ISSN:0003-2654    

DOI:10.1039/AN96186FX045

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

No. 101 November, I96 I THE SOCIETY FOR ANALYTICAL CHEMISTRY BULLETIN FORTHCOMING MEETINGS Joint Meeting of the Society and the Infra-red Discussion Group, December 15th, 1961 A JOINT Meeting of the Society and the Infra-red Discussion Group will be held on Friday, December 15th, 1961, at King’s College, Strand, London, W.C.2. The subject of the meeting will be “Applications of Infra-red Spectroscopy to Quantitative Analysis.” Programme 11.15 a.m. to 12.40 p.m. First Session- Introductory Paper by Dr. W. R. Ward. “The Analysis of Agricultural Chemicals by Infra-red Spectroscopy,” by P. G. Marshall. 2.00 p.m. to 4.00 p.m. Second Session- I “Quantitative Analysis of Milk and Other Emulsions by Infra-red Absorption Spectro- scopy,” by Dr. J. D. S. Goulden. “Quantitative Analysis of Phosphonitrilic Chloride Polymer Mixtures by Infra-red Spectroscopy,” by Dr.A. C. Chapman, R. T. Baggott, R. Harper and Miss I. Walker. “Some Applications of Infra-red Spectroscopy to Quantitative Analysis in the Pharma- ceutical Industry,’’ by Dr. H. D. C. Rapson, K. Austin and A. Cutmore. Joint Meeting of the North of England Section and the Manchester and District A JOINT Meeting of the North of England Section and the Manchester and District Section of the Royal Institute of Chemistry will be held at 2 p.m. on Friday, December lst, 1961, in the Large Lecture Theatre, Manchester Literary and Philosophical Society, 36 George Street, Manchester, 1. Section of the Royal Institute of Chemistry, December lst, 1961 The following paper will be presented and discussed- “The Design and Construction of Laboratories,” by R.R. Young, F.R.I.B.A., and P. J. Harrington. The Ramsay Dinner THE Ramsay Dinner will be held once again this year in the Central Hotel, Glasgow, on Thursday, December 7th, 1961, at 6.30 for 7 p.m.. The Principal Guest will be Principal F. C. Curran, F.R.S., of the Royal College of Science and Technology, Glasgow, and the Chair will be taken by Professor J. Monteath Robertson, F.R.S. Joint Meeting of the Scottish Section with the Chemical Society, the Glasgow Section of the Society of Chemical Industry and the Glasgow and West of Scotland Section A JOINT Meeting of the Scottish Section with the Chemical Society, the Glasgow Section of the Society of Chemical Industry and the Glasgow and West of Scotland Section of the Royal Institute of Chemistry will be held at 7.15 p.m.on Friday, December 8th, 1961, a t the Royal College of Science and Technology, George Street, Glasgow. of the Royal Institute of Chemistry, December 8th, 1961.The following paper will be presented- “The Structure of Natural Products by Direct X-ray Analysis,” by Professor J. Monteath Robertson, M.A., Ph.D., D.Sc., F.R.S. Joint Meeting of the Western Section and the Cardiff and District Section of the Royal A JOINT Meeting of the Western Section and the Cardiff and District Section of the Royal Institute of Chemistry will be held on Friday, December 8th, 1961, at University College, Cardiff. Institute of Chemistry, December 8th, 1961 The following paper will be presented and discussed- “Analytical Research,’’ by J.Haslam, D.Sc., F.R.I.C. Ordinary Meeting of the Midlands Section, December 13th, 1961 AN Ordinary Meeting of the Section will be held at 7 p.m. on Wednesday, December 13th, 1961, at the University, Edgbaston, Birmingham, 15. The following paper will be presented and discussed- “Fluorescent Indicators for Metals,” by W. I. Stephen, B.Sc., Ph.D., A.R.I.C. London Discussion Meeting of the Microchemistry Group, December 13th, 1961 THE thirty-second London Discussion Meeting of the Group will be held at 6.30 p.m. on Wednesday, December 13th, 1961, at “The Feathers,” Tudor Street, off Bouverie Street, Fleet Street, London, E.C.4. Annual General Meeting of the Biological Methods Group, December 14th, 1961 THE Seventeenth Annual General Meeting of the Group will be held at 6.30 p.m.on Thursday, December 14th, 1961, at “The Feathers,” Tudor Street, off Bouverie Street, Fleet Street, London, E.C.4. The Annual General Meeting will be followed by a Discussion Meeting of the Group at which the subject will be “Assessment of Antiatherosclerotics.” BRITISH STANDARDS INSTITUTION DRAFT SPECIFICATIONS A FEW copies of the following draft specifications, issued for comment only, are available to members of the Society, and can be obtained from the Secretary, The Society for Analytical Chemistry, 14, Belgrave Square, London, S.W.1. Draft Specifications prepared by Technical Committee NFE/$-Zinc. AB(NFE)6120--Draft B.S. Methods for the Sampling and Analysis of Zinc and Zinc AB(NFE)6121--Draft B.S. Methods for the Sampling and Analysis of Zinc and Part 5 : Determination of Iron in Ingot Zinc and Zinc Alloys AB(NFE)6122--Draft B.S.Methods for the Sampling and Analysis of Zinc and Part 4: Sampling of Ingot Zinc, Zinc Alloy Ingots and Zinc Alloy Alloys. Zinc Alloys. (Photometric Method). Zinc Alloys. Die-castings for Spectrographic Analysis. Part 1 : Sampling of Ingot Zinc and Zinc Alloy Ingots. COMMUNICATIONS ACCEPTED FOR PUBLICATION IN THE ANALYST THE following communications have beea accepted for publication in The Analyst, and are expected to appear in the near future. “The Emission Spectroscopy of Solutions,” by L. G. Young. “Polarographic Micro-determination of Parathion and Malathion in Admixture,’’ by “The Determination of Traces of Silver in Lead and Lead Oxides with Dithizone,” by (Review.) D.E. Ott and F. A. Gunther. P. D. Jones and E. J. Newman. (Note.)“The Influence of Foreign Ions on the Determination of Potassium as the Tetraphenyl- (Note.) “The Estimation of Stibine,” by R. Holland. “The Determination of Iron in Metals and Minerals by Controlled-potential Coulometry,” “Fluorimetric Determination of Very Small Amounts of Aluminium,” by W. T. Rees. “A Micrometer-syringe Storage Burette for Small-scale Titrations with Air-sensitive Solutions,” by A. D. Wilson and G. A. Sergeant. “Spectrophotometric Determination of Magnesium in Uranium,” by V. T. Athavale, R. L. Bhasin and B. L. Jangida. “A Method for High Precision Assay of Uranium Metal,” by J. A. Duckitt and G. C. Goode. “Losses of Trace Elements During Oxidation of Organic Materials: The Formation of Volatile Chlorides During Dry Ashing in Presence of Inorganic Chlorides,” by T.T. Gorsuch. boron Salt,” by J. D. R. Thomas. (Note.) by G. W. C. Milner and J. W. Edwards. “The Determination of Sulphur in Organic Compounds,” by M. Ellison. Notices LIBRARY OF THE CHEMICAL SOCIETY Christmas Closing, 1961 THE Chemical Society Library, which members of the Society for Analytical Chemistry have the privilege of using, will be closed for Christmas from 7.30 p.m. on Friday, December 22nd, and will reopen at 9.30 a.m. on Thursday, December 28th, 1961. ROYAL INSTITUTE OF CHEMISTRY SUMMER SCHOOL IN ANALYTICAL CHEMISTRY, 1962 THE fifth Summer School in Analytical Chemistry will be held at the Manchester College of Science and Technology from September 9th to 15th, 1962.Course I: Physical Methods of Organic Chemistry The School will consist of the following four separate but concurrent courses- Course Organiser : Dr. D. W. Mathieson, F.R.I.C., Reader in Pharmaceutical Chemistry, School of Pharmacy, University of London. Section A : Infra-red spectroscopy-A one-week intensive course on structure - spectra relationships in organic molecules. Lectures and seminars will be held on the interpretation of spectra. A wide range of recent instruments will be available. Section B: An omnibus section comprising nuclear magnetic resonance, mass spectrometry and spectropolarimetry. Lectures and seminars will be held on the basic theory of these topics and the applications of the techniques in organic chemistry.Demonstrations and practical work will be carried out on the latest instruments. Course 11: Recent Developments in Inorganic Analysis Course Organiser : Mr. W. T. Elwell, F.R.I.C., Chief Analyst, Imperial Chemical Industries Ltd., Metals Division, Birmingham. Lectures and practical work will cover the following topics : atomic absorption spectrophoto- metry ; solid source mass spectrometry; electrometric titrimetry; complexometric titrations ; X-ray fluorescence ; analysis for the newer metals; solvent extraction; ion exchange; trace inorganic constituents in soils ; applications of modem analytical methods in ceramics; new physico-chemical techniques in iron and steel analysis. Some of the lectures will be held jointly with Course IV. Course 111: The Determination of Toxic Substances in the Air and in Effluents Course Organiser : Mr.H. E. Stagg, F.R.I.C., Chief Analyst, Imperial Chemical Industries Ltd., Dyestuffs Division, Manchester. This is an essentially practical course on: the sampling of gases and vapours and their deter- mination by titnmetric, absorptiometric, test paper, indicator tube and instrumental methods ; the sampling and analysis of dusts ; detection and assessment of hazards from radio-active materials; . the control of aqueous effluents. Course IV: Newer Instrumental Methods Course Organiser : Dr. V. S. Griffiths, F.R.I.C., Reader in Spectroscopy, Battersea College of Technology, London. This course will carry lectures on the following topics : atomic absorption spectrophotometry ; electrometric titrimetry; solid source mass spectrometry; X-ray fluorescence ; paramagneticresonance of inorganic compounds : scattering spectrophotometry of emulsions ; flame photometry ; ultrasonic techniques ; infra-red techniques in inorganic chemistry ; thermogravimetric analysis.Some of the lectures will be held jointly with Course 11. The practical sections will provide an opportunity to use the latest instrumental methods for visible and U.V. spectroscopy ; electrochemical determinations ; flame photometry ; fluorescence (electron spin resonance) ; and automatic techniques in analysis. Course I is expected to appeal mainly to organic chemists in universities, higher techno- logical institutions, research organisations and research departments of industrial firms-in the U.K.and overseas-but it will also be of interest to analytical chemists who use modern instrumental methods of organic analysis. It is believed that this will be the first occasion that an intensive residential post-graduate course of this nature has been organised in this country or in Europe. Courses I1 and IV will be of general interest to analytical chemists in industry and to inorganic - physical chemists in academic or research institutions who wish to develop or apply the latest techniques of analysis. Course I1 is concerned with the applications of these techniques to inorganic analysis, whereas Course IV will provide a general survey of recent instrumental methods. Course I11 is expected to appeal to those analytical chemists, and others, in industry whose special concern is the detection and determination of toxic substances, including radio- active waste, in the air and in effluents.Further details and registration forms will be circulated to all members of the Institute and to members of the Society for Analytical Chemistry in January, 1962. The Summer School will be open to any qualified chemist in the U.K. or overseas, but a large proportion of the places will be reserved, up to March lst, 1962, for members of the Royal Institute of Chemistry or the Society for Analytical Chemistry. Residential accommodation will be available. Publicity leaflets are already being distributed to universities, technical colleges, research institutions and many industrial firms. Additional copies may be obtained from the Royal Institute of Chemistry, 30 Russell Square, London, W.C.1.ROYAL INSTITUTE OF CHEMISTRY Meldola Medal for 1961 THE Meldola Medal is the gift of the Society of Maccabaeans and is normally awarded annually. The next award will be made early in 1962 to the chemist who, being a British subject and .under 30 years of age at December 31, 1961, shows the most promise as indicated by his or her published chemical work brought to the notice of the Council of the Royal Institute of Chem- istry before December 31st, 1961. No restrictions are placed upon the kind of chemical work or the place in which it is conducted. The merits of the work may be brought to the notice of the Council, either by persons who desire to recommend the candidate or by the candidate himself, by letter addressed to The President, The Royal Institute of Chemistry, 30 Russell Square, London, W.C.1, the envelope being marked “Meldola Medal.” The letter should be accompanied by six copies of a short statement on the candidate’s career {date of birth, education and experience, degrees and other qualifications, special awards, etc., with dates) and of a list of titles, with references, of papers or other works published by the candidate, independently or jointly.Candidates are also advised to forward one reprint of each published paper of which copies are available. JOHN MURDOCH’S TRUST THE late John Murdoch, by his Will, directed his Trustees to employ the residue of his Estate in instituting and carrying on a scheme for the relief of indigent Bachelors and Widowers, of whatever religious denomination or belief they may be, who have shown practical sympathy either as amateurs or professionals in the pursuits of Science in any of its branches, whose lives have been characterised by sobriety, morality, and industry, and who are not less than fifty-five years of age. John Murdoch’s Trustees resolved to carry out the terms of the bequest by granting donations or pensions to persons who comply with these conditions. Pensions will be given from year to year only, and may be increased, reduced, or withdrawn altogether as the Trustees see fit. Application forms for pensions or donations may be had on application to Messrs. Shepherd & Wedderburn, W.S., 16 Charlotte Square, Edinburgh. ‘ PRINTED BY W. HEFFER & SONS LTD.. CAMBRIDGE.

