ISSN:0003-2654    

DOI:10.1039/AN95883FX043

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883BX045

出版商:RSC    

年代:1958

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95883FP187

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

November 19581 THE ANALYST ... XlllThe rate for classified advertismzenls is 5s. a line (w spweequivalent of a line), with an extra charge of 1s. for theuse of a Box Number. Smi-displayed classifiedANALYST back volumes and sets wanted to buy for cash.Also other scientific journals. Write to A. Ashley,27, East 21 Street, New York, 10, N.Y., USA.ALBR1,GHT ,& WILSOS (MFG.) LTD., require a qualifiedChermst in its Analytical Section of the Research Dept. atOldbury. Duties include training and supcrvising juniorstaff and working as Assistant to the Chemist in Charge.It is dcsircd to appoint a man possessing a BSc. or A.K.I.C.with sevpral years experience of analytical chemistry. 4ge26-35. Nan-contributory pension and housing schemes inoperation. Apply, stating age, qualifications and cxperience,to Staff Officer (Ref.5071, Albright & Wilson (Mfg.) Ltd.,P.O. Box 3, Oldbury, Birmingham.CHEMIST required for research and development workon adhesives for plastics and synthetic rubbers. A.R.I.C.or equivalent. Apply, stating expericncc and salary requiredto Technical Director (A.22), Hellemian Limited, Crawlcy:Sussex.M A L E ASALYSTS are required for work on vitaminsand synthetic drugs in a new well-equipped laboratoryin U‘clwyn Garden City. Somc previous experience ofindustrial analysis is essential. Commencing salary accordingto qualifications, age and experience. Please write with fulldetails to the Secretary, Roche Products Limited, 15, Man-Chester Square, London, W.1. ~BRITISH INDUSTRIAL PLASTICS LIMITEDI.P.CHEMICALS LTD., Oldbury, have the followingB;acancy for an Analytical Chemist:-Analytical Research Chemist to take charge of a laboratoryengaged on the investigation of analytical problems associatedwith the Plastin Industry with particular reference tothermosetting resins. The work will involve the use ofmodern techniqurr, including spectroscopy and gas-chromatography, together with the investigation of newmethods of analysis. A.R.I.C. or equivalent qualificationis essential and previous industrial experience is desirable.Preferred age 30-35 years. The company offers goodconditions of employment and a generous pension and lifeinsurance scheme.Applications, which will he treated in strict confidence,giving full details, should he made in writing to: PersonnelManager, B.I.P.Chemicals Ltd., Oldbury, Birmingham.BRITISH INDUSTRIAL PLASTICS LIMITEDI.P. CHEMICALS LTD., Oldbury, have the followingBbacancy for an Analytical Chemist:-Analyst to take charge of a works control laboratory.Minimum qualification A.R.I.C. Previous experience oforganic and inorganic analysis and works control is desirable,together with ability to control staff. The position offersscope for initiative as early expansion of the work of thelaboratory is planned. The company offers good conditionsof employment and a generous pension and life insurancescheme.Applications, which will be treated in strict confidence,giving full details, should be made in writing to: PersonnelManager, B.I.P.Chemicals Ltd., Oldbury, Birmingham.RITISH ACHESON ELECTRODES LIMITED inviteBapplications from Spectroscopists for a position in theiranalytical laboratories. Applicants should be under 30 yearswith a t least 2 years’ experience of emission spectroscopyand preferably they should hold H.N.C. or its equivalent.A competitive salary will be paid, normal welfare facilitiescontributory superannuation and free life insurance available:Apply in writing, giving details of experience and salaryexpected, to The Chief Industrial Relations Officer, GrangeMill Lane, Wincobank, Shcffield, 9.HEMIST 25-30 with dcfinito mineralogical interestsCand prefgrably &th experience in the ceramic industryrequired for research work on coal minerals and slags:Starting salary k700-L1,000 p.a.according to qualificationsand experience. Five-day week. Superannuation andgrading schemes. Apply in writing to the Assistant Secretary(Ref. E D ) , The British Coal Utilisation Research Association,Randalls Road, Leatberhead, Surrey.ANALYST B.Sc./A.R.I.C. rcquired for work of an investi-gational nature involving work in inorganic chemistry.Some experience of organic chemistry would be desirable butis not essential. Applicant shculd have initiative and heable to suDervise the work of iunior staff. The oost ispermanent and pensionable. Five day week. Cantek andsports club facilities. Apply in writing giving age, qualifica-tions and experience to Personnel Manager (ref. A.C.l), JohnLaing and Son Limited, London, N.W.7.RICHARD THOMAS & BALDWINSLIMITEDrequire anANALYTICAL CHEMISTfor advanced research on analytical methdsand modem physical techniques.Applicants should be of University Degrceor equivalent standard with expericnce inrcsearch or industry.Commencing salary in the range 6750-6850according to agc, qualifications and experi-ence, but a higher salary may be offered toan exceptionally qualified applicant.Please nsrite in confidence to thoDirector of Research,Central Research Laboratories,Whitchurch, Nr.Aylcsbury, Bucks.PA.RT-TIME assistant to the Editor of Analytical AbstractsA i s required. Applicants should have a considerableknowledee and exuerience of analvtical chemistrv and heahle l o prepare ahtracts of pap& publlshed i< EnglishFrench, German and preferably other languages; the;should be prepared to spmd three days a week or thewequivalent mainly in libraries for this purpose.person might be suitable.Abstrwts, 14 Brlgrave Square, London, S.W.1.A retiredApply to the Editor, AnalyticalFOR SALEThe -following lahoratory equipment:-1.Hilger Photo-electric Absorbtiometer “Spekker.”2. Fine Balance by “Stanton.”3.4.Pirani Vacuum Gauge by “Edwards.”High Vacuum Pump by “Edwards.”All tho above arc in first class almost new conditions. Furtherparticulars can he obtained from the Mulberry Co., 23a,Sekforde Street, E.C.1.CITY OF BIRMINGHAMPUBLIC HEALTH DEPARTMENTDEPUTY CITY ANALYSTPI’LICATIONS are invited for the post of Deputy CityAAnalyst and Deputy Official Agricultural Analyst, theappointment to commence in February, 1959.Candidatesmust hold a Diploma of Fellowship or Associateship of theRoyal. Institute of Chemistry of Great Britain and Irelandand the Branch E Certificate of the Royal Institute ofChemistry of Great Britain and Ireland.Salary scale: if1405 x 655-Ll625 per annum’(Seniorofficer, Scale “D”). Commencing salary within the scalewill depend upon the candidate’s experience. Pensionscheme (including widows and orphans) ; medical examination.The officer appointed will be required to devote his wholetime to official duties and the appointment will he subjectto one month’s notice on either side. The appointmentwill be subject to the approval of the Minister of Agriculture,Fisheries and Food.AplJIications, together with the names of three personsto whom reference may be made, should state age, qualifica-tions and experience, and be sent to the Medical Officer ofHealth, Council House, Birmingham, 3, not later than1st December, 1958.MALL CHEMICAL LABORATORY, London, N.W.10for nak, freehold, owing to wmoval to new premises.Details apply Box No. 3975, The Analyst, 47, GreshamStreet, London, E.C.4.I-- I/ HEFFER’S OF CAMBRIDGE1 publish from time to time catalogues andannouncements of individual new booksof special importance. Lee us add yourname to our mailing list.W. HEFFER & SONS L I M I T E D3 & 4 P E l l Y CURY, CAMBRIDGEI lists of books on various subjects, and1I

ISSN:0003-2654    

DOI:10.1039/AN95883BP197

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

NOVEMBER. 1958 THE ANALYST Vol. 83, No. 992 EDITORIAL The First Ten Volumes “THE reprinting of the first ten volumes of The Analyst warrants an Editorial,” said the Publication Committee; and nothing seemed easier. Our publishers, W. Heffer & Sons Ltd., of Cambridge, have rendered a real service to the Society and to analysts in general by taking full financial and organisational responsibility ; publication in America is through the Johnson Reprint Corporation, of New York. The photolithographic reproduction has been excellently carried out by Lowe & Brydone (Printers) Ltd., and the binding matches the original. The technical problems were not inconsiderable; most of the volumes contain inserted folders, one of which is folded no less than six times (compare our September issue, where the folder has only two folds-and yet is the largest in living memory).Our publishers had given much thought over a number of years to the need for reprinting the earlier volumes of the journal; the first ten volumes were eventually chosen, not only because they hold the greatest historical interest, but also because they were to a large extent out of print within the decade in which they appeared. Indeed, so scarce are these volumes (the Society’s file copies being for technical reasons not available for this purpose) that the Society is deeply indebted to Mr. Thomas McLachlan, D.C.M., A.C.G.F.C., F.R.I.C., for his kindness in lending to the publishers his set of original volumes for reproduction. And here the difficulties began. To start with, we were only briefly acquainted with these volumes; and so we found our interest caught by the “serial story” quality of the analytical and legal reports, the corre- spondence and the editorials-to such an extent that several days’ work was neglected while we dipped and read at intervals.Then, when we began to write, it seemed as if a book would be needed to do justice to the contents of the volumes. So finally, ruthlessly, we had to prune. Since our Society had been in existence for only eighteen months when the story told by these ten volumes opens, most of the tale is of the workings of “The Sale of Food and Drugs Act, 1875,” which governed the actions of the Public Analysts. The trials and tribula- tions described in the first three volumes, as defences to charges of adulteration became more and more technical, come to a (triumphant) climax (Vol.IV) when the Queen’s Bench Division decided that Inspectors under the Act were prejudiced when served (for the purpose of analysis) with an adulterated article-and a legal quibble that had threatened to make this Act even less useful than its predecessors of 1860 and 1872 was finally overcome. Perhaps, after this decision, the joke reprinted from Funny Folks on the last page of Volume 111 lost some of its poignancy. But, although the first volume starts with DuprC on whisky, and the bulk of the scientific material deals with food and drink-mainly milk and butter-it also contains papers on the determination of sulphur in coal and on the analysis of plating and gilding solutions; and (p. 37) a report of an Extraordinary General Meeting a t which a resolution to omit the word “Public” from the Society’s title was referred back to Council.Even then, the Society’s membership did not “consist exclusively of analysts holding public appoint- ments. . . .” It is a matter for reflection that a proposal made by Council when the Society was no more than twenty-one months old, intended to recognise the true situation, was eventually given effect when the Society was nearly eighty years old. It is, of course, quite impossible to do more than hint a t the contents of the other volumes. The paper used by the contemporary daily press was examined (IV, p. 161): 697 “Mention the historic contents,” said the Committee.598 PROCEEDINGS [Vol.83 A. H. Allen found the Morning Post the weightiest (literally), Times running it close, the rest much lighter in quality. An abstract (p. 204) “proved” the non-existence of nascent hydrogen, and (p. 223) arsenic “more than enough to kill a hundred children” was found on the green backs of playing cards. In Volume V, G. W. Wigner (joint Editor with John Muter for much of the period) contributes a “Note on an Old Tin of Preserved Meat”-over thirty years old. Even in 1880 tinplate was not what it used to be, however: the 1840 plate was much thicker and the tin was apparently lead-free. One would like to quote from each volume in turn, but the last line of Volume X: must suffice, with its intriguing promise of good things to come. It is an Editorial Notice to Correspondents, and reads simply: “A.P.S. (Rugby). Crowded out-next month.’’ We commend these reprinted volumes to any reader who would gain a background to the times-times when Editorials were pungent to the point of bias, and Presidents, Vice-presidents and Treasurers (or, at any rate, one of each) resigned “on principle” from the Society (all save one soon rejoined)-times when our new Society bitterly opposed the foundation of a rival which appeared to be about to trespass on its preserves, welcomed another (I, p. 94) and, apparently, ignored a third, except for a brief mention of its new Journal under “Books, etc., Received” (VII, I?. 107)---and times when the foundations of analytical chemistry were being well and truly laid. As Winter Blyth wrote (IX, p. 163) “. . . he is a poor student of science, who takes no heed of the road hewn out by his pre- decessor. ”

