Abstract

Over the years questions have been raised by tanners concerning dyes which are based on benzidine and benzidine derivatives and also whether such dyes are present in various dye mixtures. It has now become accepted that benzidine itself has a positive cancer response in humans. While dyes based on benzidine are themselves not so critical, these dyes can undergo degradation by light or chemicals to form benzidine. Additionally in the production stage it is possible to have small quantities of benzidine present. Consequently it is very clear why these dyes based on benzidine have a high toxicity potential and are forbidden in many countries. More recent is the move to question the use of dyes containing certain benzidine derivatives, i.e. ortho-tolidine and ortho-dianisidine, since these intermediates test positive in some standard laboratory mutagenicity tests. The dyes containing the sulphonated benzidine moiety are not classified as mutagenic and continue to be in many companies’ dye ranges. The sulphonation gives these more hydrophilic derivatives a quite different metabolic breakdown. A relatively simple analytical test has been developed for benzidine and non-sulphonated diaminobiphenyl bases (e.g. orrho-tolidine, ortho-dianisidine, ortho-dichloro benzidine etc.) using thin layer chromatography. The method has been optimised to separate benzidine from the other diaminobiphenyl bases.