ISSN:0003-2654    

DOI:10.1039/AN95176FX025

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176BX027

出版商:RSC    

年代:1951

数据来源: RSC

ISSN:0003-2654    

DOI:10.1039/AN95176FP063

出版商:RSC    

年代:1951

数据来源: RSC

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THE ANALYST viiMINISTRY OF SUPPLY: PRISCIP.41- SCIESTIFICOFFICER OK SESIOR SCIESTIFIC OFFICER.HE Civil Service Couiniissioners invite applications fromTCHEMISTS for a permanent appoiiitnieiit a t the AtomicEnergy Research Lstablishnierit, Harwell, nr. Didcot, Berks.,for work on the electro-magnetic method of separation ofstable isotopes. The duties of the post includes:-(a) Supervision of junior staff in the preparation of iiiater-ials for separation;( 0 ) The establishment of efficient methods of processingseparated isotopes to produce thein in forms satis-factory for use;Acting as deputy to the project leader with particularresponsibilities for the promotion of the use of stableisotopes in physical and radio chemistry.Candidates niust have been born on or before 1st August,1920, and must possess a 1st or 2nd class honours degree inChemistry or equivalent qualification and haw had consider-able relevant experience.The electro-inagiletic method ofseparation is applicable to all plyisotopic elements so thatthe qualification required for ( a ) and (6) above is a wide know-ledge of annlytical inorganic chemistry.Tht, Coinriiissioners may, at their discretion, admit a candi-date with high professional attainments notwithstanding thathe or she niay not possess the above qualifications.Salary scale Principal Scientific Officer (men) L960-L1,295,(wonmi) LMO-L1,140, Senior Scientific Officer (men) L520-/l!)lO, (woiiien) L595-LXlO. Post carries benefits underFederated Superannuation System for Universities.Goodhonsirig prospects for selected candidate if married.Further particulars and application forms from the Secre-tary, Civil Service Conitiiission, Scientific Branch, TrinidadHouse, Old Burlington Street, W.l, quoting So. S 4045/51.Cornpleted applications must be returned by Xth .4ugust,1951.Candidates born between 211d August, 1920, and 1st August,1925 (inclusive), may be considered for appointment as SeniorScientific Officer but must apply through the Open Competi-tion urider Sonnal Regulations already announced (So.(c)3 3 9 9).HIS MAJESTY’S COLONIAL SERVICE, h1.4L.4Y.4BIOCHEMIST is required to carrv out Research andAother routine work in the Institute of Medical Research,Federation of Malaya. The post is pensionable but theofficer will be on agreement for three years in first instance.Salary according to aualifications and experience in scaleLiOO-L1,652 including pensionable expatriation allowance.Cost of Living Allowance of between La36 and L507 accordingto salary and family coniniitinents is also payable.Govern-ment quarters and heavy furniture, if available, are provideda t norniiial rent. Officers occupying private quarters maybe granted an assistance allowance towards rent. Incometax a t local rates which are much lower than in UnitedKingdom. Free first-class passages for the officer, his wifeand children under age of ten, not esceeding four personsbesides himself, once each way during each tour of service.Leave at the rate of 15 days for each year of resident service.Free niedical attention for officer, wife and children, but acharge is made for hospital maintenance.Candidates who,sliould be under 35, should possess a British Honours degreein Chemistry or cqriivalent qualification plus at least oneyear’s approved post-graduate Biocheriiistrv experience. A1’h.D. in organic cheniistrv or eqiiivalerit post-graduateresearch is desirable. Application should be made, givingbrief particulars of qualificatioris and experience to theDirector of Recruitment (Colonial Service), 2 , SanctuaryBuildings, Great Smith Street, London, S.W.1, quotingrcference 2 7 lO6/49/51.OCHr PRODUCTS LIMITED have an opening for assist-five years, of B.Sc. or A.K.I.C. standard, who are trained orwish to do cheiiiicd analysis.Write stating qualifications,experience and salary required to the Secretary, RocheProducts Limited, Welwyn Garden City, Herts.R; ints in ? their .4nalytical Department, age about twenty-CHli?lIST, qualified, required for control of analyticalsection of laboratory at our Shaftnioor Lane worksBirmingham. Previous experience in this class of work i;essential. The position is permanent and pensionable andoffers excellent scope for initiative. State age, qualificationsand experience to Personnel Manager, Joseph Lncas Liniited,Gt. King Street, Birmingham.~~~~OMMONWEALTH BLREAU OF ASIMAL HErZ1,TH.c.4 few additional part-time abstractors are required forthc “Veterinary Bulletin ” particularly for literature onChemistry, Biochemistry, ’Physiology and Pharmacology inFrench, German, I tnlian, Spanish and Scandinavianlanguages. Details on application to the Dircctor, Corrinion-wealth Bureau of ii~iirnal Health, Veterinary Laboratory,Sew Haw, Weybridge, Surrey.SSISTANT CHEMIST, male or female, required forAgenerd analytical work.Position offers good prospects otadvancement. Work varied and interesting. Excellentcanteen facilities. Write, stating age, experience, andsalary required to Personnel Department, E.M.I. FactoriesLtd., Hayes, bliddleses.CHE!lIST (male or feiiiale) required for laboratory of largeengineering works in West London area. The workinvolves analysis of ferrous and non-ferrous alloys and inves-tigation of various problems in connection with metal finishingand corrosion.5-dav week. Pension fund. Good prospectsfor advancement. write Box No. 3577, THE ANALYST, 47,Gresham Street, London, E.C.2.UALYST required having wide experience in generalAjnalytical technique to supervise routine tests and developnew methods for a food laboratory in the North-West. Someexperience iii microbiological work an advantage. The manappointed will have considerable responsibility and be givena corresponding salary. Write Box 3 5 5 8 , THE AXALYST,17, Gresham Street, London, E.C.2.VACASCY occurs for a senior analvtical cheniist in aAlarge consulting laboratory dealing with foods andpharmaceuticals in London. Must be capable analyst andorganiser. Good prospects and experience. Conlinenringsalary L50(J-L650. Write Box 3779, THE ~ A L Y S T , 47,Gresham Street, London, E.C.2.TAFFORD ALLEN & SONS LTD require a seniorSassistant analvst for their Lo& Melf‘drd Suffolk labor-atory. Applicants should have several yea&.’ exper;ence Ofpharmaceutical analysis and should have a pharmaceuticalor A.R.I.C. qualification. Salary according to qualificationsand experience. Apply-The Directors, Stafford Allen &Sons, Ltd., Long Melford, Sudbury, Suffolk.HEFFER’SOF CAMBRIDGEare always glad to buySCIENTIFICJOURNALSespecially complete sets andruns ofT H E ANALYSTalso scientific and techaicallibraries, early books, bookson the history of science,etc.W. HEFFER & SONSLimitedPetty Cury, CambridgeEnglan

ISSN:0003-2654    

DOI:10.1039/AN95176BP067

出版商:RSC    

年代:1951

数据来源: RSC

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JULY, 1951 Vol. 76, No. 904 Addendum* to Report No. 137 of the Essential Oils Sub-committee of the Analytical Methods Committee THE DETERMINATION OF ESTERS THE Analytical Methods Committee has received from the Essential Oils Sub-Committee3 the following Addendum to their Report No. 13, ‘‘ The Determination of Esters ” (A~alyst, 1937, 62, 541), and its publication has been duly authorised. ADDENDUM Twenty millilitres of distilled water shall be added to the contents of the flask after saponification and before titration; a similar addition shall be made to the blank. This modification makes the end-point sharper and is particularly helpful for dark-coloured oils. * Individual copies of this Addendum will be supplied, without charge, on application. t Analyst, 1937, 62, 541. $ Membership as published in Analyst, 1950, 75, 286. 387

