ISSN:0003-2654    

DOI:10.1039/AN95883FX005

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX007

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP015

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

THE ANALYST xviiGeroldSchwarzen bachTranslated byHarry IrvingCOMPLEXOMETRICT I T R A T I O N SThe only full-scale book on a subject which is of very recent growth and of importancet o all analytical chemists in whatever field they may be working. The author first openedup this entirely new field and he has made the most substantial and fundamental advancesin it. The detailed procedures for volumetric determinations of metals are so clearlywritten that they are immediately available for use by analysts or technical assistantspreviously unfamiliar with this important new development.The author is Professor of Chemistry in the University of Zurich. The translator is Vice-President of the Society of Analytical Chemistry.With 41 diagrams. 21s.G. CharlotandDenise BdzierTranslated byR. C. MurrayQUANTITATIVEINORGANICANALYSIS‘Professor Charlot’s earlier book on qualitative iriorganic analysis is already well knownt o teachers of analytical chemistry. His new book with Mme BCzier is also unusual andstimulating in its approach.. . the reviewer has no hesitation in recommending this bookas a n excellent text for students a t university entrance level. Both teacher and studentwill find it delightful to use. . . Dr. Murray’s translation of the second French edition isan excellent one.’With 21 1 diagrams. 84s.The Chiwicul Age.METHUEN & CO. LTD36, Essex Street, London, W.C.2 I Published b

ISSN:0003-2654    

DOI:10.1039/AN95883BP025

出版商:RSC    

年代:1958

数据来源: RSC

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FEBRUARY, I958 Vol. 83, No. 983 THE ANALYST PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY ORDINARY MEETING AN Ordinary Meeting of the Society, organised by the Microchemistry Group, was held at 7 p.m. on Friday, February 7th, 1958, in the meeting room of the Chemical Society, Burlington House, London, W.l. The Chair was taken by the President, Dr. J. H. Hamence, M.Sc., F.R.I.C. The following papers were presented and discussed : “Applications of the Conway Diffusion Technique to the Analysis of Radioactive Materials for Trace Impurities,” by J. K. Foreman, B.Sc., A.R.I.C.; “The Use of Long Chain Quaternary Amine Salts in the Solvent Extraction of Metal Ions,” by R. Powell, A.R.I.C. NEW MEMBERS ORDINARY MEMBERS James Alexander, A.H.-W.C. ; Robert B. Carson, B.A., M.Sc.(Wisconsin), F.C.I.C. ; George Anthony Davidson, A.M.C.T., A.I.M. ; Robert Greenhalgh, B.Sc. (Lond.) ; Harry Ashworth Main, BSc. (Manc.) ; Lloyd A. McDonald, B.S. ; Eric Morris, L.I.M. ; Nakaaki Oda, Dr.Tech. (Tokyo) ; Eric Hodson Paulson, M.Sc. (Manc.) ; Eric Herbert Brodie Sellwood, B.Pharm. (Lond.), F.P.S., A.R.I.C.; Brian Alan Wills, B.Pharm. (Nottingham), Ph.D. (Lond.), M.P.S., A.R.I.C. WESTERN SECTION A JOINT Meeting of the Section with the Cardiff and District Section of the Royal Institute of Chemistry was held at 7 p.m. on Wednesday, December 18th, 1957, at the King’s Head Hotel, Newport. The Chair was taken by the Chairman of the Western Section, Mr. P. J. C. Haywood, B.Sc., F.R.1 .C. A lecture on “Inorganic Chromatography” was given by F. H. Pollard, Ph.D. MIDLANDS SECTION AN Ordinary Meeting of the Section was held at 6.30 p.m. on Thursday, January 16th, 1958, in the Mason Theatre, The University, Edmund Street, Birmingham, 3.The Chair was taken by the Chairman of the Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. The following paper was presented and discussed : “The Analytical Chemistry of Nitrogen,” by A. F. Williams, BSc., F.R.I.C. . MICROCHEMISTRY AND PHYSICAL METHODS GROUPS A JOINT London Discussion Meeting of the Microchemistry and Physical Methods Groups was held at 6.30 p.m. on Wednesday, January 8th, 1958, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4. The Chair was taken by the Chairman of the Physical Methods Group, Mr. R. A. C. Isbell, A.1nst.P. A discussion on “Advantages of Spectrophotometric Titrations” was opened by R.A. Chalmers, BSc., Ph.D. 6566 HASLAM, HAMILTON AND JEFFS : THE DETERMINATION OF [Vol, 83 MICROCHEMISTRY AND BIOLOGICAL METHODS GROUPS A JOINT London Discussion Meeting of the Microchemistry and Biological Methods Groups was held at 6.30 p.m. on Wednesday, December 18th, 1957, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4. The Chair was taken by the Chairman of the Biological Methods Group, Dr. S. K. Kon, F.R.I.C. An informal discussion on “The Weighing and Measuring of Small Quantities’’ was opened by G. F. Hodsman, BSc., Ph.D., A.Inst.P., and R. Goulden, A.R.I.C. BIOLOGICAL METHODS GROUP THE thirteenth Annual General Meeting of the Group was held at 6.30 p.m. on Wednesday, December 18th, 1957, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4, immediately before the joint discussion meeting reported above. The Chair was taken by the Chairman of the Group, Dr. S. K. Kon, F.’R.I.C. The following Officers and Committee Members were elected for the fortlicoming year :-Chairman-Dr. S. K. Kon. Vice-Chairman-Dr. J. I. M. Jones. Hon. Secretary and Treasurer-Mr. K. L. Smith, Standards Department, Boots Pure Drug Co. Ltd., Notthgham. Members of Committee- Miss J. Stephens, Messrs. G. C. Ashton, W. A. Broom, s. A. Price, Magnus Pyke and J. Simpson. Mr. J. W. Lightbown was re-appointed Hon. Recorder and Messrs. D. M. Freeland and J. H. Hamence were re-appointed Hon. Auditors.

