High‐throughput determination of carbocysteine in human plasma by liquid chromatography/tandem mass spectrometry: application to a bioequivalence study of two formulations in healthy volunteers

A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method to determine carbocysteine in human plasma was developed and fully validated. After methanol‐induced protein precipitation of the plasma samples, carbocysteine was subjected to LC/MS/MS analysis using electrospray ionization (ESI). The MS system was operated in the selected ion monitoring (SRM) mode. Chromatographic separation was performed on a Hypurity C 18 column (i.d. 2.1 mm × 50 mm, particle size 5 µm). The method had a chromatographic running time of 2.0 min and linear calibration curves over the concentration ranges of 0.1–20 µg/mL for carbocysteine. The lower limit of quantification (LLOQ) of the method was 0.1 µg/mL for carbocysteine. The intra‐ and inter‐day precision was less than 7% for all quality control samples at concentrations of 0.5, 2.0, and 10.0 µg/mL. These results indicate that the method was efficient with a simple preparation procedure and a very short running time (2.0 min) for carbocysteine compared with methods reported in the literature and had high selectivity, acceptable accuracy, precision and sensitivity. The validated LC/MS/MS method has been successfully used to a bioequivalence study of two tablet formulations of carbocysteine in healthy volunteers. Copyright © 2006 John Wiley & Sons, Ltd.