by longer paper, or the rate of solvent flow could be decreased to allow more time for separation. The size and design of paper and the concentration of solvent used are a practical comproniise among these factors. Continuous separations of some mixtures of the four metals, -sere successful. The actual paths and locations of the separated metals on the paper were observed by stopping the process and spraying the paper with stannous chloride-potassium iodide reagent. Platinum was indicated by yello\\- t o brownish color, palladium by pink to dark purple, and rhodium by orange to maroon. Detection of iridium requires application of concentrated nitric acid, which produces a b r o m color. By this means, the sharpness of separation can be shown. Continuous separations were first attempted with mixtures containing 10 mg. of the metals. Later, 100 mg. of each metal were used with equal success. Continuous paper electrochromatography is possible only if the rate of movement in descending chromatography for each metal is different from the rate of horizontal migration. If not, the metals reach the drip point a t different times. The wide differences betrveen separations by horizontal electroniigration and descending chromatography indicate that a continuous process can be developed. HolTever, best separation of the four metals with horizontal electromigration occurred a t pH 9, a t which rhodium precipitated and remained a t the point of application. A continuous process would hare to avoid precipitation of rhodium. The purity of metal obtained a t separated drip points was studied by x-ray fluorescence analysis as in horizontal paper electrochromatography. In each example described below, the impurity metal did not exceed 1 part per thousand of the metal collected a t any drip point. Platinum and Palladium. Platinum(1V) and palladium(I1) in chloride solution were evaporated just to dryness and the residue was diluted nith O . 1 M hydrochloric acid until the total concentration of metal was 0.05M. A twofold excess of solid (ethylenedinitri1o)tetraacetic acid v a s added and the p H of the solution adjusted to 9 with dilute sodium hydroxide. The solvent was 0.1X (ethylenedinitri1o)tetraacetic acid adjusted to p H 9. The paper was placed in the apparatus ivith half the length of the feed points immersed in solvent. Solvent f l o ~began and was allom-ed to \\et the paper before the sample was added. The sample was applied by dipping the wick, attached to feed point 3, into the sample solution. A potential of 130 volts n-as applied
and the resulting current was 120 ma, Under these conditions the two metals reached the lower edge of the paper in 2.5 hours. Palladium appeared exclusively a t drip point 5, while platinum appeared only a t points 6 and 7. Palladium and Iridium. Palladium(I1) and iridium(1V) in chloride solution were mixed with twofold excess of solid (ethylenedinitri1o)tetraacetic acid and the p H tvas adjusted t o 9 with sodium hydroxide. A potential of 120 volts was applied, and a current of 200 ma. passed. Palladium appeared a t drip point 5 and iridium a t points 6 and 7. Rhodium and Iridium. Rhodium(111) and iridium(1V) in chloride solution were mixed with a twofold excess of solid (ethylenedinitri1o)tetraacetic acid. The solution was then made strongly basic with sodium hydroxide to convert the rhodium to the yellow cationic form. The p H of the solution wis then adjusted to 4 with hydrochloric acid. The solvent was O . 1 M (ethylenedinitri1o)tetraacetic acid adjusted to pH 4. A potential of 150 volts was applied, a current of 180 ma. passed; rhodium appeared entirely a t drip points 4 and 5 and iridium a t drip points 8 and 9. Rhodium and Platinum. Rhodium(111) and palladium(I1) in chloride solution were made strongly alkaline with sodium hydroxide, to convert rhodium to the yellon, cationic form. A twofold excess of solid (ethylenedinitri1o)tetraacetic acid was added and the pH adjusted to 4. The solvent was 0.1M (ethylenedinitrilo) tetraacetic acid adjusted to p H 4. At 140 volts the current was 180 ma. Rhodium appeared entirely a t drip points 4 and 5, while platinum appeared a t points G, 7, and 8. Rhodium and Palladium. Palladium(I1) and rhodium(II1) in chloride solution were made strongly basic with sodium hydroxide, a tIvofold excess of (ethylenedinitri1o)tetraacetic acid added, and the p H adjusted to 4. At 150 rolts, rhodium appeared only a t drip points 4 and 5 , m-hile palladium appeared exclusively a t points 6 and 7. Rhodium, Palladium, and Iridium. Rhodium(III), palladium(II), and iridium(1V) in chloride solution were made strongly alkaline with sodium hydroxide, a twofold excess of solid (ethylenedinitri1o)tetraacetic acid added, and the p H adjusted to 4. At a potential of 150 volts, rhodium appeared entirely a t drip points 4 and 5 , palladium a t points 6 and 7, and iridium a t points 8 and 9.
separated a t pH 4, although the platinum is more diffusely located. It may be concluded: The use of (ethylenedinitri1o)tetraacetic acid to complex palladium and iridium makes it possible to work in alkaline solutions a t p H 9, a t which platinum behaves as a single species. Platinum(IV), palladium(II), rhodium(III), and iridium(1V) can be separated in limited amounts by horizontal paper electrochromatography with 0.1M (ethylenedinitri1o)tetraacetic acid as solvent a t pH 9. These metals cannot be separated in the same solvent by simple descending chromatography. The difference in rates of movement of the four metals in descending chromatography and in horizontal electrochromatography makes possible the establishment of a continuous process separation for certain combinations of the four metals. Continuous separations of mixtures of platinuin(1T’) and palladium(II), palladium(I1) and iridium(IV), rhodium(II1) and iridium(rV) ,rhodium(II1) and platinum(IV), and rhodium(II1) and palladium(I1) and iridium(1V) have been accomplished. Rfixtures of all four metals have not been successfully separated because of the diffuse behavior of platinum a t pH 4.
REFERENCES
(1) Anderson, J. R. A., Lederer, XI., Anal. Chim. Acta 5 , 321 (1951). (2) Burstall, F. H., Davies, G. R., Wells,
R. A., Tinstead, R. P., J. Chem. SOC.1950, 516. (3) Durrum. E. L.. J . Am. Chem. Soe. 73, 4875 (1951).’
Kriege, 0. H., Ph.D. dissertation, Ohio State University, 1934. MacXevin, W.&I.,Hakkila, E. A., ASAL. CHEW.,2 9 , 1019 (1957). MacNevin, W. M., Kriege, 0. H.,
Ibid., 26, 1768 (1954). I b i d . , 27, 535 (1955). I b i d . , 28, 16 (1956). MacNevin, W. M., Kriege, 0. H., J . Am. Chem. SOC.77,6149 (1955).
MacNevin, TV. X, McKay, E. S., ;IXAL. CHEX. 29,
1220 (1957).
Ward. F. L.. Lederer. M., Anal. Chim. Acta’6, 355 (1952): RECEITEDfor review March 14, 1957. Accepted August 15, 1937.
DISCUSSION
A mixture of all four metals could not be continuously separated. The presence of rhodium requires a slightly acid solution (pH 4), to prevent precipitation of rhodium hydroxide. At pH less than 9, platinum distributes in several diffuse zones involving palladium and iridium. However, a mixture of rhodium(II1) and platinum(1V) can be
Argentimetric Method for Epoxides-Correction I n the article on “Argentimetric Method for Epoxides” [Stenmark, G. A,, ANAL.CHERI. 29, 1367 (1957)], the fifth line from the bottom of the second column should read 2,6-di-tert-butyl-4methylphenol instead of 2,4-di-tertbutyl-6-methylphenol. VOL. 29, NO. 12, DECEMBER 1957
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