SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF THORIUM AND RARE-EARTH-METALS WITH META-CARBOXYCHLOROPHOSPHONAZO (CPAMK) AND CETYLPYRIDINIUM CHLORIDE

Th and rare earth elements (REE) react with m-carboxychlorophosphonazo (CPAmK) in the absence of cetylpyridinium chloride (CPC) to form colour complexes. The molar absorptivities for Th and Ce are 1.03 x 10(5) and 1.06 x 10(5) 1.mole-1.cm-1 respectively. In the presence of CPC, REE-complexes are not formed because of micellar masking, while Th gives a more sensitive reaction with CPAmK (epsilon = 1.50 x 10(5)). Most of the foreign ions are tolerated in considerable amounts; 360-1000-fold amounts of rare earths do not interfere with the determination of Th. The optimum conditions of the complex-formation reactions and the compositions of Th-CPAmK complexes are described. A simple method is proposed for simultaneous determination of Th and rare earths without previous separation.