ISSN:0003-2654    

DOI:10.1039/AN95176FX021

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BX023

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176FP049

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BP057

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

JUNE, 1951 Vol. 76, No. 903 ’THE ANALYST PROCEEDINGS OF THE AND OTHER SOCIETY OF PUBLIC ANALYSTS ANALYTICAL CHEMISTS AN Ordinary Meeting of the Society was held at 7 p.m. on Wednesday, April 4th, 1951, in the Meeting Room of the Chemical Society, Burlington House, London, W.l. The chair was taken by the President, Dr. J. R. Nicholls, C.B.E., F.R.I.C. The following papers were presented and discussed: “The Determination of the Relative Availability of the Nitrogen in Nitrogenous Fertilisers. Part 11,” by J. Hubert Hamence, MSc., Ph.D., F.R.I.C.; “The Determination of the Acidity of Milk,” by E. I. Johnson and J. King, O.B.E., F.R.I.C.; “An Improved Volumetric Method for the Determination of Hydrogen Sulphide and Soluble Sulphides,” by J. A. Kitchener, Ph.D., A. Liberman, BSc., Ph.D., D.I.C., and D.A. Spratt, B.Sc., A.R.C.S. NEW MEMBERS Doris Emily Butterworth; Arthur Leslie Davis, A.R.I.C. ; Ann Taylor Dix; Eric Reginald William Fogden, B.Sc. (Lond.), A.R.I.C. ; Alfred Edward Lambden, B.Sc. (Lond.) ; Ernest Charles Mills, A.R.I.C. ; Richard Colin Norris, BSc. (Liv.), A.R.I.C. ; Kenneth Alfred Palmer; Ronald John Thompson, A.R.I.C. ; Geoffrey Alison Vaughan, A.R.I.C. DEATH WE regret to record the death of Walter Collingwood Williams. SCOTTISH SECTION AN Ordinary Meeting of the Section was held in the Central Hotel, Glasgow, on Wednesday, March 7th, 1951, at 7 p.m. Mr. H. C. Moir presided and 32 members and friends were present. A number of scientific films were shown by Dr. H. Dryerre. MICROCHEMISTRY GROUP THE Spring Meeting of the Group was held jointly with the Edinburgh and East of Scotland Sections of the Royal Institute of Chemistry and the Society of Chemical Industry in Edin- burgh on Friday and Saturday, April 13th and 14th, 1951.The proceedings on the afternoon of the first day consisted of a Symposium on Newer Biochemical Methods and, by courtesy of Professor G. F. Marrian, F.R.S., were held in the Department of Biochemistry at the University of Edinburgh. The papers presented were as follows: “Recent Developments in the Use of Isotope Techniques in Biochemistry,” by Professor J. N. Davidson, M.D., DSc., F.R.I.C., F.R.S.E. ; “The Fractionation of Plasma Proteins and its Clinical Significance,” by C. P. Stewart, Ph.D., M.Sc. ; “Amino-Acid Analysis,” by G. R. Tristram, Ph.D. A discussion followed each paper.On the following morning a visit was made to the Organon Laboratories Ltd., at New- house, Lanarkshire. 325326 0BITUAR.Y [Vol. 76 PHYSICAL METHODS GROUP THE Thirty-first Ordinary Meeting of the Group was held at 6.30 p.m., on Tuesday, April loth, 1951, in the Meeting Rooms of the Iron and Steel Institute, 4, Grosvenor Gardens, London, S.W.l. This meeting was organised by the Polarographic Discussion Panel, and Mr. J. Haslam, Chairman of the Panel, was in the chair. The following papers were presented and discussed : “Vibrating Electrodes in Polarography. The Effect of Frequency and Amplitude of Vibration on Diffusion Current,” by A. J. Lindsey, MSc., Ph.D., F.R.I.C., and E. D. Harris, M.Sc., A.R.I.C. ; “The Polaro- graphic Behaviour of Iodo-organic Compounds,’’ by J. E. Page, B.Sc., Ph.D., F.R.I.C. ; “Selected Applications of Polarography in Inorganic Analysis,” by G. W. C. Milner, B.Sc., F.R.I.C., A.1nst.P. BIOLOGICAL METHODS GROUP AN Ordinary Meeting of the Group was held at 6.30 p.m. in the Meeting Room of the Chemical Society, Burlington House, London, W.l, on Monday, March 12th, 1951. Mr. N. T. Gridgeman was in the chair, and thirty-two other members and guests were present. The following papers on “The Evaluation of Drugs in Man” were presented and discussed : “The Evaluation of Drugs in Man, with Special Reference to Antihistaminics,” by Professor W. A. Bain; “Tests on Analgesic Drugs in Man,” by Dr. C. A. Keele.

ISSN:0003-2654    

DOI:10.1039/AN9517600325

出版商:RSC    

年代:1951

数据来源: RSC

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326 0BITUAR.Y [Vol. 76 Obituary ALEXANDER HENRY MITCHELL MUTER ALEXANDER HENRY MITCHELL MUTER was born in Kennington in 1873. He was the elder son of Dr. John Muter, who was one of the founders and third President of the Society and part proprietor of The Analyst for several years. As he was intended to follow his father’s career, he was sent to Germany to be educated according to the Victorian custom for boys intended to become chemists. On returning to London he entered the laboratory at Kennington, where his father had built up a large practice in the analysis of drugs, food and water, and held several appointments as Public Analyst. He took classes in chemistry at King’s College , London, and passed the examinations for the Associateship and Fellowship of the Institute of Chemistry in 1896 and 1899 respectively.His first public appointment was to Tunbridge Wells in 1908. On the death of his father he succeeded to several appoint- ments for which he had been deputy, including the Boroughs of Wandsworth and Lambeth, the Parts of Lindsey and the Metropolitan Asylums Board; and in later years he became Public Analyst to the Parts of Holland and Kesteven, Lincolnshire, and to the Borough of Colchest er . He prepared his certificates with great care; he took pains to appreciate and appraise both sides of a case and gave his evidence in moderate terms, conveying the impression that his function was to assist the Court only. He would never appear against another Public Analyst and held strong opinions against the etiquette of this practice. In 1912 he took into partnership Charles Hackman, with whom he had formed a friendship at King’s College while studying for the examination of the Institute of Chemistry in Branch E.Hackman was an excellent analyst, very receptive to new ideas and, as befitted a pupil of Chaston Chapman, a stickler for accuracy, method and neatness. Though the friends were very unlike in temperament and outlook, their association proved a felicitous one during the long period of the partnership. One curious feature they shared in common was a dislike of publishing new work, with the natural result that someone else had to go over much the same ground before the results were available to the profession. Hackman trained for some years as an engineer and he had a flair for designing and con- structing apparatus for speeding up routine work or for some special type of work.Hackman Muter acquired a large experience in the Courts.June, 19511 POLAROGRAPHIC CONGRESS ; PRAGUE, 1951 327 died in December, 1940, and Muter relinquished his daily attendance at the laboratory from that time. Muter was a prominent Freemason for over half a century and attained high office in the fraternity. In his youth, Muter played the violin in some South London orchestras. In those days meetings of the Society used to be followed by informal concerts; Bernard Dyer, in his 91st year, writing to Muter, recalled his playing at these functions. He had many hobbies, with strong preferences for out-door occupations in the country. An almost life-long motorist, he was one of the earliest members of the A.A. But gardening was his greatest delight. He built a house near Charing, some years ago, for week-end residence. In 1940, his house in Dulwich having become damaged in an air-raid, he retired to Charing. He continued to visit the laboratory every week, and on most Saturdays during the winter months came to town to carry out his masonic duties. He passed away on February 7th, 1951, after a few days’ illness. His never-failing good humour, open-handed generosity and readiness to help his professional friends will long be remembered by those who were privileged to know him. J. E. WOODHEAD

