摘要:

Proceedings of the Society for Analytical Chemistry CONTENTS Proc. SOC. Analyt. Chem. Vol. 4 No. 10 Pages 151-166 Reports of Meetings . . .. 151 Chemistry " . . .. 153 "Research Topics in Analytical Membership changes . . .. 165 Papers Accepted for The Analyst I65 Publications Received . . .. 165 Notices . . .. .. .. 166 Forthcoming Meetings . . Back cover October 1967 Vol. 4 No. 10 October I967 PROCEEDINGS THE SOCIETY FOR ANALYTICAL CHEMISTRY OF President of the Society A. G. Jones Hon. Secretory of the Society S. A. Price Hon. Treasurer of the Society G. W. C. Milner Hon. Assistant Secretaries of the Society W. H. C. Shaw D. W. Wilson Secretary Miss P. E. Hutchinson 9/10 SAVILE ROW LONDON W.1 Telephone 01-734 6205 Editor J. B. Attrill Telephone 01-734 3419 Proceedings is published by The Society for Analytical Chemistry and distributed to members and all subscribers t o The Analyst without charge Single copies may be obtained direct from the Secretary The Society for Analytical Chemistry at the above address (NOT through Trade Agents) price 2s.6d. post free. Remittances payable t o “Society for Analytical Chemistry” MUST accompany orders Determination of Trace Elements with Special Reference t o Fertilisers and Feeding Stuffs A Report of the Analytical Methods Committee Recommended methods for determining traces of- B Ca CI- Cr Co Cu F I Fe Mg Mn Mo Ni Se Zn Pp. viii + 39 21s. net Members of the Society for Analytical Chemistry are entitled t o buy copies a t the special Members’ price of 12s. 6d. provided they order direct from The Society for Analytical Chemistry Book Department 9/10 Savile Row London W. I Remittances made out t o “Society for Analytical Chemistry” must accompany Members’ orders Published for the Society for Analytical Chemistry W. HEFFER AND SONS LTD. PETTY CURY CAMBRIDGE by

ISSN:0037-9697    

DOI:10.1039/SA96704FX033

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

THE SOCIETY FOR ANALYTICAL CHEMISTRY Tuesday 21st EASTHAM Tuesday 2 1st 1,OK IION Forthcoming Meetings (continued) Thursday 16th “Automatic pH Control in the Fermentation Industry,” by B. IT. Francis “Automated Analysis in 13rewing,” by J . R. Hudson. Wellcome Building Euston Road London N.W. 1 ; 3 p.m. THERMAL ANALYSIS GROUP Annual General Meeting followed by the Address I>oKno;\; of the Retiring Chairman. “Differential Thermal Analysis-TZ’hence and Whither?” by R. C. Mackenzie Ph.D. D.Sc. F.R.I.C. F.G.S. F.R.S.E. Geological Society Burlington House London W. 1 ; 6 p.m. RADIOCHEMICAL ~/IETHODS GROUP Annual General Meeting followed by an “Application of Isotope Sources in Analytical Chemistry,” by P. G. Jeffery “Isotopic Radiation Sources for X-ray Analysis,” by K. H. Ansell B.Sc.Ph.1). “Bremsstrahlung Methods in Industry,” by J . Johnston. Lecture Theatre Pharmaceutical Society of Great Britain 17 Bloomsbury Square London W.C.1; 6 p.m. KORTH OF ENGLAND SECTIOK jointly witlt the Carlett Park Chemical and Physical Society. “liecent Developments and Applications of Liquid Chromatography,” by R. P. W. Scott. Carlett Park Central College of Further Education Eastham TYirral Cheshire ; 6.30 p.m. SPECIAL TECHKIQUES GROUP Annual General Meeting follolved by the Address of the Retiring Chairman. “Advances in Electrophoresis,” by G. F. Keynolds bl.Sc. Ph.D. F.R.S.H. M.I.T.E. F.R.I.C. Royal Astronomical Society Burlington House London TI-. 1 ; 7 p.m. LONDON and A. Diggens. Friday 17th Monday 20th r,OsnOK Ordinary Meeting. M.Sc. Ph.D. D.I.C. A.R.C.S. F.R.I.C. Tuesday 28th PARTICLE SIZE ANALYSIS GROUP Annual General Meeting followed by a LOSUOX meeting on “Light Scattering Methods.” Speakers R.H. Ottewill and 13. H. h-apper. Physics Lecture Theatre Imperial College London S.1T5‘.7 ; 6.30 p.m. Wednesday 29th THIN-LAYER CHROMATOGRAPHY GROUP A4nnual General Rleeting followed L O s u 0 ix by an Ordinary Meeting. Speakers P. E. Macey D. F. G. Pusey and \Ir. E. Rupprecht. Borough Polytechnic London S.E. 1 ; 2.30 p.m. XORTH EAST SECTION jointly with the Tees-side Section of the Royal Institute “The Analysis of New Metals,” by W. T. Elwell F.R.I.C. Constantine College of Technology Middlesbrough ; 8 p.m. Thursday 30th ~~III)DLESBROUGH of Chemistry. THIRD POLISH ANALYTICAL CONFERENCE WARSAW POLAND SEPTEMBER ~ O T H TO 1 5 ~ ~ 1968 THE Third Polish Analytical Conference organised by the Commission of Analytical Chemistry of Polish Academy of Sciences under the auspices of the International Union of Pure and Applied Chemistry will be held in Warsaw Poland from September 10th to 15th 1968.The main topics will be basic problems of analytical chemistry new reagents new reactions ionic equilibria accuracy and precision etc. ; analytical methods in inorganic industry ; analytical methods in organic industry; and techniques of analytical chemistry new apparatus automation standards sampling etc. The final date for sending abstracts of papers to be read at the conference is January 15th 1968. Information may be obtained from the Secretary of the Organising Committee Dr. Adam Hulanicki Warszawa 22 ul. Pasteura 1 Poland. THE SOCIETY FOR ANALYTICAL CHEMISTRY Forthcoming Meetings October Thursday 26th EAST KILBRIDE November Tuesday 7th COLCHESTER Friday 10th YORK Tuesday 14th COVENTRY Tuesday 14th SHEFFIELD Wednesday 15th HARWELL Thursday 16th BRIDGEND Thursday 16th LONDON SCOTTISH SECTION and RADIOCHEMICAL METHODS GROUP.Opening address by Professor H. W. Wilson B.Sc. Ph.D. F.Inst.P. F.K.S.E. “Some Feasibility Studies of the Applications of Thermal Neutron Capture “Activation Analysis in Forensic Science,” by H. Smith B.Sc. Ph.D. “The Absolute Measurement of Radioactive Nuclides and the Provision of “Surface Kadiochemistry,” by S. J. Thomson B.Sc. Ph.D. The meeting will include a tour of the Scottish Research Reactor Centre and Scottish Research Reactor Centre East Kilbride; 10 a.m. Gamma-ray Analysis,” by J .R. Whitley B.Sc. Ph.D. Standards,” by A. McXair. on F d u y 27th a visit to Xuclear Enterprises Ltd. Edinburgh. SOCIETY Inauguration of East Anglia Section. “Nuclear Methods in Trace Element Analysis,” by A. A. Smales O.B.E. “Absorption Spectrophotometry and Fluorimetry,” by Professor T. S. West University of Essex Wivenhoe Park Colchester ; 3.30 p.m. NORTH OF ENGLAND and h T ~ ~ ~ ~ EAST SECTIONS on “The Analysis of Milk Rowntree & Co. Ltd. York; 2 p.m. MIDLANDS SECTION. “Organic Polarography,” by P. 0. Kane. Lanchester College of Technology Priory Street Coventry; 7 p.m. ATOMIC-ABSORPTION SPECTROSCOPY GROUP joiu2tZ-y witlh the Modern Methods of Analysis Group of the Sheffield Metallurgical and Engineering Association on “Uses of Atomic-absorption Spectroscopy.” I).Sc. F.R.I.C.D.Sc. Ph.D. F.R.I.C. Chocolate and Sugar Confectionery.” Speakers R. J . W. Powell P. Scholes and K. A. Stewart. New Lecture Theatre B.I.S.R.A. Sheffield; 7 p.m. SOCIETY Meeting on “So me Aspects of Inorganic Trace Element Analysis.” “Recent Advances in Applications of Mass Spectrometry to Analysis,” by “The Use of Lasers in Spectrochemical Analysis,” by RI. S. W. Webb “Recent Advances in Neutron-activation Analysis,” by D. Mapper B.Sc. “Gamma-activation Analysis,” by C. A. Baker B.A. D.Phil. “Activation Analysis with Fast Neutrons and Charged Particles,” by T. B. The meeting will include a tour of the laboratories and nuclear reactor Atomic Energy Research Establishment Harwell Didcot ; 10.15 a.m. WESTERN SECTION. “The Work of a Public Analyst,” by L. E. Coles B.Pharm. Ph.D. F.P.S. Engineering Lecture Theatre Bridgend Technical College Bridgend ; 4.30 p.m. AUTOMATIC METHODS GROUP Annual General Meeting followed by a meeting “The Automatic Determination of Alcohol in Fermented Beverages,” by [continued inside back covey R. K. Webster B.A. D. Phil. B.Pharm. F.P.S. F.R.I.C. Pierce M.A. D.Phi1. (BEPO). F.R.I.C. on “Automatic Methods in the Fermentation Industry.” R. Sawyer and E. J. Dixon. Printed by W Heffer & Sons Ltd Cambridge England

