Liquid chromatography tandem mass spectrometry method for determination of N-acetylcysteine in human plasma using an isotope-labeled internal standard

A liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed to determine total N‐acetylcysteine in human plasma. Mass spectrometric detection was achieved in positive electrospray ionization and multiple reaction monitoring mode. The mass transition pairs of N‐acetylcysteine and the isotope‐labeled internal standard d3‐N‐acetylcysteine were 164 → 122 and 167 → 123, respectively. The method was linear over the range of 10–5000 ng/mL in human plasma. The adoption of trichloroacetic acid significantly enhanced the extraction recovery. The blank matrix was screened to minimize the influence of endogenous N‐acetylcysteine. After being fully validated, the method was successfully applied to the pharmacokinetic and bioequivalent study of N‐acetylcysteine after oral administration of 600 mg tablets to 24 healthy Chinese volunteers. Copyright © 2010 John Wiley & Sons, Ltd.