The quantitative spectrographic analysis of the rare earth elements.

Spectrographic methods applicable to the determination of major rare earth constituents in complex mixtures are described. The specific examples discussed are the determination of yttrium and gadolinium in the concentration range of 10 to 100 per cent. The procedures involve the high current DC arc excitation of rare earth oxide sample-ceric oxide-graphite mixtures. Selected lines of cerium are used as internal standards. The choice of cerium as internal standard was based on the relative ease with which any cerium, if present in a mixture, could be preferentially separated from the mixture, and then reintroduced in a standard amount. Precision studies show a standard deviation of about ± 2.5 per cent of the amount present. Data are included which indicate that the high precision is attributable to excellent internal standard control of excitation variables. INTRODUCTION In a previous paper on this subject/ spectrographic methods for the determination of small amounts of rare earth impurities in other rare earths were discussed. These procedures were designed to supplement the useful spectrophotometric methods, by providing a means for determining the rare earths below the concentrations detectable by spectrophotometry. Since several of the rare earths, namely, cerium, lanthanum, yttrium, terbium, and lutecium possess no appreciable absorption in the wavelength regions accessible by ordinary spectrophotometers, it has not been possible to determine even large amounts of these members of the group by spectrophotometric methods. Gadolinium possesses an absorption band in the ultraviolet, but background uncertainty and other interferences limit the general usefulness of this band for analytical purposes. Although spectrographic methods are not generally used for the determination of major constituents, the increasing number of publications"on these determinations during the last few years indicate that there are no fundamental reasons which prevent these applications. The very limited scope of chemical and other analytical procedures for the analysis of the rare earths especially favored the extension of the spectrographic method to major constituent determinations. In the present paper a method is described for the determination of gadolinium and yttrium in complex mixtures in the concentration range 8 to 100 per cent. The method is so designed, however, that it should be adaptable to the determination of any major rare earth constituent except cerium. HISTORICAL Hopkins and co-workers have investigated the determination of major constituents in rare earth mixtures. Their method was based on the evaporation of rare earth nitrate solutions on graphite electrodes and the excitation of these electrodes with a low voltage DC arc. The variations of their results AECD 2154 *