Jan., 1961
COMMUNICATIONS TO THE EDITOR
191
the concentration of tantalum in solution in the range studied from 10 to 100 pg. Ta/ml. with an average deviation of 5%. From pH 3.3 to 4.0 the diffusion current is reasonably constant, then it decreases for a given concentration of tantalum as the pH of the solution increases. The wave obtained by the conventional polarographic method is d s c u l t to analyze because TABLEI solvent reduction occurs before a well-defined GAS CHROMATOGRAPHIC ANALYSESOF HYDROGEP; I plateau is formed on the Ta-EDTA wave. (For AND ISOMERS (VOLUME yo) this reason, and because the reduction wave of Sample Para-Hz Ortho-Ha HD Da Nb(1V)-Nb(II1) occurs in this r e g i ~ n , ~the ,~ I Calcd. 9.3 27.9 48.0 14.8 method is not recommended as an analytical Found 9.0 24.6 48.9 17.2 procedure for tantalum.) However, the above 18.5 I1 Calcd. 32.7 37.5 11.5 results are reproducible if proper precautions are 15.1 Found 36.3 37.5 11.7 observed. Stock solutions were prepared for this investigaDEPARTMENT OF CIKEMISTRY tion by fusing Taz05 (Electro Metallurgical Co., OF SCIENC!E FACULTY HOKKAIDO UNIVERSITY SHOZO FURUYAMADivision of Union Carbide Corp., 99.6% Ta206 SAPPORO, JAPAN min.) in K2C03-KOH in a nickel crucible. The CHEM~CAL LABORATORY melt was leached in water, filtered and made up to FACULTY OF PHARMACEUTICAL SCIENCES UNIVERSITY OF TOKYO TAKAO KWAN volume. Final solutions were prepared by taking aliquots of the stock solution and adding, dropwise TOKYO, JAPAN with constant swirling, to acidified solutions of RECEIVED NOVEMBER 7, 1960 EDTA (usually sufficient EDTA t o make the final solution 0.1 M in this reagent). Adjustments in pH were also made gradually and with constant POLAROGRAPHY OF TANTALUMswirling of the solution. This procedure insured ETHYLENEDIAMINETETRAACETATE getting stable tantalum solutions. Final solutions COMPLEX mere stable for at least one week. Nickel does not interfere in this procedure. Sir: Platinum crucibles cannot be used because the I n the course of a study of complexing agents for small amount of platinum taken into solution niobium and tantalum, we have found a hitherto during the fusion process with K2C03gives a large unreported complex of tantalum(V) and EDTA. catalytic wave in the presence of EDTA (not Milligram quantities of tantalum may be held in previously reported in the literature) at about solution in the p R range from 3 to 6 with EDTA of - 1.1 v. which makes analysis of the Ta-EDTA at least 0.01 M concentration. Furthermore, these wave even more difficult. solutions exhibit reduction of Ta(V) to Ta(1V) at Acknowledgment.-Financial assistance from the dropping mercury electrode. The only previWright Air Development Division is gratefully ously reported examples of the existence of tantalum(1V) in aqueous media, by Zeltzer' in HC1 acknowledged. solutions and by Elson2 in acid tartrate solutions DEPARTMENT OF CHEMISTRY OF ARIZONA ROBERT E. KIRBY are somewhat doubtful inasmuch as the phenomena UNIVERSITY ARIZONA HENRY FREISER could not be reproduced either by Ferrett and TKCSON, RECEIVED XOVEMBER 7, 1960 Milner3 or by ourselves. The polarographic investigation of the tantalum complex indicates that a one electron reversible reduction takes place a t the dropping mercury SURFACE RECOMBINATIONS OF electrode. This is similar to the behavior of the CHLORIKE AND BROMINE ATOMS Nb(V)-EDTA cjomplex reported by Ferrett and Milner3 and studied in greater detail by US.^ The Sir: half-wave potential is independent of EDTA conI n 1933 Rodebush and Klingelhoeferl and centration, but it is pH dependent. In the pH Schwab and F r i e d independently reported the region of 3 . 3 to 5.6 the half-wave potential varies production of chlorine atoms in a flow system (with linearly from - 1.23 v. to - 1.36 v. vs. the S.C.E., an electrical discharge). Though their results on indicating that one hydrogen ion takes part in the the rate of surface recombination of these atoms reduction of the Ta(V)-EDTA complex. The disagree markedly, their conclusions apparently temperature coefficient of the half-wave potential have discouraged anyone else from attempting to is negative and less than 1 mv. per degree which is produce halogen atoms in a flow system. Schwab, characteristic of a diffusion controlled process. who reported on both bromine and chlorine atoms The diffusion current of the Ta-EDTA complex, in greater detail in 1934,384concluded that: (1) in solutions of given p H values, is proportional to (1) W. H. Rodebush and W. C. Klingelhoefer, J . A m . Chem. SOC.,
then weighing each portion. The area thus determined was assumed to be proportional to the amount present. Such analysis data, obtained for hydrogen samples of different isotopic compositions, are shown in Table I. The result seems to be satisfactory, if one considers the approximations involved.
(1) (2) (3) (4)
8.Zeltzer, Collectbn Czech. Chem. Commzlnzcat~ons,4 , 319 (1932). R. E. Elson, J. Am. Chem. Soc., 76, 4193 (1953). D. J. Ferrett and 12. W. C. Milner, J . Chem. Soc., 1186 (1956). R. E. Kirby and 1%.Freiser, to be published.
55, 130 (1933). (2) G. M. Schwab and H. Friess, Naturwisssnsckaften, 21,222 (1933). (3) G. M. Schwab and H. Friess, Z . Elektrochem.. 89, 586 (1933). (4) G. M. Schwab, 2.physik. Chem., B W ,452 (1934).
