摘要:

Proceedinas - - - - ~of the Analytical Division ofThe Chemical SocietyCONTENTS77 Reports of Meetings78 Summaries of Papers78 'Fourth International SACConference'11 0 Correspondence110 Conferences and Meetings112 Courses114 Analytical Division DiaryVolume 15 No 3 Pages 77-1 14 March 197PADSDZ 15(3)77-114(1978)ISSN 0306-1 396March 1978PROCEEDINGSOF THEANALYTICAL DIVISION OF THE CHEMICAL SOCIETYOfficers of the Analytical Divisionof The Chemical SocietyPresidentD. W. WilsonHon. SecretaryP. G . W. CobbSecretaryMiss P. E. HutchinsonHon. Treasurer Hon. Assistant SecretariesJ. K. Foreman D. I. Coomber, O.B.E.; D. C. M. Squirrel1Editor, ProceedingsP. C. WestonProceedings is published by The Chemical Society.Editorial: The Director of Publications, The Chemical Society, Burlington House, London, W1 V OBN.Telephone 01 -734 9864.Telex 268001.Subscriptions (non-members): The Chemical Society, Distribution Centre, Blackhorse Road,Letchworth, Herts., SG6 1 HN.Non-members can only be supplied with Proceedings as part of a combined subscription with The Analysrand Analytical Abstracts.@ The Chemical Society 1978SCOTTISH REGION MEETINGIntensive Zourses onHIGH PERFORMANCE LIOUID CHROMATOGRAPHYat theDepartment of Chemistry, University of Edinburgh3n3rd-5th July, 1978 Introductory Course on HPLC6th-7th July,1978 Advanced Seminar Course on HPLCA basic Introductory Course on the practice of mDdern liquid chromatography will be run inassociation with Professor J. H. Knox and leading equipment manufacturers. The intensivecourse will cover the principles, equipment and applications in clinical, pharmaceutical and in-dustrial analysis. Practical sessions on column packing and testing and a wide range ofmanufacturers' experiments using the latest equipment in the field will be based on small groups,limiting the maximum number of participants t o 60.The Advanced Seminar Course on HPLC that follows will feature small group discussionseminars on method selection and optimisation and current developments in LC techniques.An Exhibition of HPLC Equipment will be held on Thursday, 6th July 1978, in associationwith both these courses.For application forms and further information send SAE to: Dr. D. E. Wells, DAFFS FreshwaterFisheries Laboratory, Faskally, Pitlochry, Perthshire

ISSN:0306-1396    

DOI:10.1039/AD97815FX009

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

Vol. 15 No. 3 Proceedings March 1978 of the Analytical Division of the Chemical Society Reports of Meetings Special Techniques Group The thirty-third Annual General Meeting of the Group was held at 10.45 a.m. on Wednesday, November 30th, 1977, at the Education and Training Centre, AERE, Harwell, Didcot. The Chair was taken by the Chairman, Dr. P. B. Smith. The following office bearers were elected for the forthcoming year : Chairman- Dr.T. B. Pierce. Vice-Chairman-Mr. J . T. Davies. Honorary Secretary and Treasurer- Dr. R. Mounce, British Gas Corporation, London Research Station, Michael Road, London, S.W.6. Members of Committee-Dr. M. Adams, Dr. D. Betteridge, Dr. D. H. Christopher, Dr. A. G. Fogg and Mr. J . S. Hobbs. Dr. G. Duff and Dr. J. N. Miller were re-appointed as Honorary Auditors.Atomic Spectroscopy Group The thirteenth Annual General Meeting of the Group was held a t 2.15 p.m. on Tuesday, December 6th, 1977, in the Geological Society Lecture Theatre, Burlington House, London, W.l. The Chair was taken by the Chairman of the Group, Mr. C. P. Cole. The following office bearers were elected for the forthcoming year : Chairman-Mr.C. P. Cole. Vice-Chair- man-Dr . W. J . Price. Honorary Secretary- Mr. D. J . Willis, Rank Hilger, Westwood, Margate, Kent. Honorary Treasurer-Dr. G. B. Marshall. Honorary Assistant Secretary- Mr. C. A. Watson. Members of Committee- Mr. R. P. Blakemore, Dr. J. E. Cantle, Dr. L. Ebdon, Mr. D. L. Miles, Dr. A. Townshend and Dr. J. Warren. Mr. D. Moore and Mr. R. A. White were re-appointed as Honorary Auditors.Chromatography and Electrophoresis Group The thirteenth Annual General Meeting of the Group was held a t 2.30 p.m. on Tuesday, December 6th, 1977, at the Geological Society Lecture Theatre, Burlington House, London, W.l. The Chair was taken by the Chairman of the Group, Dr. G. H. JGlliffz. The following office bearers were elected for the forthcoming year: Chairman-Mr.D. A. Elvidge. Vice- Chairman-Dr. F. K. Butcher. Honorary Secretary and Treasurer-Dr. D. Simpson, Analysis For Industry, Factory 2, Bosworth House, High Street, Thorpe-le-Soken, Essex, C016 OEA. Members of Committee-Dr. G. H. Jolliffe, Dr. C. E. R. Jones (co-opted) and Mr. V. C. Weaver. Dr. S. J. Purdy and Mr. J . S. Wragg were re-appointed as Honorary Auditors.Thermal Methods Group The thirteenth Annual General Meeting of the Group was held at 9.30 a.m. on Tuesday, December 13th, 1977, at the University, Northumberland Road, Sheffield. The Chair was taken by the Chairman of the Group, Dr. F. W. Wilburn. The following office bearers were elected for the forthcoming year : Chairman -Dr. R. H. Still. Vice-Chairman-Mr. E. L. Charsley. Honorary Secretary-Dr.C. J. Keattch, Industrial and Laboratory Services, P.O. Box 9, Lyme Regis, Dorset. Honorary Treasurer-Dr. A. A. Hodgson. Members of Committee-Professor L. S. Bark, Dr. A. W. Benbow, Dr. G. M. Clark, Mr. F. G. Davidson, Miss J . P. Dixon, Dr. S. A. A. Jayaweera, Dr. R. C.,Mackenzie (co-opted) and Dr. F. W. Wilburn (co-opted). Dr. W. Boardman and Mr. P. J. Haines were re-appointed as Honorary Auditors.Particle Size Analysis Group The twelfth Annual General Meeting of the Group was held a t 2.45 p.m. on Thursday, December lst, 1977, at the Wellcome Building, Euston Road, London, N.W.1. The Chair was taken by the Vice-chairman of the Group, Mr. R. W. Lines. The following office bearers were elected for the forthcoming year: Chairman- Mr. B.Scarlett. Vice-Chairman-Mr. R. W. Lines. Honorary Secretary and Treasurer- 7778 FOURTH INTERNATIONAL SAC CONFERENCE Proc. AnaZyt. Div. Chem. SOC. Mr. M. W. G. Burt, Building B9C5, Atomic Weapons Research Establishment, Alder- maston, Berks. Honorary A ssistant Secretary- Dr. R. Wilson. Members of Committee-Dr. T. Allen, Dr. W. Carr, Dr. N. A. Orr, Mr. J . Spence and Dr. N.G. Stanley-Wood. Mr. W. G. King and Mr. P. W. Shallis were appointed as Honorary Auditors. Electroanalytical Group The eighth Annual General Meeting of the Group was held a t 2.15 p.m. on Wednesday, December 7th, 1977, a t the Wellcome Founda- tion, Euston Road, London, N.W.l. The Chair was taken by the Chairman of the Group, Dr. W. F. Smyth. The following office bearers were elected for the forthcoming year : Chairman -Dr.W. F. Smyth. Vice-Chairman-Dr. B. J. Birch. Honorary Secretary-Dr. H. Thomp- son, Electronic Instruments Ltd., Hanworth Lane, Chertsey, Surrey, KTl6 9LF. Honorary Treasurer-Dr. A. G. Fogg. Honorary Assis- tant Secretary-Dr. B. Fleet. Members of Committee-Mr. A. E. Bottom, Mr. I. Davidson, Dr. P. Kane, Dr. T. Ryan, Dr. M. Smyth and Dr. J.D. R. Thomas. Dr. J. A. W. Dalziel and Mr. J. H. Glover were re-appointed as Honorary Auditors. Education and Training Group The seventh Annual General Meeting of the Group was held a t 2.30 p.m. on Thursday, December lst, 1977, at the Wellcome Building, Euston Road, London, N.W.l. The Chair was taken by the Chairman of the Group, Professor D. Thorburn Burns. The following office bearers were elected for the forthcoming year: Chairman-Professor D. Thorburn Burns. Vice- Chairman and acting Honorary Secretary-Dr . J. G. Pritchard, Department of Chemistry, North East London Polytechnic, West Ham Precinct, Romford Road, Stratford, London, E. 15. Honorary Treasurer-Mrs. M. I. Arnold. Members of Committee-Dr. D. M. W. Ander- son, Dr. G. S. Davy, Mr. D. Glastonbury, Dr. E. J. Greenhow, Mr. B. Mills and Dr. W. I. Stephen. Mr. J. Bassett and Dr. J. A. W. Dalziel were re-appoint ed as Honorary Auditors

