combinod n ith the first one in the 25-ml. volumetric flask. Determination of Rhodium. T h e yellow organic phase was drained into a 50-ml. calibrated volumetric flask. T h e separatory funnel was washed three tinies with isopentyl ashings n ere drained alcohol, and the i~ into t h e 50-ml. volumetric flask. T h e volume wis brought u p t o the mark with isopentyl alcohol, and the rhodium was dctcmnincd spectrophotometrically inmctliatcly, a t 429 nip ( I O ) using 1-cm. inatc.licd hilira crlle. RIXsults are listrd in Tnbk I. Determination of Iridium. T h e perchloric acid solution (3.3 ml.) \ \ a s added to t h e 25-mI. volumetric flask containing the iridium solution. T h e solution was mixed n ell b y shaking, and the flask 11x3 placed in a boiling distilled water b a t h where i t T\ as left for 3 niinutcxs for color devclopment aftrr tliv tempi ratiirc of the bath renchetl 00’ Cy. The flask was air. coolrd for 5 minut(’q and then rinsed with tap n.atcv K a t c r was added to the mark. and iiidium nas determined spectro~~liotomctrically a t 403 mp (4, 10) using 1-cm. niatchc>d silica cells. Results are listed in Table I. Standards of rhodium and iridium were carried siniultaneously with the analysis of the rhodium-iridium mivtures. These n err treated as above but with the following two modifications for tht. iridium. The evaporation residue of iridium. moistwed with drops of redistilld hydrobromic acid, was transferred to a 25-nil. volumetric flask with
Table 1.
Added 10
25 50 100.9
Separation of Rhodium from Iridium by Solvent Extraction
Rhodium, pg. Found
Difference
Added
...
7 5
10.0 9 6 9.8 10.4 10.4 10.4 24.2 24.2 24.5 49.8 49.8 49.8 101.9 100.0 99.0
Iridium, pg. Found 7 0 T3 7.3 7 3 7.0 7.3 18.4 18.4
-0 4 -0.2 +0.4 +0.4
+0.4 -0.8 -0.8 -0.5 -0.2 -0.2 -0.2 +1 . 0 ... -1.9
18.4
73.8
wash the beaker and then transferred to the 25-ml. volumetric flask. The color of the iridium complex was stable over a period of 2 hours. ACKNOWLEDGMENT
The authors express their appreciation to Norman Stewart Roberson for a fellowship given to G. G. Tertipis. LITERATURE CITED
(1) Ayres, G. H., Bolleter, W. T., ~ ~ X A L CHEM.29, 72 (1957). (2) Barefoot, R. R., McDonnel, W. J., Beamish, F. E., Zbid., 23, 514 (1951). (3) Beamish, F. E., Talanta 5 , 1 (1960).
18.4 35.6 36.6 35.6 TI .9 73.9 73.1
36.i
.
Difference -0 5 -0 2 -0.2 -0 2 -0.5 -0.2
... ... ... -1.1 -0.1 -1.1 -1.9 +0.1
-0.7
(1946). (6) Gilchrist, R., J . Research iYatl. Bur. Standards 9. 547 (1932). (7) Jackson, E., Analyst 84, 106 (1!)59). (8) Karpov, B. G., Ann. inst. platine (U.S.S.R.) 4, 360 (1926). (9) Karpov, B. G., Fedorova, A. N., Zbid., 9, 106 (1932). (10) Pantani, F., Piccardi, G., Anal. Chim. Acta. 22, 231 (1960) (11) Tertipis, G. G., Beamish, F. E., AKAL.CHEM.32, 486 (1960). (12) Westland, A. D., Beamish, F. E., Mikrochim. Acta 10, 1474 (1956). (13) Ibid., 5 , 625 (1957). (14) Zhemchuzhnij, S. T., Ann. inst. pZatine (U.S.S.R.) 5 , 364 (1927).
RECEIVEDfor review January 2 , 1962. Accepted February 26, 1962.
Quantitative Radiochemical Determination of Molybde num-99 by Solvent Extraction LEON WISH U. S. N a v a l Radiological Defense laboratory, San Francisco 24, Calif.
b In the ion exchange separation for the determination of molybdenum-99 from fission product mixtures, low results a r e obtained because of its p r e treatment with perchloric acid a n d its reduction by the anion resin. Since the molybdenum i s eluted last, the reduced form m a y elute too soon a n d contaminate the other radionuclides. A method has been developed for the r a p i d quantitative separation of molybdenum-99 from gross fission product mixtures. It i s based on the extraction of molybdenum into a solution of a-benzoin oxime in chloroform. The analyses of fission product mixtures by this method a n d b y a standard radiochemical gravimetric procedure a g r e e d within 1 to 2%.
T
HE RADIOCHEMICAL ASSAY of
molybdenum-99 as a n indirect determinant for the number of fissions in fission product mixtures is well established. The carrier-free quantitative ion exchange separation for the determination of molybdenum-99 (b) has shown insufficient reliability. The yield occasionally may be low, and other radionuclides become contaminated with the molybdenum. This behavior may be due to partial reduction of the niolybdenum(V1) b y the anion resin and to partial formation of nonadsorbable species in the perchloric acid dissolution of various types of samples. Also, since molybdenum is eluted last in the ion evchange procedure. a rapid initial separation of molybdrnuni from the
fission milture would be quite advantageous. It vould simplify and speed up the other ion evchange separations in the procedure. I n addition, i t would permit more rapid estimates of the number of fissions which produce a given fission product sample. Solvent extraction is an ewellent process for achieving this separation without materially disturbing the subsequent ion exchange radiochemistry for scquential analysis. Allen and Hamilton ( 1 ) evtracted macroamounts of molybdenum(T’1) and tungsten(V1) as compleves with cupferron into isoamyl alcohol. However, they did not obtain a good separation from other ions. Jeffery ( 3 ) extracted molybdenum(V1) and tungsten(V1) with a-benVOL. 34,
NO. 6 , M A Y 1962
625
zoin oxime into chloroform from acid solution. The molybdenum was first complexed with the oxime in aqueous medium and then extracted. Jeffery found that chromium, vanadium, aluminum, iron, titanium, fluoride, and phosphate did not interfere in the process. More recently, Goldstein, Manning, and Menis (2) determined microamounts of molybdenum in thorium dioxide, uranyl sulfate, and steel. The molybdenum was extracted into a solution of a-benzoin oxime in chloroform, after which the complex of molybdenum and quercetin was formed by the addition of quercetin in ethyl alcohol. The complex was measured spectrophotometrically. Maeck, KUSSY,and Rein (4) determined fission product molybdenum-99 by extraction of the a-benzoin oxime complex into ethyl acetate after addition of 3 mg. of carrier. The molybdenum was back extracted into dilute hydrochloric acid. The extraction of the oxime itself into chloroform is incomplete after a few minutes. There was sufficient reagent remaining in the aqueous phase to precipitate molybdenum. When the oxime was dissolved in chloroform and shaken with 1N hydrochloric acid solution, no precipitate was detected on the addition of molybdenum. Since the solution
Table I. Extraction of Molybdenum-99 with a-Benzoin Oxime in Chloroform from 1N Hydrochloric Acid Solution
CHCla Layer
Extraction Time, Minutes
Residual Aqueous Layer
Per Cent of Initial Mo9o Recovered
