Analytical Oxidation of Americium with Sodium Perxenate SIR: I wish to report a successful application of sodium perxenate, NaaXe06, to the analytical oxidation of Am(II1) to Am(V1). This work may be the first report of a practical use of this compound. Since the first discoveries that xenon would react with other elements (2, 3) , much research effort has been put forth in this new field of the noble gas compounds. One of these compounds, sodium perxenate, appears to be potentially useful as an analytical reagent. Sodium perxenate was first prepared by Malm, Holt, and Bane (6),who found the compound to be a stable solid under ordinary conditions. Later studies by Appelman and Malm ( I ) revealed t h a t the compound had a high oxidation potential of about 3 volts in acidic solutions. However, they also found that the reaction Xe(VII1) Xe(V1) was almost instantaneous below p H 7 . I n view of these properties sodium perxenate appeared to be a convenient, stable analytical reagent for methods requirigjya”readi1y available and powerful oxidant. Commercially prepared sodium perxenate was studied as a n oxidant in the separation of americium in tracer quantities from curium by means of calcium fluoride ( 4 ) . Originally, in this separation, americium(II1) was oxidized to the (VI) state with silver catalyzed persulfate. Following the oxidation, the solution was passed through a column of calcium fluoride, which retained the fluoride-insoluble trivalent actinides and lanthanides but allowed the fluoride-soluble Am(V1) [and Pu(VI)] to pass through the column. The silver catalyzed persulfate oxidation required about 30 minutes at elevated temperature. When solid sodium perxenate in the presence of silver(1) was used, oxidation was complete in less than 30 seconds at room temperature, thus reducing the time required for the separation.
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EXPERIMENTAL
Reagent. A t t h e author’s request, the sodium perxenate was prepared by Peninsular ChemResearch, Inc., Gainesville, Fla., according to the method of Malm, Holt, and Bane ( 5 ) . The material was a fine, slightly offwhite powder. Analysis of the material showed a weight loss of 9.1% on drying a t 125” C. for 16 hours. On a dry basis, the compound had 95.370 of its theoretical oxidizing
Table I. Influence of Silver(1) on the Oxidation of Americium with NadXeO6
Americium oxidized, % Silver(1) present Silver(1) absent 91.2 95.2 85.0
96.2
Av. 95.3 Rel. std. dev.: 1 . 0 % (11. =
90.6 7)
4.6% (n = 7 )
capacity (as Na4XeOB) and contained ess than 0.1 wt. % fluoride (as NaF). The only other observed impurity was sodium carbonate. Separation of Americium from Curium. Use t h e previously described procedure (4) with the following modifications: I n Pretreatment C under Sample Preparation following the wash of the precipitate with 3 ml. of water, dissolve the precipitate i n 4 drops of 1M nitric acid. Do not dilute. Repeat Pretreatment C if necessary. Then to the solution from Pretreatment C , add 1 drop of 0.1% silver nitrate and, if necessary, enough water to give a solution volume between 0.3 and 0.5 ml. Add about 5 mg. of solid sodium perxenate and immediately mix well. Dilute the solution with water to approximately 1.5 ml. and transfer to the calcium fluoride column. Wash the column with three 1-ml. portions of fresh 0.001M ammonium persulfate, and continue as in the previously described procedure (4). DISCUSSION AND RESULTS
Sodium perxenate alone will quickly oxidize tracer amounts of Am(II1) to Am(V1) in acidic solution and in the presence of lanthanum(II1). However, because of the high oxidation potential of the Am(V1)-Am(II1) couple, tracer quantities are difficult to keep oxidized unless stabilized or kept in a strongly oxidizing medium. Table I shows the influence of silver(1) on the oxidation. I n this comparison, solutions containing 1.05 X lo5 d.p.m. (disintegrations per minute) Am241were oxidized with sodium perxenate in the presence or absence of silver(1). Instead of using the calcium fluoride column, Am(V1) was determined by alpha counting after removal of any remaining Am(II1) by coprecipitation with lanthanum fluoride, a technique similar to Moore’s method (6).
Moore (6) found a similar effect of silver(1) in his study of the persulfate oxidation of americium. The role of the silver ion in the perxenate oxidation is thought to be that of a holding oxidant. When sodium perxenate is added to an acidic solution containing silver(I), the amber color of argentic ion is immediately seen, remains for some time, and gradually fades. Since sodium - perxenate is such a powerful oxidant, it probably oxidizes both americium and silver and almost instantaneously decomposes, leaving argentic ion, which serves as a holding oxidant for Am(V1). The determination of americium was made in five synthetic samples with the sodium perxenate-calcium fluoride procedure. Each sample contained 1.05 x lo6 d.p.m. of americium, 1.13 x 108 d.p.m. of curium, and 0.5 mg. of La (111). The average americium recovery was 98.4% with a relative standard deviation of 2.1%. Curium impurity averaged less than 0.5% by alpha counting. These results are quite similar to those obtained in the silver-catalyzed persulfate oxidation-calcium fluoride procedure (4). ACKNOWLEDGMENT
The author thanks J. G. Malm, E. H. Appelman, C. L. Chernick, and Henry Selig of Argonne National Laboratory for their helpful discussions of xenon chemistry. LITERATURE CITED
(1) Appelman, E. H., Malm, J. G., J . A m . Chem. SOC.86, 2141 (1964). (2) Bartlett, N., Proc. Chem. SOC.,1962,
218. ( 3 ) Claassen, H. H., Selig, H., Malm, J. G., J . A m . Chem. SOC.84, 3593 (1962). ( 4 j Holcomb, H. P., ANAL. CHEM.36, 2329 (1964). Malm, J. G., Holt, B. D., Bane, R. W., (5’Woble-Qas Compounds,” H. H. Hyman, ed., p. 167, University of Chicago Press, Chicago, 1963. (6) Moore, F. L., ANAL.CHEM.35, 715 (1963). H. PERRY HOLCOMB Savannah River Laboratory E. I. du Pont de Nemours and Co. Aiken, S. C. RECEIVED for review Yovember 25, 1964. Accepted December 21, 1964. Information contained in this article was developed during the course of work under contract AT(07-2)-1 with the U. S. Atomic Energy Commission. VOL. 37, NO. 3, MARCH 1965
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