ISSN:0037-9697    

DOI:10.1039/SA96704BX035

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

October I967 PROCEEDINGS OF THE SOCIETY Vol. 4 No. 10 FOR ANALYTICAL CHEMISTRY Reports of Meetings SOCIETY MEETING AN Ordinary Meeting of the Society was held at 7 p.m. on Wednesday October 4th 1967 in the Department of Mechanical Engineering Imperial College London S. W.7. The Chair was taken by the President Mr. A. G. Jones B.Sc. F.R.I.C. A lecture on “Some New Reagents and Reactions in Analytical Chemistry” was given by Professor R. Belcher Ph.D. DSc. F.R.I.C. F.1nst.F. SCOTTISH SECTIOK AN Ordinary Meeting of the Section was held at 10 a.m. on Tuesday September 12th 1967 in the College of Technology High Street Paisley. The Chair was taken by the Chairman of the Section Mr. J. W. Murfin B.Sc. F.R.I.C. The subject of the meeting was “Auxiliary Techniques in Chromatography” and the following papers were presented and discussed “Thin-layer Chromatographic Separation- spectroscopic Analysis,” by J.C. Wright B.Sc. Ph.D. ; “Gel Permeation Chromatography,” by R. L. Fenwick B.Sc.; “Infrared and Mass Spectra of Column Eluents by Stop - Start Chromatography,” by T. Wilkins B.Sc. ; “Investigation into the Separation of Organic Chelates of Metals by Column Chromatography,” by D. A. Pantony T.D. B.Sc. Ph.D. A.R.C.S. F.R.I.C. ; “Techniques and Applications of Gas Chromatography - Mass Spectro- scopy,” by G. Eglinton B.Sc. Ph.D. and A. McCormick B.Sc. Ph.D. WESTERN SECTION A JOINT Meeting of the Section with the Cardiff and District Sections of the Royal Institute of Chemistry and the Society of Chemical Industry was held at 7 p.m. on Friday September 22nd 1967 at the University College Cardiff.The Chair was taken by the Chairman of the South Wales Section of the Society for Chemical Industry Mr. P. J. C .Haywood BSc. F.R.I.C. A JOINT Meeting of the Section with the Bristol Sections of the Royal Institute of Chemistry and the Society of Chemical Industry was held at 6.30 p.m. on Thursday September 28th 1967 at the University Bristol. The Chair was taken by the Chairman of the Bristol Section of the Royal Institute of Chemistry Dr. D. Woodcock D.Sc. F.R.I.C. A lecture on “Recent Applications of Infrared Spectroscopy” was given by H. E. Hallam M.Sc. Ph.D. A lecture on “The Work of the Alkali Inspectorate,” was given by J. C. Peabody B.Sc. MIDLANDS SECTION AND AUTOMATIC METHODS GROUP A JOIKT Meeting of the Midlands Section and Automatic Methods Group with the Midlands Section of the Royal Institute of Chemistry and the Birmingham and Midlands Section of the Society of Chemical Industry was held at 3 p.m.on Wednesday September 20th 1967 in the Large Physics Lecture Theatre Poynting Building The University Edgbaston Birming- ham 15. The Chair was taken by the Chairman of the Midlands Section Mr. H. E. Brookes B.Sc. F.R.I.C. The subject of the meeting was “Automation in Analysis,” and the following papers were presented and discussed “Critical Analysis in Process Optimisation,” by H. E. Stagg B.Sc. F.R.I.C.; “Unique Automatic Continuous Flow Analysis,” by H. W. Holy B.Sc. 151 152 REPORTS OF MEETINGS [P~oc. SOC. Aqzalyt. Clzenz. Ph.D. ; “Some Industrial Uses of the Technicon AutoAnalyzer,” by S. Greenfield L.I.M. M.Clift A.R.I.C.and T. P. Sutton; “New Approach to Automation in Clinical Laboratories,” b y M. H. Jones B.Sc.; “Automatic Analysis Applied to Automatic Process Control,” by G. 1’. R. Mattock B.Sc. Ph.D. F.R.I.C. MIDLANDS SECTION AND PARTICLE SIZE ANALYSIS GROUP A JOIST Meeting of the Midlands Section and Particle Size Analysis Group was held a t 2.30 p.m. on Tuesday October 3rd 1967 at Loughborough Vniversity of Technology Loughborough. The Chair was taken by the Chairman of the Midlands Section Mr. H. E. Brookes B.Sc. F.R.I.C. The subject of the meeting was “On-stream Methods of Particle-size Analysis” and the following papers were presented and discussed “Methods for the Continuous Determination of Particle-size Distributions,” by A. S. Joy B.Sc. A.M.I.M.M. F.R.I.C. C.Eng. ; “On-stream Analysis of Particle-size Distributions,” by A.B. Holland-Batt B.Sc. (Eng.) A.R.S.M.; “On-stream Particle-size Analysis,” by G. Treasure B.Sc. Grad.Inst .P. and Mrs. M. Warren L.K.I.C. NORTH EAST SECTION AN Ordinary Meeting of the Section was held at 6.30 p.m. on Thursday September 14th 1967 in Sunderland Technical College Sunderland. The Chair was taken by the Chairman of the Section Mr. F. C. Shenton F.R.I.C. A.R.T.C.S. The subject of the meeting was “Pesticide Residues” and the following papers were presented and discussed “History Alternatives and Methods of Analysis,” by J. Thomson Ph.D. LA.H.-W.C.; “Pesticides in Food Rain Air Eggs,” by J. O’G. Tatton M.Sc. F.R.I.C. MICROCHEMICAL METHODS ASD SPECIAL TECHNIQUES GROUPS A JOINT Meeting of the Microchemical Methods and Special Techniques Groups was held on Frida3- and Saturday September 22nd and 23rd 1967 at the University of East Anglia Korwich.The subject of the meeting was “Molecular Spectroscopy in Microanalysis.” A4t the Scientific Session on Friday the Chair was taken by the Chairman of the Micro- chemical Methods Group Mr. T. R. F. W. Fennell B.A. and the following papers were presented and discussed “Steric Requirements of Lone Pairs and Conformational Analysis,” by Professor A. R. Katritsky M.A. B.Sc. D.Phil. Ph.D. Sc.D.; “Microwave Spectroscopy and its Potentialities for Analysis,” by Professor D. J. Millen Ph.D. D.Sc. -4t the Scientific Session on Saturday the Chair was taken by the Chairman of the Special Techniques Group Dr. G. IT. Reynolds F.R.S.H. M.I.T.E.. F.R.I.C. and the following papers were presented and discussed “The Scope and Limitations of Low Resolution Mass Spectroscopy in Organic Analysis,” by A.R. Philpotts M.A. and G. Gough M.A.; “The Direct Spectroscopic Measurement of Microgram Quantities in Thin-layer Chromatography,” by A. C. Parker M.A.; “Some Computer Techniques in Spectroscopic Analysis,” by G. E. Hall R.A. Ph.D. ; “The Development of Michelson Interferometers for Far Infrared Spectro- scopy,” by G. W. Chantry &LA. D.Phil. The meeting also included a visit to J. & J. Colman Ltd. Carrow Works Norwich a tour of the University of East Anglia at which a lecture on the concepts of the University was given and a Discussion Meeting on “Molecular Spectroscopy and Microanalysis,” introduced by G. F. Reynolds M.Sc. Ph.D. F.R.S.H. M.I.T.E. F.R.I.C. THIN-LAYER CHROMATOGRAPHY GROUP AN Ordinary Meeting of the Group was held at 2.30 p.m. on Wednesday September 27th 1967 at Ipswich Civic College Rope Walk Ipswich. The Chair was taken by the Chairman of the Group Mr. J. D. R. Thomas M.Sc. F.R.I.C. The subject of the meeting was “Thin-layer Chromatography Applied to Foods and Related Compounds” and the following papers were presented and discussed “High-voltage Paper Electrophoresis of Sugars A Comparison with Thin-layer chromatography,” by D. Gross Ph.D. ; “The Place of Thin-layer Chromatography in Residue Determination,” by J. Thomson Ph.D. A.H.-W.C. A.R.I.C.; “Thin-layer Chromatography of Some Food Addi- tives,” by G. J. Dicltes A.R.I.C.

