SPECTROPHOTOMETRIC DETERMINATION OF CERIUM SUBGROUP RARE-EARTHS IN NICKEL-BASE ALLOYS IN THE PRESENCE OF YTTRIUM WITH P-ACETYLCHLOROPHOSPHONAZO AND MIXED SURFACTANTS

Rare earth elements react with p-acetylchlorophosphonazo (CPApA) to fo rm colour complexes. In the presence of emulsifier OP and cetylpyridin ium chloride (CPC), the yttrium complex is not formed because of micel lar masking, while the cerium subgroup rare earths give more sensitive reactions with CPApA(epsilon(Ce) = 1.16 x 10(5) l.mol-1.cm-1) due to micellar sensitization. Most foreign ions can be tolerated in consider able amounts. The optimum conditions of the complex formation reaction and the composition of the Ce-CPApA complex are described. A simple m ethod is proposed for the determination of cerium subgroup rare earths in nickel-base alloys with satisfactory results.