Histochemical staining of cadmium with benzothiazolylazophenol derivatives.

As part of the continuous developmental research for a highly sensitive chelating agent for cadmium, benzothiazolylazophenol derivatives (BTAP) were synthesized and their staining properties for cadmium were examined. The compounds synthesized for this study were identified as being BTAP by analysis of their melting points and C,H,N,S content. Benzothiazolylazo-p-methoxyphenol, -p-chlorophenol and -p-cresol stained cadmium with the highest optical density and the most precise localization amongst dyestuffs reported to date. Differential sequestration by pyrophosphate makes it possible to distinguish cadmium masked by the presence of zinc. With the modification of a chelating agent to increase sensitivity, the improvement in molar absorptivity was also considered theoretically.