ISSN:0003-2654    

DOI:10.1039/AN951760387b

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

388 LEWIS AND GRIFFITHS : DETERMINATION OF INORGANIC COMPOUNDS [Vol. 76 Inorganic Chromatography on Cellulose Part IV* Determination of Inorganic Compounds by Paper-Strip Separation and Polarography BY J. A. LEWIS AND J. M. GRIFFITHS (Presented at the meeting of the Society on Wednesday, February 7th, 1951) Separations are described in which problems of interference in quantita- tive analysis are overcome by using paper-strip chromatography. These separations can be divided into three type:; : (a) the separation of one individual from a number of metals, (b) the separation of a group of metals into individual metal salts and (c) the separation of a larger group into smaller groups of metal salts in which interference no longer occurs. Final estimations have been carried out by polarography.THE separation of inorganic salts by a chromatographic technique using absorbent paper in conjunction with organic solvents has already been the subject of a number of publications from this 1 a b o r a t 0 r y . l ~ ~ ~ ~ ~ ~ ~ ~ The work with paper strips has, however, mainly been con- cerned with qualitative analysis, although the application of the technique as a basis for quantitative estimation of metals has been indicated. This paper presents details of the separation and determination of a number of metals and mixtures of metal salts by means of chromatography on paper strips followed by polarography for the final determination. The separation3$4 is performed by placing an accurately measured volume of the test solution near one end of a strip of absorbent paper.The end of the strip nearest the test patchis then immersed in the organic solvent, which is allowed to diffuse through the paper and over the sample of metal salts; one or more of the metal salts dissolve and move down the paper to form well-defined zones. The regions containing the metal salts are then separated from the rest of the paper strip and the amount of metal in each region, after solution, is deter- mined by the polarograph. Three types of separation are described, ( a ) the separation of one metal from a mixture, exemplified by uraniuin in the presence of a large number of other metals, (b) the separation of several metal salts in a mixture, such as cobalt, nickel and copper in a sample of alloy steel and copper and cobalt in iron pyrites and (c) the separation of a mixture of metals into groups containing several metals that can be determined by polaro- graphy without further separation, represented by ten metals separable into two groups of five containing (2) vanadium, copper, uranium, lead and titanium and (ii) iron, molybdenum, bismuth, antimony and cadmium.A new supporting electrolyte for polarography that makes use of salicylic acid to form complex ions with certain metals has been found valuable for determination of several metals in a mixture. This combination of chromatographic separation and polarography has proved satis- factory, the procedure being both rapid and reasonably accurate when the smallness of the quantities of material required for test is borne in mind.Moreover, the method shows promise of wide application in micro-analytical work. EXPERIMENTAL The extension of paper chromatography to a quantitative method required rigorous attention to details, i.e., the acidity of the metal solution, the effects of interfering anions, the composition of the solvent and sometimes of the atmosphere in the gas-jar. Methods for the removal of metals or groups from the paper and subsequent treatment to produce a convenient solution for estimation have been investigated. Volumes were measured on to the paper (Whatman No. 1) with a micrometer syringe. * For particulars of earlier papers in this series (not in The Analyst), see reference list, p. 395.July, 19511 BY PAPER-STRIP SEPARATION AND POLAROGRAPHY 389 THE SEPARATION AND DETERMINATION OF ONE METAL FROM A GROUP OF METALS- The first type of paper strip separation investigated was the isolation of one element, and the first element so examined was uranium. The isolation of this element on a semi- quantitative basis has been described by Arden, Burstall and Lin~tead.~ The solvents used were tetrahydrosylvan and tetrahydropyran with additions of small amounts of nitric acid and saturated with water.For quantitative separation it was found necessary to use a t least 5 per cent. of nitric acid with tetrahydrosylvan and at least 7 per cent. of nitric acid with tetrahydropyran. Among simple solvents, nitromethane shows promise of being useful for the separation. The original metal solution was in nitric acid of 50 per cent. v/v concentration.I t was found that the whole of the uranium was always present in the leading 6 cm of the solvent run and that a run of 10 cm was sufficient to separate uranium from the common metals. To test the effects of other metals a run was carried out with trace amounts of the following present: Li, Re, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, Ce, La, Pr, Ta, W, Os, Ir, Pt, Au, Hg, T1, Pb, Bi, Th. The effect on the quantitative separation of uranium was negligible. With regard to anions, phosphate can be tolerated in amounts up to 0.7 M in the original metal solution provided there is an excess of ferric iron present and provided a run is continued for 16 cm in order to obtain a section of paper sufficiently free from phosphate to be ignited.Sulphate can be tolerated in amounts up t o 0.8 M . Above these concentrations, phosphate and sulphate cause the uranium to spread over the paper. These high concentrations, however, are unlikely to be encountered in a solution of a sample. Chloride ions promote the movement of other metallic ions, notably iron, on the paper. A solution of the uranium is made by removing the paper from the gas-jar, drying it, tearing out the last 6 cm of solvent run and burning this section of paper. It was found that heating the paper in a crucible to reduce it to ash led to low results, so the paper is held by one corner in glass forceps and burnt, the ash being dropped into a beaker. The unburnt corner, remote from the leading solvent edge, can be rejected.The ash is then twice taken to dryness with a few drops of diluted perchloric acid, 2 ml of acid (0-1 N hydrochloric acid saturated with alkali-soluble methyl cellulose) are added, the whole is stirred with a glass rod and 1 ml of the resulting solution is taken for polarographic estimation between 0 and - 0.4 volt. The results shown in Table I are for synthetic solutions used in the course of a study of the method. With synthetic solutions it was found necessary to add ammonium nitrate to the original solution as “salting-out” agent; this is unnecessary with sample solutions. TABLE I DETERMINATION OF u308 I N SYNTHETIC SOLUTIONS Quantity of U308 on absorbent paper, pg . . 20 70 100 150 200 24 68 101 141 21 1 68 101 142 193 Observed quantities of U308 determined by 72 101 142 197 99 145 204 93 147 20 1 polarograph, pg .. .. . . . .[ k% 69 24 72 21 67 102 147 204 Mean observed quantities of U,O,, pg . . 23 69 99 144 202 Solutions of ores and other products have given results of which a selection are shown The first five results on siliceous ores have been published by Arden, Burstall The method has been used with satisfactory results for routine estimations and exemplifies in Table 11. and Lin~tead.~ the isolation of one element for analysis. THE SEPARATION OF A GROUP OF METALS INTO INDIVIDUAL METAL SALTS- For some groups of metals, estimation in the presence of one another is difficult and the chemical separation tedious. As an example of the application of paper-strip separation to such a group, a mixture of the chlorides of nickel, manganese, cobalt, copper and iron can be separated into individual metal salts and taken into solution for estimation.The polarograph was used for final determination. In simple chloride solution, polarographic estimation390 LEWIS AND GRIFFITHS: DETERMINATION OF INORGANIC COMPOUNDS [VOl. 76 presents problems of interference within this group, but the metals, once separated, can be estimated in any desired supporting electrolyte. For the purpose of the extraction, the atmosphere in the gas-jar was brought to equilibrium with separate vessels, together in the same gas-j a]:, containing (a) saturated ammonium nitrate solution (giving 65 per cent. relative humidity) and (b) acetone. The paper strips were allowed time to “condition” in this atmosphere after placing the spot of solution 12 cm from the top of the paper.The solvent used for extraction was 50 parts by volume of acetone, 8 parts of concentrated hydrochloric acid and 42 parts of methyl n-propyl ketone, b.p. 98” to 100” C. This solvent was allowed to seep down through the spot for a distance of at least 30 cm. The separation was usually complete in about 6 hours at normal room temperature TABLE I1 COMPARISON BETWEEN DETERMINATIONS OF URANIUM BY CHEMICAL AND PAPER-STRIP METHODS Uranium as U,O, determined by Chemical Polarographic Type of ore analysis, analysis, f A 1 % Yo Pitchblende . . . . . . 26.46 26.4 Siliceous . . . . . . . . 1.33 1-25 1.26 1.16 0.31 0.30 0.69 0.70 0.91 0-94 0.045 0.050 1.28 1.53 0.19 0.21 Monazite .... .. 0.37 0.35 0.34 0-34 0.38 0.38 Phosphate . . .. .. 0.024 0-039 0.015 0.020 0.009 0.01 1 of about 20” to 25” C. By tapering the upper end of the paper to less than 1 cm to reduce “wick” action and using a strip 40 cm long and 3.5 cm wide, it was possible to allow the run to proceed overnight. When the run was completed, the strip was removed and dried and the positions of the various metals ascertained by exposing the strip to strong ammonia vapour and then spraying it with a mixture of equal volumes of rubeanic acid (a 0.25 per cent. solution in alcohol) and 1 per cent. of benzidine in a 10 per cent. aqueous solution of acetic acid. The two stock solutions were mixed just before use. Nickel, manganese, cobalt and copper, under this treatment, give deep blue, pale blue, yellow arid greyish-green stains, respectively, which appear in that order down the paper.Iron gives a very pale brown self-colour below all the foregoing metals. The manganese position is marked lightly with pencil as the colour is transient. The sections of the strip containing the various metals were then cut out and ashed in separate crucibles, the ash being taken just to dryness with the appropriate fuming agent, dissolved in 2ml of supporting electrolyte and a polarogram taken with the conditions as indicated in Table 111. In the fuming process, the use of industrial infra-red lamps over the vessels was found most valuable in avoiding spil:ting, baking and the necessity for constant supervision. In Table I11 mean results found by this procedure are shown, the maximum deviation from the mean being 5 per cent.in the region of 75 to 100 pg; the deviation increases as the amount of metal decreases. For iron, a blank of about 30 pg has been measured on a strip of filter-paper cut adjacent to that on which the estimation was carried out, and this figure has been subtracted from the observed result. .Because of this blank with Whatman No. 1 filter-paper, no determination of iron has been made below 30 pg. Filter-papers of lower ash content have been shown to give a lower blank, but do not give quite such good separations. An alloy steel and a sample of iron pyrites have been analysed for some of these elements by this technique. The alloy steel was digested with aqua regia, taken to dryness severalJuly, 19511 BY PAPER-STRIP SEPARATION AND POLAROGRAPHY TABLE I11 391 MEAN RESULTS OF POLAROGRAPHIC DETERMINATIONS BY THE PROCEDURE DESCRIBED Ion r Nickel Hydrochloric acid Manganese Hydrochloric acid Cobalt Aqua regia, then hydro- chloric acid potassium chloride + 0.02 per cent.of agar-agar 100 98 75 75 10 12.5 0.1 N Copper Nitric acid Remarks - Iron Nitric acid Fuming agent Supporting electrolyte 0.1 N potassium chloride + 0.01 per cent. of gelatin 100 96 75 71 10 10 10 per cent. sodium potassium tartrate M potassium oxalate Dissolution of copper is very slow N potassium chloride satu- rated with alkali-solu ble methyl cellulose 100 99.5 75 75 10 10 100 97.5 75 76 10 10 100 102 75 77 30 33.5 All from one strip of paper All from.one strip of paper Each extracted from 100 pg of each of the other metals times with hydrochloric acid and then digested with hydrochloric acid, diluted and filtered.The residue was dissolved in caustic soda and tungstic acid was precipitated by acidifying the solution with hydrochloric acid. The mixture was filtered and the bulked filtrates were made up to 50 ml; 0.10 ml of this solution, representing 2135 pg of sample, was taken for estimation. The iron pyrites was dissolved in aqua regia, evaporated to dryness and then taken to dryness several times with, and finally dissolved in, hydrochloric acid. The solution was made up to 25 ml, and 0.05 ml, representing 4956 pg of sample, was taken for estimation. Both experiments were performed in quadruplicate with the results shown in Table IV. TABLE IV ANALYSES FOR COBALT, NICKEL AND COPPER IN AN ALLOY STEEL AND A SAMPLE OF IRON PYRITES Element in alloy steel Amount present as stated by the British Chemical Standards, % ..4-35 (4-26 to 4.46) .. 0.43 (0.42 to 0.47) .. 0-05 approx. Found, % 4.40 0.46 0-04 approx. Remarks Cobalt .. Nickel .. Copper . . By comparison of standard stains Element in iron pyrites Copper . . Cobalt .. Amount present as stated by Bureau of Analysed Samples, Ltd., O/ Found, % 2-70 0.12 Remarks /O 2.69 0.10 .. .. Cobalt section taken up in base contain- ing some cobalt* Rubeanic acid stain Nickel .. .. Trace (one observer) Trace * This was found to aid consistent results for the very small amount of cobalt on the paper. Notes-Technical grades of methyl n-propyl ketone were tested for discolouration with concentrated hydrochloric acid and grades that did not discolour were chosen for this work.The ketone as obtained was distilled and the fraction boiling in the range 98" to 100" C was used. Occasional cleaning and recharging of gas-jars is advisable for the maintenance of good results. The elements gallium, zinc and uranium, which tend to interfere with the polarographic estimation of nickel and cobalt in chloride solution, move into the copper - iron region on the paper strip and do not interfere with the estimation of these in their respective supporting electrolytes.392 LEWIS AND GRIFFITHS : DETERMINATION OF INORGANIC COMPOUNDS [Vol. 76 The effect on the separation of anions other than chloride has been examined, and it was found that up to 20 per cent.of nitric acid or calcium nitrate and 10 per cent. of sulphuric acid or sodium sulphate (in the original metal solution) could be tolerated. Above these limits, the separations were progressively less satisfactory. THE SEPARATION OF A GROUP OF METALS INTO SMALLER GROUPS- In the course of a search for supporting electrolytes of wide application to the polaro- graphic determination of metals, salicylic acid in aqueous solution was found to be valuable in giving well-defined waves at convenient intervals for certain metals. This supporting electrolyte can be used, for example, in the estimation of commonly occurring groups of metals, such as (a) vanadium, molybdenum and titanium, ( b ) iron, copper and uranium and (c) bismuth, antimony and lead, in one operation. Other possible combinations can be derived from Table V on p.394. During the investigation of this supporting electrolyte containing salicylic acid, it was found that iron interfered with vanadium, molybdenum and bismuth with copper, antimony with uranium, and titanium with cadmium. A simple paper-strip separation was therefore used to divide these metals into two groups in which each metal could be directly estimated. Investigation showed that n-butyl alcohol in conjunction with hydrochloric acid* separated the chlorides of these ten elements into two group:; within which all interference was eliminated. The promise shown by the early work was mentioned by Burstall, Davies, Linstead and Wells4 in Part I1 of this series, but some modification has since been made to render the separation quantitative.Molybdenum is estimated after conversion on the paper strip to molybdenum blue, which reduces at a potential less negative than does molybdic acid. This fortunate discovery was useful in that the half-wave potential was thereby separated from that of bismuth in the same sub-group. SALICYLIC ACID AS A SUPPORTING ELECTROLYTE FOR POLAROGRAPHY Among a number of organic acids, salicylic acid showed promise of being useful in com- plexing certain metals so that waves were produc'ed on the polarograph at convenient intervals. The satisfactory use of salicylic acid appears to depend on the following factors- (a) Salicylic acid concentration is not critical, but 1 volume of saturated solution in 4 volumes of final solution gives good results. (b) Sulphuric acid (about 5 per cent.v/v) should be present so that the pH of the final solution is less than 2. (c) Chloride ions should be absent. The presence of chloride alters the anode potential and prevents the appearance of waves for vanadium, iron and molybdenum blue at the start of the polarogram. If these metals are to be estimated, chloride can be removed by shaking the solution with solid mercurous sulphaie and then filtering it, although an allowance must be made for a mercurous wave at 0 volts. (d) Phosphate ions should be absent. The presence of this anion causes coalescence of polarographic waves in salicylic acid. (e) Nitrate must be absent. In acid solution, attack on the anode by any appreciable amount of nitrate ion renders zero setting difficu1.t and vitiates readings for iron and vanadium.I t also has a slight effect on wave heights generally. (f) Alizarin may be present with advantage. A small amount of solid AnalaR alizarin, added to the final solution, prevents the appearance of maxima, e.g., on the copper wave. After a paper-strip separation, this addition of alizarin is not necessary, probably because the maxima are suppressed by cellulose dissolved when the metals are taken into solution for polarography. Routine estimations of iron have been performed with satisfactory results, in the absence of vanadium, by adding 1 volume of solution in sulphuric acid to 1 volume of an aqueous solution comprised of- Half-saturated salicylic acid.Half-saturated A.R. alizarin. 10 per cent. v/v concentrated sulphuric acid, A.R., sp.gr. 1-84. * Solvent suggested by Mr. N. F. Kember of this laboratory.July, 19511 BY PAPER-STRIP SEPARATION AND POLAROGRAPHY 393 A procedure found satisfactory for evaluation of waves in the region of zero e.m.f. (e.g., that for iron) is to measure wave heights from a line obtained by polarography of the supporting electrolyte only, before the metal solution is added. The other nine elements can be estimated to an accuracy of k3 per cent. (& 1 per cent. for copper) in concentrations of 30 to 1500 pg per ml in the final solution, estimations being made in triplicate. Between 5 and 30 pg per ml the accuracy of the determinations decreases to k20 per cent. Other common cations with the exception of tin do not interfere.PAPER-STRIP SEPARATION TO ELIMINATE INTERFERENCE Solutions were made up to contain the chlorides of copper, uranium, lead, iron, bismuth, antimony and cadmium together with titanium hydroxide (precipitated from sulphate) and ammonium vanadate and molybdate. The best separations in the initial experiments were attained with 20 per cent. of hydrochloric acid in the aqueous solution of metal salts, with the spot left wet on the paper, and with 5 per cent. v/v of concentrated hydrochloric acid in the butyl alcohol used as separating solvent. These conditions were therefore used in all subsequent investigations. Separations have been made on Whatman Nos. 1 and 3 filter- papers. The former gives a slower run of about 9 hours or, conveniently, overnight and will take a maximum of 0.1 ml of solution on a strip 2.5 cm wide.The No. 3 paper permits separation in 3 hours and 0.25 ml of solution can be taken up on the paper without impairing results. The groups into which the metals separate are: (a) vanadium, copper, uranium, lead and titanium in the upper section of the paper; (b) iron, molybdenum, bismuth, antimony and cadmium in the lower quarter of the solvent run. There is a metal-free space between these two groups which facilitates division. The line at which to part the paper is detected by producing molybdenum blue on the strip. This is visible only when at least 100 pg of molybdenum is present. With smaller amounts, the leading quarter of the solvent run is assumed to contain group (b) ; alternatively, a known amount of molybdenum is added to the sample solution.The colour of the reduced molyb- denum compound is developed by drying the strip under an infra-red lamp, followed by spraying with a saturated aqueous solution of butyl alcohol and again drying. The strip is then exposed simultaneously to air and the vapour from dilute ammonia. Infra-red radiation or sunlight and a pH of about 4-0 appear to be essential to the production of the colour. Should the colour appear before completion of the treatment, the treatment is discontinued. The strip is torn immediately above the blue spot and the metals are extracted for polarography. Some trouble was experienced in removing the groups quantitatively from the paper before the polarographic determination.The methods tried were (i) ashing, (ii) macerating with cold acid and (iii) digestion with hot acid. A limitation was imposed by the requirements for the final solution. The procedure finally adopted was to boil the section of the paper concerned for 1 minute, first with water, then with saturated aqueous salicylic acid, and then to heat with 2 N sulphuric acid. The last stage had the effect of pulping the paper, which was then filtered through sintered glass, together with added mercurous sulphate (see later) before adding the filtrate to the other extracts. It was also found necessary to cool the solutions before combining them in order to avoid decomposition of molybdenum blue. Chloride was removed from the combined water and salicylic acid extracts before adding the chloride-stripped sulphuric acid leach.Removal of chloride was achieved by shaking with a small amount of solid mercurous sulphate, 1 drop of which was added as a slurry with dilute sulphuric acid; the solution was then filtered through sintered glass, conveniently from a Schwarz - Bergkampf micro-beaker, into the sulphuric acid filtrate. On subsequent polarographic estimation, a mercury wave is produced at 0 volts, and a correction must be made when estimating vanadium or iron. THE EFFECT OF VARIOUS IONS ON THE SEPARATION Most common cations, tin being an exception, do not give waves in the salicylic acid medium and hence do not interfere in these determinations. Tin, however, prevents the development of molybdenum blue in the paper separation and also interferes by interaction with ferric iron.In addition, tin gives a wave that interferes with cadmium, but only if present in excess of the equivalent of any ferric iron that is present. Phosphate ions interfere with the paper-strip separation when present in concentrations394 LEWIS AND GRIFFITHS DETERMINATION OF INORGANIC COMPOUNDS [VOl. 76 above the equivalent of 0.03 M orthophosphoric acid in the sample solution. Phosphate also inhibits the formation of the molybdenum blue compound. Sulphuric acid in the sample solution can be tolerated up to 0.2 M , but interferes with the development of the molybdenum blue colour and slows down the movement of the metals in relation to that of the solvent front on the paper strip. Where phosphate or sulphate, or both, are present, two paper strips are run in parallel.One is then developed with potassium ferrocyanide to find the position of the molybdenum, which shows up as a dull brown stain. The other strip is then assumed to have the molybdenum in a corresponding position and is divided above this to give the two groups for estimation. HALF-WAVE POTENTIALS IN SALICYLIC ACID The half-wave potentials of the elements, determined after the separation and solution These potentials are determined against procedures already described, are given in Table V. an internal mercury anode. TABLE V HALF-WAVE POTENTIALS IN SA:LICYLIC - SULPHURIC ACID Element Ei, volts Group Vanadium . . . . .. .. .. - 0.025 Copper .. .. .. .. * . Uranium . . .. . . . . .. - 0.575 Lead .. -0.375 1 Upper section of .. .. .. .. .. - 0.725 1 ‘lter-paper Titanium . . .. .. .. .. - 1.026 J Iron . . .. .. .. .. .. -0.025 7 Lower section of filter-paper Molybdenum blue . . .. .. .. -0.20 Bismuth . . . . . I .. .. - 0.40 Antimony .. .. .. .. .. - 0.60 Cadmium . . .. .. .. .. - 1.126 REsuL:rs The quantities that can be estimated by the combined paper-strip - polarograph method are limited (a) by the amount of the metal chlorides that will dissolve in 0-25 ml of solution and (b) by the amounts that can be quantitatively removed from the paper and estimated on the polarograph. TABLE VI QUANTITATIVE RESULTS Observed amount A f I Calculated Vanadium, Copper, Uranium, Lead, Titanium, amount, Ilg Pg Pg Pg Pg Pg 995 1000 985 960 960 1000 96 102 97 97 92 100 28 29 29 30 29 30 Calculated Ferric iron, Molybdenum, Bismuth, Antimony, Cadmium, amount, Pg r g Pg r g PLg Pg 965 955 1020 1035 960 1000 94 99 100 104 98 100 27 28 31-5 31 30-5 30 For routine work, preliminary experiments indicate that the use of the method of stan- dard addition for one element can be followed by the use of that element as internal standard for the others.Disproportionate amounts can easily be separated and can be estimated within the usual limits of polarograph:y, i.e., a small wave for a metal can be esti- mated accurately when it occurs before, but not after, a large one. Means of three results are quoted in Table VI: the maximum deviations from the mean were 6 per cent. in the 1OOO-pg range and in the 100-pg range, becoming progressively greater as the amount of the metals decreased.The determinations were carried out by comparison with standard wave heights. Each measurement was made in the presence of a similar concentration of the other nine elements.July, 19511 BY PAPER-STRIP SEPARATION AND POLAROGRAPHY 395 A standard mercury wave height has been subtracted from the values for iron and vanadium. The solubility of lead in sulphuric acid is greatly increased by the prior addition of salicylic acid. The lead wave is always small, and it has been found that the use of a nearly neutral nitrate solution instead of sulphate is advisable where the estimation of lead is important. The original chloride solution of titanium must be freshly prepared to avoid hydrolysis. The tendency for high results to be obtained for bismuth and antimony may be due to molybdic acid regenerated by the ferric iron, and the estimation of this group must be carried out quickly after the metals have been removed from the paper.The polarograph has been shown to be a useful instrument for the final estimation of quantities separated by paper-strip extraction, and conversely the extractions are considered a valuable complement to polarography by extending the scope of the technique. These investigations have been carried out in part for the Ministry of Supply and in part for the Chemistry Research Board, D.S.I.R., and are published by permission of the Director of the Chemical Research Laboratory. REFERENCES 1. Report of the Chemistry Research Board, 1947. 2. 3. 4. 5. Arden, T. V., Burstall, F.H., Davies, G. R., Lewis, J. A., and LirIJcGau, R. P., Nature, 1948, Arden, T. V., Burstall, F. H., and Linstead, R. P., J. Chew. SOC., 1949, S 311. Burstall, F. H., Davies, G. R., Linstead, R. P., and Wells, R. A., Ibid., 1950, 616. Burstall, F. H., Davies, G. R., and Wells, R. A., Disc. Farad. SOC., 1949, No. 7, 179. 162, 691. NOTE-References 3, 4 and 5 are to Parts I, I1 and I11 of this series. CHEMICAL RESEARCH LABORATORY TEDDINGTON, MIDDLESEX DISCUSSION DR. H. LIEBMANN asked whether RF values individually determined were a reliable guide to the possibility of separating a given metal from others, and if the presence of other metals influenced the RF values. MR. LEWIS replied that, while other metals had some effect on the movement of a particular element, the RF value individually determined was a very strong indication of its behaviour in other circumstances.Anions, however, had great effects on RF values. MR. D. G. HIGGS asked whether it was possible to separate very small quantities of metals such as iron from relatively pure metals such as molybdenum. Would i t be possible, for example, to separate 0.01 per cent. of iron from more than 99.5 per cent. pure molybdenum? MR. LEWIS answered that the problem of separating trace amounts (and parts per million could be successfully dealt with) was best solved by the use of upward development on a paper cone. A large amount of sample could be put on the paper around the base and the solvent chosen so that the trace element was concentrated a t the apex.DR. J . H. HAMENCE asked the authors whether from their very wide experience of inorganic chromato- graphy they could give an opinion as to the best technique to apply in developing a chromatograph. Various workers had used different techniques, some with the paper in a vertical and others with it in a horizontal position. MR. LEWIS said that the workers a t the Chemical Research Laboratory had found downward displace- ment the best technique in most circumstances and held that the assistance of gravity was useful. MR. J. HASLAM asked whether, in the determination of the general metal content of foodstuffs after a preliminary wet digestion, i t was likely that addition of salicylic acid and subsequent polarography of the wet digestion product would give a useful general picture of the metal content of the foodstuff. MR. LEWIS replied that the salicylic acid supporting electrolyte would undoubtedly be useful for the estimation of small amounts of lead, antimony or copper in a sulphuric acid digestion product, but that the commonly occurring tin might cause complications. DR. LIEBMANN asked whether tin produced a curve in the salicylic acid medium, and if so, which metals would interfere. MR. LEWIS said that tin did produce an ill-defined wave in salicylic - sulphuric acid a t 1-1 volts, where it interfered with cadmium, but only if present in excess of its equivalent of ferric iron. It interfered with iron by reducing it, and was itself oxidised. MR. N. STRAFFORD asked whether arsenic would give a wave in the determination of poisonous metals in foodstuffs, medicinals, and so on, by polarography. If it did not, then polarography would not provide a universal method for the determination of poisonous metals. MR. LEWIS stated that arsenic did not give a wave in the salicylic medium, but that useful waves had been reported in other media. In a limited experience of this particular element, he had not found a wave suitable for analysis. Which did the authors consider to be the better?