ISSN:0306-1396    

DOI:10.1039/AD9781500077

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

78 FOURTH INTERNATIONAL SAC CONFERENCE Proc. AnaZyt. Div. Chem. Soc. Fourth International SAC Conference The following are summaries of ten of the papers and posters presented in the Sessions on “Electroanalytical Methods,” “Atomic Spectrometry,” “Instrumentation in Analysis” and “Molecular Spectroscopy” at the Conference, which was held on July 17th-22nd, 1977, in Birmingham. Summaries of twenty of the papers given at the Conference appeared in the January and February issues of Proceedings (pp.1 and 43). New Chloramine T and Picrate Ion-selective Electrodes T. P. Hadjiioannou, M. A. Koupparis and E. P. Diamandis Laboratory of Analytical Chemistry, University of Athens, 104 Solonos Street, Athens (144), Greece Chloramine T Electrode The electro-active material of the chloramine T (CAT) electrode is the [ (bathophenanthroline),- Nil - chloramine T salt dissolved in 2-nitro-fi-cymene.This sensor was obtained by convert- ing the liquid ion exchanger of the Orion nitrate-selective electrode into the CAT form. The CAT electrode exhibits Nernstian response to chloramine T ion activity for concentrations of from 10-1 to M, which is unaffected by pH in the range 5 to 9.The dynamic response times tested for the linear response range of the electrode were <2 s for a 6-fold increase or 20% decrease in CAT concentration. The operative lifetime of the electrode was about 1 month. Various ions have been tested for their interference with the CAT electrode and potentiometric selectivity coefficients have been eva1uated.l KE;,j values for various j ions are : for 10,- and C104-, -10; for benzoate and NO,-, for phthalate, H2B03-, HCO,-, HP0,2- and CH,COCOO-, -lo-,; and for malonate, tartrate, citrate, F-, Cr042-, Mo042- andMarch, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 79 Applications The CAT electrode has been used for indirect potentiometric determination of arsenic( 111), ascorbic acid, hydrazine, isonicotinic acid hydrazide (isoniazid) , S2- and S2032-.The reduct- ants react stoicheiometrically with a known excess of chloramine T and the unconsumed excess of chloramine T is measured with the CAT electrode. Aqueous samples of the afore- mentioned reductants were analysed with an average accuracy and precision of about 1-2% (Table I). The method was applied successfully to the determination of ascorbic acid and isoniazid in pharmaceutical preparations.TABLE I RESULTS FOR INDIRECT POTENTIOMETRIC DETERMINATION OF REDUCTANTS WITH THE CHLORAMINE T ION-SELECTIVE ELECTRODE Reductant Arsenic( 111) Ascorbic acid Hydrazine Isoniazid Sulphide Thiosulphate Rangklrng 0.5-1.7 0.06-3 0.7-40 0.3-14 0.01-1.6 0.06-5.6 Relative standard Error, yo deviation, yo 2.4 0.9 1.8 1.2 1.4 0.6 2.0 1.4 2.6 0.8 2.6 1.2 The CAT electrode has been used for the semi-automatic potentiometric titration of ascorbic acid and chloramine T, with continuous addition of titrant, in the ranges 440 and 7-70 pg, respectively, with accuracy and precision of 1 yo.The CAT electrode has also been used as a monitor in a kinetic potentiometric method for the micro-determination of iodide and osmium(VIII), based on their catalytic effect on the CAT - As(II1) reaction.The time required for this reaction to consume a fixed amount of chloramine T, and therefore for the potential to increase by a pre-selected amount (25 mV), is measured automatically with a solid-state “double switching’’ network and related directly to the catalyst concentration.Commercial equipment and an auxiliary relay system are easily combined and provide automatic results shortly after the start of the reaction. Trace amounts of iodide in the range 1.5-30 pg and of osmium in the range 10-150 pg were determ- ined with relative errors and coefficients of variation of 1-2y0.2 Iodide has also been deter- mined on the basis of its catalytic effect on the CAT - H20, reaction.Measurements made with a combination of glass and CAT electrodes in acidified chloramine T solutions of various ionic strengths have been used to determine the dissociation constant of chloramine T acid. The value obtained for K , for this acid at 25 & 0.2 “C and at zero ionic strength was 2.5 x which is in close agreement with reported values. Picrate Electrode The water-insoluble salt of tetrapentylammonium picrate, dissolved in 2-nitrotoluene, is the active electrode substance of the picrate ion-selective membrane electrode.Nernstian behaviour is obtained in the p(picrate) range 2-5 ; potentials are established rapidly (dynamic response time (4 s) and are unaffected by pH in the range 3-10. Common ions (Cl-, F-, NO,-, HCO,-, CH,COO-) do not interfere.The potentiometric selectivity coefficients for 2- nitrophenol, 2,4-dinitrophenol, phthalate, benzoate, 10,- and ClO,- were about 0.01 ., Applications A method has been developed for the semi-automatic potentiometric titration of thiourea with silver nitrate and of silver ions with thiourea, in the presence of picrate ions, using as indicator electrode the picrate ion-selective electrode.The method is based on the formation of insoluble complexes of silver, thiourea and picrate. Micro-amounts of thiourea and silver in the ranges 15-1 500 and 200-1 800 pg, respectively, were determined with relative errors and relative standard deviations of about The rapid response of the picrate electrode to changes in picrate concentration makes it a valuable sensor for following the rate of picrate reactions.A kinetic potentiometric method80 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chem. SOC. was developed for the determination of creatinine in urine, based on the reaction that takes place between creatinine and sodium picrate in alkaline medium (Jaffk reaction). Under controlled conditions a linear relation exists between the increase in electrode potential within a fixed period of time (90 s) and the amount of creatinine present.Recovery and comparison experiments gave satisfactory results. This research was supported in part by a research grant from the Greek National Institute of Research and by NATO Research Grant No. 1000. References 1. 2 . 3. 4. 5. Koupparis, M.A., and Hadjiioannou, T. P., Analytica Chim. Acta, in the press. Koupparis, M. A., and Hadjiioannou, T. P., Analytica Chim. Acta, in the press. Hadjiioannou, T. P., and Diamandis, E. P., Analytica Chim. Acta, in the press. Diamandis, E. P., and Hadjiioannou, T. P., Microchim. Acta, in the press. Diamandis, E. P., Koupparis, M. A., and Hadjiioannou, T. P., Microchem. J . , in the press.Potentiometric Determination of Iodine in Pharmaceutical Preparations and in Biological Material M. Vandeputte, L. Dryon, L. De Hertogh and D. L. Massart Farmaceutisch Instituut, Vrije Universiteit Brussel, Bosstraat, B- 1090 Bvussels, Belgium The increase in the number of commercially available ion-selective electrodes has stimulated their use in many fields, including pharmaceutical analysis.The potentiometric determin- ation of halide salts of pharmaceutical compounds has been described by several workers1-3 The micro-determination of halogen-containing organic compounds requires a preliminary liberation of the halide to be determined. This reaction is usually performed after destruction of the organic matter.3-11 The micro-determination of halogens in organic compounds was described by S ~ h o n i g e r .~ ~ , ~ ~ With iodine, some workers reported the liberation of the organic- ally bound iodine with a metallic reductor without preliminary destruction of the organic matter. Egli14 described catalytic dehalogenation with sodium tetrahydroborate in the presence of palladium for the analysis of X-ray contrasting products.Paletta and Pazenbeck15 proposed the use of an aluminium foil in alkaline solution for the determination of the iodine content of hormones. The last method was applied by us for the analysis of Iodoxyl, an X-ray contraster, using an aluminium wire of length 30 cm. After the reduction, the solution was either neutralised or not. The iodide determination was performed by direct potentiometry using an iodide-selective electrode in conjunction with a single-junction reference electrode.Neither method (with or without neutralisation) yielded satisfactory results, the recovery being 32.3% in the first instance and 72.6% in the second. These results lead us to conclude that the use of a metallic reductor does not permit the quantitative liberation of the organically bound iodine.A preliminary mineralisation of the sample was thought to be preferable, and Schoniger combustion was employed. As direct potentiometry of the iodide ion is used, reduction of the 10,- obtained has to be carried out, and several reductors were tested. The proposed method has been employed for the determination of iodine in X-ray con- trasters. Pure compounds and pharmaceutical preparations were investigated.Finally, the method was used for the investigation of the iodine content in thyroid gland material. Experimental Apparatus An Orion, Model 94-53, iodide electrode, an Orion, Model 90-01, single-junction reference electrode, an Orion, Model 801, digital pH meter and a Heraeus, Model Mikro K, Schoniger combustion system were used. The measurements were carried out in a thermostated (25.0 -J= 0.1 "C) polythene vessel.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 81 Reductors The following were tested: Devarda's alloy powder at room temperature, Raney nickel at 55 "C and aluminium wire at 60 "C.A 5-ml volume of 10,- solution is mixed with 20 ml of sodium hydroxide solution (pH 13). After shaking for 30min at the required temperature, the iodide content of the solution obtained is determined by direct potentiometry.Determination of Iodine in Pharmaceutical Compounds Pure compounds An amount of sample is weighed accurately on ashless Whatman paper. The products of combustion are absorbed in 20 ml of sodium hydroxide solution Reduction step. The reduction is performed with 1 g of Devarda's alloy powder (at room After reduction the solution is filtered and made up Determination of iodide.The solution obtained is diluted 1 + 1 with 2 M potassium nitrate Schoniger combustion. (PH 13)- temperature with shaking for 30 min). to 100 ml. solution and the iodide content is determined by direct potentiometry. Pharmaceutical preparations Twenty tablets are ground to powder and the active compound is extracted with a suitable solvent, spotted on ashless Whatman paper and analysed as described under Pure compounds.The determination is also performed directly on the ground tablets by weighing a certain amount of powder. Solutions are spotted directly (or after dilution if necessary) on an ashless Whatman paper and analysed as described under Pure compounds.Tablets. Solutions. Determination of Iodine in Thyroid Gland Material is performed as described under Pure compounds. The sample is dried by lyophilisation and ground to powder, then the iodine determination Results and Discussion The best results for the reduction of an 10,- solution were obtained using Devarda's alloy powder. These reductions often are more rapid in strongly alkaline solution and we therefore decided to employ Devarda's alloy powder at pH 13 for the reduction of the samples after Schoniger combustion.For the pure compounds, accurate and reproducible results were obtained ; the accuracy was &5% and the precision of the method was &0.9%. The results were also compared with those obtained with the method proposed by the British Pharmacopoeia16 for the determin- ation of organically bound iodine.Sodium iopodate was analysed by the two methods. The accuracy and reproducibility of the two methods were comparable, but our method is to be preferred for routine analysis because it is less cumbersome and more rapid. For the tablets, the yield was greater when the determination was performed directly on the ground tablets.The lower results obtained after extraction are probably due to incomplete extrac- tion of the active compound. Finally, the proposed method was applied to the determination of iodine in biological material. The accuracy for the method when applied to thyroid gland material was tested by standard addition using an 10,- solution. Both results were in satisfactory agreement.The precision was 8.5%. We can conclude that the proposed method is suitable for the determination of iodine in pharmaceutical compounds and in biological material. It is rapid and can therefore be used for routine analysis. The recoveries for the pharmaceutical preparations were in the range 95.0-101 3%.82 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.16. FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chenz. SOC. References Papp, E., and Pungor, E., 2. Analyt. Chem., 1970, 250, 31. KBlmBn, J., T6th, K., and Kuttel, D. Acta. Pharm. Hung., 1972, 42, 152. Pungor, E., T6th, K., and- PBpay, M. K., Chemia Analit., 1972, 17, 947. MBzor, L., PBpay, M. K., and KlatsmAnyi, P., Talanta, 1983, 10, 557. Willemart, R., and Robin, J,, Annls.Pharm. Fr., 1963, 21, 423. Pellerin, F., Annls. Pharm. F r . , 1970, 28, 685. Dessouky, Y . M., T6th, K., and Pungor, E., Analyst, 1970, 95, 1027. Potman, W., and Dahmen, E. A. M. F., Mikrochim. Acta, 1972, 303. Hassan, S. S. M., 2. Analyt. Chem., 1973, 266, 272. Rittner, R. C., and Ma, T. S., Mikrochim. Acta, 1976, 1, 243. Friedrich, F., and Kottke, K., Zentbl. Pharm., 1976, 115, 235.Schoniger, W., Mikrochim. Acta, 1955, 123. Schoniger, W., Mikrochim. Acta, 1956, 869. Egli, R. A., 2. Analyt. Chem., 1969, 247, 39. Paletta, B., and Pazenbeck, K,.: Clin. Chirn. Acta, 1969, 26, 11. “British Pharmacopoeia 1973, The Pharmaceutical Press, London, 1973, p. A93. Separation and Determination of Co-existing Forms of Silicic Acid in Natural Waters G. M. Varshal, L. V.Dracheva and N. S. Zamokina V . I . Vernadsky Institute of Geochemistry and Analytical Chemistvy, USSR Academy of Sciences, Moscow, USSR Silicic acid is a macrocomponent of natural waters,l and exists in at least three main forms: the monomeric - dimeric form, polymeric forms and forms bound in the form of biopolymers with the dissolved organic matter of water~.~-5 For efficient deionisation of water, quantit- ative data not only on its bulk content but also on its co-existing forms in solution are needed.These data are also of interest in geochemistry. Direct photometric determination in the form of yellow or blue molybdosilicic acid permits only the content of the monomeric - dimeric form to be determined.6-12 The total content of silicic acid can be determined after depolymerisation by heating in alkaline solutions or by fusion of residues obtained from the evaporation of water ~ i l m p l e s .