ISSN:0037-9697    

DOI:10.1039/SA9670400151

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

October 19671 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY 153 Research Topics in Analytical Chemistry Some Current Work in Universities and Colleges of Advanced Technology The following arc summaries of some of the papers presented at an Ordinary Meeting of the Society held on May 3rd 1967 and reported in the May issue of Proceedkgs (p. 71). Analysis through Ligand-exchange Kinetics J. M. CARTER AND G. NICKLESS (De$avtnzent of Iyzovganic Chemistry School of Chemistry The Univevsity Bristol 8) THE methods of trace analysis commonly used in industry such as absorption spectrophoto- metry polarography and flame spectroscopy have limiting concentrations at about the M level. In all cases the concentration limits i.e. the minimum concentration detectable will refer to the final solution. Because of this general limit it was decided to try a relatively new approach by investigating methods based on catalysis of metal - chelate exchange reactions by traces of metals.A method has been devised based on the catalysis of reactions of the type M + M’Y + M’ + MY where M and 111’ are two different metals and Y is an anionic form of EDTA. exchange reactions i.e. X + MY + Y + MX where X is the anionic form of another complexing agent. Since the late 1940’s or early 1950’s there have been several isolated papers on this type of reaction and the associated kinetics. The only systematic and qualitative investigations have been made by Margerum et al. who have published a series of papers beginning in 1958. There have been no reported analytical applications of metal-exchange reactions although Margerum and Steinhaus (Aizalyt.Chem. 1965,37,222) published a method based upon catalysis with traces of EDTA of the reaction CuY + Ni triethylenetetramine + NiY + Cu triethylenetetramine. The study of such reactions has not been nearly as extensive as work on the ligand- In this method the trace metal reacts with a known amount of EDTA and the excess of EDTA is determined by catalysis of the above reaction. Measurements down to the lo-* M level were reported and it was predicted that the method should be suitable for measurements down to 10-10 M. We attempted to repeat this work at Bristol to gain experience in this field but found that significant results were obtained only down to the lo-’ M level. The lack of success with this method led us to look at metal-exchange reactions as a possible basis for an analytical method.The source of information was Margerum (Inorg. Chew. 1962 1 852) and it was found that the reaction Zn + NiY + ZnY + Ni is catalysed by traces of copper ions as low as Margerum used high concentrations of reagents as he was following the reaction spectrophotometrically and the species have low absorption coefficients. Our idea was to use a cathode-ray oscilloscope polarograph to follow the reaction as we thought it might be possible to determine ultra-trace amounts of copper by following reactions at the or M level. Unfortunately the reaction between zinc and nickel - EDTA cannot be followed polarographically as the half-wave potentials are very close (for zinc -1.06 and nickel -1.09 volts versus the S.C.E. in neutral or acidic solutions).Thus the attack of other metals on nickel - EDTA was investigated. Pb + NiY + PbY + Ni was found to be most suitable. The half-wave potential for lead is -0-46 volt (versus S.C.E.) the stability constant for lead - EDTA (18.0) is close to that of the nickel - EDTA (18.6) and M. The reaction 154 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY [PYOC. SOC. AfiaZyyt. Chem. the reaction is catalysed by traces of copper. The above reaction is very slow while the reactions Cu + NiY + CuY + Ni Pb + CuY + PbY + Cu and are relatively fast and therefore catalysis appears to take place. The rate of reaction is proportional to the amount of copper present and a typical calibra- tion graph is given in Fig 1. One millilitre of 5 M potassium nitrate solution and 1.00 ml of 0.1 M lead perchlorate were transferred by pipette into a 100-ml beaker and the mixture was diluted to about 40ml with de-ionised water.The pH was then adjusted to about 4.8 with dilute nitric acid or potassium hydroxide solution 1.00 ml of nickel - EDTA solution was added and the pH adjusted to exactly 4.5. The solution was diluted to 50 ml with distilled water. The solution was then allowed to react in a thermostatically controlled water-bath at 80" C and 5 to 10-ml samples were taken after 0 25 50 75 and 100 minutes. The nickel content was measured on a Davis cathode-ray oscilloscope polarograph. From these results the rate constant was calculated as usual. The potassium nitrate acts as a supporting electrolyte for polarographic measurements and as an ionic-strength buffer for the reaction.The various factors influencing the reaction have been investigated to find the optimum analytical conditions. The calibration is obtained as follows. Concentration of copper M x I O ~ Fig. 1. Calibration graph for copper I I I I t 65 70 7s 80 60 Temperature " C Fig. 2. Graph of temperature uevsus rate of reaction for the reaction between lead and nickel - EDTA TEMPERATURE- Fig. 2 depicts the effect of temperature on reaction rate over the range 60" to 80" C for 2 x It can be seen that the temperature coefficient is about 2.7 per 10" C. The reaction needs to be fairly rapid to keep the time of analysis as low as possible and 80°C was taken as the highest practical value. M reactants. CONCENTRATION OF REACTANTS- The concentration of the reactants must be kept as low as possible to make the limit of detec- tion as low as possible.However a compromise must be made as the reaction rate decreases with decreasing reactant concentrations. The optimum value was decided as 2 x 1 0 - 4 ~ because a t this concentration the rate constant can be determined accurately in 100 minutes. If time is no problem lower concentrations can be used to increase sensitivity but the polaro- graph must be used at full sensitivity and the calibration graphs are not as good. October 19671 RESEARCH TOPICS I N ANALYTICAL CHEMISTRY 155 The effect of pH on reactions of the type M + M’Y + M‘ + MY is illustrated by the graph given in Fig. 3. The rapid increase in reaction rate as the pH decreases is due to the reaction going predominantly via an S.E. 1 course instead of an S.E. 2 course i.e.dissociation is taking place followed by the reaction As this type of reaction is not desired pH 4.8 was decided upon. PH- M’Y + M’ + Y Y + M + MY. PH Fig. 3. Graph of pH vcysus rate of reaction for the reaction between lead and nickel - EDTA Ionic strength x lo2 Fig. 4. Graph of ionic strength ucysus rate of reaction for the reaction between lead and nickel - EDTA IONIC STRENGTH- It can be seen that an increase in ionic strength decreases the reaction rate. However an ionic strength of 0.1 M was chosen because the rate of change of reaction is lowest at this level and it is necessary to have a fairly high ionic strength as sample preparation will probably involve addition of electrolytes. Vnder these conditions the limit of detection is 5 x 10-8 M taking a 5 per cent. change in reaction rate as the minimum that can be recognised (Fig.1). The interference of other metals on the method has been investigated (see Table 1). Other metal ions can interfere in several ways. (i) They can catalyse the reaction in the same way as copper. The only definite example of this is the mercury(I1) ion. The noble metals palladium platinum and gold also produce a catalytic effect but this is probably due to their displacing the mercury(I1) ion from the mercury electrodes. Obviously such metals must be removed from a sample before the copper content can be determined. (ii) They can interfere polarographically i.e. produce a peak or background in the region of the nickel peak. Examples are arsenic antimony and tin. Fortunately most metals form weaker complexes with EDTA than lead or nickel and therefore if present only at the level of the reactants cause little interference.The only common metal ions with stronger complexes are mercury(II) iron(II1) and cobalt (111). (iv) Interference from lead or nickel is obvious and about 1 x l o - 5 ~ is the highest concentration of either that can be tolerated. Sample treatment must therefore include the removal of any major metal constituent and traces of mercury and the noble metals. An ion-exchange procedure has been developed to remove the latter. All of the metal ions in the sample are first absorbed on a column of D o ~ e x - l x 10 200 to 400-mesh resin and the column is eluted with 5 ml of M nitric acid The effect of ionic strength on the rate of reaction is shown in Fig. 4. The level of interference varies for different interfering metals.