ISSN:0003-2654    

DOI:10.1039/AN961860X047

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186BX051

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186FP227

出版商:RSC    

年代:1961

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN96186BP237

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

NOVEMBER, 1964 THE ANALYST Vol. 86, No. 1023 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY ORDINARY MEETING , 4 ~ Ordinary Meeting of the Society was held at 7 p.m. on Wednesday, November lst, 1961, in the Meeting Room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the President, Dr. A. J. Amos, F.R.I.C. The following papers were presented and discussed : “Precipitation from Homogeneous Solution by Cation Release at Constant pH,” by P. F. S. Cartwright, MSc., F.R.I.C.; “The Application of Atomic Absorption to the Rapid Determination of Magnesium in Electronic Nickel and Nickel Alloys,” by T. R. Andrew, B.Sc., F.R.I.C., and P. N. R. Nichols; “Rapid Identification and Determination of Residues of Chlorinated Pesticides in Crops by Gas - Liquid Chromatography,” by E.S. Goodwin, A.R.I.C., R. Goulden, F.R.I.C., and J. G. Reynolds, F. R. I .C. NEW MEMBERS ORDINARY MEMBERS Richard Hampton Biddulph, M.A., B.Sc. (Oxon.), Ph.D. (Manc.) ; Cyril Aaron Blau; Jillian Mary Bond, BSc., Ph.D. (Bris.); Harold Burnham, B.Sc. (Lond.), A.R.I.C.; William Allan Cregeen, A.M.C.T., F.R.I.C. ; James Andrew Walter Dalziel, B.Sc., Ph.D., A.R.C.S., D.I.C., F.R.I.C. ; Adrian John Eve, M.Sc. (Rhodes), A.R.I.C. ; John Esam Fairbrother, BSc. (Hull); Eric Minshall, MSc. (Lond.), F.R.I.C. ; James Arnold Palgrave, BSc. (Dunelm.), F.R.I.C. ; Derrick George Porter, B.Sc. (Lond.) ; Khawaja Salah-ud-din, B.A., M.Sc. (Lond.), A.M.I. Chem.E., A.R.I.C. ; Rudolf Schacherl; Edward Alexander Simpson, B.Sc., Ph.D. (Lond.) ; Elizabeth Margaret Speed, B.Sc.(Southampton) ; Robert P. L. V. Taubinger, A.R.I.C. ; Walter Henry Walker, F.R.I.C. ; Raymond Waspe, B.Sc. (Lond.). JUNIOR MEMBERS John Harvey; John Michael Ottaway, B.Sc. (Exeter) ; Derek Robinson, M.Sc. (Manc.). DEATHS WE record with regret the deaths of Claude Leopold Leszynski Claremont Alan French. NORTH OF ENGLAND SECTION AN Ordinary Meeting of the Section was held at 2.15 p.m. on Saturday, September 30th, 1961, at the City Laboratories, Mount Pleasant, Liverpool, 3. The Chair was taken by the Chairman of the Section, Mr. J. Markland, B.Sc., F.R.I.C. The following paper was presented and discussed : “Some Analytical Problems in the Baking Industry,” by R. A. Knight, B.Sc., F.R.I.C. NORTH OF ENGLAND SECTION AND PHYSICAL METHODS GROUP -4 JOINT Meeting of the North of England Section and Physical Methods Group of the Society and the Modern Methods of Analysis Group of the Sheffield Metallurgical Association was held at 7 p.m.on Tuesday, October loth, 1961, in the Conference Room of the British Iron 685686 PROCEEDINGS [Vol. 86 and Steel Research Association, Hoyle Street, Sheffield, 3. The Chair was taken by the Chairman of the Modern Methods of Analysis Group, Mr. F. Goodbold. The following payers were presented and discussed : “Application of Atomic-absorption Spectrophotometry to Metallurgical Analysis,” by W. T. Elwell, F.R.T.C. ; “Some Inter- ferences in Flame Photometry,” by M. s. W. Webb, B.Pharm., F.P.S., F.R.I.C., and P. C . Wildy, B.Sc. (see summaries below). The meeting was preceded by a visit to the United Steel Companies Research Laboratories, Swinden House.APPLICATIOX OF ATOMIC-ABSORPTION SPECTROPHOTOMETRY TO METALLURGICAL ANALYSIS MR. W. T. ELWELL said that a major problem in metallurgical analysis was the determination of an element in the presence of an overwhelming excess of another, usually the matrix element of the sample. Chemicar procedures frequently involved either removal of the major constituent from the dement to be determined, or concentration of the latter. Both procedures were often tedious and time-consuming, and not free from inherent shortcomings. Determinations of trace constituents made directly in the presence of the major constituent had advantages, and atomic-absorption spectro- photometric methods were usually applied in this way.After outlining a description of the equipment used in his laboratory, Mr. Elwell gave details of fundamental considerations in the development of analytical procedures involving this relatively new analytical technique. He gave examples to illustrate the relative simplicity and reliability of atomic- absorption procedures when applied to the examination of ferrous and non-ferrous materials. Results obtained in this way were then compared with comparable values obtained by conventional analytical procedures, particularly in relation to speed and accuracy. SOME INTERFERENCES IN FLAME PHOTOMETRY MK. M. S. W. WEBB said that flame photometry was the familiar technique in which the solution to be analysed was introduced under carefully controlled conditions into a flame possessing sufficient thermal energy to excite the spectra of the elements of interest. The required radiation was isolated, either by a monochromator or a filter system, and the intensity measured by means of a photo-electric detector and recorded on a meter.After careful calibration the intensity of the element line could be interpreted in terms of concentration. Good precision and sensitivity could be attained for many elements provided that care was taken in standardisation. The chief factor affecting accuracy was the composition of the basic matrix and this could affect the apparent concentration of an element in a sample in many ways. Optical inter ference-(a) Direct spectral interference was due to incomplete resolution of the analytical and interference lines or bands. (b) Interference could be due to a continuous background arising from an interfering element.Background radiation was normally “backed off” by injecting a suitable d.c. signal into the measuring circuit-the so-called zero control. A far superior method was to use a photomultiplier to monitor the background on either side of the spectral line of interest and to inject the output from this into the measuring circuit. This automatically corrected any background fluctuation and improved stability. Chemical interference efects-Incomplete dissociation due to the formation of refractory compounds gave rise to serious suppression (e.g., aluminium, phosphate). Ionic interference efects-Although a sample could be evaporated and vaporised in a reproducible manner, the atoms might be distributed in a variable manner between the ionised and un-ionised state ( e g ., mutual enhancement of the alkali metals). Efect of solution profierties-Acids and salts hindered the evaporation of the spray droplets. Surface tension, density and viscosity all affected the mean size of droplets produced by atomisation (Nukiyama and Tanasawa) . Techniques for minimising inter ference- (a) Standards might be prepared in the same basic matrix as the samples.November, 19611 PROCEEDINGS 6 S i (b) “Self standardisation” in which the desired element was determined in an aliquot of the solution and further aliquots were “spiked” with known amounts of the element to be determined. (c) Radiation buffers might be used to overcome some ionic interferences.(d) Internal standards might be used to overcome differences in solution properties. (e) The interfering element could be removed completely. (f) In the case of aluminium or phosphate suppression, for example, various cations (e.g., lanthanum, iron) might be added to compete with the suppressing agent. An excess of EDTA or sucrose, for example, which probably caused disruptive decomposition of the dried spray, reduced particle size and resulted in an increased rate of evaporation, thereby relieving suppression. Woolwich Flame Photometer-This was based on a commercial monochromator and had a burner using premixed oxygen - propane fuel with direct oxygen atomisation of the sample. A filtered air jacket round the burner virtually eliminated atmospheric Contamination and improved flame stability.The incorporation of automatic background correction contributed markedly to the sensitivity and stability of the instrument and provision was made for an internal-standard channel. This flame photometer was demonstrated after the lecture; a full description has been given in A.E.R.E. report C/R 2659: “A general purpose flame photometer,” by H. M. Davis, G. P. Fox, R. J. Webb and P. C. Wildy. Both direct reading and integration recording were available. SCOTTISH SECTION A JOINT Meeting of the Scottish Section of the Society and the Glasgow Section of the Societj- of Chemical Industry was held at 7.15 p.m. on Friday, October 6th, 1961, in the Royal College of Science and Technology, Glasgow.The Chair was taken by the Chairman of the Glasgow Section, Professor J. Monteath Robertson, M.A., Ph.D., D.Sc., F.R.S. The subject of the meeting was “Pentaerythritol” and the following papers were pre- sented and discussed: “The Applications of Pentaerythritol,” by A. W. E. Staddon, B.Sc. (read on his behalf by R. S. McKee, B.Sc., A.R.I.C., A.R.C.S.T.); “Analysis of Penta- erythritol,” by A. F. Williams, B.Sc., F.R.I.C. MIDLANDS SECTION-ELWELL AWARD, 1961 THE Elwell Award for 1961 was presented to M. L. Richardson, A.C.T., A.R.I.C., of J. 8z E. Sturge Ltd., Birmingham, for his paper entitled “The Determination of Manganese in High Quality Calcium Carbonate by Means of Tetraphenylarsonium Chloride,” at a meeting of the Section held at 6.30 p.m. on Thursday, September 14th, 1961, at Regent House, St.Philip’s Place, Birmingham, 3. The Chair was taken by Professor R. Belcher, Ph.D., DSc., F.R.I.C., F.1nst.F. The following papers, which had been submitted for the award, were also presented: “A Simple Chromatographic Gas Analysis Apparatus,” by G. Blakemore ; “The Determination of Trace Amounts of Cobalt in Titanium,” by J. S. Caslaw. MIDLANDS SECTION A JOINT Meeting of the Midlands Section of the Society and the Birmingham and Midlands Section of the Royal Institute of Chemistry was held at 7 p.m. on Tuesday, October loth, 1961, at the University, Edgbaston, Birmingham, 15. The Chair was taken by the Chairman of the Birmingham and Midlands Section, Mr. G. King, M.B.E., M.Sc., F.R.I.C. A lecture on “Research Work in Analytical Chemistry at the Technical University of Budapest” was given by Professor L. Erdey. BIOLOGICAL METHODS GROUP AN Ordinary Meeting of the Group was held at 7 p.m. on Wednesday, October 18th, 1961, in the Meeting Room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the Honorary Secretary of the Group, Mr. I(. L. Smith, M.P.S. The following paper was presented and discussed: “The Use of Bacteriophages in Epidemiology,” by Miss E. Maureen Wilson, B.Sc.