ISSN:0003-2654    

DOI:10.1039/AN9517600326

出版商:RSC    

年代:1951

数据来源: RSC

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June, 19511 POLAROGRAPHIC CONGRESS ; PRAGUE, 1951 327 Polarographic Congress : Prague, 1951 A POLAROGRAPHIC Congress was held in Prague from February 4th to 8th, 1951, in honour of Professor J. Heyrovskp’s sixtieth birthday. It was not possible for the Society to be represented a t the Congress, but the following letter of congratulation was sent to Professor Heyrovsky, and his reply follows. A report of the Congress is appended. December 28th, 1950. Dear Professor Heyrovskjr, I write to convey to you the congratulations of the President, Council and Members of the Society of Public Analysts and Other Analytical Chemists on your recent attainment of your sixtieth birthday. As you know, we, in this Society, have the highest admiration for the pioneer work that you carried out in establishing polarography as a tool of analytical chemistry, and we are proud to think that much of the early work was undertaken a t University College, London, in 1924.Since then, of course, polarography has found applications in every field of analytical chemistry, and over 2000 original papers have been published on the subject. We are glad to hear that you have been nominated as Director of the Polarographic Institute in which you will be able to apply polarographic methods to both pure and applied science; and we trust that you will be able to spend many happy years there working in the field of which you are a master. Yours sincerely, K. A. WILLIAMS, Honorary Secretary. March 4t12, 1951. Dear Dr. Williams, Accept my belated thanks for your very kind congratulations on my sixtieth birthday and for your words of appreciation, consideration and encouragement, which you express in your letter as to the development of polarography.In connection with my birthday we had the First International Polarographic Congress held in Prague, a report of which I enclose as it may interest the members of your Society I was very sorry that owing to the circumstances only a few visitors were able to come from abroad. Please convey my warm thanks to your President, to the Council and to all members of the Society of Public Analysts. With best regards, Yours very sincerely, J. HEYROVSKP.328 POLAROGRAPHIC CONGRESS; PRAGUE, 1951 [Vol. 76 REPORT OF THE. CONGRESS A SUCCESSFUL meeting of some 400 polarographists of Czechoslovakia and visitors from Poland , Hungary, Roumania and Bulgaria has shown the great interest in the new branch of science, polarography .The Congress was organised by the Centre of Research and Technical Development in Prague. The President was Prof. J. Heyrovskf, Director of the Central Institute of Polarography, and the Vice-president was Prof. R. BrdiCka, Director of the Physico-chemical Institute of the Charles University, Prague. An evening session to welcome the visitors, held in the spacious rooms of the old palace of Sylva Taroucca, preceded the opening of the Congress. The Congress was inaugurated in the large theatre of the PurkynG Medical Institute on the morning of Monday, February 5th, by the Minister of Planning, Dr. J. Dolanskp, and the Director of the Centre of Research and Technical Development, Prof.J. FukAtko. Minister Dr. Dolansky spoke on the cardinal tasks of science in building up socialism and Prof. FukAtko spoke on the important r61e of planning in scientific research. Then Prof. J. Heyrovsk9 gave his review on the “Fundamentals of Polarography.” The communications at the Congress were divided. into eight reviews, each of about one hour’s duration, in which the modern development of polaxography was surveyed, and into discussioiis , of about fifteen minutes’ duration’ of new papers submitted to the Congress. The morning sessions were devoted to pure science and the afternoons to applied polarography. The following reviews were given: “Inorganic Analysis, ” by V1. Majer ; “Polarography of Organic Compounds,” by V1.Hanu5 ; “Organic Analysis,” by P. Zuman ; “E’olarography in Biochemistry and Medicine, ” by F. Santavf ; “Instruments for Oscillographic Polarography, ” by J. Forej t ; “Applications of Oscillographic Polarography, ” by J . Heyrovskf ; “Kinetics of Electrode Processes in Polarography,” by R. BrdiCka. There were 65 communications presented as follows- On February 5th: “The Validity of the Nernst Formula in Deducing the Equation of the Polarographic Wave,” by M. Kalousek and A. Tockstein ; “Polarography in Concentrated Sulphuric Acid,” by A. VlCek; “Study of the Discontinuities of Current on Polarographic Curves,” by P. Valenta; “Some Examples of the Analysis of Alloys,” by M. SpAlenka; “Determination of Phos- phates,” by J. V. A. NovAk; “Determination of Small Quantities of Thorium,” by K.KomArek; “Determination of Alkalinity,” by K. KomArek; “Experience in the Control of Steel Manufacture,” by J. Koreckf, F. Nademlejnskf and B. Neliba; “Determination of Manganese by Means of Triethanolamine,” by J. Mojiis; “Determination of Gold,” by F. Linhart. On February 6th: “Determination of Oxygen, Benzene and Hydrogen Sulphide in Lighting- gas,” by J. Prchlik; “Reduction of Hydrogen Peroxide Catalysed by Complexes of Iron with Catechol, Pyrogallol and Ascorbic Acid, ” by J. DoskoCil; “Polarographic Analysis of Benzoic Acid and of Phthalic Anhydride,” by B. G. Simelr, F. Majer and G. Sebor; “Polarography of Coumarine, ” by 0. Capka; “Polarography of Alkaline Products of Glucose, ” by J. Trnka; “The Reaction of Carbonyl Compounds with Primary Amines,” by P.Zuman; “Cyanuric and Rubeanic Acid,” by K. Such$; “Some Complexes of Amino-acids with Metals,” by R. Pleticha; “Determina- tion of Phenol in Water and in Urine,” by J. Roubal and J. ZdraZil; “Determination of Pentosans,” by R. Domanskf; “Determination of Barbiturates by Titration with Mercuric Salts,” by R. Kalvoda and J. Zyka; “Polarometric Determination of Unsaturated Compounds, ” by A. Blaiek; “Determination of Diacetyl, ” by R. Pleticha; “Colchicine in Meadow-saffron during Growth,” by J. Buchnitek; “Applications in Paper Industry, ’’ by B. Sandholec; “Sulphydryl Compounds in Fruits,” by P. Zuman. On February 7th: “Hydrolysis of the Oxidation Product of Vitamin K,,” by E. Knobloch; “Ascaridol,” by B. Bitter; “Muconic Acid in Bacteria,” by A.Kleinzeller and 2. Fencl; “Polaro- graphy of Sterols,” by J. Nosek; “Heart Poisons with a Five- or Six-membered Lactone Ring,” by F. Santavp; “Oxidation Products of Morphine,” by F. Santavy; “Determination of Oxygen in Blood,” by M. SimAnB; “Biological Redox Indicators,” by J. DoskoCil; “A Contribution to the BrdiEka Filtrate Reaction in Serum,” by J. Homolka and D. KrupiEka; “Determination of Thallium ‘in Urine,” by 2. ZAbranskf; “Studies of Peroxidase Reactions,” by J. DoskoEil; “The Electronic Polarograph,” by K. E n ; “Artificial Control of the Drop-time,” by 0. Nesvadba; “A New Apparatus for Oscillographic polarography,” by J. Vogel; ‘Vibrations of Drops due to Currents of High Frequency,” by W. Kemula. On February 8th: “Catalysed Depolarisations in Inorganic Redox Systems,” by E. SvAtek; “The Rate of Dissociation of the Complex of Cadmium with Nitrilotriacetic Acid,” by J.Koryta;June, 19511 ANALYSIS OF MEAT EXTRACT 320 “Recombination of the Ions of Phenylglyoxylic Acid,” by V1. Hanu:; “Linear Systems of Electrode Reactions,” by J . Kouteckq ; “Slow Electrode Reactions,” by M. Smutek ; “Irreversi- bility of Electrode Reactions,’’ by A. Tockstein; “Generalisation of the Theory of Linear Diffusion Currents,” by J . Pliva; “The Hydrogen Overvoltage with a Controlled Drop-time,” by J. K6ta; “The Discontinuity on the Polarographic Curve in the Reduction of Nitrates,” by J. MaSek; “A Study of the Complexes of Tervalent Chromium,” by H. T. Arend; “Complexes of Sucrose with Ferric and Ferrous Ions,” by M.Kfivhek; “The Control of the Sutdace Adjustment of Metals,” by T. Jelinek; “The Derivative Curves in Polarography,” by J. Riha; “The Effect of Thymol and Gelatin on Polarographic Waves,” by M. DrAtovskl and M. Ebert; “The Influence of Capillary Constants on Maxima,” by J. Dvo%k; “The Classification of Refined Sugars,” by I. Vavruch. The Congress ended with a social gathering in the Sylva Taroucca palace, when all who had attended expressed their appreciation in speeches and toasts. The guests were: Prof. W. Kemula, Prof. M. Michalski and J. Chodkowski of Warszaw University, Prof. L. Erdey and Mrs. Ajtai of Budapest, Prof. A. P%rvu and Prof. E. Macovschi of the University of Bucharest and Dr. A. Trifonov of the Institute of Technology, Sofia. Reports of the communications and discussions will be published in full in three volumes of Proceedings, of which the first will also contain contributions, in English, French and German, that were not communicated a t the Congress, the second a full critically revised bibliography of Polarographic papers from 1922 to 1950, and the third the reports of the meetings themselves. Single volumes will be on sale to those who did not attend the Congress. The eight meetings were fully attended right to the end.