(iii) They can contribute to the attack on the nickel - EDTA. 156 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY iP1foc. SOC. AYtaZyt. Chem. followed by 20 ml of de-ionised water. To the column effluent 5 ml of M potassium hydroxide are added and the copper is determined in the manner previously described. The nitric acid removes the copper(I1) while mercury(I1) and the noble metals are retained by the column This separation was developed from the method reported by O’Connor Weiner and Rubin (Analyt. Chem. 1964,36 1157) in which the nitric acid distribution curves for about 70 metals are given. Ion-exchange resins that are specific for copper have been reported (2. analyt. Chem. 1964,202,321) but are not yet readily available and therefore we have not been able to use them.TABLE I INTERFERENCE OF OTHER METAL IONS Concentrations quoted produce a 5 per cent. change in reaction rate. Concentration Metal 1 x 1 0 - 7 ~ Mercury (I I) Platinum Palladium 1 X 1 0 - 6 M Bismuth( 111) Arsenic (I I I) ‘1 Antimony Tin(I1) I Comments Reacts as for copper. Displace mercury(I1) from dropping-mercury electrodes. Produce polarographic background slope i n region of nickel reduction in wave. Iron(II1) Cobalt (11) Manganese(I1) Silver (I) Thorium (IV) Vanadium Uranium Beryllium A1 uminium Chromium Gives a peak a t about - 0.95 volt. 1 x 1 0 - 4 ~ Cadmium Cerium Lithium Zinc Barium Reduce the rate of Strontium reaction. Magnesium Gives a wave a t - 1.02 volts. 1 x 10-*M The method as yet has only been carried out with distilled water. Various amounts of copper were added to l-litre portions of de-ionised water and the method was applied to the samples produced.Similar samples were finished by measuring the copper polarographic- ally and by measuring the colour produced with zinc - diethyldithiocarbamate. The results of these experiments are shown in Table 11. TABLE I1 COMPARISON OF THE KINETIC METHOD FOR COPPER WITH THE ZINC - DIBENZYLDITHIOCARBAMATE AND THE DIRECT POLAROGRAPHIC METHODS WITH 1 LITRE O F DISTILLED \VATER Copper recovered per cent. by Concentration I A > pg per litre Kinetic method Polarographic method carbamate method of copper added Zinc - dibenzyldithio- 0-2 0-5 1.0 2.0 91 90 105 94 Not detectable 75 96 98 92 92 98 98 It can be seen that the kinetic method is not as good as conventional methods a t the higher concentrations but is a t lower levels.This is encouraging but at present the method will find few practical applications because of the length of time for analysis and the high October 19671 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY 157 degree of operator technique required as compared with the comparison methods or other trace techniques. However if the method could be made to work satisfactorily with 2 x 10-5 M reactants the increase in sensitivity obtained would outweigh these disadvantages. In conclusion it should be remembered that this reaction was discovered only by chance and therefore more suitable analytical reactions proSably exist. Before any predictions in this direction can be made a comprehensive study of metal - ligand exchange reactions must be made for a wide range of ligands and metals.A study of the mechanism of the reactions is also required. Such investigations are now under way at Bristol but because of the size of the task the present work can only be regarded as preliminary. Heterocyclic Selenium as a Ligand in Transition-metal Complexes BY D. GRIFFIN AND r,. S. BARK (Depavtment of Chemistfly and .4pplied Claenzistvy Royal College of Advanced Technology Salfovd Lmicnshire) IN order to find organic reagents that are highly selective for some of the platinum metals systems containing the bidentate grouping ,Se...C...C,TV. . . in which the selenium is part of a heterocyclic ring are being studied. Following the work by L. S. Bark and D. Brandon (Talanta in the press) on 2(-2 pyridy1)- 1-selenaphthene I as an organic reagent for palladium a simpler organic compound con- taining this grouping vix selenophene-2-aldoxime 11 has been studied by L.s. Bark and D. Griffin (Analyst 1967 92 162). I HO I t is known that the most stable complexes are formed when the chelate-ring system contains 5 or 6 atoms including the metal and for greatest stability of such a chelate ring we require maximum overlap of ligand and metal orbitals; the optimum distance between the two ligand atoms for the particular metal being chelated; and de-localisation of electron density around the metal. In selenophene and related compounds the selenium atoms form 0 bonds with the carbon atoms by using two sP2 hybridised orbitals. The third sp2 of the selenium is a1-ailable for CT bonding with the metal. The aromaticity of the selenophene arises from the formation of the 7~ bonds between carbon and selenium the carbon using p orbitals and the selenium using pd2 hybridised orbitals.Only two of these are used the vacant $d2 orbital of the selenium is in the same direction as the selenium-to-metal bond but in a plane at right angles to that of the heterocyclic ring. This orbital is well placed to form r bonds with the d, orbitals of the metal and hence some de-localisation of electron density leading to greater bond stability will occur. Selenophene-2-aldoxime was found to react quantitatively with palladium in hydro- chloric acid solutions and an addition complex of empirical formula Pd(C,H,NOSe),Cl, was formed. The complex was analysed for carbon hydrogen nitrogen palladium selenium and chlorine. The palladium was determined by atomic-absorption spectrophotometrv on a solution of the complex that had previously been decomposed by wet oxidation with a mixture of nitric and perchloric acids.A fresh sample was decomposed by the oxygen-flask technique and the solution from this was analysed for selenium by iodimetric titration and for chloride by coulometric titration. The infrared spectrum of this complex showed that strong hydrogen bonding is present and in the structure we propose 111 such hydrogen I11 158 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY [Proc. SOC. Analyt. Chem. bonding will occur between the chlorine and oximino hydrogen atoms forming two extra chelate rings thus increasing the stability of the complex. The chemical and spectral properties of this complex and those of the analogous nitrogen oxygen and sulphur complexes were compared and a structure for the palladium - selenophene-2- aldoxime complex IV in which a Pd-Se bond occurred was postulated.A neutral chelate complex with empirical formula Pd(C,H,NOSe), was also prepared. Pd IV When the neutral palladium chelate was refluxed with excess of reagent in chloroform solution a new complex of empirical formula Pd(C,oH,,N4Se4) was formed. This proved to be a tetrakis complex in which the palladium is bonded only to the nitrogen of 4 oxime molecules. Other substituted selenophene-2-aldoxime derivatives including the 2,5-di-aldoxime in which there is the possibility of a tridentate ligand are being studied. An Investigation of the Analytical Potentialities of the Phototropic Effect BY D. H. CHRISTOPHER AND T.S. WEST (Chemistry Department Imperial College London S. W.7) PHOTOTROPISM may be defined as the phenomenon by which a system undergoes reversible changes in its spectral absorption characteristics on exposure to ultraviolet or visible light. In the absence of activating irradiation the phototropic system exists in a dark stable form with a characteristic absorption spectrum. On exposure to light of a suitable wavelength a n equilibrium between the reactant and the unstable photo-product is established character- ised by an “equilibrium” absorption spectrum. The dark stable state may be regenerated photochemically by alteration of the wavelength of irradiation or in the absence of light b y a thermal process. The phototropic compounds of analytical interest are those that exhibit the effect in solution at normal temperatures and of which one or both of the photo-sensitive forms are highly coloured.There are several factors that determine the position of phototropic equilibrium in solution ; viz. the wavelength and intensity of irradiation the solvent the nature and concentration of the solute and the solution temperature. Consequently any analytical investigation of the effect requires carefully controlled conditions of irradiation and absorption measurement. Two methods have been developed whereby the spectra of solutions containing large and reproducible amounts of the photo-product can be examined. About 90 ml of sample is circulated in the closed circuit by the peristaltic pump P. Filtered light from the source S enters the irradia- tion cell C, and the absorbance spectrum of the resultant solution is followed at the cuvette C, contained in the cell compartment of a recording spectrophotometer.By this means the photo-induced changes can be measured immediately after irradiation. The cell C, is a quartz cylinder 8 cm long and contains over 90 per cent. of the sample at any one time. It is coated with aluminium on the sides and the remote end to ensure maximum light absorption Fig. 1 illustrates a “flow-through” technique. October 19671 RESEARCH TOPICS I N ANALYTICAL CHEMISTRY 159 F S = Source F= Filter C,= Cuvette C,= Irradiation cell P= Peristaltic pump Fig. 1. Arrangement for “flow- through” irradiation - absorption technique and is housed in a cooling jacket that maintains a temperature of 25” 1” C. The side- arm illustrated is used to drain and fill the circuit to minimise pressure fluctuations during pumping and to de-gas the solutions.It is graduated to ensure constant sample volume. Connections are made with nylon-66 tubing and fluorosilicone and silicone rubber tubing are used in the pump. The entire system is blacked out to eliminate extraneous effects from laboratory lighting. Here light from the source S is focused into a diffraction-grating monochromator M. The emergent monochromatic beam passes through the quartz lenses L and L, and a wide collimated beam of light is incident at the two cuvettes C and C, housed within the spectrophotometer. The following Fig. 2 illustrates a direct irradiation-measurement technique. S=Source M= Diffraction grating Fig. 2 L, L and L,=Quartz lenses C and C,=Cuvettes monochromator Arrangement for direct irradiation - absorption 160 [Pvoc.SOC. ,-1 naljlt. Chewz. precautions were necessary to eliminate interference of the activating beam with the monitor- ing beams from the spectrophotometer source. (i) The cuvettes are optically polished on the four sides and C is silvered on the remote (ii) The cell holder is of special design incorporating knife-edge slits through which the (iii) The height and lateral position of the source S and the position of the plano - convex optic L, are adjustable. (The mirrored cuvette results in the formation of an image of the monochromator exit slit at the slit when the optical alignment is correct.) Diffraction a t the knife-edge slits results in a sluggish recorder response but this is readily compensated for by reduction of the spectral scanning speed.The collimator is telescoped to facilitate access to the cell compartment. The above techniques have been used to examine the cis - trans photo-isomerisation of aromatic azo compounds. Hydroxyl groups adjacent to the azo-bond prevent the photo-isomerisation because of hydrogen bonding between the hydroxyl group and the P-nitrogen. Azo compounds containing hydroxyl groups in the @a or more remote positions have very unstable cis-isomers. This instability increases markedly with solvent polarity and such compounds show no phototropic effect under the conditions used in polar solvents. Methylation of the hydroxyl groups yields compounds that are strongly phototropic in all solvents and are characterised by xw-y slow rates of thermal reversal.RESEARCH TOPICS IN ANALYTICAL CHEMISTRY side to reduce light scatter in the cell compartment. monitoring beams pass. The behaviour of hydroxyazo compounds is of interest. trans The effects of complexation rather than methylation of the hydroxyl groups in azo compounds containing suitable cation-complexing centres are currently under examination to determine the possibilities of non-phototropic reagents yielding phototropic complexes. The gallium complex of the non-phototropic reagent sulphenazoxine the beryllium and iron(II1) complexes of C.I. Direct red 37 and the iron(II1) complex of the azo dyestuff Brilliant Crocein have been shown to exhibit the phototropic effect. We are grateful to I.C.I. (Agricultural Division) for the provision of a research grant and to the Science Research Council for a grant for the purchase of apparatus.Thanks are also given to M. Cresser of this department who assisted with some of the experimental work. The Determination of Metal Ions by a Catalytic Reaction BY D. MEALOR Defiavtment of Chemistvy The University Edgbaston Birmingham 15) THE effect of nickel ions on the formate -alkaline permanganate reaction leading to the development of a method for the determination of nickel based on the decomposition of permanganage in alkaline solution is described. The reactions of alkaline permanganate that lead to the formation of manganate can be followed spectrophotometrically at 505 nm (disappearance of permanganate) or at 600 nin (appearance of manganate). In alkaline solution formate reduces permanganate to manganate 2Mn0,- + HCOO- + 30H-+ 2Mn0,2- + COS2- + 2H20.Further reaction of manganate with formate is negligible. When small amounts of nickel are added to this system there is not continuous catalysis but only a short period of catalysis October 19673 RESEARCH TOPICS IT\; ANALYTICAL CHEMISTRY 161 at the beginning of the reaction. It is assumed that nickel is removed as an insoluble species formed with manganate. When the nickel concentration is greater than 10 p.p.m. a brown precipitate appears. Organic complexing agents that were added to try to keep the nickel in solution were rapidly oxidised. Only 1-hydroxyethylidene-1 1-diphosphonic acid (aceto- diphosphonic acid) (HO),P(O)-L-(O)P(OH),) was not oxidised and it allowed nickel to retain its catalytic activity throughout the reaction.It was found that in the presence of aceto- diphosphonic acid nickel catalysed the decomposition of permanganate at a suitable rate for the determination of traces of nickel. The initial rate of catalysed decomposition of alkaline permanganate was shown to be given by CH3 I OH d[Mn0,2-1 = k [MnO,-] [OH-]n [Ni2+]2 dt where n = 1 or 2. This can be compared with - d [MnO,-] a+ = k’ [MnO,-] [OH-] LC I/ given by Veptek-Siska V. Ettel and A. Regner (CoZZn Czech. Chem. Commun. 