ISSN:0003-2654    

DOI:10.1039/AN9588300065

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

66 HASLAM, HAMILTON AND JEFFS : THE DETERMINATION OF [Vol, 83 The Determination of Poly(Ethy1 Esters) in Methyl Methacrylate Copolymers BY J. HASLAM, J. B. HAMCLTON AND A. R. JEFFS (Imperial Chemical Industries Ltd., Plastics Division, FVelwyn Garden City, Herts.) A method has been devised for the determinakion of poly(ethy1 esters), e.g., poly(ethy1 acrylate), in methyl met hacrylate copolymers. The alkoxyl groups in the sample are converted to the corresponding iodides, which are then determined by gas - liquid chi-omatographic test. THE determination of small proportions of poly(ethy1 esters) in methyl methacrylate copoly- mers is an interesting analytical problem. Its solution appeared to depend on a quantitative determination of the total alkoxyl groups present in the polymer, followed by an effective separation of the individual alkyl iodides formed.Our original efforts were directed to finding a simple process by which, for example, the methoxyl group of poly(methy1 methacrylate) could be converted to methyl iodide in very high yield. Such a process has been devised and is essentially based on the method for determining alkoxyl groups in cellulose ethers worked out by Easterbrook and one of us (J. B. H.).l The method that we adopted differs from that of Easterbrook and Hamilton only in the following respects- (a) nitrogen was used in conjunction with a mercury lute and a flowmeter as the sweeping-out gas, instead of carbon dioxide, ( b ) the spiral scrubber contained 4 ml of 25 per cent. w/v sodium acetate solution, and (c) the bromine solution absorber was modified so that a second bromine solution absorber could be fitted in series, as a precautionary measure.Preliminary experiments showed that the phenol used in Easterbrook and Hamilton’s method to solubilise the cellulose ether was also necessary when working with polymers. Experiments carried out without phenol gave only two- thirds of the theoretical yield of alkyl iodide. When this modified method was applied to known samples (about 20 mg) of disintegrated poly(methy1 methacrylate) sheet, samples of pcily(methy1 methacrylate) moulding granules and a sample of poly(ethy1 acrylate), the results shown in Table I were obtained. From these results it was seen that the recovery of iodides was sufficiently satisfactory for a ratio method to be used for the determination of the relative proportions of the two iodides. It was now necessary to distinguish between the iodides in a quantitative manner.February, 19581 POLY(ETHYL ESTERS) IN METHYL METHACRYLATE COPOLYMERS TABLE I 67 DETERMINATION OF ALKOXYL CONTENT BY A MODIFIED METHOD Theoretical methoxyl content of poly(methy1 methacrylate) = 31.03 per cent.w/w Theoretical ethoxyl content of poly(ethy1 acrylate) = 45-06 per cent. w/w Sample Alkoxyl content, Conversion, 01 01 70 70 Sample A [disintegrated unplasticised poly- Sample B [disintegrated unplasticised poly- Sample C [poly(methyl methacrylate) mould- ing granules] . . .. .. . . . . 30.32, 30.27 (-OCH,) 97.8, 97.7 Sample D [poly(methyl methacrylate) mould- inggranules] , . .... . . .. 29.98, 29.94 (-OCH,) 96-7, 96.6 Sample E [poly(ethyl acrylate)] . . . . 44.09, 44.13 (-OCH,CH,) 97.8, 97.9 (methyl methacrylate) sheet] . . . . 30.45, 30.56 (-OCH,) 98.2, 98-6 (methyl methacrylate) sheet] . . . . 30.23, 30.21 (-OCH,) 97.5, 97.5 Many methods of separating mixed alkyl iodides derived from alkoxyl groups have been suggested, and a review of these was included in a paper on the subject by Gunnar Gran.2 However, gas - liquid chromatography seemed to offer great advantages over ordinary chemical methods. Indeed, a paper entitled “Selective Microdetermination of Alkoxy Groups by Gas - Liquid Chromatography” by Martin and Vertalier3 was read at the Congress on Analytical Chemistry, Lisbon, September, 1956. Cotton-wool pads . B 10 , G lass-rod spiral Fig.1. n-Heptane trap with an extension for an absorber containing buffered bromine soh tion In their paper these authors were concerned with monomeric substances and distilled the iodides liberated by the Zeisel method into an absorber containing 0.2 ml of chloroform, which in turn contained 5 per cent. w/v of methylene dichloride. The latter acted as an internal standard in their subsequent gas - liquid chromatographic procedure. For methoxyl and ethoxyl groups, Martin and Vertalier found it was possible to ascertain the ratio in which the groups occurred in a single molecule (molar ratio) and to determine them at the same time in an approximate manner (with an error of 5 to 10 per cent.) by working on 20 mg of substance. This knowledge permitted the exact determination of each group when this.information was supplemented by an iodimetric determination of the total alkoxyl groups.68 HASLAM, HAMILTON AND JEFFS THE DETERMINATION OF [Vol. 83 Since copolymers may contain the polymerised esters in any ratio, it seemed important to devise an absorber for retaining the liberated iodides quantitatively. The absorber shown in Fig. 1 was found tolbe satisfactory and was used in all our work. This contained 0-5 ml of solvent and was attached to the spiral scrubber of the apparatus used by Easterbrook and Hamilton. A drying agent was included, since water interfered with the gas-liquid chromatographic procedure. I t was necessary that the solvent employed in the absorber should not interfere with the separation of the two iodides in the subsequent chromatographic test and several solvents were tried, the trap being kept at 0" C and at -80" C (i.e., the temperature of a solid carbon dioxide - methanol mixture). Eventually, pure synthetic n-heptane was used at -80" C and proved ideal for the purpose.Its efficiency was evaluated by connecting a second absorber containing buffered bromine solution in series with the n-heptane absorber to retain any iodides escaping absorption. Determination of the iodides in this buffered bromine solution indicated the proportion of the alkoxyl groups converted to iodide that were retained in solution by the n-heptane absorber. The results, which are based on the mean values for alkoxyl content given in Table I, were 99.4 and 99.2 per cent. of methyl iodide retained by the n-heptane absorber for Sample A and 99.9 and 99.9 per cent.of ethyl iodide for Sample E. Further preliminary experiments showed that, if n-heptane containing a small amount of methylene dichloride as internal standard was employed as absorbing solvent, loss of methylene dichloride (about 5 to 10 per cent.) resulted with the passage of nitrogen through the absorber even at -80" C. This was overcome by absorbing the alkyl iodides initially in 0.500 ml of n-heptane; after absorption was complete 0.500 ml of n-heptane, containing internal standard, was then added to the contents of the absorber. In fact, we found it advantageous to use two internal standards in the n-heptane-methylene dichloride for comparison with the larger methyl iodide peak and a smaller amount of ethylidene dichloride for comparison with the smaller ethyl iodide peak.Our full method for the determination of poly(ethy1 acrylate) in copolymers with poly(methy1 methacrylate) is described below. APPARATUS- and the absorber shown in Fig. 1. METHOD The reactionJEask, spiral scrubber and glass spoon as used by Easterbrook and Hamilton, Conventional gas - liquid chromatographic aj!$aratus. Agla micrometer-syringe pipette. Hydriodic acid, sp.gr. 1.17-The M.A.R. reagent, which is supplied in 6-in1 ampoules. Phenol-Analyt ical-reagent grade. n-Heptane-The pure synthetically prepared material. Sodium acetate solution-A 25 per cent. w/v solution in water. Methylene dichloride. E thylidene dichloride. Methyl iodide. E thy1 iodide. The column used consisted of a U-tube having a total length of 6 feet and a nominal bore of 0.25 inches, packed with a 30 per cent, w/w mixture of dinonyl sebacate on Celite 545 that had been graded as described by Martin and James.* REAGENTS- PROCEDURE FOR CALIBRATING THE GAS - LIQUID CHROMATOGRAPHIC APPARATUS- The conditions were as follows- Column temperature, 75" c; Inlet pressure, Exit pressure, Nitrogen flow-rate, Bridge current, 140 mA; Katharometer temperature, 650 mm o f mercury; 150 mm of mercury; 3.0 litres per hour ; room temperature (22" C).Add 0.500 ml of methylene dichloride and 0.250 ml of ethylidene dichloride accurately to n-heptane contained in a 100-ml calibrated flask by means of an Agla micrometer-syringe pipette. Dilute the contents of the flask to the mark with n-heptane and shake thoroughly.February, 19581 POLY (ETHYL ESTERS) IN METHYL METHACRYLATE COPOLYMERS 69 1 ml of this n-heptane solution contains 0405 ml of methylene dichloride and To 10.0-ml aliquots of the n-heptane solution add various known volumes of methyl and ethyl iodides accurately by micrometer-syringe pipette (see Table 11).Subject 2 to 5 drops of each of these solutions to gas - liquid chromatographic test under the above-mentioned conditions (the actual amount depending on the iodide content). From the chromatograms determine the ratios of (a) peak height of methyl iodide to the peak height of 0.005 ml of methylene dichloride and (b) peak height of ethyl iodide to peak height of 0.0025ml of ethylidene dichloride, and construct calibration curves, with the weights of iodide as ordinates and these ratios as abscissae.Our results are summarised in Table I1 and the calibration curves are shown in Fig. 2. 0.0025 ml of ethylidene dichloride. Ratio of peak height of iodide to peak height of corresponding internal standard Fig. 2. Calibration curves: curve A, methyl iodide ; curve B, ethyl iodide TABLE I1 RESULTS OBTAINED IN THE CONSTRUCTION OF THE CALIBRATION CURVES d2izg for methyl iodide 2.279 for ethyl iodide 1.933 Standard Volume of methyl iodide No. added, ml 1 0.170 3 3 0.100 4 0.080 5 0.050 6 0.020 - Weight of methyl iodide, mg per ml of solution 38.63 - 22.79 18.23 11.40 4.56 Volume of ethyl iodide added, ml 0.170 0.010 0-030 0.060 0.100 - Weight of ethyl iodide, mg per ml of solution Ratio (a) Ratio (b) - 5-79 - 32.86 - 7.96 1.93 3-33 0-42 5.79 2-62 1.40 11.58 1-66 2-87 19-33 0.67 4.68 PROCEDURE- Clean the reaction flask, spiral scrubber and the n-heptane absorber assembly with chromic - sulphuric acid mixture and wash them thoroughly with distilled water.Dry the apparatus by washing it with acetone and allowing residual acetone to evaporate. Place 2-5 g of phenol and the contents of a 6-ml ampoule of hydriodic acid in the reaction flask. Put 4ml of 25 per cent. w/v sodium acetate solution in the spiral scrubber and place the stopper in the open end. Connect the spiral scrubber to the reaction flask with suitable tension springs. With water flowing through the condenser and a nitrogen flow of 6 ml per minute passing through the apparatus, heat the contents of the reaction flask to boiling and maintain gently boiling for 30 minutes.This serves to condition the apparatus for the test. Withdraw the burner and allow the reaction flask to cool. Measure accurately 0.500 ml of n-heptane into the absorber by micrometer-syringe pipette and fit the absorber assembly to the spiral scrubber by means of tension springs. Weigh out accurately about 20 mg of copolymer into the glass spoon and lower the spoon plus sample carefully down through the condenser into the reaction flask. Reconnect the spiral scrubber and when assembled submerge the n-heptane absorber in solid carbon dioxide - methanol mixture.70 pol. 83 Heat the contents of the reaction flask to boiling and maintain boiling for 1 hour. Disconnect the absorber assembly.Add 0.500ml of a rt-heptane solution containing 1 per cent. v/v of methylene dichloride and 0.5 per cent. v/v oE ethylidene dichloride (made up accurately by micrometer-syringe pipette) to the contents of the absorber by micrometer-syringe pipette and mix the solutions. Hence the absorber now contains 0405 ml of methylene dichloride, 04025 ml of ethylidene dichloride, n-heptane up to 1 ml and the evolved iodides. Subject 1 to 6 drops of this heptane solution to chromatographic test under the conditions of calibration. With copolymers having a low poly(ethy1 acrylate) content, it is necessary to run two chromatograms to find the ratios (a) and ( b ) , Le., 1 drop of solution to obtain ratio (a) and 5 or 6 drops of solution to find ratio (b) (see Fig.3). This would be unnecessary with a gas - liquid chromatograph fitted with an attenuator. Calculate the ratios (a) and (b) and from the calibration curves find the weights of each iodide evolved from the polymer. Calculate the percentage of poly(ethy1 acrylate) in the copolymer from the yield of the two iodides. HASLAM, HAMILTON AND JEFFS : THE DETERMINATION OF 4 f /B / c /D D Sample I" -- Time Chromatograms: (a), 6 or 7 drops of trap solution; and ( b ) , 1 drop of trap solu- tion. A, methyl iodide; 13, methylene dichlor- ide; C, ethylidene dichloride; D, eth:yl iodide ; E, n-heptane Fig. 3. RESULTS A 19-9-mg sample of a copolymer known to consist of 91 per cent. of poly(methy1 meth- acrylate) and 9 per cent. of poly(ethy1 acrylate.) was subjected to the procedure described above. The peak heights of methyl iodide, methylene dichloride, ethylidene dichlclride and ethyl iodide were measured and the ratios (a) and (b) were calculated. By means of the calibration curve it was found th.at the trap therefore contained- The chromatograms obtained are shown in Fig.3. These ratios were 3.75 and 0.66, respectively. 25.6 mg of methyl iodide = 18.05 mg of poly(niethy1 methacrylate) and 2.8 mg of ethyl iodide = 1-80 mg of poly(ethy1 acrylate). (NOTE-Methyl methacrylate and ethyl acrylate are isomeric and have a molecular weight of 100.1 1 .)February, 19581 POLY (ETHYL ESTERS) IN METHYL METHACRYLATE COPOLYMERS :. Recovery (in terms of original polymer) = 19.85 mg. 71 :. Poly(ethy1 acrylate) in copolymer = - x 100 19.85 = 9.07 per cent.Other results found for this copolymer were 9.04 and 9-09 per cent. Similarly for a copolymer known to consist of 97 per cent. of poly(methy1 methacrylate) and 3 per cent. of poly(ethy1 acrylate), the results were 2-96, 3-15 and 3.09 per cent. When our control samples, i.e., Samples A and E in Table I, were subjected to the complete pro- cedure as described above, Sample A [poly(methyl methacrylate)] yieIded no trace of ethyl iodide and Sample E [poly (ethyl acrylate)] yielded no trace of methyl iodide. Incidentally, experiments in the presence of dibutyl phthalate indicate that this plasticiser does not interfere with the test. The accuracy of the gas - liquid chromatographic method, with close control, is generally accepted as being within 2 per cent. of the percentage determined and within these limits we believe our test to be quite satisfactory. As far as we are aware, this is the first time that the determination of alkoxyl groups in polymers has been recorded, and we consider that the principles of our test may prove useful in the general determination of the proportions of mixed alkoxyl groups in monomeric substances. The n-heptane trap, which has proved so efficient for absorbing methyl and ethyl iodides, may (with some modification) have other useful applications, e.g., for absorbing substances from the gas stream in gas - liquid chromatography for examination by ultra-violet and infra-red methods. REFERENCES 1. 2. 3. 4. Easterbrook, W. C., and Hamilton, J. B., Analyst, 1953, 78, 551. Gran, G., Suensk Papperstidning, 1954, 57, 702. Martin, F., and Vertalier, S., Presented at the XVth International Congress on Pure and Applied Martin, A. J. P., and James, A. T., Biochem. J., 1952, 50, 679. Chemistry (Analytical Chemistry), Lisbon, September 8th to 16th, 1956. Received August 13th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9588300066

