Determination of N-acetyl-S-(N-alkylthiocarbamoyl)-L-cysteine, a principal metabolite of alkyl isothiocyanates, in rat urine

A simple and rapid analytical procedure is described for N-acetyl-S-(N-alkylthiocarbamoyl)-L-cysteine (alkyl = benzyl, allyl, methyl, ethyl or n-butyl), a mercapturic acid with an unstable dithiocarbamic acid ester structure, which is found in rat urine as the principal metabolite of the corresponding alkyl isothiocyanate. Because such mercapturic acids decompose at pH values greater than 5 to N-acetylcysteine and alkyl isothiocyanate, the free isothiocyanate is converted with n-butylamine into the corresponding disubstituted thiourea, and, after extraction, measured by high-performance liquid chromatography using an ultraviolet detector. The recovery is ca. 100% and the precision is very good. The lower limit of detection is ca. 0.5 microgram of thiourea. The 24-h renal excretion of these mercapturic acids was determined in rats after administration of benzyl, allyl, methyl, ethyl or n-butyl isothiocyanate.