ISSN:0003-2654    

DOI:10.1039/AN9588300597

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

598 PROCEEDINGS [Vol. 83 PROCEEDINGS OF THE SOCIETY FOR ANALYTICAL CHEMISTRY ORDINARY MEETING AN Ordinary Meeting of the Society was held at 7 p.m. on Wednesday, November 5th, 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 : “Volumetric Analysis of Stannous and Total Tin in Acid-soluble Tin Compounds,” by J. D. Donaldson, B.Sc., and W. Moser, BSc., A.R.I.C. ; “Modification to the Unicaml SP500 Spectrophotometer for Single-beam Recording,” by D. D. Shrewsbury, B.Sc., Grad.1nst.P. ; “0-Dithiols in Analysis. Part VIII. The Use of the Zinc Complex of Toluene-3 : 4-dithiol in the Field Testing of Ores and Minerals,” by R.E. D. Clark, M.A., Ph.D., and C. E. Tamale-Ssali; “Micro-determination of Calcium and Magnesium in Blood Serum and Cerebrospinal Fluid,” by G. Hunter, M.A., D.Sc., F.R.S.C. ORDINARY MEETING AN Ordinary Meeting of the Society, organised by the North of England Section, was held at 7.15 p.m. on Thursday, November 6th, 1958, in the Main Building, The University, Oxford Road, Manchester, 13. In the absence through illness of the President, Mr. A. N. Leather, B.Sc., F.R.I.C., Chairman of the North of England Section, introduced Dr. J. Haslam, F.R.I.C., who took the Chair. The following paper was presented and discussed : “The Chemical Examination of Textiles,” by J. M. Bather, M.Sc. The meeting was preceded a t 2.30 p.m. by a, visit to the laboratories of the British Cotton Industry Research Association, Shirley Institute, Didsbury, Manchester.NEW MEMBERS ORDINARY ‘MEMBERS Keith Lawrence Butcher; Edith Margaret Dodson, B.Sc. (Lond.); Gordon L. Evans, A. B. (Cornell) ; Barbara Anne Ferriday, B.Sc. (Liv.) ; Alan Henry Gunn; Stedman David Morrison; William Harold Redmayne, B.Sc. (Lond.) ; Richard Paton Reynolds ; Mervyn Lewis Richard- son, A.C.T. ; Samuel Ernest Terrill, B.Sc., A.R.A.C.I., F.G.A.A., F.G.S. JUNIOR MEMBER John Francis William Smith.Nov., 19581 PROCEEDINGS 599 NORTH - OF ENGLAND SECTION AN Ordinary Meeting of the Section was held a t 2.15 p.m. on Saturday, October 4th, 1958, a t the City Laboratories, Mount Pleasant, Liverpool. The Chair was taken by the Chairman of the Section, Mr. A. N. Leather, B.Sc., F.R.I.C.A discussion on “Laboratory Balances” was opened by J. C. Lunt, BSc., F.R.I.C., and G. F. Hodsman, B.Sc., Ph.D., A.1nst.P. NORTH OF ENGLAND SECTION AKD PHYSICAL METHODS GROUP A JOINT Meeting of the North of England Section and the Physical Methods Group with the Modern Methods of Analysis Group of the Sheffield Metallurgical Association was held a t 7 p.m. on Tuesday, October 21st, 1958, in the Conference Room of the British Iron and Steel Research Association, Hoyle Street, Sheffield, 3. The Chair was taken by the Chairman of the Modern Methods of Analysis Group, Mr. P. H. Scholes, A. Met., L.I.M. The following papers were presented and discussed: “The Determination of Gases in Metals by the Micro Vacuum Fusion Method,” by E. Booth, BSc.; “The Determination of Oxygen and Hydrogen in Steel,” by C.E. A. Shanahan, R.Sc., F.R.I.C., F.I.M. (see summaries below). The meeting was preceded a t 2 p.m. by a visit to the laboratories of the British Iron and Steel Research Association. THE DETERMIKATIOS OF GASES IN METALS HI’ THE MICRO VACUUM FUSION METHOD MR. E. BOOTH said that the vacuum fusion technique, pioneered by Sloman a t the National Physical Laboratory for the analysis of iron and steel, had been considerably developed in recent years, and had been applied to the analysis of many metals of current metallurgical interest and importance. He gave a brief account of the fundamental basis of the method, referring to important features in apparatus design. This was followed by an account of the application of the method to the determination of oxygen, nitrogen and hydrogen in beryllium, titanium, thorium, uranium and zirconium, THE DETERMIXATION OF OXYGEK AND HYDROGEN IN STEEL XR.C. E. A. SHANAHAS gave a brief outline of existing procedures for the determina- tion of oxygen and hydrogen in steel and showed that these methods suffered from several disadvantages when used in steelworks laboratories. The author’s laboratory had recently developed carrier-gas techniques for oxygen and hydrogen determination, and the remainder of the paper was devoted to descriptions of the development work and the finally recommended methods. Oxygen was determined by high-temperature reaction between the steel sample and graphite; the carbon monoxide evolved was oxidised to carbon dioxide, which was absorbed and weighed.Details were presented of the precision and rapidity of the method and their dependence on carrier-gas flow rate. Hydrogen was determined by a low-temperature carrier-gas extraction procedure whereby the hydrogen was evolved and oxidised to water, which was then absorbed in methanol and titrated with Karl Fischer reagent, a dead-stop end-point method being used. The accuracy and precision of the technique had been examined by the introduction of known amounts of hydrogen into the apparatus and by a comparison of hydrogen deter- minations made on steel samples by the present technique and the well known vacuum heating procedure. MIDLANDS SECTION AN Ordinary Meeting of the Section was held a t 7 p.m. on Wednesday, October 8th, 1958, in the Technical College, The Butts, Coventry. The Chair was taken by the Chairman of the Section, Dr.R. Belcher, F.R.I.C., F.1nst.F. A discussion on “The Determination of Trace Impurities in Metals” was opened by B. Ragshawe, A.Met., and W. T. Elwell, F.R.I.C.600 TIMMS, KONRATH AND CHIRNSIDE THE DETERMINATION OF [Vol. 83 AN Ordinary Meeting of the Section was held a t 7 p.m. on Tuesday, October 14th, 1958, in the Gas Showrooms, Nottingham. The Chair was taken by the Chairman of the Section, Dr. R. Belcher, F.R.I.C., F.1nst.F. A discussion on “The Identification of the New Permitted Food Colours” was opened by P. S. Hall, F.R.I.C. MICROCHEMIS’TRY GROUP THE sixteenth London Discussion Meeting of the Group was held at 6.30 p.m. on Wednesday, October 15th, 1958, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4. The Chair was taken by Dr. G. F. Hodsman, 13.Sc., A.1nst.P. A discussion on “The Role of the Microchemist in Industry” was opened by C. Whalley, B.Sc., F.R.I.C., and G. Ingram, A.R.I.C. BIOLOGICAL METHODS GROUP AN Ordinary Meeting of the Group was held at 6.30 p.m. on Thursday, October 9th, 1958, in the restaurant room of “The Feathers,” Tudor Street, London, E.C.4. The Chair was taken by the Chairman of the Group, Dr. S. EL Kon, F.R.I.C. A discussion on “Strategy in the Assessment of Disinfectants” was opened by G. Sykes, M.Sc., F.R.I.C.