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

February, 19581 POLY (ETHYL ESTERS) IN METHYL METHACRYLATE COPOLYMERS 71 The Separation of Quaternary Halides by Paper Chromatography BY H. HOLNESS* AND W. R. STONE (Chemistry Department, South West Essex Technical College, Walthamstow, London, E . 17) Separations within the homologous series of certain surface-active cationic germicides by means of paper chromatography are described. By using a new spray reagent, the detection on the paper of as little as 0.6p.g of the quaternary base is possible. WITHIN recent years increasing use has been made in both industry and medicine of germicides whose activity is derived from the presence of surface-active quaternary ammonium or pyridinium salts, and this entails a need for their recognition. Since the publication of our Notel on the paper chromatography of cationic surface-active agents, three papers2JA have been published on this subject.An electrochromatographic method used by Fumasoni, Mariani and Torraca2 for the separation of the homologous series of n-alkylpyridinium halides requires amounts of material greater than 50 pg and the spots formed exhibit “tailing.” An ascending chromatogram described by Garcia and Couerbe3 separates commercial products having mixtures of chain lengths in the n-alkyl radical, but the minimum amount detectable is 5 pg. Negoro and Sen04 also used electrochromatography to separate quaternary bases from non-ionic surface- active agents when present in admixture, but they again experienced considerable “tailing.” The method described in this paper allows separations within the homologous series of saturated ut-alkyltrimethylammonium halides, n-alkylbenzyldimethylammonium halides and * Present address : Chemical Engineering Department, College of Science and Technology, Manchester, 1.72 HOLNESS AND STONE: TH:E SEPARATION OF [Vol.83 n-alkylpyridinium halides when the alkyl chain possesses from twelve to eighteen carbon atoms. The limit of detection is of the order of 0.6pg. EXPERIMENTAL APPARATUS AND TECHNIQUE- All the chromatograms were prepared by using the ascending-solvent technique and Whatman No. 1 paper (for chromatography). Two types of container were used, the first a rectangular tank, which allowed two sheets, 15.75 cm x 33.5 cm, to be run simultaneously. The second container was a large cylinder with vertical sides 30 cm high and with a diameter of 15 cm.This allowed one sheet, 33.5 cm x 31.5 cm, to be used, this sheet being rolled into a tube as described by Wolfson, Cohn and De~aney.~ In this manner a dozen spots could be run on the one sheet. The containers were closed and sealed by covering the top with a sheet of polythene film and securing it round the sides with a strong rubber band. Both the containers were placed in a thermostatically controlled oven adjusted to a temperature of 30" C. All the quaternary salts used in this work were white crystalline products and were supplied as single substances containing only the walkyl chain length indicated by its name. For application to the chromatogram, the salts were dissolved in 50 per cent. aqueous ethanol to concentrations that allowed volumes not greater than 0.003 ml to be spotted on the paper. These spots were applied along a line 3 cm from the base by means of a capillary pipette graduated in 0401 ml.When the chroniatograms had run the required distance, they were removed from the container and allowed to dry by exposure to air at room tem- perature. In this connection it is of interest to note that at a certain time in the process of drying, the separated spots of the quaternary base became faintly visible by reflected light as lighter and more opaque areas on the still damp paper. I t is thought that this might be due to a decreased rate of evaporation of the solvent from the paper in the presence of the surface-active agent. It is, however, unlikely that this could be of general use for determining the position of the spots, since the phenomenon was only observed when the material was present in relatively high concentr, t' ions. When the papers were dry, they were sprayed with the reagent and examined under ultra-violet light while damp.The spots of the quaternary base fluoresced a bright vermilion on a bright white background only faintly tinged with pink; their positions were marked by means of a soft pencil. REAGENTS- The solvent mixtures used in developing the chromatograms, 35 per cent. and 40 per cent. aqueous ethanol, were prepared by mixing 35 and 40 ml, respectively, of 96 per cent. V/V industrial methylated spirit with 5 ml of concentrated. hydrochloric acid and diluting each mixture to 100ml with water.The indicator spray reagent was freshly prepared immediately before use by mixing 5 ml of a 0.2 per cent. w/v aqueous solution of rhodamine BS with 10 ml of a 0.2 per cent. w/v aqueous solution of Tinopal WG, adding 40 ml of ammonia solution, sp.gr. 0.880, and diluting with water to 100ml. RESULTS With both the developing solvents clear separations were obtained within each homo- logous series of the lauryl, myristyl, cetyl and stearyl derivatives. The RF values quoted in Table I represent the average in each case of at least thirty determinations carried out with a solution containing equal weights of each member in the series. It was unfortunate that no pure sample of benzyldimethylmyristylalnmonium chloride was available and the R, value quoted in this instance is that found when a commercial product was examined.It will be seen that the benzyldimethyl-la.urylammonium, benzyldimethylmyristyl- ammonium and benzylcetyldimethylammonium halides can be differentiated from the corres- ponding n-alkyltrimethylammonium and n-alkylp~7ridinium halides, but only poor separation of the stearyl derivatives is shown. The R, values of the n-alkyltrimethylammonium and n-alkylpyridinium salts in both solvents are practically identical and separations could not be achieved, although the pyridinium salts generally showed slightly lower R, values. Better separations might well be achieved by allowing the solvent to run a greater distance, but limitation of the size of the containers available did not allow the examination of this possibility,February, 19581 QUATERNARY HALIDES BY PAPER CHROMATOGRAPHY TABLE I R, VALUES FOR PUKE COMPOUNDS Paper, Whatman No.1 Temperature] 30' C n-A lkyltrimethylammonium salts- Lauryl .. .. .. Myristyl . . .. .. Cetyl . . .. .. Stearyl . . .. .. Lauryl . . .. .. Myristyl* .. .. Cetyl . . .. .. Stearyl . . .. .. n-Alkylpyridinium salts- Lauryl . , 6 . .. Myristyl . . .. * . Cetyl . . .. .. Stearyl . . .. .. n-A lkylbenzyldimethyl- ammonium salts- RF with 35 per cent. ethanol 0.86 0.65 0.36 0.10 0.7 1 0.39 0.20 0-06 0.81 0.58 0.3 1 0.08 Time of run, 7 hours approximately Length of run, 27 cm approximately Standard deviation 0-03 0.03 0.02 0.01 0.04 0.02 0.04 0.01 0.03 0.05 0.04 0.02 RF with 40 per cent. ethanol 0.92 0.79 0-65 0-23 0.85 0.61 0.40 0.14 0.90 0-76 0.64 0-20 Standard deviation 0.02 0.02 0.04 0.04 0.02 0.01 0.03 0.03 0.01 0.02 0.03 0.03 73 * These values were found by using a commercial material of mixed chain lengths.In Table I the figures for the standard deviations are derived from the values for several separate runs. Some of these values are rather large, but this is due to variation from one sheet of paper to another. When several spots of identical material are run simultaneously on the same sheet of paper, the spread of R, values for each component is seldom greater than +0*01. It is therefore recommended that, for purposes of identification, control spots of Known composition should be run on the same sheet as spots of an unknown mixture. Number of carbon atoms in n-alkyl chain Graph of RM values plotted against n-alkyl chain length, with the 35 per cent.ethanol mixture as developing solvent: curve A, n-alkylbenzyldimethy1ammonium homologues; curve B, n-alkylpyridinium homologues; curve C, n-alkyltrimethylam- monium homologues Fig. 1. The R, value, log (l/RF - l), proposed by Bate-Smith and WestallJ6 was evaluated from the R, values shown in Table I and the values obtained within each homologous series were plotted against the corresponding number of carbon atoms in the 12-alkyl chain. The points74 HOLNESS AND STONE: THE SEPARATION OF [Vol. 83 on each graph fell close to the straight line drawn through points calculated by the method of least squares to give the best fit to the experimental data. It is of interest to note that the R, value obtained from the graph for the n-octyl, n-decyl and n-tetradecyl derivatives of the homologous series of n-alkylbenzyldimethylammonium salts were in close agreement with those found experimentally from the chromatogram of the commercial alkylbenzyl- dimethylammonium halide by using the 35 per cent. ethanol solvent.With 40 per cent. ethanol as solvent (see Fig. 1), the rt-octyl and rt-decyl derivatives formed only one spot near the solvent front. LIMIT OF DETECTION- but the cetyl and stearyl derivatives required 0.6 pg for positive identification. The lower members of the series gave definite spots when present to the extent of 0-2 pg, DISCUSSION In the initial stages of the work the chromatograms were run at room temperature, but it soon became evident that the variation in temperature was having an effect on the R, values.It was therefore decided to run the chromatograms at a temperature sufficiently above average room temperature to allow thermostatic control. The temperature selected was 30” C and was obtained by using an electric oven thermostatically controlled to +lo C. In a search for a sensitive means of revealing the position of the spots of the quaternary base on the developed chromatogram, a similar line of reasoning was followed to that which led to the formulation of the mixed indicator used in the scheme of semi-micro qualitative analysis of surface-active agents recently p~blished.~ Initially, a series of anionic dye-stuff s that had the property of fluorescing in ultra-violet light was tested, and with many compounds it was found that the presence of a quaternary base quenched or modified the colour of the fluorescence.Anionic optical bleaches were also found to have their fluorescence quenched by quaternary bases, but the background was then too bright to give a sensitive contrast. In order to increase this contrast, fluorescent ca.tionic dyestuffs were added to the optical bleach and this improved the sensitivity. The most sensitive reagent found was the optical bleach Tinopal WG mixed with the dye-stuff rhodamine BS or rhodamine B5OO. Previously,l we developed the chromatogram by spraying with a solution of these two materials and then exposing to the vapours of ammonia to neutralise any mineral acid remaining on the paper. Here the spray reagent contains ammonia in solution and the additional stage of exposing to ammonia vapours is unnecessary. The position of the spots must be marked while the paper is still damp, since the change in fluorescence in ultra-violet light caused by the presence of the quaternary base is substantially eliminated when the paper is dry.Several solvent systems were originally tried and were composed of various concen- trations of aqueous ethanol. In an effort to reduce “tailing,” 5 per cent. v/v of ammonium hydroxide, of glacial acetic acid and of concentrated hydrochloric acid were added in turn to the solvent, replacing an equivalent volume of water. Of these additions only concentrated hydrochloric acid proved satisfactory, as the lauryl and myristyl derivatives gave good circular spots, the cetyl derivatives gave rather elongated ovals and only the stearyl derivatives showed signs of “tailing.” It was found that, when a mixture of equal amounts of all four members of a given homologous series was chromatographed and allowed to run approximately 27 cm, the spots of the lower members became too large to allclw satisfactory separation when each spot contained more than 6 pg of material. This fact combined with the limit of detection of the spray reagent would suggest that approximately 10 per cent.of any particular chain length within a mixture of members of an homologous series could be detected when run from a single spot under the experimental conditions described. It would seem possible that a smaller percentage of any given chain length in a mixture of chain lengths might be detected if the solvent were allowed a longer run. This .would allow a greater separation between adjacent spots with the consequence that each could contain more than 6p.g of material. We should like to place on record our thanks to Mr. P. A. Lincoln, M.Sc., of Milton Industrial Chemicals Ltd., for the supply of the pure salts used in this work. We also thank Messrs. Leda Chemicals Ltd., for the commercial sample of “benzalconium” chloride, Messrs.February, 19581 QUATERNARY HALIDES BY PAPER CHROMATOGRAPHY 76 Geigy & Co. Ltd. for the Tinopal WG and Imperial Chemical Industries for the rhodamine dye-stuff. REFERENCE s 1. 2. 3. 4. 5. 6. 7. Holness, H., and Stone, W. R., Nature, 1955, 176, 604. Fumasoni, S., Mariani, E., and Torraca, G., Cham. & Ind., 1956, 69. Garcia, I., and Couerbe, J., Chim. Anal., 1956,38, 432. Negoro, H., and Seno, S., Ann. Rep. Takamine Lab., 1957, 8, 119. Wolfson, W. Q., Cohn, C., and Devaney, W. A., Science, 1949, 109, 541, Bate-Smith, E. C., and Westall, R. G., Biockim. Biophys. Acta, 1950, 4, 527. Holness, H., and Stone, W. R., Analyst, 1957, 82, 166. Received August 19th, 1967

