMidlands Region, jointly with the WestMidland Region of the Association ofClinical Biochemists, on “Practical Im-munoassay-The Present State of the Art.”Chairman’s Introduction by llr. D. N. Raine.“An Overview of Immunoassay, ” by ProfessorV. Marks.“Techniques of Iodination, ” by ProfessorW. I<. Butt.“Fluorescence-Linked Immunoassay,” byJ. N. Miller.“Chemiluminescence-Linked Immunoassay,”by J. S. Woodhead.“Enzyme-Linked Immunoassay,” by 14. J .O’Sullivan.“Immunoprecipitation and the CentrifugalFast Analyser,” by I. Deverill.A small commercial exhibition is to be held inconjunction with this meeting. ByngKenrick Suite, The University of Rston,Birmingham.Printed by Heffers Printers Ltd Cambridge Englan

ISSN:0306-1396    

DOI:10.1039/AD97916BX044

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Vol 16 No. 12 December 1979 of the Analytical Division of the Chemical Society New Members of Council Although of Doncaster origin, Edmund Bishop was educated in Glasgow a t Allan Glen’s School. With the aid of various scholarships and prizes he gained Firsts in Chemistry and Chemical Engineering a t the University of Glasgow and a t the Royal College of Science and Technology (now the University of Strathclyde) took an Associateship in Applied Chemistry.Later, he was awarded the Degree of 1Xc by Glasgow University. After a short spell in a Public Analyst’s Laboratory, he spent the war years in the Explosives Directorate of the Armaments Research Department, engaged in both pure research and field work. Invalided out in 1944, he became an Assistant Lecturer in the University of Strathclyde, where, under the inspiration of the late Archie Crawford, his research interests turned entirely to analytical chemistry and he began to work on oxidation - reduction theory, titrimetry and indicators.In 1946 he moved to a Lectureship in the University of Newcastle upon Tyne, inheriting Hriscoe’s balances and developing a deep interest in high-precision analytical processes.In 1953 Bishop moved to a Lectureship in the Iiniversity of Exeter and enjoyed a couple of years encouragement from the late H. T. S. Britton, acquiring his first postgraduate student. *\t Exeter, he was promoted to Senior Lecturer in 1961, t o a Readership in 196s and finally in 1974 to a Personal Chair in Analytical Chemistry. Regular work a t the bench con- tinued until about 1961 when the disease of administration overtook him, but by that time his research school had become well established.His main contribution to the work of the team has long been theoretical, being the mathe- matical rationalisation of analytical processes, Microanalysis and trace analysis crop up frequently. Electrometric methods, particu- larly differential electrolytic potentiometry in its various forms, kinetics and mechanisms of electrode processes, and high-precision coulo- metry have formed a substantial programme.Investigations of titrimetric reagents, reactions and indicators, with increasing emphasis on kinetics and mechanisms, have formed another. Professor Bishop is currently a member of the AL) Council and was a member of the SAC Council a t various times during the period from 1959-1972.He has been a member of the SAC since 1948 and his numerous activities for the Society have included the Chairmanship of several committees : the Microchemical Reagents and Standards Committee (1958-69) ; the ,4MC Fluorine Panel (1963-65) ; the AMC Phosphorus Panel (1967-68); the Joint Panel on Organic RiIicrochemical Standards and Reagents ; the -4nalytical Standards Committee ; and the Compleximetric Standards Committee.Also during 1970-73 he served on the Committee for the amalgamation of the SAC with the Chemical Society. He has been a member of The Analyst Editorial Board since 1969 and was an editorial adviser to A nalyticn Chimica Acta and Talanta. Professor Bishop is married, with an adult family, and finds that he lacks the time for the considerable number of activities that he pursued in social and youth work, and for the lay preaching that he formerly undertook.His main relaxants are music and photography, his remaining exercise being swimming. Photopapk: E . Bishop Pvofessor E. Bishop Dv. G. C. Cochrane After attending a typically small Scottish country secondary school, Alva Academy, for three years, Gordon C.Cochrane started work 343344 G BO RG L.: P I1 A 160 N Proc. Annlyt. Di7). Chcm. SOC. in 1950 a t The Glenocliil "cast 12esearch Out- station, Distillers Co. Ltd., Menstrie, Clack- mannanshire, as the proverbial lab boy; he was eventually engaged in inorganic analytical work. Night school was then still the order of the clay for those who wanted to progress to an HNC, but towards the end of the course this was replaced by the luxury of day-release classes a t Paisley Technical College.Possession of an HNC in chemistry, together with passes in additional mathematics and physics, enabled him to carry on with his studies by entering the third year of the full-time four-year Applied Chemistry Course a t the then Heriot-Watt College, Edinburgh, in 1956.On obtaining the Associateship of the college, two years National Service in the Army followed, most of which was spent in West Germany. Im- mediately after demob, Cochrane was employed by the Arthur D. Little Research Institute at Musselburgh outside Edinburgh, which under- took contract rcsearch. He became involved in a long-term contract concerned with investiga- tion into why wooden packing cases made from certain woods produced a very corrosive atmos- phere (mainly acetic acid) under conditions of high temperature and humidity, whereas cases made from other woods did not.This involved bucket chemistry, organic structural work and various analytical techniques ranging from acid titrations to gas - liquid Chromatography.An external PhD was awarded for a thesis written on this work by the now Heriot-Watt Univer- sity in 1967. This was, in fact, the first higher degree awarded by the Science Faculty of the new University. A41tliougl~ his earliest chemistry training was in analytical chemistry, he had set his sights against being an analytical chemist when he received his A4ssociateship as he thought that analytical work was a poor alternative to research. However, during his six years of fairly fundamental research work a t Arthur D.Little Research Institute it became apparent to him that there was very little chemical work, research or otherwise, that did not rely heavily on analysis. Once this had sunk in he was prepared to consider employment as an analy- tical chemist and, in 1966, ten years after having left Distillers, he rejoined them a t their Glenochil Research Station in order to develop new methods of analysis using gas - liquid chromatography.Six years later, Dr. Cochrane was transferred to Glenochil Technical Centre to take charge of the gas-chromatography section in the Potable Spirits Department run by the DCL Chief Chemist, Rill Dunnet, former Chairman of the Scottish Region. His work now includes HPLC, together with other analy- tical techniques. Seven papers have been publislied by him, either alone or jointly, including a review paper on the gas - liquid chromatography of volatile free fatty acids, which was written a t the request of the Jouvnal of Chromatogvnphic Science. He became a member of the SAC in 1972, a Fellow of the RIC in 1974 and was elected Chairman of the Scottish Region of the Analytical Division last year. Marriage and two sons and a daughter, all a t school, do not prevent Dr. Cochrane from golfing, gardening and hill-walking.

