ANALYTICAL CHEMISTRY
1594 (10) Cupples, H. L., Ibid., 14, 53 (1942). (11) Davies, 0. L., “Statistical Methods in Research and Production,’’ pp. 76, 79, Oliver and Boyd, London, 1947. (12) Deichman, W., and Scott, E. W., ASAL. CHEM.,11, 423 (1939). (13) Eddy, C. Fv.,and DaEds, F., Food Research, 2,305 (1937). (14) Emerson, E., J . Org. Chem., 8, 417, 433 (1943). (15) Ettinger, M.B., ASAL. CHEM.,23, 1783 (1951). (16) Evans, T. W., IND.ENCI. CHEM.,ANAL.ED.,6,412 (1934). (17) Feicht, F. L., Schrenk, H. H., and Brown, C. E., U. S. Dept. Interior Bureau of Mines, Rept. Invest. 3639 (1942). (18) Fischer, H., and Leopoldi, G., 2. and. Chem., 107, 241 (1937). (19) Foerster, P., Ann. chim. anal., 14, 14 (1909). (20) Gardiner, K. W.,and Rogers, L. B., - ~ N A L .CHEM.,25, 1393 (1953). (21) ~,~Gibbs. H. D.. J . B i d . Chem.. 72. 649-64 (1927). (22) Gilman, H., ‘and Blatt, A. H., ’“Organic Syntheses,” 2nd ed. p. 463, Wiley, New York, 1941. (23) Gottlieb, S.,and Marsh, P. B., IND.EKG.CHEM.,.%K.AL. ED., 18, 16-19 (1946). (24) Hibbard. P. L., Ibid., 9, 127 (1937) : 10, 616 (1938) (25) Hicks, E. F., I n d . Eng. Chem., 3,86 (1911). (26) Holland, E. B., and Ritchie, UT. S., J . Assoc. Ofic.Agr. Chemists, 22,333 (1939). (27) Jones, J. H., Ibid., 28, 398 (1945). (28) Karush, F., and Sonenberg, hl., ANAL.CHEM.,22, 175-7 (1950). (29) Kaye, F., India-Ruhher J . , 66, 43542 (1922). (30) Ihtd., 67,233-8 (1924). (31) Kniaseff, Vasily, AXAL.CHEM.,20,329-30 (1948). (32) Lott, W. L., IND.ENG.CHEM.,ASAL. ED.,10,335 (1938). (33) hlantell, C. L., and others, “The Technology of Katural Resins,” p. 441, Wiley, New York, 1942. (34) illellon, M. G., “ilnalytical Absorption Spectroscopy,” p. 93, Wiley, New York, 1950. (35) Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 111, pp. 158, 160, 161, 178, Lonnmans. Green. Kew York. 1938. (36) llenrei, R. G., and Jackson, 11. L., - 4 s ~CHEM., ~. 23, 1861 (1951); 24,732 (1952). (37) Nimer, E. L., Harnm, R . E., and Lee, G. I., Ibid., 22, 790 (1950). (38) O’Conner, R. T., IKD.ENG.CHEM.,ANAL.ED.,13, 597 (1941). (39) Oliner, A. W., and O’Keil, F. W., Paper Trade J . , 125, 55-62 (1947). (40) Overholser, L. G., and Yoe, J. H., IND.EXG.CHEM.,Ss.4~. ED.,14,646 (1942). ~I
(41) Owens, A. F., U. S.Patent 2,474,801 (June 28. 1949). (42) Payfer, R., and Narshall, C. V., J . Assoc. Ofic.Agr. Chemists, 28, 429 ( I 945). (43) Prudhomme, R. O., Bull. soc. pathol. ezotique, 31, 929 (1938). (44) Prudhomrne, R. O., J . pharin. chim., 1, 8 (1940). (45) Reed, J. F., and Cummings, R. K., ISD. EKG. CHEM.,A s . 4 ~ . ED.,12,489 (1940). (46) Reiniteer, F., Z . anal. Chem., 69, 114-21 (1926). (47) Reenek, S..J . Am. Pharm. dssoc., Sci. Ed., 42, 289 (1953). (48) Rodden, C. J., “Analytical Chemistry of the Rlanhattan Project,” 1st ed., pp. 392-5, McGraw-Hill, Sew York, 1950. (49) Rogers, L. H., and Gall, 0. E., ISD.EXG.CHEM.,AXAL.ED.,9, 42 (1937). (50) Sandell, E. B., “Colorimetric Determination of Traces of hletals,” 2nd ed., pp. 620-3, Interscience, New York, 1950. (51) Ibid., pp. 623-8. (52) Sandermann, W., A s a ~ CHEM., . 