ISSN:0003-2654    

DOI:10.1039/AN9588300071

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

February, 19583 QUATERNARY HALIDES BY PAPER CHROMATOGRAPHY 75 Precise Determination of Plutonium by Differential Spectrophotometry BY G. PHILLIPS (Analytical Chemistry Group, A .E.R. E., Harwell, nr. Didcot, Berks.) A method is described for the determination of milligram amounts of plutonium by differential spectrophotometry with a precision (u) of & 0.05 per cent. The sample is dissolved in hydrochloric acid and maintained in the reduced state by the presence of hydroxylamine hydrochloride in the solution. The relative absorbancy of the sample is then measured against that of an accurately known standard solution at 5650 A. The optimum solution conditions to give highest precision have been selected and the effect of the presence of some foreign cations has been investigated.THE metallurgical investigation of plutonium alloys necessitates the development of accurate methods of analysis for that element. A gravimetricl and volumetric methods213 are avail- able, but are subject to interference from other elements. Spectrophotometry offers the possibility of determining the plutonium content of an alloy with the minimum of chemical pre-treatment, a factor of some importance when dealing with radio-toxic materials. To achieve absorptiometrically the accuracy normally required for major constituents of an alloy, a differential t e c h n i q ~ e * ~ ~ ~ ~ must be employed. Differential absorptiometry with use of a Spekker absorptiometer has been employed in the analysis of plutonium alloys by Atkins and Jenkins,' but it was considered that the use of a spectrophotometer offered the advantage of improved precision, e.g., uranium has been determined with a precision of 1 part in 1000.889 PRELIMINARY CONSIDERATIONS Aqueous solutions of plutonium may contain the metal in the ter-, quadri- and sexa- valent forms, or less commonly the quinquivalent form, the spectra of which all show the characteristic narrow absorption bands.1° Chemically it is convenient to work with the lowest valency that is relatively stable in acid solution in the presence of excess of reductant, e.g., hydroxylamine hydrochloride.Plutonium111 has narrow peaks at 5650 A (E = 35.5) and 6030 A (E = 35.0); the peak at 5650 A was selected for a number of reasons. Although previous investigators have usually worked at 6030 A, they have done so to permit the deter- mination of plutonium111 to be made in the presence of plutoniumIv and plutoniumv1.For the determination of total plutonium, it is not necessary to employ a wavelength that is characteristic of one valency state, and hence it is better to work at 5 6 5 0 ~ . From the instrumental point of view, the transmission of the optical system of the Beckman spectro- photometer is at a maximum at about 5000 A, and so narrower slit widths can be used, and this results in a greater intrinsic scale length. Finally, the peak at 5650 A has a lower tem- perature coefficientlo and is less subject to changes of anion concentration.ll It will be shown that Beer's law is obeyed up to absorbancies of 2.0, when the slit width is 0-34 mm. EXPERIMENTAL A series of standard plutonium solutions having concentrations of from 5 to 40 mg per ml was prepared by dissolving weighed amounts of the pure metal in dilute hydrochloric76 PHILLIPS : PRECISE DIETERMINATION OF Wol.a3 acid. Impurity analyses on the metal in other laboratories had revealed less than 0-1 per cent. total weight of all likely impurities. The metal was freshly cut in an atmosphere of argon and was weighed before appreciable surface tarnishing had occurred. The solutions were finally diluted to a known volume in molar hydrochloric acid and 5 per cent. w/v hydroxyl- amine hydrochloride at 25" C. By using aliquots from the standard solutions and diluting them to 2500ml with a molar solution of hydrochloric acid containing 5 per cent. w/v hydroxylamine hydrochloride, a series of calibration curves was prepared with use of reference standards of increasing concentration and by adjusting the slit width as necessary to achieve balance (see Fig.1). These cali- bration curves show marked deviations from linearity at the higher concentrations. By using methods described by Hiskey and Young, the optimum concentration of the reference solution to give greatest precision was calculated. The calculations indicate that the optimum concentration is in the region of 8 mg per ml and it is seen that, at slit widths greater than 0-35 mm, the beam band width is greater than the absorption band width at 5650 A with consequent loss of precision. An accurate calibration graph was next prepared with use of a reference standard having a concentration of 8.23 mg per ml and a series of solutions of various concentrations up to 13-90 mg per ml.All these solutions were made to volume in molar hydrochloric acid and 5 per cent. w/v hydroxylamine hydrochloride at 25" IfI 0.2' C. This procedure is known to give plutoniumII1. Concentration of plutonium. mg per ml Fig. 1. Absorbancy results for solutions of plutonium111 The cell compartment of the spectrophotometer was also maintained at this temperature during absorption measurements. Concentration of plutonium, mg per ml . . . . 8-23 9.49 10.27 11.12 12.84 13.90 Relative absorbancy (l-cm cells and slit width of The results were as follows- 0.34mm) . . .. .. .. .. . . 0.000 0.180 0.296 0.421 0.659 0.820 Absolute absorbancy . . .. .... . . :La240 1.420 1.536 1.661 1.899 2-060 From the results it is seen that when a reference standard containing 8-23 mg of plutonium per ml is used the concentration of an unknown sample in the range 8-23 to 13.90 mg per ml can be determined with a precision (a) of kO.O!i per cent. It was convenient for working purposes to calculate a calibration factor from the values given above. The calculation was as follows- A Concentration of plutonium, mg per ml . . 1.26 2.04 2-89 4.61 5-67 Total = 16.47 A Absorbancy a . .. .. . . 0.180 0.296 0.421 0.659 0.820 Total = 2.376 Calibration factor = - = 6.93 mg per ml per unit of absorbancy. 16.47 2.376 EFFECT OF VARIATION OF CONDITIONS- to decide how critical slight variations might be. The solution conditions used were selected more or less arbitrarily and it was necessaryFebruary, 19581 PLUTONIUM BY DIFFERENTIAL SPECTROPHOTOMETRY 77 Temjwatzlre-From previous work7 it was known that the slope of the calibration curve would decrease with temperature.This was confirmed and the rate of change was deter- mined by measuring the difference in absorbancy between two standard solutions, each at the same temperature, over the range 16" to 35OC, the results being as follows- Temperature, "C . . .. 16 21 25 30 35 Relative absorbancy , , +0.304 +Om294 +0.287 +Om279 +0.273 The absolute absorbancy was 1-5 and the results gave a slope of -0.0016 units of absorbancy per "C. In terms of absolute absorbancy this is equivalent to an error of 0-1 per cent. per "C. It is therefore necessary, for highest accuracy, to measure absorbancy differences within +06" C of the temperature used for preparation of the calibration curve. Hydrochloric acid concentration-A series of solutions of identical plutonium concen- tration, but containing different concentrations of hydrochloric acid, was prepared.By using the solution that was molar in hydrochloric acid as the reference standard, the other solutions were compared differentially with it. No systematic trend was observed, the variations in relative absorbancy being of a random nature. The results were as follows- Concentration of hydrochloric acid, M . . 1.0 0-56 0-75 1.25 1-50 2.0 Relative absorbancy . . .. .. . . O*OOO +0*002 -0.004 0.000 +0.001 -0.003 The absolute absorbancy was 0.765 and the precision (a) of the results was k0.2 per cent.Hydroxylamine hydrochloride concentration-The effect of variation of the concentration of hydroxylamine hydrochloride was tested by the same differential technique as described above. Again only random variations in absorbancy difference were observed, the results being as follows- Concentration of hydroxylamine hydrochloride, yo w/v 5 1 2-5 5-0 7.5 10.0 Relative absorbancy . . .. .. .. . . 0-000 - 0.002 - 0.002 - 0.001 - 0.001 + 0-002 The absolute absorbancy was 0.765 and the precision (a) of the results was k0.2 per cent. Nitric acid concentration-In the separation of plutonium from uranium as described by Atkins and Jenkins,' there is the possibility of some nitric acid being present in the plutonium fraction. The effect of added nitric acid on the relative absorbancy of a number of solutions was tested.It was found that moderate concentrations of nitric acid, e.g., 3 M , had no effect on the relative absorbancy measured. Concentration of nitric Relative absorbancy The results were as follows- acid, M . . .. . . 