ANALYTICAL CHEMISTRY
1276
nianner illustrated. A similar piece of asbestos cloth is overlaid and the jacket is sewed together. Homogenizing Pestle (Figure 3). The end of the pestle is roughened with emery aper, coated with a layer of phenolic thermosett,ing resin, a n a dipped into sharp silicon carbide particles, 6/30 grit. o n e half hour in an oven at 50” to 60” c. firmly sets the part,icles in place. ACKNOWLEDGMENT
This hark was aided by a grant from the National Foundation For lnfaiitile Paralvsiq. LITERATURE CITED (1)
t l h , 11. B
Gwt.H.. and Kamen, M. D.. Arch. Bwchem., 14,
xx5 (1947)
(2) Dreywood, R., IND.ENG.CHEM.,ANAL.ED., 18,499 (1946’. (3) Hassid, W. Z., McCready, R. M., and Rosenfels, R. S., Itid., 12, 142 (1940). (4) Kamen, M. D., in “Isotopes in Biology and Medicine.” pp. I 51-2,
Madison, University of Wisconsin Press, 1948. (5) Linch, 8.L., private c o m m u n ~ c a t ~ o n ~ (6) Morris, D. L., Science, 107,254 (1948). (7) Potter, V. R., and Elvehjem, C. A., J. B k l . Chew., 114, 195 (1936). (8) Potter, V. R., in Umbreit, W. W., Burris, R . H., and Stauffer, J. F., “IManometric Techniques and Related Methods for the Study of Tissue Metaholisni,” pp. 92-9,Minneapolis, Burgess Publishing Co., 1945 EECEIVED December 21, 1948. Presented before the Division of .-inalyti~al and Micro Chemistry a t the 115th Meeting of the A U E R I C ~ VC H F I I I ~ ~ L S O C I ~ San Y . Francisco, Calif
Organic Onium Compounds as Inorganic Analytical Reagents Detection of Bismuth and Cobalt HERBERT A. POTRATZ’AND JEKOME M. ROSEK* University of Colorado, Boulder, Colo. The action of various organic ammonium, phosphonium, arsonium, stibonium, oxonium, sulfonium, selenonium, telluronium, and iodonium ions on iodide and thiocyanate complexes of a number of metals was investigated. On the basis of the reactions observed new- tests are praposed for the detection of hisrnuth and cobalt.
tili organic reagents used most frequently in the detection and determination of metals are compounds that contain in the molecule acidic groups, the hydrogen atoms of which may be replaced by metal atoms. Such reagents ionize to give organic anions m-hich react with metal ions to form simple or inner-complex salts. Compounds that ionize to give organic cations have been used less frequent,ly as analytical reagents. Because many metals readily form complex anions, the possibility of employing organic cations for the detection and determination of these metals through salt format’ion is evident. The particular organic cations which have come into use a8 reagents for metals are predominantly nitrogen compounds. Tetraphr:n~larsoniumion stands out as an important exception. Willard and Smith (21) have shown that this cation may be used for tho determination of mercury, tin, cadmium, zinc, and rhenium. Smith (18) has recently employed this same cation for the d d erinination of thallium. Dwyer, Gibson, and Nyholm (9) have reporkd t,he use of methyl aryl arsonium compounds in the dekction of bismuth and cadmium and in the detection and estiinat,ion .of cobalt. Possible analytical applications of onium compounds of elements ot,her than nitrogen and arsenic have not thus f w r been report,ed. IBETECTION OF BISMUTH
Alkyl ltiiiniuiiiuin salts, aniline, pyridine, quinoline, certain alkaloids, and a large number of other nitrogen bases are known to react with bismuth in the presence of iodide to give colored, insolublr: reaction products (20). That this type of reaction is not, limited t,o nitrogen compounds is indicated by the fact that 1
Present addreis. I k p a r t irirnt of Clirinistry, Washington University,
tit. Louis, hlo.
