ANALYTICAL CHEMISTRY
1510 In the application of al)sorl)ancy ratios t o deteniiine purity it is assumed that the absorbancy of the compounds obeys Beer's 1x1~. This point may be readily checked by taking the eluate corresponding to the purest sertion of a zone (generally the peak) and making several dilutions thereof. If the ahsor1)ancy doer not obey Beer's law a graph may he plotted for any oiie (>ompound, from which the adjustrd al)sor\)anryratio for a n y coiirc~i!tration may he read. At)sorbanc.y ratios m a y lie applied n-hen R pure (bornpound or o i i (.lose ~ to purity may I)e oI>tained. They n-ould probably be u.ir~lesson a (.rude mixture. The method does not detect ztn impurity that has an :ihsorlxinc.~. i,:rtio ideiitical with that of the desired compound, urilrsa t h e impurit!. separates enough to distort the shape of th(1 chromutographic z o n e , nor docs it detect rantaminants that, do not ahsoi,l) :it the I\ ave lengths measured. Sources of Error. I t is necessary t o correct for differences in absorbanc,ies of the cells themselves. Temperature effects should tie hrltl to a minimum. T h e column should be developed with :t uniforni tior$- rate of solvent, as stoppages for an extended tinw in the middle of a zone may cause distortion of the elution pattern. Tf neccssary, the c.olumn may t)r interrupted or speeded up het w e n zones. I n adsorptive chi~omatographyit is a good idea to equilibrate the solvent and adsorbant prior to column formation. Scrupulous care must be eserrised to avoid contamination. Glass-stoppered glassware is preferable, although corks or rubber stoppers may be used if they arc covered with a metal foil t h a t does not react with the mohile solvent. T h e column should he connected to the source of pressure lvith a ground-glass joint, and if it is t o be plugged, glass wool rinsed with the mobile solvent is preferred. Cotton should not be used, as it contains materials that absorb in the ultraviolet. Finally, a parallel t)lank drtci~ninationis necaessary to show that all iiitert'eiwic.es h:tve 1)et.n c.liminated. OTHER APPLlCATlOY S
.4bsorbancty ratios are b y no means limited to partition chromatography, b u t may be applied to straight chromatographic separations as well as t o countercwrent distribution.
In instances in \vhicah c ~ h r o ~ n s t o g ~ ~ or s p 1countercurrent ~~distribution is used to determine purity, a constant absorbancy ratio of the fracntions tvould make the proof of purity more rigid. Sensitive compounds may he sqxtrated ir! pure form I)>- several ratios heing used t o deterquick passes on a column, a1isoi~l~aiic.y mine which is the desired matt>ri:iI, .\l)wrh:tncy ratios should ;tlso prove useful in control ivork, ljec*:tuseit is possihle to detect rontamiiiation in a zone that appears t o he homogeneous. The use of al~sorl~ancy ratios i i i quantitative anal> OF the constituents are k n o ~ v nhas Iwen men Ahsorhancy ratios of c.hroni:rtogial,hi(, frnctiona in the v i ~ i h l c or infrared may also he uic3ful. SL.11 hI Z R Y
Uy use of a systematic. cdlec.tion of c.hromatographic fi~actious from n-hich ultraviolet ahsorhancy ratios are determined, it has been possihle t o detect impurities in cahromatographic zones. The method has been used to isolate the two main constituents of the cbrystalline alkaloid ir-ilfordine. T h e method may he generdl>- applicable t o the vhromatographic or countercurrent separation of compounds Lvhich :~IIsoI,I) in the ultraviolet and possibly to compounds which ahso~,l)in other parts of the spectrum. LITERATPRE CITED
(1j Acree, F.,and Hailer. H. L.. J . A m . Chenz. S o c . , 72, 1608 (1950). (2) Craig. L. C., and Post, O., .IX.%L. CHEM.,21, 500 (1949). (3) Gibson. 51. R., and Bchwarting. A. E., J . A 7 n . P h a r m . Assoc., Sci. Ed., 37, 206 (1948). (4) Haskins. .L L., Shermali, A . I., and Allen, W. lI,,6.Bi'ol. C h e m . , 182,429 (1950). (5) Hotchkiss, R. D., I b i d . , 175, 315 (1948). (6) Martin, -I.J. P., Endearour, 6, 21 (1947). (7) Martin, A. J. P., and Synge. R. L. M., Biocheni. J . , 35, 1358 (1941). (8) ,\1oore, S.,and Stein, If-. H., A m . S. I'. A c a d . Sci., 49, 265 (1948). (9) IVilliamsoii, B., and Craig, L. C., J . B i d . Chem., 168, 687 (1947). RECEIVED April 28, 1950. P a r t of Ph.D. thesis submitted by hiorton Beroza to Graduate School of Georgetown University. Report of a study made under the Research and 3larketing Act of 1946.