ISSN:0306-1396    

DOI:10.1039/AD9791600343

出版商:RSC    

年代:1979

数据来源: RSC

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344 Proc. Annlyt. Di7). Chcm. SOC. The Analytical Work of George Pearson MD, FRS (1751-1 828) In continental countries, many advances in analytical chemistry were made by men whose initial training had been in pharmacy; of thestJ Vauquelin and Proust in France, and Stromeyer and Klaproth in Germany are obvious examples. In Britain, where scientific pharmacy developed much later, the corresponding role was often played by medical men with a taste for chem- istry, such as Wollaston, Ure and Henry.George Pearson was of this class. Born in Rotherham in 1751, Pearson studied medicine a t Edinburgh (attending Joseph Black’s lectures in chemistry and materia medica), where hc: graduated in 1773.l His postgraduate training was impressive, although by no means uncommon a t that time; 1 year at St.Thomas’s Hospital in London was followed by a period of study a t Leyden and a further 2 years of walking the hospitals of France and Germany. Thus equipped, he established himself in practice in Doncaster where he stayed for 6 years. His first analytical project (on the mineral waters of Buxton) was accom- plished during his Doncaster years.2 After moving to T,ondon, Pearson was appointed senior physician at St.George’s Hospital in 1784, one of his duties being to lecture on chemistry, mxtcria medica and theDecember, 1979 GEORGE PEARSON 345 practice of physic a t the hospital’s medical school. One of his pupils there was William Thomas Brande, later to become professor of chemistry a t the Royal Institution; the -%merican chemist, Benjamin Silliman, also attended his lectures.In 1791 Pearson was elected FRS. ?Lpart from the Buxton spa water, the principal items that Pearson analysed were the Indian steel known as “wootz” (undertaken a t the request of Sir Joseph Banks, President of the Royal Society) ,3 the popular febrifuge James’s P ~ w d e r , ~ white lac,5 urinary concre- tions6 and some ancient weapons and vessels.’ Certain characteristics are common to all Pcarson’s investigations and enable us to form an estimate of his capacity as an analyst.He always determined the specific gravity, often recording the results to three decimal places, although his method sometimes lacked precision, cspecially where powders were concerned. He compared melting-points with those of known substances, sometimes employing Wedgwood’s pyrometer cones, two decades before Chevreul made the melting-point a respectable tool of identification.8 Bunsen introduced the capillary melting-point tube,g but without this refinement Pearson achieved an acceptable melting-point for beeswax (61.1 “C) by simply immersing a lump of wax in warmed water and observing the water temperature when the wax melted.In nearly every instance, Pearson checked his analysis by synthesis, making a preparation on the basis of his conclusions and comparing its chemical and physical properties with those of the original sample. He was adept a t devising comparative methods; in the analysis of white lac he made candles of the lac and compared their burning properties with those of candles made from various known waxes. I t is worth noting that comparative tests were invoked more than a century later when a comprehensive investigation of secret remedies was undertaken on behalf of the British Medical Association, direct analysis proving too difficult.10 Pearson’s armoury of reagents (see Table I) is wide-ranging, and it is possible to discern a transition from the concensus approach used by Bergman to the specific reagents of Rose and Fresenius.Not everyone believed in the relia- bility of reagents (known as “tests”); it was widely held that evaporation of solutions to dryness, followed by blowpipe examination and observation of crystal shape, yielded less ambiguous results. Pearson, in fact, used both approaches. TABLE I PEARSON’S CHEMICAL REAGEX‘TS Sulphuric acid Nitric acid Hydrochloric acid Acetic Acid Oxalic acid Caustic soda Caustic potash Ammonia solution Sodium carbonate Potassium carbonate Calcium carbonate Ammonium carbonate Quicklime Lime water Borax Sodium phosphate Potassium f errocyanide Tincture of galls Iron(I1) sulphate Mercury(I1) nitrate Potassium nitrate Potassium tartrate Potassium cyanide Litmus Turnsole Silver nitrate Barium chloride Lead acetate Gold solution Manganese dioxide Chlorine water Calcium sulphide Alcohol Turpentine Ether His papers all display a broad scholarship, quoting opinions and observations that range from classical antiquity to his own times.In the account of his examination of Roman weapons there are passages in Greek, Latin and Saxon.Perhaps this investigation of archaeological finds (from a river bed in Lincolnshire) best illustrates Pearson’s style of working. The solder was shown to be pure tin by three tests; a solution in nitric acid was evaporated to give a white residue insoluble in water (SnO,); a solution in hydrochloric acid reduced gold solution t o purple of Cassius (colloidal gold); and no lead acetate was formed on treatment with acetic acid.The bodies of the objects consisted of an alloy of copper and tin. Iron was eliminated by the Prussian blue test, zinc by the absence of colour change on heating the oxide, bismuth by diluting the nitric acid solution, manganese by the colour of the solution and arsenic by the absence of garlic smell on heating with charcoal. Fusion points on the Wedgwood scale were compared with samples of copper, tin, zinc and various alloys of these elements.Pearson’s tests were destructive in every sense of the word. Articles were cut through with a chisel to expose the inner surface, and some were melted down and cast into ingots so that specific gravity, hardness and malleability might be more conveniently determined.In examining urinary calculi, Pearson com- mented that the analytical work of Scheele and Bergman was comparatively unknown in this country. He found the major constituent to be phosphate of lime, a substance with which he was familiar, having exhaustively proved its presence in James’s Powder. In fact, he was something of an expert on phosphorus com-346 ANALYTICAL CHEMISTRY pounds ; he had introduced sodium phosphate into medicine, and had discovered calcium pliosphide, which he made and sold commcr- cially.When the calculi were powdered and boiled with caustic soda, ammonia was given off, which Pearson suggested might come from an “animal oxide.” Scheele had called this “lithic oxide,” but after much phiIologica1 heart- searching Pearson named it “uric oxide.” This paper contains the first chemical description of uric acid.Pearson’s major non-analytical contribution to chemistry lay in pioneering tlie introduction into England of the new nomenclature from France, through his annotated translation of the TRUST FUND Proc. Analyt. Div. Chem. SOC. “Table de la Komenclature Cliimique” of Guyton de Morveau, Lavoisier, Berthollet and Fourcroy.ll He was generous in liis opinions of other chemists, referring to “the unrivalled Scheele” and “the immortal and ever to be deplored Lavoisicr.” His contemporaries knew him as a jovial companion and a good raconteur.The pen-and-ink sketch made by a pupil, and reproduced in the GentZenzm’s Magazi fie, reveals a solidly-built man looking over his spectacles with a quizzical and amusctl exprcssion.1. 9 I . 3. 4. 5. 6. 7. 8. 9. 10. 11. References Dict. Nut. Biog., I.ond., 1909, XV, 610; Gentleman’s Magazzne, 1828, 98(ii), 519 and 1829, 99(i), 125; Dzct. Sci. Riog., X.l’., 1974, X, 445. Pearson, G., “Observations and Experiments for Investigating the Chemical History of the Tepid Springs of Buxton,” London, 1783, 2 voluines. Phzl. Trans. 22. SOC., 1795, 85, 322. Phzl. Trans. R. SOC., 1791, 81, 317; I s i s , Phzl. Trans. R. Soc., 1794, 84, 383. Phzl. Trans. R. SOG., 1798, 88, 15. Phzl. Trans. R. Soc., 1796, 86, 395. Awz. Chzgn., 1813, 88, 225; 1815, 94, 125. Bunsen, K., “Gesammelte Abhandlungen,” Volume 1, 1904, Leipzig, p. 247 (footnote). “Secret Remedies, What they Cost and What they Contain,” British Medical -\ssociation, 1909, preface vi. Pearson, G., “Translation of the Table of Che~nical Nomenclature. . . . t o which are prefixed an Explanation of the Terms and some Observations on the Xew System of Chemistry,” London, 1794. W. A. CAMPBELL 1978, 69, 226.

