Determination of pseudoprotodioscin in rat plasma by UPLC–MS/MS: Assay development and application to pharmacokinetic study

An original and sensitive ultraperformance liquid chromatography–tandem mass spectrometric (UPLC–MS/MS) method for the determination of pseudoprotodioscin (PPD) in rat plasma was developed and validated. Digitoxin was applied as an internal standard. Plasma samples were processed by acetonitrile-mediated plasma protein precipitation and chromatographed using a step gradient program on a C18 column (2.1   ×   50   mm i.d., 1.7   μm). The mobile phase was comprised of acetonitrile and 0.1   mmol   L −1 aqueous lithium acetate mixed with 0.03% formic acid at the flow rate of 0.2   mL   min −1 . Multiple reaction monitoring (MRM) transitions were performed for detection and lithium adduct ions were employed with a significant improvement of the response of the analytes in electrospray positive ionization mode. The concentration range of calibration curve was linear over the range 2–5000   ng   mL −1 . The intra- and inter-day precisions were all less than 11.5% and accuracies were within the range of 94.1–103.5%, and the analytes exhibited no severe matrix effect. The validated method was successfully applied in the pharmacokinetics of PPD after intragastric (50   mg   kg −1 ) and intravenous (4   mg   kg −1 ) administration in rats. PPD showed rapid excretion and with bioavailability of simply about 5.7% in rats.