~ , ~ ~ , ~ ~ For the separation of co-existing forms of silicic acid in natural waters, filtration through Sephadex has been u ~ e d . ~ J ~ - l ~ Samples of river waters and model solutions of silicic acid with concentrations from 5 to 2 000 mg 1-1 (calculated as SiO,) were fractionated on columns of Sephadex G-25, G-75 and G-200, with calibration according to the molecular masses with the aid of standard materials.The contents of the monomeric - dimeric forms of silicic acid in the eluate fractions were determined by the direct photometric method in the form of blue molybdosilicic acid, and the total content of silicic acid after depolymerisation in alkaline solutions.The results were identical only for fractions with a yield corresponding to the elution of substances with a relative molecular mass less than 180, i.e., only monomeric- dimeric forms of silicic acid react with molybdate ions in the solution. Forms with a higher degree of association were revealed in corresponding fractions only after alkaline depolymer- isation.For photometric determination of silicic acid, the blue form of molybdosilicic acid has two main advantages over the yellow form : (1) an order of magnitude higher sensitivity (0.1 mg 1-1 SiO,) and (2) the absence of influence of dissolved organic matter in surface waters, which absorbs intensely over the whole absorption band of yellow molybdosilicic acid (300450 nm).The methol- sulphite reagent (2% aqueous solution of N-methylaminophenol sulphate +1.3% sodium sulphite) has been used for the reduction of the yellow form of molybdosilicic acid to the blue form.10J6,17 The most important stage in the photometric determination is the formation of the yellow molybdosilicic acid. As is shown here, high reproducibility and precision are achieved if conditions for the predomination of the cc-form of the yellow heteropoly acid in the solution are ensured.At a silicic acid concentration characteristic of natural waters (0.1-25 mg 1-I), complete conversion into the yellow molybdosilicic acid is achieved if the ratio of silicon to molybdenumMarch, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 83 concentration is not less than 1 : 1 000.Under these conditions, predominance of the a-form of the yellow heteropoly complex is possible at pH >1.7. As can be seen from Fig. 1, the acidity of the initial solution of silicic acid has a dramatic influence on the yield of the blue molybdo- silicic acid. The most reproducible results were obtained when the pH of the initial water sample was maintained a t 2.0 0.3, which was accomplished by using /3-dinitrophenol as indicator.This pH corresponds to maximum stability of monomeric - dimeric forms of silicic acid in solution1* even at concentrations that substantially exceed the solubility of amorphous silica (100-110 mg I-'). This is clearly demonstrated by the fractionation on Sephadex of a silicic acid solution of concentration of 126 mg 1-1 at pH 2.All of the silicic acid is eluted in the fractions corresponding to substances with relative molecular masses < 180. The other advantage of photometric measurement at pH 2 2 0.3 is accounted for by the state of molyb- denum(V1) in the solution. mol 1-l) trimers of molybdic acid prevail in the solution,1g and these trimers are the main structural units that form molybdosilicic acid.At pH 2 and CMLl0(\=~ = I x - Er 0 0.2 ' II x - a, C rn * E a 0 0.1 IL I I 0 I I 1 2 3 PH Fig. 1. Dependence of the ab- sorbance of the blue molybdosilicic acid on the pH of the initial silicic acid solution. Csio2 = 1 pg ml-l. Spectrophotometer : Specord, h = 750 nm, I = 10 mm. The photometric determination of silicic acid was carried out as follows.To the initial solution containing 5-125 pg of silicic acid in a measuring flask of 50-ml capacity, 1-2 drops of a 0.1% solution of /3-dinitrophenol were added and the pH of the solution was adjusted to 2.0 Then 2.5 ml of a 5% solution of ammonium molybdate were added and the mixture was stirred. After standing for 10 min, 2.5 ml of a 10% solution of tartaric acid were added, followed by 10 ml of the methol - sulphite reagent.After 1-2 h, the solutions were measured photometrically at 750 nm in a cell of length 30 mm. The regress- ion equation is 0.3. The calibration graph is linear in the concentration range 3-125 pg per 50 ml. Y = (0.001 2 & 0.0003) + (0.0044 & 0.0009) X where X is the silicic acid concentration (pg per 50 ml) and Y is the absorbance at 750 nm.The accuracy of the method was confirmed by the results for the analysis of river water sample No. 1 (USA), which was carried out in accordance with the international programme of IAGC20 (Table I). In fresh surface waters, the content of highly associated forms averaged from 10 to 40%) including associates of silicic acid and high relative molecular mass compounds of silicic acid with humic substances of waters.The latter associates were demonstrated by the increase in the proportion of high relative molecular mass forms of silicic acid with an increase in the84 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chew Soc. colour of surface waters. This conclusion is supported by the results obtained from spectro- photometric measurements of silicic acid (Table I), during dialysis through cellophane membranes and filtration through Sephadex of concentrates of highly coloured water samples (Fig.2). Depolymerisation by fusion with a mixture of borax and soda (1 + 2) of residues obtained by evaporation of water samples would result in a 100% yield of monomeric - dimeric forms of TABLE I RESULTS OF PHOTOMETRIC DETERMINATION OF SILICIC ACID IN SAMPLES OF SURFACE WATERS No.1 2 3 4 5 6 7 8 9 10 Origin of sample PH River Volga (source) 6.9 Lake Seliger 7.6 Blezna River 6.6 Lake Pen0 7.7 Lake Velikoye 6.7 River Soz 6.3 River Volga (Volgograd town) 7.2 River hoskva (source) 4.6 River Moskva (Rublevo IAGC International Pro- village) 7.7 gramme river water No.1* - Content of silicic acid/ mg 1-1 SiO, 7 Colour units on Chemical Direct After platinum - oxygen photometric depolymer- cobalt demand/ deter- isation scale mg 1-1 mination by fusion 136 73.6 3.10 5.12 25 45.0 3.10 3.76 225 86.4 5.45 6.85 35 53.5 2.98 3.08 84 69.6 2.84 3.20 148 76.4 3.21 4.82 - - 4.95 7.20 400 56 4.87 6.70 28 39 8.20 8.96 - - 4.23 4.77 Content of polymeric form of silicic acid, yo 39 18 20 3 19 33 31 30 9 11 * The average value from 30 laboratories in the USA, Canada, Norway, UK, East and West Germany, Japan and other countries who participated in the programme is 4.7 mg 1-’ SO,.0 2 4 6 8 1 0 1 2 14 Fraction number 30 40 50 60 70 80 90 100 I I I I I I I I V/ml Fig. 2. Silicic acid forms occurring in highly coloured water from the Moskva River source.Silicic acid elution curve from Sephadex G-75 column: 1, direct photometric determination of silicic acid in the fractions ; 2, photometric determination of silicic acid in the fractions after depolymer- ioation ; 3, photometric determination of dissolved organic substances (mainly humic substances). Column : length = 55 cm, i.d. = 1.5 cm, bed mass = 7.5 g .March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 85 silicic acid, which can be determined by the direct spectrophotometric method.During depolymerisation by heating with 0.05 N sodium hydroxide solution the conversion of assoc- iated forms into monomeric-dimeric forms occurs within 10-30 min for most water samples. However, for highly coloured *ater samples and strongly mineralised underground waters depolymerisation by fusion is preferable.By subsequenf fractionation of concentrates of river-water samples on columns of Sephadex G-25, G-75 and G-200 a wide range of relative molecular masses of silicic acid associates has been revealed (from 180 to 70 000-100 000). For a model equilibrium solution at pH 7 within the investigated range of silicic acid concentrations (5-2 000 mg 1-l) the content of monomeric - dimeric forms did not exceed the solubility of amorphous silica under normal conditions (100-1 10 mg 1-l) , only monomeric - dimeric forms of silicic acid being present in the equilibrium solution below this concentration.At higher concentrations, silicic acid is present in solution in the form of monomeric - dimeric and high relative molecular mass forms with relative molecular masses of 70 000-150 000.Forms with an intermediate degree of polymerisation are lacking in equilibrium solutions. When the solutions are diluted, rapid destruction of high relative molecular mass associates with the formation in the solution of intermediate forms with relative molecular masses of about 1 000 was observed (Fig.3). Subsequently, a slow formation of monomeric - dimeric forms of silicic acid occurs and equilibrium is attained, as can be seen from the gel-chromato- graphic results (Fig. 4), over a period of 1.5-6 months. 300 250 200 150 100 50 p0,4 000 4J 1000 I I 1 i I I I 0 2 4 300 180 Vi I ! I I I I 1 I I I I 1 ; I I I 1 I I 1 I # 6 8 10 12 Fraction number 43 53 63 73 83 93 103 V/ml Fig.3. Silicic acid elution curves from Sephadex G-25 column. Con- centrations of silicic acid in solution : Cinitial = 1930 mg 1-1 of SiO, and Cfinal = 240 mg 1-1 of SO,. pH = 7. 1, Direct photometric determination of silicic acid in the fractions; 2, photo- metric determination of silicic acid in the fractions after depolymerisation. Distribution of silicic acid forms according to values of molecular masses.Time: 1 h after dilution of the initial solution. .g 0" i3 100 300 180 v* I I I o 2 4 6 a 1 0 1 2 Fraction number 43 53 63 73 83 93 103 V/m I Fig. 4. As Fig. 3, but 600 h after dilution of the initial solution. Correlation of the silicic acid forms corresponds to the equili- brium form. The order of the depolymerisation reaction of silicic acid in solution was calculated to be 1.1 and the rate constant is Kassumed = (3-10) X lo7 (mg l-l)-o-l s-l.The apparent activation energy of silicic acid depolymerisation reaction is Eaqp. = 36 kcal mol-l. The presence of highly associated forms of sificic acid and of intermediate forms in natural waters is accounted for by the slow depolymerisation rate. Their quantitative determination is possible after separation on Sephadex and alkaline depolymerisation.86 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC Silicic acid bound in the form of biopolymers with humic and fulvic acids has been deter- mined. Experimental evidence for the presence of non-equilibrium forms of silicic acid in initial samples has been obtained for a series of natural waters.After the samples had been kept in the laboratory for a year, coincidence of the results of the direct photometric determin- ation and the determination after depolymerisation by fusion was, in fact, observed for all samples. References 1. 2. 3. Strakhov, N. M., Editor, “Geochemistry of Silica,” Nauka, Moscow, 1966. Okamoto, G., Okura, T., and Goto, K., in Ronov, A. B., Editor, “Geochemistry of Lithogenesis,” Varshal, G.M., Dracheva, L. V., Zamokina, N. S., and Ksenzenko, V. I., “Proceedings of the XXVth Novocherkassky Hydrokhimichesky Institut, Novocherkassk, 1972, Foreign Literature Publishing House, Moscow, 1963, pp. 196-209. Hydrochemical Conference, 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. p:33. Nikitina, I. B., in Batulin, S .G., Editor, “Geochemistry of Landscapes and Processes of Hypergenesis,” Dracheva, L. V., Varshal, G. M., Ksenzenko, V. I., and Zamokina, N. S., Izv. Vyssh. Uchebn. Zaved., Atkins, W. R. G., J . Mar. Biol. Assoc. U.K., 1923, 13, 157. Weitz, E., Franck, H., and Schuchard, M., Chem. Ztg, 1950, 74, 256. Strickland, J . D. H., J . A m . Chem. SOC., 1952, 74, 862. Chow, D. T.-W., and Robinson, R.J., Analyt. Chem., 1953, 25, 646. Mullin, J. B., and Riley, J. P., 4naZytica Chzrn. Acta, 1955, 12, 162. Lurye, Yu. Yu., Editor, “Unified Methods of Analysis,” Khimiya, Moscow, 1971, pp. 234-238. Morrison, I. K., and Wilson, A. L., Analyst, 1963, 88, 446. Varshal, G. M., and Dracheva, L. V., Theses of the All-Union Seminar “Geochemical and Analytical Methods of Studying the Material Composition of Sedimentary Rocks and Ores, Part 11,” Moscow, Varshal, G.M., in Varshal, G. M., Editor, “Analytical Chemistry and the Environment,” “Interan,” Czechoslovak Society for Science and Technology, Prague, 1974, pp. 13-14. Varshal, G. M., in Senyavin, M. M., Editor, “Methods of Analysis of Natural and Sewage Waters,” Probleme Analitzcheskoi Khimii, Volume 5, Nauka, Moscow, 1977, p.94. Dorokhova, E. N., “Chemical-analytical Study of the Conditions of Silicomolybdic Acid Formation and Reduction,’’ Thesis, Moscow State University, 1965. Gelman, E. M., and Starobina, I. Z., “Rapid Chemical Methods for the Determination of Rock- forming Elements,” Instruction No, 138-X, Mingeo SSSR, Moscow, 1976. Iler, R. K., “Colloid Chemistry of Silica and Silicates,” Foreign Literature Publishing House, MOSCOW, 1959, p.49. Nabivaneits, B. I., “State in Solutions and Reactions of Compounds of Some Elements of the IV-VI Groups of the Periodical System,” Doctoral Dissertation, Institute of Geochemistry and Analytical Chemistry, USSR Academy of Sciences, Moscow, 1969. Nauka, Moscow, 1973, pp. 36-44. Khim. Khim. Tekhnol., 1975, 18, 1968.1974, pp. 149-151. Ellis, A. I., Geochim. Cosmochim. Acta, 1976, 40, 1359. Coulometry in Non-aqueous Media E. A. M. F. Dahmen and M. Bos Department of Chemical Technology, Twente University of Technology, P.O. Box 217, Enschede, The Nether- lands The difficulties encountered in coulometry in non-aqueous media are particularly connected with the requirements that must be fulfilled in order to obtain lOOyo current efficiency at the generator electrode.However, apart from the current efficiency aspect, one should bear in mind that coulometry is a technique often used in continuous and automatic analysis, and therefore, if applied in non-aqueous media the normal precautions necessary in aqueous media should be even more strictly adhered to. For example, if we consider Fig.1, the following observations can be made : (a) an inductive effect on higher resistance leads must be eliminated by appropriate shielding ; (b) a current path effect, i.e., a voltage drop across the indicator electrodes, caused by the generating current, should be avoided by positioning the indicator electrodes close together and far from the generator electrode and its counter electrode, as shown in Fig.2;March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 87 (c) a closed loop effect should be eliminated by galvanic separation of the indicating and generating circuits. Inductive effects Indicator Fig. 1. Disturbance of electrometric indicator function by generating current. Generator circuitry d Fig. 2. performance. Connection diagram for non-disturbed indicator It is most important, of course, also to solve the diaphragm problem of mutually separating (1) by use of porous materials, such as sintered glass discs of adequate porosity, when using solvents of high viscosity such as m-cresol or dimethyl sulphoxide; or (2) by ion-exchange membranes when using solvents of low viscosity such as water or acetonitrile ; Du Pont supply special membranes for organic media. With regard to the ion-exchange membranes, we use a particular coulometry electrode set, originally designed by a former collaborator, Mr.J. Dubbeling, and shown in Fig. 3. A pH generator of platinum wire is wound around the tip of a glass stem, which, by pressing the rubber balloon and allowing it to expand after each coulometric titration, remains filled with fresh end-point liquid ; this contacts the membrane and its counter-electrode compartment behind. One can also use a combination of two membranes, each with its own counter-electrode compartment, opposite to one another, one serving the acid titration and the other the base titration.As far as the indicating system is concerned, we use a glass electrode, periodically reconditioned in aqueous acid, and a silver - silver chloride reference electrode each time in the medium under investig- ation, but with additions of 0.1 M tetramethylammonium chloride (TMAC) (in m-cresol) , saturated TMAC (in dimethyl sulphoxide) or saturated TMAC with 0.01 M silver nitrate, in which case a silver electrode is used (in snlpholane). In each instance these are connected via salt bridges of 0.1 M tetraethylammonium perchlorate (TEAP) (in m-cresol), or of 0.2 M TEAP (in dimethyl sulphoxide) or a sintered-glass disc (in sulpholane).As far as the counter- the generat or and coun ter-elec t rode compartments, either Next we can consider the precautions more specific to non-aqueous media.88 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. /- lon-exchange Rubber balloon lon-exchange membrane Counter electrode Diaphragm Exchangeable holder Generator electrode Glass balls Fig. 3. Coulometry electrode set. electrode department is concerned, the simplest combination is a 1 M TEAP solution in the solvents together with either a TEA cation membrane in base titration or a perchlorate anion membrane in acid titration.So far we have dealt only with the precautions necessary for coulometry in non-aqueous media, and not with the most important problem of lOOyo generation efficiency. We can dis- regard the possibility of adding trace amounts of water, as its absence is required in principle and is therefore essential in many sophisticated titrations in non-aqueous media.In general, we can find conditions for lOOyo coulometric acid and base generation, but in this connection each solvent leads to different problems, which can be illustrated with a few examples. Coulometric Acid - Base Titration in m-cresoP Fig. 4 shows a schematic diagram of the coulometric titration of acids and bases in m-cresol. Whenusing this equipment, we had no difficultyin obtaining lOOyo current efficiencyin cathodic reduction in the titration of acids, as is shown in Table I.However, lOOyo current efficiency could not be obtained in anodic oxidation in base titrations in m-cresol. The electrode reactions involved were therefore studied by means of techniques such as polarographic oxidation, constant-potential coulometry at a platinum gauze, voltammetry at a rotating platinum-disc electrode and chronopotentiometry at a mercury pool.Without going into the details of this study, which has been published elsewhere,2 the reaction scheme shown below seems the most probable. B i- HCres BH'Cres- @ BH+ + Cres- Cres- Cres' + e 2 Cres' --b