*
Pre-rnt
adrlrvsr, Sa\-al Orduance Laboratory, Whitn Oak, h f d .
alkyl sulfonium iodides react with bismuth in a similar maimer (2, IS). The observations cited are perhaps best interpreted b> assuming that in each case reaction has occurred between an organic cation and a bismuth-containing anion or anions. I n beginning a survey of the reactions of onium ions, varioue organic onium compounds of nitrogen, phosphorus, arsenic, antimony, oxygen, sulfur, selenium, tellurium, and iodine were tested with respect to their reartivitv toward BiIa-. (The reactions here described are attributed to BiL-, which is taken as the probable formula of the predominant bismuth anion present in a bismuth solution containing excess iodide. No evidence is prestwted to support this formula.) The fourteen potential reagents which ssere investigated are listed in Table I. Optimum conditions for reaction, limits of sensitivity, and interfering effects of foreign ions were determined for each of the compounds tested. Cinchoninc was included because i t is a spot test reagent commonly used in bismuth detection (10) and could therefore serve as a convenient standard of reference. Tetramethylammonium bromide (IS), triinethylsulfoniuin iodidt, (Z), and triethylsulfonium iodide (13) had been observed to react nith bismuth, but no study had been made of the possible analytical applications of the reactions. The limits of sensitivity given in Table I are in terms of mioiograms of bibmuth per drop (0.05 ml.) of test solution. The reactions were carried out on spot test paper (Schleicher and Schuli No. 601), following the technique recommended by Feigl ( I O ) The compounds tested were found to be remarkably similar 111 their behavior toward Bi14- in that all reacted to give insolublc: orange or red-orange products. Preliminary studies indicated that froin considerations of specificity and sensitivity the aryl sulfoniuni, triphenylselenoniuni, tetraphenylphosphonium, tetraphenylarsonium, and tetraphenylstibonium compounds were the best of the reagents tested Iu
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 Tahle 1.
Limits of Sensitivity of Onium Compounds Detection of Bismuth
(:niuiiound' 2. i'ilenyl-8-naphthopyryliuni vliloride (0.0370solution in inethyl alcohol) T r i niethvlsulfonium iodide (5% . . .iolutiGn) Triethylsulfonium iodide (.5('; solution) Triphenylsulfonium chloridc (.-)rh solution) ,rt- Sslyldiphenylsulfoniula chloride ( 5 % solution) Triphenylselenonium chloritk ( 5 0 i solution) 'Trlphenyltelluronium iodidix isaturated solution) l)iGheni,-liodoniumiodidf. isaturated solution) 1)i-p-chlorophenyliodoniulll bromide (saturated solution) Tt.tramethylammonium bromide (5% solution) Tctraphenylphosphoniiim brirmide (1% solution) l'~.traohenvlarsonium bromide 1% soI;tion) .~~.traphenylstibonium hromidt. :saturated solution) C'ihrhonine (1% solution in di:rite nitric acid ~
1277
k oi mula
tkferrnt~r
in
denqitivity. y
0.I I) . 2
0.2 0.1
0. 1
.~...