ISSN:0003-2654    

DOI:10.1039/AN9517600388

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

396 BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC [Vol. 76 Inorganic Chromatography on Cellulose The Use of Columns of Cellulose in Combination with Organic Solvent Extraction for the Separation of Uranium from Other Metals BY F. H. BURSTALL AND R. A. WELLS (Presented at the meeting of the Society o:a Wednesday, February 7th, 1951) A new method is described for the separation of uranium from other metals; it is based on the extraction of uranyl nitrate with ether containing 6 per cent. v/v of nitric acid in the presence of cellulose. The method has been applied to the determination of uranium in minerals and ores with results that compare favourably in simplicity, rapidity and accuracy with other methods. The behaviour of a number of other anions and cations in the process has been investigated and methods have been devised for overcoming difficulties caused by the presence of some metals and acid materials on the extraction process.IT has been known for many years that uranyl nitrate is soluble in ether and other organic solvents, and this fact has been widely used as a basis for the separation of uranium for the determination of the element in minerals, ores and other products. The method, however, does not always give a pure extract of uranyl nitrate and further treatment is necessary. In early work with paper strips and organic solvents containing nitric acid, Arden, Burstall and Linsteadl found that very good separations of uranium from a large number of other metals could be achieved. The use of paper strips limits the quantity of material that can be used, but in later work by Burstall, Davies and Wells2 it was found possible to separate much larger quantities of metallic products by using columns of cellulose pulp packed in organic solvents and contained in glass tubes, and the application to uranium was briefly indicated. A detailed account is now given of the use of ethyl ether containing 5 per cent. v/v of nitric acid as solvent and cellulose pulp asl adsorbent, for the quantitative extraction of uranium from a variety of materials.The method consists in preparing a nitrate solution of the sample for analysis in dilute nitric acid and transferring this mixture to the top of a column packed with cellulose in the presence of the ethyl ether - nitric acid solvent. The solvent is allowed to percolate through the column; uranyl nitrate is dissolved and passes quantitatively into the liquid eluent, whereas a larger number of other metals remain stationary or move only slowly in comparison with uranium.The uranyl nitrate is readily recovered from the eluent after it has been diluted with water and the solvent removed by distillation ; the uranium can be determined by gravimetric, volumetric, colorimetric, polaro- graphic or fluorimetric techniques. The method has proved widely applicable in the separation of uraniumL from minerals, ores and other products. The procedure is simple and rapid and has given results comparable in accuracy with those of other methods. The mechanism of the separation process is complicated and is dependent chiefly on the following factors- (a) Selective extraction of uranyl nitrate by ,!he solvent-Nitrates of metals other than uranium (e.g., ceric, ferric, mercuric and thorium nitrates) also dissolve in ether, but under the conditions of the extraction these metal salts are retained by the cellulose.Ceric nitrate is reduced to the cerous condition and is then retained, mercuric nitrate is also retained by the cellulose, and movement of ferric and thorium nitrates depends largely on the amount of water present in the system. The solubilities of metal nitrates are substantially dependent on the concentration of nitric acid in the solvent, an increase in nitric acid concentrationJuly, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 397 causing an increase in solubility.The use of 5 per cent. v/v of nitric acid in ethyl ether for the extraction of uranium has been found most satisfactory for analytical work; it provided a suitably pure uranyl nitrate with a small amount of solvent. (b) Partition between the nitrates dissolved in the organic solvent and water present in the celldose-This is also important ; indeed, water is a key factor in chromatography with organic solvents and solid adsorbents. (c) Adsorption of metals on the cellulose-This also plays a part in the separation. Uranyl nitrate in ethyl ether containing 5 per cent. v/v of nitric acid is not adsorbed although many other metals are strongly retained on the cellulose. This chemical adsorption is due to the presence of reactive groups in the cellulose, and can be increased by pre-treatment such as boiling the cellulose with dilute nitric acid.The foregoing factors are still being investigated in order to gain further details of the mechanism of chromatographic separation, but lack of information on this aspect of the process does not affect the value of the experimental technique in the analysis of uranium. EXPERIMENTAL SOLVENT PREPARATION AND RECOVERY- The solvent was freshly prepared each day by mixing ethyl ether, free from peroxide, with concentrated nitric acid, sp.gr. 1.42, in the proportion of 5 ml of acid to 100 ml of ether. The ether was recovered by addition of water followed by distillation and purified for re-use by neutralisation with caustic soda, treatment with alkaline permanganate, distillation, drying over caustic soda and a final fractionation. Each batch of ether was tested for peroxide with potassium iodide solution before use.Estimations by the Fischer method indicated that the water content was less than 0.1 per cent. PREPARATION OF CELLULOSE- The cellulose pulp was prepared by boiling 450 g of cellulose (Whatman Ashless Tablets) with 3 litres of 5 per cent. v/v nitric acid for 2 minutes. Other forms of cellulose can be used, for example, Whatman No. 1 Waste Paper Clippings, which require boiling for 20 minutes, however. The pulp is filtered and washed free from nitric acid with water and then washed with 2 litres of ethyl alcohol and finally with about 2 litres of ether. After draining at a filter-pump, the pulp is stored in a closed container and is ready for use.Experiments were carried out to ascertain the amount of inorganic impurities extractable from a column of cellulose pulp, 2 cm in diameter and 25 cm long, by the mixed ether - nitric acid solvent. As shown in Table I, the pulp made from No. 1 clippings is sufficiently pure for most purposes provided that the column is first washed through with 250 ml of solvent. TABLE I INORGANIC MATERIAL EXTRACTABLE FROM CELLULOSE Volume of ether - nitric acid mixture passed Weight of ignited Source of pulp through 25-cm column, residue from eluent, Dl1 g Ashless tablets . . .. .. 250 o*oooo J 1st 250 0.0008 2nd 250 o*ooo 1 No. 1 clippings . . . . THE EXTRACTION TUBE- The adsorption apparatus consists of a glass tube about 2 cm in diameter and 40 crn long, the upper end being widened to form a funnel to allow easy transfer of material to the tube.The lower end of the tube is narrowed and is closed by a short length of polyvinyl chloride tubing carrying a screw clip or a tap. The inside surface of the glass extraction tube was treated with dichlorodimethyl silane, (CH,),SiCl,, which conferred strong water- repellent properties to the glass surface (see Burstall, Davies and Wells,, Part I11 of this series, p. 180). Another method of achieving water-repellent properties was to use Fluid 200 (Albright and Wilson Ltd.) in carbon tetrachloride solution; with this, the tube must be heated to 250" C to provide a stable water-repellent film. The adsorption tube was packed with cellulose pulp in the following way. The tube was first half-filled with ether -nitric398 BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC [VOl.76 acid mixture and cellulose pulp was added in sniall quantities. Each portion of pulp was gently pushed down with a glass rod flattened at one end to form a plunger of diameter slightly less than that of the tube; a brisk up and down movement of the plunger then served to b r e a up any aggregated pieces of pulp. A column properly packed in this way allowed ether solution to pass freely through the cellulose at a rate of approximately 100ml in 20 minutes with the end of the tube completely open. Cellulose columns from 5 to 8cm in length were ultimately used, but initial experiments were made with 25-cm columns. PREPARATION AND TRANSFER OF SAMPLE- A solution of the sample was prepared in aqueous nitric acid.Use of a high concentration of nitric acid favoured the rapid extraction of uranium in a narrow band. The movement of many impurities, however, decreased with the concentration of the nitric acid. A suitable compromise was found to be a solution containing 25 per cent. v/v of nitric acid. The method of preparing a nitric acid solution of the sample varied with the type of mineral, and is described later separately for each type of ore, together with any special treatment of the solution found necessary. The acid solution of the sample could be transferred directly to the top of the column, but the following method was usually adopted. Sufficient cellulose pulp was added to the sample solution to ensure complete adsorption; the amount required was 2 g of pulp for 10 ml of 25 per cent. v/v nitric acid.This wad of cellulose was then transferred to the top of the tube, gently beaten with a plunger and prelssed down to fonn a continuous part of the column. THE EXTRACTION OF URANIUM- After transfer of the sample, successive small volumes (10 ml) of the ether containing 5 per cent. v/v of nitric acid were added and the solvent was allowed to flow through the tube. This procedure was continued until 150ml of solvent eluent had been collected, this quantity being adequate for an 8-cm cellulose column, although proportionately larger quantities must be used with longer columns. ‘The solvent was added in such a manner that the level of the solvent a t the top of the column fell to the top of the cellulose packing, but not below, between successive additions. The extraction column was not allowed to run dry at any stage.To the eluent from the extraction was added water in the proportion of 50 ml of water to each 100 ml of solvent and the ether was removed by distillation. The uranium was then determined by one of the following methods: (a) evaporation and ignition to U,O,; (b) precipitation with oxine, filtration amd ignition to U,O,; (c) evaporation with sulphuric acid and heating to fumes followed by dilution, reduction in a Jones reductor and titration with ceric sulphate; (d) evaporation with sulphuric acid and heating to fumes followed by a colorimetric estimation with alkaline solution and hydrogen peroxide; (e) as method (d) but with a polarographic determination in place of the colorimetric method.THE BEHAVIOUR OF ELEMENTS OTHER THAN URANIUM- A study has been made of the behaviour on *a cellulose column of other elements under the conditions used for uranium extraction and of the effect of these elements on the extraction of uranium. The following observations are based on a preliminary study. A more detailed account will be given in a further paper. The nitrates of Li, Na, K, Cs, Rb, Cu, Ag, Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Al, Y, La, Ce, Pr, Nd, Sm, Eu, Ho, Er, Ga, In, T1, Ti, Hf, Ge, Sn, Pb, Nb, Ta, Cr, W, Te, Mn, Fe, Co and Ni all remained stationary or moved only very slightly. These metals, therefore, do not interfere with the estimation of uranium. The reimaining elments are dealt with separately. Gold-The dilute solution of gold prepared by the action of nitric acid on gold metal was partly reduced by the cellulose of the column and gave a purple tint to the absorbent.There was also a tendency for colloidal gold to pass through the column. Prior reduction of the gold by treatment of the sample solution with ferrous sulphate resulted in its complete retention at the top of the extraction column. In presence of chloride, gold was extracted readily from the column. Mercury-Mercury was found to move only in the mercuric state and then not sufficiently rapidly to affect the estimation of uranium. Mercuric salts are partly reduced by the ether - nitric acid solvent in presence of cellulose, and this aided the retention of mercury. A solutionJuly, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 399 of 0.5 g of mercuric nitrate in 5 ml of 25 per cent.v/v nitric acid was extracted with ether containing 5 per cent. v/v of nitric acid through a 10-cm cellulose column. After the passage of 200 ml of solvent, mercury was detected 3 cm from the bottom of the column, but not in the eluent. Selenium, arsenic, antimony and bismuth-Selenium, arsenic, antimony and bismuth in a column all moved, but not at sufficient speed to be extracted with uranium. For example, bismuth nitrate had moved only 5 cm down a column after the passage of 200 ml of ether containing 5 per cent. v/v of nitric acid. The effect of large amounts of arsenic on the extraction of uranium will be dealt with in a later paper. Cerium-Ceric nitrate is appreciably soluble in ether - nitric acid mixtures; in addition, its coefficient of partition between ether - nitric acid mixtures and water is high.Since ceric nitrate is absorbed by cellulose from ethereal solutions to a small extent only, steps must be taken to ensure that any cerium is reduced to the cerous state, in which form it is insoluble in most organic solvents. Reduction of ceric nitrate takes place in ether solution in the dark and in the absence of added acid, but the process is slow. For the extraction of uranium from monazite sands, ferrous sulphate was first added to reduce cerium, but a better method was to boil the original solution in dilute nitric acid with hydrogen peroxide. Thoriztm-Thorium was extracted in small amounts with ether containing 5 per cent.v/v of nitric acid, but the extraction was very sensitive to the concentration of acid in the solvent. The use of ether containing 3 per cent. v/v of nitric acid permitted uranium to be extracted completely before thorium was detected in the eluent, as shown in Table 11. TABLE I1 EXTRACTION OF THORIUM Volume of test Weight of Tho, Nitric acid in Length of Weight of Tho, solution (in extracted with solvent, column, in test solution, 40% HNO,), 400 ml of solvent, % cm g ml g 3 15 0.450 5 nil 5 25 1.027 10 0.170 When uranium is present as phosphate, as in monazite sands, special conditions must be observed for its extraction; this is referred to later. Zirconium-Zirconium was also extracted by ether containing nitric acid. Table I11 shows the results of an extraction of a solution of zirconyl nitrate containing the equivalent of 0.19 g of ZrO, dissolved in 3 ml of water and 2 ml of nitric acid, sp.gr.1.42, when ether containing 5 per cent. v/v of nitric acid was used as solvent. The extraction of zirconium was inhibited by the presence of a number of anions, e.g., phosphate, sulphate, oxalate and tartrate. The use of tartrate for retention of zirconium in the analysis for uranium in zircon- bearing minerals is mentioned later in this paper. TABLE I11 EXTRACTION OF ZIRCONIUM Fraction of eluent r A 3 1st 2nd 3rd Total Proportion 200 ml 200 ml 200 ml 600 ml extracted, % Weight of ZrO, extracted . . 0.8 mg 26.0 mg 30.4 mg 57.2 mg 31 Scandium-The behaviour of scandium was similar to that of thorium.The movement of scandium can be inhibited by the addition of tartrate. Tin-In nitric acid tin is precipitated as insoluble meta-stannic acid, which does not move in the column. But in order to avoid the risk of occlusion of uranium when dealing with minerals containing large amounts of tin, it is best 'to remove the tin by volatilisation as the iodide. In presence of chloride, tin was extracted very readily from a cellulose column. Vanadiztm-Vanadium was immobile in a cellulose column provided that the ethereal solvent used is free from peroxides. In the presence of ether peroxides, a pink peroxy- vanadium compound was formed and moved rapidly down the column. The presence of400 BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC [Vol. 76 reducing agents such as ferrous sulphate in the column converted the pink compound to a non-moving vanadium salt.Phosphorus-Phosphoric acid was readily extracted from cellulose by ether - nitric acid mixtures. In combination with metallic radicals, however, phosphoric acid was much more strongly retained; ferric nitrate has been found a particularly useful complexing agent for this purpose. A small amount of the acid, presumably resulting from the dissociation of ferric phosphate, was, however, still extracted in trace amounts. The presence of a trap of freshly prepared meta-stannic acid in the column reduced the amount of extracted phosphoric acid further, but trace amounts were still detectable in the eluent. The presence of phosphoric acid inhibited the extraction of uranium, but addition of ferric nitrate overcame this effect.Molybdenum-The behaviour of molybdenum in cellulose columns appears to vary with a number of factors. When added as a dilute nitric acid solution of ammonium molybdate to a cellulose column and extracted with an ether - nitric acid solvent, the bulk of the molybdenum moved only slightly, but a low concentration of molybdenum was detect- able in the eluent. In sunlight there was a strong tendency for molybdenum to be reduced t o molybdenum blue and this reaction was catalysed by the presence of uranium. There are indications that there are two forms of the blue complex, one of which was almost immobile and another that was readily extracted from the column. There is also some evidence to show that in concentrated solutions a molybdenum - uranium complex is formed.This behaviour results in a small but definite quantity of molybdenum being present in uranium oxide samples extracted from molybdenum-bearing ores. The proportion of molybdenum in twenty such samples of oxide varied between 7 and 200 p.p.m. Although small, these quantities of molybdenum interfered with the vo'lumetric estimation of uranium by catalysing the aerial re-oxidation of U"" to UO," ions. Decrease in the concentration of nitric acid in the solvent or in the aqueous test solution showed little effect. Similarly, carrying out the extraction in the absence of sunlight gave no improvement. It was found that molybdenum could be reduced to an insoluble trioxide by standing it overnight with an excess of ferrous sulphate.The large excess of ferrous sulphate required, however, made this method in- convenient, and other methods, which have been more successful, will be described in a further paper. The platinum metals-Of the six platinum metals, osmium was neglected, since once it is in solution it is removed by evaporation with nitric acid. Iridium and rhodium were not extracted and hence gave no trouble. Platinum, palladium and ruthenium behave differently. Ruthenium was fused with potassium hydroxide and a solution of the melt was acidified with nitric acid. The resulting suspension of ruthenium hydroxide was absorbed on cellulose and treated with ether - nitric acid solvent. 