ISSN:0003-2654    

DOI:10.1039/AN9517600327

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

June, 19511 ANALYSIS OF MEAT EXTRACT 320 Analytical Methods Committee RECOMMENDATIONS OF THE MEAT EXTRACT SUB-COMMITTEE Analysis of Meat Extract THE Analytical Methods Committee has received the following Report from the Meat Extract Sub-committee, and its publication has been duly authorised. CONSTITUTION OF THE SUB-COMMITTEE The Sub-committee consists of: G. Taylor, O.B.E., F.R.I.C. (Chairman) ; R. Gordon Booth, Ph.D. (from December, 1949) ; Osman Jones, F.R.I.C. ; the late E. C. Keeley, B.Sc., A.R.I.C. (until December, 1949) ; J. King, O.B.E., F.R.I.C. ; G. Spall; R. G. Westall (nominee of Dr. E. C. Bate-Smith); H. G. Rees, B.Sc., Ph.D., A.R.C.S., D.I.C., F.R.I.C. (Honorary Secretary). The Sub-committee wish to place on record the loss sustained by the untimely death of Mr.E. C. Keeley on December ZOth, 1949. INTRODUCTION The terms of reference of the Sub-committee are: “to consider whether standard analytical methods are necessary for meat extracts and similar products and to carry out such investigations as may be deemed necessary. ” The Sub-committee agree that Standard Methods of Analysis are required and that they should be so formulated to give the maximum information as to the detection of possible adulterants . They further consider, however, that it is desirable that a standard method for this purpose should be one that is both sufficiently accurate and precise for all commercial purposes and also capable of adoption in any analytical laboratory; on this basis, in fact, the experi- mental work has been designed and the suggested methods have been formulated.The Sub-committee do not regard the prescription of standards of composition for meat extracts and similar products as coming within their terms of reference. Nevertheless they have thought it desirable to define products that they regard as being within the general330 ANALYSIS OF MEAT EXTRACT [Vol. 76 description of meat extracts and similar products, in order to indicate suitable methods of analysis. These definitions are given immediately below. DEFINITIONS- Meat extract-The product obtained by extracting fresh lean meat with boiling water and concentrating the liquid portion after removal of fat. Meat stock-The product obtained by the extraction of meat trimmings, bones, rind and edible offal with boiling water and concentrating the liquid portion after removal of fat, with or without the addition of salt.Bone stock-The product obtained by the extraction of fresh trimmed bones with boiling water, with or without pressure, and concentrating the liquid portion by evaporation after removal of fat, with or without the addition of salt. Essence of beef-The product obtained by the extraction of minced beef with boiling water, such extraction being sufficiently prolonged to produce a jelly on cooling. Meat juice-The fluid portion of fresh lean meat obtained by pressure and concentrated by evaporation at a temperature below the coagulating point of the soluble proteins. Similar firoducts-Products or composite products more or less simulating the charac- teristics of the various extracts obtainable from meat or bones but containing products other than meat, for example, yeast extract, hydrolysed protein, vegetable soup stock, meat extract cubes or gravy cubes and soup powders.SCOPE OF THIS REPORT- This Report of the Sub-committee deals only with meat extracts as defined above, but is generally applicable to materials other than “similar products.” Additional methods of analysis are necessary to cover these and, to a less extent, meat stock and bone stock, and it is the intention of the Sub-committee to undertake further work for this purpose. DISCUSSION AND EXPERIMENTAL WORK To assess the quality and genuineness of meat extracts it was considered that the deter- minations listed below should satisfactorily serve the purpose for products of the nature of meat extracts, and accordingly only such determinations are dealt with in this Report- Water.Ash. Chloride. Total nitrogen. Total creatine and creatinine (determined as creatinine). Some consideration was also given to organoleptic tests, but although these are of con- siderable value to an observer with a trained pala.te, it was decided that they cannot be recom- mended for an analyst without this experience. For the purpose of a more detailed analysis, particularly to assess and estimate adulterants or the addition of non-meat ingredients, it was thought that some or all of the further deter- minations specified below would be necessary-- Phosphate. Fat. Soluble and insoluble nitrogen. Amino nitrogen. Gelatin. Tannic acid precipitate. Nicotinic acid.Starch. Qualitative tests for extraneous ingredients. PREPARATION OF THE SAMPLE FOR ANALYSIS- Meat extracts contain significant proportions of constituents that tend to separate after the extract is filled into the containers; for this reason, and owing to their viscous condition when cold, the extracts are usually transferred slightly warm to the containers. On storage there is a tendency for creatine, together with some mineral matter, principally phosphate, to separate out. I t is therefore necessary to mix the sample thoroughly beforeJune, 19511 ANALYSIS OF MEAT EXTRACT 331 taking portions for analysis. A cautious warming will expedite the blending of pasty samples and any sediment must be thoroughly incorporated. However carefully such mixing is carried out there is still a danger that very small portions of the mixture do not accurately represent the bulk. Accordingly it was decided that a satisfactory method of overcoming this difficulty would be to take a portion of 10 & 1 g dissolved in water to a bulk of 100 ml and to use aliquots of this solution for the various deteminations. It is desirable that a specially calibrated pipette be used as it has been realised that use of a pipette with such a solution may lead to a slight error due to differences in viscosity and surface tension from those of water.DETERMINATION OF WATER- Considerable discussion ranged around the question of determining the water content of meat extract, since it was accepted from the beginning that such a determination must be an arbitrary one, there being no assurance that any method would yield a true figure for water, that is to say for free water or free and bound water as distinct from water produced by protein breakdown. The Sub-committee were fortunate in having at their disposal copies of a recent monograph reprinted from the Journal of the Co.unciZ for ScientiJic and Industrial Research, AuskaZia,l in which the theoretical considerations are dealt with in considerable detail.They accepted the conclusions given in the monograph, viz., that it is not possible to obtain a true value for the water content by any known method and that therefore some arbitrary method carefully defined and rigorously followed should be adopted. As a basis for experimental work by members of the Sub-committee, it was agreed that an empirical standard method could be based on the Society's method for sweetened condensed milk.2 Comparative determination of loss of weight at 100" C were then made under various conditions of time, size and type of dish, weight of sample, and with and without sand.The results of this experimental work led the Sub-committee to the conclusion that the method based on drying for a fixed time 1 g of meat extract after solution in water yielded results satisfactorily comparable with the method using sand and was therefore to be preferred on account of its simplicity. A series of collaborative determinations was carried out by all the members of the Sub-committee on two samples of meat extract having moisture contents of approximately 20 and 27 per cent.Statistical examination of these results by Dr. E. C. Wood showed that the variance between laboratories was very significantly more than the variance within laboratories, The precision of the method from both points of view is summarised in the following statistics- This means that 19 out of 20 determinations of moisture on the sample, in the same laboratory, should differ from their mean by not more than 0.2 per cent.; but if one determination were made in each of 20 different laboratories, 19 out of 20 should differ from their mean by not more than 1-1 per cent. DETERMINATION OF ASH AND CHLORIDE- Ash-The direct ashing method was compared experimentally with a method involving charring, leaching out and complete ashing. As the results by the direct ashing method were found not to be significantly different from those by the alternative method, it was decided that the former should be recommended.Due care must be exercised to ensure that there are no losses due to decrepitation or volatilisation. The latter may be avoided by ensuring that a temperature of 550" C is not exceeded. As an alternative method when no temperature control is available for this purpose, details of a leaching-out process are included, Chloride-Methods examined included determination of chloride obtained (a) by direct ashing, ( b ) by ashing and leaching and (c) directly in the extract solution. An ashing process is recommended, but it is essential to avoid fusion of the ash and possible loss by volatilisation. Standard error, calculated from the within-laboratories variance = 0.096% Standard error, calculated from the between-laboratories variance = 0-501 yo DETERMINATION OF TOTAL NITROGEN- The determination of nitrogen has been so thoroughly examined by various workers that the Sub-committee considered it necessary only to survey the literature, particularly as regards the time of digestion and the type of catalyst, and to carry out collaborative work on given samples of meat extract by the accepted method.332 ANALYSIS OF MEAT EXTRACT [Vol. 76 The method for the determination of total creatine and creatinine (recommended to be expressed as total creatinine) has been very thoroughly investigated in the laboratories with which members of the Sub-committee are associated, since it is realised that this value is probably the most important index of quality of a meat extract and that on which analysts will largely base their conclusions. All stages of the process, including the method of hydrolysis, influence of volume, and concentration of caustic soda and picric acid on the development and stability of colour, have therefore been examined in great detail. The recommended method is based on the results of this investigation; it also incorporates as far as possible the techniques readily available for the evaluation of colour.As creatinine zinc chloride is now obtainable in a crystalline form of guaranteed purity, it is recommended as a standard. "Creatinine Zinc Chloride, 99 to 100% (standard for creatine and creatinine determinations)" may now be obtained from The British Drug Houses, Ltd.TOTAL CREATINE AND CREATININE- RECOMMENDED METHODS OF ANALYSIS All reagents should conform to recognised analytical standards. Stock soZution-A cautious warming will expedite the blending of pasty samples and any sediment must be thoroughly incorporated. Take 10 & 1 g of meat extract, accurately weighed, and dissolve with successive small quantities of hot distilled water to ensure so1ut:ion of all soluble material; cool and make up to 100 ml. Shake the solution before taking aliquots for the various determinations. DETERMINATION OF WATER- Procedure-Pipette 10 ml of stock solution into a nickel dish approximately 3 inches in diameter, preferably fitted with a close-fitting lid (see Report of the Milk Products Sub- Committee2) and evaporate to apparent dryness on an open steam-bath, adjusting the level of the dish to ensure an even film.Transfer to a drying oven at 100" C, insulate the dish from the shelf and dry for 8 hours. Replace the lid, which has also been in the oven, before removal to the desiccator. Cool for 30 minutes before weighing. DETERMINATION OF ASH- Procedure-Evaporate 10 ml of the stock sol.ution in a platinum dish on the steam-bath and char thoroughly over a low flame. Complete the ashing (preferably in an electric muffle) at a temperature not exceeding 550" C to avoid loss of volatile ash. AEternatzve procedzcre-Evaporate 10 ml of the stock solution in a platinum dish on the steam-bath and char thoroughly over a low flame. Cool and extract with three portions of hot water (10, 5 and 5 ml).Decant through a filter-paper and wash the paper with a few ml of hot water. Return the filter-paper to the dish, dry on the steam-bath and incinerate the contents completely. After cooling, return the filtrate to the dish, evaporate it to dryness and heat at a temperature not exceeding 550" C, preferably in a muffle, until the weight is const ant. DETERMINATION OF CHLORIDE- Procedure-Take 20 ml of the stock solution in a platinum dish and evaporate to dryness with 10 ml of 5 per cent. sodium carbonate. Ignite as thoroughly as possible at a temperature not exceeding dull redness. Extract with hot water, filter and wash. Return the filter-paper and residue to the dish and moisten with a few drops of carbonate solution, evaporate and ignite to a white ash.Filter from any insoluble matter, wash thoroughly and add to the previous filtrate. Determine chloride by the Volhard method. Dissolve in dilute nitric acid. DETERMINATION OF TOTAL NITROGEN- Digestiout-Digest 5 ml of the stock solution with 25 ml of sulphuric acid, 10 g of anhydrous sodium or potassium sulphate and a catalyst (0.2 g of copper sulphate, 0.7 g of mercuric oxide or 50 mg of selenium). The time of digestion should be 3 hours after clearing, irrespective of the catalyst used. Distillation of ammonia-Dilute the digest with 100 to 200 ml of water, according to whether a steam-distillation or boiling method is used, and make it alkaline with 100 ml of 40 per cent. sodium hydroxide, free from carbon dioxide, with addition of sodium sulphideJune, 19511 ANALYSIS OF MEAT EXTRACT 333 where mercury has been used as a catalyst. The method of distillation and absorption of ammonia shall be left to the discretion of the analyst.Note-(;) The clear layer of a 40 per cent. solution of caustic soda is satisfactory for rendering Note-(ii) Methyl red is a satisfactory indicator if the ammonia is absorbed in standard sulphuric Note-((iii) An appropriate blank determination should be carried out. the solution alkaline. acid. DETERMINATION OF TOTAL CREATINE AND CREATININE AS CREATININE- Solutions required- Hydrochloric acid-A 2 N solution. Sodium hydroxide-A 2 N solution. Picric acid-A 1 per cent. solution (see Note ii, below). Stock creatinine zinc chloride solfition-1.603 g of pure crystalline creatinine zinc chloride made up to 1000 ml with 0.1 N hydrochloric acid.This solution is stable for a t least six months, and an aliquot should be diluted ten times, immediately prior to use, so that 1 ml = 0-1 mg of creatinine. HYDROLYSIS OF MEAT EXTRACT soLuTIoN-Heat under reflux 10 ml of the stock solution of the extract with 10 ml of 2 N hydrochloric acid in a boiling water-bath for a t least 2 hours, or autoclave for 20 minutes at 117" to 120" C. Cool the hydrolysed solution and add 10 rnl of 2 N sodium hydroxide solution. Dilute to a volume of (a) 250 ml for Duboscq method, or (b) 500 ml for the absorptiometer method. (a) Duboscq and other visual methods such as Nesslerising-Measure from a burette two aliquots of 7ml and 10ml from the 250-ml dilution (see Note i) into clean, dry 100-ml graduated flasks.Make each quantity up to 20 ml with distilled water, add 20 ml of 1 per cent. picric acid solution, then 2.5 ml of 2 N sodium hydroxide, and maintain at 20" * 1" C for 15 minutes. Filter, rejecting the filtrate until the solution is clear and bright. Compare with a standard made up at the same time and under the same conditions from 20 ml of standard creatinine zinc chloride solution (equivalent to 2 mg of creatinine). The colour can be read immediately and is stable for 30 minutes. h'ote-(i) These two aliquots will indicate the approximate percentage of creatinine ; an aliquot can then be calculated which, after development of colour and dilution, will compare closely with the standard . (b) AbsorPtiometer method-Measure an aliquot of 5 ml from the 500-ml dilution into a clean, dry 100-ml volumetric flask and make up to 20 ml with distilled water.Add 20 ml of 1 per cent. picric acid solution and 2-5 ml of 2 N sodium hydroxide; maintain at 20" 1" C for 15 minutes. Filter; reject the first few millilitres until the solution is clear and bright. Readings are made in the absorptiometer with an Ilford filter No. 604 and a l-cm cell; a reagent blank composed of all the reagents minus the creatinine is used. The colour can be read immediately and is stable for 30 minutes. Prepare a standard curve covering a range of 0 to 1.0 mg of creatinine. Into clean, dry volumetric flasks measure quantities of 2, 4, 6, 8 and 10 ml of the standard creatinine zinc chloride solution. Add distilled water to bring the volume of solution in each flask to 20 ml. To each flask add 20 ml of 1 per cent. picric acid solution and 2.5 ml of 2 A' sodium hydroxide. Maintain at 20" & 1" C for 15 minutes and dilute each volvme to 100ml. Note-(ii): 1 per cent. picric acid solution-This strength is chosen owing to the difficulty of maintaining complete solution a t a concentration of 1.2 per cent. during winter conditions. I t should be standardised against 0.1 N sodium hydroxide, phenol red being used as indicator. Note-((iii) In a determination where Nesslerising is involved i t is essential that colour comparisons be carried out under optimum conditions in order to obtain good contrast and reliable results. These include employment of a good north light with no artificial light illuminating the Nessler tubes. Due consideration should be paid to the colour vision of the operator: i t is desirable that this should be normal in the region of the colour to be observed. Dilute to 100ml with distilled water. Dilute to 100 ml with distilled water. These flasks contain creatinine in amounts of 0.2 to 1.0 mg. REFERENCES 1. 2. Riddle, A. R., J . Council Sci. & I n d . Res., Australia, 1944, 17, 291. Analytical Methods Committee, "Report of the Milk Products Sub-committee," AnaZyst, 1927, 52, 402.

