A hybrid method for the determination of tubeimoside I in rat plasma after oral administration by LC-IT-TOF and UPLC-MS/MS.

Tubeimoside I (Tub) is a triterpenoid saponin isolated from Bolbostemma paniculatum[Maxim]Franquet. A sensitive and validated method was developed to determine Tub in rat plasma. This method combined the qualitative and quantitative advantages from liquid chromatography coupled with hybrid ion trap-time of flight mass spectrometer (HPLC-DAD-IT-TOF-MS) and a triple quadrupole-linear ion trap mass spectrometer 5500 (Qtrap 5500), owing to the narrow molecular range of Qtrap 5500 relative to the molecular weight of Tub. Initially, ion detection was achieved using negative ionization mode along with full scan on IT-TOF-MS. The detected precursor and product ions of Tub with the optimal mass parameters were determined on Qtrap 5500 by an online stepped optimization strategy and operated in negative multiple reaction monitoring mode. A simple methanol precipitation was employed with saikosaponin A as internal standard. The method was validated over the range from 20 to 2000 ng/mL with a lower limit of quantification of 20 ng/mL for Tub in plasma. The developed method was successfully applied to the pharmacokinetic study of Tub in rats following oral administration. Moreover, this method has some directive significance for the determination of other drugs whose parent ions exceeding the upper detection limit in Qtrap 5500.