21, 587-9 (1949). (53) Schatr, F. I-.,Specfrochim. Acta, 6, 198-210 (1954). (54) Schniteer, R. J., and others, Can. Public Health J . , 17, 24 (1942). (55) Schrapper, I., and hdler, I.. ASIL. CHEM.,21, 939 (1949). (56) Smith, L. E., ISD.ESG.CHEM., .ki.%L. ED.,10, 60 (1938). (57) Snell, F. D., Snell. C. T., “Colorimetric Methods of hnalysis,” Vol. 11, pp. 369-71, Van Sostrand, New York, 1936. (58) Stout, P. R., Levy, J., and Williams, L. C., Collection Czechoslou. Chem. Communs., 10, 129 (1938). (59) Swann, 11. H., i i l v . 4 ~ .CHEM.,23, 885 (1951). (60) Theis, R. C., and others, J . B i d . Chem., 61, 67-71 (1924). (61) United States Dispensatory, Osol, A , , and Farrer, G. L., editors, 24th ed., p. 289, Lippincott, Kew York, 1947. (62) Vallee, B. L., .%NAL. CHmi., 26, 914 (1954). (63) Yon Richter, Victor, “Organic Chemistry,” Vol. 3, p. 266, Blackstone’s, Philadelphia, Pa., 1923. (64) Walsh, R. H., Abernathy, H. H., Pockman, W.W., Galloway, J. R., and Hartsfield, E. P., T a p p i , 33, 232-237 (1950). Borders, A. ll., Swanson, J. W., and Sears, (65) Wheeler, G. W., G . R., Ibid., 34, 297-301 (1950). (66) Wolff, H., and Toeldte, IT., Farben-Ztg., 31, 2503-5 (1926). (67) Yost, D. bl.,and Aiken, W. H., T a p p i , 34, 30-9 (1951). (68) Ibid., pp. 40-8. RECEIVED for review September 27, 1951. Accepted July 5 , 1966. Contribution No. 172 from Jackson Laboratory. Division of Rubber Chemistry, 126th hleeting ACS, New York, September 19.51.
Precipitation of Metals with Potassium Ferrocyanide in Presence of Complexing Agents KUANG LU CHENGI D e p a r t m e n t o f Chemistry, University o f Connecticut, Storrs, Conn.
The reactions of metals with potassium ferrocyanide in the presence of complexing agents have been studied. By utilizing (ethylenedinitri1o)tetraacetic acid, thiosulfate, and fluoride to sequester interfering ions, a qualitative test for zinc and manganese in the presence of other metals has been developed. The test is capable of detecting 1 y of manganese at a limiting concentration of 1 to 1,000,000 and 50 y of zinc at a limiting concentration of 1 to 20,000. A quantitative volumetric determination of manganese with ferrocyanide has also been developed. No prior separations are necessary.
OTASSIUM ferrocyanide is used extensively for titration of p z i n c . Because more than two dozen metals form precipitates or colored complexes vrith ferrocyanide, its use as an analytical reagent is rather limited. It was found t h a t ferrocyanide was a very selective precipitant for manganese and zinc if (ethylenedinitri1o)tetraacetic acid (ethylenediaminetetraacetic acid, 1
Present address, R‘estinghouse Electric Corp., E a s t Pittsburgh. Pa.