ISSN:0003-2654    

DOI:10.1039/AN9517600329

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

334 BREALEY AND ROSS : FLAME PHOTOMETERS A DESCRIPTION [Vol. 76 Flame Phot,ometers : A Description of Two Instruments BY L. BREALEY AND R. E. ROSS (Presented at the meeting of the Physical Methods Group on Friday, October 6th, 1950) Two flame photometers are described ; the first a simple instrument for the determination of sodium and potassium, and the second, a versatile general purpose instrument. Some results are given to show the effect of other ions upon that under examination. DURING the past ten years, several flame photometers have been described.192 13,495,6 These instruments have varied from the simple, which could be built easily in almost any laboratory, to complex commercial equipment. Many types of flame have been described, those most used being air or oxygen with illuminating gas or propane, or air - acetylene.For isolating light of the required wavelengths either filters or a monochromator have been used. Most types of light detector, from barrier layer photo-cells to photomultipliers have been used; commercial instruments are readily obtainable in. America, but in this country they are sold only as accessories to other expensive equipment, and even these have not been available until recently; consequently, the majority of workers have built their own apparatus. This paper describes two instruments that have been built in the laboratory. The first is simple and limited in its application to the determination of sodium and potassium; the second is capable of determining any element that will give suitable emission from a flame.In designing these instruments the following four points were regarded as fundamental requirements of any flame photometer- (1) It should be robust and simple to operate so that it can be used by laboratory assistants as a routine instrument. (2) It should give a steady final reading, free from drift and accurately repeatable. (3) It should be sufficiently sensitive to give useful readings on very dilute solutions. (4) It should be as free as possible from interference by ions other than that being determined. THE FIRST INSTRUMENT Probably the most difficult parts of a flame photometer to design satisfactorily are the atomiser and burner. Many types of flame are available, from the very hot oxy-hydrogen to the comparatively cool mixture of air and coal gas. For the simpler of the two instruments a cool air - propane flame is preferable, as this type of flame has a low propagation velocity and can therefore be burned at an ordinary Meker type of burner without much risk of explosion by striking back.The atomiser and flame unit is shown in Fig. 1. The atomiser needs to be of a rigid structure if it is to be robust and give a constant spray; the one used was of the concentric type, similar to that on the Beckman instrument and described by Gilbert et aZ.6; from which it differs, however, in that the annular space between the outside of the sample capillary and the inside of the surrounding air nozzle is smaller and a somewhat higher air pressure is used; this gives rise to a denser spray and so introduces a larger sample into the flame.The larger droplets are removed from the airborne spray by the decreased air velocity in the expansion chamber, a 750-ml conical flask, and are run to waste from the bottom of the flask. The fine mist that remairis in suspension is carried directly into the flame. In order to achieve a steady reading it is of primary importance to have a flame that is perfectly steady and free from flicker; to ensure this, the gas and air must be supplied at constant pressure. The air supply is particularly important since any drop in pressure will, besides affecting the flame itself, result in a fall in the rate at which the solution is atomised. Both gases are supplied from cylinders, the propane through a needle-valve a t a pressure of 9 inches water and the air through a two-stage regulator at 35 lb per square inch.In use, the flame is protected from draughts by a chimney, which also serves to prevent errors in the readings from extraneous light.334 BREALEY AND ROSS : FLAME PHOTOMETERS A DESCRIPTION [Vol. 76 Flame Phot,ometers : A Description of Two Instruments BY L. BREALEY AND R. E. ROSS (Presented at the meeting of the Physical Methods Group on Friday, October 6th, 1950) Two flame photometers are described ; the first a simple instrument for the determination of sodium and potassium, and the second, a versatile general purpose instrument. Some results are given to show the effect of other ions upon that under examination. DURING the past ten years, several flame photometers have been described.192 13,495,6 These instruments have varied from the simple, which could be built easily in almost any laboratory, to complex commercial equipment.Many types of flame have been described, those most used being air or oxygen with illuminating gas or propane, or air - acetylene. For isolating light of the required wavelengths either filters or a monochromator have been used. Most types of light detector, from barrier layer photo-cells to photomultipliers have been used; commercial instruments are readily obtainable in. America, but in this country they are sold only as accessories to other expensive equipment, and even these have not been available until recently; consequently, the majority of workers have built their own apparatus. This paper describes two instruments that have been built in the laboratory. The first is simple and limited in its application to the determination of sodium and potassium; the second is capable of determining any element that will give suitable emission from a flame.In designing these instruments the following four points were regarded as fundamental requirements of any flame photometer- (1) It should be robust and simple to operate so that it can be used by laboratory assistants as a routine instrument. (2) It should give a steady final reading, free from drift and accurately repeatable. (3) It should be sufficiently sensitive to give useful readings on very dilute solutions. (4) It should be as free as possible from interference by ions other than that being determined. THE FIRST INSTRUMENT Probably the most difficult parts of a flame photometer to design satisfactorily are the atomiser and burner.Many types of flame are available, from the very hot oxy-hydrogen to the comparatively cool mixture of air and coal gas. For the simpler of the two instruments a cool air - propane flame is preferable, as this type of flame has a low propagation velocity and can therefore be burned at an ordinary Meker type of burner without much risk of explosion by striking back. The atomiser and flame unit is shown in Fig. 1. The atomiser needs to be of a rigid structure if it is to be robust and give a constant spray; the one used was of the concentric type, similar to that on the Beckman instrument and described by Gilbert et aZ.6; from which it differs, however, in that the annular space between the outside of the sample capillary and the inside of the surrounding air nozzle is smaller and a somewhat higher air pressure is used; this gives rise to a denser spray and so introduces a larger sample into the flame.The larger droplets are removed from the airborne spray by the decreased air velocity in the expansion chamber, a 750-ml conical flask, and are run to waste from the bottom of the flask. The fine mist that remairis in suspension is carried directly into the flame. In order to achieve a steady reading it is of primary importance to have a flame that is perfectly steady and free from flicker; to ensure this, the gas and air must be supplied at constant pressure. The air supply is particularly important since any drop in pressure will, besides affecting the flame itself, result in a fall in the rate at which the solution is atomised.Both gases are supplied from cylinders, the propane through a needle-valve a t a pressure of 9 inches water and the air through a two-stage regulator at 35 lb per square inch. In use, the flame is protected from draughts by a chimney, which also serves to prevent errors in the readings from extraneous light.Fig. 4. The second instrumentJune, 19511 OF TWO INSTRUMENTS 335 The light from the flame emerges from two diametrically opposed windows in the chimney and passes into the units that separate and detect the light due to potassium and sodium respectively. The isolation of the potassium doublet 7660 and 7690 A is achieved by means of filters.Those used are Wratten 88A, with a Chance ON20 heat-absorbing filter included to cut down the background due to water molecular bands, which occur at about 10,000 A. As a further precaution a Chance ON16 (dense didymium) has been used since it has a strong absorption band at about 5 8 9 0 ~ ~ the wavelength of the sodium doublet 5890 and 5 8 9 6 ~ . This filter was included because, in many applications, we desired to determine potassium in the presence of large excesses of sodium, e.g. , potassium as an impurity in sodium salts. The use of filters in this application is permissible because the general flame background is fairly low in the region of 7500 A and even with low potassium concentrations, a reasonably high ratio of potassium line radiation to general background radiation is possible.With the filters used, the response from the background with water running through the instrument is perfectly steady and is the same as that from about 3 parts per million of potassium. It must be remembered, however, that several elements give lines that pass this filter system, for example, caesium 8521 A and 8594 A, rubidium 7800 A and 7948 A, barium 7450 A, 8300 A and 8 7 3 0 ~ . Several types of detecting circuits were tried ; that giving the most satisfactory results and finally adopted for use comprised a “Cinema-Television” photomultiplier MS20 followed by a simple single-stage battery amplifier (see Fig. 2). The photomultiplier has an internal P.M. P.M. Dark Current H.T. - -Check - Read 45v Battery Switch Fig.2. Circuit of battery-operated D.C. amplifier The valve filaments are supplied with current from a 6-volt constant-voltage transformer amplification of about 1000 and the amplifier gives a further amplification of ten. The output is measured on a sensitive spot galvanometer with a scale from 0 to 100 and a full- scale sensitivity of 2 microamps. With this system, full-scale deflection is easily obtained from a solution containing 10 p.p.m. of potassium. Provision is made to back off the dark current including flame background and the sensitivity is adjusted by means of an Ayrton shunt on the galvanometer. This shunt comprises a helical potentiometer, the total resistance of which is arranged to be the critical damping resistance of the galvanometer. In considering the method of isolation of the sodium doublet, the type of sample in which sodium was to be determined had to be taken into account.Since these samples were to contain, amongst other elements, fairly large concentrations of calcium, it was decided that the use of filters was likely to prove inadequate since the molecular bands associated with calcium at about 6 0 3 0 ~ , 6 2 4 0 ~ and 6 4 8 0 ~ spread considerably and therefore produce considerable background in the region of the sodium doublet. For this reason it was necessary that some form of