0.0002 0.001 0.002 0.004 0.01 0.04 0.08 0.2 0.6 1.3 3.2 . . 0.000 0.000 - 0.005 + 0.005 - 0-004 0.000 - 0.002 - 0.001 + 0.006 + 0.010 0.000 The absolute absorbancy was 0.765 and the precision (a) of the results was k0-33 per cent. It should be noted that, in the tests to determine the effect of variation of concentrations of hydrochloric acid, hydroxylamine hydrochloride and nitric acid, the concentration of plutonium in the solutions used was unavoidably lower than is required for highest precision.INTERFERENCE BY ADDED CATIONS- The effect of adding cations likely to be met in the analysis of plutonium alloys was tested in the same manner as was used for the solution conditions. Reference standards and proposed solutions of identical plutonium concentrations were used, the absolute absorbancy being 1-5, and various amounts of the second cation were added to the prepared solutions. The standard and sample solutions were then adjusted to volume and compared differentially. From this it is seen that excess of thorium, uranium, calcium and cerium (cerous) can be present in the solution without greatly affecting the precision of the plutonium determination. Iron added as ferric chloride interferes seriously, even at ratios of iron to plutonium as low as 0.1.Greater amounts can be tolerated, up to a ratio of 1.0, by the inclusion of 5 ml of a 5 per cent. w/v solution of stannous chloride in the 25 ml of alloy solution. Aluminium causes a slight decrease in absorbancy at ratios of 1.5 and greater. This was observed to be due to a slight turbidity formed on the addition of zirconium (as the oxychloride) to the solution. ANALYSIS OF PLUTONIUM - THORIUM ALLOYS The results are given in Table I. Zirconium increases the absorbancy of a plutonium solution, It has been shown that excess of thorium does not interfere in the differential spectro- photometric determination of plutonium. Accordingly, the plutonium contents of some plutonium - thorium binary alloys were determined, without separation, by direct comparison78 PHILLIPS PRECISE DETERMINATION OF [Vol.83 of the absorbancy of the alloy solution in molar hydrochloric acid and 5 per cent. w/v hydroxylamine hydrochloride against that of a plutonium standard of concentration 8.30 mg per ml. The results are shown in Table 11. TABLE I EFFECT OF ADDED CATIONS Ratio of added cation Added cation tonium to plu- Thorium 0.80 1.55 3.90 Precision (u) when no definite Relative trend is absorbancy observable, % f0.15 - 0.001 - 0.004 + 0-003 Iron (as Fe*+) 0.13 $0.012 0.63 +0.020 2.5 +0.085 6.3 +0-213 Iron (in 1.6 +0.007 presence of 3.2 +0.028 stannous 4.9 +0*026 chloride) 6.5 +Om122 Aluminium 1.5 - 0.020 3.8 - 0.038 5.3 - 0.050 Ratio Precision (u) of added when no cation definite to plu- Relative trend is Added cation tonium absorbancy observable, Uranium 0.4 - 0.002 1.0 +0*005 2.0 +0-004 4.0 - 0.003 8.0 +0.004 Zirconium 1-0 3-0.020 6.0 +0*050 6.0 +Om065 % f0.31 k0.17 Cdcium 1.2 - 0.004 2.4 - 0.001 6.0 +0-002 G2rium 1-7 3.0.002 3.4 - 0-001 8.6 0.000 } 0.08 TABLE :I1 ANALYSIS OF PLUTONIUM - THORIUM ALLOYS Relative Relative Absoliite absorbancy of concentration of concentration of Plutonium Thorium Alloy solution plutonium, plutonium, .in alloy, in alloy, Total, 1 +0.017 +om12 8-45! 96.0 rt: 0.1 3.9 f 0.2 99-9 No.mg per ml mg per ml Yo % Yo 2 + 0.050 + 0.35 8-65 94.8 & 0.1 4.8 f 0-2 99-6 3 + 0.300 + 2.08 10.38 94-2 f 0.1 5.8 f 0.2 100.0 4 + 0.639 + 4.42 12-75! 67.3 rfi 0.07 32-8 f 0.1 100.1 5 + 0.034 + 0.24 8.54: 42.8 f 0.04 57.4 & 0-1 100.2 METHO:D REAGENTS- Hydrochloric acid, s$.gr.1.18-Analytical-reagent grade. Hydroxylamine hydrochloride-Analytical-reagent grade. Hydroxylamine hydrochloride solution, 5 per ceiat . w /v-Dissolve 50 g of the hydroxylamine Dilute with distilled hydrochloride in distilled water and add 90 ml of the hydrochloric acid. water to 1 litre. APPARATUS- Beckmavt DU spectro$hotometer-For highest precision, the temperature of the water circulated through the cell chamber block must be thermostatically controlled. A more even temperature throughout the cell chamber is attained if excess heat from the lamp housing is prevented from reaching it. This can be done by circulating cooling water through a metal coil welded underneath the lanip housing. Thermostatically controlled water tank maintained at 25" & 0.20" C-It is convenient to circulate water from this tank through the cell chamber block.Beckman l-cm cells-These must be identifiable and always used in the same position and in the same orientation in the cell carrier. One cell and position is reserved for the reference solution and corrections are applied for any differences in absorbancy due to the sample cells. The correction for each sample cell is determined experimentally by filling both standard and sample cell with the reference solution and comparing the two differentially.February, 19581 PLUTONIUM BY DIFFERENTIAL SPECTROPHOTOMETRY i !I SAFETY PRECAUTIONS- The general type of facilities necessary for the safe handling of plutonium in laboratories have been described elsewhere.12 In this work, plutonium samples were dissolved and the temperature of the solutions was thermostatically controlled in a “glove box.” The spectro- photometer itself was partly enclosed in a “glove box,” in such a way that solutions could be transferred to the cell compartment without exposing them to the open laboratory.PROCEDURE FOR DETERMINING THE CALIBRATION FACTOR- Weigh a number of plutonium samples that on dissolution will provide a series of standard solutions of various concentrations within the range 8 to 14 mg per ml. Place each sample in a beaker together with sufficient distilled water completely to immerse the metal. Add hydrochloric acid drop by drop as the reaction proceeds, but do not allow the reaction to proceed too vigorously. On nearing completion, add sufficient hydrochloric acid to make the solution molar in acid.Warm the solution for a few minutes, cool it and then transfer it to a calibrated flask and add sufficient solid hydroxylamine hydrochloride to make the solution 5 per cent. w/v. Thermostatically control the temperature of the solution for 1 hour and then adjust it to volume with hydroxylamine hydrochloride solution. By using the most dilute solution as the reference standard and balancing the instrument at a slit width of 0-34 mm, measure the relative absorbancy of each solution. Make any necessary cell corrections and calculate the calibration factor as shown on p. 76. PROCEDURE FOR DETERMINING PLUTONIUM- Carry out a preliminary assessment of the concentration of plutonium by direct spectrophotometry.To do this, prepare a dilution of the solution to give an absorbancy of less than 1.0. Knowing the approximate concentra- tion of plutonium in the sample, select a standard the concentration of which is nearest to that of the unknown. Measure the difference in absorbancy between the unknown and the reference standard and calculate the concentration of plutonium by using the calibration factor. Should the reference standard selected be more concentrated than the sample solution, balance the instrument on the more dilute of the two solutions and measure the relative absorbancy, which will be negative. I acknowledge valuable discussion with Mr. E. N. Jenkins, under whose general guidance this work was carried out. Dissolve the sample containing plutonium as before. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. REFERENCES Westrum, S. F., in Seaborg, G. T., Katz, J. J., and Manning, W. M., Editors, “The Transuranium Elements,” National Nuclear Energy Series, Volume 14B, The McGraw-Hill Book Co. Inc., New York, 1949, paper 6-57. Koch, C. W., in Seaborg, G. T., Katz, J. J., and Manning, W. M., Editors, op. cit., paper 17.4. Milner, G. W. C., and Woodhead, J. L., Analyst, 1956, 81, 427. Hiskey, C. F., Anal. Chem., 1949, 21, 1440. Hiskey, C. F., Rabinowitz, J., and Young, I. G., Ibid., 1950, 22, 1464. Hiskey, C. F., and Young, I. G., Ibid., 1951, 23, 1196. Atkins, D. H. F., and Jenkins, E. N., in preparation. Bacon, A., and Milner, G. W. C., Ibid., 1956, 81, 456. Susano, C. D., Menis, O., and Talbot, C. K., AnaZ. Chem., 1956, 28, 1072. Connick, R. E., Kasha, M., McVey, W. H., and Sheline, G. E., in Seaborg, G. T., Katz, J. J., and Hindman, J. C., ila Seaborg, G. T., Katz, J. J., and Manning, W. M., Editors, op. cit., paper 4.4. Dunster, H. J., and Bennellick, E. J., Atomics, 1955, 6, 312. Received July loth, 1957 Manning, W. M., Editors, op. cit., paper 4.20.

