Simultaneous spectrophotometric determination of thorium and the rare earths with Xylenol Orange

Abstract

A spectrophotometric method is described for the determination of microgram amounts of thorium-rare earth mixtures with Xylenol Orange. Advantage is taken of the fact that only thorium forms a colored complex (λ max 576 mμ) with the reagent at 2 pH and the rare earths do not. At 6 pH, however, both thorium and the rare earths form complexes and the absorbances are additive. Concentration range for the determination effects of pH time and reagent and interferences are discussed. Reproducibility is excellent with an average error of ±1.2%.