Determination of Traces of. Silicon in Vanadium and Uranium Spectrophotometric Method RUTH GUENTHER ~ N D RICHARD H. GALE Knolls .4tomic Power Laboratory, General Electric Company, Schenectady,
1 9 ' .
Y.
-4 spectrophotometric method for the determination of silicon in vanadium
and uranium metals is described. The metal is removed by chloroform extraction of its cupferrate, the silicomolgbdate color is developed in the residual solution, and the transmittancy is determined at 390 m p . The system shows an adherence to Beer's law over the range of 0.02 to 0.28 mg. of silicon per 100 ml. with a reproducibility of 10.004 mg.
T
HE procedure described herein was developed during a research program t h a t necessitated a precise analysis of microgram quantities of silicon in high purity vanadium and uranium. Silicon is present in these metals as a silicide capable of being transformed into a soluble silicate. For trace quantities of silica, a microtechnique is available if a gravimetric method is desired (2); however, the generally applicable procedures for traces of
silicba utilize either the yellow silicomolybdate color developed in dilute acid (3, 4)or the molybdenum blue color developed in a reducing medium ( I ) . There appears to be nothing gained through u,ye of the molybdenum blue complex, for accuracy and precision in the two processes are comparable. A separation of the silica M as necessary, because both uranium and vanadium interfere in the above methods.
,
1511
V O L U M E 22, NO. 12, D E C E M B E R 1 9 5 0 'Table I . Yo. rri I)i~tn-.
SI l'rrccnt,
Arc.
Ilecov~eriesof Silicon
Si Foiind, 31g.
.iv. I k v i a t i o n , 1Ig.
Mau. Deyiatiuii, AI&
'I'ablc I I. 'Tolerance of l'roceditre f o r Diverse Ions .\rnoiint
l)i\-rr>c
.Added,
Irin
I',p.in,
'rl -
r
- 4
zro---
c'o
,
1 2
I
Ratio oi Diverse 1,111 t o Hi 1 :5 l:4
Effwt o n 'I'rai~siiiittanc~
100-niI. \-(11iini('t1i(.flask, : i r i r I c l i l u t i ~ t l to vi>lutn[s,'rlicu pI1 u l t.ho final solution was rtdjustd to i~ valuc of 0.8 t'o 1.0. T u o 20-nil. aliquots of this solution n w c pipetted into 25-nil. volunictric flasks. On(. w!ution \\-as d i l u t d t o volumr n-itli n.:iter; to the second \wre addP(i 2 ml. of IZ.,i70 :tnnnonium molybdate and sufficient watrr t o make 25 nil. The solution from the first aliquot was utilized I : bliznk t,o cornpenrat(. for pos:"il)lc interferrnces from reagents. The v:tnwdium stock solution \\;is found to J-icld a small ( ' o 1 1 stant blank and the deionized ivater of the laboratory yieldctl :I varJ-ing hlank. The deionizrd \v:ttcli, \vas i,rplar.ed with distillctl water, and a constant correction wis madc on rwovcrics from t h o vanadium solutions, ltecovc~i,ies,r o r r w t d for this I ilank, :it,(: given in Table I. Interferences of other c~lc~iiicntx i i i t1,:ic.e (pantitic,; ~ i i ' c intiic,:itc,tl i n Tnhlc IT.