ISSN:0003-2654    

DOI:10.1039/AN9588300075

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

so BOOTH AND EVETT : TH:E ABSORPTIOMETRIC [Vol. 83 The Absorptiometric Determination of Traces of Iron in E!ismuth BY E. BOOTH AND T. W. E:VETT (U.K.A.E.A ., Research Group, WooZwich Outstation, Woolwich, S.E. 18) The development of an accurate method for the determination of traces of iron in bismuth is described. Of the many reagents considered, 4 : 7-di- phenyl-1 : 10-phenanthroline was found to be the most suitable, both in specificity and sensitivity. In a hydrochloric acid solution of the sample, iron111 is reduced to iron11 by stannous chloride. The 4 : 7-diphenyl-l : 10-phenanthroline is then added, followed by a mixture of disodium ethyl enediaminetetra-acetate and sodium citrate. This serves the dual purpose of adjusting the pH and complexing the bismuth, hence preventing its precipitation.The iron complex is extracted with n-hexyl alcohol and the optical density of the solution is measured at 633mp. AN analytical method was required that woulcl permit the iron content of bismuth to be determined accurately in the range 2 to 100 p.p.m., the range 2 to 10 p.p.m. being particularly important. Of the many reagents available,l potassium thiocyanate appeared to be an obvious choice and was found to be satisfactory at levels a.bove about 10 pg, but, below this, interference from bismuth and the instability of the coloured complex caused us to abandon its use. Smith, McCurdy and DiehP describe a new reagent, 4: 7-diphenyl-l : 10-phenanthroline (bathophenanthroline) for the determination of very small amounts of iron. This reagent is almost specific for iron11 and is twice as sensitive as 1 : 10-phenanthroline, and the ferrous complex can easily be extracted with isoamyl alcohol or rt-hexyl alcohol.The general behaviour of bathophenanthroline is similar to that of other phenanthrolines, and, since the method of Smith, McCurdy and Diehl, as described, was inapplicable in the presence of bismuth, attention was directed to existing methods applicable to bismuth that make use of 1 : lO-phenanthr~line?,~ In general, they appear to suffer from poor reproduci- bility, together with other undesirable features, such as slow formation of colour, fairly critical adjustment of pH and occasional precipitation of basic bismuth salts. There are also con- siderable differences of opinion on the choice of reductant for iron111 and on the order of addition of the reagents.Since the substitution of bathophenanthroline for 1 : 10-phenan- throline could not be expected to overcome these difficulties, our attention was turned to the factors affecting the formation of the ferrous plhenanthrolines. At pH 4, in non-complexing media, the rate of formation of ferroin (ferrous 1 : 10-phenan- throline) from iron11 and the usually employed 100 to 200-fold excess of reagent is im- measurably fast. A slow rate of colour formation indicates, therefore, a deficiency of some or all of the reacting ionic species. In the presence of bismuth, the iron complex must be finally formed in the presence of appreciable arnounts of reagents such as ethylenediamine- tetra-acetic acid (EDTA), tartrate or citrate, the last named being the most effective complexing agent.Both iron111 and iron11 are complexed by citrate5 and the greater stability of the iron111 complexes makes the rcduction of iron111 more difficult. Further, there will be competition for iron11 between the citrate and the phenanthroline. Hence it may be assumed that attempts to form the ferrous complex in the presence of citrate a t pH 4, with reducing agents such as hydroxylamine or hydroquinone, are not likely to be entirely satisfactory . EXPERIM:ENTAL From the above-mentioned consideration, the reduction stage was carried out in 2 M acid with tin11 as the reductant. The order of addition of the other reagents was then investigated. It was immediately apparent that the bathophenanthroline must be added before the citrate, otherwise little or no colour was produced and the rate of formation of the colour was far too slow.It was further observed that, when iron11 was added to a solution already containing bathophenan- throline and citrate at pH 4, no trace of the coloured complex was visible, even after a long period of time.February, 19581 DETERMINATION OF TRACES OF IRON IN BISMUTH 81 From the work of Lee, Kolthoff and LeussingJ6y7 and our observations on the lack of reactivity of iron11 in the presence of citrate, it appeared likely that the intermediate ionic species occurring in the presumably stepwise formation of Fe(bathophenanthroline)2+ are present in relatively concentrated acid solutions. When the pH is subsequently raised to 4, the final complex should be formed rapidly and quantitatively.The rate of formation of the ferrous complex was, however, still slow, and this could only be attributed to too small a concentration of bathophenanthroline. Owing to the low solubility of bathophenanthroline in water, further addition of the reagent was impracticable, but the addition of 10ml of ethanol before the addition of the citrate ensured that all the added reagent remained in solu- tion. This produced a striking improvement-the red colour now appearing instantaneously. This marked dependence of the rate of formation of the complex on the concentration of bathophenanthroline agrees qualitatively with the findings of Lee, Kolthoff and Leussing6 who have shown that the law governing the rate of formation of ferroin involves a third-power dependence on the concentration of phenanthrolinium ions.Recoveries of added iron from the proposed base solutions were, however, not very satisfactory, since they are dependent on the amount of citrate present. The results are shown in Table I. TABLE I RECOVERY OF IRON FROM VARIOUS BASE SOLUTIONS Iron Iron Optical density at Base solution added, p g recovered, pg 533 mp in 4-cm cell Acetate . . .. .. .. .. . . 11.2 11.2 0-710 10 ml of a 50 per cent. solution of sodium citrate 11-2 10-3 0.650 25 ml of a 50 per cent. solution of sodium citrate 11.2 8.2 0.520 Trials with other complexing agents were carried out, but finally the most satisfactory was found to be a mixture of 20 ml of 0.1 M EDTA and 10 ml of a 50 per cent.solution of sodium citrate. Recoveries of added iron were then carried out at various levels, both in the presence and absence of bismuth. The results are shown in Table 11. TABLE I1 RECOVERY OF ADDED IRON BY THE PROPOSED METHOD Bismuth present, Iron added, Iron recovered, g Pg Pg 11.2 11.2 11.3 11.2 { ;;:; 11-6 5.8 5-6 { 4.7 4-9 1.4 1.1 1.4 1.4 1.1 i 1.1 1 1.1 Optical density a t 533 mp 0.653 0.658 0.654 0.628 0.683 0.342 0.276 0.286 0.085 0.064 0.082 0.086 0.062 0-066 in 4-cm cell It can be seen that the optical density equivalent to 11.2 pg of iron is lower in Table I1 than it is for the experiment in an acetate base solution in Table I. This is because recoveries from the citrate base solution are reproducibly lower than those from the acetate base solution.If the calibration is prepared in the citrate solution, 100 per cent. relative recoveries will be obtained. The above-mentioned differences in optical densities would no doubt disappear if the concentration of bathophenanthroline were increased to the point where a vanishingly small amount of iron11 remained uncomplexed in acid solution. Since the free acidity of the bismuth solution must be 1 to 2 M to prevent precipitation of oxy salts, and since the complexing of iron11 is dependent on the ratio of the concentration of reagent to hydrogen82 BOOTH AND EVETT [Vol. 83 ions, it is impracticable to attempt to achieve the conc:entration of reagent likely to be necessary. The proposed method gives excellent results at all levels down to 1 pg of iron.Levels below this can be determined, the limits being dependent on the magnitude and reproducibility of the blank value. METHOD REAGENTS- water should be used throughout. throline in 175 ml of ethanol. All reagents should be of recognised anal.ytica1 grade. Redistilled or demineralised Bathophenanthroline solution, 0.2 per cent.-Dissolve 0.5 g of 4 : 7-diphenyl-l : 10-phenan- Sodium citrate solution, 50 $er cent. w/v. EDTA solution-A 4 per cent. w/v solution of the disodium salt of ethylenediaminetetra- Stannous chloride solution-A 10 per cent. w/v solution of stannous chloride dihydrate. Hydrochloric acid, concentrated, 6 M and 2 M. Nitric acid, 16 M. n-Hexyl alcohol. Ethanol. Dilute to 250 rrtl with wa.ter and store in polythene. acetic acid. PROCEDURE- Dissolve the bismuth in a mixture of 6 M hydrochloric acid and 16 M nitric acid (10 ml of hydrochloric acid and 0-5 ml of nitric acid per g of bismuth). Evaporate the solution almost to dryness under an infra-red lamp.Re-dissolve the solid in concentrated hydro- chloric acid and repeat the evaporation. Dissol.ve the residue in concentrated hydrochloric acid and dilute with water so that the solution contains 0.2g of bismuth per ml and is approximately 2 M with respect to hydrochloric acid. With a pipette, place 5 ml of the bismuth solution in a 10-ml beaker, add 0-2 ml of stannous chloride solution and boil. Coo1 to room temperature and transfer the solution to a 100-ml separating funnel. Rinse out the beaker with two 5-ml portions of ethanol, and finally with 2 ml of 2 M hydrochloric acid, transferring the washings to the funnel.Add 4 ml of bathophenanthroline solution and mix thoroughly. Mix 20 ml of EDTA solution with 10 ml of sodium citrate solution, and add it to the solution in the funnel, swirling to dissolve any precipitate formed. Set the solution aside for 5 minutes and then extract the ferrous complex with 10 ml of n-hexyl alcohol. Discard the aqueous phase and transfer t.he alcohol extract to a 25-ml cali- brated flask, rinsing the funnel with ethanol. Ililute almost to the mark with ethanol, add 0.2 ml of 2 M hydrochloric acid and shake until a clear solution is obtained. Dilute to the mark with ethanol, filter the solution into a 4-cm cell and measure the optical density at 533 mp. Carry out a blank exactly as described above, but omitting the sample. PROCEDURE FOR RECOVERING THE BATHOPHENA.NTHROLINE- The present price of bathophenanthroline makes it desirable to recover it for further use, Evaporate the n-hexyl alcohol extract to dryness under Warm the residue with 1OIV sodium hydroxide and then extract with and this can be done as follows. reduced pressure. hot benzene. Evaporate the benzene; the residue should be fit to use again. REFERENCES 1. 2. 3. Holmes, D. G., Atomic Energy Research Establishment Report CE/R 2025, Harwell, 1956; 4. 5. 6. 7. Sandell, E. B. , “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience Smith, G. F., McCurdy, W. H., jun., and Diehl, H., Analyst, 1952, 77, 418. Austing, C. E., personal communication. Hamm, R. E., Shull, C. M., and Grant, D. M., J . Amer. Chern. Soc., 1954, 76, 2111. Lee, T. S., Kolthoff, I. M., and Leussing, D. L., Ibid., 1948, 70, 2348. -,-,- , Ibid., 1948, 70, 3596. Publishers Inc., New York and London, 1950. Analyst, 1957, 82, 628. Received July 2nd) 1967