Cres - Cres OH Cres-Cres = H3C -cH3 OHMarch, 1978 PH - meter - FOURTH INTERNATIONAL SAC CONFERENCE r Recorder 3 Fig.4. Schematic diagram of the equipment for coulometric titration of acids and bases in m-cresol. (1) Working electrode ; (2) auxiliary electrode ; (3) stirrer; (4) glass electrode; (5) Ag - AgCl reference electrode; (6) G4 sintered-glass discs. TABLE I COULOMETRIC TITRATION OF ACIDS IN m-CRESOL Amount added/ Amount found/ Recovery, Compound pequiv pequiv % 2,4-Dinitrobenzenesulphonic acid 8.51 8.53 - 100.2 8.51 8.53 100.2 8.51 8.55 100.5 17.02 17.04 100.1 17.02 17.04 100.1 Renzenesulphonic acid Bromochlorophenol blue Iodoacetic acid 9.39 9.39 9.39 9.39 18.78 7.78 7.78 7.78 15.56 15.56 50.05 50.05 50.05 9.52 9.49 9.52 9.62 18.92 101.4 101.1 101.4 102.4 100.7 7.81 100.4 7.78 100.0 7.77 99.9 15.40 99.0 15.40 99.0 49.95 49.80 50.50 99.8 99.5 100.9 Current 99.8 99.8 99.5 99.9 99.9 efficiency, yo 98.6 98.9 98.6 97.6 99.3 99.6 100.0 100.1 101.0 101.0 100.2 100.5 99.1 89 According to the first reaction sequence, near the end-point of the base titration there is virtually no base left to provide the anodic oxidation with sufficient m-cresolate ion.This difficulty can be overcome by previously adding to the titration medium a large amount (e.g., 0.2 M) of urea, a base much weaker than that to be titrated but still sufficiently basic to provide the m-cresolate ion required.Table I1 shows that in this way a lOOyo current efficiency for base titration in m-cresol was obtained, except for butylamine, the reason for which has not yet been clarified. Coulornetric Acid - Base Titration in Dimethyl Sulphoxide3 It is interesting to know whether and how coulometric acid - base titrations in dipolar aprotic solvents, such as dimethyl sulphoxide, might be performed.Except for some minor alterations we used the same equipment as for m-cresol. I t was found that lOOyo current efficiency could not be obtained for cathodic reduction in acid titration in dimethyl sulphoxide alone.However, this difficulty could be overcome by the prior addition of 0.1 M m-cresol to90 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Cheun. SOC. TABLE I1 COULOMETRIC TITRATIONS OF BASES IN WZ-CRESOL Amount added/ Compound pequiv Tribenz ylamine 30.0 Butylamine 35.61 Diphen ylguanidine 30.0 Trieth ylamine 43.20 Tetrameth ylguanidine 37.8 * Mean of 10 determinations.Amount Standard Current found/ Recovery. deviation, efficiency, 30.15 100.5 1.0 99.5 34.49 96.8 0.8 103.2 30.06 100.2 0.8 99.8 43.29 100.2 0.7 99.8 37.62 99.4 0.4 100.6 pequiv % % % the titration medium; its effect is based on the fact that the cathodic reduction leads to evolution of hydrogen gas and m-cresolate anion formation, confirmed by an increasing ultra- violet absorption peak at about 325 nm.The addition of 0.1 M m-cresol to the medium restricts the titration method to acids with pK, values of less than 7 in dimethyl sulphoxide, owing to the acidity of m-cresol. We found that at a platinised platinum-gauze electrode, 100 yo current efficiency is obtained directly, without any m-cresol, as is shown in Table 111. When we used the equipment for the titration of bases, lOOyo current efficiency still could not be obtained in the anodic oxidation unless we previously added 0.2 M hydroquinone to the titration medium, according to a proposal by Vajgand and MihajloviC.* However, the slight acidic properties of hydroquinone decrease the acid - base range that can be used in titrations in dipolar aprotic solvents such as dimethyl sulphoxide. We then realised that the beneficial effect of urea in m-cresol and of hydroquinone in dimethyl sulphoxide was based on their playing a role in proton transfer, and we concluded that anodic oxidation of hydrogen gas a t the generator electrode could be a more logical supply of protons.As a consequence, we studied first at a rotating platinum-disc electrode the anodic voltammetric curve for hydrogen TABLE I11 COULOMETRIC TITRATION OF SOME ACIDS IN DIMETHYL SULPHOXIDE - 0.2 M TEAP Platinised platinum-gauze (4 cm2) working electrode. Current = 3 mA.Compound Benzoic acid 2,4-Dinitrobenzenesulphonic acid Salicylic acid m-Cresol 2,4-Dinitrophenol 2-Nitrophenol Perchloric acid Current efficiency, yo 100.2 100.0 99.9 99.4 100.2 100.2 100.3 Number of measurements 6 Standard deviation, yo 0.6 0.2 0.6 0.7 0.4 0.2 0.1 TABLE IV COULOMETRIC TITRATION OF BASES IN DIMETHYL SULPHOXIDE - 0.2 M TEAP - HYDROGEN Platinised platinum-gauze (4 cm2) working electrode.Current = 3 mA. Current Number of Compound efficiency, yo measurements 1,3-Diphenylguanidine 99.9 11 Piperazinet 99.8 7 Sodium benzoate* 100.8 6 Tris (hydroxymethyl) amino- methane 99.9 7 1,1,3,3-Tetramethylguanidine 99.4 6 * Dissolves during titration.t Titration to the second end-point. Standard deviation, yo 0.4 1.5 0.4 0.7 0.4March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 91 gas in order to find conditions for lOOyo current efficiency. Without going into details of this study, which has been published,2 we can say that it is essential to use a platinised platinum-gauze electrode and that under such conditions 100~o current efficiency is easily obtained, as is shown in Table IV for four bases and sodium benzoate.A typical coulometric titration curve in dimethyl sulphoxide for 1,3-diphenylguanidine is shown in Fig. 5. We have found that this procedure with platinised platinum-gauze electrodes and hydrogen gas is of more general application in these non-aqueous media.We have confirmed this finding for acetonitrile and sulpholane, but this investigation has not yet been completed. 0 10 20 30 40 50 Eq u ivalen ts Fig. 5 . Titration curve of 1,3-diphenyl- guanidine in dimethyl sulphoxide. We are grateful to Elsevier Scientific Publishing Company for permission to reproduce some of the figures and tables, which were originally published in AnaZytica Chimica Acta.References 1. 2. 3. 4. Uos, M., and Dahmen, E. A. M. F., Analytica Chim. Acta, 1974, 72, 345. Hos, M., and Dahmen, E. A. M. F., Analytica Chim. Acta, 1974, 72, 169. Ros, M., Ypma, S. T., and Dahmen, E. A. M. F., Analytica Chim. Acta, 1976, 83, 39. Vajgand, V. J and Mihajlovic, R., Talanta, 1969, 16, 1311.Study of Processes Occurring in the Spectral Determination of I m pu r i t ies L. I. Pavlenko, L.V. Simonova, G. G. Babicheva,A.V. Karyakin and I. A. Popova V . I . Verrtadsky Institute of Geochemistry and Analytical Chemistry, USSR Academy ojsciences, Moscow, USSR A promising method of increasing the sensitivity and accuracy of spectroscopic methods of analysis is the study and employment of the regularities of processes occurring in the electrode crater and in the zone of spectrum excitation.The study of the physics and chemistry of processes of matter transition to the plasma state has helped in the development of techniques for the control of these processes in methods for the determination of impurities, including platinoids in solids and solutions. Promising methods for the determination of platinoids in the range 10-8-10-570 are chemical spectral methods, which require the development of direct spectral methods.In order to conduct the investigations, standard samples on carbon powder (the collector used in the chemical spectral analysis) containing complex chlorides of platinoids were92 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. analysed using medium- and high-dispersion spectrographs, a d.c. arc and vaporisation from the channel of the carbon electrode. The way in which elements enter the plasma state is, to a considerable extent, connected with primary processes occurring in the electrode crater. In order to establish this connection a thermodynamic examination of possible chemical reactions has been carried out, using standard samples (complex chlorides with graphite) for platinum and palladium.The temperature dependence of the saturated vapour pressure of these elements and their chlorides has been calculated (Fig. 1). These results allow the assumption that the greater amount of the elements enters the gaseous phase as a result of the reduction and the vaporis- ation of the reduction products.In heating the samples concerned it is most probable that sublimation of platinum(1V) chloride (reaction 1, see Fig. 1) and thermal decomposition of platinum(1V) chloride to platinum(I1) chloride (reaction 2) occurs. Further heating (from 700 to 2 000 “C) causes decomposition of platinum( 11) chloride to the metal with evolution of chlorine and sublimation of both platinum(I1) chloride and the metal (reactions 6 and 7).The probability of reactions 4 and 5 occurring is much less than that of reaction 2. The thermodynamic calculations are in good agreement with the evaporation curves for complex chlorides of platinum (Fig. 2). As can be seen from Fig. 2 the curve of hexachloro- platinate( IV) evaporation has three maxima corresponding to sublimation of platinum( IV) , platinum(I1) and metallic platinum.The presence of metallic platinum in the residues of the standard samples has been confirmed by radiographic analysis data. All of this enables us to assert that the duration of platinoid evaporation is accounted for by the formation of metals with high boiling-points (4 000-5 000 “C) in the electrode crater.An exception is palladium, which completely evaporates in a relatively short time (1 min) in the form of palladium(I1) chloride. Thermodynamic calculations have confirmed that the evaporation rate of palla- dium(I1) chloride is substantially higher than the rate of thermal dissociation of the initial product into metallic palladium and chlorine.0 1 2 3 Temperature x 10-3/K Fig. 1. Dependence of saturated vapour pressure on temperature for the following reactions : PtCl,(s) + PtCl,(g) (1) PtCl,(s) 3 PtCl,(s) + Cl,(g) (2) PtCl,(s) 3 Pt(s) + Cl,(g) (3) PtCl,(s) -+ PtCl,(s) + W,(g) (4) (5) PtCl,(s) + PtCl,(g) ( 6) Pt(s) + PW (7) PtClJs) + PtCl(s) + ;cl,(g) \ . L.5’, , ,\‘l-.L [ 0 30 60 90 120 150 180 Time,’s Fig. 2. Platinum evaporation in the form of: 1, hexachloroplatinate- (IV) : 2, tetrachloroplatinate(I1) ; and 3, metallic platinum.11 is the intensity of a spectral line; If is the intensity of the background. In order to shift the reaction equilibrium towards the formation of easily volatilised com- pounds of the platinoids “carriers,” sodium chloride and gallium(II1) oxide, were added to the samples, which changed the evaporation character and did not change the average volatil- isation rate.In addition, the presence of carriers changes the conditions of element excitation. The arc temperature is lowered from 7 000 to 6 500 K when gallium(II1) oxide is added and to 5 000 K when sodium chloride is added. The inter-electrode distribution of palladium, ruthenium and rhodium atoms is also changed in the presence of gallium(II1) oxide (Fig.3). The addition of carriers to the samples increases by one and a half or two times the duration of the platinoid atoms in the zone of discharge. The average duration of atoms in the arc was measured by the method of pulse introduction ofMarch, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 93 the matter into the plasma of discharge.carrier and varies depending on their relative atomic mass. For platinoids it is equal to about 2 ms without (a 1 1.0 - - 0.5 I I 1 2 3 0 1 2 3 Cathode 0 Anode Cathode Anode Distance/mm Fig. 3. Inter-electrode distribution of (a), iridium and (b), rhodium atoms in the absence, (1) and in the presence, (2) of 3% Ga,O,. Thus, the carriers change the conditions of evaporation and excitation of plat inoids, increas- ing the sensitivity of their determination by an order or more.In order to improve the method arc discharge in an argon atmosphere (the Stelwood method) was used, which allowed the lowering of the detection limits of platinoids by half an order? Another method of raising the sensitivity is the analysis of dry residues of diluted solutions on the electrode butt.The efficiency of this method is explained by a rapid and non-selective supply of the sample into the discharge as a result of instantaneous evaporation and sputtering, which creates a high concentration of atoms in the plasma and favourable conditions for their excitation, and also by the absence of base.2 When platinoids in extracts are determined by means of analysis of the dry residue on the butt of the electrode the use of sodium and gallium chlorides slightly increases the intensity of their lines.A most effective carrier is barium nitrate, which raises the intensity of platinoid metal lines from five to ten times. This increase is connected with the fact that chemical reactions also proceed on the end face of the electrode.However, as the reducing atmosphere is much lower here (in comparison with the crater), reactions between impurities and the chemically active carrier favouring the transition of platinoid compounds to more easily volatile compounds are most probable, according to data obtained by means of thermodynamic calculations. This supposition is confirmed by curves of the volatilisation of platinoids, which have only one maximum in the presence of barium nitrate as compared with curves obtained without carrier, while their evaporation time decreases to 10 s.In the presence of barium nitrate the electronic pressure increases, while the arc temperature decreases to 5 500 K and varies depending on the concentration of ~ a r r i e r . ~ For the spectral determination of the most widespread impurities (magnesium, nickel, chromium, manganese, cobalt, boron, iron, aluminium, etc.) a great number of carriers with different anions and different cations have been investigated in diluted solutions by the thin- layer method.Investigation of the increase in mineral content of natural waters while determining certain impurities by the method of analysis of dry residues on the electrode butt has shown that sensitivity increases and has an optimum value at a mineral content of 2-10 g 1-l.Hence, macro-components of waters (calcium, magnesium, potassium, sodium) serve as carriers up to a certain concentration. The method developed with the use of effective carriers allows the determination of mag- nesium, iron, cobalt, nickel, copper, zinc, molybdenum, lead, chromium, vanadium, tin and titanium with a limit of detection of 1 x 10-3-3 x A further lowering of the limit of detection of impurities was achieved when the magnetic field created by a permanent magnet or an electromagnet was applied to the discharge. A field intensity of 200-300 Oe is the optimum for an increase in the intensity of the spectral lines of the elements of 2-10 times The most effective carriers are barium nitrate and indium sulphate. mg l-1.494 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chem. SOC. on average. The use of a carrier leads to the reduction of the positive influence of the magnet- ic field of solenoids. It has been established that the simultaneous action of the carrier and the magnetic field being created by permanent magnets, with the use of the thin-layer method, still further raises the intensity of the lines of a number of elements. An increase in intensity is observed both with ionic and atomic lines of element^.^ When the magnetic field is applied to the arc discharge, an arc temperature rise from 5 900 K without the magnet to 6 500 K is observed, the electron concentration increasing and the plasma geometry and the movement of the charged plasma particles being changed also. This study has made it possible to elaborate sensitive methods of spectral determination for more than 20 impurities, including platinoids, both in the crater and on the end face of the electrode in various samples using, in some instances, preliminary chemical concentration with the aid of extraction and co-precipitation methods. The detection limits of direct spectral methods are from to and of chemical spectral methods (at an enrichment coefficient of one hundred) from The relative standard deviation is from 0.10 to 0.15, depending on the element and the concentration. to References 1. 2 . 3. Pavlenko, L. I., Simonova, L. V., Karyakin, A. V., Ozhegov, P. I., and Popova, I. A., Zh. Prikl. Zilberstein, Kh. I., “Spectral Analysis of Pure Matter,” Khimiya, Leningrad, 1971. Pavlenko, L. I., Ozhegov, P. I., Popova, I. A., Simonova, L. V., and Karyakin, A. V., 212. Analit. 4. Karyakin, A. V., Pavlenko, L. I., and Safronova, N. S., Zh. Analit. Khim., 1975,30, 775. 5. Karyakin, A. V., Pavlenko, L. I., and Babicheva, G. G., Zlz. Analit. Khim., 1973,28, 2402. Spektrosk., 1974,20, 962. Khim., 1977,32, 1564.

