Determination of 20(S)-protopanaxadiol ocotillol type epimers in rat plasma by liquid chromatography tandem mass spectrometry.

To study stereoselectivity in the pharmacokinetics of each epimer, a rapid, specific and reliable liquid chromatography tandem mass spectrometry method has been established for simultaneous quantitation of both epimers in rat plasma. Plasma samples were pretreated by liquid-liquid extraction. Chromatographic separations were performed on a Shim-pack XR-ODS C18 column (50 mm × 2.1mm, i.d., 2.2 μm) with an isocratic elution. Both epimers and the internal standard tanshinone II A were ionized with an ESI source operated in positive ion mode and measured by selective reactions monitoring mode. Calibration curve was linear over the concentration range of 1-1000 ng/mL with the lower limit of quantitation of 1 ng/mL for both epimers. Intra and inter-day precisions were less than 6.7% and 9.5%, and the accuracy was within ±5.8% for both epimers. The validated method has been successfully applied to a pharmacokinetic study of the two epimers in rats after oral administration.