in a 500-ml. Erlenmeyer flask and organic matter was destroyed by heating t o heavy fumes with 10 ml. of concentrated sulfuric acid and portions of concentrated nitric acid; the resulting solution was diluted with 20 ml. of water and heated t o light fumes. Rhodium was removed from the solution by 20y0 titanous chloride solution (6). To eliminate contamination of the rhodium precipitate by iridium, the rhodium n a s precipitated three times and the third precipitate was filtered through an A2 filter crucible. I n the three filtrates combined, titanium was precipitated by cupferron three times and the three filtrates were again combined. Subsequent to destruction of the organic matter by concentrated sulfuric and nitric acids and evaporation of the solution to 2 ml., iridium was determined colorimetrically according to the Berman-McBryde procedure (5) for samples previously fumed with sulfuric acid. Reagent blanks were used. Results are listed in Table 111. When more than about 5 mg. of iridium are present, the amount recovered from the rhodium (Table 111) is less than that retainecl by the rhodium as indicated in Table 11. This is due to the difficulty of isolating micro amounts of iridium from the bulky cupferron precipitate, because treatment of the final cupferron precipitate with concentrated sulfuric, nitric, and 707, perchloric acids (2) yielded a mauve color only when rhodium and iridium were present in excess of about 5 mg. Honever, in any case, the amount of iridium lost is small. REPRECIPITATION
From the results (Table 11) when both rhodium and iridium metals are present in more than .5-mg. amounts, the rhodium values are slightly high and the iridium values slightly low, by about 30 to 40 y. This is in agreement with the recorded values of iridium in Table I. When maximum accuracy is required, rhodium can be reprecipitated by copper in the effluent of the large exchanger. This reprecipitation could decrease the amount of iridium reduced 1%ithout increasing the filtrate losses of rhodium beyond 0.01 mg. A second precipitation of rhodium and iridium, separately, was applied as follow: Rhodium was precipitated and filtered as described above in the separation of rhodium from iridium. The filtrate and washings were kept (filtrate B). The residue was dissolved by aqua regia and dry chlorination treatments. Copper was eliminated in the resulting solution through the large exchanger as described, subsequent to conversion of the metals to chlorides. The effluent was adjusted to 30 ml. in 1.ON hydrochloric acid and rhodium was reprecipitated by copper and filtered as previously recom-
Table IV.
Iridium Reduced and Filtrate Losses of Rhodium Applying Reprecipitation
Copper, Added, Mg. 550 200
+
Rhodium Added, mg. Unreduced, y 10.57 8
... ... ... ... .
Table V.
.
I
7 7
... ...
...
Iridium Added, mg. Reduced, ... ... ... ... ... ... 9.28 7.2 ... 7.0 ...
y
7.1
Separation of Rhodium from Iridium Applying Reprecipitation of Rhodium Added, Mg. Recovered, Mg.
Copper 550 200
Rhodium 10.57
+
mended. The filtrate and washings were combined with filtrate B. After removal of the copper, rhodium was determined colorimetrically in these combined filtrates as described under the recovery and determination of rhodium. The same procedure was followed for iridium. The residue of the iridium reprecipitation was dissolved in aqua regia followed by dry chlorination, the metals were converted to chlorides by hydrochloric acid, copper was eliminated through the cationic exchangers, and iridium was determined colorimetrically (Table IV). The results of separation of rhodium from iridium, applying reprecipitation of rhodium in the effluent of the large exchanger and proceeding according to recommended method of separation, are recorded in Table V. SUMMARY
A method for separating rhodium from iridium in a solution of both metals is successful in a range from 5-mg. to 50-7 amounts of these two metals. Losses of either rhodium or iridium to iridium or rhodium precipitate, respectively, are negligible and in accordance with the filtrate losses of rhodium and iridium. This procedure could be applied also for the metals present in excess of 5 mg. after a reprecipitation of rhodium in the effluent of the larger exchanger. ACKNOWLEDGMENT
The authors express their appreciation to National Research Council of Canada for financial support in the form of a grant given to G. G. Tertipis. LITERATURE CITED
(1) Aoyama, S., Watanabe, K., J. Japan. Chem. 75, 20-3 (1954).
Iridium 9.28
Rhodium 10.54 10.53 10.55
Iridium 9.26 9.24 9.25
(2) Barefoot, R. R., McDonnell, W. J., Beamish, F. E., A N ~ LCHEM. . 23, 514 (1951). (3) Berman, S. S., McBryde, W. A. E., Analyst 81,566 (1956). (4) Berman, S. S., McBryde, W. A. E., IND.ESG. CHEM.,ANAL.ED.’ 18, 120 11946). (6) Gilihrist, R., J. Research Natl. BUT. Standards 9,547 (1932). (7) Hill, M. A., Beamish, F. E., ANAL. CHEM.22,590 (1950). (8) Icarpon, B. G., Federova, A. N., Ann. inst. platine (U.S.S.R.) 11, 135 (1933). (9) Latimer, W. M., “Oxidation Potentials,” 2nd ed., pp. 342-4, Prentice-Hall, Sew York, 1952. (10) Marks, A. G., Beamish, F. E., ANAL. CHEM.30,1464 (1958). (11) Maynes, A. D., McBryde, W. A. E., Analyst 79,230 (1954). (12) Pshenitsyn, K. K., Federov, I. A., SimanovskiI,P. V., Izvest Sectora Platiny i Drug. Blagorod. Metal. Inst. Obschei i Neorg. Khim. A k a d . N a u k . S.S.S.R. 22, 16-21 (1948). (13) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., pp. 523-5, Interscience, New York, 1950. (14) Westland, A. D., Beamish, F. E., Mikrochim. Acta 10, 1474 (1956).
RECEIVED for review October 1, 1959. Accepted December 17, 1959.
Correction Precision in X-Ray Emission Spect rogr a phy, Background Present I n this article by P. D. Zemany, H. G. Pfeiffer, and H. A. Liebhafsky [ANAL. CHEM. 31, 1776 (1959)], on page 1778, column 1, line 2, the amount should be 4 y instead of 40 y. VOL. 32, NO. 4, APRIL 1960
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