E D T A ) and other complexing agents \yere used. I n the presence of (ethylenedinitri1o)tetraacetic acid, ferrocyanide formed a. specific deep blue color with ferric iron and a specific bluish tur-bid solution with ferrous iron. I n t h e presence of (ethylene-. dinitri1o)tetraacetic acid, copper(I1) was reduced b y ferro-cyanide, which formed a brownish red soluble complex with copper(1). REAGENTS AND INSTRUMENTS
Potassium ferrocyanide solution, 0.05M, stored in a brown bottle. (Ethylenedinitri1o)tetraacetic acid sol,ltion, 5y0. Five grams of the disodi7im snlt of (ethylenedinitri1o)tetraacetic acid were. dissolved in 100 nil. of w-at,er. Nitrilotriacetic acid, 5%. Five grams of nitrilotriacetic acid were dissolved in 100 ml. of water. Thiosulfate solution, 5%. Five grams of sodium thiosulfatepentahydrate were dissolved in 100 ml. of water. Fluoride solution, 5%. Five grams of potassium fluoride were, dissolved in 100 nil. of water. This solution should be stored in a waxed bottle. Potassium ferricyanide solution, 1%, freshly prepared. Indicator solution, 1%. One gram of diphenylamine was dis--
1595
V O L U M E 2 7 , NO. 1 0 , O C T O B E R 1 9 5 5 solved in 100 ml. of glacial acetic acid. This solution should be freshly prepared. Manganese chloride solution, 0.1X. T h e solution was standardized by the complexometric method ( 2 ) . Zinc chloride solution, 0.1M. The solution was prepared by dissolving pure zinc in 1 to 1 hydrochloric acid and diluted with a n appropriate amount of m t e r . Other reagents used were reagent grade. Coleman spectrophotometer and Beckman p H meter QUALITATIVE REACTION
One drop of the solution containing 1000 p.p.m. of metal was treated with 1 drop of 5 % (ethylenedinitri1o)tetraacetic acid solution, or 1 drop of another compleving agent solution, 1 drop of glacial acetic acid, and 1 drop of 1% potassium ferrocyanide solution. A positive test was claimed if a precipitate or different coloration was formed upon addition of ferrocyanide. The results in Table I show t h a t only silver(I), iron(lI),,manganese(II), zinc(II), and zirconium(1V) were precipitated with ferrocyanide i n the presence of (ethylenedinitri1o)tetraacetic acid and other complexing agents. Nitrilotriacetic acid (XTA) showed a masking effect on the interfering ions similar t o that of (ethylenedinitri1o)tetraacetic acid, except that mercury(I1) was precipitated with ferrocyanide in the presence of nitrilotriacetic acid.
Table 11. Titration of Manganese with Ferrocyanide in Presence of Other Metals Manganese, 1\lillimoles F Found 0.500
0.500 0.487 0,493
Error, SC 0.0 -2.6 -1.4
Fe(III), 5
0.500 1.000
0.504 1.014 0.998
+0.8 i1.4 -0.2
C a ( I I ) , 10
1.000
0.958 1.000 1.000
-0.2
Alg(II), 10
1.000
0.994 1.007 0.982
-0.6 +0.7 -1.8
B a ( I I ) , 10
1.000
1.000 0.598 0.954
0.0 -0.2 -0.6
S r ( I I ) , 10
1.000
0.998 1.014
-0.2 +1.4
1.007 0.982 0 480 0 490
-0.7 -1.8 -4.0
0.500 0.504
0.0 +0.8
Metals Added, JIg. .4l(III), 10
Ni(II), 10
T
1.000
n-o,--, 10
0.500
P b ( I I ) , 10
0.500
0.0 0.0
-2.0
EFFECT OF pH ON PRECIPITATION OF MANGANESE AND ZINC
l l o s t bi- and trivalent metals are precipitated \Tith ferrocyanide in acid medium. I n order t o consider the complesing ability of (ethylenedinitri1o)tetraacetic acid as a masking agent, the highest p H value permissible for the precipitation of manganese and zinc with ferrocyanide in the presence of (ethy1enedinitrilo)tetraaretic acid was determined. T o 10 ml. of 0.1JI manganese or zinc solution, 70 ml. of water and 20 ml. of 5 % (ethylenedinitri1o)tetraacetic acid s o h tion were added. T h e p H of the niisture (originally approsimately 3.9) was adjusted to about 9.5 Kith 10% sodium hydroxide. Yo precipitate was formed when 1 ml. of potassium ferroc.yanide was added. The absorbance (turbidity) of the solution was measured a t 600 mp using t,he Coleman spectrophotometer after adjusting the p H of the solution with dilute hydrochloric acid. Both manganese and zinc were precipihted with ferrocyanide a t a pH from 1 to 3.
Table I.
Effect of Complexing Agents on Reactions of 3Ietals with Ferrocyanide
Metal AntimonyiIII) Bismuth(II1) Cadmiu in (II) Ceriuni(II1) Cobalt(I1) Copper (I1j Gadolinium (111) Gallium(II1) Germanium Indium(II1) Iridium (111) Iron(1I) Iron(II1) Lanthanuni(III) Lead(I1) Rlanganese(I1) %Iercury(II) Molybdate Neodymiuiu(II1) Kickel(I1) Palladium(I1) Ruthenium(II1) Samarium(II1) SrandiuxnfIII) Silver(1j Tellurium(1V) T horiurn (IV) Titanium(1V) Tungstate Uranium(V1) Vanadate I-ttrium(III) Zinc(I1) Zirconium (IV)
+
precipitate; G green.