ISSN:0306-1396    

DOI:10.1039/AD9781500078

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

94 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chem. SOC. Furnace Atomic-absorption Spectrometry Using an Atomiser with a Resistance Sensor for Precise Temperature Control J. E. Cantleand C. J. Kirby Technical Services Division, Instrumentation Laboratory (U.K.) Ltd., Edgeley Road TYading Estate, Cheadle Heath, Stockport, Cheshire, SK3 OXE There has been a considerable improvement in furnace atomisers, and present units give better analytical results and are easier to use than the devices of only 3 years ago.Neverthe- less, they should not be used unless it is absolutely necessary. For the analyses that can be done with flames, flames are nearly always the best choice. If a sample can be dissolved readily to obtain at least 1-2 ml of solution with a reasonable viscosity and containing the analyte element at least five times the flame limit of detection, then it should be nebulised into a flame.If any of these criteria cannot be met then furnace atomic absorption may well make the analysis possible. The purposes of a furnace temperature programme are drying liquid samples, melting solid samples, removing or partially removing a matrix, catalysing chemical changes to enhance atomisation, catalysing chemical changes to ensure that only one form of analyte is present at atomisation, catalysing reactions intentionally used for matrix modification, atomisation and cleaning of the furnace.Precise control over furnace temperature is essential during all stages of an analytical programme, no matter how simple it is; for example, a liquid sample must be evaporated carefully to avoid spattering.In the analysis of a volatile metal the pyrolysis stage must be carefully monitored in order to prevent premature volatilisation of analyte. The requirements of the atomisation stage vary: sometimes a very rapid tempera- ture rise-time is required to produce clean sharp signals ; alternatively, a con trolled tempera- ture ramp can often assist where complete destruction of the matrix has not been possible. In this last instance the heating ramp must be accurately reproducible. It is easy to use a transformer to produce a low voltage (10-20 V) on the atomiser and thereby obtain low current consumption on the Every furnace system is a.c.-heated.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 95 primary side of the transformer.There are, in principle, different ways of controlling the heating of the atomiser, vix., voltage, current, power and measured temperature. In the first instance a voltage is applied across the furnace, which will be heated to a temperature at which the supplied power (Pin) is dissipated by conduction (Pc), radiation (P,) and increase in atomiser temperature (Pt). Pi* = P, + PI- + pt The heating is not uniform along the graphite tube.The ends of the tube are pressed into electrical contacts that are water-cooled. There is thus a strong temperature gradient in the tube, to which the effect of conduction is directly coupled. The dimensions of the atomiser will control the amount of radiation losses.Further, the behaviour of Pt is a function of the dimensions, the resistivity of the material (varies from one graphite quality to another) and the contact between the electrical terminals and the graphite tube. This clearly implies that the part used for the temperature increase may vary, depending on several factors. Another way of supplying power to the atomiser is to use constant current.This provides no improvement compared with constant voltage. In both instances no back coupling from temperature to supplied power is achieved. A further result is that two different voltages or currents will not only give different final temperatures, but also different heating profiles, as will be shown below. By applying a constant voltage and measuring the current in the circuit, an expression for power is obtained.This information can be used to supply a fixed power, which compensates for changes in graphite tube resistance. Significantly, however, the be'st method of programme control is to use a sensor that actually measures the temperature of the tube. This information is then fed back in order to control the power supply. One can liken the operation to that of a thermostat controlling and regulating the temperature of a water-bath or oven.Temperature-controlled heating (TCH) of graphite furnace atomisers was first described by Lundgren et al. ,l working in Sweden at the University of Umea. They described an optical sensor, a photodiode, mounted at a distance from the tube and providing the fast response needed for exact regulation of heating rates.They claimed an operating temperature range down to as low as 550 "C, although the practical lower limit was probably higher ; the lowest temperature, for instance, at which they measured regulation accuracy was 765 "C. In practice, this limitation prevents the desired control at the drying and pyrolysis stages. This paper describes a commercially available graphite furnace atomiser equipped with a resistance sensor in order to measure tube temperature.The temperature sensor is a U- shaped wire loop mounted immediately behind and in contact with the graphite tube. This is a tungsten-based resistance thermometer. The resistance of the material rises directly as the temperature of the furnace rises, and this parameter is used directly as part of an electronic feedback circuit to operate from room temperature up to 2 900 "C, the melting-point of the sensor.There are two fundamental attractions of TCH, viz., the furnace temperature is controlled and regulated more precisely and accurately to enable careful and reproducible sample evaporation and pyrolysis, and it enables the most rapid temperature-rise time (if required) during atomisation, independent of final furnace temperature, thus producing tall, sharp peaks.Some examples of these benefits to furnace atomic absorption analysis will now be presented. The easiest way is to use constant voltage or current programming. A third way is to use a combination of these two earlier mentioned methods. Determination of Cadmium in Blood This determination is illustrated in Fig.1 ; the method of standard additions was used. The levels of cadmium present in blood permit dilution ratios of 1 : 50 or even 1 : 100 without losing detectability. In this experiment a pooled blood specimen was diluted fifty-fold with water and 10-pl sample volumes of this and the addition solutions were determined. It was found that pyrolysis pro- ducts (smoke) were observed from 220 "C, but that cadmium was volatilised at temperatures in excess of 285 "C without any matrix modification.The programme used was therefore a ramp dry from ambient temperature to 285 "C in 3045 s; this temperature was then held The dilution of the matrix reduces the degree of pyrolysis needed.96 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. precisely for a further 60-75 s in order to destroy the majority of the organic constituents. Atomisation then followed using a step to around 1 500 "C which effectively cleaned the tube prior to the next sample injection. The sensitivity of the analysis was calculated from the 2.36 pg per 100 ml solution giving an absorbance of 0.44.The characteristic concentration (1% absorption) for cadmium is, therefore, 0.05 pg as an absolute mass or 0.005 pg 1-1 based on a 10-p1 injection. As a demonstration of the reproducibility of the furnace programme, a relative standard deviation of 2-4% was readily achieved using manual pipetting of a 10-p1 sample. Determination of Cadmium in 4% Brine This determination resembles the previous example but is, however, a totally different analysis, illustrating a powerful feature of TCH.As is shown in Fig. 2, there isinsignificant non- specific absorption (pyrolysis products) until 750-800 "C is exceeded. The matrix cannot be destroyed without loss of cadmium. An atomisation temperature of 800 "C was used; at this value the non-atomic signal was well within the capability of the background corrector.The cadmium atomic signal was the optimum, a feature of the heating system, because although the final temperature was kept low to minimise the sodium chloride signal, the heating rate was still at full power to produce the maximum cadmium absorbance. Even under these unusual conditions nine 10-p1 injections of 5 p.p.b. (parts per 1012) of cadmium returned a relative standard deviation of 2.8%.TCH of the furnace in this application facilitated this analysis. A voltage- or current-controlled furnace atomiser set at 800 V on atomise would produce an inadequate heating rate to give anything other than a very broad cadmium atom signal. 2 pg per 100 ml 0 0.4 0.2 0.1 I- 0 Fig. 1. Determination of cad- mium in whole blood by the stand- ard additions method.Sample 3 Q) E 2 +? 0, a 51 1 / C fi 50 pg Cd 0 ' I I I 600 700 800 900 1000 1100 1200 Atomisation temDerature/OC .~ _. ~ DreDaration. dilute 1 : 50 with wat'er : r r sample injections, 10 pl; pyrolysis, Fig. 2. Determinaton of cadmium in 4% a t 285 "C for 60-75 s. brine. Uetermination of Kefractory Metals Fig. 3 shows the determination of indium, plotting absorbance versus atomisation temperature with and with- out temperature feedback.On the lower graph an absorbance of 0.08 is obtained at 2 300 "C and this builds up gradually to about 0.3 at 2 900 "C. Using feedback, however, the upper graph is obtained and an absorbance of 0.4 is produced at a temperature as low as 2 300 "C. This results directly from the rapid temperature gradient independent of final temperature.Without feedback lower and broader peaks are obtained, and only at high temperatures does the sensitivity approach that obtained using TCH. Other obvious advantages of the top curve are the improved lifetime of the tube, running at lower powers, and the improved precision from working on a plateau part of the graph. Maximum sensitivity could be These determinations can be made more easily and sensitively using TCH.Platinum behaved similarly although less dramatically.March, 1978 0.4 0.3 0 m -2 0, 0.2 a I) 0.1 FOURTH INTERNATIONAL SAC CONFERENCE - - - - - 97 Feedback in I I I I I 2 300 2 500 2 700 2 900 Atomisation temperature/OC Fig. 3. Determination of indium with and without temper- ature feedback.obtained at 2300 "C, whereas without any feedback one would need to atomise close to 3 000 "C. The detection limit is clearly much lower. This element has not been determined to this sensitivity on alternative systems. Fig. 4 illustrates titanium signals at 0.1 and 0.2 p.p.m. The blanks at the beginning and end are a sign of little or no memory. 0.4 T 0 2 0.2 a .L 2 0.1 pg mt-' ' 1 .0.2 pg mI-' 1 Blank t 11 I T i m e d Fig. 4. Signals obtained in titanium determination for 0.1 and 0.2 pg ml-1. Sample volume, 25 pl; atomisation temper- ature, 2 750 " C ; pyrolysis, 1 200 "C; sensitivity, 55 x 10-l2 g. Uranium is a still more refractory element, yet even this element was measured below 1 p.p.m. reasonably well. Fig. 5 shows six peaks obtained at full power with feedback (2 900 "C).Uranium has generally been regarded as an element that is too insensitive for furnace atomic absorption, but it is clearly possible to measure it with this apparatus. One final benefit of furnace TCH is the possibility of dual-element analysis using dual- channel instrumentation. It has been shown that all elements have a long flat portion in their graph of absorbance veysus atomisation temperature. Thus, once a certain threshold temperature has been reached, a higher value neither adds to nor detracts from the results.To determine two elements at once it is only necessary to set the atomisation temperature to that required for the more refractory of the two metals. Thus, in order to determine arsenic and iron simultaneously, for example, the atomisation temperature would be set to 2 200 "C.The attractions of simultaneous measurement are clear; less sample is needed and the analysis time is halved. A dual-channel spectrometer can also use its second channel as an internal98 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chem. SOC. standard. This technique makes furnace results completely independent of injection volume as the instrument is computing a ratio.Thus, all irreproducibility associated with sample injection suddenly vanishes. 0.03 0.02 al 0 ru f 9 0.01 0 0.9 pg mi-' a 4 I Time Fig. 5. Uranium peaks obtained a t full power with feedback. Sample volume, 25 pl; atomisation, 2 900 " C ; pyrolysis, 1 100 " C ; sensitivity, 3 100 X 10-12 g. Conclusion Furnace atomic-absorption analysis has developed significantly, complementary to flame atomic absorption.Temperature- controlled heating of the furnace, and furnace auto-sampling accessories, will assist the tech- nique to assume a similar degree of instrumental maturity and enable furnace methods to attain their deserved place in modern ultra-trace metal analysis. All of its advocates and users are probably still learning.Reference 1. Lundgren, G., Lundmark, L., and Johansson, G., Analyt. Chem., 1974,46,1028. Mass Spectrometric Study of Metal Chelates J. R. Majer and K. Al-Kuwaity Chemistry Department, University of Birmingham, P.O. Box 363, Birmingham, B15 2TT While it is only the chelates of metal ions derived from 1,3-diketones or their derivatives that are sufficiently volatile and stable to be distilled without decomposition or passed through a gas-chromatographic column, there are many other metal chelates that are sufficiently volatile and stable to permit their direct evaporation into the ion source of a mass spectrometer and the recording of their mass spectra.Since the first observation, in 1967, that nickel butane-2,3-dione dioximate and the nickel derivatives of other dioximes could be examined in this way,l a variety of metal chelates with widely different properties, including the metal derivatives of quinolin-S-o1,2 fluorinated 1,3-diketone~,~ thioketones4 and azo dyes,5 have been studied.Many of these compounds are those which have been used by analysts for many years to detect and quantify metal ions. The mass spectra that have been obtained have been easy to interpret because of the stability of the chelating agent, and peaks due to the molecule ion, the molecule ion with successive losses of one, two or three ligand fragments and to metal ions, have been predominant.The mass spectrum of a metal chelate has thus provided a great deal of information, including structural details, the purity of the sample of the metal ion and the isotopic constitution of the metallic element.An example of this ability to resolve structural detail is given by a study of the precipitation of nickel ions in the presence of twoMarch, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 99 different dioximes, vix., butane-2,3-dione dioxime and cyclohexane-l,2-dione dioxime.6 It can be seen from the mass spectrum of the precipitate that not only are there present the nickel derivatives of both dioximes, but also a metal chelate in which the nickel atom is attached to one of each of the dioximes.Further, it can be shown that this mixed nickel chelate is formed during the precipitation process and not during the evaporation into the ion source by compar- ing the spectra obtained with those from a simple mixture of the two separate metal chelates.The high sensitivity of the mass spectrometer can be used to determine very small amounts of metal chelates, and hence of metal ions, provided that pure samples are available for prior calibration. It is possible to record the ion current at one, or several, selected mass values continuously instead of recording a complete mass spectrum.If, for example, the mass value corresponding to the molecule ion of a metal chelate is selected, then it is possible to record the change in the ion current at this particular mass value during the course of the evaporation of a small known mass of sample. Then, the area under the curve of ion current plotted against time is proportional to the amount of sample evaporated. A calibration curve of peak area against the amount of sample evaporated can thus be constructed and the amounts of unknown samples determined by reference to this curve.In this way, metal chelates, or the metal ions from which they have been derived, can be determined in the nanogram range, or, in advan- tageous cases, at the picogram 1evel.l The sensitivity of the method depends only upon instrumental characteristics and the nature of the mass spectrum. The particular mass values chosen for integration should correspond to those at which large peaks are obtained in the conventional mass spectrum.On the other hand, the mass value chosen should be characteristic of the metal chelate being evaporated so as to avoid the possibility of undesirable interferences. A factor that reduces sensitivity is the polyisotopic character of the metal ion, in that the total current due to, for example, the molecule ion is distributed over a number of mass values.The one disadvantage of this technique is the necessity to maintain constant the sensitivity of the instrument or to provide some internal standard.One approach has been to maintain a constant pressure of a second reference substance within the ion source during the course of the evaporation of the metal chelate. Any variation in instrumental sensitivity is then reflected in the variation of the signal due to the reference compound. A more successful method has been to use a variation of the isotope-dilution technique and to mix the unknown sample with an appropriate amount of a second metal chelate, identical in structure, but hav- ing an isotopic constitution which differs from the natural.The ion current is then recorded at two mass values corresponding to ions containing two different isotopes, and the amount of the unknown sample determined by comparing the areas under the two peaks. It has been assumed so far that the ion current a t one particular mass value is derived from only one molecular species, but it is possible that ions derived from different molecules will have the same atomic constitution and will therefore contribute to the ion current at the same specific mass value.If there is no difference in the rate of evaporation of the two different molecular species, then the curve of ion current against time will remain as a single peak of approximately Gaussian shape.If, on the other hand, there is a difference in the rate of evaporation, then the peak shape will be distorted, and under favourable circumstances two peaks will be recorded, each due to ions derived from a single molecular species.' An