ISSN:0003-2654    

DOI:10.1039/AN9588300598

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

600 The TIMMS, KONRATH AND CHIRNSIDE THE DETERMINATION OF [Vol. 83 Determination of Impurities in Carbon Dioxide Gas Chromatography, with Special Reference to Coolant Gas for Nuclear Reactors BY D. G. TIMMS, H. J. KONR.ATH AND R. C. CHIRNSIDE (Research Laboratories of the General Electric Company Limited, Wernbley, England) It has been shown that, with a 25-ml sample, hydrogen, argon, oxygen, nitrogen, methane and carbon monoxide present at levels as low as 5 to 20 p.p.m. in carbon dioxide can be determined by a gas-chromatographic method. Special features of the technique are the use of a molecular sieve as the solid adsorbent, the high speed of analysis and the use of a katharometer of high sensitivity. IT is necessary to determine the impurities in the bulk supplies of carbon dioxide supplied for use as coolant in a gas-cooled reactor and also to detect and determine the level of these impurities and any others that may be present while the reactor is in operation.The main problem is the detection and determination of small concentrations of per- manent gases. These might normally include hydrogen, oxygen, argon, nitrogen, carbon monoxide and methane in the range 10 to 3000 p.p.m. v/v. As argon can become radioactive under irradiation, it may be necessary to detect this at even lower levels, say, 1 p.p.m. At present, the mass spectrometer is in use for these analyses, and, although we have no direct experience of the merits or demerits of the technique for this particular purpose, it seemed likely that a reliable alternative method would be of considerable interest, par- ticularly if it were cheaper and simpler to operate than the mass spectrometer.Classical methods of gas analysis, apart from their other shortcomings, are much too insensitive for the purpose. Ideally, an appar,atus is required by means of which the com- position of the gas can be automatically monitored, the different impurities continuously resolved and measured and the values for the measurement presented directly. It should be reliable and give results that are reproducible and of reasonably high accuracy. In some circumstances the infra-red gas analysers commercially available readily meet certain of these requirements; unfortunately, a number of the gases in which we are particularly interested cannot be determined in this way, since they have no characteristic infra-red absorption spectra.This is true, for example, of argon, nitrogen, oxygen and hydrogen.Nov., 19581 IMPURITIES IK CARBON DIOXIDE BY GAS CHROMATOGRAPHY 601 We have therefore chosen to investigate the feasibility of analysing the coolant gas for impurities by means of gas chromatography. Although by far the greatest developments have been in gas - liquid partition chromatography, introduced by James and Martin in 1952,l gas-adsorption chromatography in some form is of longer standing. Originally, “displacement” techniques were devised by Claesson,2 in which the components of a mixture are first adsorbed and then displaced successively from the solid phase by a more strongly adsorbable gas or vapour introduced into the carrier-gas stream.Later, elution techniques were used by JanAk3 in Czechoslovakia, Ray“ in England and Patton, Lewis and Kaye5 in the U.S.A. In these, the gases are reversibly adsorbed on the solid phase and are separated by virtue of their different adsorption coefficients. The elution technique would seem t o be essential if any rapid separation of the per- manent gases is to be achieved, In a series of paper^,^ JanAk has described the application of this technique to the separation of a large number of gases, and, for example, to the analysis of mine gases. His technique involves the use of carbon dioxide as carrier gas, which is subsequently absorbed in alkali in a nitrometer. The gases that have been separated from the column are measured volumetrically.The chief adsorbents used have been activated charcoal, silica gel and alumina, but these have not been wholly satisfactory for the separation of permanent gases; although charcoal has been used with moderate success, it gives a poor separation of oxygen and nitrogen. In the face of this difficulty and stimulated by some comments of van der Craats during the discussion at the Symposium on Vapour Phase Chromatography in 1956,6 it was decided to investigate the use of molecular sieves as solid adsorbents for our particular problem. We were encouraged to think that they might be of particular value, because Kyryacos and Boord’ had shown in another context that the permanent gases could be separated very effectively on a column with a molecular sieve as adsorbent.EXPERIMENTAL ADSORBENTS- It was mentioned earlier that charcoal had been used by other workers for the separation of the permanent gases, apparently with only moderate success. Our initial experiments were carried out on activated charcoal, but, with a short column, only a partial separation of oxygen and nitrogen could be achieved. We have subsequently confirmed experimentally that hydrogen, oxygen and nitrogen are separated more effectively on molecular sieves than on charcoal. Of the three grades of molecular sieve commercially available-Linde 4A, 5A and 13X -experiment showed that, although both 5A and 13X are effective, grade 5A gives the best separation, and most of the subsequent work has been carried out with this material. blolecular sieves are synthetic zeolites from which the water of constitution has been removed to leave a lattice containing holes of molecular dimensions.Polar compounds are strongly adsorbed and carbon dioxide in particular is de-sorbed only slowly from a molecular sieve. It is not possible, therefore, to effect a rapid direct separation and determination of the different impurities with which we are concerned and which are present in the carbon dioxide in low concentration. This difficulty has been readily overcome by passing the gas first through a soda lime tube to remove the carbon dioxide quantitatively; only the impurity gases pass into the column, from which they can be rapidly eluted and a complete analysis effected in a few minutes. Moisture will de-activate the molecular sieve and must also be removed from the gases entering the column ; this too is absorbed chemically by means of magnesium perchlorate.Any moisture that may get through will give rise to tailing, and this gives an immediate warning of the need to replace the desiccant. The need for the prior removal of carbon dioxide might seem at first sight a disadvantage, but in one important respect it simplifies the subsequent procedure, for if the carbon dioxide is absorbed, it becomes possible to carry out the analysis with carrier gases of ordinary commercial purity. If carbon dioxide were allowed to enter the column, it would displace from the adsorbent any impurity gas that might be present in the carrier gas. The impurities so displaced would then be eluted from the column and would be recorded as apparent impurities in the carbon dioxide.It would be essential therefore to use only carrier gases of very high purity.602 TIMMS, KONRATH AND CHIRNXDE THE DETERMINATION OF [Vol. 83 CARRIER GASES- It was found by experiment that, on a column 6 feet long containing granules of molecular sieve 5A, a satisfactory separation of hydrogen, oxygen and argon (together), nitrogen, methane and carbon monoxide can be effected. In our particular work it was found that the maximum amount of information could be obtained at one time by the use of either h,ydrogen or argon as the carrier gas. However, within the range of experimental conditions we have tried, it was not possible to separate oxygen from argon. When argon is used as the carrier gas, i%ny argon that may be present in the sample is not detectable and does not interfere with the oxygen signal; hydrogen, oxygen, nitrogen, methane and carbon monoxide can, however, be separated and detected or determined.When hydrogen is used as the carrier gas, it is possible to achieve a greater general sensitivity, but argon and oxygen are not separable and they appear together as a single peak. The argon can therefore be determined if first argon and then hydrogen is used as carrier gas, but only as a difference figure. An alternative method that we have investi- gated involves the use of De-oxo catalyst*; the gas remaining after absorption of the carbon dioxide is passed through a short column containing crushed pellets of De-0x0, the oxygen is removed and a signal for argon alone is obtained.It is understood that the determination of argon in coolant gas is of special importance, and, if the argon should be present in very low concentration, the direct method just described would be preferable to the difference method. It could be carried out conveniently on a separate apparatus. APPARATUS- METHOD The apparatus required for gas - solid chromatography consists of- (i) a regulated supply of carrier gas, (ii) a gas-sampling system, (iii) a chromatographic column, (iv) a thermostatically controlled heating jacket for the ( v ) a detector and measuring equipment. To columns column, and Fig. 1. Gas-samplin: system. Scale: 1 to 8 (i) Carrier gas supply-Hydrogen and a.rgon are used for this particular application of the gas-chromatographic technique ; they are obtained from high-pressure gas cylinders.A gas pressure of 40 lb per sq. inch is provided by the usual type of cylinder regulator and it is further reduced and accurately regulated at 3 to 10 lb per sq. inch by a precision gas regulator (Negretti & Zambra or Norgren). The supply to the columns is finally regulated * De-oxo is a platinum catalyst marketed by the Baker Platinum Company, and, as the name implies, oxygen IS removed by catalytic reaction with hydrogen t o form water.Nov., 19581 IMPURITIES IN CARBON DIOXIDE BY GAS CHROMATOGRAPHY 603 by means of fine-adjustment needle valves V,, V, and V, (see Fig. 1). Valves V, and V, serve to equalise the gas flow through each column. The carrier gas is left flowing, even when the apparatus is not in use, in order to prevent atmospheric moisture from entering the columns.(ii) Gas-sampling system-This consists of a gas-sampling valve and a carbon dioxide absorption tube. The sampling valve shown in Fig. 2 provides a means of introducing a sample into the stream of carrier gas with the minimum interruption of flow and with no risk of contamination from the atmosphere. With the gas channels in position A, carrier gas passes directly to the column while the sample loop is swept with sample gas. On rotation of the channels to position B, the carrier gas passes through the sample loop and sweeps the sample into the column. The main flow of sample gas meanwhile passes out to the atmosphere. Fig. 2. Gas-sampling valve.Scale: Full size Since this valve was designed, we have learned that valves operating on a similar principle have been available commercially for some time. The carbon dioxide absorption tube is made from 20 s.w.g. copper tubing, 28 inches long and $g inch external diameter. It is packed for about three-quarters of its length with fresh 14 to 20-mesh soda lime. The exit end of the tube is packed with a mixture of 2 parts by volume of 16 to 36-mesh magnesium perchlorate and 1 part of 16 to 36-mesh crushed firebrick. I t is emphasised that the soda lime should contain an appreciable propor- tion of moisture, about 15 to 20 per cent., as it was found in the course of this work that dry soda lime will not absorb carbon dioxide quantitatively; indeed, if it is very dry, no absorption appears to take place.As a consequence, it is necessary to refill or replace the absorption tubes daily, even if no carbon dioxide has been passed through the apparatus, for the stream604 TIMMS, KONRATH AND CHIRNSIDE : THE DETERMINATION OF [Vol. 83 of carrier gas, which we prefer to keep flowing through the apparatus, slowly removes moisture from the soda lime and eventually makes it ineffective. Soda asbestos has been found to be completely inactive under these particular conditions; it appears to be even more sensitive to the dryirig effect of the carrier gas than is soda lime. The magnesium perchlorate serves to prevent moisture from passing into the column, where it would de-activate the molecular sieve. The crushed firebrick is used to prevent the hydrated perchlorate from blocking the absorption tube.The amount of magnesium perchlorate used is obviously insufficient to absorb all the moisture present in the soda lime, but serves to prevent moisture from entering the column over a period of a t least 1 day under normal conditions of use. (iii) Column-Two interchangeable columns are used, one for the separation and the other to equalise the gas paths. Both consist of 6-foot lengths of &inch external diameter 20 s.w.g. stainless-steel tubing packed with Linde 5A molecular sieve. Copper tubing was used originally, but it was found that, when hydrogen was used as carrier gas, some reaction took place on the copper surfaces and gave rise to anomalous results for oxygen. When heating is provided by means of a vapour jacket, we have used simple U-shaped columns, but coiled columns are used in a more compact form of the apparatus in which a hot-air bath is provided.From gas-sampling system A = Sunvic thermostat, type TS.3 B = Serum cap C = Katharometer D = Column (approxi- mately 5 turns of 4-inch diameter) $ 8 1 I.