Determination of solifenacin in human plasma by liquid chromatography–tandem mass spectrometry

A liquid chromatography–electrospray tandem mass spectrometry method was developed and validated to quantitate solifenacin in human plasma. The assay was based on protein precipitation with methanol and liquid chromatography performed on a pentafluorophenylpropylsilica column (50 × 4 mm, 3 μm particles), the mobile phase consisted of methanol – 100 mM ammonium acetate containing 1% of formic acid (90:10, v/v). Quantification was through positive-ion mode and selected reaction monitoring at m/z 363 → 193 and 368 → 198 for solifenacin and the internal standard solifenacin-D5, respectively. The lower limit of quantitation was 0.47 ng/ml using 0.25 ml of plasma and linearity was demonstrated up to 42 ng/ml. Intra-assay and inter-assay precision expressed by relative standard deviation was less than 11% and inaccuracy did not exceed 11% at all levels. The assay was applied to the analysis of samples from a pharmacokinetic study.