TITRATION O F MANGAYESE WITH FERROCY4NIDE
rlccording to the reactions previously described, it seems that manganese may be titrated with ferrocyanide in the presence of other metals which can be masked by the complexing agents. Glacial acetic acid \vas used for adjusting the p H of solution because it gave a pH of about 2.3 to 2.5. T o an aliquot of manganese solution containing from 0.5 to 2 millimoles of manganese(II), an excess amount (20 ml.) of 5% (ethylenedinitri1o)tetraacetic acid solution, 70 ml. of water, 20 ml. of glacial acetic acid, 4 drops of 1% potassium ferrocyanide solution, and 4 drops of diphenylamine were added. The mixture was titrated with 0.05M potassium ferrocvanide solution. T h e end point was from purple t o colorless or light yellow. Alternatively, the end point was from colorless or light yellow t o purple if the solution was back-titrated mith a standard manganese solution after the addition of a n excess amount of ferrocyanide. T h e results shown in Table I1 were obtained using the back titration method, which gave a better end point. DISCUSSION
+-
+
-
+
- no precipitate; (S)solution; R red;
B blue: P sellow;
Although potassium ferrocyanide is widely used for the titration of zinc, lack of specificity made it unsatisfactory for detecting zinc in the presence of other interfering metals. I t was felt that greater specificity would be obtained if the interfering metals could be masked b y the addition of complexing agents. If (ethylenedinitri1o)tetraacetic acid w nitrilotriacetic acid, thiosulfate, and fluoride are used as the complexing agents, only manganese and zinc are precipitated with ferrocyanide under the conditions described. T h e use of citric acid, tartaric acid, and thiourea for masking the interfering metals was unsatisfactory. Zinc could not be titrated with ferrocyanide a t p H 2.5 in the presence of (ethylenedinitri1o)tetiaacetic acid using ferricyanide and diphenylamine as the indicator. However, a satisfactory end point was obtained M hen the (ethylenedinitri1o)tetraacetic acid was omitted. This is possibly explained by the fact that the presence of small amounts of zinc or manganese ions is necessary for the oxidation of the diphenylamine b y ferricyanide. h t pH 2.5, zinc is so strongly complexed by (ethylenedinitri1o)tetraacetic acid that the concentration of free zinc ion is too small for the ferricyanide to oxidize the indicator. On the other hand, (ethylenedinitri1o)tetraacetic acid does not complex manganese strongly a t p H 2.5 and there is a sufficient amount of
ANALYTICAL CHEMISTRY
1596 manganese ion present for the oxidation of the indicator by ferricyanide, thereby making the quantitative titration possible. Other methods of detecting the end point of the zinc determination were attempted in place of the diphenylamine and ferricyanide. Variamine blue ( I , 3 ) was tried, but proved uneatisfactory because it took 10 to 15 seconds after the addition of each drop of the ferrocyanide solution for the color t o become stable. iln attempt was made t o measure the turbidity of the solution containing zinc ferrocyanide precipitate and (ethylenedinitri1o)tetraacetic acid. For t h e complete precipitation of small amounts of zinc in the presence of much excess of (ethylenedinitri1o)tetraacetic acid, a longer time of standing or a large amount of ferrocyanide wab required. Manganese, if present, formed a precipitate almost immediately with the ferrocyanide in the presence of (ethylenedinitri1o)tetraaceticacid. Other interferences 15 ere encountered in the end point determination for the manganese titration: Though cobalt(I1) is not precipitated by ferrocyanide at p H 2.5, the red colored cobalt(111)-(ethylenedinitri1o)tetraacetate complex is formed in the acetic acid medium upon the addition of ferricyanide (6). Therefore manganese cannot b e titrated with ferrocyanide wing diphenylamine and ferricyanide as the indicator when mhalt is
present. Interfering coloration caused difficulty when manganese was titrated in the presence of molybdate or uranyl ion. T h e manganese and zinc can he titrated with ferrocyanide in the presence of (ethylenedinitri1o)tetraacetic acid a t p H 2.5 by a high frequency method ( 4 ) . T h e high frequency method gives two breaks in t h e titration of a mixture of manganese and zinc. The ferrocyanide precipitates the zinc first and the manganese next. Further investigation of a better means of detecting t h r end point for both zinc and manganese determinationq is needed. ACKNOWLEDGMENT
T h e author is indebted to H. Flaschka for providing variamine blue. LITERATURE CITED
(1) Erdey, L., 2. anal. Chem., 137, 410 (1953). (2) Flaschka, H., Mikrochim. Acta, 1953, 414.
