Histochemical staining of cadmium with benzothiazolylazonaphthol derivatives

Searching for a chelator with increased sensitivity for use as cadmium stain, a number of benzothiazolylazonaphthol derivatives were synthesized and their staining properties for cadmium and zinc were examined. Benzothiazolylazo-beta-naphthol and -naphthol AS (BTAN-AS) stained cadmium with the highest staining intensity and the most precise localization. Poststaining techniques for differential staining using oxine solution made it possible to distinguish cadmium in the presence of interference by other metals. The observed lowered molar absorptivity of BTAN-AS is believed to be due to the ortho effect of the anilide group of naphthol AS. The solubility of the chelator appears to be a critical factor in the formulation of molecules with higher chelator sensitivities for metal staining.