ISSN:0003-2654    

DOI:10.1039/AN9618600685

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

ti88 CARTWRIGHT : STUDIES IN PRECIPITATION FROM HOMOGENEOUS [Vol. 86 Studies in Precipitation from Homogeneous Solution by Cation Release at Constant pH Part I. Oxidation of EDTA Solution by Hydrogen Peroxide* BY P. F. S. CARTWRIGHT (Departnzent of Chemistry, Sir John Cuss College, London, E.C.3) Precipitation from homogeneous solution by cation release at constant pH may be achieved by the controlled release of cations from their EDTA complexes by oxidation with hydrogen peroxide. A study has been made of the effects of variations in concentration of hydrogen peroxide and pH of solution on the rate of oxidation of EDTA solution. The presence of certain precipitates has been found to be detrimental, causing rapid break-down of the hydrogen peroxide, thus rendering the method ineffective.This may be Overcome by the addition of phosphate ions and the precipitation of metal phosphates. THE object of precipitation from homogeneous solution is to bring about precipitation at slow, controllable rate from an initially unsaturated solution, resulting in the formation (If larger, more perfect crystals, with fewer errors owing to adsorption and co-precipitation. This is achieved by generating the necessary ions by chemical reaction in the solution. The technique has been widely applied to the precipitation of many compounds; much of the earlier work has been collected and described by Gordon, Salutsky and Willard.1 The methods employed may be broadly classified as pH increase, anion release, cation release and synthesis of the precipitant I% sit$$.Methods of pH increase and anion release have been studied by earlier workers,l and methods involving the synthesis of the precipitant are restricted to use with certain organic reagent^.^^^,^ Comparatively few instances have been reported of the use of cation release, in which the cation to be precipitated is first held in solution as a complex and subsequently released by the slow, controlled destruction of the complex in the presence of a suitable anion. Cation release may be brought about either by changing the pH of the solution to a value at which the complex is no longer stable or by chlemical attack of the complex at constant pH. The former has been used for precipitating barium sulphate5 and silver chloride6,' and the latter has been described by MacNevin and Duntons for precipitating hydrated iron oxide and by Gordon, Salutsky and Willard for precipitating hydrous thorium oxide, MacNevin and Dunton obtained dense precipitates of hydrated iron oxide by oxidising an EDTA - iron complex with hydrogen peroxide, but Gordon reported that the precipitates of hydrous thorium oxide obtained h3r oxidising an EDTA - thorium complex were unsatisfactory from the analytical viewpoint.MacKevin and Dunton's paper was short and contained few details of experimental work. Thus, although the rate of oxidation of EDTA solution by hydrogen peroxide was studied at various pH values, the effects of variations in pH were not reported. The rate of oxidation of EDTA was said to be slower in the presence of ferric iron and was accompanied by the evolution of oxygen.It was considered that a more thorough investigation of the method of cation release by oxidation of metal complexes at constant pH would allow the value of the technique to be more fully assessed. The use of EDTA as the complexing agent was of particular interest, since it forms water-soluble complexes with many cations and since the conditions of complex formation and factors influencing coniplex stability have been widely investigated. Hydrogen peroxide was a suitable oxidising agent, since the products of its break-down-water and oxygen-were not likely to interfere in any precipitation reaction. TO obtain a fuller understanding of the reactions involved it was first necessary to investigate the break-down of EDTA in solution by hydrogen peroxide, This paper describes * The substance of this paper and other parts of the series was presented at the meeting of the Society on Wednesday, November lst, 1961.November, 19611 SOLUTION BY CATION RELEASE AT CONSTANT pH.PART I 685 experiments carried out to determine the effects of variations in pH and in concentration of hydrogen peroxide and the effect of the presence of precipitate particles. EXPERIMENTAL RE-AGENTS- ED TA -Disodium e t hylenediaminetetra-acet ate dihydrat e. Hydrogen peroxide, 100-volume-Analytical-reagent grade. All other reagents were of analytical grade. All volumetric glassware was calibrated before use. A PI'ARA4TU S- During precipitation from homo- geneous solution it was essential to use unscratched beakers to avoid losses owing to adherence of the precipitates to the walls of the vessels.All pH measurements were made to the. nearest 0.05 unit of pH with a Pye meter having a glass electrode and a calomel reference cell. METHOD 1. Variations in pH and concentration of hydrogen peroxide Reaction solutions consisted of 2 g of EDTA, different amounts of 100-volume hydrogen peroxide and water to a total volume of 300ml. The pH of each solution was adjusted to the required value by the addition of nitric acid or ammonia solution. Reactions were carried out in a flask fitted with a reflux condenser and a thermometer to measure the solution temperature. During the reaction the flask was placed in a boiling- water bath to maintain a reaction temperature of 98" to 100" C.EDTA and the necessary amount of water were placed in the flask, and were brought up to the required temperature; the hydrogen peroxide was then added. Timing of the reaction began when the solution temperature again reached 98" to 100" C. Samples of reaction solution were withdrawn at intervals and cooled, and the amounts of EDTA remaining in solution were determined by titrating with standard bismuth solution, pyrocatechol violet being used as indicator. The effects of variations in pH and concentration of hydrogen peroxide were studied; a blank determination was carried out in the absence of hydrogen peroxide. The results were expressed graphically by plotting the logarithm of the concen- tration of EDTA remaining in solution against time ; straight-line graphs were obtained from which values for K, a constant for the rate of reaction under the conditions of the experi- ments, were calculated.The variation of K with changes in concentration of hydrogen peroxide and pH is shown in Figs. 1 and 2. ' O k Y 1 20 0 Volume of hydrogen per-oxide per Fig. 1. EfTect of variation in hydrogen 300 ml of solution, mi peroxide concentration pH of solution Fig. 2. Effect of variation in pH690 CARTWRIGHT : STUDIES I N PRECIPITATION FROM HOMOGENEOUS [Vol. 86 2. The effect of precipitate particles Experiments were carried out to determine the effect on the break-down of hydrogen peroxide solution of particles of precipitated hydrated oxides ; precipitates of iron and bismuth were used. Preparation of precipitates-Hydrated iron oxide was precipitated from homogeneous solution by MacNevin and Dunton's method.Hydrated bismuth oxide was prepared by boiling a solution containing bismuth - EDTA complex (500 mg of bismuth) with 50 ml of hydrogen peroxide at pH 4.0. The precipitates were collected in sintered porcelain filter crucibles, washed with water and dried at 105" to 110" C. Reaction with hydrogen peroxide-Reactions were carried out under reflux with gentle boiling. Reaction solutions were prepared by diluting 25 ml of hydrogen peroxide to 500 ml with water and adjusting the pH values to 4.5 with nitric acid or ammonia solution. The solutions were gently boiled, and a sample was removed from each to determine the initial concentration of hydrogen peroxide. The required weights of precipitate were then added, and boiling was continued; samples were withdrawn at intervals, and the amounts of hydrogen peroxide remaining in solution were determined by titrating with standard potassium per- rnanganate solution.A blank determination was carried out in the absence of precipitate particles. The results were expressed graphically by plotting the percentage of hydrogen peroxide remaining in solution against reaction time; from the graphs, the times for 90 per cent. break-down of hydrogen peroxide were calculated, as shown in Table I. ( a ) HYDRATED OXIDES-- TABLE I TIME FOR 90 per cent. BREAKDOWN OF HYDKOGEN PEKOXIDE Weight of precipitate, Cation present mg Blank.. . . . . . . Bismuth . . . . . . 7.0 28.0 100.0 Iron . . . . . . . . 14-0 32.0 __ Time for 90 per cent.breakdown, seconds 2470 1400 750 280 1820 1330 jb) BISMUTH PHOSPHATE- The experiments were repeated in solutioris containing bismuth phosphate precipitate at various pH values. A study was also made of the reaction in solutions containing phos- phate ions at various pH values in the absence of precipitate, and the effect of variation in concentration of phosphate at one pH value was investigated. Preparation of bismuth @hos@hate-Bismuth phosphate was precipitated by boiling a solution containing EDTA - bismuth complex (500 mg of bismuth) and 10 ml of phosphoric acid with 25ml of hydrogen peroxide at pH 1.0. The precipitate was filtered, washed, and dried at 106" to 110" C. TABLE I1 DECOMPOSITION OF H Y-DROGEN PEROXIDE I N THE PRESENCE OF BISMUTH PHOSPIIATE PRECIPITATE pH of Weight of precipitate, Break-down after solution mg 3000 seconds, O/(, 1-5 100 3.5 1.5 Nil 67.0 4.5 100 5.0 4.5 Nil 63.5 The results were expressed graphically by plotting the percentage of hydrogen peroxide remaining in solution against reaction time, and the percentage break-down of hydrogen peroxide after 3000 seconds was calculated from the graphs.These results are shown in Tables 11, I11 and IV.November, 19611 SOLUTION BY CATION RELEASE .4T CONSTANT pH. PAKT I 691 TABLE I11 DECOMPOSITIOK OF HYDROGEN PEROXIDE IN THE PKESENCE OF PHOSPHATE ION pH of Phosphoric acid Break-down after solution present, ml 3000 seconds, 1.2 1.2 4.5 4.5 6-2 6.2 5.0 Nil 5.0 Nil 5.0 Nil 5-0 > 90.0 30.0 > 95.0 65.0 n.d. TABLE IV VARIATION IN CONCENTRATION OF PHOSPHORIC ACID AT CONSTANT pH Phosphoric acid present, ml Nil 0.25 0-50 1.00 2-50 5.00 Break-down after 3000 seconds, yo 45.0 25.0 23-0 23.0 20-0 3.0 DISCUSSION OF EXPERIMENTAL WORK OXIDATION OF EDTA SOLUTION- No attempt was made to derive true specific reaction constants for the reactions, since these were not necessary for this investigation and because insufficient was known about the mechanism of the reaction.The values of K shown in Figs. 1 and 2 provide a convenient method of expressing the rate of reaction, but apply only to the experimental conditions prevailing at the time. Certain of the results obtained served to confirm the expected behaviour ; the investi- gations were necessary, however, to provide a clearer understanding of subsequent experiments. Thus, the rate of oxidation of EDTA at constant pH was found to increase with increase in concentration of hydrogen peroxide.This agrees with the findings of MacNevin and Dunton, who reported that the rate of oxidation of an iron - EDTA complex could be increased by increasing the amount of hydrogen peroxide used. The variation in the rate of oxidation of EDTA with change in pH is interesting; it can be seen from Fig. 2 that the rate is little changed over the pH range 1 to 4, but increases rapidly at higher pH values. This fact was found to have an important bearing on the ease of precipitation of certain metals; it will be referred to again at a later stage. During these oxidation reactions there were no signs of vigorous effervescence; some bubbles appeared to originate at imperfections in the wall of the flask, but these only served to prevent the solution from bumping during boiling.EFFECT OF PRECIPITATE PARTICLES- The addition of hydrated oxide precipitates caused an increase in the rate of break-down of hydrogen peroxide (see Table I), bismuth being more effective than iron; this was subse- quently found to have a serious detrimental effect. In the precipitation of hydrated bismuth oxide, for example, all the peroxide present was destroyed by the first-formed precipitate particles, and further oxidation of the bismuth - EDTA complex ceased. To study the precipitation of various metals it was necessary to find a method of over- coming the effect of the precipitate on the hydrogen peroxide. Phosphate ions were known to exert a stabilising action on hydrogen per~xide,~ and consequently the effects of phosphate ion and phosphate precipitate were investigated.The results shown in Tables 11, I11 and IV confirm the stabilising action of phosphate ions and indicate that bismuth phosphate precipi- tate is not only inert, but also has a slight stabilising power. In the absence of precipitate,692 CARTWRIGHT : STUDIES IN PRECIPITATION FROM HOMOGENEOUS [Vol. 86 the stabilising action of phosphate ions was found to be more effective in acid solution, whereas at constant pH the effect increased with increasing phosphate concentration. Thus, by carrying out the reactions in the presence of phosphate ions it should be possible to avoid undue decomposition of the hydrogen peroxide by the precipitate particles, and so to study the effects of complex stability and concentration of reagents on the ease of precipi- tation of metals. The method was then applied to the precipitation of a number of metals, as phosphates, to determine the effect of change of cation. This work is described in Part 11. 1. 2. 3. 4. 6. 6. 7. 8. 9. REFERENCES Gordon, L., Salutsky, M. L., and Willard, H. H., “Precipitation from Homogeneous Solution,” Salesin, E. D., and Gordon, L., Talanta, 1959, 2, 392. Pino Pkrez, F., Burriel-Marti, F., and Martinez Conejero, I,., An. Real SOC. Esp. Fis. Quim., B, Salesin, E. D., and Gordon, L., Tulanta, 1960, 4, 75. Heyn, A. H. A,, and Schupak, E., Anal. Chem.. 1954, 26, 1243. Gordon, L., Peterson, J. I., and Burtt, B. P., Ibid., 1955, 27, 1770. Firsching, F. H., Ibid., 1960, 32, 1876. MacNevin, W. M., and Dunton, M. L., Ibid., 1964, 26, 1246. Schumb, W. C., Satterfield, C. N., and Wentworth, R. L., “Hydrogen Peroxide,” ACS Monogrupk Received June 12ih, 1961 John Wiley and Sons Inc., New York, 1959. 1959, 55, 331. No. 128, Reinhold Publishing Co., New York, 1955.