monochromator, no matter how simple, should be used. A small glass spectroscope was available from which the eyepiece was removed and replaced by an exit slit made from two razor blades positioned at the focal point of the sodium doublet. The entrance and exit slits were both fixed at a width of about 0.3 mm.336 BREALEY AND ROSS : FLAME PHOTOMETERS : A DESCRIPTIOK [Vol.76 The detector first used was a Mazda 27M1 photomultiplier but a Government surplus RCA931A has recently proved satisfactory, although the dark currents of the latter are usually some three to ten times those of the former. The output is measured directly on a second galvanometer similar to that used for potassium and provision is again made for backing off dark current and adjusting sensitivity. Both photomultipliers are supplied with 960 volts from eight dry batteries. The complete instrument is shown in Fig. 3. It is built on a table at which the operator sits, all the controls being on a panel mounted in the table top.The water manometer for the propane and the pressure gauge on the air supply are mounted on a vertical panel at the back of the table. On the same panel is a voltmeter connected across the battery supplying the amplifier in the potassium circuit. RESULTS- The standard curves obtained from solutions of “Specpure” sodium and potassium chlorides are curvilinear over the range 0 to 50p.p.m. and both follow precisely the same points. When the instrument was set to read 100 with a solution co.ntaining 50 p.p.m. of sodium or potassium, the standard deviations of the points obtained with solutions containing 10, 20, 30 and 40 p.p.m. were all below 0.2 per cent. It can be seen that in general the error due to the effect of cations is small over a wide range of concentration while anions depress the readings, particularly those of potassium.It has been shown that there is no optical interference on potassium by sodium or calcium since solutions of the latter of concentrations up to 1 per cent. give no reading for potassium. Similarly, 1 per cent. solutions of potassium and calcium give no reading for sodium. These points have been checked many times and are reproducible. Interference effects have been studied and a few are given in Table I. TABLE I[ INTERFERENCE EFFECTS Sodium Potassium Interfering substance, p.p.m. K 100 K 1000 K 10,000 Na 100 Na 1000 Na 10,000 Ca 100 Ca 1000 Li 100 Li 1000 Sr 100 Sr 1000 0.01 N HC1 0.1 N HC1 N HC1 0.01 N H,SO, 0.1 N H,S04 N H,S04 0-01 N H3P04 0.1 N H,P04 N H,PO, - Added, p.p.m.30 30 30 - - - 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 Found, p.p.m. 30.0 30-0 30.0 - - - 29.2 29-2 30.0 31.0 30.0 30.8 30.0 26.6 22.0 30.0 27.2 27.2 30.0 26-6 23.6 0. -11.4 - 27.0 0 - 9.7 - 9.7 0 - 11.4 - 23.1 Added, p.p.m. - - - 30 30 30 30 30 30 30 30 30 THE SECOND INSTRUMENT 30 30 30 30 30 30 30 30 30 Found, p.p.m. - - - 30.0 30.0 33.2 30.0 30.0 30.0 31-0 30.0 30.0 30.0 25.0 13-2 30.0 25.2 13.4 30.0 17.0 17.0 7 Error, % - - - 0 0 + 10.1 0 0 0 + 3.3 0 0 0 - 16.6 - 55.3 0 - 16.0 - 55.3 0 - 43.0 - 43.0 In-designing an instrument that will be as versatile as possible, it is necessary to consider it as three units. First, the flame must be of a sufficiently high energy to excite as many elements as possible, secondly, the method of isolating the required radiation must be such that any wavelength may be easily selected at will, and thirdly, the detecting and measuring device must be capable of giving readings for solutions varying from the very dilute to the more concentrated.June, 19511 OF TWO INSTRUMENTS 337 The second instrument, which was constructed with these points in mind, is shown in Fig. 4.The source unit consists of an atomiser, similar to the one on the first instrument, an expansion chamber and an air - acetylene burner of the Lundegiirdh type. A spiral tube was used as the expansion chamber, because it was found that it gave a very much steadier flame than any of the other types tried, owing perhaps to the long distance from atomiser to burner. The spiral is constructed of +inch glass tubing and consists of four turns about 6 inches in diameter. The total distance taken by the spray from atomiser to burner is approximately 6 feet.Both air and acetylene are supplied from cylinders, the air at 301b per square inch through a B.O.C. two-stage regulator, and the acetylene first through a two-stage regulator, which drops the pressure to 30 lb per square inch, followed by a needle-valve, which is adjusted to give a final pressure of 16 inches of water. The burner is placed at a distance of 44 inches from the entrance slit of a Hilger D246 monochromator. This admirably fulfills the second condition stated above, as it is a high dispersion instrument calibrated from 2000 A t o 3.5 p, the wavelength required being selected by turning a calibrated drum. For wavelengths of more than about 6 0 0 0 ~ a CV148 infra-red image converter is used, followed by a Mazda 27M1 photomultiplier, whilst for the shorter wavelengths a Mazda 27M3 photomultiplier is used.The D.C. electrical supplies to the image converter and either photomultiplier are obtained from valve-stabilised, mains- operated power packs. The housings containing the two units are easily interchangeable as they are secured by two screws to the existing fitting at the exit slit of the monochromator. The photomultiplier output is amplified and read on a robust meter calibrated from 0 to 100. The amplifier used is a conventional valve voltmeter, so modified as to permit the use of photo-cell load resistors of very high values. Its basic circuit, shown in Fig. 5, Two detecting units are used.I I l- For Fig. 5. Basic circuit of D.C. amplifier is of the balanced bridge type, the output to the meter being taken from points A and B. an input voltage across R1 of 1.5 volts, an output current of 1 milliamp is obtained, and the response is linear over this range, but to reduce grid current effects and to make quite sure that the response cannot become non-linear the input is limited to 1 volt. This is done by so arranging the shunt across the output meter that in no position is it possible to obtain a reading from more than 650 micro-amps. Seven sensitivity ranges are provided, by having seven input resistors ranging from 200,000 ohms to 200,000 megohms, the appropriate resistor being selected by means of a rotary switch. The input resistor so chosen forms the load resistor of the photomultiplier; and, since full-scale deflection can be obtained when 1 volt is developed across it, it is possible to obtain full-scale deflection from current output from the photomultiplier between 5 micro-amps and 5 x micro-amps.When photomultipliers are used, this gives far more sensitivity than will be required, as it has been estimated that when a solution containing 10p.p.m. of potassium is put into this apparatus, the photo- multiplier signal current is about 0.05 micro-amp. The control R8 is used to reduce the grid338 BREALEY AND ROSS : FLAME PHOTOMETERS : A DESCRIPTION cvoi. 76 current of valve Vla to a point where it is negligible and R7 is the "set zero" control. The 280- volt supply is valve stabilised to counteract fluctuations in mains voltage.The flame photometer has proved easy to use and extremely stable in operation, Provided that the flame conditions are kept constant, no drift is encountered during a run of 2 hours or more, and once the 'instrument has been set up by means of standard solutions, it is unnecessary to put through the standards as a check more frequently than every 10 or 15 minutes. The c a p i l l q of the atomiser dips into a small vessel of about 2 ml capacity which has a funnel side-arm for filling and a tap for emptying. This greatly facilitates the handling of the solutions and speeds up operations to an a.verage of about 30 seconds per sample. RESULTS- A few interference results are shown in Tables 11, I11 and IV. These make it clear that although the hotter air - acetylene flame is desirable from the point of view of exciting more elements than a cooler flame, the interference effects of cations at any rate upon the alkali metals is more severe.The anionic effect,, however, is perhaps a little less serious. TABLE I1 INTERFERENCE OF VARIOUS IONS IN THlI DETERMINATION OF POTASSIUM Interfering ion Na' Ca" Mg" NH,' PO,"' SO,'' * HCl 99 0 Concentration, p.p.m. 10 100 10 100 10 100 20 200 25 250 50 500 0.001 N 0.01 N 0.1 N 7- Added, p.p.m. 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 Potassium Found, p.p.m. 5.08 6.40 4.96 5.05 4.98 5.02 5.00 4.98 4.92 4.90 4.98 4.96 - 4-98 4-90 4.73 1 Error, + 1.6 + 28.0 - 0.8 + 1.0 - 0.4 + 0.4 0 - 0.4 - 1.6 - 2.0 - 0.4 - 0.8 % - 0.4 - 2.0 - 5.4 TABLE IlII MUTUAL INTERFERENCE OF SODIUM, POTASSIUM AND CALCIUM Interfering ion, p.p.m.K 10 K 100 Na 10 Na 100 Ca 10 Ca 100 Percentage error on 6 p.p.m. of- K Na Ca f A > 0 + 5-0 - - + 5.8 + 10.0 + 1-6 - + 3-3 + 28.0 - + 10.2 - 0.8 0 + 1.0 + 4.2 - I TABLE IV EFFECT OF MINERAL ACIDS ON DETERMINATION OF POTASSIUM Percentage error on 5 p.p.m. of potassium Acid 0.001 N 0.01 N 0.1 N HCl - 0.4 - 2.0 - 5.4 - 0.4 - 0.8 - 4.6 - 1.6 - 2.0 - 24.0 H W , Hap04 A f \June, 19511 OF TWO INSTRUMENTS 339 DISCUSSION- Of the original aims all have been fulfilled on both instruments except the fourth, that there should be freedom from interference by ions other than the one being determined. The experience of other workers and of ourselves is that these interference effects present the greatest difficulty in this type of work.Parks et a1.' have surveyed the effect of many anions and cations on the results obtained for potassium. They used a source unit which burned coal gas and found that most substances depressed potassium readings. Higher temperatures such as are obtained in the air - acetylene flame have been found by other workers, Riem* and Domingo and Klyne? to cause an enhancement effect when alkali metals mutually interfere. This agrees with our findings and it was checked that, on our instruments, this effect was not due to light from the interfering elements getting past the optical systems. The effect therefore occurs in the flame and is a true enhancement such as is encountered in all types of emission spectroscopy. The anionic effect is usually a depression of the reading and is reported by Parks et aZ.' and Berry et aZ.3 Phosphate seems to give most trouble in this respect, and it would appear that the hot flames give the better results. A systematic study of as many types of flame as possible is indicated as a profitable line of investigation. ACKNOWLEDGMENT The authors are much indebted to the directors of Boots Pure Drug Co., Ltd., for permission to publish this paper and to Mr. I?. T. Turner for the determination of interference effects. REFERENCES 1. LundeGrdh, H., 2. Phys., 1930, 66, 109. 2. Barnes, R. B., Richardson, D., Berry, J. W., and Hood, R. L., Ind. Eng. Chem., Anal. Ed., 1945, 3. Berry, J. W., Chappell, D. G., and Barnes, R. B., Ibid., 1946, 18, 19. 4. Domingo, W. R., and Klyne, W., Biochem. J., 1949, 45, 400. 5. Mitchell, R. L., Spectrochimica Acta, 1950, 4, 62. 6. Gilbert, P. T., Hawes, R. C., and Beckman, A. O., Anal. Chem., 1950, 22, 772. 7. Parks, T. D., Johnson, H. D., and Lykken, L., Ibid., 1948, 20, 822. 8. Riem, H., 2. Anal. Chem., 1948, 128, 249. 9. Shapiro, S., and Hoagland, H., Amer. J . Physiol., 1948, 153, 428. BOOTS PURE DRUG Co., LTD. 17, 606. STANDARDS DEPT. STATION STREET, NOTTINGHAM