'The ruthenium appeared to be completely retained at the top of the column, but traces were found in the ethereal eluent.Platinum behaved in a similar manner to ruthenium, the main bulk of the platinum being retained at the top of the column, although small quantities were extracted. Palladium in nitric acid solution was readily extracted from a cellulose column. Reduction of the platinum and palladium solutions with ferrous sulphate before extraction was only partly successful in overcoming this difficulty. The bulk of the paliadium was retained, but traces of platinum and palladium were still found in the eluent. SuZphate-Small quantities of sulphuric acid do not appear to have any appreciable effect on the extraction of uranium, but this question has been the subject of a fuller investigation that will be described in a later paper. Free dphuric acid under normal conditions was retained at the top of the cellulose column.Halides-Halide ions must be absent from samples used for the estimation of uranium since extraction of other elements is greatly increased. Under normal conditions hydrochloric acid is retained in the column. Both hydrobrornic acid and free bromine move slowly down the extraction column. Hydriodic acid and iodine behave similarly. RESULTS- Initial experiments were made with nitrate solutions prepared from weighed quantities of pure U,O, with and without added impurities. With a 25-cm column of cellulose,. 250 ml of ether - nitric acid solvent were necessary for the complete extraction of uranium, in the absence of phosphate, as shown in Table IV. The presence of phosphate slowed the rateJuly, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 401 of extraction of uranium considerably, but the addition of ferric nitrate complexed phosphate sufficiently to allow uranium extraction to proceed normally.TABLE IV EXTRACTION OF URANIUM FROM SYNTHETIC MIXTURES Weight of U,08 g Elements present taken, Uranium . . .. .. .. .. 0.0975 Uranium . . .. .. .. 0.1721 Uranium . . .. .. Uranium + 0.2 g of each of Fe, Zn, Mn, .. .. .. 0.9992 * Uranium + 0.3 g of Fe(NO,), . . .. 0.0808 Cr, V and Cu nitrates . . .. .. 1-0053 Weight of U,O, found, U,08 found, f3-0970 99-5 0.9960 99.7 0.1721 100.0 100.0 0.0808 g % 1-0043 99.9 APPLICATION TO ANALYSIS OF SILICEOUS MATERIALS The method was then applied to a number of low-grade siliceous materials. These were all ores that could be dissolved completely by the action of nitric and hydrofluoric acids, Fluoride was removed from the test solution by repeated evaporations with con- centrated nitric acid and the residue was finally dissolved in 10 ml of 25 per cent.v/v nitric acid. The weight of sample taken for analysis varied between 0.5 and 5 g; in Table V results are compared with those found by standard methods of chemical analysis. TABLE V EXTRACTION O F URANIUM FROM SILICEOUS ORES ON 25-CM COLUMNS Sample 1 2 3 4 5 6 7 8 9 10 U,O, by cellulose column 0.36 0.29 0.20 0.20 0.36 0.17 0.38 1.39 0.77 5-03 % U,08 by standard chemical methods3s4 (mean value), 0.35 0.28 0.19 0.22 0.36 0.16 0.39 1.41 0.73 4.98 % The effect of decreasing the column length was then investigated and results with a It will be observed that for some estimations 5-cm column of cellulose are shown in Table VI.TABLE VI EXTRACTION OF URANIUM Sample 10 10 10 10 11 11 11 11 Weight of sample, g 0.5670 0.5019 2.5024 0.5180 2.7869 2.5933 2-4818 2.2242 FROM SILICEOUS ORES ON 5-CM COLUMNS U,08 by standard Volume of U,O, by cellulose chemical methods**P ether, column, (mean value), ml % % 250 4-92 165 100 100 100 2.13 100 100 2.15 4-98 ::;; } 75 4-96 the amount of solvent used was only 75 ml. Further experiments (Table VII) in which known weights of uranium oxide were added to a standard ore indicated that results were slightly low when 70ml of extracting solvent were used; 100ml were used, therefore, in further experiments. Although the results shown in Table VI were considered satisfactory, the ores used in these experiments contained neither vanadium or molybdenum.In view of the tendency for small amounts of molybdenum to be extracted and because of the possible formation402 BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC [Vol. 76 of a solvent-soluble peroxy-compound of vanadium with traces of ether peroxides, further analyses were carried out in which small quantities of vanadium and molybdenum were added. The results, as shown in Table VIII, were not unsatisfactory, but during these estimations it was noted that vanadium moved rapidly as a pink band and had usually TABLE VII EXTRACTION OF URANIUM ADDED TO SILICEOUS ORES Weight of U,O, Weight of Volume of ether Weight of U,O, added, vanadium added, used, found, mg mg ml mg 20 10 70 19-85 20 3 80 19.99 20 10 80 19.91 reached the bottom of the column before 100ml of ether had passed through the column.Movement of molybdenum under the same conditions appeared to be slight. Addition of ferrous sulphate to the dilute nitric acid solution of the ore maintained the vanadium in a reduced immobile form and did not interfere with the extraction of uranium (Table IX). TABLE VIII THE EFFECT OF VANADIUM AND MOLYBDENUM ON THE EXTRACTION OF URANIUM Sample 10 11 11 11 12 12 13 Weight of sample, g 0.9665 2.5000 2.4494 2.5012 3.0526 2.4996 2.4994 Volume of ether used, ml 80 100 100 100 80 100 100 Molybdenum added, mg nil 25 nil 25 nil 25 25 Vanadium added, mg 5 25 25 nil 5 25 25 U,O, found by cellulose column, Yo 4-95 2.08 2.17 2-07 0.63 0.66 0.54 U30, found by standard chemical (mean value), % 4.98 2.13 2.13 2-13 0.66 0.66 0.54 TABLE IX EXTRACTION OF URANIUM AFTER ADDITION OF FERROUS SULPHATE U308 found by standard chemical Sample added, added, cellulose column, (mean value), Molybdenum Vanadium U,O, found by methods3$* mg mg YO Y O 11 25 25 2.13 .2.13 11 nil 25 2.13 2.13 11 25 nil 2-15 2.13 If the strength of the nitric acid in the test solution was allowed to fall there was a tendency for molybdenum to be reduced to a mobile molybdenum blue by ferrous sulphate. In view of this and because of the undesirability of adding solid material to the original solution, further experiments were made in which the column length was increased to 7-5 cm. Columns of this length allowed the uranium extraction to be completed before the pink peroxy-vanadium band reached the bottom of the column.The formation of peroxy- vanadium compounds was later avoided by the iise of fresh peroxide-free ether. RECOMMENDED METHOD FOR SILICEOUS ORES Cellulose PuZP-This should be prepared as (described on p. 397. Ether - nitric acid solvent-A 5 per cent. v/v solution of nitric acid in ether prepared Nitric acid-Concentrated, sp.gr. 1.42. REAGENTS- by mixing 5 ml of nitric acid, sp.gr. 1-42, with 100 ml of dry peroxide-free ethyl ether.July, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 403 PROCEDURE- Add 2 ml of concentrated nitric acid, sp.gr. 1.42, and 5 ml of hydrofluoric acid and evaporate the mixture just to dryness on a hot-plate. Wash the sample with a minimum of water into a 100-ml beaker.After evaporation to dryness, add 10 ml of concentrated nitric acid and again evaporate the solution just to dryness, Redissolve the residue in 8ml of water containing 2ml of concentrated nitric acid. Prepare a cellulose column, as described on p. 397, 7.5 cm in length, and wash it through with 100 ml of ether - nitric acid solvent. Adjust the solvent level in the column until it coincides with the top of the cellulose. Add sufficient cellulose pulp to the solution of the sample to absorb completely the aqueous nitric acid solution. Transfer the wad containing the absorbed sample to the top of the extraction column with the aid of the glass rod. Wash final traces into the column with not more than 10 ml of ether - nitric acid solvent from a wash bottle; care must be taken to avoid “ether creep.” Break up the pulp containing the sample with a glass plunger and gently press it down t o form a continuation of the original column of cellulose.Remove the clip and tubing from the bottom of the column and allow the ether to run out into a 250-ml Kjeldahl flask until the level of ether solution in the extraction tube reaches the top of the cellulose column. Add a further 10 ml of ether - nitric acid solvent to the top of the extraction tube and repeat the procedure with successive 10-ml portions of the solvent mixture until 100 ml of eluent have been collected. Use each 10 ml of ether - nitric acid mixture to wash out the sample beaker. Add 50ml of water to the eluent ether solution and remove the organic solvent by distillation on a steam-bath.Add 5 ml of sulphuric acid and 5 ml of perchloric acid to the aqueous solution and evaporate to fuming. Complete the estimation by any suitable r n e t h ~ d . ~ ~ ~ RESULTS- 100 ml when using a 7.5-cm column. 2.5-g portions of ore are shown in Table X. strated the suitability of the method for the analysis of low-grade siliceous materials. Weigh about 2.5 g of sample into a platinum dish. Stir the mixture thoroughly with a glass rod. It was not found necessary t o increase the volume of ether required for extraction beyond Results obtained on columns of this length with It was considered that these results demon- TABLE X EXTRACTION OF URANIUM FROM SILICEOUS ORES BY RECOMMENDED METHOD Sample 11 11 14 13 13 13 15 16 17 Molybdenum added, mg nil 25 25 25 nil 25 25 25 25 Vanadium added, mg 25 nil 25 25 nil 25 25 25 25 U,O* by Yo cellulose column, 2.14 2-17 0.06 0.57 0.55 0.54 2.09 2.88 3-35 u30, by standard chemical methods394 (mean value), Yo 2-13 3-13 0-06 0.54 0-64 0.54 2-16 2.89 3-16 APPLICATION TO ANALYSIS OF MONAZITE SANDS AND OTHER REFRACTORY ORES The application of the cellulose column technique to the analysis of monazite sands presented several difficulties.A fusion was necessary in order to obtain a nitrate solution of the mineral, and this gave rise to the presence of large amounts of neutral salts in the test solution. Most of the ores contained considerable quantities of phosphate, which inhibited the extraction of uranium; others contained large amounts of zirconium, which was partly extracted. The addition of ferric nitrate to the test solution overcame the retaining effect of phosphate and addition of tartaric acid prevented the extraction of zirconium.A large amount of cellulose was needed to absorb the test solution, the volume of which was increased to cater for the high concentration of potassium salts, but this large wad did not impair theBURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC [Vol. 76 404 extraction of uranium. A number of different types of mineral have been studied, including “pure monazites,” consisting mainly of rare earth and thorium phosphates ; “crude monazite,” consisting of a small quantity of monazite with a large quantity of other refractory ores; and zircons, which were mainly zirconium silicate.The development of the method is described immediately below. SOLUTION OF THE SAMPLE- In order to obtain a nitric acid solution of monazite, advantage was taken of the observa- tion that treatment of the sample with hydrofluoric acid followed by fusion with potassium hydroxide gave a melt that was soluble in nitric acid. This procedure was improved by fusing with potassium hydroxide, dissolving in nitric acid and then adding dilute hydrofluoric acid to the solution. Except for a trace of gelatinous silica, complete solution was obtained. Excess hydrofluoric acid was avoided, as it precipitated thorium and the rare-earth fluorides. With a pure monazite, 2 or 3 drops of a 2 per cent. solution of hydrofluoric acid were found sufficient. The same effect was obtained by the addition of potassium bifluoride to the potassium hydroxide fusion, but addition of hydrofluoric acid, as described, was preferred, because potassium bifluoride rapidly attacked the nickel crucible.The amount of potassium hydroxide required for fusion varied with each sample, but for pure monazite a 5 to 1 ratio of potassium hydroxide to sample, heated for 30 minutes at red heat, was found sufficient to ensure complete breakdown, although for crude monazite the ratio was increased to 8 to 1 and the heating time to 1 hour. For the present work, 2.5-g portions of sample were used for each estimation. EXTRACTION OF URANIUM- Initial experiments with a 25-cm column of cellulose showed that uranium could be completely extracted by 300ml of ether containing 5 per cent.v/v of nitric acid. The nitric acid solution of the sample was evaporated t o about 25 ml, 4 ml of water were added and the resultant solution was absorbed on a wad of cellulose. During these experiments it was noticed that a dark orange band, identified as cerium in the ceric state, moved rapidly down the column and coloured the effluent. This did not affect the result if a titrimetric finish was used, but interfered with a colorimetric determination. Since cerous nitrate showed little movement in the column, further experiments were made with a ferrous sulphate trap to reduce cerium. This method was found to hold back cerium satisfactorily and results are shown in Table XI for extractions both with and without the ferrous sulphate trap. TABLE XI EXTRACTION OF URANIUM FROM PURE MONAZITE SANDS USING A 25-CM COLUMN u3°8 by standard chemical Volume of U30, found meth0ds~9~ Sample ether, U30, found, (mean value), (mean value), ml % % % Without ferrous sztlphate trap- 1 500 1 300 1 300 1 300 1 300 With ferrous sulphate &up-- 2 300 2 300 2 300 2 300 2 300 300 300 0.37 0-37 0.37 0.35 0.40 J 0.36 7 0.39 I 0.38 J 0.37 0.40 1 0.38 0*37(5) 0.37 0.37 } 0‘37 0.37 300 0.35 0.35 0.37 300 0.41 0.41 0.36 As about 8 g of cellulose were used in absorbing the solution of the sample, the total In an length of both wad and column, when a 20-cm column was used, was about 50 cm.July, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 405 attempt to use a column of more manageable length, experiments were carried out with a 5-cm column of cellulose.Addition of hydrogen peroxide to reduce cerium was also tried, as being a more convenient method than the use of a ferrous sulphate trap. About 2 ml of 20-volume hydrogen peroxide were added to the nitric acid solution of the sample while it was being evaporated to dryness. Figures shown in Table XI1 indicate that satisfactory extraction of uranium is obtained with a 5-cm column and 100 ml of ether - nitric acid solution. TABLE XI1 EXTRACTION OF URANIUM FROM PURE MONAZITE SANDS WITH A 5-CM COLUMN Sample Length of column, cm 25 25 5 5 5 5 5 Volume of ether, ml 300 300 300 100 100 100 100 U308 found, % 0-37 0-37 0.37 0.37 0.37 0.39 0.34 uZ08 by standard chemical U,08 found methods3 94 (mean value), (mean value), Yo % ] 0.37 0.3 7 0.39 0-36 0-34 0.30 EFFECT OF ZIRCONIUM AND PHOSPHORIC ACID ON THE EXTRACTION PROCESS- The materials so far studied were all pure monazite samples. When the method was applied to crude monazites, particularly those containing a large amount of zircon, difficulty was encountered from some zirconium passing through the column and contaminating the eluent.The results of uranium determinations on samples containing zirconium were very erratic, as shown in Table XIII. TABLE XI11 THE EFFECT OF ZIRCONIUM ON THE EXTRACTION OF URANIUM FROM CRUDE MONAZITES Sample 7 8 9 10 7 7 7 8 10 10 Length of column, cm 25 25 25 25 5 5 5 5 5 5 Volume of ether, ml 300 300 300 300 100 100 100 100 100 100 U308 found, % 0.54 0-06 0.32 0.18 0.42 0-46 0.35 0.07 0.26 0.21 u.3°8 by standard chemical methods3$* (mean value), % 0-48 0.05 0-25 0.18 0.48 0.48 0-48 0.05 0.18 0.18 Accordingly, factors affecting the movement of zirconium were investigated in the following manner.A known weight of zirconium nitrate was dissolved in 10-ml portions of nitric acid