$ @ n,,,,,,,,, < ,I,,,,,,, <,# l,,,,,,, n l ' r l , l l r r m l l l , l l l , , , , , , , , , , , Fig. 3. Section through heating jacket With the straight column it is customary t o activate the molecular sieve before packing by heating it in air to 350" C for a few hours, but it is possible to activate or regenerate a packed column by heating it to 350" C for about 3 or 4 hours while it is being purged with a stream of dry air. The coiled columns are packed, before they are bent, with granules of 36 to 52-mesh molecular sieve and the ends are plugged with glass-wool; they are then coiled round a 4-inch mandrel and the ends are bent to shape.(iv) Heating jacket-Two types of heating jacket have been used, a simple steam jacket and a thermostatically controlled air jacket. The steam jacket has certain advantages for laboratory use; in particular, the column and t'ne katharometer block may be heated quickly t o the operating temperature (100" C) and temperature fluctuations are negligible.Nov., 19.581 IMPURITIES IN CARBON DIOXIDE BY GAS CHROMATOGRAPHY 605 The air jacket is provided by means of an electrically heated aluminium pot, 6 inches in diameter, with a flanged end 8 inches in diameter.The coiled column and the katharometer block are located in the pot as shown in Fig. 3. -3 oe 0'205" diam. A Filament R, R, = 30-ohm resistors R3 = 10-ohm resistor R4 = 20-ohm 10-watt potentiometer K1, K, = Katharometer filaments G = 2.5-mV recording voltmeter Fig. 4. Construction and mounting of katharometer : ( a ) , section through one channel; ( b ) , section showing double-channel arrangement; (c), bridge circuit; ( d ) , filament mounted on copper - glass seal The pot is heated by means of Nichrome wire wound on glass tape round the outside It was wound originally with a single coil, but this was found to give rise to of the pot.606 TIMMS, KONRATH AND CHIRNSIDI3: THE DETERMINATION OF [Vol. 83 electrical noise. By replacing the single coil with a non-inductive winding consisting of 40 turns of 0.0142-inch diameter Nichrome wire, mains-borne noise has been reduced to a minimum, The current is supplied through a Sunvic hot-wire relay operated by a thermo- stat that dips into the pot.The dissipation of the winding is about 300 watts at 240 volts. The temperature of the pot can be adequately controlled, but the rate of heat transfer to the katharometer block is low and the time taken to reach equilibrium (2 to 3 hours) greatly exceeds that required by the column in the steam jacket (4 hour). This problem could be largely overcome by pre-heating the katharometer block by means of an auxiliary heating coil. A layer of lagging material, eg., cotton-wool, is required over the tops of the heating jackets to minimise thermal e.m.f.s in the leads from the katharometer. (n) Detector-A sensitive katharometer is used as the detector.It is made from a copper block, 2 inches x 21 inches x 4 inches, through which two &inch diameter gas channels are drilled, a reference and a detector channel; these operate under identical conditions. Tungsten filaments having a resistance of about 30 ohms a.t 20" C are mounted on copper - glass seals and are held in the gas channels under slight tension by means of grooved sapphire or ceramic pegs. Details of the construction and mounting of the katharometer and of the associated circuitry are shown in Fig. 4. It has been found convenient to use a recording millivoltmeter that has a range of 0 to 24mV. PROCEDURE- The apparatus is calibrated by the injection of small volumes of the appropriate gas through a serum cap on the inlet to the column and measurement of the height of the peak produced on a recording millivoltmeter in the katharometer circuit, A suitably small volume of gas for calibration purposes may be obtained from the dead space in the end of a syringe.A tuberculin syringe of about 1-ml capacity is flushed with the gas and then, with the needle of the syringe close to the serum cap on the column inlet, the plunger is slowly pushed down to its full extent. The needle is inserted im- mediately into the serum cap, the plunger is withdrawn to the 1-ml mark so as to draw in carrier gas and is then quickly pushed down again to its fullest extent. The gas in the dead space is thus diluted with carrier gas and eFfectively introduced into the column.The syringe is calibrated by weighing it before and after flushing with water. The volume of the dead space in the syringe is about 45 cubic millimetres and a correction must be made for the gas remaining in this space. We have used the following gases for purposes of calibration- The pegs are located symmetrically by means of grub screws. Oxygen and nitrogen-Air. Hydrogen-2 per cent. of hydrogen in air. Methane-Commercial, first passed through an absorption tube to remove carbon dioxide Carbon monoxide-Commercial. With methane and carbon monoxide, corrections have to be made for hydrogen, oxygen and nitrogen present as impurities. and moisture. TABLE I APPROXIMATE AMOUST OF IMPURITY REQ'LTIRED TO GIVE A 1-mm DEFLECTION Amount of impurity with Amount of impurity with Impurity argon as carrier gas, hydrogen as carrier gas, P.P.m.(./V) P,P.m. (v/v) . . 0.5 - 3 Hydrogen . , . . Argon . . .. * . . . Oxygen . . . . . . . . 5 3 Nitrogen . . .. . . 10 3 - Methane . . . . . . 5 7 Carbon monoxide . . .. 20 6 An alternative method of calibration involves a direct comparison of the unknown sample with one of known composition. The reference gas is made up to be similar in com- position to the sample under test. This method. has the advantages that no corrections for temperature and pressure need be applied and the time required for calibration is reduced.NOV., 19581 IMPURITIES IN CARBON DIOXIDE BY GAS CHROMATOGRAPHY 607 The apparatus has been calibrated for these impurity gases with both argon and hydrogen as carrier gases and it has been found that over the range covered there is a linear relationship between peak height and concentration.It will be appreciated that all calculations must include corrections for temperature and pressure unless the calibration is carried out at the same time as an analysis. The sensitivity is determined by a number of factors-katharometer wire temperature, nature of carrier gas, size of sample, etc. Under our conditions of operation and with a 25-ml sample, the approximate amount of each impurity required to give a 1-mm deflection is shown in Table I. RE s u LTS At this stage of the development of nuclear power plant, trials of these proposed methods of analysis have been restricted to samples of commercial-quality carbon dioxide and to pure carbon dioxide to which various impurities have been added in known concentrations.COMMERCIAL CARBON DIOXIDE- Two different rates of withdrawal were used from each cylinder; it will be noted that there were significant differences in the concentrations of the impurities in the two samples from either cylinder. This effect is due to a different distribution of impurity gases between the gas and the liquid phases in the cylinder. At fast rates of withdrawal the composition of the gas would be expected to approach the composition of the liquid phase; at slow rates it may resemble more closely the equilibrium composition of the gas phase. The results of one examination with argon as carrier gas are shown in Table 11.TABLE I1 DETERMINATIOS OF IMPURITIES IN COMMERCIAL CARBOY DIOXIDE FROM CYLINDERS Column temperature, 100" C Argon flow rate, 50 ml per minute Katharometer current, 300 mA Sample volume, 25 ml Samples were taken from small cylinders supplied by two manufacturers. .\mount of impurity found in carbon dioxide from cylinder A at a rate of Amount of impurity found in carbon dioxide from cylinder B a t a rate of Impurity withdrawal of- withdrawal of- I A > f A > 100 ml per minute, 3000 ml per minute, 100 ml per minute, 3000 ml per minute, p.p.m. p.p.m. p.p.m. p,p.m. Hydrogen . , 9.5 11 110 60 Oxygen . . 85 not detected 1500 1000 Nitrogen , . 500 360 6600 4400 The input t o the recorder was attenuated where necessary. SYNTHETIC CARBON DIOXIDE MIXTURE- Impurities were added in known amount to the gas obtained from solid carbon dioxide; the levels of impurity were of the same order as those expected to be present in the coolant from a nuclear power plant.The main analysis was carried out with argon as carrier gas and the results are shown in Table 111. TABLE I11 DETERMINATION OF IMPURITIES IN SYNTHETIC CARBON DIOXIDE MIXTURE Column temperature, 100" C Argon flow rate, 30 ml per minute Katharometer current, 300 mA Sample volume, 25 ml Impurity iZmount of impurity added, Amount of impurity found, Peak height, P.P.m. (v/v) P P.m. (v/.9 mm Hydrogen , . . . 41 40 85 Oxygen . . . . 101 100 21 Nitrogen . . . . 390 400 49 Methane . . .. 175 180 35 Carbon monoxide 1260 1280 69608 TIMMS, KONRATH AND CHIRNSIDE: THE DETERMINATION OF [Vol.83 The analysis of a sample similar in composition was also carried out with hydrogen as carrier gas. For this analysis the apparatus was modified by the insertion of a De-oxo tube between the carbon dioxide absorption tube and the separating column on one side of the apparatus. The De-oxo pellets remove oxygen and so allow the direct determination of argon. Carbon monoxide is also removed during this process, so that the analysis is restricted to the determination of argon, nitrogen and methane. However, by reversing the functions of the two columns, and thus obviating the need to remove the De-oxo catalyst tube, nitrogen and methane, and also carbon monoxide and argon plus oxygen can be determined in the other side of the apparatus. By the use of both columns in this way the full analysis of the mixture, including argon, was carried out.The results are shown in Table IV. The actual chromatograms obtained during this and the analysis in which argon was used as carrier gas are shown in Fig. 5 . Fig. 5, Chromatograms of impurities in a prepared sample of carbon dioxide: ( a ) , argon used as carrier gas: ( b ) , hydrogen used as carrier gas, oxygen removed with De-oxo catalyst TABLE IV DETERMINATION OF IMPURITIES IN SYNTHETIC CARBON DIOXIDE MIXTURE Column temperature, 100" C Hydrogen flow rate, 40 ml per minute Katharometer current, 750 mA Sample volume, 25 ml Impurity Amount of impurity added, Amount of impurity found, Peak height,* p.p.m. (v/v) P.P.m. (v/v) mm Oxygen . . . . 106 100 40 Xitrogen . . . . 405 400 141 hlethane .. . . 173 170 28 Carbon monoxide 1250 1240 241 * The input of the recorder was attenuated in order to fit the peak for carbon monoxide into the Argon( . . . . - 5 7 3.5 chromatogram.Nov., 19581 IMPURITIES IN CARBON DIOXIDE BY GAS CHROMATOGRAPHY 609 DISCUSSION OF THE METHOD The work described represents a preliminary survey of the potential application of the principle of gas chromatography to the analysis of reactor coolant gases. Although the experimental work has been restricted to synthetic mixtures of carbon dioxide with minor concentrations of added impurity gases, the results suggest that the method should be of value for the analysis of coolant gases. It is simpler and more rapid than mass spectrometric measurements and we believe it may be sufficiently sensitive. The time required for a complete analysis is inversely proportional to the rate of flow of carrier gas, but some loss of sensitivity and resolution occurs at high rates of flow. It has been found experimentally that the optimum performance of the apparatus described is obtained at a flow rate of about 30 t o 40 ml per minute. Under these conditions, a complete analysis can be carried out in about 8 minutes. The accuracy with which any particular impurity can be determined is finally set by the volume of sample taken. Most of the analyses have been carried out on 25-ml samples of gas, but this could be increased with advantage for the determination of argon. The disadvantage of a larger sample is the need to absorb larger amounts of carbon dioxide and thus to require more frequent replacement of the absorption tubes. Experiments now in progress with more sensitive methods of detection may provide a better solution to the problem. REFERENCES 1. 2. 3. 4. 5. 6. 7. James, A. T., and Martin, A. J. P., Analyst, 1952, 77, 915. Claesson, S., Ark. Kemi. Min. Geol., 1946, 23A, No. 1. Janak, J., Chem. Listy, 1953, 47, 464, 817, 828, 837, 1184, 1190, 1348 and 1476. Ray, N. H., J . Appl. Chem., 1954, 4, 21 and 82. Patton, H. W., Lewis, S. J., and Kaye, W. J., Anal. Chem., 1955, 27, 170. Desty, D. H., Editor, “Vapour Phase Chromatography” (Proceedings of the Symposium sponsored by the Institute of Petroleum, 1956), Butterworths Scientific Publications, London, 1957. Kyryacos, G., and Boord, C. E., Anal. Chem., 1957, 29, 787. Received September Sth, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300600

