Determination of total tiopronin in human plasma by LC–ESI–MS using tris (2-carboxy-ethyl) phosphine as reducing reagent and methyl acrylate as derivatization reagent for the thiol group

A quantitative method for the determination of total tiopronin (TP) in human plasma was developed by liquid chromatography with electrospray ionisation (ESI) mass spectrometric detection. After reduction with tris (2-carboxy-ethyl) phosphine (TCEP) and derivatization with methyl acrylate (MA) for the thiol group of TP, plasma samples were processed successively by deproteinization and solid phase extraction. N-acetyl-l-cysteine (NAC) was selected as internal standard undergoing the same treatment as TP. The method was validated that it could meet the need of biological analysis. The lower limit of quantitation (LLOQ) of TP in plasma was 0.02 μg/mL. Finally, the method was successfully applied to a pharmacokinetic study in 20 healthy Chinese male volunteers after an oral dose of 200 mg TP tablets.