Developments in Applied Spectroscopy.

Abstract

a Based on six analyses for each mixture. cedure includes a neutralization of acid samples with ammonium hydroxide. Analysis of Rare Earth Mixtures. The recovery data of two mixtures of the four lanthanides carried through the recommended procedure are summarized in Table III. The recoveries were computed by comparison to standards of the individual lanthanides which were processed concurrently in random order with the mixtures. Six of each of the mixtures and three of each level of the individual lanthanides were processed. The absorbance values used were the peak value minus background at a selected wavelength. The background wavelengths, selected on the basis of minimum absorbances, were Nd 560 µ, Sm 430 µ, Ho 430 µ, and Er 550 µ. The absorbances contributed by each of the three lanthanides to the major peak of the fourth lanthanide were corrected. These corrections were computed from the individual lan-thanide scans as the ratios of the absorbances at the wavelengths corresponding to the peaks and backgrounds of the other three lanthanides to the major peak of the lanthanide being scanned. The corrections were both positive and negative, positive if the absorbance contributed by a diverse lanthanide is greater at the background wavelength than at the peak wavelength of the lanthanide being measured. With equal mole levels of the four lanthanides, the corrections are on the order of 1% except for samarium. With samarium, whose molar absorptivity at the peak is much less than the other three lanthanides, the correction was a maximum 4%. From scans that were obtained with the other lanthanides with the same extraction conditions, their interference effects have been estimated. For the Sm 404-µ and Er 517.4-µ peaks, there are no apparent interferences; for the Ho 450.6-µ peak, the molar ab-sorptivities of praseodymium, pro-methium, and dysprosium are V20 that of holmium; and at the Nd 583-µ peak, only praseodymium absorbs but less than V100 on an equal mole basis. Precision of Procedure. From various phases of the study, a precision of 1% relative standard deviation seems attainable. As previously mentioned, the relative standard deviation of the linearity response with varying levels of neodymium was 0.6%. This same degree of precision was obtained for a series of neodymium samples at a fixed level of 7.55 mg. with a 5-cm. cell. In analyzing the mixtures of rare earths, the pooled standard deviation was 0.5% for the six levels (12 degrees of freedom) of individual lanthanides that were processed. With mixtures (Table III) the pooled standard deviation was 0.5%. LITERATURE CITED (1) Abrahamer, I., Marcus, Y., Israel At. Cation exchange equilibrium distribution coefficients with BIO-RAD AG 50W-X8, 100-to 200-mesh, a sul-fonated polystyrene resin, are presented for 49 cations in nitric acid and 45 cations in sulfuric acid media. The coefficients were determined at a total amount of cation to total resin capacity ratio q = 0.4, to ensure comparability with coefficients in hydrochloric acid determined previously. Acid concentrations from 0.1 N to 4 .ON were used. The coefficients are arbitrarily arranged into selec-tivity scales according to their values in 1N acid. Included are elution curves for the multicomponent systems V(V)-U(VI)-Sc(lll)-Y(lll); Na(l)-BeUl)-Ba(tl)-Y(lll)-Zr(IV); and Hg(ll)-Cd(ll)-Be(ll)-Fe(III)-Ba(ll)-Zr(IV) to demonstrate some possibilities inherent in cation exchange separation. Systematically compiled data on ion exchange equilibrium distribution coefficients are very useful to the analytical chemist for planning separations. This has been generally recognized since Kraus (6) and his co-workers presented their pioneer work on the anion exchange of metal chloride complexes. Nevertheless, information of this kind is still fairly limited in the literature. The situation is worse for cation exchange than for anion exchange. Only the hydrochloric acid system (7, 9) seems to have been investigated fairly thoroughly. Nelson (8) and coworkers have studied the HC1 and HC104 systems at high acid concentrations. Information of a more limited nature is available for cations in hydrobromic acid (1), hydrofluoric acid (2), thiosulfate (5), and EDTA media (4), as well as for hydrochloric acid containing acetone as an organic constituent (8). The senior author (14) published 106 · ANALYTICAL CHEMISTRY