ISSN:0003-2654    

DOI:10.1039/AN9588300080

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

February, 19581 ROONEY 83 The Determination of Trace Amounts of Lead and Bismuth in Cast Iron BY R. C. ROONEY (The British Cast Iron Research Association, Bordesley Hall, Alvechurch, Birmingham) Trace amounts of lead and bismuth are separated from cast iron by extraction of the iron with isobutyl acetate from hydrochloric acid solution, and then by extraction of the lead and bismuth as their diethyldithiocarba- mate complexes with chloroform from ammoniacal tartrate - cyanide solution. The lead and bismuth are then determined simultaneously with a cathode-ray polarograph, an acidified tartrate base electrolyte being used. The purification of the reagents is described. BOTH lead and bismuth are rarely encountered in cast iron in other than trace amounts, almost invariably less than 0.1 per cent.and frequently less than 0.01 per cent. being present. At these concentrations the classical methods of separation, e.g., of lead as sulphide,l*2,3 are not satisfactory and at concentrations of less than 0-001 per cent. are completely inapplicable, even in the presence of carriers.4~~ The direct polarographic procedure6 for lead in unalloyed steel and cast iron can be used for as little as 0-001 per cent. if a modern polarograph, such as the cathode-ray polaro- graph, is available, but it is open to interference by copper and tin. Most ,cast irons contain sufficient copper to interfere. For bismuth the direct iodide colorimetric procedure7 is satisfactory down to about 0.01 per cent., but below this a preliminary separation becomes necessary. Morrogh* and DawsonQ have recently shown that very small amounts of various elements (titanium, lead, bismuth and antimony) have a markedly deleterious effect on the structure and physical properties of nodular-graphite cast iron.Their work has emphasised the need for accurate methods of determining these “subversive elements” at concentrations below 0.001 per cent. The work described in this paper has been carried out as part of the British Cast Iron Research Association’s research programme in this field. EXPERIMENTAL It has been statedlo that, in the presence of cyanide and tartrate at a pH of approxi- mately 11, sodium diethyldithiocarbamate reacts only with lead, bismuth, thallium and cadmium. This statement was investigated with reference to the extraction of microgram amounts of both lead and bismuth from pure solutions.Final determination of the two elements was to be carried out simultaneously with the cathode-ray polarograph. POLAROGRAPHY- When 0.1 N hydrochloric acid was used as base electrolyte, it was not possible to deter- mine less than 10 p.p.m. of bismuth in solution, owing to the severe distortion of the trace that occurs as the sweep passes through zero potential. The bismuth wave occurs at -0.15 volt* and is found on the steeply sloping part of the trace, which makes measurement impos- sible at low concentrations. In 0-1 N nitric acid, the wave is shifted to -0.35 volt, whereas the lead wave occurs at -0.76 volt. This bismuth wave, however, is closely followed by a large rounded wave, which has been attributed to the electro-capillary maximum.11 According to Lingane,12 the most satisfactory base electrolyte for the simultaneous determination of lead and bismuth is a solution of sodium tartrate of pH 4 to 5.When a solution that was 0.1 N in nitric acid and approximately M in sodium tartrate (pH 4-5) was used, it was found that bismuth gave a very well defined wave at -0.45 volt and lead at -0.72 volt. Minor variations of pH resulted in slight shifting of these peak potentials, but had no apparent effect on the values of the peak current. By using this base electrolyte, it was found possible to determine bismuth and lead down to as little as 0.02 p.p.m. When a 1-g sample and a final volume of solution of 5 ml are used, this corresponds to O-ooOOl per cent., which was considered a satisfactory extension * All potentials are given against the mercury-pool anode.84 ROONEY: THE DETERMINATION OF TRAC.E AMOUNTS OF [Vol.83 of the lower limit of determination for all samples, with the possible exception of very pure iron. EXTRACTION- Pure solutions of lead and bismuth were used and extraction was carried out from a solution containing 2 g of sodium tartrate, 1 g of potassium cyanide and 0.01 g of sodium diethyldithiocarbamate. The pH was adjusted to approximately 10 with ammonium hydroxide and the added lead and bismuth were extracted with chloroform. It was found to be most satisfactory to wash three times with chloroform, first with 15 ml and then with 10 and 5ml. The chloroform extracts were transferred to a 50-ml beaker and evaporated to dryness, the organic residues were destroyed.with nitric and perchloric acids and the excess of perchloric acid was removed by evaporating to dryness. The residues were dis- solved in 1.0 ml of 5 per cent. nitric acid, 4.0 ml of sodium tartrate solution (200 g per litre) were added and the solution was transferred to the polarograph cell. With the lower range of concentrations, it was found to be necessary to de-oxygenate for at least 20 minutes. The oxygen step is never completely removed, but if it is sufficiently reduced the bismuth wave can be measured. The results of this series of extractions were as follows- Lead and bismuth added, pg of each 1000 100 10.0 1.0 0.1 0.05 Lead found, pg . . .. . . 1000 100 10-5* 1*4* 0*51* 0*60* Bismuth found, pg * .. . 1000 100 9-8 0-97 0.11 0-04 * The blank value for lead in the reagents was 0.4B pg, but bismuth was not detected. The reagents used for this series of determinations were purified as described later, p. 86. As the results were satisfactory and since, under these conditions, the extraction is said to be nearly specific for lead and bismuth, a direct extraction procedure from a solution of a sample of iron was investigated. A l-g sample of pure iron and some lead and bismuth were dissolved in dilute nitric acid, the iron was complexed with tartrate and, after the pH had been adjusted, traces of other metals, e.g., copper and nickel, were complexed with potassium cyanide. Sodium diethyldithiocarbamiate was then added and the extraction was carried out as before.The results were extremely unsatisfactory; approximately 20 per cent. of both elements was recovered from each addition, the range of additions being the same as that used in the previous series of determinations. In order to complex all the iron, it had been necessary to increase the amount of tartrate and the increased buffering action had necessitated the use of more ammonium hydroxide to attain the desired pH. A systematic investigation into the effect of the concentrations of tartrate, cyanide and diethyldithiocarbamate and the pH showed that none of the com- plexing agents had any deleterious effect when present in very large amounts. The effect of up to 20 g of tartrate and 5 g of cyanide in 100 ml of solution were investigated. Between pH 7 and pH 11 the recovery was quantitative.It appears that ferric iron interferes in the extraction in some manner. A further series of additions and extractions was made, in which the iron was dissolved in hydrochloric acid and any ferric iron was reduced to ferrous iron with hydrazine dihydrochloride immediately before the extraction. The results were still very low. The next series of additions was made to iron dissolved in aqua regia, and the bulk of the iron was removed by extraction with isobiutyl acetate. Results were still low, and it was noticed that, after the addition of sodium diethyldithimarbamate, the solution acquired a blue tinge. It was thought that this was due to ferro-ferricyanide formed by the reduction of some of the ferricyanide present by the diethyldithiocarbamate.This possibility was investigated further. A further series of determinations was carried out with 4-g samples of pure iron, in which the residual iron present after the extraction with isobutyl acetate was reduced before extraction of the lead and bismuth. The results were very satisfactory and are shown in Table I. It is apparent that reduction of the iron is necessary for complete extraction. When this is done, however, the extraction of bismuth under the conditions used is quantitative at least down to 0.1 pg, and the extraction of lead at least down to 3 pg. It has been shown in our laboratory that, by using pure solutions of lead, the lead can be extracted quantitatively down to our lower limit of determination, i.e., 0.05 pg.February, 19581 LEAD AND BISMUTH IN CAST IRON TABLE I RECOVERY OF LEAD AND BISMUTH FROM PURE IRON Lead and bismuth added to 4 g of pure iron, Pg Nil 0.1 1-0 10.0 100 1000 Lead found, Pg 3.7 3.7 4.7 13.5 117 1030 Lead Bismuth recovered, found, Plz Pg - 0.18 - 0.29 1.0 1.2 9-8 10.2 113 98 1026 997 Bismuth recovered, I*g 0.11 1.02 - 10.0 98 997 The effect of ferric iron on this extraction does not appear to have been reported previously in the literature. It is suggested that the effect is due to oxidation of the sodium diethyl- dithiocarbamate by ferric iron, when it is reasonable to assume that sulphide-type compounds are formed.These sulphide-type compounds would then react with lead and bismuth ions to form unionised compounds insoluble in chloroform, thereby removing them from the solution and preventing the extraction.Some support for this theory is given by the fact that the ferro-ferricyanide colour appears when sodium diethyldithiocarbamate is added to an ammoniacal tartrate - cyanide solution containing a small amount of ferric iron, but no ferrous iron. Further, on addition of the reagent a white turbidity similar to colloidal sulphur has been observed. Finally, solutions of sodium diethyldithiocarbamate on ageing for 24 hours deposit sulphur, and in this condition, as in the presence of ferric iron, the results are low. By using the recommended procedure, a number of samples of iron were examined, and the results are shown in Table 11. Corrections for the blank values of the reagents have been applied and the results show satisfactory reproducibility, even at the lowest levels investigated, TABLE I1 Sample Mild steel .. . . Pure iron , . .. Spectrographically Grey cast iron . . pure iron . . .. REPRODUCIBILITY OF RESULTS Weight of sample taken, Lead found, g % 0.0025, 0.0025 0.0028, 0.0028 0.0073, 0.0075, 0.0070 0.0049, 0.0051, 0.0048 0.0067, 0,0067, 0.0067 1.0 { 5.0 0-00019, 0~00019 5.0 0-00009, 0~00009 0.00014, 0.00015 4.0 { 0*00013, 0.00014 Bismuth found, % 0.00004, 0-00005 0~00002, 0~00002 0.0007 1, 0-00076 0*00002, 0.00003, 0.00003 0~00001, 0~00002, 0-00002 0*000008, 0.000007 0.000004, 0.000004 0.000006, 0.000007 0.00015, 0*00015 The extraction of cadmium and thallium was also investigated, but under the conditions used the recoveries were very low, probably owing to the high concentration of ammonium ions present.Recoveries varied from 10 to 60 per cent. of the amounts added. As thallium and lead will give superimposed polarographic waves in acidified tartrate media, it is suggested that, if the presence of thallium is suspected, the lead should bedetermined in a sodium hydroxide base electrolyte. The cathode-ray polarograph will indicate the presence of thallium by giving a wave with a slight kink in the face of the peak, and will give a flat, or sometimes even a double-peak when the derivative circuit is used. Generally speaking, however, if thallium is present, it will have been added to the metal and its presence will therefore be suspected. None of the cast irons examined in our laboratory has been found to contain thallium, and cadmium has only been found at concentrations much lower than 0.0001 per cent.86 ROONEY: THE DETERMINATION OF TRACE AMOUNTS OF [Vol.83 INTERFERENCE- The two major interfering elements in the direct polarographic determination of lead in iron are copper and tin. To check the effect of these elements, 0.05 g of copper and tin, and various amounts of lead and bismuth were added to a series of 1-g samples of pure iron. The lead and bismuth were determined and corrections were applied for the blank values of the reagents, the results being as follows- Lead and bismuth added, pg of each 1000 100 10 1.0 Lead found, pg . . .. .. 