Determination of N-acetyl-L-cysteine in biological fluids.

For determination of a drug in biological fluids, accuracy and sensitivity of detection of the adopted method are decisive parameters, but practical aspects such as time and necessary instrumentation are equally important. In the case of N-acetyl-L-cysteine, sample pretreatment can be kept at a minimum if sufficiently selective modes of derivatization, chromatography and detection are employed. Its concentration in serum is between 1 and 20 mumol/l; for quantitative analysis capillary gas chromatography and mass fragmentographic detection are employed. For urine with its ten-fold higher concentration the preferred method is reversed-phase high-performance liquid chromatography after thiol-selective derivatization.