1961 31 1237; J . Inovg. NucZ. Chem. 1864 26 1476) for the uncatalysed reaction rate. These workers showed that when all of the impurities are removed the decomposition of alkaline per- manganate is very slow. Some of these impurities were believed to originate in the sodium hydroxide and so may have caused the reaction to appear to be second order in hydroxide.Over the range 0.0005 to 0-0032 M the reaction rate was independent of the concentration of acetodiphosphonic acid. A mechanism involving the oxidation to nickel(II1) of one of the nickel atoms in a binuclear hydroxo - nickel species was proposed to account for the second order dependence on catalyst concentration. To analyse for nickel the time taken for the reaction to occur to a fixed extent i.e. for a certain absorbance to be reached is measured. This time T is inversely proportional to [Ni2+I2. The concentration of an unknown is found from a linear calibration graph of T-l veysus [Ni2+I2. Of 34 metals tested only Ag+ Cu2+ and Co2+ catalysed the reaction in trace amounts. The relative molar amounts of these ions required for a given increase in reaction rate are Ag+ (1.0); Co2+ (8-8); Ni2+ (9.0); and Cu2+ (101) Solvent extraction as nickel - dimethylglyoximate with subsequent back extraction into dilute hydrochloric acid gives a solution suitable for analysis by the above method when all of the chloroform has been removed.This can be used to separate nickel from interferences and to concentrate more dilute solutions before determination. This method can be used to determine nickel a t concentrations of greater than 0.2 p.p.m. with a precision of 3 to 4 per cent. A paper by A. Townshend and D. Mealor describing the investigation in detail has been accepted for publication in Analytica Chimica Acta. Some Observations on Alternating Current Differential Electrolytic Potentiometry BY T. J. N. WEBBER DIFFERENTIAL electrolytic potentiometry (DEY) is a method for studying electrode processes and titrimetric reactions (AutaZyyt.Chem. 1964 36 726; 1965 37 962). It involves the observation of the potential generated between two polarised indicator electrodes immersed in the stirred test solution the polarisation being produced by the passage of a minute heavily stabilised current that is smaller than the limiting diffusion current. In extension of this work on direct current polarisation an investigation is in progress on the polarisation of metallic indicator electrodes with alternating current of various wave forms with and without d.c. bias. An examination is being made of the potentialities of this method as an analytical tool and as a source of information on electrode response and mechan- isms.The possibilities of its use in process control are also being considered because i t (Department of Chemislvy The University Exeter) 162 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY [Proc. SOC. AnaZyt. Chem. offers several advantages e.g. minimisation of electrode fouling by alternating cathodic and anodic polarisation faster response and the fact that an alternating current signal is electronic- ally simpler to handle than a direct current signal. The circuit used in similar to that for d.c. DEP except for the voltage source and the detector; for the source either a Heathkit Audio Signal Generator or a Feedback Waveform Generator TWG 300 are used. The latter provides sine square triangular and clipped triangular outputs from 0.0008 to 1200 Hz and 80 volts peak-to-peak signal.The detectors used are a pH meter and recorder for the lowest frequencies and an a.c. millivoltmeter or a measuring oscilloscope for higher frequencies. A third zero-current electrode and a calomel cell are also included so that the d.c. and a.c. voltages developed at each of the indicator electrodes can be followed as well as the mean a.c. and d.c. potentials between them. The mechanism of polarisation is basically related to the d.c. method which has been described fully by E. Bishop (in P. W. Shallis Editor “Proceedings of the SAC Conference Nottingham 1965,” W. Heffer & Sons Ltd. Cambridge 1965 p. 416). With alternating current polarisation and considering a single electrode the maximum amplitude of the voltage produced at the electrode will be equal to the d.c.differential poten- tial. For two electrodes one will be anodic while the other is cathodic and vice veysa i.e. the currents at the two electrodes will be out of phase by 180” and the potential between them will have double the amplitude of that at a single electrode. This assumes that the electrodes have time to reach the equilibrium state postulated for d.c. DEP and this is most likely with square wave and least likely with triangular or pulse operation. The output amplitude therefore decreases as electrode response speed decreases and as the applied frequency increases. The response time of polarised electrodes depends on several factors such as the nature of the electrode and electrode reaction the kinetics of the reaction under investigation the ionic strength of the medium and the impressed current density.Several redox reactions have been studied and the a.c. amplitude signal (peak-to-peak or r.m.s.) from these titrations gave the same basic forms of titration curve as for d.c. PEP i.e. type I or type I1 (AnaZyyst 1958 83 212) depending on whether the titrant or titrand were reversibly electrolysed or not. The sharpness of the titration curves was comparable with that for the d.c. method (slopes well in excess of 10,000mV per ml at 0 . 1 ~ concentrations) but the a.c. potentials equilibrated more rapidly than the d.c. potentials. Ion-combination reactions such a s silver halide titrations gave the same forms of curve as for the d.c. method. For a given peak height the a.c. current density required was higher by as much as 10- fold than that required for d.c.DEP and this requirement arises mainly from loss of response due to the electrode response speed ; supply of double layer capacitance charging currents each half-cycle ; and supply of activation energy each half-cycle. The relationship between the a.c. peak potential at the equivalence point and the applied frequency has been investigated over the range 100 to 0.01 Hz and it was found that VA max. was directly proportional to l/f4 over the range 50 to 2 Hz. ,4 comparison was made of the effects of applying a sine or a square-wave signal. A square-wave alternating supply gives the electrodes the longest time to reach equilibrium and as the charging current can occur as a pulse at the beginning of each half-cycle then an improvement over sine-wave supply should result.However it was found that for equal values of I A r.m.s. there was little difference in either the peak a.c. amplitude at the end- point or the sharpness of the titration curve between square or sine-wave input. For equal values of IA peak-to-peak there was of course an advantage with square-wave input. Work is also being directed to the examination of the effects of a d.c. bias on the applied signal which can be obtained in several ways a pure a.c. signal with a d.c. offset superimposed an a.c. signal with an amplitude bias or an a.c. signal with a mark - space bias. For example; it was found that if the applied signal had even a small amount of d.c. superimposedonit then the sharpness of the curve was considerably reduced. Depending on whether the d.c. bias was anodic or cathodic the shape of the curve became more rounded on either the rising The signal is applied to a pair of indicator electrodes in the titration solution.October 19671 RESEARCH TOPICS I N ANALYTICAL CHEMISTRY 163 or falling side and the peak potential a t the equivalence point was reduced. As the amount of d.c. was increased the peak gradually broadened into a flat top and eventually split into two peaks. Polarography of Organic Peracids BY I. W. SIDDIQI AND R. M. JOHNSON" (Department of Chemistry Chelsea College of Science and Technology Unzvevsity of London ,?.lawesa Road London S. W.3) ORGANIC peracids may be regarded as mono-acyl derivatives of hydrogen peroxide. The peroxide group is reduced polarographically and this is often used in analysis. The half- wave potential for various peroxides is dependent upon the functional groups present in the molecule and thus different classes of organic peroxides give distinct polarographic waves (e.g.peracids hydroperoxides and dialkyl peroxides). Although it is often possible to dis- tinguish between homologues within the same class (e.g. methyl ethyl and propvl hydro- peroxides) the peracids are all reduced at the same potential in media a t present investigated. An analysis of the polarographic waves of the organic peroxides shows clearly that the waves are irreversible. Little work has appeared on the polarography of organic peracids (I. W. Siddiqi and R. M. Johnson J . PoZarogr. SOC. 1966 10 78). H. Briischweiler and G. J. Minkoff (_4naLytica Chim. Acta 1955 12 186) studying the polarography of performic peracetic and perpropionic acids in 0.004 N sulphuric acid and 0.1 M lithium sulphate found that these peracids are all reduced a t half-wave potentials of +0.2 volt veyszis S.C.E.E. J. Kutta and F. W. Quacken- bush (AfiaZyt. Chem. 1960 32 1069) reported that in methanol - benzene containing lithium chloride peracetic and perbenzoic acids are reduced at zero volt. W. E. Parker C. Riccuitti C. C. Ogg and D. Swern ( J . Amer. Chem. SOC. 1955 77 4037) studied the reduction of