t.hr. detection of bisniuth thrse compounds arc fully as sensitivr and somewhat more selective than cinchonine. They form stable aqueous solutions. (Tet,raphenylaraoniuni chloride is conimrrcially available through tho Hach Cheniic~aland Oxygen ('ompany. Ames, Iowa.) In making t h r detailed iriterfert:ncts studies dcacribd below only two reagents, triphenylsulfoniuni broniitlc and tetraphmylarsonium bromidr, ~vcrtsust~cl. Tetiaphen?.larsoniuIri bromide was made by the procedure of Blicke and Monroe ( 3 ) . Triphenvlsulfonium bromidc wits prt~part~(1 H S folloxvs: Phrnylniagnesiuin bromide and diphenylsulfoside were heated under reflux in a benzene ether mixture a t 65' t o 68" C. for 27 hours. The misture obtained was hydrolyzed with 40% hydrobromic acid. The aqueous phase was separated and the triphenylsulfonium bromide was extracted from it with chloroform. The c,rude material obtained upon evaporation of the chloroform W:LS crystallized from acetone and chloroform by addit,ion of diethvl et,her. Triphenylsulfonium bromide, a white, crystalline, water-soluble substance, was obtained in 32% yield. The compound melts with decomposition a t 286-288" C. (uncorrected). It was identified by bromine analysis. Calculated for (CsH&SBr: 23.28% bromine. Found: 23.21, 23.30% bromine. Procedure for Detection of Bismuth. One drop of the slightly acid test solution is treated on spot test paper (or spot plate, with one drop of triphenylsulfonium (or tetraphenylarsonium) reagent solution and one drop of 10% potassium iodide. In t,he presence of bismuth an orange precipitate forms. The acidity need not, be carefully controlled, but# because the sensitivity of the test falls off slightly a t high acidity t,he hydrogen ion concentration is kept below 0.1 Jf, or below 0.01 .lf if very small amount; of bismuth :ire trc4ng sciught. Interferences. The behavior of elements other t ha11 bismuth under the conditions of the bismuth test was investigated b y experiments in which a variety of inorganic ions were treated wit,h triphenylsulfoniurn bromide and tetraphenylarsonium bromide reagents. Stock solutions (containing 1 mg. per ml. or 10 mg. per ml. of the test constituent) were prepared using the substances shown in Table 11. Test solutions were made a t the t>imeof use by diluting the stock solutions. 1n making tests 1 ml. of the test solution containing 500 niicrugrams of the test constituent was treated with e x m s potassium iodide and reagent solution (3 drops of 10% potassium iodide plus 3 drops of 0.05 11.1 triphenylsulfonium trromide or 0.04 M tetraphenylarsonium bromide). The extent of interference in the bismuth ttsst~was in-
vestigated by repeating thach t,rst in the prcaciiccs of I)isrnut,h,usiiig rolutions in which bismuth and the foreign test, constituent, w w presclnt a t concentrations of 5 and j00 micrograms ptar n i l . , rixspectively. The ions that inteifcre are listtd i r i Tahlc 111. C'd(II), Hg(II), and In(II1) gavr. evidence of reactiiig ~ i t t Il 1 1 t . onium reagents (in t,he presence of excess iodide). Cd(I1) N I I ~ I Hg(I1) gave precipitates with both reagents. The Cd(I1) pwcipitates were white, th,e €Ig(II) precipitates creani whitt.. In(II1) gave a white precipitate with t~!traphen?.larsoriiumbroinitlt. but gave no reaction with triphenylsulfonium bromide. It was fouiitl. however, that bismuth could be readily dcteotctl \vi t t i t4thrr rtsagent. w e n when C'd(II), Hg(II), or In(II1) was I I I I W ~ I I I in 100-fold excess [5 micrograms of Ri(II1) to 500 ni crogranis 0 1 Cd(II), €Ig(II), or I n ( I I I ) ] . For this reason Cd(I1) t l ~ ( l I ) , and In(II1) are not classed as interferenrrs. Tetraph~~riylarsonium iotlide is insoluble and may separate, as a white crystalliiir precipitatt., from solutions to which t~,traphrii?.larsoniiii,i NII(I iodidrs have twen added. The estent of interference by the coninionrr