Decomposition of Sudan Black B Causing an Artefact in the Staining of Lipids

Sudan black B was found to be decomposed in acid solutions. This decomposition was rapid below pH 4. Above this pH the decomposition was markedly slower. After mild acid hydrolysis, the product was studied chromatographically and found to contain a basic dye with a pK of about 4, a brown color above, and a red color below pH 4. The nature of the product of hydrolysis indicates that it can stain nucleoproteins and mucopolysaccharides, hence a brownish stain is more indicative of artefact than the staining of lipids.