extreme example of this duality is where the two different molecular species are structural isomers.Many metal chelates exist in two or more isomeric forms, and it has been shown that the difference in their rates of evaporation is sufficient to permit the recording of ion current curves against time which exhibit peaks due to the separate isomers. Among the metal chelates that have been shown to exist in isomeric forms by this method are those derived from quinolin-8-ol,* asymmetrical 1 ,3-diketonesg and monothio-1 ,3-diketones.1° As the ionisation cross-section for two isomeric forms does not differ perceptibly, it is not necessary to carry out any prior calibration before determining the relative amounts of two isomeric forms in a sample.Salicylaldoxime forms metal chelates with nickel and palladium, and these are sufficiently volatile at a temperature of 245 "C to be evaporated into the ion source of a mass spectrometer.The resulting mass spectrum exhibits an intense molecule ion peak, and this mass value has been selected for integration. When 1 pg of nickel salicylaldoximate is evaporated a t 245 "C and the ion current at m/e 330 is recorded continuously, the resulting ion-current curve is in the form of a pair of peaks.These two peaks correspond to the cis and trans isomers of nickel100 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chem. SOC. salicylaldoximate, and when the chelate is precipitated from ammoniacal solutions containing nickel, the cis :trans ratio as determined from the areas of the two peaks is 0.88.When nickel salicylaldoximate is stirred with ice-cold acetone, preferential solution of the cis isomer occurs, and the trans isomer is left after filtration in the form of dark green crystals. The deep yellow filtrate, upon evaporation, yields light green crystals of the cis isomer. After two such equilibr- ations, the two isomers are completely separated. Upon evaporating each sample into the ion source and recording the molecule ion current, the resulting record shows only a single peak in each case.The nuclear magnetic resonance spectra of the two samples are identical, and there are only very slight differences in the infrared spectra. The ultraviolet spectrum is also the same for both isomers, consisting of a single peak with a maximum at 372 nm, which is virtually identical with that of salicylaldoxime itself.There is, however, a difference in the visible region of the spectrum, the trans isomer showing a small peak in the red with a maximum at 610 nm. This peak is weaker andshifted to the blueend for the cisisomer. The irradiationof theisomers of nickel salicylaldoximate in the two separate regions of absorption was now studied.When a 0.1% solution of the trans isomer in dimethyl sulphoxide was irradiated at 330 nm with the light from a cadmium-vapour lamp and samples examined in the mass spectrometer at l-min intervals, a second peak due to the cis isomer appeared, and this increased in size steadily until the ratio of cis to trans isomers was0.8. When asecond sample of the trans isomer was irradiated at 610 nm with the light from a tungsten lamp, the rate of isomerisation was much slower, but after 2.5 h the cis :trans ratio had become 0.83.The thermal isomerisation of the isomers of nickel salicylaldoximate was now studied by placing 0.1 yo solutions of the isomers in dimethyl sulphoxide into a thermostatically controlled bath and measuring the change in the cis:trans isomer ratio at 15-min intervals.The bath was maintained at a series of temperatures between 50 and 100 "C. In all instances, after 15 min at the elevated temperature the second isomer began to appear in the curve of molecule ion current against time. The ratio of the two isomers rose and then became approximately steady after heating for 1 h. The variation in the cis : trans isomer ratio with time at constant temperature can be expressed in an equation of the form where [M,] and [M,] are the concentrations of the cis and trans isomers in mole l-l, k, and k , are the rate constants for the forward and back reactions, t is the time in s and K the equili- brium constant or the cis:trans isomer ratio at equilibrium.A graph of [M2]/[Ml] against t takes the form of a curve, rising steeply at first and then increasing slowly to the equilibrium value.Experimental results obtained for the thermal isomerisation of nickel and palladium salicylaldoximate can be fitted to a curve of this type, typical values of k, and k , at 50 "C being 1.4 and 4.6 x lo-* s-l. The value obtained for the cis: trans isomer ratio under steady condi- tions increased with increase in temperature.The variation in the final cis : trans isomer ratio, which can be identified as the change of equilibrium constant K with temperature, can be used to calculate the free energy change for the isomerisation at any temperature using the relationship Combination of the results obtained for the free energy change can now be used to calculate the TABLE I ISOMERISATION OF NICKEL SALICYLALDOXIMATE AG = --RTlOg,K K AS*/ AH*/ 4 450 333 0.29 816.1 - 343 0.35 713.0 11.3 4 450 353 0.43 589.7 12.3 4 440 363 0.49 512.7 7.7 4 470 373 0.58 389.3 12.4 4 450 cal I<-l mol-1 cal mol-l Temperature/ (average peak AG/ K area ratio) cal mol-' * The average value for A S is 10.9 cal K-l mol-l and the average value for A H using this value is 4.45 kcal mol-l.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE enthalpy of isomerisation, AH, and the entropy change, AS, using the relationship AG = AH - TAS Typical results for the isomerisation of nickel salicylaldoximate are given in Table I. 101 1.2. 3. 4. 5 . 6. 7. 8. 9. 10. References Jenkins. A. E., and Majer, J. R., Talanta, 1967, 14, 777. Jenkins, A.E., Majer, J. R., and Reade, M. J . A., Talanta, 1967, 14, 1213. Kowalski, B. R., Isenhour, T. L., and Sievers, R. E., Analyt. Chem., 1969, 41, 998. Belcher. R., Stephen, W. I., Thomson, I. J., and Uden, P. C., J . Inorg. Nucl. Chem., 1971, 33, 1851. Betteridge, D., and John, D., Talanta, 1968, 15, 1227. Charalambous, J ,, “Mass Spectrometry of Metal Compounds,” Butterworths, London, 1975.Majer, J. R., and Perry, R., J . Chem. SOC., 1970, 822. Majer, J. R., and Reade, M. J . A., Chem. Commun., 1970, 58. Belcher, R., Majer, J. R., Perry, R., and Stephen, W. I., Analytica Chim. Acta, 1968, 43, 461. Thomson, I. J., Ph.D. Thesis, University of Birmingham, 1970. Some Applications of Newer Mass Spectral Techniques in the Analysis of Organic Compounds D. E. Games, J.L. Gower, M. G. Lee, I. A. S. Lewis, Margaret E. Pugh and M. Rossiter Department of Chemistry, University College, P.O. Box 78, Cardiff, CF1 lXL, Wales For a number of years we have been concerned with the application of mass spectral methods in the identification and quantification of organic compounds, particularly when these com- pounds are present in crude mixtures. In the main our studies have concentrated on extracts of drugs and their metabolites from biological fluids and extracts of natural products from plant or animal sources.To date we have concerned ourselves with the way in which soft- ionisation mass-spectral techniques, chemical ionisation (CI) , field ionisation (FI) and field desorption (FD), can supplement and complement the information obtainable from electron impact (EI) mass spectrometry.FI and CI used with combined gas chromatography - mass spectrometry (GC - MS) have proved particularly effective in the determination of relative molecular masses of compounds that do not readily provide this information on being subjected to EI,1-4 and these techniques have been useful in quantitative studies of drugs and their metabolites as higher mass ions can be monitored by selected-ion monitoring (SIM) and hence there is less interference from ions of endogenous materials in the crude extracts4 Many thermally labile compounds or compounds of low volatility do not provide useful mass-spectral data when examined by EI, CI or FI.We have found FD mass spectrometry particularly effective in many of these instances because it provides relative molecular masses and often structurally significant fragment ions2y5-7 for many of these compounds.A second area in which FD has proved effective is in providing relative molecular mass profiles of mixtures of compounds, and in monitoring extracts prior to GC examination, thus providing a check for decomposition and for absorption during GC or GC - MS.2,5-7 This technique has proved effective in many instances, particularly for crude extracts of the plant CaZophyZZum inophyZZum, where many compounds decompose or are not amenable to GC studies.* Liquid chromatography (LC) is an effective method for studying thermally labile or involatile com- pounds and we have effected separations of crude extracts of C.inophyZZum by this technique, collecting the components of interest, and subjected these samples to mass-spectral study.This is an extremely time consuming process if complex mixtures are being investigated and an on-line LC - MS system would be preferable. Such a system would also enable multi- component peaks to be resolved by use of SIM or mass chromatography and enable quantit- ative results to be obtained by means of the techniques used in GC - MS.102 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. Recognising the need for a combined LC - MS system, we have recently acquired a moving belt interface of the type developed by McFadden et for our Finnigan 4000 mass spectro- meter. The interface is based on the moving-wire system developed by Scott et aZ.,lO but has a higher sample yield, 2540°/0, and is a continuous system.We present here some of the data that we have recently acquired by use of this system. All of our studies have used a system similar to that described by McFadden et a1.,9 except that a kapton belt was utilised instead of the stainless-steel belt originally de~cribed.~ Initially, we placed solutions of a wide variety of organic compounds (e.g., steroids, triglycerides, plant phenolics, drugs and their metabolites, aminoglycosides) directly on to the belt and compared their EI and CI spectra with those obtained by conventional probe techniques.This was followed by an examination of the spectra obtained from single compounds injected on to the LC and by the obtaining of spectra using the LC - MS interface. Table I gives two examples of the results obtained from these studies.The compounds selected were both thermally labile and were not readily amenable to GC study. The EI data is comparable except that there is some CI [i.e., enhanced (M + 1)+ ions] character in the spectra obtained. CI data is more difficult to compare as CI spectra can show considerable variation depending on source temperature and pressure and it is difficult to obtain a direct comparison.In both instances the ions obtained when using CI corresponded well, but there were marked relative abundance differences. This difference was less noticeable with less labile compounds, e.g., phenobarbi- tone and its hydroxy metabolite. Since it takes approximately 20 s to record spectra when the sample is loaded directly on to the belt, we have found little evidence of memory effects.The system provides an efficient automated probe and we have already made considerable use of the system in this context. TABLE I COMPARISON OF SPECTRA FROM BELT AND PROBE Compound Ionisation m/e (% relative abundance) Isoimperatorin (I) EI* Probe 270(1), 203(12), 202(100), 174(19), 69(82) Belt$ 271(6), 270(12), 203(58), 202(100), 174(83), 69(90) CI(methane) Probe? 271(69), 231(23), 203(100), 69(18) LC-MSf 271(42), 231(16), 203(100), 69(20) LC-&IS$ 387(3), 386(2), 203(20), 202(42), 185(38), 83(100) LC-MSf 387(100), 369(13), 287(38), Ostruthol (11) EI* Probe 386(3), 202(11), 185(32), 83(100) CI(methane) Probe? 387(100), 369(10), 185(62), 83(19) 203(100), 185(36) * Vaiian CHBD, source 210 "C, 70 eV.t Finnigan 3200, source 150 "C. $ Belt speed 2.4 cm s-l, vaporiser 200 "C (indicated), clean-up heater 200 "C (indicated), source 200 "C (indicated). The quantitative possibilities of the system have been partially assessed by loading solutions containing 1-2 ng of the drug bethanidine (111) and 20 ng of its diethyl analogue (IV) on to the belt and monitoring the M+ or (M + 1)+ ions in the EI or CI mode, respectively.In both instances sharp SIM traces showing no memory effects were obtained and a linear relationship was found for a plot of the ratio of peak heights versus mass ratio of I11 to IV. The detection limit in the CI mode was 50 pg. Thus, this system can be utilised for carrying out assays normally carried out by direct probe in the EI or CI mode, with a considerable saving in the time required for such assays.To date on-line LC -MS quantification has not been attempted, but we feel that it should be possible with many types of compound. Most of our attention has been directed to evaluating the use of the LC - MS interface for obtaining qualitative data.We have examined a wide variety of compound types in this context, e.g., steroids, natural coumarins, flavanoids, drugs and their metabolites and trigly- cerides. In all instances good quality EI and CI spectra have been obtained; however, the quality of the total ion current traces (TIC) has been very dependent on the solvent systems and flow-rates used. Fig. 1 shows the TIC and ultraviolet traces for a mixture of hydroxy- coumarins ; the resolution shown here has recently been considerably improved by utilising a lower dead volume system for feeding the eluting agent on to the belt.More polar solventMarch, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 1 03 CH3 OCOC-CH 1 I II NR II O/CHzNHCNHH I l l , R=CH3 IV, R = C2H5 systems often cause problems by yielding very crude TIC traces and this appears to be due to solvent passing into the source.The problem can be alleviated by using a splitting system, so that the sample is not fed on to the belt at the flow-rate used to conduct the separation, or by use of an infrared reflector.ll This latter technique has resulted in a considerable improve- ment in the types of solvent system that can be handled; for example, acetonitrile, ethyl acetate or propanol can be handled at flow-rates of 0.8-1.0 ml min-l and water at 0.2-0.3 ml min-l, andthus data from reversed phase systemsisobtainable.One major advantage of this type of interface over some others reported to date is that it can handle gradient elution systems and we have used it in order to study the LC of crude extracts of C.inophyZZum,8 both in the EI and CI mode. Excellent spectra were obtained throughout the runs, comparing well with spectral data obtained from samples that had been collected from peaks of interest. A A L Fig. 1. Combined LC - MS of 7-hydroxy-4- phenylcoumarin (A) and 5,7-dihydroxy-4- phenylcoumarin (B): (a), TIC trace; (!), ultraviolet trace at 280 nm.Column, Partisil 5 ; solvent, hexane - ethanol - acetic acid (90 + 10 + 0.1) at 1 cm3 min-l; methane CI; source temperature, 200 "C (indicated) ; vap- oriser, 200 "C (indicated) ; clean-up heater, 200 "C (indicated) ; belt speed, 2.4 cm s-1.104 FOURTH INTERNATIONAL SAC CONFERENCE Proc. Analyt. Div. Chern. SOC. Although we have, as yet, had insufficient time fully to evaluate our system, we believe that it provides good qualitative mass-spectral data for most compounds that are amenable to direct-probe examination. Some compromises will have to be made if high flow-rates (i.e., greater than 1 ml min-l) are to be used for LC separations, but our experiences to date indicate that mass spectral information is readily obtainable from most types of non-reverse phase systems.For reverse phase separations we believe that the infrared-reflection method is necessary and that this will also improve our non-reverse phase data. We look forward to studying the usefulness of this modification in the near future. A major limitation of the system in its current form is that it will be unable to provide data from compounds that are not amenable to direct-probe EI or CI rnass-spectral examination and that it is unlikely to provide data from systems using inorganic buffers.However, we believe that although it is desirable to be able to obtain data from these compounds and elution systems, a suitable interface and mass spectrometer, which can routinely provide data of this type, is not going to be available for some considerable time.1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Games, D. E., Jackson, A. H., Millington, D. S., and Rossiter, M., in West, A. R., Editor, “Advances in Mass Spectrometry,’’ Volume 6, Academic Press, 1974, p. 137. Evans, N., Games, D. E., Hewlins, M. J. E., Hughes, J . F. J., Jackson, A. H., Jackson, J. R., Kahn, N. A., Matlin, S. A., Rossiter, M., Saxton, R. G., Swaine, H.A., and Taylor, K. T., in Frigerio, A;: and Castagnoli, N., Editors, “Advances in Mass Spectrometry in Biochemistry and Medicine, Volume 1, Spectrum, New York, 1976, p. 357. Games, D. E., Jackson, A. H., and Millington, D. S., Tetrahedron Lett., 1973, 3063. Games, D. E., Lee, M. G., Lewis, I. A. S., and Rossiter, M., in Daly, N., Editor, “Advances in Mass Spectrometry.” Volume 7, Heyden, London, 1977.Games, D. E., Games, M. L., Jackson, A. H., Olavesen, A. H., Rossiter, M., and Winterburn, I-’. J., Tetrahedron Lett., 1974, 2377. Games, D. E., Trans. Biochem. SOC., 1975, 455. Mathias, A., Williams, A. E., Games, D. E., and Jackson, A. H., Organic Mass Spectrom., 1976, 11, Games, D. E., Gower, J. L., Haskins, N. J., Rossiter, M., and Scourides, P., in Daly, N., Editor, McFadden, W.H., Schwartz, H. L., and Evans, S., J . Chromat., 1976, 122, 389. Scott, R. P. W., Scott, C . G., Munroe, M., and Hess, J., Jr., J . Chromat., 1974, 99, 395. McFadden, W. H., personal communication. 266. “Advances in Mass Spectrometry,’’ Volume 7, Heyden, London, 1977. Digital Electrical Detection Spark-source Mass Spectrometry F. De Ceuninck, E. Van Hoye and F.Adams Department of Chemistry, University of Antwerp (U.I.A.), 2610 Wilrijk, Belgium In its basic configuration, spark-source mass spectrometry (SSMS) uses ion-sensitive emulsions for the measurement of the mass spectrum. The photoplates provide an integrative simul- taneous detection of the entire mass range, with high sensitivity and reasonable precision at high mass resolution of the spectrometer. The disadvantage is that even when automated microdensitometers are used for the processing of the plates and the evaluation of the data, the method is very time consuming and tedious.More recently, electrical detection methods based on the use of ion multipliers have been developed. In the scanning mode, the magnetic field intensity is varied so as to sweep the individual isotopic species over the first dynode of the multiplier in sequence and to record the mass spectrum on an analogue recording device.In the peak-switching mode, the magnetic field is switched to pre-set values that correspond to specified ions on the dynode and the collector current is integrated, Scanning electrical detection is fast, allows multi-element analysis but is inherently inaccurate because of the loss of mass resolution (about 500 instead of 5 000-10 000 with ion-sensitive plates).It is also rather imprecise owing to the short measurement time available for the analysis of each iso- tope. Indeed, small amounts of sample are consumed and consequently inhomogeneities of the constituents give rise to unreproducible results.Peak switching is more reliable in this respect but it is a mono-element method. These are used in two operational modes.