anions was turf I1t.r. invcstigatetl by making the bismuth test in the presence of a 1000fold gravimrtric mcess ( 5 micrograms of bismuth to 5000 micrograms of test anion pw nil.) of each of the following anions added in the form of ammonium or sodium salts: Ac-, SO;. SOr- ~, HSO,-. F-. ('I-, Br . Of t h ( w anions, only fluoride irltt>rfvrt.tl slightly wht'n prescxIit in 1000-fold t'scess I m t showed n o intt.1,i t i n 100-fold t:xcr.ss. Ions 1vhic.h oxidize I - t o Ia~'-e.g., ferric: and cupric~ -iritt.r,t'er.t, in the bismuth test, the broivri color of I, . t i d i n g to ohscurc tllc oniumiodobismuthitc,. To climinatc this iritc~rfrrc~ricc.thtx Ia -- i h reduced with bisulfite. The test is made o n spot rest papcr. One drop of tt'st solution is trrati,d n.itl-1 O I I I ~d r o p of onirini (triphcbnyl-
Table 11. Composition of Stock Solutions Nitrates Li(I), Na(I), K(I), "4-, Be(II), IIg(II), Ca(II), Sr(II), Ba(II), Y(II1). La(III), Th(IV), Cr(III), U(VI), Mn(II), Fe(III), Co(I1) Ni(II), Cu(II), Ag(I), Zn(II), Cd(II), Hg(I), .ll(III), GaCIII). In(III), TIII), Pb(II), Bi(II1) Chlorides Zr(IF), Ru(I111, Rh(III), Pd(I1, P t ( I \ I , \ i i ( l L I ~ ttg(11). SII(IIJ. Sn(IV), As(III), Sb(II1) Sulfates Ce(III), V(IV), Ye(111 Alkali or ariinionium salts Acetate, fluoride, bromide, bisulfite, 51senate, d e l i n t e . selerilte, tellurite -
~
__
'rahle 111.
Te.r Constitrimtu Sn(I1) Pb(I1) Sh(II1) (:I1 (I1j
. ._ ___ Interferences in Detection of Bisniuth
K I f PhsSBr Light yellow ppc. Yellow ppt. (PbId Yellow ppt. Brown (Ia-) plus put. Light yellox ppt.
(.id)
Light brown ppt. Yellowppt. Gray ppt.
(TII)
Brown (Is) plus PPt. Dark reddishviolet ppt. Brown ppt. Dark brown p p t . Brown (k)
+
+
Kl PhrAsBr Light yellow ppt. Yellow ppt. (PbIzj Yellow ppt. Brown (I3-) plus ppt. Light yellow ppt. (.W) Brown ppt. Gray upt. Yellow ppt. (TIC Brown (13) plus PPt.
Reddish-violet Brown PPt. upt.
Interferencr in BI Test Prebented by 4ddition o f SHlF lVaHSO, NHiF SaH80.
NaHSOs (or "IF) SaHSOl
Dark brown ppt. Brown (Is-)
+
rie i1-1)
ppt. (Se) PPt. (Se) TtS(I1 j Brown ppt. Brown ppt. "4F Fer 'rahle 11 for rompoundi used In preparatlorl of tr,t d u t i o n s
a
..
1278
ANALYTICAL CHEMISTRY Table IV.
Detection of Cobalt
Onium Compounda KOCN KSCX 2-Phenyl-8-naphthopyrylium chloride methyl alcohol) Trimethylsulfonium iodide Triethylsulfonium iodide Triphenylsulfonium ohloride rn-Xylyldiphenylsulfonium chloride Triphenylselenonium chloride Triphenyltelluronium chloride Diphenyliodonium chloride Tetramethylammonium bromide Cinchonine (in dilute HSOs) Tetraphenylphosphonium bromide Tetraphenylarsonium bromide Tetraphenylstibonium bromide Compounds dissolved in water unless otherwise indicated
+++ +++ +++ ++ ++ +++ +++ +
KSeCN
-
++ ++ ++ ++ + -
++ ++ -
eulfonium or tetraphenylarsonium) reagent, one drop of 10% potassium iodide, and one drop of 10% sodium bisulfite. In the presence of certain oxidizing substances-for example, selenite and selenate-bett1.r results are obtained if the bisulfite is added to the test solution before addition of the other reagents. Bisulfite is effective also in preventing interference by Pt(IV), Au(III), and Pb(II), the colored reaction products of platinum, gold, and lead being converted by bisulfite to colorless substances. If platinum or lead is present, the bisulfite is added to the test solution before addition of the onium reagent and iodide. Sb(II1) reacts under the conditions of the bismuth test t o give a bright yellow voluminous precipitate. The formation of the yellow antimony compound can be prevented by the addition of fluoride. In the presence of antimony, the bismuth test is made on a spot plate, 1 or 2 drops of 10% ammonium fluoride solution being added to the test solution before addition of iodide and onium reagent. An excessive amount of fluoride is to be avoided, as it decreases the sensitivity of the bismuth