Qualitative Analysis of Microgram Samples Separation, Estimation, and Identification of the More Common Ions of the Hydrogen Sulfide Group A. A. BENEDETTI-PICHLER' AND MICHAEL CEFOL4' Washington Square College, New York University, New York, N. Y. ESTIMATION OF TEE QUANTITY OF PRECIPITATES. Figure 2 (left) shows a sulfide precipitate containing 0.1 mierogram of antimony and 0.01 microgram of bismuth. Figure 2 (right) shows the Same precipitate after whirling in the centrifuge. Obviously, it is collected in the point of the cone, but inspection under higher magnification would conrlusively demonstrate that the point of the taper is free from precipitate. Neither base nor top of the truncated cone fillrd by the precipitate presents a plane surface. Since Some arbitrary lines must be d r u m when the calculation of the volume of precipitate is based dn the assumption of a truncated cone, it seemed well to imagine a
The teohnique of working in the capillary cone has been applied t o analyses requiring lengthy separations followed by sedimetrio estimations and eonikmatory tests. Various improvements h a v e been made in the performance of manipulations, a n d a method for fractional distillation has been developed, which m a y be applied to liquids of approximately 0.1- to 0.01-cu. mm. volume. The complete analysis of a particle of Wood's alloy of l-microgram mass required approximately 12 hours. Such effiaienoy can be expected only after a period of training. Manual dexterity is perhaps of less importanoe than methodical organieation of work. Proper design of work bench a n d t h e nee of microprojection will considerably reduce fatigue, if work of this kind has to be performed for a n y length of time.
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3) was tested by application t o the analysis OS rather complex mixtures containing ions of the hydrogen sulfide group. T o make the test more severe a scheme of macroanalysis was chosen, which emphasizes quantitative separations and estimation of the amount of the ions.
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Technique The experience gaiued led to various improvements and extensions of t h e techniques employed in the transfer of solutions to capillary cones and in the mixing, stirring, and heating of the contents of such cones. These, as well as the procedure for distillation from one capillary cone t o another, have been described in detail (2). Some advice may be added.
deGeased t o t h i t required for a screen image of 10- to 20-cm. diameter. Under this condition, the use of projection will reduce eyestrain, and the operator will be able to assume a more restSul posture.
TR~NSFER OF SOLIDS TO CAPILLARY CONES. When a sample is selected for analysis, it is desirable to have the material spread for microseo ic inspection. The procedure described for the transfer of soid reagents (#) has the disadvantage that the use of an inclined slide does not permit a sharp focus for the entire field of vision. If the microscope slide with the material is placed level an top of the chamber containing the capillary cone, a suitable needle for the transfer of particles is obtained by sealing the tip of a micropipet and bending it through an sngleof 30 degrees (4,g). Theshankof the pipet is then inserted into the holder, so that the tip oints downward. When the selected article bas gee, picked up with the needle, the c i m p of the manipulator is released for a moment, and the^ pipet holder is rotated to bring the tip of the needle into a horizontal plane. It is then easy to introduce the particle into the capillary cone. The rocedure is illustrated by Figure 1. Filings of d o d ' s alloy (specificgravity 7) are first shown on +microscope slide. An approximately spherical particle, 6 6 in ~ diameter which may be expected to have a mass of 1 kicrogram, bas been brought into the center of the field and is just being touched with the point of the needle. On the ri ht is the same particle just before it is deposite% inside the capillary cone.
Scheme of Analysis The scheme of Swift (Id) was adopted with some modifications. The return, in a sense, of the mercury t o the copper
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Present address. Queens College, Flushing, N. Y. 2 Present addreas, Metaliurdoal Laboratory. The University oi Chioepo, Chicago, Ill. L
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of the i&r {s bent downward, s o that the openiig of the mikepipet makes contact with the paper. Test solutions and reagent solutions are transferred from capillary cones or reagent Eontainers t o the paper by means of the micropipet. The colorations uroduced are best observed with low mamificatian and refleehd light of low intensity. The technique was employed when testing the acidity of solutions with litmus paper and in the confirmatory tests far cadmium (cadion) and tin (molybdenum blue). PROJECTION OF MICROSCOPIC IMACES. The operations performed under the microscope are just m easily controlled by
HE technique described in preceding papers of this series
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time when collecting precipitites for the purpose of estimation. As a rule, 1 minute of centrifuging with a relative centrifugal
FIGURE1. TRANSFER OF A PARTICLE O F WOOD'S ALLOYOF APPROXIMATELY MICROGRAM MASSFROM A SLIDETO CAPILLARY CONE One division of micrometer scale corresponds to 22 microns.