ISSN:0306-1396    

DOI:10.1039/AD9791600344

出版商:RSC    

年代:1979

数据来源: RSC

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346 ANALYTICAL CHEMISTRY TRUST FUND PYOC. Analyt. DZV. Che??Z. SOC. Analytical Chemistry Trust Fund SAC Fellowships The Trustees invite proposals for research projects likely to make major contributions to the advancement of analytical chemistry in the UK. Proposals will be considered from applic- ants with a first class research background in non-academic establishments such as industrial organisations, government laboratories and Research Associations, as well as from those in academic institutions.Applications must be made by prospective Fellows only. The value of a Fellowship is related t o the Lecturer scale for University academic staff (k4333 per annum minimum, subject to revision, plus a London allowance where applicable). SAC Studentships The Trustees invite proposals from supervisors for research projects likely to make important contributions to the advancement of analytical chemistry in the UK and which are suitable for well qualified postgraduate students.Appli- cations may be submitted by research super- visors who must be members of the Analytical Division of The Chemical Society of a least 2 years’ standing. Proposals for projects to start in the Autumn term of 1980 will be considered early in that year when a tentative award may be made, subject to the Trustees being satisfied by the Summer of 1980 that a student acceptable to them is available.The value of a Student-Deccmber, 1979 EIGHTH THEOPHILUS REDWOOD LECTURE 347 ship is between A1370 and A2250 per annum minimum, according to circumstances, plus fees. Application Studentships can be obtained from the Secre- tary, Analytical Division, The Chemical Society, Burlington House, London, W1V OBN. The closing date for applications is January 31st, Regulations for the Fellowships and the 1980.

ISSN:0306-1396    

DOI:10.1039/AD9791600346

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

Deccmber, 1979 EIGHTH THEOPHILUS REDWOOD LECTURE 347 Eighth Theophilus Redwood Lecture* Analysis in Non-segmented Flowing Systems E. Pungor, G. Nagy, Zs. Feher and K. Toth Institzite.for General and Analytical Chemistry, Technical University, Budapest, Hungary The development of analytical chemistry in the last few years has been considerably character- ised by endeavours to find methods and solutions that would satisfy the increasing demands for information arising in various fields of application.In our opinion, one of the most important developing research fields in analytical chemistry is mechanised and automated analysis. Further developments in analytical chemistry in this area will be based on results of research activities effected in three funda- mentally important areas: investigations must be made in order to find new sensors, the matrix effects influencing sensors that have already been developed should be examined and solved, and finally data processing techniques must be further developed in an appropriate way.All of these developments can provide a good basis for work on developing newer techniques, the final aim of which is the production of reliable and rapidly operating analytical devices that reduce the amount of human labour required to a minimum.The application of flow systems has been a very fruitful approach in this area. Skeggsl developed an automated analytical system employing segmented flow in the 1950s. For a long time, since the development of the chromatographic technique^^-^ in gas chroma- tography and later in liquid chromatography, non-segmented flow systems have been employed in which, owing to the well defined circumstances, the concentration profiles are followed continuously in non-segmented flow systems with appropriate flow-through detectors.Ten years ago, when starting our measurements5 in flow-through systems, we wanted to apply this approach to direct sample analysis.Our studies have shown that, by employing electroanalytical sensors for detecting the con- centration changes in a flowing solution resulting from the injection of a sample solution into the flow stream, homogeneity of the solution in the detector section should be ensured. This can be explained generally by the non-integrating characteristics of electroanalytical sensors.This result led to the development of an analytical system with a continuous flow stream in which a mixing chamber was situated between the injection and detection points. Of course, a non-segmented flow system with Taylor diffusion without a mixing chambere,' can be used, but in this instance the analytical result can be rendered false by some physical parameters of the solution (e.g., viscosity or surface tension).The injection technique developed in this way can be used successfully in different fields of analytical chemistry.*-lO As the evaluation of the results is based on a peak-height or peak-area measurement, the accuracy and reliability of the technique are similar to those of any analytical method based on direct signal measurements.To combine the accuracy and reliability of analytical methods based on a titration process and the advantages of analytical techniques carried out in stream- Professor E. Pungor * Presented by E. Pungor on April 4th, 1979, at the CS Annual Congress, The University, Bristol.348 EIGHTH THEOPHILUS REDWOOD LECTURE PYOC. Analyt. Div. Clzenz. soc. ing solutions, a flow-through titration technique was developed in our 1aboratories.ll A brief description of the principle of these two techniques is given below. Details of the techniques and their applications can be found in the l i t e r a t ~ r e .l ~ ~ l ~ - ~ ~ Injection Technique The principle of the injection technique is that a small volume of a sample or reagent is injected into a solution streaming at a constant flow-rate.The solution stream carries the injected species, which are diluted or react with the constituents of the carrier solution. The concentration change in the carrier stream with time caused by the injection is followed at a certain point in the analysis channel with the help of an appropriate detector. In our studies mainly electroanalytical, i.e., voltammetric and potentiometric, methods have been used for the detection, but we have also used spectrochemical detectors.16 The shape and charac- teristic parameters of the peak-type dynamic response curves obtained depends on the special features of the sensors used.However, in all instances these signals provide analytical information about the concentration of the solution streamed or injected.For potentio- metric measurements the following equation describes the potential values : At 0 <r<t M n I and a t t> T L where Ki is the selectivity coefficient, M the amount of material injected (in mol), V the flow- rate, VV the volume of the mixing chamber, T the time of passage of the injected plug through the entrance of the mixing chamber, S the Nernst factor, c, the concentration of the appropriate ion in the ground electrolyte, E , the potential measured and ci the concentration of the inter- fering ion in the carrier solution.Using voltammetric signals, the following relationships are valid : At 0 < t < T and at t > T where K and a are constants involving the electrochemical and hydrodynamic parameters of the system.Triangle-programmed Titration Technique The addition of the reagent to the streaming sample solution according to a triangle pro- gramme makes it possible to record real titration curves. It is obvious that in this way analyti- cal results independent of the detector properties can be obtained. In addition, the recording of two titration curves as a result of the increasing and decreasing reagent mass flow ensures an accurate evaluation of concentration.The determination of the concentration is based on the equivalence points of the two titration curves.December, 1979 WHY TEACH ELECTROANALYTICAL CHEMISTRY ? 349 In the course of a triangle-programmed titration the solution to be analysed is streamed a t a constant flow-rate. At a certain point in the sample solution carrying tube, the reagent, the mass flow of which is altered with time according to an isosceles triangle, is introduced into the analysis channel.The solution segments, which can be characterised with different sample to reagent ratios, and thus with different degrees of titration, flow through a detector cell. According to the mass balance, the mass flow, and thus the concentration of the sample solu- tion, can easily be calculated.Considering the following titration process : aS + b R +fP, + gP, the concentration of the sample (S) solution is given by c = ( 2 v Q)$ where 27 is the time duration of the triangle-shaped reagent addition programme, Q is the time interval between the appearance of the two equivalence points, a and b are the stoicheiometric constants of the titration reaction and n is the slope of the reagent addition programme.Although there are different possibilities for accomplishing the reagent addition, one of the most convenient methods is by electrolytic generation of the reagent1’ by current-controlled electrolysis. In our laboratories different reagents (silver, mercury and hydroxyl ions, bromine and iodine) have been produced in this way, and using different methods of detection (potentiometric, biamperometric and photometric) various analytical tasks have been solved.1. 3. 4. 5. 6. 7 Y. c S. 9. 10. 11. 12. 13. 14. 15. 16. 17. References Skeggs, L. T., A m . .I. Clin. Path., 1957, 28, 311. Pungor, E., Tbth, K., Fehkr, Zs., Nagy, G., and VAradi, M., Analyt.Lett., 1975, 8, 9. Icemula, W., Roczn. Chern., 1952, 26, 281. VAradi, M., Balla, J., and Pungor, E., Pure A p p l . Chem., 1979, 51, 1175. Nagy, G., Fehkr, Zs., and Pungor, E., Analytica Chim. Acta, 1970, 52, 47. RBiiCka, J., and Hansen, E. H., Analytica Chirn. Acta, 1975, 78, 145. Pungor, E., Fehkr, Zs., Nagy, G., Tbth, K., Gratzl, M., and Horvai, G., Analytica Chiwa. Acta, 1979, Fehkr, Zs., Nagy, G., Tbth, K., and Pungor, E., Analyst, 1974, 99, 699.Fehkr, Zs., and Pungor, E., Analytica Chim Acta, 1974, 71, 425. Xagy, G., Fehkr, Zs., Tbth, K., and Pungor, E., Hung. Sci. Instrum., 1977, 41, 27. Nagy, G., Tbth, K., and Pungor, E., Analyt. Chem., 1975, 47, 1460. Xagy, G., Fehkr, Zs., Tbth, K., and Pungor, E., Analytica Cham. Acta, 1977, 94, 87. Nagy, G., Fehkr, Zs., Tbth, K., and Pungor, E., Analytica Chim. Acta, 1977, 91, 97. Nagy, G., Fehkr, Zs., Tbth, K., and Pungor, E., Analytica Chim. Acta, 1978, 100, 181. Nagy, G., Lengyel, Z., Feher, Zs., Tbth, K., and Pungor, E., Analytica Chim. Acta., 1978, 101, 261. Sagy, G., Fehkr, Zs., T6th, K., Pungor, E., and Ivaska, A . , Talanta, in the press. Nagy, G., Fehkr, Zs., T6th, K., and Pungor, E., in Pungor, E., Editor, “Coulometric Analysis,” Conference held a t Mgtrafiired, Hungary, October 17-1 9th, 1978, Akadkmiai Kiadb, Budapest, 1979, p. 123. 109, 1.

