Determination of 3-mercaptolactate, mercaptoacetate and N-acetylcysteine in urine by gas chromatography.

A method is described for the determination of 3-mercaptolactate, mercaptoacetate (thioglycolate) and N-acetylcysteine in urine. As these compounds are mainly excreted as their mixed disulfides with cysteine, they are first reduced to the free thiols by an insoluble polymer containing thiol groups. After purification by chromatography on an organomercurial adsorbent, the compounds are converted to benzyl derivatives by extractive alkylation and determined by gas chromatography. The identity of the compounds analyzed was verified by mass spectrometry. It was demonstrated that mercaptolactate and mercaptoacetate are almost entirely excreted as their mixed disulfides with cysteine, whereas appreciable amounts of N-acetylcyteine are present as the symmetrical disulfide and the free thiol. The urinary excretion of the compounds from healthy human beings was also studied.