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Magnification. X 46
228
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group probably is t h e most pro1 tion, and i t was introduced whe (6,lO) t h a t t h e extraction of n from t h e suffide precipitate rer plete wh,en medium t o large mercury svere present. Various had t o be made because of t h e I sedimetriio estimations followed . . . . .L.L wiy LIWU for t h e titrimetric ( employed by Swift. 1
PREPARATION OF SOLUTION. I of Wood's alloy a particle of a
a white precipitate startgd imm mixture of solution and precipit:
residue dissolved, and the mixtu with 0.1 cu. mm. of water previ ing with hydrogen sulfide. Known solutions were DreDan scale and made approxirdatdy spect to acid. Of these solutions u.u1 cu. mm. was taken for analysis, transferred to the capillary cone, and diluted with 0.1 cu. mm. of water. Precipitates separating because of hydralysis appear brown in transmitted light and white in reflected lipht. They were left in suspension for the treatment with hydrogen sulfide. PRECIPITATION OF THE HYDROGEN SULFIDE GROUF. The solution or mixture of solution and precipitate was saturated with hydrogen sulfide, as described in an earlier communication (I). The reaction mixture was heated a t 60" to 70' C. for half a minute and then dowed to stand for 1 hour a t room temperature. The precipitate was collected by means of the centrifuge and its volume was estimated. Another portion of 0.1 cu. mm. of water was added, and saturation with hydrogen sulfide, heating, standing, centrifuging, and estimation of volume were repeated. The solution was removed, and the precipitate was washed once with 0.01 cu. mm. of 0.12 M nitric acid. SEPARATION OF THE Copma AND ARSENICGROUPS. The sulfide precipitate was immediately treated with 0.02 cu. mm. of sodium sulfide-hydroxide reagent (8, 48 grams of sodium sulfide novahydrate and 4 grams of sodium hydroxide in 100 ml. of solution). The capillary cone was sealed into a capillary and inserted in a water bath at 60' to 80' C. for one minute. The
mm. of 1 per cent stanno,us chloride. ' . ' . 'Lhe -. whi: . 'tish gray precipitate produced by the 1ittter reagent is easily observed with reflected light after collectiion in the point of the capillary cone bv means of the centrifuee. PRECIPITATION OF THE f i m m ~unuur. ~ 1ue centrifugate from the mercuric sulfide precipitate, which may contain thio complexes of arsenic, antimony, and tin, was treated with 1 M sulfuric acid. Approximately 0.2 cu. mm. of this acid are required, but the relatively large volume is of little consequence. Stronger acid reacts so violently that some of the reacting matter mav be eiected from the cone as a conseauence of the rauid liberation of liydrogen sulfide. The sulfuric acid was added in small portions while stirring Y
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pl&e by heating in sealed capill&y for a few minites a t 80" to 90" C. The mixture was centrifuged and the solution removed befare removal of the second extract. The extracts were combined, and the residue was washed with 0.01 DU.mm. of water by stirring and centrifuging. DISSOLVING THE SULFIDES O F THE COPPER "ms^-s n"Yr. rnL^ LlLLi residue from the extraction with sodium sulfide W ELs immediately ?d into 8. ,.+I,fides appeared small residue of white sulfur was collected bv means of the cent rifuge, and the 0.01 cu. mm. was repeated. r. Itsvolume may be estimated immediately or after solution i.n nitric-hydrachlorio acid and reprecipitation with hydrogen sulfide. Ohviously, the solution in nitric-hydrochloric acid m.ay he set aside and later used for dissolving any mercuric sulfide 88epareting from the extract containing the arsenic group. ISOLATION OF MERCURY.The cone with the sodium sulfide large drop of :n treated with 2 mixture was stirred by means of the buzaer (2). The preeiriitate was collected by whirling in the centrifuge. Particles adhering to the walls of the capillary cone were loosened with t he micropipet. The volume of the precipitate was estimated, an d the mpmnatant solution was immediatelv transferred to anpther cone. All these operations were perfonhed without delay, for evaporation of ammonia from the capillary cone may lead to separation of the sulfides of arsonic, antimony, and tin from the solution of thpir thio complexes.
