Sensitive LC–ESI–MS method for determination of tiopronin in human plasma
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A sensitive liquid chromatographic-electrospray ionization-mass spectrometric (LC-MS) method has been developed for direct measurement of the concentration of tiopronin in human plasma. Hydrochloric acid solution was used to stabilize the tiopronin and prevent formation of a dimer, or reaction with endogenous thiols. The method involved liquid-liquid extraction of tiopronin from plasma samples with ethyl acetate, simple reversed-phase chromatography, and mass spectrometric detection with nanogram detection limits. Acetaminophen was used as internal standard (IS). The limit of quantification was 5 ng mL-1 (RSD 4.3%). The method was validated within the linear range 5-500 ng mL-1. The correlation coefficient for the calibration regression line was 0.9997 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for a pharmacokinetic study with human subjects. Among the pharmacokinetic data obtained, t 1/2 was 2.37 ᠰ.63 h and T max was 4 h.