test. Dark brown substances precipitate when certain onium ions are added to solutions containing the iodotellurite ion. The formation of these precipitates can be prevented by adding ammonium fluoride, and carrying out the bismuth test in the same manner as when antimony is present. Sn(I1) interferes slightly in the bismuth test, forming a light yellow precipitate with iodide and triphenylsulfonium or tetraphenylarsonium ion. This interference also is prevented by addition of fluoride. By making use of ammonium fluoride a few micrograms of bismuth are readily detected even in the presence of a 100-fold excess of Sb(III), Te(IV), or Sn(I1). It was observed that a number of the compounds precipitated by iodide and onium ions-tetraphenylarsonium iodobismuthite, tetraphenylarsonium iodoantimonite, tetraphenylarsonium iodotellurite, tetraphenylarsonium iodopalladite, and triphenylsulfonium iodotellurite -are readily soluble in chloroform. This circumstance makes possible the separation of certain elements from aqueous solution by chloroform extraction of their onium iodide complexes, A procedure for the determination of tellurium is based on the chloroform extraction of the highly colored metaxylyldiphenylsulfonium iodotellurite followed by colorimetric analysis of the chloroform solution (11). DETECTION O F COBALT
When triphenylsulfonium ion is added to a solution containing Co(I1) and excess thiocyanate ion, a blue, chloroform-soluble substance precipitates. The formation and chloroform extraction of the blue substance are made the basis of a sensitive test for cobalt. The limit of identification under the conditions described is about 0.05 microgram of cobalt per test drop. This correeponds to a dilution limit of 1 to 1,000,000. These limits were determined by using a volume of chloroform equal to the volume of the test solution. Greater sensitivity is achieved by using a volume of chloroform less than that of the test solution.
Some aryl onium ions other than triphenylsulfonium give similar color reactions. Cyanate may be used in place of thiocyanate, but the test is less sensitive. Selenocyanate was also tried but was found to possess no apparent advantage over thiocyanate. In Table IV are summarized results of tests carried out using equal concentrations of cobalt with excess cyanate, thiocyanate, or selenocyanate and various onium reagents. The plus signs indicate approximate, relative intensities of the blue color in the chloroform layer under essentially identical test conditions. Attention is directed to the fact that the oxonium, ammonium, and alkyl sulfonium compounds n-hich were used gave no observable reactions. The tests with these compounds moreover remain negative even when large amounts of cobalt are present. The blue substances that precipitate from the cobalt solutions result, presumably, from interaction of the onium ions with cobaltous thiocyanate complex (or complexes). Chemical analyses on one of these substances, the m-xylyldiphenylsulfonium compound, gave results in agreement with the formula, [ C ~ H S ( C & , ) ~ S ] ~ C O ( S C S ) ~The . analytical data are given in Table IT.
Table V.
Analysis of rn-Xylyldiphenylsulfonium Cobaltothiocyanate Calculated for [CsHe(CeHs)zS]zCO(SCN)r
Found
% N
60.46 4.38 6.41 6.74
6.50
% ' Co 6.70, 6.67
Analyses by Huffman AIicroanalytical Laboratories, Denver, Colo.
Procedure for Detection of Cobalt. One half milliliter or less of the slightly acid test solution is treated in a small test tube with 1 or 2 drops of triphenylsulfonium (or tetraphenylarsonium) reagent solution and 1 or 2 drops of 10% ammonium thiocyanate. A few drops of chloroform are added and the mixture is shaken vigorously. In the presence of cobalt the chloroform layer becomes blue. Rlaximum color development is obtained a t a p H of approximately 3.5. The acidity, however, is not critical.
Table VI.