ISSN:0306-1396    

DOI:10.1039/AD9791600347

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

December, 1979 WHY TEACH ELECTROANALYTICAL CHEMISTRY ? 349 Why Teach Electroanalytical Chemistry ? The following are summaries of two of the papers presented a t a Joint Meeting of the Electro- analytical and Education and Training Groups held on June 6th, 1979, at the Chemistry Department, Loughborough University of Technology. Why Teach Analytical Potentiometry ? J. D. R. Thomas Chemistvy Department, University of Wales Institute of Science and Technology, Cavdifl, CF1 3N U Analytical potentiometry provides many answers for those interested in fundamental and industrial research, in process and effluent control and in a variety of other fields.Such wide- spread use of potentiometry on the analytical scene gives an essential sense of direction to the teaching of electrochemistry. Through this, a better appreciation of several important350 WHY TEACH ELECTROANALYTICAL CHEMISTRY? Proc.AnaZyt. Diu. Chenz. SOC. concepts can be given, such as electrode potentials and free energy, solution concentration and activities, common-ion effects and buffer action. Further, the inclusion of analytical potentio- metry in the curriculum provides a basis for introducing the principles of method development in analysis and of progressive designs in the developing world of analytical instrumentation.Uses in Analytical Measurements The scope of potentiometry in analytical measurements provides a helpful link between the essentially academic approach and the harsh realities of the technological world, such as occurs in the use of the Orion 94-16 sulphide ion-selective electrode for the difficult problem of monitoring the oxidation of very alkaline spent “black liquor” in the pulp and paper trades1 The sulphide electrode provides more specific information than either glass pH or platinum electrodes, and monitors the sulphide ion level over the range 5 x to about 10-lS M.The ability of potentiometric sensors to cover several orders of magnitude compensates for their limited precision by the response - log (activity) relationship of the Nernst equation, where an uncertainty of 0.1 mV in the measured response is related to about 0.4% error in univalent ion activity. Potentiometric ion sensors can conveniently be used in remote situations and it is easy to perform supplementary sample pre-treatment as in the addition of TISAB in monitoring fluoride.However, neither ease of use nor the fact that potentiometry is the most widely used electroanalytical technique can stand alone to merit the teaching of analytical potentiometry. Rather, it is the increasing importance of information on pIon levels and of potentiometric acid - base and redox titrations. By considering just the water industry, it is possible to realise the importance of analytical potentiometry2 for determining pH, sodium in highly pure water, fluoride and nitrate in potable water, sulphide and cyanide in industrial effluents, etc.This has arisen because of the development of new ion sensors, some of which have made their way into texts of standard analytical methods, for example, the fluoride electrode3,* and, tentatively, the nitrate and cyanide electrode^.^ Apart from potentiometric ion sensing, there is also the importance of the reference role of potentiometry for calibrating indicators in acid - base, redox and non-aqueous titrations, for monitoring (potentiometric and coulometric) titrations and following the electrode reactions of other electroanalytical methods.Appreciation of Chemical Concepts The inclusion of potentiometry in the curriculum helps to stress the importance of concepts such as solution and ion concentration, common ion effects, hydrolysis, neutralisation, com- plexation and buffer action. It also succinctly demonstrates, by the non-linearity of the e.m.f. response - log (concentration) relationship under conditions of high ionic strength, the importance of activities and activity coefficients, and in this respect the development of ion- selective electrodes has renewed interest in the electrochemistry of solution^.^ The concepts of free energy and electrode potentials, and their interactions, can effectively be conveyed to students by analytical potentiometry approached from either the Daniell cell or from the standpoint of, say, the Fe2+i3+ and Sn2+i4+ couples.Thus, taking the Daniell cell as an illustration, it can be emphasised that the negative left-hand (zinc) pole has the more negative standard (reduction) potential and that the cell will produce an e.m.f. given by Ee (right-hand +ve electrode) - E0 (left-hand -ve electrode) = +0.337-(-0.763) = +].lo v The cell reaction can then be considered by describing the reduction at the right-hand (copper) electrode and the oxidation at the left-hand (zinc) electrode, followed by the relation AG = nFEcell to give AG = - 212.3 kJ, which shows the cell reaction to be thermodynamically feasible.From this stage, the concepts of indicator and reference electrodes are introduced and it is now only a small step to the membrane-type ion-selective electrodes.The concepts of analytical potentiometry are effectively conveyed in the laboratory by the potentiometric titration of Fez+ with Ce4+ using a saturated calomel and platinum electrodeDecember, 1979 WHY TEACH ELECTROANALYTICAL CHEMISTRY ? 351 pair. The titration is carried out in the presence and absence of orthophosphoric acid.The student plots the e.m.f. response versus volume (cm3) titration curves and is required (a) to calculate ETe3+,Fe2+ and Eze4+,Ce3+ for both titrations; ( b ) to calculate the equivalence point potentials from (a) and by a graphical method; and ( c ) to plot AElA(cm3) and A[AE/A(cm3)]/A(cm3) versus cm3 of Ce4+ added in each instance. In addition, the student answers questions concerning the advantages of derivative and second derivative plots and on offsetting of the titration curve by orthophosphoric acid.Method and Instrument Development Method development is illustrated by the above derivative methods of end-point location, but this and the choice of electrodes and general cell conditions can be taken together with developments in instrumentation for analytical potentiometry.At their simplest, progressive stages in instrumental design can be introduced by developing the theme of the potentiometer as a null instrument in the need to draw zero current from the cell. This will include the elementary refinements of breaking up the slide wire into components of separate resistances and the introduction of a range switch.The special cases of high-resistance glass and other membrane electrodes can then be conveniently dealt with by discussing potentiometric-type pH meters, with electronic amplification of the unbalance current, and of the direct-reading pH meters, which depend on the power-amplifying properties of electronic tubes or transistors and which are now provided with digital displays.Instrument and method development are taken together in describing automatic titrimeters, these being illustrated by titrimeters with automatic recording of the titration curve and those with automatic termination of titrant addition at the end-point. Such instrumentation emphasises the need to teach the essential principles of electrode and equivalence point potentials, not only to chemists but also to biologists and engineers.Emphasis of the basic principles will encourage intelligent decisions on choice and use of instrumentation and cell components, and will inform on such mundane matters as the ade- quacy of a silver wire as an indicator electrode in the potentiometric titration of iodide and chloride in admixture. As in this example, there is frequently no need to use expensive ion- selective electrodes and, further, a laboratory exercise on the titration of chloride and iodide is another opportunity for providing student experience in concepts.Of course, potentiometry is not simply a matter of cells with indicator and reference electrode pairs ; the concentration cells of differential and null-point potentiometry are sensitive analytical tools and should not be ignored. The standard additions method and the modification used by Gran for presenting potentio- metric titration data in linear form provide interesting examples of method development in ion- selective electrode applications.5,6 The taking of antilogarithms of the known additions equation is cumbersome, while direct plotting of e.m.f.response versus volume of standard added with special Gran’s-plot paper depends on Nernstian electrode calibration slopes and a steady volume change on the addition of a standard.6 Nevertheless, in these enlightened times, developments in microprocessors have ensured the availability of e.m.f. measuring equipment that can cope with the mathematical operations and with different electrode slopes and concentration of standards.For example, the Orion, Model 901, meter has a high- impedence amplifier and analogue-to-digital converter, the output of which is fed to a micro- processor pre-programmed with the appropriate equations for calculating pH and concentra- tion.’ Thus, for example, for a solution of unknown concentration the programme within the instrument is based on providing a set of input data, namely the cell potential for the unknown solution.Concentration of standard, electrode slope, and/or blank correction and MODE (KA,known addition in the present context) are stored in the memory and permit the micro- processor to solve the electrode equations.’ Other MODES are available in the instrument, for example, Analyte Addition (AA) and Analyte Subtraction.Conclusion I t is the key to electroanalytical chemistry and educated electroanalytical chemists are needed in these days of continuing improvements in ion sensors in a world increasingly dominated by microelectronics. Sources of potential are Why teach analytical potentiometry ?352 Proc. Analyt. Div. Chenz. SOC. one of the three major categories in which operational amplifiers in their transducer applica- tions can be considered to act (the others are variable resistors and sources of current).Cells for analytical potentiometry are the most notable providers of potential in an area that also includes thermocouples, cells for chronopotentiometry and photovoltaic cells. WHY TEACH ELECTROANALYTICAL CHEMISTRY ? References 1.2. 3. 4. 5. 6. 