If there is reason to believe that too much acid had been added, one may test for absence of tin from the centrifugate by dihAne iL wit,h 0.05 an. mm. of wnter. saturstinc with hvdraeen estimation of the volume of &e sulfides of th quires subtraotion of the volume of the sulfi preoipitste. The volume of the sulfur left sulfides are dissolved allows a crude approximrhion. ISOLATION OF ARSENIC. The sulfides of the arsenic group were treated with 0.03 cu. mm. of 12 M hydrrxhloric acid. The ter bath and then The capillary cone s contents were inie was discovered, the mixture was treated with potassium bronlate. One particle of the potassium hromete was added a t a tirne, whereupon the solution was stirred. The addition of hromrLte was stopped as soon as all the sulfide mas dissolved. The SIilfur was then collected by means of the centrifuge, and the clear solution was transferred to another capillary cone. The residue of sulfur was washed with 0.03 cu. mm. of 12 M hydrochlorie acid, and this acid was then added to the solution of the sulfides. The solution of the sulfides was treated with 0.01 cu. mm. of 9 M hydrochloric acid and 0.02 cu. mm. of 3 M phosphorous acid. The cone was sealed into a capillary, inimersed for 5 to 10 seconds in water at 80' to 90" C., and cooled in a stream of tap water. A!fter 1insertion of the capillary con , l:-l:lll:-.. ~ ~ .A.-L.J I_ ~
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reduced to 0.01!5 or 0.01 eu. mm. The residue of the distillation was treated wit1I 0.01 eu. mm. of 12 M hydrochloric acid, and the
ANALYTICAL EDITION
March 15, 1943
229
cesium ohlorostar cult to identify, p preferred. A smr obtained by scrap magnesium ribboi solution. A tion N S ~immedii
ite are very small and d i 5 formance of a spot test was particle of magnesium metal, g with a razor on the edge of
dmolybdate test paper &(?). observed with the use of the istion and a magnification of
28 diameters.
CONFIRMATION OF LEAD. The m of the sulfides of the capper ,ated to dryness on the steam 6ath; the residbe was treated with 0.015 cn. mm. of 6 M sulfuric ac:id, and the volume of the lead sulfate N&Sestim ferred to auother tate NBS washed o sulfuric wid. whit:h was then added t o the oentrifugate ebntaiiling bismuth, copper, and FIGURE 3. DISTILLATION FROM ONE CAPILLARY CONETO ANCTHER cadmium. . . , . . . .. .... ... ._ .^ . . . -. , ,* moromlcrogrhpns snow S W O nawes O f same CLLBrllllng Oeplilary. magnmoamon x au .. l n e ieaa suirate was dissolved by adding Ldt. Start of distillation. Heating ele*ent.is "isible above opening of disti? 0.02 cu. mm. of 3 M ammonium acetate and law containing ~apillarycone with l i q u d to be distilled stirring. To the solution was added 3 M Riuhr. Cloae of distillation. Distillate oolieeted at sealed end 01 distilling c sodium chromate in small portions until ION coloration of the solution indicated an excess of the reagent. The lead ohromate was collected by means of the centrifuge, and its volume was distillation was repeated until again a residue of the above inestimated. dicated volume remained behind. ISOLATIOX OF BISMUTH. The capillary cone with the centrifuThe distillate (Figure 3, right) NaS transferred to a capillary gate from the lead sulfate was transferred to a dry chamber, and cone of the standard type, diluted with water to a volume of the solution was treated with small portions of concentrated approximately 0.1 cn. mm., treated with 0.04 cu. mm. of 12 M ammonia until a whitc precipitate could be perceived with hydrochloric acid, and saturated with hydrogen sulfide. Floercflccted light. Then 0.005 cu. mm. more of the ammonia. was culation of the precipitate was brought about by heating for 30 added, and the mixture N&S heated for 15 seconds a t 90' C. to 45 seconds st 60" to 70" C. and agitation by means of the after being sealed into a capillary. After centrifuging, the bueaer. The volume of the precipitate w&6 estimated after capillary cone was transferred to a moist chamber far the detercentrifuging. mination of the volume of bismuth hydroxide. Confirmatoru Test for Arsenic. The supernatant solution was Because of the transparent appearance of the precipitate, the removal of the supernatant solution and washing of the precipitate with 0.01 cu. mm. of 1 M ammonia were observed with reflected light. The washing was combined with the centrifugate evaporated almost to dryness by heating in steam, the residue containing capper and cadmium. was treated with approximately 0.05 cu. mm. of 16 M nitric aoid, and the mixture was evaporated to dryness. The residue was Confirmtm7~Test for Bismuth. The bismuth