Interferences in Detection of Cobalt Interference in Co T0.t
Test ConstituNHaSCS enta PhsSBr U(V1) Yellow ppt. soluble in CHCh Fe(II1) Deep red ppt. somewhat soluble in CHCIS Ru(II1) Dark purplish-red ppt. very slightly soluble in CHCla Pd(I1) Orange ppt. readily soluble in CHCls Pt(1V) Yellow ppt, soluble in CfIC13 Cu(I1) Red-brown ppt. soluble in CHCls Bi(II1) Yellow ppt, soluble in CHC13
+
NHISCK PhrAsBr
*+
by PrtvYb"ted Addition of
Yellow ppt. soluble in CHCls Deep red ppt. readily soluble in CHCls
KHaF
Dark purplish-red ppt. slightly soluble in CHCI, Orange ppt. readily solnble in CHCls Yellow ppt. soluble in CHC13 Red-brown ppt. soluble in CHCls Yellow ppt. soluble in CHCla
KaHSOs (or NazSzOs)
NHpF
SazSzOa KaHSOa (or KazSzOs) KIxLO, NHIF
a See Table I 1 for compounds used i n preparation of test solutions, Tetraphenylarsonium thiocyanate is insoluble and separates a s white precipitate from solutions to which S C N - and Ph4.h have been added. I t dissolves in CHCla t o give colorless solution.
*
+
Interferences. Interference experiments for the cobalt reaction were carried out by a procedure similar to the one that was followed in studying interferences in the bismuth reaction. One milliliter of the test solution containing 500 micrograms of the test constituent (Table 11) wm treated with excess thiocyanate and onium reagent (3 drops of 10% ammonium thiocyanate and
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9
.
3 drops of 0.05 M triphenylsulfonium bromide or 0.04 M tetraphenylarsonium bromide solution). Approximately 1 ml. of chloroform 15 as added and the mixture was shaken. The extent of interference in the cobalt test was investigated by repeating each of the tests in the presence of cobalt, using solutions in which cobalt and the foreign test constituent were present at concentrations of 5 and 500 micrograms per ml., respectively. Triphenylsulfonium bromide and tetraphenylarsonium bromide n hc,n used a s reagents in thc cobalt test w r e found to be subject to the sanie interferences. Zn(I1) and Sn(IV) give slight ncgative intcrference, preventing full dpvelopment of the blue rolor. This interference is minimized by using a large excess of thiocyanate and onium reagent. Masking interference was observed in the presence of U(VI), Fe(III), Ru(III), Pd(II), Pt(IV), Cu(II), and Bi(II1). The nature of these interfcwnces and methods of preventing them are indicated in Table VI. The very pronounced interference by Fe(II1) and slight interfervnces by Bi(II1) and U(V1) are easily prevented by adding to the solution to be tested 1 or 2 drops of 10% ammonium fluoride. (The bismuth thiocyanate complcx unlike B i L is readily decompostJd by fluoride.) Cu(I1) interference is prevented by reducing to Cu(1) with iodide. Thiosulfate serves to remove the iodine formed. One drop each of 10% potassium iodide and 10% sodium thiosulfate are added to the solution to be tested. The feasibility of employing the onium-thiocyanate-chloroform extraction procedure for the separation and colorimetric determination of cobalt has been demonstrated ( 1 ) . Studies on applications of the procedure are in progress. CONCLUSIONS
Triphenylsulfonium and tetraphenylarsonium chlorides and bromides used in conjunction with iodide are particularly suitable reagents for the detection of bismuth. They are fully as sensitive a9 the common~yused cinchonine reagent and are somewhat less subject to interferences* They possess an advantage Over nine of being water-soluble. The same compounds used with
1279