7. Swartz, J. L., and Light, T. S., Tappi, 1970, 53, 90. Midgley, D., and Torrance, K., “Potentiometric Water Analysis,” John Wilcy, Chichester, 1978. Department of the Environment, “Analyses of Raw, Potable and Waste Waters,” HM Stationery Office, London, 1972. American Public Health Association, American Water Works Association and Water Pollution Control Federation, “Standard Methods for the Examination of Water and Waste Water,” Fourteenth Edition, American Public Health Association, Washington, D.C., 1975.Moody, G. J., and Thomas, J. D. K., Sel. A . Rev. Agzalyt. Sci., 1973, 3, 59. Craggs, A., Moody, G. J., and Thomas, J . D. R., J . Clzem. Edzcc., 1974, 51, 541. Moody, G. J., and Thomas, J. D. R., Lab. Pract., 1970, 28, 125.The Teaching and Importance of Polarography A. G. Fogg Chemistry Department, Loughborough U,tiversity of Technology, Loughborough, Leicestershire, LEI 1 3T U Polarography is essentially a technique that involves the plotting of current vcwus voltage curves for a dropping-mercury electrode. Conventional d.c. polarography originated with Heyrovsky in 1922 but there have been many advances in methodology, notably the intro- duction of pulse polarography by Barker in 1958.Polarography is versatile in that it can be used to determine metal ions and organic species that are reducible at the dropping-mercury electrode. The technique went into decline in the late 1960s owing to the introduction of commercial atomic-absorption spectrometers for the determination of metals and the con- tinuing development of gas chromatography for the determination of organics.Seven years ago, if reminded of polarography the typical industrial analytical chemist might have said that he had a polarograph in the corner of the laboratory gathering dust. If reminded more recently he would look at the ceiling contemplatively and remember that he w e d to have one sitting in the corner of the laboratory gathering dust ! Many industrial analytical chemists believe that polarography is at the same stage now that it was at in the 1960s.They think of polarography in terms of the old Tinsley polarograph. Many laboratories had the Southern Davis differential cathode-ray polarograph, but very few had the Southern-Harwell pulse polarograph which cost about L4 000 then.There are now modern, fully transistorised potentiostat-controlled pulse polarographs available commercially for about L2 000. More sophisticated instruments have microprocessor control and other automation facilities. Even the long tube of mercury is a device of the past if a modern mercury-drop module with solenoid-valve control is obtained. Modern polarographic and voltammetric techniques are making valuable contributions in the following areas1 : (i) the determination of drug compounds, particularly after extraction from biological (ii) trace-metal determination (anodic stripping voltammetry) ; (iii) high-performance liquid chromatography (mercury and glassy carbon voltammet ric (iv) fundamental studies of large molecules such as DNA (pulse polarography).With the introduction of this relatively inexpensive modern instrumentation into labora- tories, polarography may well recover some of its lost ground for applications where it has advantages over other techniques. Yolarographic techniques have always continued to be used unobtrusively in devices such as polarographic dissolved oxygen meters and pollution monitors.fluids (differential pulse polarography) ; detectors) ; andDecember, 1979 WHY TEACH ELECTROANALYTICAL CHEMISTRY? 353 Thus, polarography and related techniques are important analytically even if sometimes only in a complementary role. When we turn to the advantages of teaching polarography we find that it has much to offer as a basis for introducing and understanding many electro- chemical principles.A close analogy is the case of classical qualitative metal-ion analysis. Most universities find it difficult to justify devoting much time to this apparently relatively unimportant technique. Unfortunately, it is, or was, a very effective practical method of teaching the chemistry of the elements. Fortunately, polarography is still sufficiently important as an analytical technique to justify teaching it.I shall now indicate some electrochemical phenomena, definitions and illustrations that can emerge in a course on polarography. As with the teaching of most analytical techniques, there are numerous approaches to the subject that can be taken: the following is the approach that I have taken recently. After describing and illustrating a simple two-electrode d.c.polarographic cell and showing the form a d.c. polarogram takes, the mean limiting diffusion current and half-wave potential are defined. It is the current at the dropping-mercury electrode that is being measured and current is the rate of electrolysis (coulombs per second). In a typical polarogram the current reaches a plateau and at potentials corresponding to this plateau the determinand concentration at the electrode surface is zero. The determinand is reduced immediately it reaches the electrode.Its rate of arrival is its rate of diffusion (which is dependent on the electrolysis time), and the rate of diffusion effectively limits the current, i.c., the current is diffusion controlled. At this point some teachers, particularly physical chemists, may prefer to develop diffusion theory and the equation for a diffusion-controlled polarographic wave.I prefer simply to present them with a simple derivation (on a handout) and to point out the main result that for a fast electrode reaction the half-wave potential is very similar in value to the standard reduction potential of the couple ('oersus S.C.E.rather than N.H.E.). This leaves me free to develop the theme of rate-controlling processes at electrodes. The following factors may limit the current at electrodes : the area of the electrode, mass transport (e.g., diffusion or convection), electron transfer rate, rate of a preceding homogeneous chemical reaction, catalytic effects and adsorption effects.The larger the surface area of the electrode the larger the limiting current will be. The physical chemist uses current density rather than current to take this into account : the analytical chemist simply draws a calibration graph (id versus concentration) for each electrode. Stirring the solution in an electrolysis cell increases mass transport and there- fore increases the current.If the electron-transfer reaction is slow an activation over- potential is introduced: the reduction is more difficult and the polarographic wave occurs at a more negative potential. At potentials on the plateau, however, the current is diffusion con- trolled again. The polarographic waves of formaldehyde and certain sugars are typical of control by a solution kinetic process.Catalytic effects (and currents) are typified by the reduction of nitrate and perchlorate in the presence of molybdenum(V1) or uranium(V1). Adsorption of determinand or its reduction product causes adsorption post-waves and pre- waves, respectively. If the reduced form is adsorbed it is stabilised and is more easily formed by reduction of determinand : if the determinand is adsorbed it is reduced with greater difficulty.X discussion of the advantages and disadvantages of mercury as an electrode, particularly as a dropping-mercury electrode, introduces more useful electrochemical theory. The large cathodic range at the mercury electrode (0 to -2 V) arises because of the high overvoltage asso- ciated with the reduction of hydrogen ions at mercury: the cathodic range of solid electrodes is more restricted.Mercury, however, has a severely restricted anodic range owing to oxidation of mercury at +0.25 V, whereas glassy carbon, for example, is useful for studying oxidations up to about + 1.5 V. Solid electrodes require careful pre-treatment owing to the formation of oxide and other factors. The dropping-mercury electrode is self-cleaning in that a new drop forms and grows at regular intervals (typically 3-4 s) : in fact, d.c.polarography is a sequence of electrolyses of duration equal to the drop time. Conventional d.c. polarography is limited in sensitivity to about the 10-5n~ level (about 1 pg ml-l). This limitation is mainly due to the capacitance current that flows to charge the growing mercury drop, which acts as a capacitor, but is also due to the long electrolysis time (i.e., the drop time).2 With shorter electrolysis times the rate of diffusion is faster and hence the faradaic current obtained is greater.This is essentially the case in pulse polarography where a potential pulse is applied for a fraction of a second. The capacitance current is also reduced and it is possible to make determinations at the lo-' M level.354 DEVELOPMENTS IN HPLC STATIONARY PHASE TECHNOLOGY Proc.A fzalyt. Div. Chenz. SOC. There are two common pulse polarographic techniques : normal pulse polarography (NPP) and differential pulse polarography (DPP). In both instances a potential pulse of short duration is applied near the end of the life of each mercury drop: the current is monitored just before and near the end of each pulse, and the difference is recorded and held on the recorder until the next sampling of current.In NPP the potential remains at its initial value except during the pulse: the pulse amplitude increases regularly with each drop to the level normally reached by the d.c. ramp. For this reason a normal pulse polarogram takes the plateau shape of the d.c.polarogram but the current is 7-10 times larger. In DPP the usual d.c. ramp is applied and a pulse of constant amplitude (typically 50 mV) is superimposed on this near the end of the life of each drop. At potentials before reduction occurs, and also at potentials corresponding to the d.c. or NPP plateaux, no change in current is observed when the pulse is applied. A difference in current is observed only at potentials corresponding to the sloping portion of the d.c. or NPP waves. Thus a derivative-shaped polarogram is observed in DPP. The faradaic current is greater in NPP than in DPP but so is the capacitance current. For this reason, DPP gives a lower limit of detection than does NPP, and further the peak-shaped polarograms are preferred by most analytical chemists. Caution is necessary, however, in using DPP as the peak heights can be highly dependent on the exact composition of the sup- porting electrolyte and on the presence of surface-active materials that can adsorb at the mercury surface-l Suitable polaro- grams to illustrate electrochemical theory can be found in the classic text of Heyrovskg and K ~ l t a . ~ Numerous examples of applications of DPP are avai1able.l For reasons of space illustrations have been omitted from this summary. References 1. 2. 3. Osteryoung, J., and Haseba, K., Rev. Polavogv., Kyoto, 1976, 22, 1. Delahay, P., “Instrumental Methods of Chemical Analysis,’’ Macmillan, London, 1957, Chapter 4. Heyrovskj., J., and Kfita, J., “Principles of Polarography,” Academic Press, New York, 1966.