of various strengths. Each 10 ml of solution was taken up on a wad of cellulose and extracted in a 5-cm column with 100ml of ether containing 5 per cent. v/v of nitric acid. The movement of zirconium down the column was measured and showed (see Table XIV) an increase with increasing nitric acid concentration. If, however, a nitric acid solution of crude monazite was evaporated to complete dryness, redissolved in 5 or 10 per cent. v/v nitric acid and extracted in a 5-cm column, zirconium was still found in the ether eluent.The increased movement of zirconium under these conditions was not due to a salting out effect of potassium nitrate, as shown in the last line of Table XIV, but in other experiments, ferric nitrate has been shown to produce such an effect. Although zirconium was still extracted from crude monazite dissolved in a 10 per cent. v/v solution of nitric acid after fusion with potassium hydroxide, the amount extracted was very much smaller than if a stronger solution of nitric acid was used. In all further estimations, therefore, the acidity was controlled by evaporating the nitric acid solution of the sample to dryness and redissolving in 20 ml of 10 per cent. v/v nitric acid. As a406 BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC TABLE :XIV [Vol.76 BEHAVIOUR OF ZIRCONIUM WITH VARIATION OF ACID CONCENTRATION Weight of zirconium nitrate taken = 0.1 g Volume of nitric acid solution, ml 10 10 10 10 10 8 20 Strength of nitric acid solution, 10 15 20 25 30 25 10 % v/v Movement of zirconium down column, cm 2.5 2.5 3.0 4.5 > 5.0 5.0 3.0 Added potassium nitrate nil nil nil nil nil nil 20 g small amount of zirconium still passed through the column, investigations were made into means of preventing the movement by complex formation. Addition of phosphoric acid to the nitric acid solution of the sample held back zirconium but slowed down the extraction of uranium. Traps of ferrous sulphate, oxalic acid or activated carbon in the column were not successful; extraction with ether containing 5 per cent. v/v of nitric acid and 1 per cent.v/v of orthophosphoric acid still resulted in zirconium being found in the eluent. Addition of sulphuric acid to the nitric acid solution of the sample did, however, result in complete retention of zirconium and so permitted extraction of uranium. In this procedure the nitric acid solution of the sample was evaporated to dryness, redissolved in 20 ml of 10 per cent. v/v nitric acid. Sulphuric acid, 6 ml of a 1 + 1 solution, was added and the mixture was boiled for 2 or 3 minutes. Zirconium was cornpletely held back on extraction in a cellulose absorption column. The results for a series of crude monazite samples treated with sulphuric acid in the above manner are shown in Table XV. TABLE XV ADDITION OF SULPHURIC ACID AS COMPLEXING AGENT FOR ZIRCONIUM U 3 0 8 by standard chemical methods3~4 Sample Type U,08 found, (mean value), % % 11 11 } 0.05 Zircon concentrate 0.045 97 0.041 Y Y Y Y 0.048 8 Crude monazite 0.048 8 0.047 8 0.051 8 0-05 1 8 0.048 Y Y Y Y Y t 0.18 10 0.16 The amount of sulphuric acid added is large, but this quantity was found necessary to cope with samples 10 and 11, which had a high zircon content.The efficiency of extraction under these conditions was shown by addition o:f a weighed amount of U,O, to a sample of known uranium content and finding the amount: of added uranium extracted, as follows- Sample No. 8: Weight of U30, added = 25 mg. Weight of U308 recovered = 24.8 mg. The results shown in Table XV were found for ores with a low monazite content. When the method was applied to pure monazite, the extraction of uranium was very poor.This was owing to retention of uranium brought about by the large excess of uncomplexed sulphate present in the absence of a high concentration of zirconium. USE OF TARTARIC ACID AND FERRIC NITRATE AS COMPLEXING AGENTS FOR ZIRCONIUM AND PHOSPHORIC ACID- Addition of either oxalic or tartaric acids to th.e nitric acid solution of a sample of monazite before absorption on a wad was found to complex zirconium satisfactorily. The procedure used was to evaporate the nitric acid solution of monazite to dryness, redissolve in 20 mlJuly, 19511 SOLVENT EXTRACTION FOR SEPARATING URANIUM 407 of 10 per cent. v/v nitric acid, add 2 ml of 20-volume hydrogen peroxide, boil for a few minutes, add 3 g of the organic acid and then cool. The use of either acid resulted in a lower rate of extraction of uranium, particularly with pure monazite, but whereas a 50 per cent.increase in the volume of ether - nitric acid solution used in extraction resulted in complete recovery of uranium when tartaric acid was used, results were still low for oxalic acid. Of the two organic acids, oxalic is the more effective complexing agent for zirconium, but tartaric acid retains zirconium sufficiently well to enable a clean extraction of uranium to be achieved. Increasing the concentration of the nitric acid in the solution of the sample before extraction did not materially affect the extraction of uranium, although some increase in the movement of zirconium was apparent. During these estimations it was noticed that, if an iron crucible was used for the fusion, results were satisfactory, but if a nickel vessel was used, the values were low.Experiments were then carried out in which fusion was carried out in a nickel crucible, but iron as ferric nitrate was added to the nitric acid solution of the sample before extraction. Under these conditions uranium was quantitatively extracted. Since a clean, easily removed melt was obtained in nickel crucibles, they were preferred and ferric nitrate was added at a later stage of the estimation. TABLE XVI USE OF TARTARIC ACID AS A COMPLEXING AGENT FOR ZIRCONIUM Sample Type With added tartaric mid- 10 Crude 10 37 1 Pure 1 99 1 99 1 93 1 39 1 19 With added oxalic acid- 10 Crude 10 99 1 Pure 1 79 1 97 Volume of ether, ml 100 100 100 100 100 150 100 150 100 150 100 150 150 Strength of nitric acid used for solution of sample, % V/V 10 10 10 10 25 25 10 25 10 10 10 25 25 Weight of ferric added, found, present, nitrate u30, U308 g % % nil nil nil nil nil nil 5 5 0.18 0.20 0.24 0.27 0.27 0.33 0.32 0.37 0.18 0.18 0.37 0.37 0.37 0.37 0.37 0.37 nil 0.13 0-18 5 0.19 0-18 5 0-32 0.37 5 0.33 0.37 5 0-34 0.37 in Table XVI.the addition of tartaric As a result of these exDeriments. summarised acid and ferric nitrate was included in the procedure recommended for the analysis of uranium in monazite sand. RECOMMENDED METHOD FOR MONAZITE SAND AND REFRACTORY ORES REAGENTS- Celldose @ul@-This should be prepared as described on p. 397. Ether - nitric acid solvent-A 5 per cent. v/v solution prepared as described on p.402. Potassium hydroxide-Solid. Nitric acid-Concentrated, sp.gr. 1.42. Hydrojuoric acid-A 2 per cent. v/v aqueous solution. PROCEDURE- Heat 12.5 to 20 g of potassium hydroxide, according to the type of mineral to be analysed, in a nickel crucible until all the water has been removed. Allow to cool slightly, add 2.5 g of sample and quickly cover the crucible with its lid. Heat the melt slowly to red heat. Continue to heat for 1 hour at bright red heat, occasionally swirling the contents of the crucible. Allow the crucible to cool and wash the contents with water into a 400-ml beaker. Make just acid with nitric acid and then add about 20 ml of concentrated acid in excess. Bring the solution to the boil with constant stirring and slowly add dropwise a 2 per cent.solution408 [Vol. 76 of hydrofluoric acid. Stop the addition of hydrofluoric acid as soon as the solution clears and evaporate to dryness on a steam-bath or under an infra-red lamp. To the residue add 20 ml of water containing 2 ml of concentrated nitric acid and 5 g of ferric nitrate. Heat with stirring until solution is complete. Add 2 :ml of 20-volume hydrogen peroxide and boil for 2 or 3 minutes to reduce cerium. Then add 3 g of tartaric acid, stir and cool rapidly. To the nearly solid mass add about 8 g of cellulose pulp and stir until a homogeneous mixture is attained. Pack an extraction tube to a depth of 5 cm with cellulose and wash the column by allowing 100 ml of ether - nitric acid solvent to flow through it. Adjust the ether level until it is about 10 cm above the top of the column. Transfer the wad containing the sample in small portions to the extraction tube.Break up each portion of pulp with a glass plunger and gently press down to form a continuous column with the original cellulose. Remove the clip and tubing from the botto:m of the extraction tube and allow the ether to run out into a 350-ml Kjeldahl flask until the level of the ether - nitric acid solution in the extraction tube reaches the top of the cellulose column. Add a further 10 ml of ether - nitric acid solution to the top of the extraction tube and repeat the procedure with successive 10-ml portions of the solvent mixture until 150 ml of eluent have been collected. Use each 10-ml portion of ethereal solvent to wash out the sample beaker.Add 75 ml of water to the eluent ether solution and remove the organic solvent by distillation on a steam-bath. Add 5 ml of sulphuric acid and 5 ml of perchloric acid to the aqueous solution and take the mixture to fuming. Complete the estimation by any suitable m e t h ~ d . ~ , ~ RESULTS- monazite minerals. BURSTALL AND WELLS: COLUMNS OF CELLULOSE AND ORGANIC Satisfactory results, as shown in Table XVII, were obtained on both pure and crude TABLE IWII EXTRACTION OF URANIUM FROM MONAZITE SANDS BY THE RECOMMENDED METHOD Sample 1 7 8 10 12 13 14 15 16 17 18 Pure Crude 1 Y Y Y Pure Crude Pure Y Y Y Y 99 Crude U308 found, % 0.37, 0.36 0.50 0.05 0.19 0:35, 0-35 0.09, 0.07 0-38, 0.42, 0.39 0.86, 0.81, 0.85 0.92, 0.96 0.26, 0.28, 0.30 0.35, 0.33, 0.33 Mean U30, by standard chemical methods334 0.37 0.48 0.05 0.18 0.35 0.07 No reliable results obtained by other methods The efficiency of the extraction, as shown in Table XVIII, was tested by addition of uranium to a standard sample of monazite of known uranium content.A determination of the total uranium was made and the “recovery” calculated by subtracting the known uranium content of the sample. TABLE XVIII RECOVERY OF URANIUM ADDED TO MONAZITE SAND Sample No. 1 I L \ Weight of U308 added, Weight of U,O, recovered, mg mg 5-0 4-96 10.0 10.07 25.0 24.94 The agreement between the two methods shown in Table XVII and the recoveries shown in Table XVIII are considered satisfactory. In spite of the special precautions necessary to prevent the movement of zirconium, the cellulose column method is preferred to normal chemical methods because of its ease and speed of operation and the accuracy and reproducibility of the results.July, 19511 SOLVENT EXTRA4CTION FOR SEPARATING URAXIUM 409 The authors wish to thank J.G. Beynon, Miss R. D. Humphreys, Mrs. P. J. Forrest and Miss P. McGlone for assistance in the experimental work. The investigations were carried out on behalf of the Ministry of Supply by whose permission this paper is published. REFERENCES 1. 2. 3. 4. “Assayer’s Guide,” A.E.C.D.-2640. NOTE-References 1 and 2 are to Parts I and I11 of this series; Part I1 is by Burstall, F. H., Davies, G. R., Linstead, R. P., and Wells, R. A., J . Chern. SOC., 1950, 516; Part IV is by Lewis, J. A., and Griffiths J.M., Atialyst, 1951, 76, 388. CHEMICAL RESEARCH LABORATORY TEDDINGTON, MIDDLESEX Arden, T. V., Burstall, F. H., and Linstead, R. P., J . Chem. SOC., 1949, S 311. Burstall, F. H., Davies, G. R., and Wells, R. A., Disc. Farad. Soc., 1949, No. 7, 179. “Handbook of Chemical Methods for the Determination of Uranium in Minerals and Ores,” H.N. Stationery Office, London, 1950. MR. C. G. DAUBNEY enquired about the of evaporation during the percolations, and the amount of water present. MR. BURSTALL replied that a normally DISCUSSION time taken for ether to run through a column, the prevention any precautions that must be taken to avoid an increase in packed column permitted a flow-rate of 100ml of ethereal solvent in 20 to 30 minutes. The eluent was collected directly in a distillation flask and no special pre- cautions were taken to prevent evaporation or to prevent an increase in the water content of the solvent.Addition of more water to the solvent tended to slow up the extraction of uranium slightly, but a t the same time the movement of other materials also was usually retarded. DR. G. E. FOSTER asked whether the presence of peroxide in the ether would affect the results. MR. BURSTALL said that peroxide in the ether should be avoided. A peroxy-vanadium compound readily soluble in the solvent was formed if vanadium was present. This substance moved down the column as a characteristic pink zone immediately following the uranium. MR. W. H. BENNETT asked, first, whether fluorides could be tolerated in the separations as described and secondly, whether the authors would comment on the use of water-repellent agents other than the toxic compound quoted in the paper.MR. WELLS said, in reply, that the presence of fluoride should be avoided because free hydrofluoric acid would remove the silicone lining from the glass tube. Hydrofluoric acid, unless suitably complexed, would also inhibit the extraction of uranium. Another, less toxic, silicone solution was now available; i t was manufactured by the Dow Corning Co. of America, and marketed in this country by Albright & Wilson under the name “Dow Corning Fluid 200.” DR. D. I. COOMBER asked whether the authors had had any experience of the use of derivatives of cellulose, for example, ethyl cellulose, in this or related problems. He thought that, with substituted celluloses, metals other than uranium would probably not be held back so much.If carboxymethyl cellulose were used the column would become an ion-exchange column rather than a chromatographic column. MR. BURSTALL said that ethyl cellulose had not, so far, been examined as an adsorbent. MR. N. STRAFFORD asked whether the authors considered the separation by cellulose to be due to partition or to adsorption chromatography. Had they tried partition chromatography on wet silica gel ? MR. BURSTALL replied that the separations possible on cellulose appeared to be due to a combination of both partition and adsorption, the predominance of either factor depending upon the metal and solvent concerned. Partition chromatography on wet silica gel has been tried for a number of inorganic separations, but without much success.DR. J. H. HAMENCE asked the authors if they would put forward any theories that they might have arrived a t in the course of their work on the mechanism of the separation. In view of the ever-increasing application of chromatography in the solution of hitherto insoluble problems, information on the mechanism of the phenomenon was always very valuable, particularly as a guide when working out conditions for a new separation. In the questioner’s experience, adsorption and solubility appeared to play the major parts in this work. The extent to which any one of these factors contributed to a separation varied considerably and difficulty was frequently experienced -in obtaining precise information as to which factor predominated. Generally, the next most important factor is the extent of partition of the material between solvent and water in the cellulose. Finally, the retention of a number of metallic salts by cellulose appeared to be far too strong to be accounted for by partition alone and for these it was possible that chemi-adsorption occurred. DR. W. STROSS asked whether the authors had found applications of this extremely elegant selective Technique (perhaps with suitable modifications) to the determinations of elements other than uranium. MR. WELLS replied that a number of factors combined to effect a separation. The solubility of the material in the solvent used was an obvious first consideration.410 OSBORN AND JOHNS: THE RAPID DETERMINATION OF SODIUM AND [VOl. 76 MR. BURSTALL said that a similar chromatographic technique had been used in a number of other separations and determinations, some of which had been published and others were to be published in the near future. These studies included the separation and estimation of nickel, cobalt, copper and iron in samples of nickel steel, the separation and determination of gold in the platinum metals, of mercury with the group IIA metals, thorium in minerals and ores, niobium and tantalum in minerals and ores and the separation of zirconium and hafnium. DR. H. LIEBMANN referred to Dr. Stross’s question and mentioned that, following very closely the methods of Burstall and his colleagues and using the polarograph for the final analysis, they had recently determined small quantities of zinc in tin - lead solders. At present they could estimate quantities of about 0.001 per cent. in a 2-g sample, but they believed that the sensitivity of the method was capable of improvement. MR. R. C. CHIRNSIDE said he would be glad to know if the work that the authors had so far carried out enabled them to give a lead as to the probable behaviour of some of the non-metals, particularly boron and arsenic, on these chromatographic columns. MR. BURSTALL replied that, although they had not studied the extraction of boron or arsenic by chromatographic means, separations that had been carried out on strips of filter-paper by the authors and others indicated that i t should be possible to develop an extraction procedure for these materials. It was hoped to publish a preliminary Note on this subject in the near future.