thiocyanate serve as sensitive and, under properly controlled conditions, highly specific reagents for the detection of cobalt. ACKNOWLEDGMENT
The authors wish to thank Bernard S. Wildi and Sedra -4nderson Barnes for their assistance in t,he preparation of triphenylsulfonium bromide. LITERATURE CITED
(1) Barnes, N.A , . MS.thesis, Washington University, 1947. (2) Blattler, H., Monutsh., 40, 417 (1919). (3) Blicke, F. F., and Monroe, E., J . Am. Chem. Soc., 57, 720 (1935). (4) Blicke, F. F.,Willard, H. H., and Taras, J. T., I b i d . , 61, 88 (1939). ( 5 ) Chatt, J., and Manri, F. G., J . Chem. soc., 1940, 1192. ( 6 ) Courtot, Ch., and Tung, T. Y., Compt. rend., 197, 1227 (1933) (7) Decker, H., and Fellenberg, T. v., Ann., 364, 42 (1909). (8) Dodonow, J., and Medox, H., Ber., 61, 907 (1928). (9) Dwyer, F. P., Gibson, N. A , and Nyholm, R. S.,J . Proc. Roy. SOC. .-\A 8. WUk8, 78, 118 (1945); 78, 226 (1946); 79, 118 (1946). (10) Feigl, F., “Qualitative Analysis by Spot Tests,” 3rd Engliah ed., New York, Elsevier Publishing Co., 1946. (11) Johnson, R. A , , M . S . thesis, University of Colorado, 1943. (12) Kondo, K., and Segawa, H., J . Pharm. SOC.Japan, 51, 869 (1931). (13) Kraut, K., Ann., 210, 310 (1881). (14) Lederer, C., Ber., 44, 2289 (1911). (15) Masson, I.,and Race, E., J . Chem. SOC.,1937, 1718. (16) Masson, O., and Kirkland, J. B., I b i d . , 55, 135 (1889). (17) “Organic Syntheses,” Vol. 18, p. 30, New York, John Wiley & Sons, 1938. (18) Smith, W.T., Jr., . ~ K A L . CHEM.,20, 937 (1948). (19) Steinkopf, W., and Muller, S., Ber., 56, 1928 (1923). (20) Welcher, F. J., “Organic Analytical Reagents,” New York. D. Van Nostrand Co., 1947. (21) Willard, H. H., and Smith, G. M., IND. EKG.CHEM.,ANAL ED., 11, 186, 269, 305 (1939). RECEIVED November 2 , 1948. Presented in part before t h e Division of Mierochemistrl a t the 100th Meeting of t h e AVERICAVCHEVICAL ~OCIST~, Detroit, hfich Some of this material IS taken from a dissertatlon aubmitted b y Jerome AI Rosen t o t h e Graduate Faculty of t h e University of Colorado In partial fulfillment of the requirements for t h e degree of dootor of phlio.oph~ in chemi-try
Determination of Hydrogen Peroxide in Small Concentrations A Spectrophotometric Method WALTER A. PATRICK AND HERlIAN B. WAGNER Johns Hopkins University, Baltimore, M d . A sensitive method of peroxide analysis which allows not only the detection but the quantitative determination of hydrogen peroxide in concentrations as small as lo-’ molar is described. The determination of the optimum wave length for the spectrophotometric determination is described. A typical standardization curve is given.
A
SENSITIVE method of peroxide analysis, which provides not only for the detection but the quantitative determination of hydrogen peroxide in concentrations as small as 10-6 molar. involves the oxidation of iodide ion to iodine, in the Deroxide solution t o be determined, and the estimation of the free iodine thus formed by measurement of its light absorption on a spectrophotometer. I n order to make the rather slow iodide ionperoxide reaction go rapidly to completion, use is made of the
catalytic action of molybdic acid discovered by Brode ( 1 ) and employed by Kolthoff ( 8 ) . The method is limited to solutione which do not contain other constituents that either oxidize iodide ion or absorb in the same spectral range - as triiodide ion.
2
m ~ e f ~ ~ ~~ ~~ ~ ~~ ~ ~ ~ ~ n o ” , ~ y ,l , $~ ~~ ~ ~o molar and then analyzing this solution accurately by thiosulfate determination of liberated iodine according to standard procedure.
