Simultaneous Determination of Oleanolic Acid, p-Coumaric Acid, Ferulic Acid, Kaemperol and Quercetin in Rat Plasma by LC–MS-MS and Application to a Pharmacokinetic Study of Oldenlandia diffusa Extract in Rats

A simple, rapid and sensitive liquid chromatography tandem mass spectrometry method is presented for the simultaneous determination of oleanolic acid, p-coumaric acid, ferulic acid, kaemperol and quercetin in rat plasma. Glycyrrhetinic acid was used as an internal standard, and sample pretreatment consisted of a liquid-liquid extraction. Chromatographic separation was achieved on a Gemini 110A C18 column (50 × 2.0 mm i.d., 5 µm) by gradient elution with a mobile phase consisting of methanol, acetonitrile and 0.01% formic acid in water. Tandem mass spectrometric detection was conducted using multiple reaction monitoring under negative ionization mode. Calibration curves offered linear ranges of two orders of magnitude with r > 0.99. The method was validated in terms of matrix effect, intra-day and inter-day precision, accuracy, linearity, specificity and stability. The relative standard deviation of intra-day and inter-day variations ranged from 2.66 to 14.74% and 1.9 to 14.55%. No substantial endogenous interference from blank plasma was observed. The method has been successfully applied to a pharmacokinetic study of Oldenlandia diffusa extract after oral administration in rats.