ISSN:0003-2654    

DOI:10.1039/AN9618600688

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

692 CARTWRIGHT : STUDIES IN PRECIPITATION FROM HOMOGENEOUS [Vol. 86 Studies in Precipitation from Homogeneous Solution by Cation Release at Constant pH Part II.* Precipitation of Various Metal Phosphatest BY P. F. S. CARTWRIGHT (Department of Chemistry, Sir Johm Cuss College, London, E.C.3) Previous studies in this field have been extended to cover the precipitation o f some metal phosphates by the controlled release of the cations from their EDTA complexes by. oxidation with hydrogen peroxide. The effect of metal- complex stability has been investigated. The method has been applied to the determination of bismuth, as bismuth phosphate, but was not found to be suitable for the separation of bismuth from lead. WHEN cation release is brought about by oxidation of metal - EDTA complexes with hydrogen peroxide, certain precipitates cause excessive break-down of the peroxide, resulting in a slowing down of the reaction and sometimes in failure to obtain complete precipitation.1 The effect of the precipitates may be overcome by carrying out the reactions in the presence of phosphate ions.This paper describes the application of the method to the precipitation of some metal phosphates to determine the effect of the cation on the ease of precipitation. Subsequently, the method was applied to the determination of bismuth as phosphate. A number of metals were chosen to cover a range of metal-complex stabilities- Metal . . . . . . Bismuth Iron Lead Calcium Barium Log k absolute . . . . 27.81 25.10 18.04 10.70 7-76 EXPERIMENTAL REAGENTS AND APPARATUS- As described in Part 1.I Stock solutions were prepared containing approximately 10 g A solution of the individual metals per litre and were used in all precipitation reactions.containing log of EDTA per litre was used when necessary to complex the metal ions. * For details of Part I of this series, see reference list, p. 697. t The substance of this paper and other parts of the series was presented a t the meeting of the Society on Wednesday, November lst, 1961.November, 19611 SOLUTION BY CATION RELEASE AT CONSTANT pH. PART II 693 PROCEDURE- Aliquots of the stock solutions were transferred to beakers, and sufficient EDTA solution was added to complex the metal ions. Phosphoric acid (10ml) was added, the solutions were diluted to about 250m1, and their pH values were adjusted to the required levels.,\fter the addition of 25 ml of hydrogen peroxide, the solutions were gently boiled for 2 hours pH of solution 0.41 I pH of solution 0.4, 1 pH of solution 1 pH of solution Fig. 1. ( d ) barium. peroxide; @, wlthout EDT.4 Precipitation of various metal phosphates: (a) iron; (b) lead; (c) calcium; 0: in presence of 25 ml of hydrogen peroxide; x , without hydrogen I I I I , I - t r. 0 I 2 3 4 5 6 7 pH of solution Fig, 2. Precipitation of bismuth phosphate: 0, in presence of 25 ml of hydrogen peroxide; A, in presence of 50 ml of hydrogen peroxide; x , blank solution without hydrogen peroxide on a hot-plate, water being added occasionally to make up evaporation losses. The precipi- tates were collected on weighed, sintered porcelain filter crucibles, washed, and then dried to constant weight at approximatel\-. 500" C.Blank determinations were carried out in694 C4KTWRIGHT STUDIES IN PRECIPITATION FKOM HOMOGENEOUS [Vol. 86 which solutions containing metal - EDTA complexes were boiled in the absence of hydrogen peroxide. A second series of blank determinations was performed in which precipitation was carried out in the absence of EDTA to determine the amounts of precipitate obtainable under the conditions of the reactions. The results of these experiments are shown in Figs. 1 and 2, in which weight of precipitate obtained is plotted against pH of solution. For bismuth, the effects of varying the concentration of hydrogen peroxide and prolonging the reaction time were investigated.The results are shown in Fig. 2 and Table I, respectively. TABLE I Complete precipitation (BiPO,) = 363.0 mg PKECIPITATIOX OF BISMUTH PHOSPHATES ; VARIATION OF REACTION TIME Weight of bismuth phosphate precipitated at- Time, pH 1.9, pH 4.0, pH 5.8, hours mg mg mg 2 308.9 72.1 264.7 4 347.8 166.1 353.4 6 360.8 212.7 359.2 8 n.d. 270.5 n.d. DISCUSSION OF THE METHOD-- In all instances dense precipitates were obtained, and reactions were not accompanied The results obtained with iron, lead, calcium and barium were in The results with bismuth by undue effervescence. agreement with the expected behaviour and will be discussed first. were anomalous and are discussed later in the paper. PRECIPITATION BY OXIDATION WITH HYDROGEN PEROXIDE The results for iron, lead, calcium and barium (see Fig. 1) show that at all pH values investigated the amounts of precipitates obtained by oxidation of metal - EDTA complexes were in good agreement with those obtained by the direct addition of phosphate ion in the absence of EDTA.There appeared to be no difference in the ease with which precipitation occurred, the amounts of precipitate obtained in axid solution being limited by the solubilities of the precipitates under the conditions of the reaction. PRECIPITATION IN THE ABSENCE OF HYDROGEN PEROXIDE When solutions containing EDTA complexes of lead, calcium and barium were boiled without the addition of hydrogen peroxide, some precipitation occurred over narrow pH ranges. This was considered to be due to the stabilities of the metal-EDTA complexes being decreased in acid solution to values too low to prevent some precipitation from occurring.This is the basis of methods of cation release in which the complex is broken up by increasing acidity. In more acid solution the weights of precipitate obtained were again limited by their solubilities in the reaction solutions. The absence of such behaviour for iron was attributed to the iron - EDTA complex still being stable in solutions too acid to permit the formation of iron phosphate precipitate. PRECIPITATION OF BISMUTH PHOSPHATE Anomalous results were obtained with bismuth, since, as can be seen from Fig. 2, the weights of precipitate were greatly decreased between about pH 1 to 5. Increasing the amount of hydrogen peroxide resulted in only a slight increase in the weights of precipitate obtained during 2 hours’ boiling.At the end of this time, the reaction solutions still contained con- siderable amounts of undecomposed hydrogen peroxide, so that failure to precipitate could not be ascribed to lack of oxidising agent. When the time of boiling was extended, more precipitate was obtained, but the results in Table I show that the reaction was not complete at pH 4, even after 8 hours. The results obtained in the absence of hydrogen peroxide showed that although the complex broke It was known that bismuth formed a very stable complex in acid solution.November, 19611 SOLUTION BY CATION RELEASE AT CONSTANT pH. YAKT I1 695 down completely below about pH 0.5, the amounts of precipitate decreased rapidly until, at about pH 2.0, no weighable amounts were formed.Over this pH range precipitation was considered to be due to the combined effects of the instability of the complex and the oxidising action of the peroxide when this reagent was present. Above pH 2.0, however, the bismuth complex is stable and any precipitation must therefore be due to the action of the hydrogen peroxide. It was previously shown1 that the rate of oxidation of EDTA in the absence of metal ions was slow in the region of pH 1-5 and remained little altered until the pH was increased to about pH 4.0; above this value the rate of oxidation increased rapidly with decreasing acidity. Thus, in the precipitation of bismuth phosphate, the rate of libera- tion of bismuth due to oxidation of the bismuth - EDTA complex remained slow up to about pH 4-0, whereas precipitation due to complex instability decreased sharply with increasing pH; above pH 4-0 the rate of oxidation increased and larger amounts of precipitate were again obtained.Thus, although most of the metals investigated gave satisfactory results when precipitated as phosphates, the method was somewhat restricted in its application to bismuth. Similar behaviour might be expected with other metals that form stable complexes in acid solution. The method was next applied to the determination of bismuth, as phosphate, and the possibility of separating bismuth from lead was examined. DETERMINATION OF BISMUTH AS BISMUTH PHOSPHATE The precipitation of bismuth phosphate has been studied by Silverman and Shideler,2 who have reported that the optimum pH range is between 0-5 and 0.7.Below pH 0-5 the results are low, and from pH 0.8 to 2.0 the results are affected by the presence of basic bismuth salts. To test the accuracy and repeatability of the cation-release method, determinations were carried out at about pH 0.7 with solutions of known bismuth content. PROCEDURE- A stock solution of bismuth was prepared by accurately weighing about 10 g of metal, dissolving it in 50ml of nitric acid and diluting to 1 litre. The bismuth content of this solution was checked by precipitation of basic bismuth formate from homogeneous ~olution.~ TABLE I1 PRECIPITATION OF BISMUTH IN PRESENCE OF EDTA Amount of EDTA present Bismuth taken, Bismuth found, Bismuth recovered, mg mg % 101.2 100.9 99.7 100.9 99.7 101.0 99.8 254.2 Sufficient t o complex the metal .. 508.4 i Threefold excess . . . . 254.2 254.1 254.2 254.3 509.3 507.6 508.0 254-1 251.6 252.3 100.0 100.0 100.0 100.2 99.8 99.9 100.0 99.0 99.3 For each determination the required amount of bismuth solution was transferred to a 400-ml beaker, and sufficient EDTA solution was added to complex the metal. Phosphoric acid (15 ml) was added, the solution was diluted to about 250 ml, and the pH value was adjusted to about 0.7 by the addition of nitric acid. After the addition of 50 ml of hydrogen peroxide, the solution was gently boiled for 2 hours, water being added to make up for evapora- tion losses. The solution was filtered through a weighed, sintered porcelain filter crucible. The precipitate was washed with water, dried at 105" to 110" C and then heated to constant weight at 600" C.The precipitate was weighed as bismuth phosphate and the bismuth content was calculated. Determinations were carried out at three levels of concentration, i.e., about 100, 250 and 500 mg of bismuth. The experiments were repeated at the 250-mg level in the presence of a three-fold excess of EDTA. The results are shown in Table 11.[Vol. 86 DISCUSSION OF THE METHOD- In the presence of sufficient EDTA to complex the bismuth, the results were in good agreement with those obtained by the basic bismuth formate method. In all experiments the precipitates were dense and readily filtered. A precipitate containing 250mg of bismuth settled to a bulk of 1-0ml in a 100-ml cylinder in 60 minutes, leaving a clear solution, whereas a similar precipitate formed by direct addition of ammonium phosphate in the absence of EDTA settled incompletely to a bulk of 3.0 ml, leaving a cloudy solution.Some darkening of the precipitates was noticed on heating, suggesting that some adsorbed organic material was present. I t was thus evident that too great an excess of EDTA should be avoided. 696 CARTWRIGHT : STUDIES IN PRECIPITATION FROM HOMOGENEOUS When a three-fold excess of EDTA was used, the results were slightly low. DETERMINATION OF BISMUTH IN THE PRESENCE OF LEAD Silverman and Shideler2 have reported a separation of 0.5 g of bismuth from 0-5 g of lead in a three-stage procedure in which lead was first removed as chloride and bismuth precipitated, first as cupferride and finally as phosphate.More recently] Ross and Hahn4 have described the precipitation of bismuth phosphate in the presence of lead by hydrolysis of metaphosphoric acid in boiling solution to liberate orthophosphate ions. A double precipitation was necessary to separate bismuth from lead completely. To test the efficiency of the present method the determination of bismuth was repeated in solutions containing known amounts of bismuth and lead. Precipitation was carried out at pH 0.7 to 0.8; the total precipitate formed was weighed as bismuth phosphate, and the apparent bismuth content was calculated. The results are shown in Table 111. TABLE I11 PRECIPITATIOX OF BISMUTH IN PRESENCE OF LEAD Bismuth taken, Lead taken, Apparent bismuth Apparent bismuth “4.2 500.0 281-6 110-8 285-5 112.3 254.2 250.0 291.9 114.8 273.1 107.4 mg mg found, mg found, yo DISCCSSIOX OF THE METHOD- The results illustrate a weakness of the technique.Hydrogen peroxide is not selective in its attack on metal - EDTA complexes, so that all metals present are released into solution. Under these conditions the EDTA is of no help in separating metals, but only serves to control the rate of cation release and improve the quality of the precipitates. To obtain a separation of metals it is necessary that there should be no overlapping of precipitation curves. However, it can be seen from Fig. 1 that the curve for lead phosphate started at about pH 0.75. Since bismuth was precipitated a t pH 0.7 to 0-8, some co-precipi- tation of lead might be expected.The results in Table I11 show that this did in fact occur. -4 better separation might have been achieved by precipitating bismuth at pH 0.5, but such a pH value would be difficult to achieve and measure accurately. Improved results would also be expected by carrying out a re-precipitation, but it was considered that no useful purpose would be served by introducing yet another multi-stage separation of the two metals. CONCLUSIONS The method has been found to be satisfactory for the precipitation of some metals, as phosphates, although the pH range over which complete precipitation can be achieved may be restricted for metals forming very stable complexes in acid solution. Single metals may be precipitated provided that the particles cause no undue decomposi- tion of the hydrogen peroxide, but the method was not selective for pairs of closely similar metals. The precipitates so far described have all been dense and readily filterable. Attention was next given to the effect of the solubility of the precipitate on the ease of precipitation; this work will be described in Part I11 of this series.November, 19611 SOLUTION BY CATION RELEASE AT CONSTANT pH. PART 11 697 REFERENCES 1. 2. 3. 4. Cartwright, P. F. S., 14naZyst, 1961, 86, 688. Silverman, L., and Shideler, M., Anal. Chem., 1954, 26, 911. Cartwright, P. F. S., Analyst, 1960, 85, 216. Ross, H. H., and Hahn, R. B., Anal. Chem., 1960, 32, 1090. NOTE-Reference 1 is to Part I of this series. Received June 12th, 1961

