Determination of zofenopril and its active metabolite in human plasma using high-performance liquid chromatography combined with a triple-quadruple tandem mass spectrometer.

A simple, selective and sensitive LC–MS-MS method has been developed and validated to simultaneously quantify zofenopril and its active metabolite zofenoprilat in human plasma, using diazepam as internal standard. 1,4-Dithiothreitol was used as a reducer to release and stabilize the thiol group of zofenoprilat from dimer and mixed forms with endogenous thiols in the treatment of plasma samples. After a liquid–liquid extraction with methyl tert-butyl ether under acidic conditions, the post-treatment samples were analyzed on an Agilent ZORBAX Eclipse XDB-C8 column interfaced with a triple-quadruple tandem mass spectrometer using positive electrospray ionization. A solution of methanol and 0.1% formic acid solution (85 : 15, v/v) was used as the isocratic mobile phase with a flow rate of 0.2 mL/min. The method was validated to demonstrate the specificity, lower limit of quantitation, accuracy and precision of measurements. The validated LC–MS-MS method has been successfully applied to study the pharmacokinetics of zofenopril calcium in healthy Chinese volunteers.