long- chain fatty peracids in methanol - benzene containing lithium chloride and in acetic acid - sodium acetate media and found half-wave potentials from zero to -0.06 volt zwsus S.C.E. Unfortunately the waves previously reported have been incomplete consisting only of the more negative part of each. In the present investigation the media used facilitate the study of the complete polarographic waves of percaprylic percapric perlauric and permyristic acids which are easily prepared and purified.These peracids are insoluble in water and there- fore non-aqueous solvents (20 per cent. benzene in methanol or dimethylformamide) are used. Few supporting electrolytes are suitable for the peracids (i.e. soluble and having a potential range from +0.4 to -1.2 volts versus S.C.E.). Results with ammonium nitrate are reported here and experiments in which tetra-alkylammonium perchlorates are used are now in progress. After purification satisfactory polarograms are obtained for these base electrolyte solutions in the absence of peracids. All four peracids were reduced with half-wave potentials +0.23 volt veysus S.C.E.in a 0.25 M ammonium nitrate solution in a 20 per cent. benzene - methanol mixture. The diffusion current is proportional to concentration a t least up to 0-5 mM (e.g. &/C = 9.7 for percaprylic acid). The half-wave potentials of the four peracids are almost identical in this medium. Plots of log [i/(&-i)] veysus E (applied potential) and of log Kf,h against E give straight lines (i is the current flowing when the applied potential is E id is the diffusion current and kf,h is the heterogeneous rate constant for the forward electron-transfer process). The similarity of the half-wave potentials and the diffusion-current constants of the four acids in this medium is further evidence for intra- molecular hydrogen bonding previously proposed by D. Swern and L. Silbert (Analjtt.Chem. 1063 35 880) on the basis of dipole moments and infrared spectroscopy. The value 14 for ma shows clearly that = 2 ( a is the transfer coefficient and f i a is the number of electrons transferred per molecule in the rate-determining step) i.e. the rate-determining step is a 2-electron transfer in methanol - benzene in accord with the following equation. An Atlas Selector Tast-Polarograph is used. A maximum appears at this concentration. 0 0 // -*... // R-C H+2e-+R-C +OH-. \ \ / 0-0 0- * Present address Department of Food Science and Technology Borough Polytechnic London S.E.l. 164 RESEARCH TOPICS IN ANALYTICAL CHEMISTRY [Proc. SOC. Analyt. Clzem. In dimethylformamide all four peracids are reduced with half-wave potentials + 0.15 volt vcysus S.C.E. in 0 . 2 5 ~ ammonium nitrate.The diffusion current is proportional to concentration up to at least 0.8 mM (e.g. i d / C = 6.1 for percaprylic acid) and no maximum appears a t this concentration. The diffusion-current constants and half-wave potentials for all four peracids are similar in this medium. Plots of log [ i / ( i d - i ) ] veysus E and of log kf,h against E give straight lines. Assuming two electrons are transferred in the over-all electrode reaction diffusion constants calculated from the Ilkovic equation are 1-04 x (in meth- anol - benzene) and 0.41 x These values differ more than can be accounted for by solvent viscosities (0.74 centipoises for methanol - benzene and 1-14 for dimethylformamide). There is evidently either a change in mechanism with only one electron transferred in dimethylformarnide or an increase in solvation.Values of Kna do not exceed 1 in dimethylformamide. The use of ammonium nitrate permits the study of entire polarographic waves for long- chain fatty peracids in methanol - benzene or dimethylformamide. Well behaved diffusion- controlled waves suitable for analysis are obtained although they are irreversible. (in dimethylformamide). Cobalt(II1) as a Coulometric Intermediate BY D. J. BARCLAY AND W. A. ALEXANDER (Chemistry Department University of Strathclyde Glasgow) COB*~LT(III) is an obvious omission in the realms of strong oxidants which have been generated as couloinetric intermediates in coulometric titrimetry. The reason for this is not difficult to find. The redox potential of the cobalt(I1) - cobalt(II1) couple is 1.9 volts (D.A. Johnson and A. G. Sharpe J . Chem. SOC. 1964 3490) and therefore water is oxidised concommitantly with cobalt(I1). At first sight this should not be an insurmountable hazard as the silver(1) - silver(I1) system with a redox potential of 1.94 volts has been successfully used by J. J. Lingane and D. G. Davis (AnaZytica Chim. Acta 1956 15 201) in coulometric titrations. The silver(1) - silver(I1) couple however is more reversible than the cobalt couple and it therefore requires a larger overvoltage to electrogenerate cobalt (111) than silver( 11). We attempted to determine optimum conditions for the generation of cobalt(III) by determining current efficiencies under various conditions by the method of R. N. Adams C. N. Reilley and N. H. Furman (AnaZyt. Chem. 1953,25 1160). Current efficiency for the oxidation of cobalt(I1) is determined by the acidity of the supporting electrolyte the con- centration of the precursor (in this case cobalt(II)) temperature current density the electrode material and the presence of any complexing agent that may alter the redox potential of the relevant couple.These parameters were varied with the exception of adding a complexing agent and it was found that increase in acidity up to 5 M sulphuric acid decrease in temperature increase in cobalt (11) concentration and a gold rather than platinum electrode increased current efficiency. This was too low for practical use in coulometric titrimetry; we were looking for at least 98 per cent. It was hoped that fluoride might form a high spin complex with cobalt(II1) in solution. In the solid state hexafluorocobalt(II1) is high spin (H.L. Friedman J. P. Hunt R. A. Plane and H. Taube J . Amer. Chem. SOC. 1951 73 4028) and cobalt(II1) in aqueous solution is low spin and as cobalt(I1) is high spin in solution the couple may be made more reversible and thus require a smaller overvoltage (A. A. Vlcek “Progress in Inorganic Chemistry,” Volume 5 Interscience Publishers New York 1963 p. 211). This was not observed. However it was found that fluoride markedly increased the overpotential for the evolution of oxygen and because of this much higher current efficiencies were obtained. This phenomenon had been noted in the anodic formation of peroxydisulphate and ascribed to adsorption of fluoride ion at the electrode surface (Tren Yin Min and Yung Chao Chu Science Reports Peking 1959 3 83).We observed this effect at a platinum electrode but not at a gold electrode. Optimum conditions of 5 M sulphuric acid 0-1 to 0.2 M fluoride room temperature saturated cobalt(I1) sulphate and with the oxidation carried out at 5 mA per cm2 at a platinum electrode gave a current efficiency of 98.9 per cent. This was considered reasonably satis- factory as there are many coulometric intermediates that are generated at less than 100 per The optimum current efficiency obtained was about 87 per cent. We then tried the effect of adding fluoride ion. October 19671 RESEARCH TOPICS IN ANhLYTICAL CHEMISTRP 165 cent. efficiency (K. Abresch and I. Claasen “Coulometric Analysis,” Chapman and Hall Ltd. London 1965). Coulometric titrations of iron( 11) and vanadium( IV) were then attempted with electro- generated cobalt (111) and with an amperometric end-point detection method described elsewhere (W. A. Alexander and D. J. Barclay J . EZectroanaZyt. Chem. 1966 12 55) titration efficiencies of 98.5 and 97.5 per cent. respectively were found. Normally in a coulometric titration titration efficiency is higher than current efficiency as during part of the titration the titrand undergoes direct reaction at the electrode a t 100 per cent. current efficiency. The fact that lower titration efficiencies are obtained here could arise from a certain amount of water being oxidised by the cobalt(II1). This would explain why lower efficiencies are obtained in the oxidation of vanadium. Vanadium reacts more slowly with cobalt(II1) than does iron(II) (D. R. Rosseinsky and H. C. E. Higginson J . Chem. SOC. 1960 31).