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 105 Method A Jeol JMS 01 BM spark-source mass spectrometer was adapted for digital recording of the mass spectra. The ion current obtained with the scanning operation was digitised using a voltage-to-frequency convertor and presented to a 1 000-channel analyser used in the multi- scaling mode.This instrument was connected to a seven-track computer-compatible mag- netic tape so that the spectra could be stored and subjected by computer calculation to operations such as smoothing of the data, background subtraction, detection of peaks and integration of peak areas. The necessary software for these operations was developed for a PDP 11/45 computer and was written in Fortran.In addition to the advantages resulting from the possibility of storing and manipulating the data in a digital form, there is the possi- bility of signal averaging. Indeed, a number of mass spectra from a given sample can be collected and summed. The mean (signal-averaged) spectrum can be expected to correspond more closely to the mean sample composition and to provide a higher sensitivity through a gain in signal to noise ratio by a factor of 1/N, where N is the number of added spectra.Multi-channel-based digital SSMS has been described before but only in an exploratory arrangement.l In this work, a systematic study was undertaken in order to evaluate its use. It was also hoped that more general information on the analytical characteristics for the scanning-type electrical detection SSMS would become available through the increased preci- sion obtainable with the modified system.Results and Discussion Standard reference iron and steel standards NBS-SRM 661-665 were used because they contain a large number of minor and trace constituents that cover the entire mass range.They are reputed to be homogeneous. These samples were also intensively studied by SSMS.2 The gain in precision resulting from digital processing of the mass spectra is illustrated in Table I for measurements of molybdenum in NBS 661. The mean standard deviation for 24 measurements is lSyo for scanning with analogue collection of the data and 9% for digital collection.The accuracy is not improved by digital scanning because the mass resolution is not significantly improved. TABLE I The inaccuracy of the measurement is due to a spectral interference (94Zr+). RESULTS FOR MEASUREMENTS ON STANDARD NBS 661 Analogue scanning Digital scanning Parameter 82Mo 04Mo 86Mo 8& 07Mo DBMo IOO& ' 98Mo 94Mo 9Sbfo 9;Mo 97Mo BSMo lo& Mean ueak height 645 440 638 644 378 1089 403 640 441 668 697 410 970 411 ~~ -- Standard devigtion, % 14.6 19.0 13.9 16.3 21.4 19.1 20.2 8.9 10.1 6.9 9.2 9.1 7.2 -11.6 Standarderror of mean, yo 3.3 4.3 3.1 3.6 4.8 4.3 4.5 1.8 2.1 1.4 1.9 1.8 1.5 2.4 Calculated abundance, % 15.22 10.39 15.06 15.20 8.92 25.70 9.51 15.11 10.41 15.77 16.44 9.67 22.89 9.70 Natural abundance, ?L 15.84 9.04 15.72 16.53 9.46 23.78 9.63 15.34 9.04 15.72 16.53 9.46 23.78 9.63 Relativedeviation,-%- -3.9 $14.9 -4.2 -8.0 -5.7 +7.5 -1.2 -4.6 +15.2 +0.3 -0.5 $2.2 -3.7 $0.7 The extent of the influence of the inhomogeneous distribution of the minor and trace impurities on electrical detection SSMS was investigated.For example, for 100 consecutive measurements of 0.2 s for 52Cr+ (5 800 p.p.m.), 51V+ (110 p.p.m.), 20gBi+ (4 p.p.m.) and 20sPb+ (130 p.p.m.), the relative standard deviations are 7, 10,30 and !joy0, respectively.It is clear that electrical detection SSMS of both modes is possible only for impurities at the highest impurity levels. In order to be able to add together digitally recorded mass spectra, it is imperative that the starting mass and the scanning speed are reasonably constant. As a result mostly of hysteresis effects in the magnetic analyser, both the starting point and scanning speed varied with time for a 2-h period after adjusting the initial field intensity of the magnet.The individual spectra were therefore adjusted to the same starting mass and scanning speed using computer calculations relying on a few intense peaks in the spectra.Fig. 1 shows an individual mass spectrum of the mass region 200-215 for one of the NBS steel samples [Fig. 1 (a)] and the summed spectrum resulting from the superposition of 25 such spectra [Fig. l(b)]. The 0.25 p.p.m. lead impurity becomes readily detectable in the summed spectrum. Signal averaging overcomes this difficulty to a considerable extent.106 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. Channel number Fig. 1. (a), Single spectrum and (b), summation of 25 single spectra, for NBS-SRM-661. It thus appears that the use of digital scanning in electrical detection SSMS gives rise to an increase in precision and sensitivity. References 1. 2. Harrison, W. W., and Mattson, W. A., Analyt. Chenz., 1974, 46, 1979.Van Hoye, E., Adams, F., and Gijbels, R., Talanta, 1976, 23, 789. Spectrophotometric Determination of Vanadium(V), Cerium( IV), Arsenic( 111) and Nitrite with Mepazine Hydrochloride H. Sanke Gowda and K. N. Thimmaiah Department of Postgraduate Studies and Research in Chemistry, University of Mysore, Manasa Gangotri, Mysore, India Sanke Gowda and co-workers proposed mepazine hydrochloride (MH) , lo-[ (l-methyl-3- piperidy1)methyllphenothiazine hydrochloride, as a spectrophotometric reagent €or the determination of palladium1 and gold.2 The authors have now investigated the colour reaction of MH with vanadium(V) and cerium(1V) and propose MH as a sensitive reagent for the spectrophotometric determination of vanadium(V), cerium(IV), arsenic(II1) and nitrite.Experimental A Beckman, Model DB, spectrophotometer with matched l-cm silica cells was used for absorbance measurements. Reagents A 0.01 N sodium arsenite solution was prepared from AnalaR arsenic(II1) oxide. Approx- imately 0.01 N solutions of sodium vanadate, cerium(1V) sulphate and sodium nitrite were prepared and standardised. A 0.2% solution of MH was prepared in doubly distilled water and stored in an amber-glass bottle in a refrigerator.Solutions of diverse ions of suitable concentrations were prepared using analytical-reagent grade reagents. Working solutions were prepared as required by dilution.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 107 Procedure for Determination of Vanadium(V) and Cerium( IV) Transfer the sample solution containing 3-127.5 pg of vanadium(V) or 15-512.5 pg of cerium- (IV), 5 ml of 5 M orthophosphsric acid and 3 ml of 0.2% MH into a 25-ml calibrated flask and dilute to the mark with doubly distilled water.Mix the solution and measure the absorbance at 515 nm against a similar reagent blank. Calculate the amount of vanadium or cerium in the sample solution from a calibration graph.Procedure for Determination of Arsenic( 111) Measure different volumes (0.5, 1.0, 1.5, . . . , 6 ml) of arsenic(II1) solution (3.75-65 pg) into twelve 25-ml calibrated flasks. Use a thirteenth 25-ml flask containing no arsenic(II1) for a simultaneous blank determination. Add 5 ml of 2 M sulphuric acid, 1 ml of osmium(VII1) (1.2 Pg) and 2 ml of 0.001 M cerium(1V) sulphate solution successively to all 13 flasks.After shaking, add 5 ml of 5 M orthophosphoric acid and 3 ml of 0.2% MH and dilute to the mark with doubly distilled water. Shake the solutions and measure their absorbances at 515 nm against the reagent blank. Deduce the amount of arsenic(II1) in the test solution from a standard calibration graph constructed by plotting the concentration of arsenic( 111) veYsus absorbance. Procedure for Determination of Nitrite Place 5 ml of 1 M sulphuric acid and 2 ml of 0.001 M cerium(1V) sulphate solution in thirteen 25-ml calibrated flasks. Add 5 ml of sodium nitrite solution containing 1 4 2 pg of nitrite to all flasks except the thirteenth.After 5 min, add 5 ml of 5 M orthophosphoric acid and 3 ml of 0.2% MH to all thirteen flasks and dilute to the mark with doubly distilledwater.Shake the solutions and measure their absorbances at 515 nm against the reagent blank. Determine the nitrite concentration of the sample solution by reference to a calibration graph of con- centration of nitrite veysus absorbance. Results and Discussion Determination of Vanadium(V) MH is readily oxidised by vanadium(V) at room temperature in the presence of hydrochloric, sulphuric, orthophosphoric or acetic acid to a red species, which is believed to be a radical cation.3 The sensitivity and stability of the radical cation depend on the nature and con- centration of the acid.The sensitivity decreases in the order HC1 wH,SO, mHH,PO, >HOAc. The stabilities in 1 M hydrochloric, sulphuric, orthophosphoric and acetic acids correspond to 35, 10,35 and 10 min, respectively.Maximum absorbance is achieved instantaneously in 0.5- 1.5 M orthophosphoric, 0.4-0.9 M sulphuric or 1.0-3 M acetic acid. A period of 5 min is required to attain maximum absorbance in 0.7-1.5 M hydrochloric acid. Orthophosphoric acid medium was selected because of the instantaneous development of maximum absorbance and less interferences from foreign ions.The absorption spectra of the radical cation and of the reagent in 1 M orthophosphoric acid are shown in Fig. 1. The maximum absorbance is at 515 nm, where the reagent does not absorb. A seven-fold molar excess of the reagent is necessary for the full development of the colour intensity. There is no appreciable change in the absorbance if the order of addition of reagents is varied.Beer's law is obeyed in the range 0.12-5.1 pg ml-l of vanadium in orthophosphoric acid. The optimum concentration range for the effective spectrophotometric determination evalu- ated by Ringborn's method is 0.54.9 pg ml-l. The Sandell sensitivity of the reaction is 6 ng cm-2 and the molar absorptivity is 8.18 x lo3 1 mol-l cm-l. The relative error is less than 2%.The absorbance is unaffected by temperature in the range 5-90 "C. Efect of diverse ions The following amounts of foreign ions that commonly accompany vanadium(V) were found to give less than a 2% error in the determination of 2.4 pg ml-l of vanadium(V) : Fe(II1) 1 200; U(V1) 1 230; Mo(V1) 672; Mo(II1) 1 200; Zn(I1) 2 040; Mg(I1) 2 000; Co(I1) 150; Ni(I1) 290; Cu(I1) 200; Th(1V) 232; Zr(1V) 152; Fe(I1) 0.6; Pd(I1) 0.2; Ru(II1) 3; Os(VII1) 8; Ir(II1) 18; Rh(II1) 19; Pt(1V) 9; La(II1) 200; Au(II1) 0.20; Ce(1V) 0.20; Cr(II1) 175; Cr(V1) 0.1; Mn(I1)108 FOURTH INTERNATIONAL SAC CONFERENCE Proc.Analyt. Div. Chem. SOC. 1 000; V(1V) 80; Cd(I1) 2 OOO; Al(II1) 4 000; As(II1) 4 000; As(V) 4 000; cbloride 400; bromide 480; iodide 0.20; fluoride 8 000; nitrate 3 000; phosphate 10 000; citrate 4 000; acetate 6 000; tartrate 4 000; sulphate 8 000; thiosulphate 1.2; and EDTA 2.4pg ml-l.The sensitivity of the proposed method is higher than those with N-phenylacetylsalicyl- h ydroxamic acid,4 2-carbethoxy-5-hydroxy- 1 - (4-t olyl) -4-~yridinone,~ N-phenyl-2-naph t ho- hydroxamic acid,6 1,2,3-phenylo~yarnidine,~ disodium maleonitrile dithiolates and N-p-tolyl-2- furohydroxamic acid,s which have been proposed as spectrophotometric reagents for vanadium.0.60 380 420 460 500 540 580 620 660 700 740 Wavelengthhm Fig. 1. Absorption spectra: A, MH; B, radical cation of MH formed with V(V) ; and C, radical cation of MH formed with Ce(1V). [MH] = 6.926 x 1 0 - 4 ~ ; [V(V)] = 2.4 p.p.m.; [Ce(IV)] = 11.2 p.p.m.Analysis of vanadium steel The vanadium steels T100V25 (1.040/, C, 0.17% Si, 0.36% Mn, 0.015y0 P, 0.008~0 S, O.lOyo Ni, 0.2% Cr, 0.03% Mo, 0.245% V and 0.10% Cu) and 20CrlMo95V85TiB (0.21% C, 0.35y0 Si, o.41y0 Mn, 0.017% P, O . O l l ~ o S, 0.16y0 Ni, 1.25% Cr, 0.94% Mo, 0.96% V, 0.06% Ti, 0.004 6% B and 0.11% Cu) were analysed by the following procedure. The accuracy of the method was determined by analysing (six times) vanadium steels to determine vanadium.The relative error was less than 2%. Weigh accurately about 0.5 g of vanadium steel into a covered 250-ml beaker and add 15 ml of 10 N sulphuric acid, 2 ml of syrupy phosphoric acid (sp. gr. 1.75) and 1 ml of concentrated nitric acid. After the initial reaction has subsided, boil for 2 4 min to expel the oxides of nitrogen. Cool, dilute to about 50 ml with doubly distilled water and add 0.1 N potassium permanganate solution dropwise until the solution just becomes pale pink. Keep the solution aside for about 5 min, then add 0.01 N oxalic acid solution slowly with stirring until the pale pink colour just disappears.Transfer the solution into a 100-ml calibrated flask and dilute to the mark with doubly distilled water.Transfer a suitable aliquot of the solution and 5 ml of tartrate solution (4 mg) into a 25-ml calibrated flask. Treat the solution and measure the absorbance as outlined in the standard procedure. Procedure. Determination of Cerium( IV) MH is oxidised to a red radical cation by cerium(1V) in sulphuric, orthophosphoric or acetic acid medium.The maximum colour development takes place instantaneously at room temper- ature (27 "C) in 0.25-0.5 M sulphuric, 0.5-1.5 M orthophosphoric9 or 1.0-3 M acetic acid, as shown by the constancy of Amax.. The sensitivity in these acids decreases in the order H,PO, mH,S04 > HOAc and the stabilities in the 1 M acids correspond to 30, 20 and 10 min, respec- tively.The absorption spectra of the radical cation and of the reagent in 1 M orthophosphoric acid are shown in Fig. 1. The maximum absorbance is at 515 nm. A seven-fold molar excess of the reagent is necessary The absorbance readings are unstable in hydrochloric acid medium.March, 1978 FOURTH INTERNATIONAL SAC CONFERENCE 109 for the full development of the colour intensity. There is no appreciable change in the absorb- ance if the order of addition of reagents is varied.The absorbance is unaffected by temper- ature in the range 10-60 "C. Beer's law is valid over the concentration range 0.6-20.5 p.p.m. of cerium(1V). The optimum concentration range for the effective spectrophotometric determination evaluated by Ring- bom's method is 1.0-20.3 p,p.m. The molar absorptivity is 6.5 x lo3 1 mol-l cm-l at 515 nm.For log (I,/I) = 0.001, the sensitivity of the reaction is 22 ng cm-2. Errors are in general about *2y0. The sensitivity of this present method is higher than those with o-aminophenol,1° sulphanilic acid11 and salicylhydroxamic acid,12 which have been proposed as sensitive spectrophotometric reagents for cerium. It was found that the following amounts of foreign ions gave less than a 2% error in absorb- ance readings in the determination of 7 pg ml-l of cerium(1V) : La(II1) 4 000; Yr(II1) 4 000; Nd(II1) 4000; Gd(II1) 4000; Dy(II1) 4000; Ho(II1) 4000; Er(II1) 4000; Yb(II1) 4000; Y(II1) 4000; Tb(II1) 4000; Os(VII1) 6; Ru(II1) 3; Pd(I1) 0.10; Pt(1V) 8.0; Ir(II1) 15.0; Au(II1) 0.2; Co(I1) 640; Ni(I1) 960; Cu(I1) 800; Fe(II1) 300; Ag(1) 6; Mg(I1) 2000; Zn(I1) 1518; Th(1V) 115; Zr(1V) 10; U(V1) 2056; As(V) 4000; chloride 8009; bromide 18720; iodide 1.5; fluoride 39 248; sulphate 7 318; acetate 8 000; phosphate 10 000; citrate 7 500; tartrate 6 400; nitrate 4 850; thiosulphate 0.9; and EDTA 2 pg ml-l.It can be seen that many cations, especially lanthanides, do not interfere in the determination of cerium(1V). The major advantage of this method is that MH can be used as a selective reagent for the determin- ation of cerium(1V) in the presence of large amounts of other lanthanides in readily attainable oxidation states without the use of masking agents. Determination of cerium in misch metal The composition of the commercial misch metal is 50% Ce, 25% La, 15% Nd, 5% Fe and 5% Pr, Eu, Gd and .Er. Synthetic mixtures corresponding to misch metal were prepared and the cerium contents were determined following the standard procedure. The accuracy of the method was studied by analysing (10 times) solutions containing known amounts of cerium(1V). The relative error was less than 2%. Determination of Arsenic( 111) and Nitrite Arselyc( 111) is oxidised to arsenic(V) quantitatively and instantaneously by a known excess of cerium(1V) sulphate (20-120%) in 0.25 M sulphuric acid'containing 1.2 pg of osmium(VII1) catalyst, which does not interfere under the experimental conditions used. Nitrite is oxidised to nitrate in 0.5 M sulphuric acid in 5 min by a known excess of cerium(1V) sulphate (20-120%). The unreacted cerium( IV) is determined colorimetrically by the proposed method. The reduction in the absorbance of the red colour produced by the fixed amount of cerium(1V) sulphate in the absence of other reducing substances is directly proportional to the amount of arsenic( 111) or nitrite present. Cerium(III), arsenic(V) and nitrate formed in the reaction are colourless and do not interfere. Amounts of 0.15-2.7 pg ml-l of arsenic(II1) and 0.05-1.76 pg ml-1 of nitrite can be determined. The method can be used for the spectrophotometric determination of micro-amounts of other substances that are quantitatively oxidised by cerium(1V) in sulphuric acid to colourless, non-interfering products. Arsenic( 111) and nitrite are indirectly determined spectrophotometrically. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References Sanke Gowda, H., and Keshavan, B., J . Indian Chem. Soc., 1976, 53, 688. Sanke Gowda, H., and Thimmaiah, K. N., Indian J . Chem., 1976, 14A, 632. Dwivedi, P. C., Gurudath, K., Bhat, S. N., and Rao, C. N. R., Spectrochim. Acta, 1975, 31A, 129. Savariar, C. P., and Jay, J., J . Indian Chem. SOC., 1973, 50, 14. Tamhina, B., and Herak, M. J., Mikrochim. Acta, 1975, 45; Chem. Abstr., 1975, 83, 172151e. Agrawal, Y. K., Analyt. Chem., 1975, 47, 940. Satyanarayana, K., and Mishra, R. K., Analyt. Chem., 1974, 46, 1609. Chatterjee, A. B., Basu, A., and Bag, S. P., Mikrochim. Acta, 1974, 275. Agrawal, Y . K., Analyt. Lett., 1974, 7, 729. Suten, A., Hodisan, T., and Naumescu, T., Stud. Univ. Babes-Bolyai, Ser. Chim., 1970, 23, 548. Sarma, P. L., and Dieter, L. H., Talanta, 1966, 13, 347. Podder, S. N., Senaguptha, N. R., and Adya, J . N., Indian J . Chem., 1965, 3, 135.

