LC-MS-MS Quantitative Determination of Ursolic Acid in Human Plasma and Its Application to Pharmacokinetic Studies

A sensitive and specific liquid chromatography-electrospray ionization-tandem mass spectrometry method has been developed and validated for the identification and quantification of ursolic acid in human plasma using glycyrrhetic acid as an internal standard. The method involves extraction with methyl tert-butyl ether. The analyte was separated on a C₁₈ column and analyzed in multiple reaction monitoring mode with a negative electrospray ionization interface using the [M-H]− ions, m/z 455.4 for ursolic acid and m/z 469.5 → m/z 425.5 for glycyrrhetic acid. The method was validated over the concentration range of 0.86-110.0 μg L⁻¹. The intra- and inter-day precisions were less than 13.53% relative standard deviation (RSD) and the accuracy was within −4.76% in terms of relative error (RE). The lower limit of quantification was 0.86 μg L⁻¹ with acceptable precision and accuracy. There were almost no matrix effects. Recovery of ursolic acid from spiked drug-free plasma was higher than 68%. The method was used to study the pharmacokinetic profile of ursolic acid in human plasma after oral administration of Jieyu capsules.