ISSN:0306-1396    

DOI:10.1039/AD9791600349

出版商:RSC    

年代:1979

数据来源: RSC

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354 DEVELOPMENTS IN HPLC STATIONARY PHASE TECHNOLOGY Proc. A fzalyt. Div. Chenz. SOC. Recent Developments in HPLC Stationary Phase Technology and Application to Analytical Chemistry The following are summaries of two of the papers presented at a meeting of the Midlands and East Anglia Regions and the Chromatography and Electrophoresis Group held on April 4th, 1979, at Unilever Research, Colworth House, Sharnbrook, Bedfordshire.Synthesis and Applications of New, Chemically Bonded Stationary Phases for HPLC S. A. Math, J. S. Tinker, A. Tito-Lloret, W. J. Lough, L. Chan and D. Bryan Chemistry Department, The City University, Northampton Squavc, London, EC1 V OHB Chemicallv bonded stationarv phases are playing an increasingly important role in the HPLC separation of complex organic molecules.We have been engaged in the synthesis of a variety of new phases incorporating functional groups designed to interact specifically with structural features present in solute molecules, thus enhancing separations. The general methods used for the synthesis of the new phases are outlined in Scheme 1.December, 1979 DEVELOPMENTS I N HPLC STATIONARY PHASE TECHNOLOGY 355 Phases bonded through a siloxane linkage were obtained by coupling silica with either organo- trichlorosilanes or organotrialkoxysilanes.As an alternative, phases linked directly through an Si-C bond were prepared by the chlorination of silica, followed by reaction with Grignard reagents. This latter method has hitherto been little used since it was first describedl about 10 years ago, but it has a number of potential advantages which appear worthy of further exploration.The Si-C bond is particularly stable to hydrolysis compared with Si-0-C, and the phases prepared by organometallic coupling with chlorinated silica must necessarily be monolayer in character. Initially, a series of w-hydroxyalkyl phases [-(CH,),-OH; n = 3, 8, 111 was prepared by both the siloxane and organometallic coupling methods, using Merckosorb SI 60 (10 pm, irregular microparticulate) and Corasil I1 (35-50 pm, pellicular) as representative silicas. Both methods gave surface coverages in the range 1-4 groups nm-,, in agreement with expectations.1,2 In general, surface coverages were slightly higher (about 15%) when using the trichlorosilane reagents (I) than with the Grignard reagents.This is consistent with the expectation that the Grignard reagents will form relatively bulky solvates (11) in ethereal solution and will thus attack fewer surface sites on the support. Further evidence for the operation of a steric effect came from the observation that both coupling procedures led to higher surface coverages on the low surface area, pellicular support than on the high surface area, microparticulate Merckosorb SI 60.3 The chromatographic behaviour of the hydroxy- alkyl phases was studied by using aromatic hydrocarbons, substituted anilines and metal P-diketonate complexes.The retention behaviour of the metal complexes, in particular, provided evidence for a specific interaction between the metal ions and the hydroxyl groups in the stationary phase.Details of the work with these new hydroxyalkyl phases have been published e l s e ~ h e r e . ~ OEt, Me3SiO- (CH2),-SiCI3 Me3SiO-(CH2),-Mg-Cl OEt2 I I I H I C02 H Aminopropyl silica is readily prepared by the coupling of silica with 3-aminopropyl- triethoxysilane and is one of the most popular bonded phas2s carrying a functional group currently in use.We have prepared a large batch (about 1 kg) of this phase, based on LiChroprep 15-25pm silica, and have used it for the preparative HPLC isolation of minor impurities arising in the fermentation production of Cephacetrile (111). The aminopropyl function is an attractive starting point for the preparation of other, modified, bonded phases by derivatisation of the amino group (Scheme 2).Picramidopropyl silica was prepared by the reaction of aminopropyl Merckosorb SI 60 (10 pm) with picrpl chloride. Under both normal and reversed-phase conditions, the picramidopropyl phase showed enhanced retention of a wide range of aromatic hydrocarbons compared with amino- propyl silica. This is consistent with the operation of a charge-transfer interaction between the nitroaryl groups and electron-rich aromatics. A series of amido phases was obtained by acylation of 3-aminopropyltriethoxysilane, followed by coupling with silica (Scheme 2 ) .A recent report5 has described the use of acet- amidopropyl silica for the molecular-exclusion chromatography of polymers. We have found this phase to be effective for the reversed-phase separation of polar compounds, such as sub- stituted anilines.The change in retention behaviour of the substituted anilines on acet- amidopropyl silica compared with aminopropyl silica under the same chromatographic356 DEVELOPMENTS IN HPLC STATIONARY PHASE TECHNOLOGY Proc. Analyt. Div. Chem. SOC. conditions suggests the involvement of a direct interaction between the amido function and the aromatic amines.A detailed study of this effect will be reported shortly. I RX I RX R = COCH3, COCsH, 3 , C02CH3 NO2 NO, We thank the S.R.C. and The City University for financial support and Dow Corning Ltd. for a gift of cliemicals. References I . 1. 3. 4. Locke, D. C., Schmcrmund, J. T., and Banner, B., Analyt. Chem., 1972, 44, 90. Ungcr, I<., Angew.Chem. Internat. Edn, 1972, 11, 267. Gilpin, R. K., and Burke, M. F., AnaZyt. Chewz., 1973, 45, 1383. Matlin, S. A., and Tinker, J . S., J . High Resolution Chromat. Chromat. Comm., 1979, 2, 507. Preparation of Stationary Phases for Food Chemistry Separations A. D. Jones, I . W. Burns, E. C. Smith and P. J. Richardson Uiiilcau Research, Colworth House, Sharnbrooh, Bedfordshire, MK41 1LQ Over the past 4-5 years there has been a rapid growth in the use of bonded phases, which have considerably enhanced the ability of the chromatographer to carry out previously difficult separations.Virtually all of these phases are prepared from either an alkoxy- or a chlorosilane because organosilanes with a wide range of functions are commercially available and also the resulting phase is stable thermally, hydrolytically and over a wide pH range.Preparation from an Alkoxysilane A particularly useful phase that can be prepared from an alkoxysilane is aminopropyl- bonded silica. The phase loading can be effectively controlled by the silica to