ISSN:0003-2654    

DOI:10.1039/AN9618600692

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

November, 19611 SOLUTION BY CATION RELEASE AT CONSTANT pH. PART 11 697 Rapid Identification and Determination of Residues of Chlorinated Pesticides in Crops by Gas - Liquid Chromatography* BY E. S. GOODWIN, R. GOULDEN AND J. G. REYNOLDS ( Woodstock Agricultural Research Centre, “Shell” Research Ltd., Sittingbourne, Kent) The development of a rapid “sorting test” for identifying traces of chlorinated pesticides in crops by means of gas - liquid chromatography with electron-capture ionisation detection is outlined. In this method, the crop is macerated with acetone and the extract partitioned into hexane before gas - liquid chromatography in nitrogen on a %foot column of 100- to 120-mesh kieselguhr supporting 2.5 per cent. by weight of E30L silicone elastomer and 0.25 per cent.by weight of Epikote 1001 maintained a t 163” C. Only conventional gas - liquid chromatographic equipment is required, and neither preliminary “clean up” nor concentration of the extract solution is necessary. The seven insecticides lindane, heptachlor, aldrin, Telodrin (1,3,4,5,6,7,8,8- octachloro- 1,3,3a,4,7,7a-hexahydro-4,7-methanoisobenzofuran), dieldrin, en- drin and DDT can be identified when in admixture in fifteen varieties of crops representative of top fruit, leafy vegetables and root crops, the first six in- secticides in concentrations generally down to 0.1 to 0.25 p.p.m. and the last generally down to 1 p.p.m. Chlordane, toxaphene and methocychlor can also be identified, but only in rather higher concentration. The procedure, which requires about 50 minutes for a single analysis and 30 minutes for serial analyses, can readily be made fully quantitative and improved in sensitivity for any particular insecticide by adjustment of sample volumes, operating conditions and/or the introduction of an extract “clean-up” stage.Inter- ference present in extracts from grain samples can be resolved by the use of a polar gas - liquid chromatographic column or removed by liquid - solid chromatography. Some indication is given of the considerable potentialities of the technique in allied fields. THE continued growth in the use of pesticides on edible crops coupled with the increased attention being paid to consumer safety has produced a pressing need for rapid “sorting tests” by means of which residues of these chemicals can be identified and determined.The im- portance of this need was recognised by the Pesticide Residues in Foodstuffs Sub-committee set up by the Analytical Methods Committee of the Society for Analytical Chemistry in the commissioning of an investigation by Needhaml into the use and potentialities of bioassay methods for the determination of pesticide residues in foodstuffs. As a complement to the bioassay approach, techniques based on the use of gas - liquid chromatography show much promise for this purpose. With katharometer detection, Coulson, Cavanagh and Stuart,2 Zweig and Archer3 and also Dimick et eL4 were able to separate, identify and determine mixtures of pesticides or pesticide isomers on the milligram or decimilligram scale. The application of such gas - liquid chromatographic methods to residue analysis on the microgram scale with more sensitive means of detection, e.g., argon ionisation, is made difficult by chromatographic interference resulting from material co-extracted from the crop, unless a “clean-up” stage is included.The need for such a “clean up” was overcome by * Presented at the meeting of the Society on Wednesday, November lst, 1961.698 GOODWIN, GOULDEN AND REYNOLDS : RAPID IDENTIFICATIOK [Vol. 86 Coulson et aZ.5 by the use of a gas - liquid chromatographic - combustion - coulometric titration procedure applicable to both chlorinated and thiophosphate pesticide residues and by Zweig, Archer and Rubenstein,6 who used a gas - liquid chromatographic - infra-red spectrophoto- metric method.To avoid the necessity for these somewhat complex combination methods, a simpler means of detection is required that possesses not only great sensitivity but also a high degree of selectivity towards the pesticides to be identified and determined. These requirements are met to a considerable extent by the electron-capture ionisation detector of Lovelock and Lipsky,7$s which can be made to exhibit exceptional response to halogenated compounds. This selective response, which is such that nanogram g) amounts of chlorinated com- pounds can readily be determined, permits the identification and determination of traces of chlorinated pesticides in crop extracts without the need either for prior “clean up” or for the preliminary concentration of the extract solution.In an earlier note9 we indicated that a readily obtainable argon-ionisation detector could be used for electron-capture ionisation detection and outlined the results of some preliminary work on its application to the analysis of crop extracts for traces of chlorinated pesticides. This paper reports the extension of this work, with particular emphasis on the development of a simple rapid “sorting test” for identifying and determining residues of chlorinated pesticides in crops. At the same time, the wide scope of the electron-capture gas - liquid chromatographic technique in the analysis of agricultural, atmospheric and industrial samples for traces of halogenated pesticides is indicated. EXPERIMENTAL AND RESULTS A. DEVELOPMENT OF THE “SORTIKG TEST” 1. EXTRACTION PROCEDURE- In order to make the “sorting test” as rapid as possible and to take full advantage of the speed of the gas - liquid chromatographic stage of the method it was considered essential to employ a quick simple extraction procedure.The use of non-polar - polar solvent mixtures, e.g., hexane - isopropanol or hexane - acetone, was found unsatisfactory in that, with crops containing a high proportion of water, emulsification problems were often encountered and two phases obtained. This resulted in partition of the polar solvent between the aqueous and organic phases; in consequence, the latter had to be completely freed from polar solvent by washing with water before a quantitative aliquot could be taken for analysis. Further, since the extraction time was to be kept as short as possible, it was desirable to use the most effective solvent available.For this reason acetone was chosen as the crop-maceration solvent. The minimum volume consistent with obtaining a fairly fluid macerate was used, the mixture then being filtered and washed with acetone and the filtrate adjusted to volume. Direct gas - liquid chromatography of the acetone extract was, however, found to be imprac- ticable, since the massive amounts of co-extracted crop material present resulted in swamping of the detector, despite its comparative insensitivity to non-halogenated compounds. The insecticide present in the acetone extract was therefore partitioned into hexane in the presence of an excess of 2 per cent. aqueous sodium sulphate solution, much of the interfering co-extrac- ted material being left behind.This process took up little time, since separation of the phases was rapid and the aliquot for analysis could be taken directly from the supernatant hexane layer. 2. GAS - LIQUID CHROMATOGRAPHIC PROCEDURE-- (a) A$$aratus zcsed-The Shandon Universal Gas Chromatograph employed comprised a U-shaped chromatographic column heated by boiling liquid under reflux and surmounted by an argon-ionisation detector, the signal from which was fed via a d.c. amplifier to a 10-inch chart width recorder (full-scale deflection, 1 mV) having a pen-response time of 2 seconds. The detector was modified only to improve its insulation, this being achieved by substitution of the Sindanyo and silicone-rubber components by polytetrafluoroethylene.This effected a three-fold improvement in detector sensitivity. The range of potentials that could be applied to this detector was extended by the use of high-tension batteries to below the minimum of 300 volts available from the instrument.November, lgfil] 699 (b) Colztmiz packings-In all of this work kieselguhr was used as supporting medium. Initially, columns up to 8 feet long of 60- to 100-mesh material packed in &-inch internal diameter copper tubing were employed, but the need to eliminate insecticide decomposition and to reduce retention times led to the use of 2-foot (and even shorter) columns of 100- to 120-mesh material. Kieselguhr from several sources appeared equally satisfactory and the use of specially acid-washed material effected no improvement.S o advantage was obtained by the use of Ballotini glass micro beads, whether plain, acid or water-washed, in place of the kieselguhr. The number of stationary phases that can be employed in gas - liquid chromatography at temperatures in excess of 200” C is limited. One of these, which is widely used, is E301 silicone elastomer (obtained from Imperial Chemical Industries Ltd.), which was employed in our earlier experiments at concentrations up to 10 per cent. of the weight of supporting medium. Under these conditions and at even lower temperatures, columns containing the stationary phase mentioned above gave satisfactory chromatography immediately for aldrin, but some conditioning with insecticide was needed (compare Coulson et al.7 before the chromatography of either lindane or dieldrin could be achieved. This effect was thought to be due to adsorption of these insecticides on to the kieselguhr, and it was for this reason that the glass micro beads referred to above were examined.Stable, involatile polar compounds have been used with successloyll for reducing the adsorptive properties of supporting media. The addition to the E301 silicone elastomer of 10 per cent. of its weight of Reoplex 400 (Geigy Co. Ltd.) or Epikote 1001 (Shell Chemical Co. Ltd.) was therefore studied and found to obviate the need for column conditioning. Further, the decomposition encountered during the chromatography of some of the insecticides examined (compare Goodwin et aL9) was either reduced or eliminated. Of the above two polar additives, Epikote 1001 was found preferable on account of its greater adsorption-suppressing efficiency and thermal stability under the conditions employed.Some tests were carried out in which the whole of the E301 silicone elastomer was replaced by Epikote 1001, but the insecticide separations obtained were much less satisfactory than with E301. As the work developed, the amount of stationary phase employed was progressively decreased. This resulted in shorter retention times and a reduction in the tendency of the stationary phase to “bleed,” with its consequent adverse effect on the detector. In most of the later work, 2.5 per cent. of E301 silicone elastomer PLUS 0.25 per cent. of Epikote 1001 on plain 100- to 120-mesh kieselguhr was used. (c) Carrier gas-Initially, argon was employed as carrier gas at flow rates of about 6 litres per hour and was dried before use by passage through indicating silica gel. Subse- quently, argon was replaced by oxygen-free nitrogen, dried as above, in order to eliminate any residual argon-ionisation response from the detector still obtaining at the low potentials employed.In addition, flow rates were raised to 12 litres per hour, so as to reduce insecticide retention times and also effect some improvement in sensitivity. (d) Column temperature-In conformity with earlier published work on the gas - liquid chromatography of chlorinated pesticides, column temperatures in the region of 230” C were employed at first. Under these conditions, some of the insecticides examined, when chromato- graphed in submicrogram amounts, decomposed with the production of multi-peak chromato- grams.Further, decomposition of co-extracted crop material coupled with “bleeding” of the stationary phase resulted in the gradual de-sensitisation of the detector. Lowering of the column temperature helped to overcome these failings, but at the same time resulted in increased retention times, which were counteracted, as already described, by employing faster gas-flow rates and lower concentrations of stationary phase. Column temperatures as low as 163” C were used, this being practicable with compounds having such low vapour pressures as the chlorinated insecticides, provided that the loads injected do not exceed a few micrograms. (e) Detector characteristics-The Shandon argon-ionisation detector is a metal-cased detector having a radium D source, When employed in the conventional manner at a potential of 1200 volts and with argon as the carrier gas, positive chromatographic peaks were obtained for both chlorinated and organo-phosphorus insecticides when injected in microgram amounts. As the potential was decreased, the peaks for the chlorinated insecti- cides became negative, indicating that the detector was exhibiting electron-capture ionisation response.This response increased steadily as the applied potential was decreased to 300 volts, the lowest potential obtainable from the power pack of the instrument. At this voltage AND DETEKMINATION OF RESIDUES OF CHLORINATED I’ESTIC IL)E:S700 GOODWIN, GOULDEN AND REYNOLDS 1 RAPID IDENTIFICATION [Vol.86 significant peaks were given by nanogram amounts of the chlorinated insecticides. It was under these conditions that much of the earlier workB was done, and it is probable that the lack of interference shown by co-extracted crop material on the injection of comparatively large volumes (100 pl) of extract was due in part to the balancing out of any negative peaks owing to electron-capture ionisation response for the non-chlorinated material by the residual positive argon-ionisation effect still obtaining at an applied potential of 300 volts. Subse- quently, lower potentials were applied by the USE! of high-tension batteries, with consequent increase of sensitivity, until a point of maximum sensitivity was reached. After the detector had been cleaned with an abrasive and washed with solvent, the optimum potential for maximum sensitivity was still further reduced (to less than 40 volts), and at the same time an additional increase in sensitivity occurred.This fact, coupled with the replacement of argon by oxygen-free nitrogen, resulted in the elimination of any argon-ionisation effect and necessitated a reduction in the volume of extract injected in order to bring the crop back- ground interference down to an acceptable level. When argon, a potential of 300 voltsand injections of 1 0 0 ~ 1 volume were used, there was a tendency for premature contamination of the column and for drift in the balance point between electron-capture ionisation and argon- ionisation effects due to de-sensitisation of the detector, e.g., by decomposition products coming from the column.Accordingly, it was considered preferable to employ electron- capture ionisation as the sole means of detection. By using the Shandon detector for this purpose it was found that the amplifier gain control could be set at up to ~ 2 0 0 before the “noise” level became significant. In the “sorting-test” procedure, therefore, the gain was normally set at x 50, so as to give adequate sensitivity and yet leave some amplification in hand. The response of the Shandon detector when used under conditions of electron-capture ionisation showed reasonable linearity over a limited range only, which varied with the insecticide under test. For example, the response of the detector was fairly linear for aldrin in amounts up to about 0.0025 pg, for dieldrin up to about 0.006 pg and for DDT up to about 0.02 pg, equivalent in the present work to about 2, 5 and 20 p.p.m., respectively, on the crop.Under the standardised conditions employed for the “sorting test ,” loss of linearity became significant when the chromatographic peak due to the insecticide exceeded about 70 per cent. of the full-scale deflection of the recorder. Thus, by setting the gain at x50, the most effective use could be made of the recorder chart width under conditions of near-linear detector response. The success of the Shandon argon-ionisation detector when employed as an electron- capture ionisation detector resulted in the construction and study of an argon-ionisation detector of the small diode pattern described by Lovelock.