DETERMINATION OF CYSTEINE AND N-ACETYLCYSTEINE IN URINE BY LIQUID-CHROMATOGRAPHY WITH INDIRECT AMPEROMETRIC DETECTION

Cysteine (CYS) and N-acetylcysteine (NAC) can be determined by liquid chromatography with indirect amperometric detection with iodine as oxidizing reagent. The linear range of detection can be adapted to the analytical requirements by adaptation of the generating current. With a generating current of 25-mu-A detection limits were found of 2 ng for CYS and 1.5 ng for NAC. Detector responses were linear up to 110 and 80 ng injected, respectively, with correlation coefficients better than 0.9998. The precision of the analysis, as assessed by repeated injection of a standard solution, was 0.6 %. After reduction of the sulphur compounds with dithiothreitol (DTT), urine samples were analyzed without further pretreatment using an ion-pair separation system. Endogenous levels of CYS and NAC in urine could be determined easily. The application to serum samples is also demonstrated.