ISSN:0306-1396    

DOI:10.1039/AD9781500094

出版商:RSC    

年代:1978

数据来源: RSC

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110 CORRESPONDENCE Proc. Analyt. Div. Chern. SOC. Conferences and Meetings Capillary Column Gas Chromatography - Mass Spectroscopy Techniques March 30, 1978, Salford The Mass Spectroscopy Group is organising a one-day meeting on this subject, to be held a t the University of Salford. Three principal speakers will introduce and discuss practical aspects of capillary column gas chromatography and gas chromatography - mass spectrometry with an emphasis on audience participation in these discussions.Invited speakers are K. . Grob, Jr. (ETH Zurich, “Critical Points in Quantitation ; Injection System and Adsorp- tion”), N. Dyson (Dyson Instruments, Durham, “Basic Capillary Column Practice”) and R. Self (Food Research Institute, Norwich, “GCMS Interfacing”). The programme will also include brief contributions from experienced users, describing the application of capillary column techniques in a number of analytical fields.Further details from the Group Secretary, Dr. J. R. Chapman, Kratos - AEI Scientific Instruments Ltd., Barton Dock Road, Urmston, Manchester, M31 2LD.March, 1978 CONFERENCES AND MEETINGS 111 Sixth Ceramic Chemists Conference April 5-7, 1978, Llandudno This conference, which will be held at the Hydro Hotel, Llandudno, is to be organised by the British Ceramic Research Association.In addition to a conference dinner, the opening event of the conference, there will be lectures from Mr. B. Bagshawe, Mr. D. G. Swinburn, Dr. G. J. Oliver, Mr. D. Newell, Dr. V. C. Farmer and Dr. G. F. Kirkbright. The conference fee will be jJ5 and the Hotel accommodation charge approximately Ll2 per night.Further information can be obtained from the Conference Secretary, Dr. G. J . Oliver, British Ceramic Research Association, Queens Road, Penkhull, Stoke-on-Trent, ST4 7LQ. Analysis 78-Microprocessors in Analytical Instrumentation April 10-12, 1978, London The principles and applications of micropro- cessor technology will be discussed by various authorities including H.V. Malmstadt, G. Horlick, M. Bonner Denton, P. Stockwell, J. Ruzicka, D. Betteridge, R. Peterson and G. J. Moody. Basic principles will be discussed at a level appealing to those who have no special expertise in electronics. Applications of micro- processors in spectroscopy, chromatography and electrochemistry will be discussed in detail, and there will be a session on data handling.This carefully balanced programme will consider all aspects of microprocessor technology as they affect analytical chemists in both industry and academic institutions. The Conference is to be held at Imperial College. For further information and registra- tion forms telephone Beverly Humphrey, 01-439-6611, Drugs and Immune Responsiveness April 17-18, 1978, London This Symposium is to be held in the Edward Lewis Theatre of the Middlesex Hospital Medical School and is to be organised by the Co-ordinat- ing Committee for Symposia on Drug Action of the Biological Council. The final session of the Symposium will be concerned with new methods of immunoassay for drugs, including enzymo- immunoassays and new approaches to the linkage of haptens used in radioimmunoassays.The Administrative Secretary is Mrs. Joan Kruger, c/o Department of Pathology, The Royal College of Surgeons of England, 35-43 Lincoln’s Inn Fields, London, WCZA 3PN. Chromatography Discussion Group Spring Symposium Afiril21, 1978, London The subject of this Symposium, which will be held in conjunction with the AGM of the group, is “Chromatographic Methods for Chemical Carcinogens.” The Symposium will be held at the Shell Centre, Waterloo, and contributors will include C.E. Searle, E. A. Walker, J. Jacob and D. W. Grant. Further details of -,the AGM (members only) and the Symposium (members and non-mem- bers) can be obtained from the Executive Secre- tary, Chromatography Discussion Group, Trent Polytechnic, Burton Street, Nottingham, NGl 4BU.Fifth International Symposium on Mass Spectrometry in Biochemistry and Medi- cine June 19-21, 1978, Rimini, Italy The Italian Group for Mass Spectrometry in Biochemistry and Medicine is organising the above Symposium; lectures will be given a t the Teatro Novelli, Rimini. The subjects to be discussed include applications of mass spectro- metry in biochemistry, medicine, toxicology, drug research, forensic science, clinical chem- istry and pollution. In addition, there will be an exhibition of instruments and publications, social and ladies’ programmes and a con- ference dinner.The official language of the Symposium will be English. Accommodation (in hotels) can be reserved on the registration form, which may be obtained from Dr.Albert0 Frigerio, Istituto di Ricerche Farmacologiche “Mario Negri,” Via Eritrea 62, 20157 Milan, Italy. Fifth International Congress of Food Science and Technology September 17--22, 1978, Kyoto, Japan The Royal Society has authorised a block travel grant to assist with participants’ travelling expenses to this Congress. Grants are available to scientists of PhD status, working in non- Government establishments within the UK.Owing to limited funds being available, it is anticipated that a maximum allocation of A250112 COURSES per person will be made. Application forms are available from the Executive Secretary, The Royal Society, 6 Carlton House Terrace, London, SWlY 5AG (closing date, 28th February, 1978). The following closing dates have been received from the Congress organisers: for an applicant who submits a paper, April 30, 1978; for other active members, May 31, 1978; for submission of the full text of a paper, July 31, 1978.Colour Measurement and Its Application October 3-4, 1978, London The Materials and Testing Group and the Optical Group of The Institute of Physics, in association with the Colour Group GB and the UV Spectrometry Group, are arranging a conference on Colour Measurement.The con- ference will be held in the Oliver Thomson Lecture Theatre, City University, London. For information on the speakers and their subjects contact The Meetings Officer, The Institute of Physics, 47 Belgrave Square, London, SWlX 8QX. Labex International 79 March 12-16, 1979, Birmingham Labex International 79 will return to the National Exhibition Centre, Birmingham, with a new title, “The Laboratory and Medical Diagnostic Instruments and Equipment Exhibi- tion.” The new title reflects a considerable expansion of the medical diagnostic side of Labex.The exhibition, to be held in Hall 4 of the NEC, will have an even stronger international aspect than ever before and buyers from all over the world will be coming to inspect, compare and place orders. Labex International 79 is sponsored by the Scientific Manufacturers’ Association of Great Britain, the British Laboratory Ware Associa- tion and Laboratory Practice. SAC 80 International Conference July 20-26, 1980, Lancaster The Analytical Division of The Chemical Society is to organise the fifth in the series of SAC Conferences started in Nottingham in 1965. The Conference is to be held at the University of Lancaster. Further details will be circulated in due course or may be obtained from Miss P. E. Hutchinson, Analytical Division, The Chemical Society, Burlington House, London, W1V OBN. Proc. Analyt. Div. Chem. Soc.

ISSN:0306-1396    

DOI:10.1039/AD978150110b

出版商:RSC    

年代:1978

数据来源: RSC

摘要:

112 COURSES Proc. Analyt. Div. Chem. Sot. Courses Gel Filtration and Electrophoresis April 3-7, 1978, Loughborough The course will cover the following topics: gel filtration in columns and on thin layers, including relative molecular mass deter- minations and other applications ; related chromatographic techniques, including affinity chromatography, hydrophobic chromato- graphy, gel filtration ion exchange, etc; cellu- lose acetate electrophoresis and paper electro- phoresis at high and low voltages; gel electro- phoresis on acrylamide, starch and agar gels; isoelectric focusing and isotachophoresis ; and immunological methods, including Laurel1 electrophoresis, electroimmunodiffusion, coun- ter immunoelectrophoresis, etc.Further details can be obtained from Dr.J. N. Miller, Chemistry Department, Lough- borough University of Technology, Lough- borough, Leicestershire, LEll 3TU. Particle Workshop 1978 April 3-14, 1978, Loughborough The Centre for Extension Studies is running this Workshop, sponsored jointly by the Particle Technology Group of Loughborough University (where the Workshop is t o be held) and the Materials Handling Division of the Warren Spring Laboratory, as four separate courses.Course I (April 3-7) is on Particle Size Analysis, Course I1 (April 5-7) on Dust Control and Gas Cleaning, Course I11 (April 10-14) on Solid - Liquid Separation and Course IV (April 12-14) on Powder Handling Systems. For full details -apply to the Centre for Extension Studies, University of Technology, Loughborough, Leicestershire, LEll 3TU. Water Pollution Measurement and Monitor- ing April 12-1 4, 1978, Loughborough This Course is to be held at the University of Technology and is primarily intended for analy- tical laboratory staff in industry and the public services.It will concentrate on the application of widely established analytical techniques to water pollution analysis, although the principles of less familiar analytical methods will be out- lined. The Course tutors will be Dr. J. F. Tyson and Dr. G. E. Chivers. Application forms are available from the Centre for Exten- sion Studies, University of Technology, Lough- borough, Leicestershire, LEll 3TU.

ISSN:0306-1396    

DOI:10.1039/AD9781500112

出版商:RSC    

年代:1978

数据来源: RSC