ISSN:0003-2654    

DOI:10.1039/AN9517600334

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

340 BREALEY: THE DETERMINATION OF POTASSIUM I X [Vol. 76 The Determination of Potassium in Fertilisers by Flame Photometry BY L. BREALEY (Presented at the meeting of the Society on Wednesday, October 4th, 1950) A description is given of the procedure for testing, calibrating and using the flame photometer described in -the preceding paper, p. 334. The degree of interference from ions other than potassium that may be found in mixed fertilisers receives special attention. The method is suitable for determining potassium within the range of 3 to 8 parts per million in the test solution. For fertilisers containing from 8 to 12 per cent. of potassium the results show satisfactory agreement mith the official method. FLAME photometric methods for the rapid detemination of the concentration of certain elements in solution are becoming increasingly popular in spite of the difficulty of obtaining suitable ready-made equipment.The basic principle of the method is simple and straight- forward; the solution containing the element under investigation is atomised and introduced into a non-luminous flame, the emitted light being passed through filters or a monochromator in order to isolate the required radiation. The selected waveband then falls on a suitable photo-electric device and the current output is measured. Several workers have designed suitable equipment for this kind of work, descriptions of which have been given by Barnes et aZ.,1#2 Boon: Domingo and Klyne4 and Mit~hell.~ The apparatus described by these workers varies from the simple to the complex, depending upon the purpose for which it is designed.The following is a brief description of the apparatus that was made in this laboratory and used in the work now described. An air - acetylene flame is used. The acetylene is delivered direct to the burner, which resembles that designed by Lundegiirdhs; the air supply is first used to atomise the sample solution and the resulting fine spray passed through a spiral to the burner. The air and acetylene pressures are read on two manometers. The light from the flame enters a monochromator where it is dispersed, and the wavelength of light which emerges from the exit slit is selected by the drum. The emergent light falls on a photosensitive element consisting of an infra-red converter and photomultiplier.The output from the latter is amplified to be read on a meter calibrated from 0 to 100. A full description of this and a simpler instrument is the subject of the preceding paper, see p. 334. In use the required wavelength is selected, distilled water placed in the vessel and, after a few seconds, the reading due to the dark current of the photo-cell and the flame background is brought to the zero mark by the “backing-off” control. A standard solution containing the largest quantity of potassium used for the most suitable standard curve is then put into the receiving vessel, and the reading adjusted to 100 by means of the sensitivity control. The solutions under investigation are thLen passed through, one at a time, and the readings noted. These readings are then converted to parts per million by reference to a curve previously produced from a set of standard solutions.One of the chief difficulties of flame photonietric methods is that cations and anions present in the analytical solution often give rise to interference in the intensity of the light emitted by the element under investigation. This phenomenon is dealt with at length by Barnes et aZ.,l Shapiro and Hoagland,’ Domingo and Klyne4 and by Parks, Johnson and Lykken.8 The experience of these investigators and of ourselves is that these effects vary considerably with different types of flame. One way of overcoming this difficulty is to use standard solutions that are similar in compositioii to the analytical solution, but this com- plicates the method and is to be avoided if possible. I t is essential, therefore, that before any analytical work is undertaken a thorough investigation should be made, by means of the apparatus that is to be used, into the effects of the other ions that are likely to be present.For determining potassium in fertilisers, the official method must be followed up to the point of getting the sample into solution. This includes leaching with hydrochloric acid and subsequent dilution to 500 ml; so that, in addition to the substances in the original sample,June, 19511 FERTILISERS BY FLAME PHOTOMETRY 341 there is also hydrochloric acid present in the final solution. Accordingly, the effect of different concentrations of hydrochloric acid, phosphate, sulphate, calcium, ammonium, magnesium and sodium on the intensity of the potassium emission was investigated.It was known from previous experience that these interferences are reduced by using very dilute solutions, so the final concentration of potassium was brought within the range of 2 to 10 parts per million. A series of standard solutions was prepared, containing respectively 2,4, 6, 8 and 10 parts per million of potassium as potassium chloride. The photometer was then set to zero with water in the spray vessel, and the sensitivity control adjusted so that a meter reading of 100 was given by the 10 parts per million standard. Readings were then taken of the other four standards and a curve plotted showing meter readings against concentration. This standard curve was checked repeatedly against different solutions and found to be reproducible. A series of solutions were then prepared each containing 5 parts per million of potassium plus varying quantities of other ions.The results from this series of experiments is shown in Table I. Interfering ion Na Ca Mg NH4 PO4 so, HC1 TABLE I THE EFFECT OF INTERFERING IONS All solutions contain 5 parts per million of potassium Concentration & found Photometer readings Potassium 10 p.p.m. 47.0 48-0 5.08 100 77 61-0 62-0 6.40 10 p.p.m. 100 79 10 p.p.m. 100 9’ 20 p.p.m. 200 77 25 p.p.m. 250 97 46.0 47.5 46.0 46.5 46.5 46.0 45.0 45.0 46-0 46.5 46.5 47.0 46-5 46.5 46.0 45-5 4-96 5.05 4.98 5.02 6.00 4-98 4.92 4.90 50 p.p.m. 46.0 46.5 4.98 500 97 46.0 46.0 4.96 0.001 N 0.01 N 0.1 N 46.0 46-5 4-98 45.0 45.5 4.90 43.0 43.5 4-73 Error, + 1.6 + 2.8 - 0-8 + 1.0 - 0.4 + 0.4 0 - 0.4 - 1.6 - 2.0 - 0.4 - 0.8 - 0.4 - 2.0 - 5.4 % The two fertilisers so far examined are typical of many commercial products, being well balanced and containing organic nitrogen, ammonium sulphate , superphosphate , bone meal and potash.The potassium content lies within the range 5 to 10 per cent. and is present as sulphate, chloride or manure salts. In the final test solution the major ions likely to be present in addition to potassium are calcium, sodium, magnesium, ammonium, phosphate, sulphate and chloride. Of these only calcium, ammonium and phosphate are likely to approach the same order of concentration as the potassium. In any event, as the final solution will contain about 3 to 8 parts per million of potassium, it is impossible that any ion can be present in a concentration exceeding 100 parts per million, indeed, the total content of the final solution cannot exceed 100 parts per million.The concentration of hydrochloric acid cannot exceed 0.005 N . The most serious interference is that from sodium, but as this will be present only in very small amount-certainly less than 5 parts per million- it is clear that there will be no significant error in the results given by this instrument. As a final check on the method, six samples each of two types of fertiliser were taken. These were ground, 10 g charred, taken up in 10 ml of concentrated hydrochloric acid, boiled with 300 ml of water, filtered and diluted to 500 ml, exactly as laid down in the official method.A portion of this solution was then examined chemically by the cobaltinitrite- perchlorate method9 and another portion examined in the flame photometer. The instrument was switched on and the flame lit, the acetylene pressure was adjusted to read 16 inches and the air 301b per square inch. The entrance slit length was set at 5 mm and the width of both entrance and exit slits at 0.20 mm. The wavelength drum was turned to read 7665 A and the position of the potassium doublet, which is not resolved atBREALEY: THE