Simultaneous spectrophotometric determination of thorium and rare earth metals with m-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. In the presence of CPC, REE-complexes are not formed because of micellar masking, while Th gives a more sensitive reaction with CPAmK. 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. (author)