Quantitative determination and pharmacokinetic study of casticin in rat plasma by liquid chromatography–mass spectrometry

A specific and sensitive liquid chromatography–mass spectrometry method has been developed and validated for identification and quantification of casticin in rat plasma after oral and intravenous administrations. Kaempferol was employed as an internal standard (IS). Liquid–liquid extraction using dichloromethane was applied to extract the casticin and the internal standard from plasma. Chromatographic separation was achieved on a Zorbax SB C18 column (100 mm × 3.0 mm, i.d.: 3.5 μm) with a mobile phase of methanol: 0.05% formic acid aqueous solution (60:40, v/v) at a flow rate of 0.4 mL/min for 10 min. The detection was performed by selected ion monitoring (SIM) mode via positive electrospray ionization (ESI) interface. The lower limit of detection (LLOD) was 7 ng/mL (S/N = 5). The calibration curves were linear (r > 0.9996) over the concentration range from 14.06 to 7187 ng/mL. Intra-day and inter-day precisions (RSD%) were within 10% and accuracy (RE%) ranged from −8.2% to 1.0%. The extraction recovery at three quality control (QC) concentrations ranged from 91% to 102%. The validated method was successfully applied to the pharmacokinetic study of casticin after both an oral and an intravenous administrations to rats and the absolute bioavailability is 45.5 ± 11.0%.