DETERMINATION OF POTASSIUM IN [Vol. 76 342 these slit widths, located by spraying a solution containing about 5 parts per million of potassium and adjusting the drum until a maximum reading was obtained. The whole equipment was then allowed to warm up for halE an hour.The fertiliser solution was diluted in two stages, 5 ml to 100 ml, and again 5 ml to 100 ml and potassium standard solutions containing 10 and 5 parts per million of potassium were prepared. The spray vessel was rinsed twice with water; then with water running through the spray the dark current control was adjusted until the meter reading was steady at zero. The vessel was emptied, rinsed twice with the 10 parts per-million potassium standard by spraying for a few seconds at each rinse; then, with this standard running through the spray, the sensitivity control was adjusted so that the meter read 100. The spray vessel was not rinsed with water again, but the 5 parts per milJion standard and the 12 diluted fertiliser solutions were put through the instrument one at.a time, giving the container and atomiser two rinses with the test solutions. The whole procedure from the point of setting the dark control for water was repeated twice. The triplicate readings for the fertilisers were averaged, and converted to parts per million from the standard curve. The final results are shown in Table 11. TABLE :[I FLAME PHOTOMETRIC AND CHEMICAL DETERMI NATIONS OF POTASSIUM I N FERTILISERS Readings % Potash A I > Sample 1 2 3 AveIage Potassium, F.P. C h e m i c H l G1 29.0 29.5 29.0 29.2 3.35 8.07 8-12 G2 27.0 28.0 27.5 27.5 3.18 7.66 7.73 G3 32.0 32.0 31.0 31.7 3.64 8.77 8.61 G4 38.0 37-0 37.0 37.3 4.15 10.00 10.27 G5 29.0 28.0 29.0 28.6 3.30 7.95 7.96 G6 29.5 29.5 29.5 29.5 3.40 8-20 8.20 T1 45.0 44.5 44.0 44.5 4.83 11-65 11.58 T2 40-0 39-0 39.0 39.3 4.32 10-40 10.29 T3 47.0 47.0 47.0 47.0 4.07 12.25 11-93 T4 39.5 39.5 39.0 39.3 4.32 10.40 10-53 T5 32-5 33.5 33.0 33.0 3.75 9.05 8.83 T6 36.5 37.5 36.5 36.8 4.10 9.88 9-74 p.p.m.The advantage of flame photometry over the official chemical method is speed; this The time taken for the dilutions, is of importance, particularly in manufacturing control. readings and calculation of results for these 12 sa!mples was about 40 minutes. SUMMARY 1. A description is given of the work done, and the preliminary results obtained, in an investigation of flame photometry for the routine control of potash in fertilisers. 2. The results on the two types of fertiliser so far examined indicate that reproducible results can be obtained that agree well with those by the official Fertilisers and Feeding Stuffs method, and save a considerable amount of time.3. The influence of interfering anions and cations likely to be present in the analysis solution has been shown to be negligible. The necessity for investigating these interferences with the particular apparatus used in the determination is emphasised. The author is indebted to the Directors of Boots Pure Drug Co., Ltd. for permission to publish this paper and to Miss B. M. Wright for the chemical analyses. REFERENCES 1. 2. 3. 4. 5. Barnes, R. B., Richardson, D., Berry, J. W., and Hood, R. L., Ind. Eng. Chem., Anal. Ed., 1945, Berry, J. W., Chappell, D. C., and Barnes, R. IB., Ibid., 1946, 18, 19. Boon, S. D., “Vlam-fotometrie,” D. B. Centen, Amsterdam, 1945.Domingo, W. R., and Klyne, W., Biochem. J., 1949, 45, 400. Mitchell, R. L., Spectrochim. Acta, 1950, 4, 62. 17, 605.June, 19511 FERTILISERS BY FLAME PHOTOMETRY 6. 7. 8. 9. Lundegsrdh, H., 2. Phys., 1930, 66, 109. Shapiro, S., and Hoagland, H., Amer. J . Physiol., 1948, 153, 428. Parks, T. D., Johnson, H. D., and Lykken, L., A n d Chem., 1948, 20, 822. Fertilisers and Feeding Stuffs Regulations, S.R. & O., 1932, No. 658, p. 19. STANDARDS DEPT. BOOTS PURE DRUG Co., LTD. STATION STREET, NOTTINGHAM 343 DISCUSSION THE PRESIDENT drew the author’s attention to a material known as “potash nitrate” that was now on the market. He noticed the author’s table of interfering substances did not include the effect of the nitrate ion. MR. BREALEY said, in reply to the President, that the influence of the nitrate ion on the determination of potassium had not been studied as i t was not present in the samples under examination.He added that the influence of other ions on the element being determined was the most difficult problem in this work. The type of flame used was always a significant factor and if in any particular application one kind of flame proved unsatisfactory, i t might be found that a cooler or a hotter flame would be better. He had tried an air - propane flame in addition to the one described and it had been found, in general, that with the cooler flame there was less interference from other cations, but more from anions than with the hotter air - acetylene flame. MR. A. A. SMALES said that he entirely agreed with the author that the effect of other elements on the emission of a given element was very important in flame spectrophotometry.There were two general methods of overcoming this difficulty in a particular estimation: (i) dilution to the point of disappearance, or a t least insignificance, of the effect, and (ii) the addition of a spectroscopic “buffer,” i.e., a fairly strong solution of a salt, which “swamped” effects due to possible variations in the amounts of other elements in the samples. The author had used the first of these methods, which was satisfactory when a major constituent was being determined, but owing to the necessity for working a t low concentrations i t could lead to difficulties from contamination. He suggested that the author should try the second method to overcome the effect of, for example, sodium, which had been mentioned.MR. R. K. MATTHEWS asked whether, in connection with the presence of substances likely to interfere in the determination of potassium, the author was of the opinion that the potash content of soils could be satisfactorily assessed by the method described. MR. BREALEY replied that Dr. R . L. Mitchell in Aberdeen was successfully using an instrument similar to the one described for soil potash determinations. MR. J. HASLAM asked if the author had any experience of the rapid determination of potassium in rocks and minerals by his flame photometric method. MR. BREALEY replied that in the short time he had been using the apparatus he had not done any work on mineral deposits.MR. R. N . WOODWARD asked what was the approximate cost of the apparatus. Could it be cheapened by the use of colour filters and a barrier-layer type of photo-cell? MR. BREALEY replied that the instrument used cost approximately j5700. An earlier model, suitable only for the determination of sodium and potassium, had been built for between L50 and L60. Domingo and Klynel described a simple apparatus for sodium and potassium determination in biological materials. This instrument used colour filters and either barrier-layer or simple photo-emmissive cells. In his opinion filters could be used satisfactorily for potassium determinations, but for sodium a monochromator was necessary, particularly if calcium was likely to be present in the sample under examination. MR. G. C. COLLINS enquired as to the concentrations in which the various interfering elements might be present in the determination of potassium in fertilisers and also if the author could recommend a technique for determining sodium in presence of calcium. MR. BREALEY said that with the dilutions described in the paper, the concentration of the interfering elements or groups could not exceed 100 p.p.m. Sodium would be present only in minor quantities, perhaps of the order of one-tenth of the amount of potassium. Phosphate and calcium would be present to about one to three times the concentration of potassium. With regard to a technique for the determination of sodium in the presence of calcium, in his opinion a monochromator was required in order to isolate a band sufficiently narrow to reduce to a minimum the background due to calcium. This background was con- siderable; for the fringe of the calcium molecular bands a t 6000 A to 6200 A overlap the sodium lines. REFERENCE 1. Domingo, W. R., and Klyne, W., Biochem. J., 1949, 45, 400 (see reference 4 above).

ISSN:0003-2654    

DOI:10.1039/AN9517600340

出版商:RSC    

年代:1951

数据来源: RSC