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Nov., 19581 IMPURITIES IN CARBON DIOXIDE BY GAS CHROMATOGRAPHY 609 The Determination of Molybdenum in Uranium and in Molybdenum - Uranium and Molybdenum - Niobium Mixtures BY C. 0. GRANGER (Research and Development Branch, U.K.A .E.A., Culcheth, n y . Warrington, Laws.) An improvement in the spectrophotometric determination of molybdenum by means of its complex with toluene-3 : 4-dithiol is described. This consists in forming the complex in an aqueous - solvent medium in which it is soluble, and therefore avoids the necessity for solvent extraction. When applied by difference, either in the presence or absence of uranium, the procedure has a coefficient of variation of k0.16 per cent. and can be applied to uranium - molybdenum alloys containing 0-2 per cent. or more of molybdenum.Alternatively, if a non-difference procedure is used, concentrations of molyb- denum in uranium down to 1 p.p.m. can be determined. With slight modification, the procedure is applicable to the determination of molybdenum in its alloys with niobium. The effects of impurities and of variations in temperature and acidity are discussed. A NEED arose for a method by which variations of about 1 per cent. in the molybdenum content of uranium - molybdenum alloys could be detected in samples containing only about 1 mg of molybdenum. A review of the literature indicated that established spectrophoto- metric methods, although not sufficiently precise, could be modified to suit the analytical requirements, especially if applied by difference. Toluene-3 : 4-dithiol (dithiol) , thiocyanates, phenylhydrazine and hydrogen peroxide were considered as possible developing agents, but the first-named seemed to be the most convenient, and experiments were confined to this compound.610 GRANGER: THE DETERMINATION OF MOLYBDENUM IN URAXIUM AND [Vol.83 EXPERIMENTAL Preliminary tests were made with a method in which the molybdenum - dithiol complex was precipitated, together with excess of reagent, in an aqueous hydrochloric acid medium and extracted by carbon tetrachloride, the optical density of the solvent extract being measured against the pure solvent. Recoveries by this method were not sufficiently con- sistent. Larger amounts of molybdenum were therefore taken, the optical density of the solvent extract being measured by difference against a similarly prepared molybdenum standard.Although this reduced the coefficient of variation from +la6 to jO.9 per cent., it was thought that a further reduction might result if the solvent-extraction stage could be eliminated. ELIMINATION OF SOLVENT EXTRACTION- Water-soluble solvents were added to the aqueous reaction mixture in an attempt to dissolve the molybdenum - dithiol complex, a!; well as any precipitated reagent, without separation of a second liquid phase. Ethanol and methanol did not yield clear solutions and acetone produced so much heat (presumably by reaction with hydrochloric acid) that its use was undesirable in view of the reputed instability of the reagent. With n-butyl alcohol, the resulting solution was clear and little heat wa.s evolved.n-Amy1 alcohol behaved similarly, but an extremely high concentration of hydrochloric acid and an inconveniently low water content were necessary to prevent separation of a second liquid phase. Ethyl methyl ketone, particularly at increased hydrochloric acid concentrations, yielded a single phase, but the yellow background colour of the solution was more intense than when the other solvents were used and appeared to be dependent on t'he concentrations of other reagents. When used in a difference technique, without solvent extraction, twenty 'determinations gave a coefficient of variation of k0.5 per cent. This procedure was, therefore, a significant improvement on the solvent- extraction procedure; it was also more rapid. n-Butyl alcohol was chosen as the most suitable solvent. SOLVENT AND ACID CONCENTRATIONS- Solutions of the complex ceased to obey the Beer - Lambert law at a concentration of about 60 pg per 60 ml, i.e., at an optical density of about 1.2 in 4-cm cells.I t seemed probable that, if this limit could be raised still further, improvements in precision would result. The concentration of hydrochloric acid was varied ; higher concentrations led to an increase in sensitivity, but not in reproducibility. When sulphuric acid was used in place of hydrochloric acid, the results were similar 'but less consistent. There was, however, at higher acidities than could be attained with hydrochloric acid, a decrease in the intensity of the green colour of the complex and even failure to form a colour, particularly when the solution was slightly warm.This suggested that dithiol is decomposed at high acidities and that temperatures should be kept low. When a solution that had failed to form a colour was diluted to an acidity at which development of the complex usually occurred, no colour was produced until a little further dithiol was added, thus confirming decomposition of dithiol at high acidity. The order in which the reagents were added was now changed, most of the 12-butyl alcohol being added before the dithiol. The concentration of the acid in contact with dithiol was thus greatly reduced, although the full final optimum acidity required for complete colour development was still maintained. This resulted in an increase in both degree and rate of colour formation.The effect of variation in acid concentration was again investigated, the new order of addition of reagents being used. TO 22-pg portions of molybdenum (as chloride) in 10ml of water were added different amounts of hydrochloric acid, sp.gr. 1.18, and the volumes were made up to 45 ml with n-butyl alcohol. The solutions were cooled to room temperature, and 4 ml of dithiol reagent solution were added to each. Each solution was diluted to 50 ml with n-butyl alcohol, and its optical density was measured in 2-cm cells with a Unicam spectrophotometer at 680 mp. The results were as follows- Amount of molybdenum present, pg . . . . Nil Nil 22 22 22 22 22 22 22 22 22 Amount of hydrochloric acid added, ml . . 10 26 10 12 14 16 18 20 22 24 26 Optical density . . . . 0.000 0.002 0.421 0.430 0.433 0.437 0.439 0.439 0.439 0.439 0.378Nov., 19581 611 From these results, it can be seen that the acid concentration should be kept between 16 and 24 ml; 20 ml were therefore used in all subsequent work.STABILITY OF THE COMPLEX- Development of the complex is complete in about 15 minutes and the optical density remains unchanged for at least 24 hours in the absence of uranium. The same is generally true in the presence of up to 0 6 g of uranium, but traces of opalescence have twice been observed on prolonged standing. However, neither opalescence nor change in optical density has been observed during a full working-day. IN MOLYBDENUM - URANIUM AND MOLYBDENUM - NIOBIUM MIXTURES EFFECT OF TEMPERATURE- When formed at room temperature, as in the final procedure, the complex is stable towards temperature changes.For example, when the temperature was raised to 50" C for 1 hour, no alteration in optical density was observed when re-measured at room temperature. The liquid medium in which the complex is formed has a thermal cubical expansion of 0.5 per cent. per "C, about five times that of water. Optical-density measurements at 680 mp, however, show a decrease of only 0.25 per cent. per "C when the temperature is raised, owing, presumably, to a reversible increase of 0.25 per cent. per "C in the absorption of the complex. OPTIMUM COXCEXTRATIOX OF MOLYBDEXUM FOR A DIFFERENCE PROCEDURE- When the final procedure was used, figures for the optical density of the complex over a wide range of concentrations were obtained by comparing the optical density at each level with that at the next lowest concentration, the lowest concentration of all being compared with a reagent blank solution.In this way, conformity to the Beer - Lambert law over the range 0 to 120 pg was demonstrated, with a deviation at 140 pg of 0.9 per cent. (see the first three columns of Table I). TABLE I COMPARISON OF OPTICAL DENSITY AND RELATIVE ACCURACY The optical-density measurements were made in 2-cm cells at 680 m p Mean Concentration concentration difference Relative Molybdenum Optical- of solutions between solutions accuracy concentration, Optical density compared (C), compared (AC), pg per 50 ml density difference (AA) p g per 50 ml pg per 50 ml (Z c) 0 25 50 75 100 120 140 160 180 200 - 0.250 0.501 0.752 1.001 1.199 1.389 1.525 1.642 1.750 0.250 0.251 0.251 0.249 0.198 1.190 0.136 0.117 0.108 12.5 37.5 62.5 87.5 110 130 150 170 190 25 25 25 25 20 20 20 20 20 0.125 0.377 0.628 0.871 1.089 1.235 1.020 0.995 1.026 To ascertain if an increase in precision was likely to result when the procedure was applied by difference at concentrations above 120 pg, values of a relative accuracy functionlp2 were calculated from these results.The values of this function- & C where AA is the increment of optical density for an increase AC in concentration C, are shown in Table I.612 [Vol. 83 For solutions that obey the Beer - Lambe:rt law, the relative accuracy is equal to the optical density. (The relative accuracy figures in Table I would have to be compared with the optical densities a t the mean concentrations of the solutions compared.) If, however, as the concentration increases, deviation from linearity occurs owing to a continuous decrease in absorption, the value of the function falls below that demanded by the Beer - Lambert law.However, the value of the function will continue to increase until the decrease in absorption nullifies any gain caused by increasing concentration ; beyond this, the value falls again. At this point of maximum accuracy the best precision is theoretically to be expected. In practice, consistent results could not be obtained a t concentrations above those at which the Beer - Lambert law was obeyed. For this reason it was decided that optical-density measurements would be made by difference between 100 and 11Opg of molybdenum per 50 ml, i.e., at optical densities of 2.0 to 2.2 in 4-cm cells.This range is unnecessarily narrow for most purposes, but was dictated by the analytical requirements, for which only the full precision of the method seemed likely to be satisfactory. EFFECT OF IMPURITIES- The effects of the major impurities normally to be found in uranium and uranium- molybdenum alloys were ascertained by applying the proposed method to known amounts of the impurities in the absence of both uranium and molybdenum. The results are shown in Table 11. GRANGER: THE DETERMINATION OF MOLYBDEYUM IN URANIUM AND TABLE I1 EFFECT OF 1,hlPURITIES The optical-density measurements were made in 4-cm cells a t 680 mp after the solutions had been set aside for 90 minutes Amount of Error (as Element element present, pg Optical density molybdenum), pg Iron .. . . . . .. 1120 Nil Xi1 Zinc . . .. . . * . 1000 0.027 1.4 Titanium . . * . .. 105 Nil Nil Vanadium . . . . .. 1000 0.020 1.0 Copper . . .. * . 1000 0.007 0.4 Tin . . . . * . . . 100 Xi1 Nil Cobalt . . . . . . 100 0.006 0.3 Nickel . . . . . . 500 0.004 0.2 Lead . . .. ,. 100 0.001 <0.1 Tungsten . . . . . . 200 0.028 1.4 Tungsten* . . .. . . 200 0.100 8.0 Tungsten* . . . . .. 200 0.2347 11.5 Tungsten plus 2 g of citric acid 200 0.010 0.5 * Not cooled t o room temperature before addition of dithiol reagent solution 7 Optical density measured after solution had been set aside overnight. R~ETIIOD REAGEXTS- beneath the surface of 500 ml of 1 per cent.w/v sodium hydroxide solution. with a glass rod and stir until dissolution is complete. 7 ml of 76 per cent. thioglycollic acid. a refrigerator. Dithiol reagent solution, 0.2 per cent. w/i~-Break a 1-g phial of toluene-3 : 4-dithiol Crush the solid Add slowly, with continuous stirring, Store the solution in small air-tight containers in Hydrochloric acid, s9.g. 1*18-Analytical-reagent grade. n-Butyl alcohol-Analytical-reagent grade. Molybdenum stock reference solutions-D issolve, separately, 15003 and 1.6503 g of analytical-reagent grade molybdenum trioxide, which has been freshly ignited at 500" to 525" C, in 2 M ammonia solution and gently evaporate the solutions t o small volume t o expel excess of ammonia. Cool, and dilute each solution to 1 litre. 1 ml = 1000 and 1100 pg of molybdenum, respectively.Molybdenum working Yeference solutions-Dilute aliquots of the stock reference solutions until they contain 10 and 11 pg of molybdenum per ml, respectively.Nov., 19581 PREPARATION OF SAMPLE SOLUTIONS- For samples containing less than 5 per cent. of molybdenum, take a weight of sample such that, when dissolved and conveniently diluted, a 10-ml aliquot of the solution contains 100 to 11Opg of molybdenum for the difference procedure or up to 30pg of molybdenum for comparison with water. The presence of at least 0.5g of uranium per 10ml can be tolerated in the difference procedure and 1 g in the alternative procedure. Digest the weighed sample with 25 per cent. v/v hydrochloric acid until all reaction has ceased. Add 100-volume hydrogen peroxide dropwise, with swirling, until the solution is clear.Evaporate, without boiling, just to dryness. To the residue, which is normallygreen or blue, add 10 ml of 25 per cent. v/v hydrochloric acid, and warm to ensure complete dissolutioii of molybdenum trioxide (water alone effects dissolution if the molybdenum content of the sample is less than 0.5 per cent.). Filter the solution through a 5 6 c m Whatman No. 40 filter-paper, and wash with 50 ml of 5 per cent. v/v hydrochloric acid. Use calibrated appara- tus to dilute the solution to a concentration of 100 to 110 pg of molybdenum per 10 ml for the difference procedure or up to 30 pg of molybdenum per 10 ml for the alternative procedure. Samples containing more than 5 per cent. of molybdenum are more difficult to dissolve than the lower alloys.At the 12 per cent. level, use 50 per cent. in preference to 25 per cent. hydrochloric acid both for the initial decomposition of the alloy and for dissolution of the residue after evaporation. Should the residue fail to dissolve completely, re-evaporate just to dryness, boil with water to dissolve uranyl chloride, add 5 g of sodium carbonate per 2 g of alloy, and warm. (In a few instances, some insoluble matter has remained after this treatment, but this has been shown not to contain significant amounts of molybdenum.) PROCEDURE- By pipette, place a 10-ml aliquot of the sample or standard molybdenum solution in a 50-ml calibrated flask. The aliquot should contain 100 to 110 pg of molybdenum if measurements are to be made by difference, but not more than 30 pg if measurements are to be made against water.Add 20 ml of hydrochloric acid, sp.gr. 1-18, and mix. (The total acid content should be between 19 and 21 ml of hydrochloric acid.) Add 15 ml of n-butyl alcohol from a measuring cylinder, and mix. Cool to room temperature to minimise inter- ference from tungsten. Add 4 m l of dithiol reagent solution, and mix. Adjust the tem- perature of the solution to 20" C by standing the flask in a constant-temperature bath for 30 minutes, and then dilute to the mark with n-butyl alcohol. If measurements are to be made by difference, compare the optical density of the solution in 4-cm cells a t 680 m p with that of a reference solution containing 100 pg of molybdenum, which has been prepared simultaneously in the same manner as the sample.Alternatively, measure the optical density in 4-cm cells at 680 mp against water or a reagent blank solution. If a Unicam spectrophotometer is used, the slit width must be such that a motion of the dial corresponding to 0.005 optical-density units produces a galvanometer deflection of 2 to 24- divisions. CALIBRATION- The high temperature coefficient of thermal expansion of solutions of the complex (0.5 per cent. per "C) and the (reversible) decrease in optical density with increase in tem- perature (0.25 per cent. per "C) make control of temperature important if the most precise results are to be obtained. Sample and reference solutions should be a t the same temperature a t both the final dilution and measurement stages.Either dilutions should be made a t a fixed temperature, e.g., 20" C as described under "Procedure," and optical densities measured a t as near to that temperature as possible or calibrations should be made at the same time as sample determinations. Provided that steady temperature conditions prevail, the latter alternative virtually overcomes both temperature errors and does not entail, a t least with the difference technique, much extra effort. The following procedure is favoured when measurements are made by difference- Prepare two 100-pg and two 110-pg molybdenum standards simultaneously with the samples. Use one of the 100-pg standards as the reference solution for both samples and all four standards ( i e . , compare the reference standard with itself also).From the average optical-density increment for the 10-pg difference in molybdenum, calculate the calibration factor. I N MOLYBDENUM - URAKIUM AND MOLYBDENUM - NIOBIUM MIXTURES 613 Do not bake.614 GRANGER: THE DETERMINATION OF MOLYBDENUM IN URANIUM AND [VOl. 83 With this procedure, the temperature of the water bath need not be specified and the risk of errors caused by using different slit widths for the sample and calibration measurements is avoided. RESULTS PRECISION EXPERIMENTS WITH THE DIFFERENCE PROCEDURE- Two sets of determinations were carried out under the conditions of the proposed method. In one set, which involved molybdenum only, the optical densities of 100 and 110-pg amounts of molybdenum were compared with that of a reference solution containing 100 pg of molyb- denum, The other set was similar, but uranium was present in most of the test solutions, the reference solution still containing 100 pg of molybdenum and being free from uranium.The results are shown in Table 111. TABLE I11 PRECISION OF THE DIFFERENCE PROCEDURE The optical-density measurements were made in 4-cm cells a t 680 m p Uranium absent Uranium present A I \ 7 7 Amount of Amount of Amount of molybdenum Optical-density molybdenum uranium Optical-density present, pg difference present, pg present, g difference loo* Nil 100' Nil Nil 100 - 0.002 100 Nil 0.005 100 0.003 100 Ni 1 0.007 110 0.198 100 0.5 0.010 110 0.196 100 0.5 0.012 110 0.197 110 0.5 0.207 110 0.200 110 0.5 0.208 110 0.199 110 0.5 0.206 110 0.199 110 0.5 0.207 110 0,199 110 0.5 0.204 110 0.195 110 0.5 0.207 110 0.200 110 0.5 0.209 110 0.197 110 0.5 0.209 - - 110 0.5 0.200 - - 110 0.5 0.208 * Reference :solution.For the figures in Table 111, the mean optical-density difference caused by the presence of 0.5 g of uranium corresponds exactly to the known molybdenum content of the uranium used (0.48 p.p.m.). Statistical analysis of the results indicates that, if sample determinations were to be made in duplicate and the optical-density increment caused by 10 pg of molybdenum were determined by using duplicate 100 and 110-pg standards, a coefficient of variation of 50.16 per cent. could be expected. for the average value of the molybdenum content of the sample. DETERMINATION OF TRACES OF MOLYBDENUM I:X VRANIUM- recovery experiments.of uranium. of 0.48 p.p.m. of molybdenum, was 0.010; that for the reagents was zero. were as follows- Uranium from the same source as in the previous experiment was used in a series of Amounts of molybdenum from 1 to 25 pg were added to 1-g amounts The blank value (optical density) for 1 g of uranium, caused by the presence The results Molybdenum added, pg . . * . .. 1 2 4 6 8 25 Optical density, corrected for blank value 0.019 0.039 0.080 0.120 0.162 0.500 Molybdenum found, pg .. * . . . 0.95 1.95 4.0 6.0 8.1 25.0 The proposed method was, after slight moclification, applied to niobium containing up to 10 per cent. of molybdenum. The alloy was, dissolved in a mixture of hydrofluoric and nitric acids, and the solution was evaporated to dryness.After the residue had been fused with potassium hydrogen sulphate, the melt was dissolved in a 50 per cent. w/v solution APPLICATION TO NIOBIUM ALLOYSNov., 19581 615 of citric acid, and an aliquot was treated by the difference procedure. Calibration factors and recoveries from synthetic mixtures of niobium and molybdenum corresponded closely to those for uranium alloys, CONCLUSIONS The proposed method has several advantages over the normal solvent-extraction pro- cedure for the spectrophotometric determination of molybdenum in uranium with toluene- 3 : 4-dithiol. It is more rapid, more precise and can be applied over a wider range of molybde- num contents. It is a robust method, in which neither acidity nor development time is critical. For the most precise results, however, the effects of temperature cannot be ignored, but errors from this source can be readily avoided. When the difference procedure is used, results as precise as those of a macro volumetric or gravimetric method can be obtained over a wide range. Below the level suitable for measurements by difference, good recoveries down to 1 p.p.m. can be made by using absolute measurements of optical density. Interferences are few, and it should be possible to adapt the method to determinations of molybdenum in a wide range of materials other than uranium. IN MOLYBDENUM - URANIUM AND MOLYBDENUM - NIOBIUM MIXTURES This paper is published by the kind permission of the Managing Director and the Director of Research and Development of the United Kingdom Atomic Energy Authority (Industrial Group). REFERENCES 1. 2. Hiskey, C. F., Anal. Chem., 1949, 21, 1440. Bacon, A., and Milner, G. W. C., Analyst, 1956, 81, 457 Received March 19th, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300609