silane ratio and can be achieved by simply shaking moist silica and the silane together in hexane at room temperature for 5 min.The phase is particularly useful for the separation of food sugars and glucose o1igomers.l Preparation from a Di- or Trichlorosilane Until recently our method of preparation involved the following: drying the silica for 16 h at 100 "C; refluxing the silica together with octadecyltrichlorosilane and a small amount of pyridine in dry xylene for 3 h ; adding hexamethyldisilazane (HMDS) and refluxing for a further 10 min; and finally Of all the bonded phases used in HPLC C,, is by far the most popular.December, 1979 DEVELOPMENTS IN HPLC STATIONARY PHASE TECHNOLOGY 357 filtering, washing with dry solvents and drying in the oven at 70 "C.Water must be scru- pulously excluded from the reaction in order to prevent phase polymerisation.The results of using dried and non-dried silica are given in Table I. The non-dried silica preparation yielded a phase with a slightly higher column back pressure and loading, but its efficiency was much reduced. It is possible that the reason for this was polymeric material blocking the small silica pores, which would produce stagnant pockets of TABLE I EFFECT OF PHASE POLYMERISATION Silane, C,,Me; column, 15 cm x 0.49 cm; support, Partisil 10.Loading, Column pressure/ Efficiencj-/ Silica pretreatment %I bar plates m-1 Oven dried 16 h, 100 "C . . 24 40 19 900 Sone . . . . . . . . 27 50 12 100 solvent leading to higher back pressures and lower efficiencies. to catalyse the reaction by removing the hydrogen chloride. surface coverage and variable loading were obtained.used. encies, normally evidenced by tailing peaks. supports. Pyridine was used in order Prior to its use phases of low In order to remove the remaining accessible hydroxyl groups hexamethyldisilazane was Residual hydroxyl groups can lead to a mixed retention mechanism and low effici- By using this procedure it is possible to prepare reversed-phase material on a range of Table I1 shows the results of a preparation using 5 pm Partisil and Lichrosorb.TABLE 11 PREPARATION OF C,, ON 5 pm MATERIAL C,, TCS 10 cm x 0.49 cm Partisil 5 90 27 33 000 C,, TCS 10 cm x 0.49 cm Iichrosorb Si 100 100 19 36 000 Both materials give high efficiencies, the main difference lying in the phase loading; this can be explained by the fact that Partisil has a surface area of 400 m2g-l, compared with 300 m2 g-l for Lichrosorb Si 100.Pressure/ Loading, Efficiency/ Silane Column Support bar %, plates m-l Preparation from Monochlorosilanes The main problem in the preparation of reversed phase from di- or trichlorosilanes is that of preventing phase polymerisation. Recently, octadecyldimethylchlorosilane was evaluated for the preparation of C,, phase. As there is only one chlorine atom per molecule no phase polymerisation can occur, although any excess water present in the reaction mixture will effectively remove organosilane molecules by causing hydrolysis and dimerisation.The effect of reaction time on loading when using octadecyldimethylchlorosilane is shown in Table 111. The reaction conditiom were otherwise identical with those of the trichloro- silane preparation.TABLE I11 THE EFFECT OF REACTION TIME ON LOADING USING OCTADECYLDIMETHYLCHLOROSILANE Support: Partisil 5 . Phase No. Reaction time/h Loading, yo R13 0.6 20 R13 1 22 R14 8 23 The reaction is characterised by a very rapid initial increase in loading followed by a slow increase, presumably caused by the steric hindrance of the bulky silane molecules. A commonly applied test of the surface coverage of a reversed phase is that of Karch et aL2 This test entails running the column with a non-polar eluting agent and injecting benzene and nitrobenzene.For a good surface coverage the k' values of these components should be358 NEW BRITISH STANDARDS Proc. Analyt. Div. Clzem. SOC. less than 0.1 and 0.5, respectively.With non-polar eluting agents and silica the retention order is created by the interaction between the silanol groups and the sample; hence the k’ values are a function of the residual silanol groups in the column. For a good reversed- phase column, therefore, these k’ values should be as low as possible. The results of this test, when applied to phases R12, 13 and 14, are given in Table IV.TABLE IV HALASZ TEST APPLIED TO OCTADECYLDIMETHYL PHASES k‘ values ---- L __-- Before HRlDS After HMDS 7 R13 20% Benzene . . . . Nitrobenzene . . . . Benzene . . . . Nitrobenzene . . .. Benzene . . .. Nitrobenzene . . .. R12 22YL R14 23% 0.34 0.19 4.39 0.S3 0.32 0.13 3.47 0.41 0.19 0.09 N = 32000 2.03 0.39 plates m-1 Although the difference between phases R13 and R14 was only 3%, the k’ values differed by a factor of 2 , indicating the importance of a long reaction time.Similarly, the value of the HMDS treatment for removal of residual silanol groups is clearly underlined. Phase R14, after HMDS treatment, exhibited low k values within the range suggested by Halasz and exhibited an efficiency of 32 000 plates m-l. In conclusion, it is possible to prepare good reversed-phase material from tri-, di- or monochlorosilanes.However, as no phase polymerisation can occur using a monochloro- silane it is both easier and far safer to use this approach. Applications Octadecyldimethylchlorosilane phase has been applied to a wide range of problems in food analysis. The six dye components of Brown FK (a synthetic dye), together with three compounds used in the dye synthesis, can be separated in 15 min by using an acetonitrile - water gradient with phosphate b ~ f f e r .~ The natural food dye Beet Red can be qualitatively assessed for colour balance by using a water - methanol gradient with acetic acid. This dye consists of two main red pigments, betanin and betanidin, which are primarily responsible for the dye’s colour, together with two yellow components which have less potency as colorants but which play an important role in achieving colour balance. By use of a methanol mobile phase it is possible to quantify a-tocopherol in animal feeds. This system is capable of separating all of the tocopherols and tocotrienols apart from 18- and y-, and has considerable advantages over the existing thin-layer chromatographic analysis. References 1. 2. 3. Jones, A. D., Burns, I. W., Sellings, S. G., and Cox, J. A., J . Chromat., 1977, 144, 169. Karch, K., Sebastian, I., and Halasz, I., J . Chromat., 1976, 122, 3. Jones, A. D., Hoar, D., and Sellings S. G., J . Chrumat., 1978, 166, 619.