1000 99 10 1.0 Bismuth found, pg .. .. 997 98 12 0.8 From these results it can be seen that there is little or no interference from these two elements.No work was done on other alloying elements, but if the concentration of other elements is sufficiently low for them to be masked by the tartrate and cyanide, there should be no interference. It has been found that, with manganese contents greater than 1 per cent., a small amount of manganese is sometimes extracted. This has no effect on the polarographic determination, unless it is present as manganese dioxide, when it colours the final solution pale yellow to brown. Under these conditions, a. wave from zero potential is obtained, but it is easily suppressed by adding 1 or 2 mg of hydrazine dihydrochloride or hydroxylamine hydrochloride. METHO:D REAGENTS- As the processing of up to 5 g of iron requires a considerable amount of reagents, the blank values are frequently so high that they render the results useless.The use of AnalaR reagents when available gave blank values of 25 pg of lead and 5 pg of bismuth. Steps were therefore taken to obtain reagents of a higher degree of purity. Nitric, hydrochloric and perchloric acids and ammonium hydroxide were originally distilled in order to purify them, but the reagents supplied as "lead free, for foodstuffs analysis'' were found to be satisfactory, having lead contents of below 0.005 p.p.m. Nitric acid, s$.gr. 1*42-"Lead free, for foo4dstuffs analysis." Nitric acid, 5 per cent.-Dilute 50 ml of the nitric acid, sp.gr. 1.42, to 1 litre with water. Hydrochloric acid, s$.gr. l*18-"Lead free, for foodstuffs analysis." Perctzloric acid, sp.gr.1.54--"Lead free, for foodstuffs analysis." Ammonium hydroxide, s$.gr. 0.880-"Lead free, for foodstuffs analysis." isoBlatyZ acetate-Carry out a blank test on each bottle by shaking 100 ml of the reagent with 10.0 ml of 2 N nitric acid and determining the lead polarographically. When necessary, purify the reagent by shaking it with 2 N nitric acid and then with 5 N hydrochloric acid to remove most of the nitric acid and leave the reagent ready to extract ferric chloride. Sodium tartrate solution, 200 g per litre-Dissolve 200 g of neutral sodium tartrate in 700 to 800 ml of water and shake with 50-ml portions of a 0.05 per cent. solution of dithizone in chloroform until there is no further colour change in the chloroform layer. Then shake the aqueous phase with chloroform until the extracts are colourless and remove the excess of chloroform by boiling.Cool and dilute the solution to 1 litre. Potassizcm cyanide solution, 200 g per litre-Dissolve 200 g of potassium cyanide in 700 to 800 ml of water and add 10 ml of a 0.1 per cent. solution of sodium diethyldithiocarbamate. Extract the solution with three 50-ml portions of chloroform and then dilute to 1 litre. This solution must be freshly prepared. Sodium diethyldithiocarbamate solzction, 0.1 per cent.--Dissolve 0.1 g of the pure salt in 100 ml of water, add 2 or 3 drops of ammonium hydroxide, sp.gr. 0480, and extract with two 10-ml portions of chloroform. This solution must be freshly prepared. Chtloroform-AnalaR chloroform has not been found to contain lead or bismuth.If the presence of these elements is suspected, shake the reagent with 2 N nitric acid and then wash it with water. GENERAL REMARKS ON REAGENTS AND APPARATUS- For lead contents down to approximately 0.O001 per cent. and bismuth contents down to approximately 0*00005 per cent., AnalaR acidls and ammonium hydroxide will give satis- factory blank figures. The normal reagent grade isobutyl acetate rarely requires purification and AnalaR chloroform has never been found to be contaminated.February, 19581 LEAD AND BISMUTH IN CAST IRON 87 For all lead contents below 0.01 per cent., however, it is necessary to purify the tartrate and cyanide solutions as described. Distilled water is satisfactory in conjunction with AnalaR acids and ammonium hydroxide. For lead contents below 0.0o01 per cent.and bismuth below 040005 per cent., it is necessary to use the highest purity reagents as already described. Distilled water can be further purified by passing it through a mixed-bed de-ionising column. De-ionised water cannot, however, be used for the final solutions, as its use has been reported to cause dif€iculty with sensitive polarographs,13 and our own experience confirms this. The sodium tartrate solution and the 5 per cent. nitric acid must be made up with distilled water and the polarograph cells must be rinsed with distilled water. Apparatus must be scrupulously clean when used for the lower levels of lead and bismuth. Pyrex glass or a similar glass should be used for all apparatus, including cover- glasses. The use of soda-glass cover-glasses led to high and variable blank values.Beakers must be covered and 2 N nitric acid boiled in them for 5 minutes before use, and they should then be thoroughly rinsed with distilled or de-ionised water. If apparatus can be reserved only for determinations of low concentrations of lead and bismuth, it will be found to give lower blank values after the first few determinations. Removal of graphite and silica residues by filtration, with subsequent evaporation of the filtrates before extraction of the iron, was found to give high blank values. Filter-papers often contain microgram amounts of lead, which are difficult to remove by washing before use. For this reason, the silica and graphite residues in cast iron are removed after centrifugation. MODIFICATIONS TO PROCEDURE- The procedure should be modified to suit the iron under consideration, as folIows- (a) For lead and bismuth contents down to 0.0001 per cent.-Use a 1-g sample and AnalaR reagents.If the contents are greater than 0.01 per cent., a base electrolyte of 0.1 N nitric acid can be used, and the solution can be made up to 25 ml in a calibrated flask. However, a blank determination on all the reagents must be carried out. (b) For lead and bismuth contents below 04001 per cent. in normal irons and steels-Use a 4-g sample and purified reagents. (c) For pure iron with low concentrations of manganese and other constituents-Omit centrifugation and use the entire 5-g sample. Transfer the dissolved residue directly to the separating funnel, hydrochloric acid being used to assist the transfer.The volume of tartrate solution can be reduced to 5ml and the cyanide solution to between 1 and Zml, and the solution made just ammoniacal before extraction of lead and bismuth. These modifications help to give a lower blank value. ( d ) For materials with low concentrations of silicon that do not contaifi graphite or other insoluble residzces-Omit centrifugation. PROCEDURE- Weigh 5 g of sample in a 400-ml squat beaker and dissolve it in 35 ml of hydrochloric acid and 10 ml of nitric acid, sp.gr. 1-42. When dissolved, evaporate to dryness, but do not allow the residue to bake. Dissolve the residue in 20 to 30ml of hydrochloric acid, with gentle warming if necessary, and cool. By using hydrochloric acid contained in a polythene squeeze wash bottle as wash liquid, transfer the solution to a 100-ml calibrated flask (or direct to a separating funnel, see modification (c)).Dilute to the mark with hydrochloric acid and mix well. Transfer the solution to a clean dry centrifuge tube and spin in a centrifuge at 3000 r.p.m. and 10-cm radius for 3 to 5 minutes. By means of a pipette, put either 20 ml (for the 1-g sample) or 80 ml (for the 4-g sample) into a pear-shaped separating funnel of suitable size and add isobutyl acetate (50 ml for the 1-g sample or 150 ml for the 4 or 5-g sample). Shake well, allow to separate and run off the acid phase into a 150-ml beaker. Evaporate just to dryness. Dissolve the residue in 10 drops of hydrochloric acid and add 15 ml of water. Heat to between 80" and 90" C and add approximately 0-1 g of hydrazine dihydrochloride; maintain at 80" to 90" C for about 3 minutes in order to reduce all the iron, and then cool.Transfer the solution to a 150-ml pear-shaped separating funnel, using water to assist the transfer. Add 10 ml of sodium tartrate solution, 30 ml of ammonium hydroxide, 10 ml of potassium cyanide solution and 10 ml of sodium diethyldithiocarbamate solution, shaking the separating funnel after each addition.88 SAINT: A MICRO PROCEDURE FOR THE ELECTROLYTIC [Vol. 83 Run off the chloroform layer into a 50-ml beaker. !Shake the aqueous layer with a 10-ml and then a 5-ml portion of chloroform and add these extracts to the contents of the beaker. If the lead or bismuth content is in excess of 0.011 per cent., use two 15-ml portions before the 10-ml and 5-ml portions and evaporate the earlier portions before adding the next.Evaporate the combined chloroform extracts to dryness, remove the beaker from the hot-plate and add 2.0 ml of nitric acid, sp.gr. 1-4-2, and 2-01 ml of perchloric acid. With the beaker covered, evaporate gently to fumes of perchloric acid and continue until all the organic material is destroyed. Cool and dissolve the residue in 1.0rnl of 5 per cent. nitric acid, added from either a l-ml pipette or a semi-micro burette, and add 4.0ml of sodium tartrate solution from a semi-micro burette. Transfer the solution to a polarograph cell and pass nitrogen through it for between 3 and 20 minutes depending upon the amount of lead and bismuth present. Record polarograms for bismuth, peak potential at -0.45 volt, and lead, peak potential at -0.72 volt, against the mercury-pool anode. For the lower range of concentrations a cathode-ray polarograph will be required. I thank the Director and Council of the €Wish Cast Iron Research Association for Add 15 ml of chloroform, shake for 1 minute and allow the layers to separate. Remove the cover and evaporate to dryness. permission to publish this paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. REFERENCES Pigott, E. C., “Ferrous Analysis. Modern Practice and Theory,” Second Edition, Chapman & Hall Ltd., London, 1953, p. 234. British Standard 1121 : Part 1C: 1943. United Steel Companies Ltd., “Standard Methods of Analysis of Iron, Steel and Ferro-alloys,” Rosenquist, I. T., Amer. J . Sci., 1942, 240, 356; see especially p. 359. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Second Edition, Interscience United Steel Companies Ltd., op. cit., p. 138. Westwood, W., and Mayer, A., “Chemical Analysis of Cast Iron and Foundry Materials,” Allen & Unwin Ltd., London, 1951, p. 76. Morrogh, H., B.C.I.R.A. J . Res. and Dev., 1952, 4, 292. Dawson, J. V., Ibid., 1956, 6, 180. Bode, H., 2. anal. Chem., 1955, 144, 165. Davis, T. R., personal communication. Lingane, J. J., Ind. Eng. Chem., Anal. Ed., 1943, 15, 582. Ferrett, D. J., Milner, G. W. C., and Smales, A. A., Analyst, 1954, 79, 731. Sheffield, 1951, p. 37. Publishers Inc., New York and London, 1950, p. 390. Received June 3rd, 1957

ISSN:0003-2654    

DOI:10.1039/AN9588300083

出版商:RSC    

年代:1958

数据来源: RSC