Application of the spectrophotometric determination of nickel and cobalt in mixtures with bipyridylglyoxal dithiosemicarbazone to the analysis of catalysts

Bipyridylglyoxal dithiosemicarbazone forms a complex with nickel(II) at pH 5·2, which can be extracted into chloroform (λmax.= 410 nm). A similar complex is obtained with cobalt(II), but is not extractable in this solvent, thus allowing nickel and cobalt to be determined in mixtures. Two procedures are proposed for the accurate analysis of such mixtures in which 1 p.p.m. of one of the ions can be determined accurately in the presence of as much as 5 p.p.m. of the other. One of the procedures has been applied to the determination of nickel and cobalt in industrial catalysts and the results obtained have been compared with those obtained by atomic-absorption spectrophotometry. Satisfactory results were obtained.