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

Nov. , 19581 IN MOLYBDENUM - URANIUM AND MOLYBDENUM - NIOBIUM MIXTURES 615 The Colorimetric Determination of Aluminium in Steel with Solochrome Cyanine BY P. H. SCHOLES AND D. VALERIE SMITH (Metallurgy (General) Divisional Laboratories, The British Iron and Steel Research Association, Hoyle Street, Shefield, 3) Eriochrome cyanine R has been used extensively in Germany for the colorimetric determination of aluminium in ferrous materials. An equivalent British dye, Solochrome cyanine R, has been examined in order to establish the best conditions for colour development. The application of Solochrome cyanine R to the analysis of steel has also been studied. A method incorporat- ing a preliminary mercury-cathode separation and then treatment with sodium hydroxide solution is proposed for the determination of aluminium in the range 0.001 to 0.035 per cent.A precision of &O.OOl per cent. is claimed. The range of the method can be extended to cover any concentration of aluminium in plain carbon and low alloy steel. IN present-day metallurgical research it is becoming increasingly important to examine the influence of small amounts of aluminium on the properties of steel. An accurate knowledge of the aluminium content of experimental test samples is an essential pre-requisite for investigations into such problems as grain-size control, the influence of aluminium on the nitrogen content and its effect on the low-temperature properties of mild steel. A volumetric oxine method for determining aluminium in steel has been recommended by the Methods of Analysis Committee of the British Iron and Steel Research Association1 and has now been adopted as a standard method by the British Standards I n ~ t i t u t i o n .~ ~ ~ Although this procedure-in the hands of a competent analyst-is capable of giving accurate results, it is less satisfactory a t aluminium levels below about 0.03 per cent. A tendency towards high results is noticeable at this concentration, which, to some extent, may be due to difficulties associated with the removal of excess of oxine from the aluminium quinolate precipitate. Non-reproducible blank values equivalent to an aluminium content of from 0.0002 to 0.002 per cent, on a 10-g sample seem to confirm this observation. The unreliability of this method at low levels is demonstrated by divergencies in the results obtained by five co-operating laboratories for aluminium in a series of mild-steel616 SCHOLES AND SMITH : THE COLORIMETRIC DETERMIKATIOK OF [Vol.83 spectrographic standards. For example, on two samples with contents of 0.01 and 0.02 per cent. of aluminium, the results ranged from 0.008 to 0.015 and 0.015 to 0.026 per cent., respectively. The Methods of Analysis Committee considered that this unreliability might be caused by contamination of the aluminium quinolate precipitate by manganese. The procedure has recently been re-examined by the Mercury Cathode Study Group of the Committee, and results obtained by the co-operating laboratories now show much closer agreement: A modified British Standard for the volumetric determination of aluminium will shortly be issued.Small amounts of aluminium are more conveniently determined by a colorimetric pro- cedure, and the literature contains many references to the use of lake-forming reagents, such as aluminon, Eriochrome cyanine R, stilbazo and alizarin. The reaction between Eriochrome cyanine R and aluminium has been studied exiensively by German worker^,^?^ and between 1938 and 1940 it was applied to the determination of aluminium in steel by Koch and his co-worker~.~?s The dye has also been used in the United States of A m e r i ~ a , ~ ? ~ ~ but does not seem to have found favour in this country. Eriochrome cyanine R is a brick-red powder that is readily soluble in water to give an orange-red solution; in the presence of an acetate buffer, a red-violet lake or complex is formed with aluminium.Werz and Neubergerll recently established the superiority of this reagent over aluminon, the reagent most widely used for determining small amounts of aluminium in steel. Essentially, the main advantage of Eriochrome cyanine R is its greater stability towards temperature change; formation of the complex between aluminium and the dye takes place at room temperature, whereas the complex with aluminon must be heated under controlled conditions to ensure reproducible colour development. In addition, the need for accurate control of pH is slightly less critical. Eriochrome cyanine R is the trade name atssigned by Geigy and Co. to the sodium salt of 2 -sulpho-3 : 3’-dimethyl-4-hydroxyfuchsone-Ei : 5 -dicarboxylic acid.In the Colour Index,12 the dye is listed under usage number Mordant blue 3 and has the constitution number 43820. The dye is also marketed under such trade names as Alizarol cyanine R, Omega Chrome cyanine R, Chromoxane cyanine RA, Solochrome cyanine R, Pontachrome blue ECR and Fenakrom blue XR. Solochrome cyanine R, available from the British Drug Houses Ltd., has been used in the work described. CONDITIONS FOR COLOUR DEVELOPMENT The literature suggests that the most import ant factors in the formation of the aluminium - dye complex are (a) pH value, (b) concentration of dye and the effect of “ageing” the dye solution, (c) time required for full development of the colour, and ( d ) effect of temperature. Since there appears to be a divergence of opinion on the optimum conditions for colour development, each variable has been examined in detail, an aqueous solution of Solochrome cyanine R being used.SELECTION OF OPTIMUM pH- Previous investigators have studied the selection of an optimum pH value and have found that complex formation is satisfactory in the pH range 5 to 7 with maximum colour development between pH 5.7 and 6.5. In order to study the effect of pH, a series of calibration graphs in the concentration range 0 to 80 pg of ,aluminium per 100 ml was prepared at various pH values. The test solutions contained 5 mg of dye per 100 ml and were buffered with a mixture of ammonium and sodium acetates. In common with all other measurements in this paper, the optical densities of the test solutions were measured against a reagent blank at 535 mp with a Unicam SP600 spectrophotometer.The calibration graphs were found to be linear in the pH range 5.7 to 6.3, but not at pH 6.4 to 6.5. Fig. 1 shows the variations in optical density of a calibration test containing 60 pg of aluminium and of the reagent blank solution. The optical density of the aluminium complex is fairly stable in the pH range 5.7 to 6.1, although that of the reagent blank diminishes with increasing pH, but is relatively stable in the pH range 5.9 to 6.2. A value of 6.0 has therefore been selected. At this pH, a variation of up to k0-l optical-density units will not affect the optical density of the aluminium complex. DYE COXCENTRATION- In order to determine the optimum concentration of dye in the final solutions, different amounts of dye were added to test solutions containing 70 pg of aluminium.A concen- tration of 5 mg of dye per 100 ml was adequate to give maximum optical density for solutionsNov., 19581 ALUMINIUM IN STEEL WITH SOLOCHROME CYANINE R 617 containing up to 70 pg of aluminium. Some workers advocate that the dye solution should be set aside for 1 hour or even overnight before use, whereas others apparently consider this I , I 0 10 20 30 40 50 60 Time, minutes Fig. I . Effect of pH on the aluminium - Solochrome cyanine R complex: curve A, Fig. 2. Effect of time for formation of the aluminium - test solution containing 60 p g of aluminium Solochrome cyanine R complex: curve A, test solution con- per 100 ml; curve B, test solution corrected taining 60 pg of aluminium per 100 ml; curve B, test solution for reagent blank value; curve C, reagent corrected for reagent blank value; curve C, reagent blank blank solution solution 0 Wavelength, mp Fig.3. Absorption spectra for the alu- minium - Solochrome cyanine R complex : curve A, test solution containing 60 p g of aluminium per 100 ml measured against the reagent blank solution; curve B, reagent blank solution to be unnecessary. effect on either the optical density or stability of the complex. This factor was examined, and tests indicate that "ageing" has little A decrease of about 0.03618 SCHOLES AND SMITH: THE COLORIMETRIC DETERMINATION OF y01. 83 optical-density units was, however, noticed in the blank value for dye solutions that had been set aside for more than 1 hour.A minimum "ageing" time of 1 hour is therefore recommended. TIME FOR NAXIMUM COLOUR DEVELOPMENT- Concurrent with the pH tests, the time required to attain maximum colour development was also studied. Optical-density measurements were made a t intervals of 10 minutes for a period of 1 hour after dilution to volume. The results (see Fig. 2 ) show a slight increase with time for the aluminium complex and an iritial decrease followed by a slight fading for the reagent blank. Hence, it is necessary to set the solutions aside for a definite period; 30 minutes was chosen. A reasonable margin in timing is permissible, but, to avoid wide variation in the time allowed for colour development of individual tests, it is advisable to restrict the number of samples in a batch to six (including a reagent blank).Approximately the same time interval should elapse before measurement of both the reagent blank and the test solution, and it is therefore recommended1 that the spectrophotometer should be set against the reagent blank solution before each individual test solution is measured. EFFECT OF TEMPERATERE- The effect of temperature in the normal laboratory range of 16" to 23" C is not critical. On heating to 30" C, however, a slight decrease in optical density was noticed, which did not exceed 1 per cent. of the optical density at 20°C. The optimum conditions for colour development having been established, a comparison was made between the absorption spectra of the aluminium complex and the reagent blank (see Fig.3). The curve for the Solochrome cyanine R - aluminium complex is in good agreement with the findings of Hill, who used the dye Eriochrome cyanine R.I0 The optical density of the aluminium complex is a maximum at 535 mp. SEPARATION OF ALUMINIUM Koch and his co-worker~~>~ separated aluminium from iron and most other heavy metals by mercury-cathode electrolysis. More recently, Werz and Neuberger,ll in a comparative study of separation methods, stated that as much as 25 per cent. of the aluminium content may be lost through adsorption of aluminium or1 ferric hydroxide during the classical separa- tion with sodium hydroxide. A loss of 11 per cent. by diethyl ether extraction was reported, and the authors concluded that mercury-cathode electrolysis was the most accurate method of separation without loss of aluminium.The separation of aluminium from iron on a cellulose column has recently been described by Bishop.13 Iron is removed from the column, and aluminium together with any nickel present is retained quantitatively. The aluminium is subsequently determined polaro- graphically by means of Solochrome violet RS. Recent work by Rooneyl4 has, however, shown that removal of titanium, vanadium, chromium, cobalt and zirconium is not complete and small amounts of these elements may remain on the column with the aluminium, MERCURY-CATHODE ELECTROLYSIS- An elaborate apparatus is not required for mercury-cathode electrolysis. The elec- trolytic cell recommended by us is a 150-ml squat beaker containing about 20 ml of mercury; a spiral of heavy-gauge platinum wire forms the anode, a platinum wire contact sealed in glass makes the electrical connection to the mercury cathode and a split clock-glass serves as a cover for the cell to prevent loss by spraying.A device for stirring the mercury cathode is not required. At a current density of 0-16 ampere per sq. cm of mercury surface, the electrolysis of a sample of plain carbon steelis complete in 1 to 14 hours. This time may be considerably reduced by using a higher current density together with a water-cooled coil to maintain the temperature of the solution below 40" C, as recommended in the British Standard procedure.2 In low alloy steels, complete deposition of chromium is often slow; chromium removal can be facilitated by neutralising most of the free acid content of the solution before electrolysis.Mercury-cathode electrolysis in dilute sulphuric acid removes iron as well as such elements as nickel, copper, chromium and molybdenum. In addition, manganese is incom- pletely deposited in the mercury and on the a.node; lead may also be partially deposited on the anode, Zirconium, titanium, vanadium and silicon, together with a small amountNov., 1958: ALUMINIUM IN STEEL ~ I T H SOLOCHROME CYANINE R 619 of mercury that enters the solution during electrolysis, remain with aluminium in the elec- trolyte. Traces of bivalent iron that have escaped separation may also be found in the electrolyte. Previous workers have shown that manganese, titanium, zirconium and residual iron interfere with complex formation in the determination of aluminium with Eriochrome cyanine R and give rise to serious negative errors.Treatment with sodium hydroxide and hydrogen peroxide, as suggested by Werz and Neuberger,ll removes zirconium, manganese and iron, but mercury and silicon are only partly precipitated. In the presence of hydrogen peroxide, which must be added to ensure complete precipitation of iron and manganese, titanium is partly converted to pertitanic acid and is therefore incompletely precipitated by sodium hydroxide. Interference by titanium can be masked by adding hydrogen peroxide to the solution before colour development. Vanadium, which accompanies aluminium into the filtrate, does not interfere with the formation of the aluminium - dye complex. At pH 6.0, the yellow colour of the combined peroxide complexes of titanium and vanadium is so pale that it does not interfere with absorption measurements.Any silicon that accompanies aluminium into the filtrate after the sodium hydroxide separation will normally be present in soluble form, but, in steels with high silicon contents, metasilicic acid may be present in the solution and would prove to be troublesome during colour development. Hence, for samples containing more than 1 per cent. of silicon, it is advisable to remove silicon by evaporating the sulphuric acid solution until fumes are evolved before insoluble matter is removed by filtration. Some workers have recommended that mercury, which is only partly precipitated by sodium hydroxide, should be removed with hydrogen sulphide before colour development. To examine the effects of mercury contamination, additions of 5 and 10mg of mercury were made to solutions containing aluminium after acidification of the filtrate from the sodium hydroxide separation; the colour was then developed in the usual way.The results indicated that the presence of mercury in the electrolyte does not affect complex formation; treatment with hydrogen sulphide is therefore unnecessary. The effects of lead have also been studied and it has been found that this element is without effect in concentrations of up to 1 mg per 100 ml (equivalent to 0.5 per cent.). CHROMATOGRAPHIC SEPARATION- The cellulose-column method of separation described by Bishop13 has been examined in our laboratory as a possible alternative to mercury-cathode electrolysis. The method was adapted as follows.After separation on the cellulose column, the eluate containing aluminium, nickel and traces of other metals was evaporated with sulphuric and nitric acids until fumes were evolved to remove organic matter. The interfering elements were then removed by a sodium hydroxide separation in the presence of 1 mg of tervalent iron to act as carrier. The filtrate was acidified and the colour developed as described on p. 621. Trials with this method of separation were promising, but the time required to prepare and regenerate the cellulose column was a disadvantage. Mercury-cathode electrolysis is more rapid and requires little or no attention during separation. The chromatographic method is, however, suitable for laboratories that have no source of direct current.METHOD The method consists in small-scale mercury-cathode electrolysis and subsequent separa- tion by sodium hydroxide in stainless-steel beakers to remove interfering elements. After careful neutralisation, a measured excess of dilute acid is added and the aluminium - SoIo- chrome cyanine R complex is developed under optimum conditions. REAGENTS- be stored in polythene bottles. All solutions must be prepared from reagents of the highest purity obtainable and should Hydrochloric acid, diluted (1 + 1). Hydrochloric acid, 0.2 N-Dilute 20 ml of hydrochloric acid, sp.gr. 1.16, to 1 litre with Sulphuric acid, dilute (1 + 4). Sul9huric acid, dilute (3 + 20). water.620 SCHOLES AND SMITH : THE COLORIMETRIC DETERMINATION OF [Vol.83 Sodium carbonate solution, saturated. Sodium hydroxide, 10 N-Transfer 400 g of sodium hydroxide pellets to a 1-litre polythene Shake Sodium hydroxide, 2 N-Dilute 20 ml of 10 N sodium hydroxide to 100 ml. Hydrogen peroxide, 5-volume. Phenolphthalein indicator solzdion-Dissolve 0.1 g of phenolphthalein in 50 ml of methy- lated spirit and dilute to 100 ml with water. Solochrome cyanine R solution, 0.1 per cent. w/v-Dissolve 0.1 g of B.D.H. Solochrome cyanine R in water, dilute to 100m1, and filter through a Whatman No. 541 filter-paper. This solution should be prepared daily and set aside for a t least 1 hour before use. Glassware that has been in contact with this solution should be rinsed with nitric acid and washed thoroughly with water before use.Buffer solution, concentrated-Dissolve 275 g of ammonium acetate and 110 g of hydrated sodium acetate in 1 litre of water. Add 10ml of glacial acetic acid, and mix thoroughly. Buffer solution, dilute-To one volume of concentrated buffer solution, add five volumes of water and adjust the pH to exactly 6.1 by adding acetic acid or sodium hydroxide solution. Standard aluminium solution-Dissolve 1.3192 g of analytical-reagent grade aluminium potassium sulphate in water, and dilute to 1 litre in a calibrated flask. bottle, add 900 ml of water and partly immerse the bottle in cold running water. until dissolution is complete, cool, and dilute to 1 litre. 