* When used at its optimum potential for electron-capture ionisation detection (about 100 volts), this detector, which contained a tritium source, exhibited a sensitivity to chlorinated compounds about ten times greater than that of the Shandon detector. By means of this Lovelock detector, chlorinated insecticides could be determined on the decinanogram scale.Despite its greater sensitivity and lower “noise” level, it was decided for the present work not to employ this detector in place of the Shandon model, since the latter had adequate sensitivity for the purpose in hand and, moreover, had the merit of being typical of detectors readily obtainable commercially. A brief study was made of the behaviour of the Shandon detector towards organo- phosphorus insecticides when used at the optimum potential for maximum electron-capture ionisation response for the chlorinated insecticides.The sensitivity of the detector to the organo-phosphorus compounds was found to be very much lower than to the chlorinated compounds. For example, the response to parathion was fifteen times lower, to malathion forty times lower and to Phosdrin three hundred times lower than it was to aldrin. B. PROCEDURE RECOMMENDED FOR “SORTING TEST” 1. INSTRUMENT PREPARATION- (a) Column packing-Weigh out amounts of 100- to 120-mesh chromatography-grade kieselguhr, E301 silicone elastomer and Epikote 1001 to give 2-5 per cent. by weight of silicone and 0.25 per cent. by weight of Epikote on the weight of support. Dissolve the mixed stationary phases in AnalaR ethyl acetate, and add the kieselguhr to the solution.Remove the organic solvent on a bath of hot water, stirring the mixture throughout the evaporation. Sift the dried material, collecting the portion between 100 and 120 mesh. A yield of about 70 per cent. is generally obtained. Fill a 2 foot long &-inch internal diameterNovember, 19611 AND DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 701 copper gas - liquid chromatographic column with 4.0 to 4.5 g of the freshly prepared graded column filling, tapping the column repeatedly during the addition in order to achieve uniform and dense packing. (b) CoZumn temperature-Maintain a constant column temperature of 163” C by boiling cyclohexanol under reflux in the surrounding vapour jacket.(c) Carrier gas-By the use of a soap-film flow meter, prepare a plot of the flow rate of oxygen-free nitrogen through the packed column against the column inlet pressure as indicated on the nitrogen cylinder reducing valve. By using this calibration, adjust the flow rate of nitrogen to a room temperature value of 12 litres per hour. The usual inlet pressure for this flow rate is about 8 lb per sq. inch gauge. (d) Column pre-treatmeltt-Condition the new column at 163” C by passing nitrogen through it at 12 litres per hour for some hours before fitting the detector in place. This process avoids contaminating detector parts during the high initial “bleed” of stationary phase. (e) Control settings-Set amplifier and recorder zero pre-set controls so that the recorder pen is 2 inches from the normal full-scale deflection side of the chart.Arrange for the chart to run at 24 inches per hour, and set the gain control at x 50. Adjust “backing off” until the pen position coincides with that for amplifier and recorder zeros when the instrument is switched to ‘ ‘READ. ” (f) Detector 9otentiaLPotentials are applied to the detector from a battery source con- nected with its positive terminal earthed. Record the detector response at applied potentials in the range 4 to 40 volts for a constant injection of a standard solution of lindane in hexane. By inspection, select the optimum potential for maximum detector response. In this con- nection it may be noted that the point of inflexion on the curve produced by plotting “backing- off” readings against applied potential gives an approximate value for the optimum potential for maximum detector response.Some slight drift from the optimum potential occurs with column use. For maximum sensitivity it is therefore advisable to check the optimum position by measurement of the detector response to lindane when the potential is varied a few volts either way. 2. SAMPLE PKEPARATIOK- From the field sample supplied, weigh a fully representative 50-g sub-sample of the crop into the 200-ml maceration jar of a high-speed top-drive macerator. Chop the crop material into small pieces with a long-bladed knife, and add sufficient redistilled AnalaR acetone just to cover the sample. The volume of solvent normally required is 60 ml, but for dry crops, such as tea and flour, and some bulky materials, such as cabbage, the volume may be increased to a maximum of 80 ml.Macerate the sample for 3 minutes, and then set aside for 5 minutes. Transfer the contents of the jar as completely as possible to a 7-cm diameter No. 3 sintered- glass funnel. Filter under reduced pressure directly into a 100-ml graduated cylinder, and press the crop material as dry as possible by means of a flattened glass rod or small beaker. Wash the crop residue on the filter with acetone so as to make the filtrate up to 100ml. Remove the filter, insert the stopper in the cylinder, and shake well. By pipette, place 5 ml of the acetone extract into another 100-ml graduated stoppered cylinder. 14dd 10 ml of redistilled laboratory-reagent grade n-hexane by pipette, and mix thoroughly by swirling.Measure 85 ml of a 2 per cent. aqueous solution of sodium sulphate into the cylinder, insert the stopper, and shake vigorously for 30 seconds. Allow the two phases to separate, then remove 5 p1 of the supernatant hexane layer by means of a IO-pl fixed-needle Hamilton syringe pipette. 3. GAS - LIQUID CHROMATOGRAPHY OF SAMPLE- Check and, if necessary, adjust the gas-flow rate, column temperature and instrument control settings. Start the chart drive, and inject the 5-pl sample via the silicone-rubber septum at the inlet to the column. Examine the chromatogram in comparison with one obtained from a control crop (if available) processed under identical conditions. When peaks are obtained compare their retention times with those obtained for mixtures of chlorinated technical insecticides run under identical chromato- graphic conditions.After about 22 minutes, stop the chart drive.702 GOODWIN, GOULDEN AND REYNOLDS : RAPID IDENTIFICATION [Vol. 86 I I I I I I \ Baselii Time, minutes 1. Q-. Scale : 0.5 I. F. - i e - 4 20 1 5 Pdseline 5 10 I I I l l I e 4 D 5 I0 I '5 i0 Time* Apples (Cox's orange pippin) / Apples (Beaucy of Bath) J 4 / - Broccoli (Purple sprouting) / Cabbage (Spring) Grapes Lettuce Tea Fig. 1. Chromatograms of technical-grade insecticide mixtures and control-crop extractsKovember, 19611 AND DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 703 r C . RESULTS OBTAINABLE BY “SORTING TEST” Control samples of the crops listed below, taken as being representative of top fruit, leafy vegetables and root crops, were processed according to the above procedure and in all instances gave chromatograms in which the level of background interference was accept- ably low- Apples (Blenheim) Cabbage (spring) Lettuce Apples (Cox’s orange pippin) Cabbage (winter) Potatoes Apples (Beauty of Bath) Carrots (English) Swedes Broccoli (purple sprouting) Carrots (Italian) Tea Broccoli (spring heading) Grapes Tomatoes.Examples of these control chromatograms are shown in Fig. 1, together with the chromatograms produced by a mixture of the technical insecticides lindane, heptachlor, aldrin, Telodrin,* dieldrin, endrin and DDT in amounts equivalent to 0.1, 0.5, 2.0, 5.0 and 10.0 p.p.m. on the weight of the crops. As would be expected, the peak heights given by the insecticides decrease as their retention times increase.With lindane, for example, 0.1 p.p.m. of insecticide is readily detectable in the crops shown, full-scale deflection of the recorder being obtained when about 1.5 p.p.m. are present. With dieldrin, on the other hand, the minimum amount generally detectable in the “sorting test” is about 0.25 p.p.m., full-scale deflection of the recorder being obtained when about 8 p.p.m. are present. The general limits of detection for the seven insecticides in the above-mentioned fifteen crop varieties are given in Table I. Sometimes, however, the control chromatograms are such that the limit of detection for one of the insecticides may be less satisfactory, e.g., aldrin in spring cabbage and DDT in tea.TABLE I 1. CHROMATOGRAMS OF INSECTICIDES AGAINST CONTROL CROPS- GENERAL LIMITS OF DETECTION OF SEVEN TECHNICAL INSECTICIDES IN APPLES, BROCCOLI, CABBAGE, CARROTS, GRAPES, LETTUCE, POTATOES, SWEDES, TEA AND TOMATOES, BY THE STANDARD ‘ r ~ ~ ~ ~ ~ ~ ~ - ~ ~ ~ PROCEDURE Insecticide . . .. .. . . Lindane Heptachlor Aldrin Telodrin Dieldrin Endrin DDT General limit of detection, p.p.m. 0.1 0.1 0.1 0.2 0.25 0-25 1.0 In the insecticide chromatograms shown in Fig. 1 a further two small peaks are evident, particularly so at the higher concentrations. The first of these peaks, which has a retention time of 6.3 minutes, is due to heptachlor epoxide. This epoxide, which is not the biological metabolite, was present in the technical heptachlor used in this work and could be isolated from it by liquid - solid chromatography on Florisil.The second peak, having a retention time of 12.2 minutes, is due to o$’-DDT present in the technical DDT employed. In addition to the seven insecticides referred to above, chromatograms were run on technical samples of chlordane, methoxychlor and toxaphene. The first of these gave a well defined chromatogram having eight peaks with retention times ranging from 1.6 to 12.8 minutes. Two of the peaks had retention times not far removed from that of heptachlor, but of only about one-tenth the sensitivity of the latter. Methoxychlor produced only one major peak of 35-minutes retention time and one minor peak of retention time between that of lindane and heptaclor, but had a peak sensitivity of only about one fifth that of chlordane.Toxaphene gave a multi-peak parabola of equally low intensity, having a retention time up to about 20 minutes. 2. TYPICAL “SORTING-TEST” RESULTS- Known amounts of three or four technical insecticides in acetone solution were added at the maceration stage to samples of apple, cabbage and potato, which were then processed as described. The chromatograms produced, which are shown in Fig. 2, indicate the kind of results generally obtained by the use of the standard “sorting-test” procedure. In the test on apple, shown in Fig. 2A, the smaller peak, of 12-3-minutes retention time, is due to the qb‘-DDT present in the technical DDT used. This peak is shown again, more clearly, in Fig. 2C in the test on cabbage. In the treated potato sample (Fig.2E) the heptachlor * Telodrin is the Shell Trade Mark name for 1,3,4,5,6,7,8,8-octachloro-1,3,3a,4,7,7a-hexahydro-4,5- methanoisobenzofuran.704 GOODLVIN, GOULDEN AND REYNOLDS RAPID IDENTIFICATION [Vol. 86 epoxide added was the biological metabolite, not the one present in the technical heptachlor. The two epoxides have different retention times and are thus readily distinguishable from each other and from the heptachlor itself. - of lindane 4 0 p.p.m. i-0 p.pm 10.0 of aldrin F -2-0 p.p.m. of heptachlor n P . P . ~ . I D heptachlor epoxide j l k Potatoes I I I I I 1 5 10 15 20 Time, minutes J 1 I I I 0 5 10 15 20 Time, minutes Figs. 2 and 3. Chromatograms of toxicant-treated and control crops obtained by using the standard “sorting-test” conditions 3.QUANTITATIVE ASPECTS- When, in the “sorting test,” chromatographic peaks due to insecticide are less than about 70 per cent. of the recorder full-scale deflection, it is possible to make a rapid approxi- mate assessment of the amount of insecticide present. When peaks exceed 70 per cent. of the recorder full-scale deflection, with the result that detector response is no longer reasonably linear, a repeat injection is necessary before making any quantitative assessment. This repeat injection is best carried out with a 5-p1 sample after appropriate dilution of the hexane extract. Alternatively, a smaller sample (say down to 1 pl) can be injected, but this leads to reduced precision. Conversely, when peaks are very small, a higher gain setting can be employed, a larger sample-say up to 25 pl-can be injected or a bigger aliquot of the acetone extract can be partitioned into the hexane.Success with any of these procedures depends on the level of crop-background interference which obtains. For quantitative work, measurement of peak areas was found, as expected, to give more reproducible results than measurement of peak heights. In the preparation of calibration graphs, the use of different volumes (4 to 40 pl) of a single standard insecticide (generally 0.1 pg per ml) solution is preferred to a fixed volume ( e g . , 5 p1) of several standard solutions, since preparation of standards in the latter method can be time-consuming when many insecticides are being studied. At the same time, it must be borne in mind that, with the smaller Hamilton micro-syringe pipettes, significant over-injection occurs owing to theNovember, 19611 AND DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 705 “flashing off” of a portion of the solution contained in the syringe needle.As an example, in this work the over-injection on a 5-pl sample in the 10-pl fixed-needle syringe pipette is +0*4pl. The use of a standardised injection procedure makes this increment fairly reproducible, so that allowance for it can be made when the syringe is filled. An indication of the recoveries obtainable by the standard “sorting-test” procedure was obtained in the following experiment. Known amounts of pairs of insecticides in acetone solution were added at the maceration stage to 50-g samples of control tomato, carrot and broccoli, which were then processed and analysed as described.The areas under the peaks in the chromatograms, which are shown in Fig. 3 (A, C and E), were determined, and the recoveries were calculated from the calibration graph resulting from the direct injection of known amounts of the insecticides on to the column. The results obtained are shown in Table 11. For lindane and DDT in broccoli, two chromatograms were run, one under the standard conditions to determine DDT and the other after ten-fold dilution of the hexane extract to determine lindane. TABLE I1 RECOVERIES BY THE STANDARD “SORTING-TEST” PROCEDURE OF PAIRS OF TECHNICAL INSECTICIDES ADDED AT THE MACERATION STAGE TO THREE CONTROL CROPS Crop treated Insecticide added .4mount present, p.p.m.Amount recovered, yo Telodrin ’ . { Endrin Aldrin . . . . { Dieldrin Lindane Tomato . . Carrot Broccoli . . ’ * { DDT 0- 5 1.0 2.0 5.0 10.0 30.0 90 93 78 77 80 83 4. GENERAL OBSERVATIONS- At the comparatively low temperature of 163” C and with the small loadings used in the “sorting test,” column life can be up to several weeks. Detector performance, on the other hand, falls off more rapidly, owing to progressive contamination resulting from a slight “bleed” of stationary phase or crop-decomposition products. This deterioration in sensitivitl- is due to a drift in the optimum potential for maximum sensitivity to a higher value. When this deterioration becomes serious, high performance can be restored by a combination of abrasive cleaning and solvent washing of the detector.With careful standardisation of the “sorting-test” conditions, insecticide retention times are generally reproducible to within ,t2 per cent. As might be expected, slight increases in retention times do, however, take place when larger (e.g., 25 pl) aliquots of the hexane extract are used. Reference chromatograms should therefore be run under identical volume- injection conditions. The time required to carry out one “sorting-test” analysis from receipt of a representative field sample to semi-quantitative assessment of results is about 50 minutes. Of this time about 20 minutes is required for the gas - liquid chromatographic stage, which requires no supervision. In consequence, serial analyses can be completed in about half an hour.D. EXTENSION OF METHOD TO INCREASE SCOPE 1. TREATMENT OF CROPS SHOWING CHROMATOGRAPHIC INTERFERENCE- On examining control grain samples by the “sorting test,” sharp interference peaks having retention times of 4.2 to 4.3 minutes were observed in the chromatograms. This interference was found present in wheat, oats, barley, maize (slight only) and rice. The rice also gave a large peak at 1.0 minutes; a sample of control onion gave a peak at 0.7 minute. These two last-mentioned peaks are, however, of no serious consequence in that they occur well before the most volatile of the insecticides studied (lindane) appears. The interference peaks appearing in the grain samples at about 4.25 minutes, on the other hand, could be confused with aldrin. (a) Two-column gas - liquid chromatography-In the “sorting-test” procedure, gas - liquid chromatography is effected on an essentially non-polar stationary phase, with the result that compounds are eluted in order of volatility.By use of a polar stationary phase, however, the order and times of elution become more dependent on the polarities of the compounds Two methods of resolving this problem were examined.706 GOODWIN, GOULDEN AND REYNOLDS : RAPID IDENTIFICATION [Vol. 86 being ctiromatographed. Thus, in this instance, a 5-pl aliquot of the control oat sample was chromatographed on a 2-foot column of 100- to 120-mesh kieselguhr supporting 2-5 per cent. by weight of Epikote 1001 maintained at 188" C by refluxing propylene glycol. Chromato- grams from both columns were also obtained from the oat sample after the addition at the maceration stage of 0.25 p.p.m.of aldrin. The results obtained, which are shown in chromato- grams A, B, C and D in Fig. 4, indicate that, although on the standard non-polar column the oat-interference peak is indistinguishable from ddrin, on the polar column complete resolution is effected: .Polar Column I 1 1 Interference Liquid - solid chromatogruphy Non - Dolor column :pp; 0.25 p.p.m. Shandon detector Standard column (2 feet) tO.01 p.p.in. of lindane Lovelock detector Shandon detector Short column (9 Inches) 0 5 10 Time, minutes Fig. 5. Chromatogram of crops treated with toxicants a t low concentrations I 1 1 0 5 10 Time, minutes Chromatograms of control and Fig. 4. aldrin-treated oats (b) Liquid - solid chromatograp~y-Differences in compound polarity form the basis of liquid - solid (adsorption - elution) chromatography.Accordingly, 5-ml aliquots of the hexane extracts of the two above-mentioned samples were chromatograplied on columns 6 cm long by 1 crn bore containing 5 g of Brockmann grade 1/11 alumina of about 1 per cent. adsorbed moisture content and eluted with n-hexane until the eluates reached a volume of 25ml. Gas chromatography of 25-pl aliquots of these eluates on the standard non-polar column at 163" C gave the chromatograms E and F shown in Fig. 4. From these it can be seen that liquid - solid chromatography on alumina has eliminated from the control sample the inter- ference peak at 4-25-minutes retention time and that, in the chromatogram of the treated sample, only the peak due to aldrin remains.Recovery of the insecticide put through this "clean-up" process was found to be quantitative.November, 19611 AXD DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 707 2. PROCEDURES FOR MAXIMUM SENSITIVITY- When small amounts (e.g., <Om1 p.p.m.) of insecticide have to be detected, the level of chromatographic interference due to the crop must be reduced, e.g., by liquid - solid chromatography, and more sample must be used in the analysis, as shown in the following example. Summer cabbage (50 g) was treated at the maceration stage to contain 0.01 p.p.m. of lindane and processed to give a 100-ml acetone extract. A 20-ml aliquot of this was parti- tioned into 10 ml of n-hexane, a 5-ml portion of which was chromatographed on a calibrated 5-g column of alumina with hexane - 1 per cent.acetone solution; a 15-ml eluate fraction was taken. Aliquots of 50 p1 of this solution were then gas-chromatographed on the standard 2-foot column, In the first instance the Shandon detector was used with a gain-control setting of x 100 and later the Lovelock detector already referred to was employed with a gain-con- trol setting of x20. The gas chromatograms obtained, which are shown in Fig. 5 (A, B, C and D), indicate that, although some control-crop interference at the retention time of lindane is still evident after liquid - solid chromatography, the presence of 0.01 p.p.m. of lindane in the crop is clearly visible. For insecticides having longer retention times, increase in sensitivity can be achieved by the use of a shorter column supporting less stationary phase and by the employment of a faster gas-flow rate.A lettuce sample was treated to contain 0.03 p.p.m. of endrin and then pro- cessed and “cleaned up” as described above. Gas - liquid chromatography was carried out on a 9-inch column of 100- to 120-mesh kieselguhr supporting 1 per cent. of E301 silicone elastomer and 0.1 per cent. of Epikote 1001. The nitrogen flow rate employed was 21 litres per hour. With the Shandon detector and a gain-control setting of x 50, the chromatograms E and F shown in Fig. 5 were obtained, which indicate that endrin is readily detected at the 0.03 p.p.m. level, despite the presence of some crop interference, and is eluted from the column in 1.5 minutes, GENERAL DISCUSSION AND CONCLUSIONS Some of the limitations in the use of bioassay techniques for the screening of foodstuffs for the presence of pesticide residues have recently been discussed by Chilwell and Hartley,l2 who observed that the only serious attention that had been given to the screening aspect of residue analysis was the possibility of identification by dual-system paper chromato- g r a p h ~ , ~ ~ so far most completely developed for the chlorinated hydrocarbons. Notwith- standing its shortcomings, a bioassay method involving, say, house-flies, fruit-flies or mos- quito larvae constitutes at the present time the most potentially useful type of “catch-all” screening procedure.After preliminary screening by such a method, those edible crops exhibiting toxicity must be examined for the identification and determination of the pesticidal residues present. These residues will generally be either organo-phosphorus compounds or chlorinated hydrocarbons.For the latter, gas - liquid chromatographic methods of analysis show much promise and have the advantage over paper-chromatographic procedures of being both rapid and quantitative. The chief merits of gas - liquid chromatography with electron-capture ionisation detection over other gas - liquid chromatographic methods for determining chlorinated pesticide residues are that it requires no ancillary equipment to effect selectivity, no preliminary concentration stage and, in general, no “clean up” of the extract solution. These factors result in both simplicity and speed.The electron-capture gas - liquid chromatographic “sorting test” described herein could therefore be a useful supplement to the primary bioassay screen and, when only chlorinated pesticides are involved, might even replace it. From the results obtained it can be seen that the “sorting test” employed in standard form permits the detection of the six chlorinated insecticides lindane, heptachlor, aldrin , Telodrin, dieldrin and endrin in concentrations down to 0.1 to 0.25 p.p,m. in most of the crops examined. For DDT, however, the general limit of detection is rather higher at 1 p.p.m., although for screening purposes this is not serious in view of the comparatively high tolerance limit normally set for this compound. The limit of detection attainable in the standard procedure is obviously dependent on the nature of any chromatographic interference arising from the crop itself.Experience with the method may show that the majority of top fruit, leafy vegetables and root crops produce satisfactorily low chromato- graphic backgrounds and that only a few types of foodstuffs, e.g., the grains, require special708 GOODWIN, GOULDEN AND REYNOLDS RAPID IDENTIFICATION p o l . 86 treatment. If this proves to be so, then most samples could be analysed by the standard “sorting-test” procedure and the two-column gas - liquid chromatographic technique or a simple liquid - solid chromatographic “clean-up” process applied only to the few crops known to be atypical. If, however, interference is exhibited in some samples of a wide variety of crops then the “sorting test” should at least serve as a rapid method of screening samples for the absence of chlorinated pesticide residues, all crops showing chromatographic peaks being examined by the above-mentioned supplementary techniques.The preliminary screening could then be made still more rapid, at the expense of individual toxicant identification, by reduction of retention times to, say, 5 minutes over-all. One limitation to the standard “sorting-test” procedure is that chlordane, toxaphene and methoxychlor would not be detected unless present in comparatively high concentrat ion, the two first-mentioned because of their multi-component nature and the last becauseof its long retention time under the conditions employed. Of these three insecticides, however, the two last-mentioned have high tolerance limits.In the quantitative work, recoveries from three crops of six insecticides added at the maceration stage in concentrations ranging from 0.5 to 20 p.p.m. average 80 to 90 per cent. and show good reproducibility for any one crop. The use of an appropriate correction factor would therefore seem to be reasonable. Since experiments have shown that the partition stage of the sample-preparation procedure is over 95 per cent. efficient, the losses encountered may well be due to retention of toxicant by the crops. Nevertheless, a rapid crop-preparation process resulting in reasonably high and reproducible recoveries is considered to be preferable for the present purpose to a longer but more exhaustive extraction procedure.When complete maceration of the sample is unnecessary, then the use of some simpler insecticide-removal process, e.g., the solvent stripping of whole fruit, should effect a further saving in time and result in a substantial reduction in the limits of detection, owing to the comparatively small amount of co-extracted crop material present. As has been shown, the general limits of detection attainable by the standard procedure can be significantly reduced by introducing a simple “clean-up” stage and by altering such variables as partition and injection aliquots and the conditions of gas - liquid chromatography employed. It should be emphasised here that the standard “sorting-test” procedure is neces- sarily a compromise method designed to give adequate results for the widest possible range of chlorinated insecticides.It follows that in more limited circumstances, when only one or two insecticides need be sought for, operating conditions can be tailored as appropriate to achieve greater sensitivity in the method. As already indicated, for example, reduction in column length and amount of stationary phase, coupled with increase of gas-flow rate, permit an appreciable lowering in the limit of detection of endrin, as well as a marked reduction in the time required for gas chromatography. The commercial detector used in this work under conditions of electron-capture ionisation detection shows exceptional response to halogenated compounds. This, Lovelock has recently pointed 0~t,1* is due to their highly “electrophoric” nature.The limits of detection in the “sorting test” are governed by the relative amounts of pesticide and co-extracted crop material present and by their respective “electrophoric” characteristics rather than by any limitation in the sensitivity of the commercial detector. Full advantage can be taken of the even greater sensitivity of the more recent detectors (see Lovelocks) only if the ratio of crop interference to pesticide is reduced. The proposed method appears to be comparatively insensitive to the organo-phosphorus insecticides, since they do not in general possess high electron affinity. One exception to this is parathion, in which the presence of the highly “electrophoric” -NO, group could explain why its limit of detection is no more than fifteen times greater than that for aldrin.I t will be obvious from the foregoing discussion that gas - liquid chromatography with electron-capture ionisation detection is a technique of some potential value for the identi- fication and determination of traces of halogenated compounds. Evidence of compound identity can be made almost certain by use of the two-column gas - liquid chromatographic technique, whereas the analysis of samples containing more heavily interfering extractables than do crops can generally be effected after the application of suitable “clean-up” procedures. As an example, the method has been used with success for determining traces of chlorinated insecticides in “cleaned-up” extracts of animal, avian and insect tissue. The last-mentioned analysis, made possible only by the ability of the method to determine nanogram amountsNovember, 19611 AND DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 709 of insecticide in very dilute solution, indicates the potentialities that this technique may have in the study of the mechanisms of insect resistance. In the same way have traces of halogenated insecticides, nematicides and herbicides been determined in soil by the method, which readily permits metabolic conversions such as aldrin + dieldrin or heptachlor -+ hepta- chlor epoxide to be followed. Finally, it may be noted that preliminary work indicates that the technique could have much value in the determination of traces of chlorinated insecticides in contaminated atmospheres and in samples as varied as wool, wood, hardboard and plastics. We thank Mr. I. G. Blackwell for carrying out much of the experimental work outlined, MI-. A. Taylor, of the Infestation Control Laboratory, M.A.A.F., Tolworth, Surrey, for a gift of pure heptachlor epoxide (biological metabolite), Dr. R. A. E. Galley, Director of the Woodstock Agricultural Research Centre, for his interest and encouragement and the Directors of “Shell” Research Ltd. for their permission to publish this paper. 1. 2 . 3. 4. 5 . 6. 7. 8. 9. 10. 11. 12. 13. 14. REFERENCES Needham, P. H., Araalvsf, 1960, 85, 792. Coulson, D. M., Cavanagh, L. h., and Stuart, J., J . Agric. Food Ckem., 1959, 7 , 250. Zweig, G., and Archer, T. E., Ibid., 1960, 8, 190. TVilkens Instrument and Research Inc., Walnut Creek, California, “-4erograph Research Notes,” Coulson, D. M., Cavanagh, L. &I., De Vries, J . E., and Walther, R., J . Agric. Food Chem., 1960, 8, Zweig, G., Archer, T. E., and Rubenstein, I)., Ibid., 1960, 8, 403. Lovelock, J. E., and Lipsky, S. R., J . Amer. Clzem. SOC., 1960, 82, 431. Lovelock, J. E., A9zaZ. Chem., 1961, 33, 162. Goodwin, E. S., Goulden, R., Richardson, A., and Reynolds, J. G., Chem. &, Iwd., 1960, 1220. Harva, O., Kivalo, P., and Keltakallio, A., Suomeiz Kemistilehti, 1957, 32B, 71; Chem. Ahstr., Bohemen, J., Langer, S. H., Perrett, R. H., and Purnell, J. H., J . Chen?. Sor., 1960, 2444. Chilwell, E. D., and Hartley, G. S., ,4?zaZyst, 1961, 86, 148. Mills, I?. A., J . Ass. 08. dgric. Chem., 19.59, 42, 734. J,ovelock, J. E., Naftrre, 1961, 189, 729. Winter Issue, 1959. 399. 1959, 53, 21359. Received Muy 1?th, 1961