Sone, reinuved as ciipferrnte None, rciiiiirecl a s ciir)ferrate
SILICO> Ih UKANIUJI
\-on? Sone None Decrease at liiplier c,oncentratioIis Decrease
The tlct ei,miriation of silicon in uranium has been cArrird out i n 11g-y I Be 1 a manner similar t o that, described above. The solution cont:tiriCrO4-2:l SrOI - 1 8 ing 0.1 gram of uranium in 10% hydrochloric acid was $haken in a AnOc 1 8 12t5-ml.srparatory funnel for 5 niinutrs with a 4yozinc anialg:im. 1'04 i f o r m e t h o d of w i u o v a l ) 1.' I The amalgam was drawn off and *e ur:rnium solution transfei,t,ed t o a healirr and chilled. T h e rupferron precipitation and cst,r;irtion were c.arried out as before, and the silicon was determined in the aqueous phase. Recoveries (Table I ) ohtained hy this This separation was :irroiiiplishcd :is tlerc~i,il)cd l)elo\v iind :i pmmethod a r c similar to those obtained with variadiurii solutions. vedure capable of tletcrmining a s littlr :ts 0.00770 silicon in a Data ohta,ined from the above procedui,rs have been f'avorahly 0.01-gr:ini s:tniplt has hecn tlevolopctl. Tlic basis of' this scparacompared with those obtained h y other methods on vanadium tiori is t h e precipitation of the n i r t d ivith vupfcrron from :in acid and uranium metals; hoa-ever, these d s t : r :iw not ;iv:iil:tl)le for a rhloroforni rlstrac4tion of t h e cupferratc. solution, folioa.ed The siliva w n t e n t is d r t r r n i i n d s ~ ~ e c ~ t r o ~ ~ h o t o i n c tin r i ~the ~ a l l y pul)lic.:ttion at, this time. Although the deseribcd method h i n optiinum lowor limit of :tqueous phase hj- USP of animonium niol!.bti:rtc. 0.02 mg. of silicon per 100 ml. of s tion, lon.el, conwnt,rations may he det,c,rmined with little difficulty. Rccoveriw in this lower STANDARD ABSOKI'TION CURVE region :we constant and rcproduc.il)le; h o a e v r ~ a~ ,separatr stand.i st:tlitlaid rolut,ion viis prc>pa,rctifrom rcagc'nt gradtx sodium ard ahsorption curve must he prepnrrd if kirtter th:in 20% orcd in it hard-rubhrr hottlc. This solution :iwuracy is desired. In t h r optiniuin rtinge, the rrcovrry of Qi1ic.a ndardizcxi gravirnet,ric.:tllv. .Iliquots of the stsnd:ird solut>ionwcrc pipetted into 100-ml. volumetric flasks is excellent and the method lias :i rrprodurihility of * 0.004 m g . containing 8 nil. of 1 to 5 hydrochloric acid; 10 nil. of 10% aniof silicon prr 100 ml. of solution. The method is suitable for nioniuni molybdates were added by pipet, and the solution was mutine control; a single analysis may he wcomplished in 2 hours niatlr u p to vohuno and UTII niisrd. after the ntand:ird ahsorption curvc has hrrn c*onstruc,trd. The optival iI(.nsitj. of tlic solution \vas tletc,rniined a t the end LITERATCRE (;ITEl) of 5 niinutrs :It 390 nip with :I I3eckni:ili llodel DC spectrophotometer. In apparent contratlication ivith the rcsults reported ( 1 ) Rrahson, .J. A , , Harvey, I. U-., 31axwrl1, G . E., and Hohaeffrr, by I,a(~roix( 5 ) , the optical tirnsity \vas tlrpcndent upon the final ENG.CHEM.,. i x \ i , . ED., 16, 705-7 (1944). , hiattraw. €1. C., Maxwell, C:. E., Darroa. Anita, m o l ~ M : ~ twncentratioii; c Iicxiice this reagmt \vas added hy m, PI.F., A s i i . . ('HEM., 20, 304 (1048). piprt, and :I hlank run was made \vith each new rnol>-hdate solu(3) Hadley, . I . . Annl,y.st. 67, 5 (1942)). tion. T h e nio1gl)date reagent maintained a ronstant opticad char(4) Iinudson, H. W.. .Juday, C . , arid AIelorhe, V. \V., I r n . Evo. a c ~ t t ~for r one a-eek. T h e color development was romplete in 5 ( l H E M . . . 4 S h I l . E D . , 12, 270 (1940). (5) Lacroix, S . , and Lahalade, hlelle, A w l . Cii niinutes and the silicomolyhdate coniples was stahlc for over 3 (6) Roeental, D., and Camphell, H. C.. Iiw. F hours. Beer's law holds at 300 mp over t h e opt,imum concentra17,222-4 (1945). tion range of 0.02 t o 0.28 mg. of silkon per 100 mi. of solution. RECEIWD.April 12. 1950. The Knolls .4tomie 1'owi.r 1.aIpratury is operated 1,aci~oix( 5 ) ,using a different typr of ini;trument, was un:ihle t o by the General Elertric Research Lahoratory for the Atomic EnerRy Coinobtiiin this rrlationship. mission. Tlie w o r k reported here was carried out iindrr contract Y o . \\'-7-31. f
-
+
~
~
109 Eng-92.
I'ROC EDUR E
.i valistlium solution was prepared by dissolving metallic vanadium (V:inadium Corporation 99.7% pure) in nitric arid, t,aking to dryness sever:rl times with hydrochloric acid, and then taking u p in dilute hydrochloric acid. Synthetic silicon-van:tdium samples w r r thrn prrpared containing 0.1 gram of vanadium with varying amounts of sodium metasilicate in 10% hydrochloric acid. Eacah solution was cooled and transferred t,o a 125-ml. separafory funncll, and 15 ml. of cold 5% cupferron solution were atldrd. T h e funnrl was shaken for 2 minutes, 50 ml. of chloroform w m ~added, and shaking was continued for 2 minutes longer. The lower Iayrr was drawn off and t h r rrm:tining solution rec.stractcad with 10 nil. of chloroform. h second 15-ml. portion of cupfcrron was added and t,he mixture \vas shaken and extracted as bcfore. With higher concentrations of vanadium, a third cupferron ext,raction was nrcdcd. Thc aqueous phase was then transferred to a beaker and heitted with stirring to remove dissolved chloroform. The solution \vas then cooled, transferred to a
Rate-Indicating Mariotte Bottle-Correction I ani indebted t o Rogrr K. Taylor for pointing out two ei'rors ivhirh occurred in m y note on thv :hove subjoct l A s . k i , . CHEU., 22, 1214 (1950)], The liquid manonietctr, I), in Figurt.2 should be conncrtcd t,o the air-intake line a n d not, to thc spac'e ahovc~the o t t r bottle H S shown. 4, the statamcnt is ni:rtfc (page, 1216) that ". , , thc solubility of the tcst gas in thc u a t w is of no importance, because the volumes of the displac'od gas alonc~i.: iii~:tsurcd." This statenicnt. is u r i ~ n gin princple: T h r trst g:cs must be insoluble in the displacing liquid in order t o obtain c q u d i t y 1:. .I SCI~WERTZ . bctivecn thc liquid and gar flow ratcs.