ISSN:0306-1396    

DOI:10.1039/AD9791600354

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

358 NEW BRITISH STANDARDS Proc. Analyt. Div. Clzem. SOC. New British Standards BS 4427: Test Methods for Condensed Phos- Timber. Part 4. Quantitative Analysis of phates. Part 12. Condensed Phosphates for Preservatives and Treated Timber Containing Industrial Use (Including Foodstuffs)-Deter- Copper Naphthenate. mination of Arsenic Content: Silver Diethyl- dithiocarbamate Photometric Method. Copies of all British Standards can be The price of Part 12 is f12.20. obtained from BSI Sales Department, 101 BS 5661: Wood Preservatives and Treated Pentonville Road, London, K l 9ND. The price of Part 4 is L1.60.

ISSN:0306-1396    

DOI:10.1039/AD9791600358

出版商:RSC    

年代:1979

数据来源: RSC

摘要:

CORRESPONDENCE 359 December, 1979 Correspondence Correspondence is accepted on all matters of interest to analytical chemists. Letters should be addressed to the Editor, Proceedings of the Analytical Division, The Chemical Society. Burlington House, London, W1 V OBN. Which Techniques are Insufficiently Taught? Sir, ;it a joint meeting of the Education and Training and Specialised Techniques Groups, held on 8 November 1978, one of the papers, entitled ‘‘A4nalytical Techniques Currently Used in Industry-Which Techniques are In- sufficiently Taught ?”, was presented by G.A. Xewman. A summary of this paper was recently published (Proc. Anal-yt. Div. CIzenz. SOC., 1979, 16, 228) and whilst I agree with the majority of Dr. Newman’s comments, I must take issue on one point, namely his statement that “thermal methods of analysis have never been appreciated by academics.” Historically, the first publication by British workers on thermogravimetry came from the Washington Singer Laboratories, University College of the South West (now Exeter Univer- sity) .l The authors constructed a thermo- balance and demonstrated its usefulness in igniting or drying analytical precipitates to constant mass.These simple experiments were incorporated into the undergraduates’ curric- ulum. Subsequently, many schools of thermal analysis were established, in both universities and polytechnics, e.g., Salford University (Dr. D. Dollimore), UMIST (Dr. R. H. Still), Huddersfield Polytechnic (Dr. G. M. Clark), Portsmouth Polytechnic (Dr. M. I. Pope) and Hatfield Polytechnic (Dr.D. V. Nowell), to mention but a few. I hope, therefore, that Dr. Kewman will agree that thermal methods are appreciated by academics, although there is clearly scope for even more widesprcad use of these techniques in i4kademia. Reference 1. Gregg, S . J., and Iliinsor, G. W., Analyst, 1945, 70, 336. C. J. Keattch Industrial and Laboratory Sevviccs, P.O.Box 9, Lyme Regis, Dorset Hazards of High-pressure Jets of Solvents Sir, Modern techniques of high-performance liquid chromatography may prove hazardous unless clue care is given to the proper handling of solvents. Some of the hazards involved are less obvious than those such as possible toxicity. When handling pressurised liquids and sources of liquid under pressure one should be especially cautious.We tend to think that liquids are soft and ignore the strength of a liquid jet. The following accident illustrates that kind of hazard. Recently one of my colleagues was trying to unpack a silica column. After taking off the metal frit that closed the column, he connected the pump, started pumping isooctane at a high flow-rate and waited. Nothing happened, the solvent percolating gently through the column.In trying t o scratch some silica out with a small wire, the chemist triggered off the rapid expulsion of all of the silica and received a powerful jet of silica and solvent on the thumb and the side of the hand. It was a slightly painful slap, but he just washed his hand and nobody else in the laboratory noticed anything . In the evening the hand was painful and the chemist could not sleep.In the morning his thumb and hand were swollen, so he went to hospital where he was given a pain killer and an appointment with a specialist for the following day. By now the hand was very painful, very swollen and discoloured. Surgery was decided on, firstly to cut off the necrosed tissues, and then to graft skin over the wound.After two weeks of care in the hospital my colleague is back in his laboratory, healthy but more cautious. It seems that the penetration of a significant amount of isooctane, a non-toxic solvent, under the effect of the shock and not the shock itself, is responsible for the necrosis of skin tissues. Consider what could happen with a toxic solvent such as chloroform, acetonitrile or methanol or with the benzene - carbon tetra- chloride mixtures used for column packing ! To the local troubles of skin necrosis could be added general poisoning.360 PUBLICATIONS RECEIVED Proc. A izalyt. Dir. Chcvz. SOC. possible jets of solvents under high pressure. Chromatographers should be concerned about G. Guiochon Ecole Polvteclanique, Labovatoivc de Chintie A nalytiqtte Ph+iqzte, Rte. de Saclay, 91 128 Palaisrau Cedex, Framc

ISSN:0306-1396    

DOI:10.1039/AD9791600359

出版商:RSC    

年代:1979

数据来源: RSC