ISSN:0003-2654    

DOI:10.1039/AN9517600396

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

410 OSBORN AND JOHNS: THE RAPID DETERMINATION OF SODIUM AND [VOl. 76 The Rapid Determination of !Sodium and Potassium in Rocks and Minerals by Flame Photometry BY G. H. OSBORN AND H. JOHNS (Presented at the meeting of the Physical Methods Group on, Friday, October 6th, 1950) A method is outlined'for the rapid and accurate determination of sodium and potassium in rocks and minerals by means of the flame photometer. It is shown that the method gives results that compare favourably with those obtained elsewhere by classical procedures, and that the saving in time required for an analysis is very great. It :is also shown that the sodium and potassium may be determined, if necessary, when only very small amounts of material are available. THE usual method for the chemical analysis of sodium and potassium in rocks and minerals is that of Lawrence Smith,l which consists essentially in fusing an intimate mixture of one part of ground rock with one part of ammonium chloride and eight parts of calcium carbonate, extracting in water and filtering to remove the silicates and aluminates of calcium, and the carbonates of iron, calcium and magnesium.The alkalis pass into the filtrate as chlorides. The rest of the procedure consists in the precipitation of the excess of lime by means of ammonium carbonate, expulsion of ammonium salts by heating the evaporated filtrate, removal of the last traces of lime, conversion of the traces of alkali sulphates to chlorides, weighing the mixed alkali chlorides and, finally, the separation and weighing of the potassium either as the perchlorate or chloroplatinate, with the estimation of sodium by difference.The drawbacks to this method are : (a) the time required by even an experienced operator is excessive-Haslam and Beeley,2 in a critical review of the method, state that they found it difficult to complete the sodium and potassium determinations in less than three days; (b) great manipulative skill is required; (c) a blan:k determination must be made for all the reagents; ( d ) there is great risk of loss of the alkalis by occlusion when filtering from the insoluble silicates, aluminates and carbonates, so that several reprecipitations are required for highly accurate work; (e) there is risk of loss of alkalis at the final volatilisation of ammonium salts. Despite its limitations this method is still very widely used in mineral analysis, as other chemical methods have not been shown to possess any outstanding advantages.Haslam and Beeley2 also proposed a modification of the method for which they claimed increased accuracy, but stated that whilst the sodium determination could normally be completed in one day, the following day was required to complete the potassium determination. In this modification sodium is determined as the zinc u.ranyl acetate complex and the potassium, if present in small amounts, as the cobaltinitrite or, if in large amounts, as the perchlorate.July, 19511 41 I Various authors, including Mitchell3 and M~ller,~ in an attempt to simplify and speed up the determination, have proposed spectrographic methods.Lundegardh and Mitchell in early experiments introduced a suitable solution of the mineral into an air - acetylene burner by means of an atomiser, passed the emitted light through a spectrometer and photographed the spectrum; the density of the spectral lines was measured by means of a photometer and compared with a composite standard solution analysed in the same manner. The results were promising, but the technique was intricate and time-consuming. Mitchell and Robertson5 noted that the intensity of the light emitted by an ion was not a simple function of its concentration in solution, but varied in a complicated manner depending on the presence or absence of certain other ions in solution. With the Lundegardh apparatus these authors observed that calcium and strontium flames were strongly depressed by aluminium, but that in the presence of an excess of calcium the depression of strontium by aluminium was considerably diminished. In controlled conditions this depression could be made use of for the indirect determination of aluminium.Many other similar interferences have been observed, both with anions and with cations, e.g., the emission from alkali metals is reduced slightly by sulphates and tartrates and very much by phosphates. More recent developments of spectrophotometric analysis have been largely concerned with studies of these and other interferences and with attempts to reduce them. The direct reading photo-electric photometer made it possible to carry out analysis much more rapidly, with consequent reduction in the errors caused by fluctuations in gas and air pressure.In some of these instruments a desired waveband is scanned through selective filters, but the difficulty of obtaining spectrally pure filters makes the more versatile instruments that are provided with monochromators much to be preferred. Two different methods have been used for relating intensity of light to concentration of the ion in solution. In the absolute method a calibration curve is drawn for solutions of known concentrations, gas, air and oxygen pressures being kept constant within fine limits. The concentrations of unknown solutions can then be determined by interpolation on the graph. The objection to this method is that interference from foreign ions may affect the sample, but not the calibrating solution, and that these interferences may be entirely unsuspected.Attempts have been made to obviate these effects by preparing calibration solutions that imitate as closely as possible the composition of the sample t o be examined. For the determination of alkali metals in cement, a method has been described6 in which a blank solution of calcium oxide in hydrochlbric acid is used as a base’ for the calibration solution. Excellent results are claimed, and it is possible that this method is satisfactory for simple routine analysis, but for more complex materials, such as rocks and minerals, containing an unknown and probably large number of constituents in unknown concentration, such an artifice would be impracticable. A recent paper7 described the addition of “radiation buffers” to calibration solutions and to samples under test.The addition consists of a large excess of an interfering ion, so that further effects due to trace constituents in the sample are negligible. A serious objection, however, to all calibration methods is that light intensity depends on many variable factors that cannot always be reproduced after an interval of time. Possibly the most difficult factor to control is rate of atomisation, which depends on air pressure, the viscosity and temperature of the solution and the width of the orifice. Slight clogging of the orifice changes the flame response profoundly. The internal-standard method, inherited from arc spectrography, has been claimed to be less affected by interferences.* A known small amount of a foreign ion is deliberately added to the material to be examined and the light intensity due to this ion is then compared with the light intensity due to the ion sought.A dual optical system is used so that fluctua- tions in pressure, viscosity and temperature are avoided. The internal standard is normally chosen so that its properties resemble those of the element sought, e.g., lithium is used in determination of sodium and potassium. Interfering effects are, however, not necessarily the same for two different ions, even if they are closely related, and in examining unknown solutions a further uncertainty is introduced by the internal-standard method, as the material may already contain some of the reference element.6 For these reasons it is difficult to apply the internal-standard method with precision to the analysis of rocks, although it is POTASSIUM IN ROCKS AND MINERALS BY FLAME PHOTOMETRY412 OSBORN AND JOHNS: THE RAPID DETERMINATION OF SODIUM AND [Vol.76 certainly satisfactory for such determinations as the sodium and potassium content of blood serum. With the shortcomings of the two methods in general use in mind, the possibility was considered of determining alkali metals by a direct addition method, i.e., by measuring the response of the sample and then measuring the increase in light intensity on adding a small amount of standard alkali to a suitable aliquot, I t was thought that, by taking readings for several aliquots containing different quantities of standard, a graph could be constructed and extrapolated to determine the amount of alkali present in the sample.The usual interference effects should in this manner be entirely obviated. Extrapolation is satisfactory only if the graph is perfectly regular .and preferably linear. Experimental work demonstrated that potassium gave an almost linear graph a t low con- centrations (0 to 10 p.p.m.) but that sodium gave a slightly curved graph even at this very small concentration. Calcium gave a linear response up to 500 p.p.m. Mr. B. S. Cooper has suggested that the parabolic shape of these graphs is due to absorp- tion of light from the rear part of the flame by the vapour of the substance in the front of the flame. It is possible that a more linear response would result from the use of a relatively flat flame of the “fish-tail” type, and experiments are being conducted to investigate this point.Alternatively, saturation emission may be prevented by working at very low con- centrations or by the addition of foreign ions known to depress emission. It has already been mentioned that certain anions depress the amount of light emitted by alkali metals, and that the phosphate ion in particular causes a large depression. The effect of phosphate ions on the shape of the graph of sodium concentration versxs light intensity was therefore investigated. The results showed that for conce:ntrations up to 20p.p.m. the graph was perfectly linear, and very much less steep than in the absence of phosphate. Similar results were obtained for potassium. The reduction of light emission in the presence of foreign substances may be due to restricted ionisation, leading to a molecular, rather than an ionic spectrum, but other factors such as absorption and alteration of flame temperature may play a part.Nitrogenous organic substances may, for instance, be expected to lower the flame temperature if they are present in a large excess, and a similar effect is possible in the presence of halogenated paraffins. However, in a series of experiments, no reduction in light intensity was observed on addition of pyridine or chloroform to a sodium solution, although a small decrease was brought about by addition of an excess of urea. Other organic substances such as acids and phenols were also found to have little or no effect, and it was concluded that at the temperature of the flame organic molecules are, €or the most part, completely destroyed.It has been reportedg that light emission is actually increased by the addition of alcohol and acetic acid, and these results have been verified by experiment. It is probable that this is a physical effect resulting from an increased rate of atomisation owing to the lowered surface tension of the test solution. Inorganic ions that were found to suppress emission of light from sodium include phosphate, borate and molybdate, which are all about equally effective, and may in some circumstances reduce the light intensity by more than half. A smaller effect is produced by addition of an excess of sulphate, but nitrate, chromate and halides give the same response as the free base.The effect of some of these anions is shown in Figs. 1 and 2, which were prepared by plotting readings on the Beckman photometer against concentration of sodium or potassium in parts per million. The curves did not pass through the origin as the galvanometer is slightly deflected even when no sodium is intentionally vaporised in the flame. This effect is due to flame background and to traces of sodium in the air and the water used for preparing solutions, and is measured by vaporising pure distilled water into the flame. In order to investigate the effect of cations, series of readings were taken to compare pure dilute solutions of sodium and potassium salts with solutions of various salts containing the same quantity of added alkali.In the first series the equivalent of 20 parts per million of sodium, as chloride, was added to various 1 per cent. solutions of metal chlorides. It was observed that the intensity of light at 5893 A was reduced by about 20 per cent. by ammonium, cupric, zinc, cadmium, magnesium, ferric , cobalt and nickel chlorides, with no appreciable difference in effect between any of these ions. Simaller effects were observed with bariumJuly, 19511 413 and calcium chlorides, the depression being about 15 per cent. In the presence of lithium and potassium chlorides no decrease in intensity of sodium emission was detected. POTASSIUM I N ROCKS AND MINERALS BY FLAME PHOTOMETRY Sodium, p.p.m. Potassium,, p. p. m. Fig. 1. Effect of anions on sodium Fig. 2. Effect of anions on potassium Curve A, free base; curve B, solution in Curve A, free base; curve B, solution in 1 per cent. boric acid; curve C, solution in 1 per cent.ammonium molybdate; curve D, solution in 1 per cent. ammonium phosphate Approxi- mately uniform depression of about 20 per cent. was noted when the sodium was determined in 1 per cent. solutions of silver, aluminium, lead, cerium, lanthanum and uranium as nitrates. Similar results were obtained on repeating these investigations with potassium instead of sodium. It appears from these preliminary results that any solids, other than alkalis and alkaline earths, have the effect of depressing the intensity. These findings were applied to the analysis of rocks and minerals by finely grinding a number of samples and analysing them on the Beckman flame spectrophotometer, model DU.PROCEDURE Use wavelengths of 5893 A for sodium and 7670 A for potassium; these are the principal lines for these elements. With a slit width of 0.1 mm, pass propane into the burner until a pressure of 2 cm is registered on the manometer. Then start the oxygen supply and increase it until a non- luminous flame is produced. At the wave- lengths specified the flame background will be found to be very slight. Weigh 0.1 g of finely ground material in a platinum dish and moisten it with 1 drop of sulphuric acid. Evaporate to dryness with 2 ml of hydrofluoric acid. If decomposition is not complete, repeat the evaporation with hydrofluoric acid. Dissolve the residue by boiling it with 10 ml of 5 N hydrochloric acid.Dilute the solutions to 500 ml with a 1 per cent. solution of ammonium phosphate. Then take four 100-ml aliquots and add to them 0, 0.1, 0.2 or 0.3 ml respectively of 0.1 N alkali according to the elements being determined. The ammonium phosphate must previously have been examined for sodium and potassium on the flame photometer. Normally, the amount present should not exceed 0-1 p.p.m. in a 1 per cent. solution. MEASUREMENT- units as follows- 1 per cent. ammonium phosphate In a second series, sodium as nitrate was determined in other nitrate solutions. Operate the atomiser at a pressure of 251b. When different solutions are vaporised, the flame intensity is measured in arbitrary (a) Prepare a reagent blank by evaporating hydrofluoric and sulphuric acids in the quantity used for the decomposition of the rock specimen and treat as described above.(b) Use a prepared solution of the sample under examination. (c, d and e) Use solution (b) containing 0.1, 0.2 and 0.3 ml respectively of 0.10 N sodium hydroxide in 100 ml.414 OSBORN AND JOHNS: THE RAPID DETERMINATION OF SODIUM AND [VOl. 76 If the increase in flame intensity between (c), (d) and (e) does not indicate a rectilinear relationship between concentration and light emitted, all the solutions are diluted with water and the determinations repeated. When the dilution has been so adjusted that a constant difference is found between (c), ( d ) and (e), the percentage of Na,O equals- (:+;) x 31/106 percentage of solution. Owing to the limifed linearity of the curve, greater accuracy is obtained if the value of (b) is kept fairly small in the above equation.If a very large deflection is obtained it is advisable to dilute the sample solution 10- or 100-fold and to repeat the determination. Some results by the above technique are shown in Table I and compared with results for the same specimens found by Dr. Max Hey of the British Museum of Natural History by the classical Lawrence Smith method of weighing the mixed chlorides of sodium and potassium, determining potassium as the perchlorate and calculating Na,O by difference. TABLE I COMPARISON OF RESULTS BY SPECTROPHOTOMETRIC AND CHEMICAL METHODS FOR SODIUM Na,O by chemical Na,O by flame Sample analysis, spectrophotometer, % Yo 1516 Rhyolite, Lupata Gorge, Nyasaland . .1.97 2.16 2358 Black manganese ore (46% of MnO), Benallt, N. Wales . . .. .. 0.27 0.3 1 2253 Limestone, Nyasaland . . .. .. 0-03 0.15 2194 Quartz - alkali - syenite, Lion Rock Gully, Nyasaland . . . I .. 3.88 4.09 2361 Chloritic mudstone, country rock of 2193 Felspar - pyroxene rock, Nkalonge Hill, Grey phosphatic manganese ore (17% of Biotite-bearing algerine - augite foyaite, manganese ores, Benallt, N. Wales . . 0.14 0.20 N yasaland .. 0.27 0.36 2018 Phenolite dike, Maize Hill, Nyasaland 10.73 11-00 2359 MnO, 10% of P,06), Benallt, N. Wales nil 0.07 2067 Basalt, Teliki Volcano, Kenya . . .. 4.14 4-13 1907 Nyasaland , . .. .. .. 8-25 8.36 Difference, % +0-19 + 0.04 +0*12 +0.21 + 0.06 + 0.09 + 0.27 + 0.07 - 0.01 +Owl1 The results with the flame spectrophotometer are usually slightly higher than those by chemical methods, but this is satisfactory if the probable loss by occlusion or volatilisation in the gravimetric method is accepted.When no sodium was detected gravimetrically we are convinced it was present in small amounts. Moreover, the concordance is much better than that of the figures quoted by Hillebrand and LundelP for sodium determinations on the same rock made gravimetrically by different analysts. The corresponding figures for potassium are shown in Table 11. TABLE :I1 COMPARISON OF RESULTS BY SPECTROPHOTOMETRIC AND CHEMICAL METHODS FOR POTASSIUM Sample 1516 2358 2194 2361 2193 2018 2359 2067 1907 K,O by chemical K:,O by flame analysis, spec.trophotometer, % % 4.86 4.86 nil 0.1 1 6-28 6-23 0.48 0.59 14.68 14.70 4.72 4.53 nil 0.04 1-91 1.90 7-53 7-64 Difference, % nil +0*11 - 0.05 + O * l l + 0.02 -0.19 -!- 0.04 - 0.01 1-0-11July, 19511 POTASSIUM IN ROCKS AND MINERALS BY FLAME PHOTOMETRY 415 It will be observed that the agreement is even better than that for sodium, and that although the deviation is random in direction, it is, as before, mostly in the positive direction, so agreeing with the findings for sodium.As before, when no potassium was reported by the gravimetric method, some was recorded by the flame photometer. Again the concordance is better than that between figures for potassium in the same rock determined gravimetrically by different analysts. CONCLUSIONS Consideration of the above results indicates that by working with suitably dilute solutions in the presence of an excess of phosphate, the graph of flame intensity versus sodium or potassium intensity is sufficiently nearly linear to permit analysis by a direct addition method, the results comparing favourably with those of the classical chemical procedure.The time taken for the analysis of an average sample of acid-soluble rock or mineral, including all preparatory work, is about one hour. If a number of samples are being examined simul- taneously, the average time would be less. All the rocks examined were found to be acid soluble after treatment as described on p. 413, but if the rocks or minerals to be examined are very refractory, e g . , tourmaline, beryl, biotite or topaz, and will not dissolve directly in acid, then, after the Lawrence Smith fusion, the mixture can be extracted with acid and, after the removal of the silica, the sodium and potassium can be determined directly on an aliquot of a measured volume. The presence of large amounts of calcium in the acid solution of the product obtained from the opening-up process will not influence the method in any way when the ammonium phosphate is added in the course of the flame photometry procedure. If only very small amounts of material are available, it would be possible to use as little as 0.005 g of material if the amount of sodium is above 0.5 per cent., or 0.02 g if the amount of sodium is 0.5 per cent.or less. Hence the method can be used as a micro-method without loss of accuracy. The authors thank the Directors of the British Drug Houses Limited for permission Thanks are also due to Dr. Max Hey of the British Museurn (Natural to publish these results. History) for providing the chemical analyses of the rocks and for helpful discussion. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Lawrence Smith, J., Amer. J. Sci., 1870, 50, 269; Ann. Cheni. Pharnz., 1871, 159, 82. Haslam, J . , and Beeley, J., Analyst, 1941, 66, 185. Mitchell, R. L., J , SOC. Chem. Ind., 1936, 55, 267. Muller, R. H., Anal. Chem., 1947. 19, part 8 (August), 21n. Mitchell, R. L., and Robertson, I. M., J. Soc. Chem. Id., 1936, 55, 269. Chemical Age, 1950, 62, 857. West, P. W., Folse, P., and Montgomery, D., Anal. Chem., 1950, 22, 667. Berry, J . W., Chappell, D. G., and Barnes, R. B., Ind. Eng. Chem., Anal. Ed., 1946, 18, 19. Parkes, T. D., Johnson, H. O., and Lykken, L., Anal. Chem., 1948, 20, 827. Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” John Wiley and Sons, New York, 1929, pp. 5, 850, 861 and 874 et seq. ANALYTICAL DEPARTMENT THE BRITISH DRUG HOUSES LIMITED LABORATORY CHEMICALS GROUP POOLE, DORSET