ISSN:0003-2654    

DOI:10.1039/AN9618600697

出版商:RSC    

年代:1961

数据来源: RSC

摘要:

November, 19611 AND DETERMINATION OF RESIDUES OF CHLORINATED PESTICIDES 709 The Determination of Phenothiazine in Commercial Preparations by Ultra-violet Absorption Spectroscopy BY A. BRIERLEY AND D. M. LANGBRIDGE (The Coopey Technical Bureau, Berkhamsted, Herls.) A rapid chromatographic method has been developed for determining phenothiazine in the technical product and in commercial preparations. Separation is achieved on a column of acid aluminium oxide having a Brock- mann activity of approximately 111, a mixture of diethyl ether and light petroleum being used as eluting solvent. Phenothiazine is determined by means of the characteristic maximum in its ultra-violet absorption spectrum a t 254.5mp. The method is thought to be specific for phenothiazine. THE need for an accurate method for the specific determination of phenothiazine in com- mercial preparations has become apparent with the wide-spread interest in the relationship between particle size and purity on the one hand and anthelmintic efficiency on the other.Several methods have been proposed, but most have the disadvantage that they are not specific. Smith1 determined phenothiazine as ether-soluble material, and Cupples2 measured the intensity of the red colour produced by oxidising an ethanolic solution with bromine water. Overholser and YO@ utilised the reaction of phenothiazine with a number of inorganic ions to produce red or green compounds. The nitrogen content of phenothiazine is used as a7 10 RRIERLEY AND LANGBKIDGE : THE DETERMINATION OF PHENOTHIAZINE [Vol. 86 method of assay in the British Veterinary Codex.4 Recently, Gunew6 described a specific method involving chromatographic separation on a mixed adsorbent of silicic acid and a synthetic magnesium silicate.The phenothiazine was determined by direct weighing and was characterised by its melting-point. EXPERIMENTAL Gunew's chromatographic method has the disadvantages that the adsorbents recom- mended are not readily available outside the United States and that the procedure is time- consuming. I t has been found that a similar separation can be achieved on a column of acid chromatographic aluminium oxide. The activity of the alumina is approximately Brockmann grade 111, and the eluting solvent is a mixture of diethyl ether and light petroleum (boiling range 40" to 60" C).The phenothiazine is determined specifically by the characteristic maximum in its ultra-violet absorption spectrum at 254.5mp. As the impurities in com- mercial phenothiazine are not known, a series of possible impurities was analysed by the proposed procedure ; only one, carbazole, showed positive interference. However, from its mode of formation, it seems unlikely that carbazole will constitute more than a trace impurity in phenothiazine. The preparation of pure phenothiazine was necessary in order to measure the extinction coefficient. Smith and Nelson6 purified phenothiazine by repeated recrystallisation and obtained a material melting at 184.2" C. However, by sublimation at 130" C and 1 mm pressure, they obtained a product melting at 185.1" C.Baker and Brickman' obtained pure phenothiazine by distilling the technical product with super-heated steam ; the melting-point of the product was 183" to 185" C. Lazarus and Rogers* obtained pale gold or faint green crystals, melting-point 182" C, by sublimation at 260" C and 25 mm pressure. Gunther and Blinng quote the extinction coefficient of pure phenothiazine, melting-point 185-2" to 186.0" C, at 254 mp as 43,200 (EiZ = 2170); the spectrophotometer used was a Beckman model DU, and 95 per cent. ethanol was the solvent. Houston, Kester and DeEdslO showed that an ethanolic solution of phenothiazine had an absorption maximum at 254 mp and that two oxidation products, phenothiazine-&oxide and phenothiazone-3, did not absorb at this wavelength. Brown, Cole and Crowellll purified commercial phenothiazine by recrystallisa- tion from a mixture of acetone and iso-octane and then two vacuum sublimations; the product melted at 185.0" to 185.5" C.They showed that the sharp peak at 255 mp in chloroform disappeared on oxidation. The absorption peak at 254 to 255 mp is characteristic of phenothiazine and is not given by its oxidation products. Pure phenothiazine was prepared by repeated vacuum sublimation until there was no further change in the value of EicZ. Diphenylamine is the only impurity identified as being present in technical phenothiazine. Sulphur may be present, but its existence is doubtful, as excess of sulphur can react with phenothiazine to form polymeric products. The existence of polymeric material was reported by Smith,l who showed that the ether-insoluble material was isomeric with, or a polymer of, phenothiazine. About 3 to 4 per cent.of technical phenothiazine is insoluble in hot light petroleum (boiling range 100" to 120" C), and this is probably polymeric. The fate of the iodine normally used as catalyst in the reaction between diphenylamine and sulphur is unknown, but about half the iodine is present in the material insoluble in light petroleum. Oxidation products are certainly present and are known to arise from the oxidation of solutions of phenothiazine.ll Phenothiazone, thionol and diphenylamine sulphoxide are possible oxidation products. If phenothiazine is heated at 250" C, especially in the presence of copper, carbazole is formed. It is unlikely that carbazole could be separated from phenothiazine by sublimation, but, as the melting-point of the pure phenothiazine agreed with that quoted in the literature, the presence of more than traces of carbazole in the technical product is doubtful.When phenothiazine is subjected to chromatography on alumina, compounds are ad- sorbed that show ultra-violet absorption characteristics similar to those of phenothiazine. These compounds are not eluted under the conditions described, but it has not been possible to separate them in amounts sufficient for their identification. Phenothiazine was found by the proposed method to contain 2.5 to 5.0 per cent. of these compounds; however, they may be present in much larger proportions by weight if they do not absorb as strongly as does phenothiazine at 254.5 mp.November, 19611 BY ULTRA-VIOLET ABSORPTION SPECTROSCOPY 71 I In view of the doubts about the nature of the impurities present in commercial pheno- thiazine, prepared mixtures of recrystallised phenothiazine (having a purity of 97 per cent .> and a number of suspected impurities were analysed by the proposed method; the results are shown in Table I.TABLE I RECOVERY OF PHENOTHIAZINE IN PRESENCE OF ADDED IMPURITIES Impurity Composition of mixture Phenothiazine found, -. % w/w % w/w % w/w Impurity, Phenothiazine, Diphen ylamine . . .. .. 10.0 87.3 86.7 10-0 87.3 91.1 Caxbazole . . . . 87-0 87-3 10.0 87.3 -=/ 87-1 N-Acetylphenothiazine . . Thionol . . . . . . Phenothiazone ,. . I . . 87.0 Diphenylamine orthosulphoxide .. ..( 200-0 0.0 44-0 ::I Sulphur .. .. .. . . 1 87.2 PREPARATION OF STANDARD PHENOTHIAZINE- Recrystallised phenothiazine, prepared in the laboratory from purified diphenylamine and sulphur, was slowly sublimed at 0.05 to 0.10 mm pressure by means of an infra-red lamp, and the sublimate was re-sublimed until there was no significant change in the value of Ei,%,. The residue from the sublimation melted at 250" C, with decomposition. The successive values of EiG and melting-point are shown in Table 11. TABLE I1 CHARACTERISTICS OF SUBLIMED PHENOTHIAZINE Value of EiZ Melting-point, "C Starting material . . .. . . 2290 First sublimation . . .. .. 2330 Second sublimation . . .. .. 2344 Third sublimation . . .. .. 2350 Fourth sublimation . . . . . . 2352 Fifth sublimation .. . . . . 2350 185.2 185.8 185.8 185-8 186.0 186.0 METHOD REAGENTS- Diethyl ether-Analytical-reagent grade. Light petroleum-Analytical-reagent grade, boiling range 40" to 60" C and free from aromatic hydrocarbons. Light petroleum - diethyl ether mixture-Mix 3 volumes of the light petroleum and I volume of the diethyl ether. Acid aluminium oxide-Brockmann activity grade I. Aluminium oxide Woelm acid (anionotropic) was used. Ethanol-Heat 4 litres of "absolute ethanol (special for spectroscopy)" under reflux with l o g of zinc dust and 40 g of potassium hydroxide pellets for 3 hours; the reactants should be of analytical-reagent grade. Immediately distil the ethanol, and reject the first and final 250-ml portions of distillate. The ethanol for use should have minimum transmission in a 1.O-cm cell at 254.5 m,u of not less than 90 per cent.PREPARATION OF SAMPLE SOLUTION- Accurately weigh sufficient sample to contain 250 mg of phenothiazine, and dissolve it in approximately 200ml of diethyl ether (it may be necessary to heat under gentle reflux on a bath of hot water for 5 to 10 minutes). Cool to room temperature, transfer quantitatively to a 250-ml calibrated flask, and dilute to the mark. Allow any insoluble residue to settle, transfer 25.0 ml of the solution to a 100-ml calibrated flask, and dilute to the mark with light petroleum; a 25-ml calibrated flask is preferred for transferring the ether solution. Aqueous7 12 BRIERLEY AND LANGBRIDGE : THE DETERMINATION OF PHENOTHIAZINE [\'Ol. 86 dispersions of phenothiazine may be treated in the same way, but an amount of anhydrous sodium sulphate sufficient to absorb residual water should be added to the ether solution.Dilute solutions of phenothiazine, especially when exposed to sunlight, tend to be oxidised, and operations from this stage onwards should be carried out as rapidly as possible. It is best to protect the chromatographic column from direct light by means of a suitable shield. PREPARATIOK OF ALUMINIUM OXIDE ADSORBENT- By pipette, pIace 5.0 ml of distilled water in a dry 250-ml conical flask that can be closed with a ground-glass stopper. Distribute the water over the glass surface, and add 1OOg of acid aluminium oxide of Brockmann activity grade I. Shake the flask on a mechanical shaker for 2 hours or until lumps and moist spots can no longer been seen, and set aside for 48 hours at room temperature before use.The criterion of adequacy of the alumina adsorbent is that all the phenothiazine should appear in the first 50ml of eluate, as described below. PROCEDURE FOR DETERMINING PHENOTHIAZINE- Set up a chromatographic tube having the dimensions shown in Fig. 1 in astand, and place a small wad of cotton-wool in the lower tip of the tube. Add sufficient of the light petroleum - diethyl ether mixture to fill the 10-cm deep section, and pour 8 g of the alumina adsorbent into the centre of the 10-cm section while tapping the tube gently to ensure uniform settling. Allow excess of solvent to drain away, but ensure that the surface of the alumina remains covered by solvent. 25 mrn I2 mm 3 mm Fig. 1 .Chromatographic tube By pipette, carefully place 10.0 ml of the light peroleum - ether solution of the sample on the column, taking care not to disturb the surface of the alumina, and collect the eluate in a 100-ml calibrated flask. When the surface of the column is nearly exposed, wash the sides of the tube with approximately 5ml of the light petroleum-ether mixture. Repeat this washing twice more, fill the column with the light petroleum - ether mixture, and collect 50ml of eluate. Thoroughly wash the tip of the chromatographic tube with the etherNovember, 19611 BY ULTRA-VIOLET ABSORPTION SPECTROSCOPY 7 13 mixture, and collect the washings in the 100-ml calibrated flask. Dilute the contents of the flask to the mark with the solvent mixture, mix thoroughly, place 10.0ml of this solution, by pipette, in a 100-ml calibrated flask, and dilute to the mark with the spectrographic-grade ethanol.Measure the optical density of the solution at 254-5mp in matched l-crn silica cells against a solution prepared by diluting 10.0 ml of the light petroleum - ether mixture to 100 ml with spectrographic-grade ethanol. Reverse the cells, again measure the optical density, and use the average of the two readings in the calculation. (For a Unicam SP5W spectrophotometer, a fixed slit width of 0.60 mm is recommended.) Calculate the percentage of phenothiazine in the sample from the value of E,I,Z for phenothiazine (2350 when a Unicam SP500 instrument is used). RESULTS Samples of purified phenothiazine treated by the proposed method gave recoveries from 99.5 to 100-0 per cent.The purity of technical phenothiazine manufactured by two different processes is shown in Table 111, in which the tern “apparent phenothiazine” refers to results obtained by the proposed method, with omission of the chromatographic stage. TABLE 111 RESULTS FOR SAMPLES OF TECHNICAL Samplf No. Apparent phenothiazine content, yo Samples mapzufactured by process A- 1 90.5 2 89.8 3 88.5 4 88.8 5 88.4 6 89.4 Samples manujactured by $vocess B- 7 87.4 8 86.5 9 88.4 10 88.0 11 90.2 12 88.0 PHENOTHIAZINE Phenothiazine content, yo 87-1 86.6 86.0 86.5 86-8 86.9 82.5 83.7 84.3 84.5 85.5 83.7 CONCLUSION The method described above has been successfully used for determining phenothiazine in the technical product and in commercial preparations. It appears to be specific for phenothiazine and has been used for the analysis of all commercial forms of phenothiazine so far encountered. We thank Cooper, McDougall and Robertson Ltd. for permission to publish this paper and express our appreciation to Misses S. Gillam-Wood and P. Morledge and Mr. A. IT. Periam for their technical assistance. 1. 2 . 3. 4. 5 . 6. 7. 8. 9. 10. 11. REFERENCES Smith, L. E., I d ENg. Chem., -4nal. Ed., 1938, 10, 60. Cupples, H. L., Ibid., 1942, 14, 53. Overholser, L. G., and Yoe, J. H., Ibid., 1942, 14, 646. “British Veterinary Codex 1953,” The Pharmaceutical Press, London, 1953, p. 275. Gunew, D., Analyst, 1960, 85, 360. Smith, L. E., and Nelson, 0. A., J . Amer. Chem. SOL, 1942, 64, 461. Baker, B. E., and Brickman, L., Ibid., 1945, 67, 1223. Lazarus, M., and Rogers, W. P., Austral. J . Sci. Res., B, 1951, 4, 163. Gunther, F. A., and Blinn, R. C., “Analysis of Insecticides and Acaricides,” Interscience Publishers Houston, D. F., Kester, E. B., and DeEds, F., J. Anzer. Chem. SOC., 1949, 71, 3816. Brown, G. P., Cole, J. W., and Crowell, T. I., J . Org. Chem., 1955, 20, 1772. Inc., New York, 1955, p. 644. Received February 22nd. I961

ISSN:0003-2654    

DOI:10.1039/AN9618600709

出版商:RSC    

年代:1961

数据来源: RSC