ISSN:0037-9697    

DOI:10.1039/SA9670400153

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年代:1967

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October 19671 RESEARCH TOPICS IN ANhLYTICAL CHEMISTRP 165 Publications Received THE publications listed below have been received by the Editor of The Analyst in which journal Book Reviews will continue to appear. CHROMATOGRAPHY. Edited by ERICH HEFTMANN. Second Edition. Pp. xlii+ 851. New York Reinhold Publishing Corporation. 1967. Price is1 1. CHEMISTRY. A CONCEPTUAL APPROACH. By CHARLES E. MORTIMER. Pp. xii+692. New York Amsterdam and London Reinhold Publishing Corporation. 1967. Price 71s. 6d. ORGANIC CHEMISTRY. VOLUME 1 THE FUNDAMENTAL PRINCIPLES. By I. L. FINAR B.Sc. PH.D. (Lond.) A.R.I.C. Fifth Edition. Pp. xiv + 906. London Longmans Green and Co. Ltd. 1967. Price 60s.

ISSN:0037-9697    

DOI:10.1039/SA967040165b

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年代:1967

数据来源: RSC

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166 NOTICES [Proc. SOC. Anal)*#. Chem. Notices THE CHEMICAL SOCIETY ROYAL INSTITUTE OF CHEMISTRY AND SOCIETY OF CHEMICAL INDUSTRY FOLLOWING discussions between their Presidents the Chemical Society the Royal Institute of Chemistry and the Society of Chemical Industry have agreed to a thorough investigation of the grounds on which amalgamation might be achieved. The following announcement has been made. INTEGRATION OF THE THREE CHARTERED CHEMICAL BODIES For some time it has been apparent that chemists in the United Kingdom suffer from the system of fragmentation whereby they are represented by three societies instead of one as in almost all other countries. The Presidents of the three bodies have met and discussed this situation and as a result each has recommended to his Council that as a first step it would be extremely helpful if an independent investigation was undertaken with a view to making recommendations for an amalgamation of The Chemical Society The Royal Institute of Chemistry and The Society of Chemical Industry.All three Councils have readily agreed to this proposal and Sir Eric Bingen has now been invited to carry out the investigation. Sir Eric is a lawyer and an ex-Deputy Chairman of I.C.I. and he recently completed successfully a similar task in bringing about the amalgamation of the Association of British Chemical Manufacturers and the Association of Chemical and Allied Employers into the Chemical Industries Association. His first task will be to assess the work done by each of the three societies and to reconcile those activities which each body regards it as essential to maintain.SECOND INTERNATIONAL CONFERENCE ON THERMAL ANALYSIS WORCESTER hfASSACHUSETTS AUGUST 1 8 ~ ~ TO 23RD 1968 THE Second International Conference on Thermal Analysis will be held at Holy Cross College Worcester Massachusetts U.S.A. from August 18th to 23rd 1968. Copies of the first circular will be available shortly from Dr. J. P. Redfern (U.K. ICTA Liaison Officer) Stanton Instruments Limited Copper Mill Lane London S.W. 17 (Telephone 01-946 7731). PURE AND APPLIED CHEMISTRY THE OFFICIAL JOURNAL OF THE INTERNATIONAL UXION OF PURE AND APPLIED CHEMISTRY VOLUME 14 No. 2 1967 THIS issue contains the Main Lectures presented at the Symposium on Carotenoids other than Vitamin A held in Trondheim Norway from June 23rd to 25th 1966. Pure and Applied Chemistry is published irregularly four issues per volume at A6 ($18.00) per volume. Reprints may be purchased; all enquiries should be addressed to the publishers Butterworths P 5 Bell Yard Temple Bar London W.C.2. BRITISH STANDARDS INSTITUTION DRAFT SPECIFICATION A FEW copies of the following draft specification issued for comment only are available to members of the Society and can be obtained from the Secretary The Society for ,4nalytical Chemistry 9/10 Savile Row London W.1. Draft Specification prepared by Technical Committee DAC/'i-Salt . 67/23756. Draft B.S. Specification for Vacuum Salt for Butter and Cheese Making (Revision of B.S. 998 Metric Units).

ISSN:0037-9697    

DOI:10.1039/SA9670400166

出版商:RSC    

年代:1967

数据来源: RSC