(3) Ibid., 1954, 361. (4) Januskiewicm, S.B., master's thesis, University of Connecticut,
1955. (5) Pfibil, R., CoZlectio?z Czechoslou. Chem. Communs., 14, 320 (1949).
RECEIVED for review .4gril 8 ,
19.55.
Accepted July 18, 1955.
Determination of Titanium and Mixtures of Iron and Titanium with Electrolytically Generated Ceric Ion ROBERT V. DILTS' and
N. HOWELL FURMAN
Frick Chemical Laboratory, Princeton University, Princeton,
Titanium sulfate solutions were reduced in a Jones reductor, caught in saturated cerous sulfate solutions, and titrated coulometrically with electrolytically generated ceric ion under an atmosphere of nitrogen. Using the sensitive amperometric end-point procedure it was possible to determine amounts of this ion ranging from 50 y to 5 mg. with an accuracy of within f 0 . 6 % . Larger samples than this cannot be determined readily, because of the insolubility of titanium sulfate in the generating medium. Mixtures of iron and titanium containing amounts of titanium from 0.013 to 0.16 meq. and amounts of iron from 0.06 to 0.12 meq. can be determined with an accuracy of within zk0.66qo or better. The titanium can be determined in this mixture with an accuracy of within 3~0.6% or better, and or better. The mixture was the iron within &O.SOq' passed through a Jones reductor, caught in a solution containing at least 90% of the amount of ceric ion calculated to be required'for the titration of titanium in the sample, and then titrated in an atmosphere of nitrogen. This procedure necessitates a prior rough knowledge of the amount of titanium in the mixture, hut if the ceric sulfate is not present initially, the results are in error.
I
N I'OLUNETRIC analysis, trivalent titanium is titrated n i t h
standard solutions of ferric iron, methylene blue, potassium permanganate, or ceric sulfate. The most widely recommended procedure is the one given by Scott ( 5 ) which involves titration with standard permanganate. From a consideration of the standard potentials of the titanous-titanic couple and of the cerous-ceric pair, i t would appear t h a t the titration of titanium I Present address, Departnrent of Chemistry, Williams College, Williamstown, hfass.
N. J.
with ceric ion should be excellent. T h e reaction would be expected to be rapid, quantitative, and the detection of the equivalence point accurate. The only information, however, concerning this titration t h a t has been published is by Takeno ( 9 ) , who ieduced quadrivalent titanium with a zinc amalgam (Jones reductor) and then, in a n inert atmosphere, titrated the trivalent titanium solution with standard ceric sulfate. The reduction of the titanium R as performed with near boiling solutions, although there appears t o be no adequate reason for this, because the reduction is just as complete when carried out in the cold. The determination of titanium has recently become more important, and since ceric ion can he generated coulometrically very readily a t a platinum anode (6) i t was decided to study the coulometric determination of this metal. The application of coulonietrir titrations has been limited almost exclusively to the determination of one species of ion in solutions of a single substance. Because it was found possible to determine titanium coulometrically with ceric ion and i t was known that iron could be easily determined by the same method ( 6 ) ,the coulometric determination of both of these metals in the preqence of one another was rtudied since they are found together frequently. The standard potentials of the titanous-titanic and ferrousferric couples are sufficiently separated (about 1 volt differenre) t o give two breaks in a potentiometric titration curve with a standard oxidant. Shippy ( 7 ) titrated mixtures of these two substances with standard permanganate and obtained good results. Under his experimental conditions the formal potentials of the two systems are about 650 mv. apart, which is more than adequate for complete and accurate determination of both metals. Shippy passed a hot fiolution of the sample through a Jones reductor, catching it in 1 to 1 sulfuric acid. The waim, reduced solution was titrated with permanganate until the titanium end point was reached using methylene blue as a n indicator, The solution was then cooled to room temperature and the iron
