Quantitative determination of tiopronin in human plasma by LC-MS/MS without derivatization

Tiopronin (TP) is a synthetic thiol compound without chromophore. By optimizing the chromatographic conditions and sample preparation processes, an improved LC-MS/MS analytical method without derivatization has been developed and validated to determine TP concentrations in human plasma. After reduction with 1,4-dithiothreitol, plasma samples were deproteinized with 10% perchloric acid. The post-treatment samples were analyzed on a C₈ column interfaced with a triple quadrupole tandem mass spectrometer in negative electrospray ionization mode. Methanol-5 mmol/L ammonium acetate (20:80, v/v) was used as the isocratic mobile phase. The assay was linear over the concentration range of 40.0-5000 ng/mL. The intra- and inter-day precisions were within 12.9% in terms of relative standard deviation and the accuracy within 5.6% in terms of relative error. This simple and sensitive LC-MS/MS method with short analytical time (3.5 min each sample) was successfully applied to the pharmacokinetic study of TP in healthy Chinese male volunteers after an oral dose of 300 mg TP.