Simultaneous spectrophotometric determination of thorium and rare earth metals with pyrimidine azo dyes and cetylpyridinium chloride

Thorium and rare earth elements (REE) react with 5-(2',4'-dimethylphenylazo )6-hydroxypyrimidine-2,4-dione (I) and 5-(4'-nitro-2',6'-dichlorophenylazo) 6-hydroxypyrimidine-2,4-dione (II) in the absence of cetylpyridinium chlori de (CPC) to form red complexes. The molar absorptivity and Sandell sensitiv ity were calculated in absence of CPC. In its presence. REE - complexes are not formed due to miceller masking, whereas Th4+ has a sensitive reaction with the studied reagents I and II. with enhancement of the color intensity of the complex. Most of the foreign ions are tolerated in considerable amo unts; 150-2400-fold amounts of rare earth do not interfere M with the deter mination of thorium. The optimum experimental conditions of the complex for mation reactions and the compositions of thorium complexes are described. A simple method is proposed for simultaneous determination of thorium and ra re earth element without previous separation. (C) 2001 Elsevier Science B.V . All rights reserved.