Histochemical staining of cadmium with thiazolylazophenol derivatives

In the search for a more sensitive and specific chelant for cadmium, thiazolylazophenol derivatives were synthesized and their staining properties for cadmium and zinc were examined. The compounds synthesized for this study were identified as being thiazolylazophenol derivatives via analysis of their melting point, absorption maxima and their C, H, N, S content. Thiazolylazo-p-methoxyphenol (TAMe) was found to stain cadmium and zinc differentially and with the highest optical density amongst dyestuffs reported to date. The plots of absorbance vs. metal concentration for thiazolylazophenol chelates gave a straight line obeying the Beer-Lambert law. Only the plot for TAMe-zinc chelates deviated significantly from a straight line above a specific concentration. The change from a 2:1 (chelant:metal) to a 3:1 (chelant:metal) complex is suggested to be the reason for the differential coloring.