Determination of N-acetylcysteine in human plasma by liquid chromatographycoupled to tandem mass spectrometry

An analytical method for the determination of total N-acetylcysteine in hum an plasma has been developed, validated and applied to the analysis of samp les from a phase I clinical trial. The analytical method consists of plasma digestion with dithiothreitol in order to reduce all the oxidized forms of N-acetylcysteine, and extraction with ethyl acetate followed by determinat ion of levels by an LC-MS-MS method. The intra- and inter-assay precision a nd accuracy of this technique were good and the limit of quantitation was 5 0 ng/ml of plasma. The concentration working range was established between 50 ng/ml and 1000 ng/ml. This method has been used in the analysis of appro ximately 800 human plasma samples from a clinical study with 24 volunteers; the precision of the quality controls was in the range 8.7 to 13.4% and th e accuracy was in the range -5.9 to 8.5%, expressed as the RSD and the rela tive error, respectively. (C) 2000 Elsevier Science B.V. All rights reserve d.