Simultaneous determination of five lignan constituents of Wuzhi capsule in rat plasma by LC–MS/MS: Application to pharmacokinetic study

A rapid sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous determination of multiple bioactive lignan constituents of Wuzhi capsule in rat plasma. The extraction, separation, and analytical conditions were optimized. Five constituents of the Wuzhi capsule (schisandrin, schisandrol B, schisantherin A, schisanhenol, and deoxyshisandrin) were determined by the LC–MS/MS method. Liquid–liquid extraction with methyl tert-butyl ether was carried out using bifendate as the internal standard. The five bioactive constituents were separated on a Zorbax SB-C18 reserved-phase column (100 mm × 2.1 mm i.d., 3.5 μm) by isocratic elution using a mobile phase consisting of acetonitrile, methanol, and 0.1% aqueous formic acid (72:18:10, v/v/v) at a flow rate of 0.3 mL/min. The total run time was only 3.5 min. All analytes showed good linearity over a wide concentration range (r2 > 0.99) and their lower limit of quantification was 0.5 ng/mL. The average extraction recovery of the five analytes from rat plasma was more than 85%, and the intra-day and inter-day accuracy and precision of the assay were less than 15%. Our method was successfully used for pharmacokinetic study of the five components in the Wuzhi capsule.