Metabolism of nine benzidine-congener-based azo dyes in rats based on gas chromatographic assays of the urine for potentially carcinogenic metabolites.

Metabolism experiments were conducted with rats dosed with nine azo dyes based on dimethyl-, dimethoxy-, or dichlorobenzidine to determine whether the free amine congeners, their monoacetyl or diacetyl metabolites, or alkaline hydrolyzable conjugates were excreted in the urine. After preliminary tests of the dyes, 2-mg doses were administered to each animal and urine samples were collected at intervals up to 96 hours. EC/GC procedures were based on the analysis of heptafluorobutyryl derivatives of the free amine congener moieties or their monoacetyl metabolites. Peak levels of metabolites were excreted either 0-12 or 12-24 hours after administration and, in seven of nine instances, no metabolites persisted in the urine after 48 hours. Minimum detectable levels of all metabolites were 12 ppb or less. All nine dyes were shown to be converted to measurable levels of their benzidine-congener-based metabolites in rats.