Identification and quantification of oleanolic acid and ursolic acid in Chinese herbs by liquid chromatography-ion trap mass spectrometry.

A rapid and sensitive method for the identification and quantification of ursolic acid (UA) and oleanolic acid (OA) in Chinese herbs is described. The method combines liquid chromatography (LC) with ion trap-mass spectrometry (IT-MS) detection. The UA and OA standard solution were directly infused into IT-MS for collecting MS(n) spectra. The major fragment ions of UA and OA were confirmed by MS(n) at m/z 455, 407, 391, 377 and 363 in negative ion mode, and m/z 457, 439, 411 and 393 in positive mode, respectively. The possible main cleavage pathway of fragment ions was studied. UA and OA provided good signals corresponding to the deprotonated molecular ion [M - H](-). The method is reliable and reproducible, and the detection limit is 5 ng/mL. The method was validated in the concentration range of 0.04-40 μg/mL; intra- and inter-day precisions ranged from 0.78 to 2.15%, and the accuracy was 96.5-108.2% for UA and OA. The mean recovery of UA and OA was 97.1-106.2% with RSD less than 1.86%. An LC-IT-MS method was successfully applied to determine the UA and OA in nine Chinese herbs.