hydroxide was extracted with a volume of 1 M nitric acid to give an approxidissolved in 0.005 cu. mm. of 3 M hydrochloric acid. Parts of mately 1 per cent solution of arsenic. Part of this solution was the solution were used for performance of the cesium and quinine treated on the plateau of the condenser rod with silver nitrate iodobismuthite tests (3)on the plateau of the condenser rod. in aeetat,e buffer solution (S) ISOLATION OF COPPER.The capper may be separated from ISOLATION OF ANTIMONY. The residue from the distillation cadmium by precipitation as cuprous thiocyanate. This method was treated with 0.02 cu. mm. of 3 M sulfuric acid and 0.01 cu. was successfully applied to the analysis of centigram and millimm. of 6 M hydrochloric acid, and xvater was added to bring the gram samples (5, lo). I n the experiments on the microgram total volume to 0.075 cu. mm. Finally 5 cu. mm. of DhosDharic scale copper never occurred with cadmium, and i t could be acid, obtained hy mixing 1 volume of ~ r u u acid v with'4 vdlumes isolated as the sulfide. The volume of the sulfide precipitate served for estimation of the quantity of copper. C a f i m a t o q Test for Copper. The copper sulfide was treated ~" ~. .... with 0.02 cu. mm. of 3 M nitric acid, the mixture WBS evaporated centrifuee. and its h u m e N Z estimated. The solution conto dryness, and the residue was stirred with 0.015 cu. mm. of taining Ehi tin II-ILS t,ransferred to another oapillary cone. The water. After centrifuging, half of the clear solution was transprecipitate mas washed with 0.01 cu. mm. of 1.2 M hydroferred to the plateau of a condenser rod and tested with salicylchlorio acid. which was then combined wit,h t,he oent,rifuoxt,e. aldoxime (S). The rest of the solution was treated on a plateau -~~--. Conjkmaiory Test fir Antimony. The antimony sulfide was with a somewhat larger volume of a saturated solution of potasdissolved by heat,ing with 0.02 cu. mm. of 12 M hydrochloric sium ferrocyanide. The brown precipitate of copper ferroacid. Part of the clear solution was transferred to the plateau cyanide was observed with a magnification of 60 diameters. of the condenser rod and tested with the quinine reagent (5). I~OLATION OF CADMIUM.The ammoniacal centrifugate from ISOLATION OF TIN.The centrifugate containing the tin was the bismuth hydroxide was treated with 0.005 cu. mm. of 10 per treated by the addition of small portitns of ooncentrsted ammonia. cent uotassium cyanide. The clear solution was then saturated until test with litmus paper indicated alkaline reaction. The with-hydrogen sdfide, heated a t 65' C. for ahout 20 seconds, solutiou was then saturated with hydrogen sulfide and briefly agitated with the buazer, and centrifuged. The volume of the heated a t 60" to 70' C. After the csoillarv cone had been vrllow cadmium sulfide was determined. "~~~~ placed in a dry chamber, 0.005 cu. mm. o? 3 M"sulfuric acid CmjEnnatovy Testfor~Cdmi&z. After removal of the ceutrifuadded to the contents. The precipitate of tin sulfide formed gate the cadmium sulfide was washed once with 0.02 en. mm. slowly. I t could not be readily seen in transmitted light, but of water and then dissolved in 0.015 cu. mm. of 6 M sulfuric was visible in reflected lieht. Stirrine with the DiDet hastened flocculation. Precipitate a n d solutionwere again 'sahrated with hydrogen sulfide, and the mixture was allowed to stand for a t least a f e v hours. It N ~ Sthen centrifuged, and the volume of bu&er solution containing 10 grak8 of Rooheile &It and 0.1 ml. the stannic sulfide was estimated. of clacial acetic acid in 100 ml. Homogeneity was obtained by Confirmatory Test f o i Tin. The centrifugate was removed from the yellow staunio sulfide, the precipitate was washed once with 0.015 eu. mm. of 1 M ammonium chloride. and the sulfide ., , was dissolved by heating in steam with 0.02 cu. mm. of 6 M D B D ~ P .6.01 cu. mm. of a solution consisting of 4 Golumes of 2 M hydroohloric acid. After addition of 0.01 cu. mm. of 12 M sodium hydroxide and 1 volume of e t h d alcohol was added. hydrochloric acid and centrifuging, parts of the clear solution The pink coloration produced by the lake of the dye with the were used for Confirmatory tests. Since the crystals of the cadmium hydroxide was distinotly visible with reflected light.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Results Application of the technique and scheme of analysis t o samples of approximately 1-microgram mass revealed the qualitative composition in each instance. The reliability of the estimation of quantities may be derived from the following three examples.
