Histochemical staining of chromium with 2-(8-quinolylazo)-4,5-di-p-tolylimidazole.

A new highly sensitive staining agent for chromium (Cr) has been introduced. This staining agent, 2-(8-quinolylazo)-4,5-di-p-tolylimidazole (QTI), was found to be more than ten times as sensitive for Cr than the conventional staining agent, Chromazurol S, and QTI also stained cadmium, copper, lead and zinc. Differentiation between the staining of Cr and other metals was achieved by immersing the tissue sections in dilute alkylamine solutions before they were stained with QTI. Thus, it was possible to selectively stain for Cr by blocking other metals.