1 ml = 75 pg of aluminium. PROCEDURE- Preparation of sample-Transfer 1 g of sample to a 125-ml conical beaker, add 15 ml of dilute sulphuric acid (3 + 20) and heat gently until dissolution is complete.(If the sample contains more than 1 per cent. of silicon, evaporate the solution until fumes are evolved, re-dissolve the salts by heating with 15 ml of water, and filter.) Cool the solution, and filter through a small pad of filter-paper pulp. Wash the pad with water and reserve the filtrate. (If separate results are required for acid-soluble and acid-insoluble aluminium, determine the former by treating this filtrate as described under “Electrolysis.”) Ignite the pad in a platinum dish, moisten the residue with 3 or 4 drops of dilute sulphuric acid (1 + 4), add 2 ml of hydrofluoric acid and evaporate under an infra-red lamp until fumes are evolved, Continue evaporation until all sulphuric acid has been removed and then heat the dish for a few minutes a t about 800” C.F ~ s e the residue with 0.5 g of sodium hydrogen sulphate, cool, add 10ml of water and warm the dish until the fused mass has dissolved. (If required, determine acid-insoluble aluminium as follows. Extract the fused mass with 10 ml of dilute sulphuric acid (3 + 20), transfer the extract to a small beaker and heat to ensure complete dissolution. Evaporate the solution to about 5 m l and then treat with 10 N sodium hydroxide as described under “Preparation for Colour Development.”) Transfer the aqueous extract to the beaker containing the filtrate, and heat the mixture to ensure complete dissolution of the fused residue. Electrolysis-Cool the solution, and, if the sample contains more than 0.5 per cent.of chromium, neutralise free acid by adding saturated sodium carbonate solution until the first appearance of a permanent precipitate. lie-dissolve this precipitate by adding dilute sulphuric acid (3 + 20), dropwise, and add 1 rril in excess. (If this procedure is necessary, treat the reagent blank solution in a similar manner.) Transfer the solution to a 150-ml squat beaker containing 20 ml of mercury, and dilute to 60 ml. Cover the beaker with a split clock-glass, electrolyse the solution at a current of 2 amperes for 1 hour and then test for completeness of iron removal by a ferricyanide spot-test. When iron has been completely removed, wash the walls of the beaker and the clock-glass with water, and electrolyse for a further 15 minutes, or, in presence of chromium, until the green colour of the solution has disappeared.Without delay, filter the electrolyte through a Whatman Yo. 541 filter-paper and wash the mercury with a minimum of water. (Procedures for the separation of the amalgam after electrolysis and for recovery of mercury from the amalgam are described in British Standard l121C.2) Preparation for colour development-Evaporate the filtered electrolyte to about 5 ml, cool and pour slowly into a 200-ml stainless-steel beaker containing 10 ml of 10 W sodium hydroxide (add this reagent from a polythene measuring cylinder). Cautiously add 5 ml of 5-volume hydrogen peroxide from a dropping pipette, cover the beaker with a clock-glass,Nov., 19581 62 1 heat to boiling-point and boil gently for 10 minutes on a hot-plate.Remove the beaker from the hot-plate, add a little Whatman ashless floc, and set aside for 5 minutes. Filter the solution through a pad of filter-paper pulp (in a polythene funnel) into a 200-ml polythene squat beaker and wash the pad with warm water. Add 2 or 3 drops of phenolphthalein indicator solution to the filtrate and neutralise by adding diluted hydrochloric acid (1 + 1) from a dropping pipette. Stir the solution during neutralisation with a polythene rod, and add 0.5 ml of acid in excess. Cool the solution and dilute to 100 ml in a calibrated flask. (If it is necessary to evaporate the solution somewhat before dilution, this can be done in a glass beaker. However, if care has been taken with washing during the treatment with 10 N sodium hydroxide, the volume a t this stage should be about 90 ml.) Colow development-Transfer a suitable aliquot of the solution, i.e., one containing from 2 to 70 pg of aluminium, to a 250-ml conical beaker.For samples containing up to 0.035 per cent. of aluminium, take a 20-ml aliquot, and for samples containing from 0.035 to 0.07 per cent. of aluminium, take a 10-ml aliquot and add 10 ml of water before colour development. (The range of the method can be extended by taking a 5-ml aliquot or by reducing the sample weight. For batch analysis, the number of aliquots taken for colour development should be restricted to six, including a reagent blank.) To the aliquot for colour development add 5 ml of 5-volume hydrogen peroxide, and mix well.Carefully neutralise by adding 2 N sodium hydroxide from a polythene dropping bottle and add 1 drop in excess. Titrate immediately with 0-2 N hydrochloric acid until the solution is colourless, add exactly 1.0 ml of acid in excess, and mix thoroughly. Add exactly 5.0 ml of Solochrome cyanine R solution, mix, add 50 ml of dilute buffer solution and dilute to 100 ml in a calibrated flask without delay. Set the solution aside for 30 minutes and then measure the optical density against a reagent blank solution in 5-mm cells with a spectro- photometer a t wavelength 535 mp. Re-set the instrument against the blank solution before each sample solution is measured. The optical density of the blank solution is approximately 0.17. Optical-density measurements can also be made with an absorptiometer ; an instrument with a mercury-vapour lamp is suitable, if Ilford No.605 and Calorex H503 filters are used. However, when an absorptiometer is used, the sensitivity is reduced by about half and it is necessary to measure optical density in 1-cm cells; in these circumstances, the optical density of the blank solution is approximately 0.30. Each batch of test solutions must be accompanied by a blank solution. Tests have shown that the reagents used may result in the introduction of up to 4pg of aluminium. Comparative tests over several months have also indicated that the pick-up of aluminium during electrolysis does not exceed 0.5 pg, and hence the blank determination can be simplified by omitting the electrolysis.The aliquot of blank solution should always be equal in volume to that of the test solution. Calibration-Prepare six solutions, each containing 1 g of aluminium-free iron dissolved in 15 ml of dilute sulphuric acid (3 + 20). To these solutions, add, respectively, 0, 1, 2, 3, 4 and 5 ml of standard aluminium solution. Transfer each solution to a mercury-cathode electrolysis cell, dilute to 60 ml and continue as for a sample solution. Measure the optical density of each solution against the solution containing no aluminium. For the instrument used by us, it was found that the optical density (measured in 5-mm cells) multiplied by a factor of 73 was equal to the number of micrograms of aluminium in the aliquot of solution taken for colour development. A factor of 0.0365 gave the percentage of aluminium in a 20-ml aliquot and a factor of 0.073 gave the percentage of aluminium in a 10-ml aliquot. When optical-density measurements were made in 1-cm cells with an absorptiometer, it was found that optical density multiplied by 77 was equal to the number of micrograms of aluminium in the aliquot taken for colour development.These factors are intended as a guide only; specific factors must be determined for individual instruments. ALUMINIUM I N STEEL WITH SOLOCHROME CYANINE R RESULTS In Table I, the results obtained by the proposed method for standard samples of mild and low alloy steel are compared with those obtained by Members of the British Iron and Steel Research Association Methods of Analysis Committee by a standard volumetric r n e t h ~ d .~ ~ ~ In Table 11, a series of results for samples of vacuum-melted mild steel is com- pared with results obtained in our laboratory by the standard volumetric method. These622 SCHOLES AND SMITH THE COLORIMETRIC DETERMINATION OF [Vol. 83 results confirm the observation made earlier on the tendency towards high results when the standard method is used in routine operation. TABLE I COMPARISON BETWEEN VOLUMETRIC ASD PROPOSED METHODS FOR DETERMINING ALUMINIUM Results by the proposed method are given t3 the nearest 0.0005 per cent. except for B.C.S. samples 272, 273 and 255, which are given to the nearest 0.001 per cent. Aluminium r- \ by volumetric Range of aluminium Sumber of Mean aluminium Aluminium by proposed method Sample No.method, % content, (x determinations content, % Santples containing 0.001 to 0.035 per cent. of alumintwn- B.C.S. 271.. . . 0.008" 0.0074 to 0.0095 10 0.0085 B.C.S. 274.. . , 0.033a 0.0315 t o 0.0337 10 0.0325 B.C.S. 275. . . . 0.020b 0.0204 to 04220 6 0,021 B.C.S. 276.. . . O.02Eib 0.0222 to 04239 10 0.023 B.C.S. 2 7 7 . . . . O.O1fib 0.0171 to 0.0198 6 0.0185 M.G.S. 183 . , 0.018C 0.0195 to 04225 6 0.021 B.C.S. 272.. . . 0.06Sa 0.0656 to 0,0703 6 0.068 B.C.S. 273.. . . 0*060* 0.0550 to 0,0598 6 0.067 B.C.S. 255.. .. ~ 0 . 0 5 7 ~ 0.0455 to 0.0503 10 0.048 (I Results obtained by B.I.S.R.A. Methods of Analysis Committee (modified British Standard method). Results obtained by B.I.S.R.A. Methods of -2nalysis Committee (British Standard method) to the c See Reference 1, Table 11.d B.C.S. certificate value. Samples containing 0.035 to 0.07 per cent. of alumzniunt- nearest 0.005 per cent. TABLE I1 COMPARISON BETWEEN VOLUMETRIC, POLAROGRAPHIC AND PROPOSED METHODS FOR DETERMIKISG ALUMINIUM Results by the proposed method are given to the nearest 0.0005 per cent. The polarographic method used was that of Rooney14 Aluminium Sample by volumetric Sample No. method, yo B1 0.002, 0.005 0.002, 0.004 0.002, 0.005 B3 B4 0.004, 0.004 0.001, 0.002 0.003, 0.003 0.006, 0.007 0.003, 0.003 0.012, 0.016 r B2 1 :: Vacuum-melted mild steel B7 _. 1 E r 1 Cast iron . . .. . I Aluminium by polarographic method, yo - 0.0049 - - 0.0022 0.0055 0.0084 < - Aluminium by proposed method, 7; 0.001, 0.001 0.0015, 0.0015 0.0015, 0.0025 0.005, 0.0055 0401.0~0015 . . . ~ . 0.001: 0.0015 0.0015, 0.0015 .0.001, < 0.001 0.005, 0.0065 0.009. 0.0095 0.0012 0.0015, 0.002 0.0061 o m j , 0.005 0.0025 0.003, 0.0035 A comparison has also been made between the proposed method and a polarographic method of exceptional sensitivity developed by 130oney.l~ The aluminium contents of three of the vacuum-melted mild-steel samples have been determined by Rooney, and, in addition, four samples of cast iron have been analysed by both methods. In general, the polaro- graphic and colorimetric results show good agreement, and, together with the results in Table I, are considered to provide satisfactory evidence of the reliability of the proposed procedure. The approximate compositions of the test samples are shown in Table 111. Sufficient results have been obtained for BI-itish Chemical Standards 271, 274 and 276 to provide an estimate of the precision of the method; the standard deviation is &0.0007 per cent.for the first sample, +0.0009 per cent. for the second and k0.0008 per cent. for theNov., 19583 ALUMINIUM IN STEEL WITH SOLOCHROME CYANINE R 623 third. In the range 0.035 to 0.070 per cent, of aluminium, the standard deviation is 10.0017 per cent. for British Chemical Standard 255. The precision of the method is limited by the reagent blank value, which includes the background colour of the dye and the pick-up of aluminium from reagents and glassware. In the tests reported here, reagent blank values were equivalent to an aluminium content of from 0.0055 to 0.0070 per cent. TABLE I11 APPROXIMATE COMPOSITION OF TEST SAMPLES Present in the sample Man- Chrom- Molyb- Vana- Tung- A I 1 Sample Silicon, ganese, Nickel, ium, denum, Copper, dium, sten, Cobalt, O/ % YO % % % YO % % /O - - - - - - - B1 t o B 9 ,.. . 0-3 0.8 B.C.S. 253 . . . . 0.2 0.4 2.9 0 4 1.0 0.5 0.2 B.C.S. 255 . . . . 0.6 1.1 0.6 1.0 1.4 0.2 0.3 B.C.S. 271 to 277* . , 0.4 0.5 0.2 0.2 0-2 0.2 0.1 0.2 0.2 Cast irons 1 to 4* . , 2 ~ 0 0.5 * The figures for these samples are the maximum amounts present. - - - - - - - - - - - CONCLUSIONS A method has been developed in which formation of a coloured lake or complex between aluminium and Solochrome cyanine R can be applied to the determination of aluminium in steel over the range 0.001 to 0.035 per cent. By taking smaller aliquots, it is possible to extend this range to cover any concentration of aluminium in carbon and low alloy steel. ik considerable reduction in the amount of mercury used is an important economic advantage of the proposed method over the standard volumetric procedure. This feature, ease of operation and the achievement of increased speed and sensitivity are the main advantages of the Solochrome cyanine R method. We thank Mr, N. McGowan for assistance in examining the chromatographic separation method and for many helpful suggestions, and Miss C. J. Arlidge for editorial assistance. We also thank Mr. R. C. Rooney of the British Cast Iron Research Association for valuable co-operation in providing a comparison between his polarographic method and our colorimetric method. This paper is published by permission of The British Iron and Steel Research Association. 1. 2. 3. 4. 5. 6. 7 . 8. 9. 10. 11. 12. 13. 14. REFEREXES R.I.S.R.A. Methods of Analysis Committee, J . Iroiz & Steel Iizst., 1954, 176, 263. “Mercury Cathode Electrolysis,” British Standard 1121C : 1955. “Aluminium in Iron, Steel and Ferro-alloys (after Mercury Cathode Separation),” British Standard B. I. S. R. A. Restricted Report MG/DC/281/57. Eegriwe, E., Z . anal. Chenz., 1929, 76, 438. Alten, F., Weiland, H., and Krippenberg, E., Ibid., 1934, 96, 91. Koch, W., Arch. Eisenhuttenw., 193S, 12, 74. ICoch, W., IClinger, P., and Blaschczpk, G., Angew. Chew., 1940, 53, 537. Ikenberry, L. C., and Thomas, A., Anal. Chew., 1951, 23, 1806. Hill, U. T., Ibid., 1956, 28, 1419. Werz, W., and Neuberger, A., Arch. Eisenhuttenw., 1955, 26, 205. “Colour Index,” Second Edition, Parts I and 11, Society of Dyers and Colourists, Bradford, 1957. Bishop, J. R., Analyst, 1956, 81, 201. Rooney, R. C., Ibid., 1958, 83, 546. 1121 : Part 35 : 1965. Received April SLh, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300615