tion of the volume and consequently the mass of the alloy may easily be affected with an uncertainty of * 50 per cent.
Literature Cited Benedetti-Pichler, A. A., IND.ENG.CHEM.,ANAL.ED., 9, 483 (1937). Benedetti-Pichler, A. A,, “Microtechnique of Inorganic Analysis”, New York, John Wiley & Sons, 1942. Benedetti-Pichler, A. A., and Cefola, M., IND.ENG. CHEM., ANAL.ED., 14, 813 (1942). Benedetti-Pichler, A. A,, and Rachele, J. R., Ibid., 12, 233 (1940). Boos, R. N., master’s thesis, New York University, 1940. Dwyer, F. P., Australian Chem. Inst. J . & Proc., 4, 26 (1937); 5, 32 (1938). Feigl, F., and Neuber, F., 2.anal. Chern., 62, 382 (1923). Hammett, L. P., “Solutions of Electrolytes”, 2nd ed., New York, McGraw-Hill Book Co., 1936. Howland, Ruth B., and Belkin, M., “Manual of Micrurgy”, New York, New York University Press Book Store, 1931. Loscalao, A. G., master’s thesis, New York University, 1941. Mahr, C., and Ohle, Herta, 2.anal. Chem.,109, 1 (1937). Swift, E. H., “System of Chemical Analysis for the Common Elements”, New York, Prentioe-Hall, 1939.
In 0.01 cu. mm. of a solution containing 0.1 microgram each of the ions copper, arsenic, antimony, and tin were found: 0.1 microgram of copper, 0.06 microgram of arsenic, 0.1 microgram of antimony, and 0.24 microgram of tin. In 0.01 cu. mm. of a solution containing 0.1 microgram each of mercuric mercury, lead, bismuth, cadmium, and antimony were found: 0.1 microgram each of mercury, lead, bismuth, and antimony, and 0.8 microgram of cadmium. I n 1 microgram of Wood’s alloy containing 0.5 microgram of bismuth, 0.2 microgram of lead, 0.125 microgram of tin, and 0.125 microgram of cadmium were found: 10 microgram of bismuth, 0.4 microgram of lead, 0.1 microgram of tin, and 0.1 microgram of cadmium. The most glaring mistakes were committed in the estimations of bismuth and cadmium, and in both instances the reason must be sought in the poor reproducibility of the volumes of gelatinous precipitates of bismuth hydroxide and cadmium sulfide. The trouble might be overcome b y converting the bismuth hydroxide to metallic bismuth and the cadmium sulfide to cadmium-thiourea Reineckate (11). The determina-
Vol. 15, No. 3
PRESENTED in part before the Division of Microchemistry at the 100th Meeting of the AMVERICAN CHEMICAL SOCIBTY, Detroit, Mioh. Abstracted from part of the thesis submitted by Michael Cefola t o the faculty of the Graduate School of New York University in partial fultillment of the requirements for the degree of doctor of philosophy.
Report on Recommended Specifications for Microchemical Apparatus SULFUR AND HALOGENS
G . L. ROYER, Chairman H. K. ALBER
FIGURE 1. PORCELAIN FILTER
STICK
L. T. HALLETT J. A. KUCK, Secretary
FIGURE 3. GLASSCRUCIBLEHOLDER FOR WATERBATH