ISSN:0003-2654    

DOI:10.1039/AN9517600410

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

416 ROBINSON AND OVENSTON : A SIMPLE FLAME PHOTOMETER [Vol. 76 A Simple Flame Photometer for Internal-Standard Operation and Notes on. Some New Liquid Spectrum Filters BY (THE LATE) A. M. ROBINSON AND T. C. J. OVENSTON (Presented at the meeting of the Physical Methods Group on Friday, October 6th, 1950) A flame photometer based on a Dutch design has been built for operation primarily by the internal-standard technique. Two beams, directed simul- taneously through “standard” and “sample” spectrum filters respectively, fall on barrier-layer photo-cells whose outputs are balanced potentiometrically by a null-point method. Special features in the design and operation of this instrument are described, and certain precautions are recommended. The choice of the internal-standard element is briefly discussed.The transmission characteristics of some new spectrum filters, made by combining layers of solutions of common substances, are given and in some instances compared with those of glass, gelatin and interference filters. FROM work already published it seems quite clear not only that sodium, potassium and related elements can be determined much more rapidly by means of a flame photometer than by the time-consuming gravimetric procedures, but also that the results so obtained for many materials are quite as reliable. It appears that useful results can be obtained with very simple apparatus in which the excited raldiation, after passage through a spectrum filter, falls on a selenium barrier-layer cell connected to a galvanometer. It was desired to explore possible applications of a simple flame photometer of this type, and one described by Boon1 in 1945 was taken as a model.Like that of Barnes, Richardson, Berry and Hood,, Boon’s instrument was designed for direct reading. From the subsequent work of Berry, Chappell and Barnes3 it appeared that the use of an internal-standard technique arid a dual optical system offered certain important advantages, so the design was modified to allow either method of measurement to be used. DESCRIPTION OF THE FLAME PHOTOMETER Fig. 1 is a general view of the flame photometer assembly. Cylinder gas is controlled by reducing valves to give a low-pressure supply, pressures being measured by a water manometer. Air from a small compressor is fed through a pressure stabiliser to the atomiser, final pressure being shown by a mercury manometer.The final pressure controls for both gas and air are glass taps that are mechanically connected to slow-motion dials of a type once common on radio sets. Attention is drawn to the cylindrical light shields, which are here shown slid back to reveal the optical assembly. In use these shields are slid forward against the vertical plates on the side limbs of the chimney so that all background radiation other than that from the flame itself is eliminated. The disposition of the principal parts and the electrical circuit used for the internal- standard method are shown in Fig. 2. The distances hetween the photo-cells, the lenses and the flame have been chosen as a satisfactory compromise between two opposing effects; greater distances tend to lower the over-all sensitivity, whereas the heat from the flame makes it undesirable to place the photo-cells any nearer. As it is, it is very important to keep the photo-cell shutters up except for the minimum time necessary to make a measurement.The electrical circuit, except for a minor modification, is that given by Berry, Chappell and Barnes.3 The filter F’ transmits only the radiation emitted by the internal-standard element, which has been included in known concentration in the sample solution, and the photo-cell C’ receiving this radiation generates a proportional amount of current, which is dispersed along resistance R,. At the same time the filter F transmits only the radiation emitted by the element being determined and the photo-cell C generates a proportional amount of current, which is dispersed along resistance R,.1 .( ;enera1 \.iew of the flame photonieter assembly SAMPLE BEAM .c-- R,= 500n t 1;ig. 2 . Optical and electrical layout of flame photometer for use with internal standardsFig. 3. The burner assembly Fig. 1. The atomising vesselJuly, 19511 AND NOTES OX LIQUID SPECTRUM FILTERS 41 7 The circuits are balanced by means of a galvanometer, used as a null-point meter, connected to tappings on R, and R,. A Cambridge spot galvanometer with a resistance of 450 ohms was found suitable. Normally, the tapping on R, is at the negative end of the resistance so that the whole of the current generated as a result of the emission of the sample element is balanced against the excess of internal-standard current, the range of the determina- tion depending on the latter.Range adjustments can sometimes be conveniently made, however, by moving the galvanometer tapping along R,, and the exact position can be found again on a subsequent occasion by resetting with the standard solutions. Once set for a given determination, this tapping must not be altered. Resistance R, is a precision potentio- meter, the galvanometer tapping on which is adjusted by means of the control knob to give no deflection of the galvanometer needle during measurement. The pointer attached to the control knob indicates in degrees the position of the tapping; this value can be related to known concentrations of a given element and hence a calibration graph can be constructed. The small resistance R, is useful for making minor adjustments in the course of a long series of determinations when the occasional introduction of standard solutions indicates that a slight drift has occurred.Cylinder gas is passed by way of the lower nozzle into the glass burner, in the body of which it is mixed with air containing the atomised solution passed in by way of the side tube. The base of the burner is pressed against a rubber washer by means of a spring held by an adjustable cross-bar. A short glass tube inserted in the rubber washer is placed over the gas inlet to protect it from the mist. The tip of the burner is a platinum collar 6 mm in diameter. The atomiser, which is based on the design of Rauterberg and Kni~penberg,~ is shown in Fig.4. Air is passed in at the bottom under pressure and is forced out of the vertical jet. The horizontal tube leading from the beaker containing the solution is so placed that the air jet, in passing the tip, causes the solution to be sucked into the atomiser, where it is blown against the baffle plate with considerable force. The only outlet for the air is through the side tube to the burner, so that the mist formed in this way is carried along with it. The un-atomised solution falls to the bottom of the vessel, where it syphons to waste. A con- siderable amount of adjustment is possible by rotation of the jets, both of which are carried on ground-glass joints. Both atomiser and burner are now obtainable commercially.* They have recently been fully described by Doming0 and K l ~ n e , ~ who have adapted Boon’s design to the deter- mination of sodium with a selenium photo-cell and of potassium with a caesium photo-cell by the direct method of measurement.The gas pressure required depends on the size of the nozzle leading into the base of the glass burner. The nozzle size is not critical, but the correct manometer reading for any given nozzle is constant and can be found by reducing the gas flame until it is as non-luminous as possible while at the same time maintaining the flame in a stable condition. The air pressure required depends on the size of the air jet in the atomiser, sufficient air having to be passed to maintain a steady flame. With the type of atomiser described here a pressure of about 40mm of mercury is usual, the exact value for a given model being found by experiment.The burner assembly is shown in Fig. 3. PRECAUTIONS IN OPEFLATION- To prevent minor explosions when lighting and extinguishing the burner for use with acetylene - air mixtures, a Y-tube was inserted in the acetylene lead just before it enters the burner. The free end of the Y-tube was permanently connected to a coal-gas supply tap. The coal gas was first turned on and lit. The air supply was then turned on and finally the acetylene. The coal gas was then turned off slowly, care being taken that sufficient acetylene was being supplied to support the flame. Final adjustments were then made in the usual way. When extinguishing the flame, the coal gas was first turned on and the acetylene then turned off.The coal gas was then turned off. This soot must be carefully removed before relighting, otherwise the flame may be so unsteady as to be uncontrollable. Even in normal usage of the burner, soot is slowly deposited near the tip; to ensure the best results, this deposit should frequently be removed. Lane End Road, Sands, High Wycombe, Bucks. Should a back-fire occur at any time, the burner quickly fills with soot. * The apparatus used by the authors was supplied by the Laboratory Glassblowers Co., Valley Works,418 cells to the flame. keep the shutters closed except for the half minute required for each measurement. in the bottom of the atomiser vessel was syphorting away. RELATIVE FLAME SENSITIVITIES- Barnes, Richardson, Berry and Hood2 preferred a flame with a relatively low temperature because less elements were excited and this made the task of isolating the required radiation simpler.Much sensitivity is lost in this way, however, and many workers prefer the hotter acetylene - air flame. In Fig. 5 are shown the relative sensitivities of acetylene - air, coal gas - air and butane - air flames as indicated by the galvanometer deflection given by various concentrations of sodium. It is clear that excitation in the acetylene - air flame is much greater than in the other two flames and that it should be used whenever sensitivity is of importance. SELENIUM CELL RESPONSE- barrier-layer photo-cells were employed. ROBINSON AND OVENSTON : A SIMPLE FLAME PHOTOMETER [Vol. 76 Another precaution that must be emphasisecl concerns the close proximity of the photo- It was found essential in order to prevent fatigue of the photo-cells to Finally, it was found desirable to avoid taking readings at the moments when the waste In the present apparatus standard Evans Electroselenium Ltd.(EEL) selenium These show good response over the whole of the Sodium, p.p.m. Curve A, acetylene - air; curve B, coal gas - air; curve C , Fig. 5. Relative sensitivities of burner gases butane - air visible spectrum and are particularly sensitive in the region near 589mp, the wavelength of the sodium doublet. Above 700mp, however, the response falls off sharply and small amounts of potassium cannot be determined. For instance, in a direct measurement circuit and with the liquid spectrum filters now recommended, a galvanometer deflection (one-tenth of the full scale) that was given by as little as 0-5 p.p.m.of sodium or 3.2 p.p.m. of lithium required 30 p.p.m. of potassium to reach the same value. For this reason it is usual to measure the potassium emission by means of a caesium photo-emissive cell. For internal-standard work, with two photo-cells in electrical balance, it is desirable to select a type of cell that covers the whole of the working range. Except for work on potassium (and on caesium and rubidium), the selenium cell described above is satisfactory and offers the advantage of cheapness and simplicity. To widen the range it has been the practice, as in the Perkin - Elmer model 52A, to use interchangeable red- and blue-sensitive photo-emissive cells in conjunction with a balanced electronic circuit and high amplification ; this, of course, involves considerable expense, and such an apparatus, combined as it is with a dual-prism monochromating.system, is possibly as, versatile an instrument as can be devised. Since the main body of this paper was written, however, attention has been drawn* to theJuly, 19511 AND NOTES Oh- LIQUID SPECTRUM FILTERS 419 recent production of selenium barrier-layer cells* having a response range extending to about 900mp. With these cells it is hoped to extend the range of the present simple assembly to cover all normal requirements. U S E OF INTERNAL STANDARDS ERRORS AND THE INTERNAL-STANDARD TECHNIQUE- Errors in flame photometry can be classified into: (a) those arising from flame fluctuations; (b) those arising from impurities affecting the viscosity or surface tension of the solution, i.e., urea, which depresses, and methanol, which enhances the emission intensity of the alkali metals3; (c) those arising from the depressing effect of acids and salts3,’; (d) those arising from inefficiency of the filters.In the direct (or absolute) method of measurement, flame fluctuations are controlled as much as possible, and it is good practice to alternate samples with standards to detect drift. To cope with the effects of impurities and of large concentrations of salt, a number of suggestions have been made. For example, Berry, Chappell and Barnes3 have recommended the making up of standards in solutions having the same composition as that containing the element to be determined.This technique is obviously limited to ranges of materials of fairly constant general composition. Shapiro and Hoagland* recommend further dilution of samples, by which means the relative effect of these interferences can be very greatly reduced. This dilution technique is certainly effective, but the sensitivity of the determination is, of course, correspondingly reduced. For water analysis, West, Folse and Montgomeryg have suggested the use of “radiation buffers,” that is, -concentrated solutions of selected salts added in fixed proportions to the sample solution to buffer any interference from small and variable amounts of these salts. By means of the internal-standard technique with a dual optical system, errors caused by flame fluctuations, by viscosity and surface tension effects and by the depressing effects of acids and salts are greatly reduced.In addition, any of the suggestions already made to cope with these effects in the direct method of measurement are equally applicable when using the internal-standard technique. Both methods are dependent on the efficiency of the light filters in cutting off unwanted radiation, but it should be mentioned that it is not necessary for the internal-standard filter to eliminate aZZ the radiation of the element being determined, or for the sample filter to eliminate all the radiation of the element used as the internal standard, as the calibration graph will take account of this. It can be concluded that the internal-standard technique can be used with advantage whenever it is appropriate.It is not appropriate unless an internal-standard element can be selected that not only provides a sufficiently strong emission at a convenient wavelength, but also does not occur in appreciable and variable quantities in the material to be analysed. POSSIBLE INTERNAL-STANDARD ELEMENTS- Until recently, lithium was the only metal that had been successfully used as an internal standard for flame photometry (excluding spectrographic applications). I t is known to be absent from many materials commonly subjected to analysis for sodium and potassium. Eubank and Bogue,lo however, prefer the direct method for the analysis of Portland cement because this material contains unknown and variable amounts of lithium.In addition to examining lithium, Berry, Chappell and Barnes,3 who used a type of photo-cell with a response similar to that of the standard Evans Electroselenium cell, examined the potentialities of rubidium, caesium and indium, but rejected them. The present authors have tried to use the weak emissions available in the blue end of the spectra of rubidium and caesium. Suitable filters were devised, but the concentrations of internal standard required to balance the common alkali metals were far too large to allow the develop- ment of practical or economical methods. However, these two metals are sufficiently rare in nature to make them valuable internal-standard elements if it were possible to utilise the radiation of their strong emissions in the near infra-red.It is hoped to give further study to this matter when the new infra-red-sensitive barrier-layer cells have been incorporated in the present apparatus. * These cells are manufactured by Megatron, Ltd., London.420 ROBINSON AND OVENSTON : -4 SIMPLE FLAME PHOTOMETER [Vol. 76 This gives a fairly strong emission a t 535 mp, which can be separated completely from the sodium doublet by means of the solution filter whose characteristics are shown in Fig. 9. No further experiments with thallium have yet been made. I t should be noted that this metal is toxic and should not be burnt in the flame photometer without an efficient flue. Finally, it should be mentioned that common elements can sometimes be used as internal standards. One of the authors (A.M. R.) has developed a method for the determination of lithium as a major constituent in magnesium - lithium alloys by using potassium as an internal standard. Sodium and other normal impurities or additions do not interfere and the amount of potassium added as standard is so much in excess of the maximum that could reasonably be expected to be present in these alloys that their true potassium content is of no account. The weak photo-cell response at 766 to 770 mp is then an advantage; in fact, with an infra- red-sensitive photo-cell it would be necessary to reduce the intensity of the standard beam by means of an iris diaphragm or similar device. This method will be described in a separate paper. FILTERS Another element worth mention is thallium. For filtering the radiation, glass or gelatin filters are undoubtedly very convenient to In addition, gelatin filters are apt to change use, but they are not particularly efficient.Wavelength, mp Fig. 6. . . . . . . . . .-._._ Cupric chloride component - - _ _ _ Transmission curves for sodium filters Complete liquid filter Sodium dichromate component Chance OY1 and Ilford 803 combined their transmission characteristics with use. It is considered preferable to use cells filled with solutions of known transmission characteristics. These are readily made up and can always be relied on. With two layers of solutions it is possible to devise combinations that completely stop all radiations outside a limited range of the spectrum. For example, potassium dichromate has a very sharp cut-off that can be varied over about 50 mp by changes of concentration. By using sodium dichromate, higher concentrat ions are possible and radiation shorter than that emitted by sodium can be readily cut off.The transmission curve of a l-cm layer of an aqueous 50 per cent. w/v solution of sodium dichromate dihydrate (Na,Cr,O,.ZH,O) is shown in Fig. 6, together with the corresponding curve for a 5.0 per cent. w/v solution of cupric chloride dihydrate (CuC1,.2H20) in 8 N hydrochloric acid. By combining these two layers in series they form an efficient filter for sodium radiation with transmission characteristics indicated by the continuous curve in Fig. 6. This filter cuts off all radiation in the photo-cell range of wavelengths from 553 mp downwards and from 671 mp upwards, and transmits 44 per cent.of the sodium radiation at 589 mp. Potassium, lithium (at 671 mp) and barium radiation are efficiently stopped. Calcium and strontium band emissions, which are most intense at about 620 mp and 605 mp, respectively, are partly transmitted. The weak lithium emission at 610mp is within theJuly, 19511 AND NOTES ON LIQUID SPECTRUM FILTERS 42 1 transmission range of this filter; fortunately, the effect of this is noticeable only when the concentration of lithium is high and, in any event, could not contribute an error when lithium is used as an internal standard, though it would increase the size of the blank measured when no sodium is present. The pecked curve in Fig. 6 shows the transmission spectrum of the combination of a Chance OY1 glass filter with an Ilford 803 gelatin filter, a system that has been recommended for the isolation of sodium radiation.The system transmits 18 per cent. of the sodium radiation and a correspondingly reduced proportion of the calcium and strontium radiation. Its use would, therefore, reduce the sensitivity for sodium to less than half of that obtained Fig. 7. . . . . . . . . ._._._ Potassium dichromate component _ _ _ - - Ilford 207 Transmission curves for potassium filters Complete liquid filter Aniline blue component (this coincides with that for the complete filter above 500mp) with the liquid filter combination, although the interference to be expected from calcium and strontium is no less. In addition, transmission down to about 490mp is appreciable, in which region the barium emission at 553 mp and various barium oxide bands at lower wavelengths occur.In Fig. 7 the transmission curves of a liquid filter for potassium and of Ilford 207 gelatin filter are compared. The liquid filter combination consists of 1-cm layers of a 2 per cent. w/v aqueous solution of potassium dichromate (K,Cr,O,) and a 0.02 per cent. w/v solution of aniline blue in 95 per cent. ethanol. The cut-off is due entirely to the aniline blue solution. The purpose of the dichromate layer is to prevent transmission below 500 mp, which would be permitted by a region of low absorption by the aniline blue solution. The concentration of the aniline blue solution has been selected so that all radiation a t 671 mp and below is stopped.At the same time, 96 per cent. of the potassium radiation at 766 mp and 770 mp is transmitted, as compared with 75 per cent. for the Ilford 207 filter. The Ilford 207 filter, however, is also very efficient in stopping unwanted radiation. Radiation from elements emitting at lower energy levels is cut off by the limiting response of the photo-cells in the infra-red. With photo-cells more sensitive to infra-red radiation it would be necessary to devise a filter to stop the lithium emission at 831 mp, the rubidium emissions at 780 mp and 795mp and the caesium emissions a t 852mp and 894mp, should these elements be present in appreciable quantities. The liquid filter combination for lithium, Fig. 8, consists of 1-cm layers of a 0-2 per cent. w/v solution of rhodamine B in water and a 1.0 per cent. w/v solution of cupric chloride dihydrate in 8 N hydrochloric acid.This combination has been designed to stop radiation at 620 mp and below and at 766 mp and above, and is thus highly efficient in isolating the lithium radiation, which is transmitted to the extent of 25 per cent. The liquid filter proposed for thallium, Fig. 9, consists of 1-cm layers of a 0.5 per cent. w/v aqueous solution of potassium dichromate and a 100 per cent. w/v solution of cupric nitrate trihydrate (Cu(N0,),.3H20) in 2 N nitric acid. The combination transmits 21 per[Vol. 76 cent. of the thallium radiation at 535 mp, while the presence of large amounts of sodium causes no appreciable increase in the total amount of transmitted radiation. Barium and barium oxide radiation and some of the calcium oxide radiation at 550 to 555 mp is partly t ransrnit t ed.The effect of increasing the optical thickness of a liquid filter is of interest. It is well known that an increase in the optical path of a homogeneous absorbing medium by a factor offwill have the effect of reducing the transmission by raising it to the power off. It follows that the efficiency of a liquid filter may be continuously increased by increasing its thickness, 422 ROBINSON AND OVENSTON : A SIMPLE FLAME PHOTOMETER Wavelength, mp Fig. 8. Transmission curves for the lithium filter ----- Rhodamine B component .-.-.- Cupric chloride component Complete liquid filter Wavelength, mp Fig. 9. Transmission curves fo:r the thallium filter Complete liquid filter ----- Potassium dichromate component ._._._ Cupric nitrate component for the smaller the transmission the greater will be the reduction in transmission.Hence, where a transmission of 50 per cent. would fall to 25 per ce:nt. on doubling the thickness of the filter, a transmission of 25 per cent. would fall to 6-25 per cent. and one of 10 per cent. to 1 per cent. In Fig. 10, curve A shows the transmission spectrum of the normal-thickness sodium filter already described and curve B shows that of the same filter made up of two 2-cm layers. The increase in efficiency is evident, for while the transmission of the sodium radiation has fallen froin 44 per cent. to 19.4 per cent., the transmission of the strontium radiation at 605 mp has been reduced more than threefold and that of the calcium radiation at 620 mp has beenJuly, 19511 AND NOTES ON LIQUID SPECTRUM FILTERS 423 reduced sevenfold. By continuing this process it is possible to obtain an almost perfect monochromatic filter.Unfortunately, with each reduction of maximum transmission the sensitivity of the determination is correspondingly decreased, and the problem resolves itself into choosing the most suitable compromise to meet any particular set of requirements. For comparison, the transmission spectrum of a typical interference filter of maximum transmission at 589 mp is shown in Fig. 10 as curve C. This curve was calculated from the Fig. 10. Transmission curves showing the effect of Wavelength, mp increasing the optical depth of the sodi<m liquid filter and a comparison with an interference filter.Curve A, normal sodium filter, 1 cm + 1 cm; curve B, double thickness sodium filter, 2 cm + 2 cm; curve C, typical interference filter (parallel beam) manufacturer’s data sheet and may be slightly optimistic, but there is no doubt that the efficiency of these somewhat costly filters is very good. It should be noted, however, that the maximum efficiency of an interference filter can only be attained when the transmitted beam consists of absolutely parallel radiation. For this reason the present optical lay-out is not considered suitable for use with these filters. By replacing the existing lenses by double lens systems designed so that the rays emanating from the centre of the flame are parallel when passing between the two parts of each lens system, it should be possible to use inter- ference filters in the present apparatus by inserting them in this part of the beam. The comparatively large flame area, however, makes it impossible to obtain a completely parallel beam. We acknowledge the helpful advice given by Dr. E. J. Bowen and Dr. L. Leyton, and also thank Dr. Bowen and Mr. L. G. Young for the loan of certain components of the first assembly. This paper is published with the approval of the Lords Commissioners of the Admiralty, but the responsibility for any statements of fact or opinions expressed rests solely with the authors.424 MILNER AND TOWNEND : THE DETERMINATION OF ALUMINIUM [Vol. 76 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REEEREWES Boon, S. D., “Vlam-fatometrie,” D. B. Centen, Amsterdam, 1945. Barnes, R. B., Richardson, D., Berry, J. W., and Hood, R. L., Ind. Eng. Chem., Anal. Ed., 1945, Berry, J. W., Chappell, D. G., and Barnes, R. I3., Ibid., 1946, 18, 19. Rauterberg, E., and Knippenberg, E., Ernahr. Pflunze, 1941. 37, 73. Dorningo, W. R., and Klyne, W., Biochem. J., 1949, 45, 400. McGowan, G. K., private communication. Parks, T. D., Johnson, H. O., and Lykken, L., Anal. Chew., 1948, 20, 822. Shapiro, S., and Hoagland, H., J . Amer. Physiol. 1948, 153, 428. West, P. W., Folse, P., and Montgomery, D., Anal. Chem., 1950, 22, 667. Eubank, W. R., and Bogue, R. H., J . Res. Nut. Bur. Stand., 1949, 43, 173. 17, 605. ADMIRALTY MATERIALS LABORATORY HOLTON HEATH POOLE. DORSET

ISSN:0003-2654    

DOI:10.1039/AN9517600416

出版商:RSC    

年代:1951

数据来源: RSC

摘要:

424 MILNER AND TOWNEND : THE DETERMINATION OF ALUMINIUM [Vol. $6 The Determination of Alumiiiium in Copper-Base Alloys BY G. W. C. MILNER* AND J. TOWNEND A method for the determination of aluininium in brasses by the selective precipitation of aluminium as its benzoate complex has been studied and modified to enable the accurate determination of this element in all types of copper-base alloys. The alloy is dissolved in nitric acid, tin is removed by filtration and then the pH of the solution j s adjusted to the region of pH 4. Copper and iron are then reduced by boiling with hydroxylamine hydro- chloride and the aluminium is selectively precipitated by the addition of ammonium benzoate, After filtration, the aluminium benzoate is dissolved in a hot ammoniacal tartrate solution, re-precipitated as aluminium oxinate and the determination completed volumetrically .The range of the method is from 0.1 per cent. to approximately 12 per cent. of aluminium. THE older methods for the determination of aluminium in copper-base alloys involve the following time-consuming processes : removal of the copper by precipitation as sulphide or by electrolysis, precipitation of aluminium and iron hydroxides together, re-solution of the precipitate in hydrochloric acid after filtration and. then selective precipitation of aluminium hydroxide by means of sodium thiosu1phate.l s 2 Later methods fall into two main groups according to whether they do or do not involve a preliminary separation of the aluminium from the other alloying constituents by electrolysis with a mercury cathode.This electrolytic procedure gives virtually complete deposition of copper, zinc, iron and nickel, but only partial deposition of mangane~e,~ and since this element interferes in the subsequent method for determining aluminium, an additional step is necessary to separate it from the aluminium. The results of the determination of aluminium by this type of procedure are very reliz~ble,~ but in the analysis of many samples in an inspection laboratory the elqctrolytic procedure can delay the determinations; it also yields large quantities of highly contaminated me:rcury that must subsequently be purified ; for this reason the A.S.T.M. method5 incorporates a mercury-cathode electrolysis after the copper has been deposited electrolytically on a platinum cathode.In the group of methods that do not use mercury-cathode electrolysis is that of Edwards,6 who recommends an 8-hydroxyquinoline procedure for the determination of aluminium in aluminium bronzes that makes use of potassium cyanide to suppress the interference of copper, iron and nickel, and ferrocyanide to remove zinc and manganese as insoluble precipitates. This method, however, is not applicable to brasses. A method proposed by Bayley7 for the determination of aluminium in.brasses makes use of ammonium benzoate as a direct selective precipitant for aluminium after the reduction of copper and iron with hydroxylamine hydro- chloride. As there is a real need of a purely chemical procedure that is both rapid and accurate and that is applicable to the determination of aluminium in many types of copper-base alloys, the benzoate precipitation procedure was studied to find if it would meet this need.* Present address : Chemistry Division, Atomic Energy Research Establishment, Harwell, Berks.July, 19511 I N COPPER-BASE ALLOYS 425 EXPERIMENTAL According to Smales,* the pH range for the precipitation of aluminium benzoate is from 3.5 to 5, with an optimum pH of about 4. In Bayley’s method the pH is adjusted to this region by the addition of diluted ammonium hydroxide (1 + 1) to a nitric acid solution of 0.5 g of the brass to give the first permanent precipitate of cupric hydroxide. This precipitate is then just cleared by the careful addition of diluted hydrochloric acid (1 + 4). The solution is brought to the boil and 20ml of a 2 per cent.solution of hydroxylamine hydrochloride containing 2 per cent. of ammonium hydroxide and 10 per cent. of ammonium chloride is added to reduce the copper completely. The aluminium is then precipitated by the addition of 10ml of a 10 per cent. solution of ammonium benzoate, filtered on a paper-pulp pad after digestion for 5 minutes and washed with 1 per cent. ammonium benzoate solution. The aluminium benzoate precipitate is dissolved in a hot ammoniacal tartrate solution, the aluminium re-precipitated as its oxinate and finally determined volumetrically in the usual way. This method applied to the determination of aluminium in a number of standard and synthetic brasses gave good results for amounts of aluminium less than 1.0 per cent., but for amounts in the region of 2 per cent.the results were from 5 to 10 per cent. below the amount present. On occasions it was observed that the aluminium precipitated as the hydroxide instead of as the benzoate; when this occurred the determinations were rendered invalid because of the insolubility of aluminium hydroxide in the. ammoniacal tartrate solution. It was considered desirable to apply a more effective buffering action in the requisite pH region to prevent any aluminium precipitating as hydroxide. The above method was therefore modified by the addition of 50 ml of a pH 4-2 buffer solution (4.1 g of sodium acetate and 35 ml of N hydrochloric acid, diluted to 250 ml) after the removal of the cupric hydroxide precipitate with dilute hydrochloric acid; the method was then applied to a number of brass samples.Although all the precipitates then had the granular form of the benzoate, the results for the higher amounts of aluminium were still low. The aluminium benzoate precipitate was allowed to digest hot for longer times of up to 30 minutes before filtration. The precipitate was also washed with a solution of ammonium benzoate adjusted to pH 4 by the addition of acetic acid. But the results for samples containing 2 per cent. of aluminium were still 3 to 5 per cent. below the amount present. In the penultimate operation the aluminium oxinate is dissolved from a fairly large paper-pulp pad with hydrochloric acid, and the low results could conceivably be caused by the incomplete extraction of the oxinate from the paper pulp.However, it was found that complete extraction was always attained on applying the same technique to known amounts of aluminium oxinate filtered on similar sized paper-pulp pads. The difficulty was eventually overcome by increasing the volume of 10 per cent. ammonium benzoate solution used to precipitate the aluminium from 10 to 20 ml, and with this modification results for four different synthetic brasses each containing 2-00 per cent. of aluminium were 2-01, 1-99, 1.99 and 2-00 per cent. It appears, therefore, that the low results for aluminium by Bayley’s method were due either to the incomplete precipitation of the benzoate or to some aluminium being precipitated as the hydroxide instead of the benzoate, or to a combination of both.This method, incorporating the use of the pH 4.2 buffer and 20ml of 10 per cent. ammonium benzoate precipitant, was next applied to the determination of aluminium in aluminium bronzes containing approximately 10 per cent. of aluminium, starting with samples weighing 100mg so as to give suitable titres in the volumetric finish. In every experiment the aluminium was precipitated as the hydroxide instead of as the benzoate, so making the determination completely useless. As in these samples there was only about 90mg of copper compared with approximately 300mg in brass samples, it was considered essential to reduce the amount of the hydroxylamine reagent; on using 6 ml of the hydroxyl- amine reagent on a synthetic bronze containing 10 per cent. of aluminium, 9.10 per cent.was found. These results indicated that the method developed for brasses is applicable only to types of alloys containing a fixed proportion of copper; before it can be satisfactorily applied to alloys containing differing amounts of copper, the amount of hydroxylamine reagent to be added must be accurately related to the amount of copper present. As the aim of this investigation was to develop a single method suitable for the determination of aluminium in all types of copper-base alloys, it was desirable to reconstruct the method completely. Other possible sources of error were next investigated.426 MILNER .4ND TOWNEND THE DETERMINATIOK OF -4LUMINIUM [Vol. 76 As the reduction of copper by hydroxylamine hydrochloride proceeds, the solution becomes increasingly acid, so that, even on starting with an aqueous solution of copper sulphate, the acidity of the solution eventually increases sufficiently to prevent further reduction and the copper is incompletely reduced.In Bayley’s method the ammonia present in the hydroxylamine reagent neutralises this developed acidity and so allows the complete reduction of the copper. But for a method of general application it seemed better to use a pure solution of hydroxylamine hydrochloride and a pH 4 buffer of such capacity that a t least 500mg of copper could be reduced without a change of pH. A series of tests was performed on 500-mg amounts of copper, the amounts of sodium acetate and hydrochloric acid used in the pH 4.2 buffer being increased by the same factor to give buffers of approxi- mately the same pH, but of increasing buffering action. The results of the tests are shown in Table I.TA4BLE 1 CHOICE OF BUFFER SOLUTION FOR COPPER REDUCTION Ratio of sodium acetate (g) to N hydrochloric acid (ml) Observations 0.82/7 Copper incompletely reduced 2/17 Copper incompletely reduced 3125.5 Copper incompletely reduced 4-1/35.5 5/42-7 7-5/64 Copper completely reduced, but pH reduced below 4 Copper completely reduced, but benzoate precipitate gelatinous Copper completely reduced and benzoate precipitate filterable It was further found that 15ml of 5 per cent. hydroxylamine hydrochloride solution was just sufficient to reduce 500 mg of copper. With this quantity of hydroxylamine hydro- chloride and 7.5 g of anhydrous sodium acetate dissolved in 64 ml of N hydrochloric acid as buffer, the method was applied to synthetic alloys with the results shown in Table 11.TABLE :“I RESULTS ON SYNTHETIC ALLOYS WITH THE CHOSEN BUFFER Composition of alloy h f v Aluminium Copper, Aluminium, Iron, found, mg mg mg mg 500 10.00 nil 10.02 100 10-00 nil 10.04 100 10.00 10 10.02 Although a good result was obtained with the alloy containing iron, a slight brown turbidity remained after the copper reduction, arid the oxinate precipitate was discoloured. This behaviour was possibly due to the formation of a basic acetate of iron; the effect was avoided by adding the hydroxylamine hydrochloride to the cold solution of the alloy and then heating to boiling. The final method is given below. METHO:D The following method is applicable to coppers, brasses and aluminium bronzes for The range of the method is samples that contain the equivalent of 0.5 g or less of copper.from 0.1 per cent. to approximately 12 per cent. of aluminium. REAGENTS- All reagents should be of the highest purity and distilled water must be used throughout. Nitric acid, 0.5 per cen,t.-Dilute 0.5 ml of concentrated nitric acid (sp.gr. 1.42) to 100 ml Hydrochloric acid, diluted (1 + 4)-Dilute 20 ml of concentrated hydrochloric acid Bufer soZution-Dissolve 75g of powdered anhydrous sodium acetate in 640ml of Hydroxylamine hydrochloride, 6 per cent. solution-Dissolve 5 g of solid reagent in 100 ml with water. (sp.gr. 1.16) to- 100 ml with water. hydrochloric acid. of water.July, 19511 I N COPPER-BASE ALLOYS 427 Ammonium benzoate, 10 per cent.solution-Dissolve 10 g of solid reagent in 100 ml of water with warming. Aminonium benzoate wash solution, 1 per cent.-Prepare by dilution from the 10 per cent. solution. AmmoniacaZ tartrate solution-Dissolve 25 g of tartaric acid in water, add 120ml of ammonium hydroxide (sp.gr. 0.880) and 5 g of potassium cyanide, and dilute to 1 litre with water. 8-Hydroxyquinoline, 2 per cent. solution-Dissolve 5 g of solid reagent in 15 ml of glacial acetic acid and dilute to 250ml with water. Potassium bromate, 0.1 N solution-Dissolve 2-7840 g of potassium bromate and 15 g of potassium bromide in water and dilute to 1 litre. Sodium thiosulphate, approximately 0.1 N solution-Dissolve 25 g of sodium thiosulphate crystals in water and make up to 1 litre.Potassium iodide, 15 per cent. solution-Dissolve 15 g of solid reagent in 100 ml of water. Starch, 0.5 per cent. solution-Make 0-5 g of soluble starch into a paste with a few milli- litres of water and add to 100ml of boiling water. PROCEDURE- as follows- Cool and filter if necessary. Cool. Weigh an amount of sample according to the percentage of aluminium in the sample For aluminium contents less than 2.0 per cent., weigh out 0.5 g. For aluminium contents from 2.0 to 4.0 per cent., weigh out 0.25 g. For aluminium contents greater than 4-0 per cent., weigh out 0.1 g. Transfer the weighed sample to a 400-ml conical beaker, dissolve it in 5 ml of concentrated nitric acid (sp.gr. 1-20), add approximately 10 ml of water and boil to remove nitrous fumes.If tin is present in the sample, evaporate the solution to a paste, re-dissolve the salts in about 15ml of 0.5 per cent. nitric acid and filter through a small, tight, paper-pulp pad. Wash well with approximately 50ml of hot 0.5 per cent. nitric acid and collect the filtrate and washings in a 400-ml conical beaker. If tin is absent, dilute the sample solution, after removing the nitrous fumes, to approximately 75ml with water. Carefully add diluted ammonium hydroxide (1 + 1) to give the first permanent pre- cipitate and then add diluted hydrochloric acid (1 + 4) dropwise to just clear the precipitate. Add 70 ml of buffer solution and 15 ml of hydroxylamine hydrochloride solution, and heat to boiling. Boil for one minute, then remove from the hot-plate and add 20ml of 10 per cent.ammonium benzoate solution in one rapid addition. Stand the solution by the side of the hot-plate for about 15 minutes to allow the aluminium benzoate precipitate to settle and the supernatant liquid to become perfectly clear. Filter through a fairly large paper-pulp pad of medium compactness* and wash the precipitate and precipitation beaker well with hot ammonium benzoate wash solution. Remove surplus liquid from the pad by suction and carefully transfer the pad and precipitate to the precipitation beaker. Wash the funnel with 50ml of hot ammoniacal tartrate solution and then with hot water, and collect the washings in the precipitation beaker. Dilute to about 150 ml with water and digest at 80" to 90" C for a few minutes to dissolve the precipitate.Then precipitate the aluminium oxinate by addition of 20 ml of 8-hydroxy- quinoline solution with constant shaking. Replace the beaker on the hot-plate and maintain the solution at 80" to 90" C until the supernatant liquid becomes quite clear. Filter through a small loosely-packed paper-pulp pad and wash the precipitate well with cold 5 per cent. ammonium hydroxide solution and finally wash once with cold water. Add 40 ml of hot (80" C) concentrated hydrochloric acid (sp.gr. 1-16) to the precipitation beaker to dissolve traces of aluminium oxinate, and then dissolve the precipitate from the pad into the bottle with this acid. Dilute the final volume of solution in the bottle to 200ml with water and cool. Add a few drops of methyl red indicator solution and run in the bromate - bromide solution with constant shaking until the colour changes from orange to yellow.Add 4 ml of bromate - bromide solution in * It is important not to make this pad too large, otherwise a t the filtration stage of the aluminium oxinate the amount of pulp is too great to facilitate efficient washing of the precipitate. Thin and loosely packed pads, however, often allow the aluminium benzoate to pass through; the ideal size can only be determined satisfactorily by experience with the method. Transfer the filter funnel to the neck of a 500-ml glass-stoppered bottle. Wash the beaker and pad well with hot water.428 MILNER AND TOWNEND: THE DETERMINATION OF ALUMINIUM [Vol. 76 excess and then 10ml of potassium iodide solution. Mix well and titrate with sodium thiosulphate solution until the brown-coloured precipitate just clears.Then add about 5ml of starch solution and continue the titration until one drop of thiosulphate turns the solution bright yellow. STANDARDISATION OF THE SODIUM THIOSULPHATE- With a pipette, place 25.0 ml of the bromate - bromide solution in a glass-stoppered bottle and add 10 ml of potassium iodide solution, 125 ml of water and 40 ml of concentrated hydrochloric acid (sp.gr. 1.16). Mix well and then titrate with the thiosulphate solution, using starch as indicator, to the disappearance of the blue colour. If x ml of thiosulphate are needed, the factor (f) of the thiosulphate is 25/x. If b = the volume in millilitres of the bromate - bromide solution added, CALCULATION OF RESULTS- t = the volume in millilitres of the thiosulphate solution added f = the factor of the thiosulphate solution, and then x 0.022475 b - - t x f the percentage of aluminium = (weight of sample in g) RESULTS Excellent recoveries of known amounts of aluminium added to pure copper have already been reported above for this method.The possible interfering effects of the alloying elements usually present in copper-base alloys were next :;tudied by adding known amounts of pure aluminium to a typical alloy brass and then determining the total aluminium by the recom- mended procedure. The brass used had a percentage composition of: Cu, 55.66; Sn, 1.30; Ni, 2.85; Fe, 0.97; Mn, 0.17; As, 0.20; Al, 0.48; Zn, remainder; volumes of a standard aluminium solution were added to increase the aluminium percentage by 0.5 and 1.0 per cent.respectively. The recoveries of aluminium under these conditions are shown in Table 111. TABLE 1111 RECOVERY OF ALUMINIUM ADDED TO A STANDARD ALLOY Aluminium Aluminium present, recovered, % % Sample only . . .. .. 0.48 0.48 0.48 0.48 Sample + 0.50% of aluminium . . .. .. 0.98 0.99 0.98 0-985 Sample + 1.0% of aluminium . . .. .. 1.48 1.49 1-48 1-49 As the results of these experiments suggested that interference from the usual alloying constituents of copper-base alloys was negligible, the procedure was applied to the determina- tion of aluminium in different types of alloys with the results shown in Table IV. TABLE :[V DETERMINATION OF ALUMINIUM IN ALLOYS OF KNOWN COMPOSITION Aluminium Composition, yo by recom- A r -, mended Type of alloy Cu Pb Fe Mn Sn Ni Zn A1 method, % Aluminium bronzes- (a) Highly alloyed .. 79.58 - 4.51 1.03 0.005 5.11 0.005 9.72* 9.70 (b) Nickel absent . . 84.90 - 3.15 1.92 0.14 - 0.80 9.17’8 9.23 (c) Low manganese . . 83.17 - 3.33 0.17 0.005 3.93 0.05 9-32* 9.33 Byasses- Rem. 0.35t 0.35 (c) Propeller metal . . 55.75 0.06 0.87 0.23 1.17 0.005 Rem. 0.2lt 0.19 (a) 60/40 type .. . . 56.08 0.92 2.01 0.28 - - (b) B.C.S. “B” . . . . 58.8 0.78 0.91 1.03 1.75 1.01 33.9 1-62? 1-58 (d) Aluminium brass . . 77.86 0-02 0.02 - 0.02 0.03 20.0 1.99t 1-96 * By a mercury cathode electrolysis method.4 t By gravimetric analysis.1JJuly, 19511 IN COPPER-BASE ALLOYS 429 This procedure is fairly rapid, as a single determination takes only about two hours. Moreover, the results obtained for aluminium in different types of copper-base alloys have been found to be reliable and in good agreement with the results obtained by classical methods of analysis. The procedure is, therefore, ideal for the inspection analysis of copper-base alloys. The Admiralty has granted permission for this paper to be published. REFERENCES 1. The British Aluminium Co., Ltd., “The Chemical Analysis of Aluminium and its Alloys,” 2. Scott, W. W., and Furman, N. H., “Standard Methods of Chemical Analysis,’’ Fifth Edition, 3. Lundell, G. E. F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” Chapman 4. Unpublished experiments of Bragg Laboratory. 5. American Society for Testing Materials, “A.S.T.M. Methods of Chemical Analysis of Metals,” 6. Edwards, W. T., Analyst, 1948, 73, 556. 7. Bayley, W. J., Lecture to the Birmingham and Midlands Section of the Society of Chemical 8. Smales, A. A., Analyst, 1947, 72, 14. NAVAL ORDNANCE INSPECTION DEPARTMENT Publication No. 405, London, 1949, p. 165. Volume 1, Technical Press Ltd., London, 1939, p. 55. and Hall, Ltd., London, 1945, p. 95. 1946, p. 206. Industry, November 16th, 1949; Chem. and Ind., January 14th. 1950, No. 2, 34. BRAGG LABORATORY JANSON STREET, SHEFFIELD, 9 November, 1950

ISSN:0003-2654    

DOI:10.1039/AN9517600424

出版商:RSC    

年代:1951

数据来源: RSC