出版商:RSC    

年代:1958

数据来源: RSC

摘要:

624 SHORT AND WILLIAMS: DETERMINATION OF SMALL AMOUNTS OF [Vol. 83 Determination of Small Amounts of Silicon in High-purity Iron BY H. G. SHORT AND A. I. WILLIAMS (National Physical Laboratory, Teddington, Middlesex) An activation method has been developed for the determination of amounts of silicon in high-purity iron clown to 0.0001 per cent. The results agree with those found for total silicon (acid-soluble plus insoluble) by an absorptiometric method !depending on formation of a molybdo- silicate complex and reduction of this to molybdenum blue. Some minor points in the chemical procedure have been re-investigated. FOR some time past in this laboratory, work on the effects of impurities on the properties of high-purity iron has necessitated the determination of amounts of silicon down to 0.001 per cent.The determinations have been carried c u t by an absorptiometric method based on the procedure described in British Standard 11211 : Part 19 : 1951. This depends on the forma- tion of a molybdosilicate complex, which is reduced to molybdenum blue by ferrous sulphate in the presence of oxalic acid. This procedure can be used only to determine silicon present in such a form as to be soluble in the 5 per cent. v/v sulphuric acid used for dissolution of the sample, and, to obtain the total silicon content, any insoluble matter must be fused with sodium carbonate fusion mixture and the silicon determined in a solution of the resulting melt by a similar absorptiometric procedure. On the whole, this technique has given acceptable results, but, from time to time, abnormally high results have been obtained, which were suspect because they could not be accounted for by the technique of manufacture. These high results were, however, repro- ducible and have been confirmed by the activation procedure.Other disadvantages are (a) the fact that at 0-001 per cent. of silicon the method is being extended to the limit of sensitivity, since this silicon content corresponds to 0.02 absorptio- meter-drum divisions and the blank value for the reagents is usually 0.03 divisions, and ( b ) the difficulty in accurately determining the blank value, which is equivalent to 0.0017 per cent. of silicon under the conditions of the method. The development of activation analysis made it possible to check silicon determinations by an independent technique.It must be emFhasised that use of the activation procedure gives the total silicon content of the sample. ABSORPTIOMETRIC METHOD- Blank determinatiovz-The determination of the blank value cannot be made by carrying out the procedure with omission of the iron sample, owing to interference by reduced molybdenum a t the colour-development stage. On the other hand, iron completely free from silicon, which could be used in a blank determination, is not so far available. This difficulty has in the past been overcome by making two determinations on each sample solution, one aliquot, A, having half the volume of other, E:. Then, if x and y are the absorptiometer readings corresponding to the silicon in the sample and the reagent blank, respectively, the reading obtained for aliquot A is (x + y ) and that for aliquot B is (2% + y).The blank value is then found by subtracting the absorptiomeler reading of aliquot B from twice that of aliquot A. When this difference procedure was used, a mean blank value of 0.042 absorptiometer- drum divisions (equivalent to 0-0024 per cent. of silicon) was obtained over a large number of tests, but the variation was considerable (standard deviation i 0.019 drum divisions). Experiments to discover the cause of this variation indicated that the potassium perman- ganate used to oxidise the sample solution was responsible. This was therefore replaced by hydrogen peroxide in a second series of tests; the blank value was then lower (0.034 drum divisions) and less variable (standard deviation & 0.008 drum divisions).Use of hydrogen peroxide for oxidation was therefore adopted as standard. In the course of the experiments it was found that potassium permanganate solutions stored in glass became contaminated with appreciable amounts of silicon in less than 1 week. EXPERIMENTALNov., 19581 SILICON IN HIGH-PURITY IRON 625 Two grams of iron, of the lowest available silicon content, were dissolved in acid, oxidised, and the solution was extracted with diethyl ether. The aqueous layer was rejected and the ethereal layer was extracted with water; this gave an aqueous iron solution free from silicon. This solution was evaporated in a platinum dish with sulphuric acid to remove hydrochloric acid, and the resulting solution was diluted to such a volume that the concentrations of iron and sulphuric acid were the same as in a normal test.The blank value obtained in the subse- quent colorimetric test was 0.03 drum divisions, which was in agreement with that found when the difference procedure was used. The reagent blank value for the absorptiometric method is therefore thought, with some confidence, to be 0.03 absorptiometer-drum divisions. This should be checked from time to time, when fresh batches of reagents are brought into use, by the difference procedure. Contamination by glassware-Since only a few micrograms of silicon participate in the final colour reaction, some suspicion has always been attached to the use of glass apparatus, particularly for dissolution of samples, for which it is necessary to heat acid solutions. Tests on one particular sample of average silicon content (0.003 per cent.) showed no detectable difference in results when the sample was dissolved and the solution prepared for colour development in either platinum dishes or Pyrex-glass beakers.Similarly, blank values determined by the difference procedure on AnalaR ferrous sulphate that had been dissolved in acid and treated as a sample were identical whether the solutions were prepared in platinum or glass. Portions of the 5 per cent. v/v sulphuric acid used for dissolution of the samples were boiled for several hours in Pyrex-glass and Hysil-glass beakers. The solution from the Pyrex-glass beaker was found to contain 11.5 pg of silicon (equivalent to 0.0008 per cent.on a 1.5-g sample) and that from the Hysil-glass beaker was found to contain 20 pg of silicon (equivalent to 0.0013 per cent. on a 1.5-g sample). The evidence is, therefore, that contamination by glassware is negligible under normal operating conditions ; nevertheless, determinations on samples known to be extremely low in silicon are now carried out in platinum dishes to avoid any possibility of error from this source. The blank value was also determined by an alternative procedure, as follows. ACTIVATION METHOD- Owing to the short half-life (2.65 hours) of the active isotope used (silicon-31), chemical treatment of the sample after activation had to be such that counting could be carried out on the same working day that the sample was received from Harwell.For this reason it was considered that what might be called the classical method for separating silicon- dehydration and subsequent filtration-was too lengthy. Trials were therefore made with a procedure in which silicon was separated by diethyl ether extraction of a complex molybdosilicic acid from acid solution. It was found, however, that the resulting compound was not of sufficient radiochemical purity to avoid previous scavenging steps, contamination with tungsten being particularly noticeable. The same disadvantages were found to apply t o precipitation as potassium fluorosilicate. Experience also showed that the established dehydration method could be carried out almost as quickly, if care were taken to keep the volume of solution to be evaporated to a minimum.The silicon was prepared for counting by collecting the separated silicic acid on a small circle of filter-paper, which was partly dried by washing with ethanol and diethyl ether. The paper was then placed on a tray for counting, and was afterwards ignited to determine the percentage recovery of added carrier silicon. To a certain extent, radio- chemical purity has been sacrificed to speed of operation. A scavenging step for tungsten was found to be necessary, but the silica isolated for counting always contained a small amount of long-lived active impurity, although the first part of the decay curve was to all intents and purposes parallel to that of the standard. The true silicon count was therefore obtained as follows. Immediately after preparation, the precipitate was counted five or six times at intervals of 30 minutes in order to obtain the slope of the main silicon-decay curve, which was then extrapolated to zero time to give uncorrected silicon counts.In the course of the next day, the precipitate was counted five or six times a t intervals of 1 hour to give the residual long-lived activity, which was also extrapolated to zero time and sub- tracted from the uncorrected silicon activity. The magnitude of this correction varied, but The procedure finally developed is described on p. 627.626 SHORT AND WILLIAMS: DETERMINATION OF SMALL AMOUNTS OF [Vol. 83 in general it formed a small proportion of the total counts; this is shown by the results in Table I. TABLE I CORRECTION OF COUNTING RATE .4mount of Uncorrected activity, Residual long-lived activity, silicon present, counts per minute counts per minute Correction, % Yo 0.0002 0~0020 0.0018 0.0050 0.0002 050015 0.0040 185 7.5 410 30 534 174 1540 40 134 6 340 23 1180 60 4 7 33 2.5 4.5 7 5 METHOD REAGEXTS- and cool the solution.Sulphuric acid, dilute (1 + 19)-To 950 ml of water add 50 ml of sulphuric acid, spgr. 1.84, Hydrogen peroxide, 20-volume-Analytical-reagent grade. Ferrous sulphate solution, 2 per cent.-Prepare a 2 per cent. w/v solution of ferrous sulphate, FeS0,.7H20, in 0.1 per cent. sulphuric acid. Ammonium molybdate solution, 10 per cent. :w/v. Oxalic acid solution, 10 per cent. w / v . Silicon carrier solution-Prepare a solution of sodium silicate containing 5 mg of silicon Manganese carrier solution-Prepare a so'lution of manganous sulphate containing Tungsten carrier solution-Prepare a solution of sodium tungstate containing 10 mg per ml.10mg of manganese per ml. of tungsten per ml. ABSORPTIOMETRIC PROCEDURE- Dissolve a 1.5-g sample of iron in 100 ml of (dilute sulphuric acid (1 + 19) in a platinum dish. Filter the solution through a pulp filter, transfer any insoluble matter to the filter and wash with water. Transfer the filtrate to a platinum dish, warm, and add 15 ml of 20-volume hydrogen peroxide. Warm until effervescence has ceased and finally maintain near the boiling-point for 10 minutes. Cool, transfer to a 250-ml calibrated flask, dilute to the mark, and mix. By pipette, place two 20-ml portions of the solution in clean dry beakers. To one portion add 10 ml of 10 per cent.w/'v ammonium molybdate solution, mix, and set aside for 15 minutes a t 20" i. 2" C. Add 20 ml of 10 per cent. oxalic acid solution and 5 ml of 2 per cent. ferrous sulphate solution. Mix well and set aside for 10 minutes. This is solution A. To the other portion add 20 ml of 10 per cent. oxalic acid solution, 10 ml of 10 per cent. w/v ammonium molybdate solution and 5 ml of 2 per cent. ferrous sulphate solution. Mix well and set aside for 10 minutes. Measure the optical-density difference between solutions A and B in 4-cm cells with a Spekker absorptiometer and Ilford No. 606 filters. Determine the amount of soluble silicon by reference to a standard graph prepared by adding known amounts of sodium silicate solution to pure iron and then carrying out the above-described procedure.Normally, allow a blank value of 0.03 absorptiometer-drum divisions, but, when a new batch of reagents is used, check this in the following manner. In addition to the two aliquots for the silicon determination, measure two 10-ml aliquots, add 10 ml of 2 per cent. v/v sulphuric acid to each and proceed as before. If the absorptiometer-drum readings of these four solutions are A , B, A' and B', respectively, the reagent blank value is given by- Reserve the precipitate for the determination of insoluble silicon. This is solution B. 2(A' - B') - ( A - B) To determine insoluble silicon, ignite the residual insoluble matter from the dissolution Dissolve the of the sample in a platinum crucible and fuse with 0.2g of fusion mixture.Nov., 19581 SILICON I N HIGH-PURITY IRON 627 melt in water, add 2.1 ml of 50 per cent. v/v sulphuric acid and dilute the solution to 100 ml.Take two 20-ml aliquots and proceed as for the determination of soluble silicon, but add 1 ml of the ferrous sulphate solution instead of 5 ml. Carry out a blank determination on a 0.2-g portion of fusion mixture in the same manner. ACTIVATION PROCEDVRE- Irradiate 1 g of iron a t pile factor 10 for 6 hours. Dissolve it in a mixture of 15 ml of hydrochloric acid, 3 ml of nitric acid and 5 ml of silicon carrier solution. Evaporate the solution to dryness, dissolve the residue in 5 N hydrochloric acid and spin the solution in a centrifuge. Discard the solution and wash the impure silicic acid with hot 5 N hydrochloric acid until the iron colour has been removed.Fuse with 40 mg of sodium tungstate and 0.3 g of sodium carbonate, and dissolve the melt in 10 ml of hot water. Add 1 ml of manganese carrier solution dropwise, stir, spin in a centrifuge and discard the precipitate. Just neutralise the solution with dilute nitric acid (methyl red as indicator), add a slight excess of saturated mercurous nitrate solution, spin in a centrifuge and discard the precipitate. Add 1 ml of tungsten carrier solution dropwise, stir, spin in a centrifuge and discard the precipitate. Precipitate the excess of mercury with hydrochloric acid, spin in a centrifuge and discard the precipitate. Add 5 ml of hydrochloric acid to the solution and evaporate to dryness. Dissolve the residue in 10 ml of 5 N hydrochloric acid, spin in a centrifuge and discard the solution. Wash the silicic acid twice with warm 5 N hydrochloric acid and transfer to a filter. Wash with water, ethanol and diethyl ether, mount, and count a t intervals of 30 minutes. Repeat the counting next day at intervals of 1 hour. Determine the percentage recovery by igniting the precipitate and weighing the silica produced. Filter, wash with water, and ignite. RESULTS The reproducibility of the absorptiometric method is shown by the results of seven determinations of soluble silicon in a particular sample; the maximum found was 0,0075 per cent., the minimum found was 0.0071 per cent. and the standard deviation was F0.00013 per cent. The amounts of total silicon in various iron samples were determined by both methods. The results were as follows- Sample No. . . . . . . . . . . &I7251 M640 111535 M554 M585 M633 Silicon by absorptiometric method, yo . . 0.0019 0.0094 0.0049 0.0020 0.0044 <0.0005 Silicon by activation method, Yo . . . . 0.0019 0.0091 0.0044 0.0015 0.0049 0.0002 The work described was carried out as part of the general research programme of the National Physical Laboratory and is published by permission of the Director of the Laboratory. Received May 'ith, 1958

ISSN:0003-2654    

DOI:10.1039/AN9588300624

出版商:RSC    

年代:1958

数据来源: RSC