Multi-stage mass spectrometric analysis of saponins in glycyrrhiza radix

The fragmentation pathways of six triterpenoid saponins from Glycyrrhiza radix were investigated using LC-MS/MS. Depending on the structure and the substitution pattern, different molecular adduct ions, [M+NH4]+ or [M+H]+, were observed in the positive ESI spectra. In the positive MSn spectra from the molecular adduct ions, characteristic product ions corresponding to the loss of dehydrated glucuronic acid or glucuronic acid were detected and they indicated the type of substitution and structural modification. Fragment ions originating from the sapogenin moiety in the positive mass spectra were predominantly provided by saponins having an 11-oxo-12-ene structure. On the other hand, the saponins gave fragment ions corresponding to the sugar moiety in the negative mass spectra. These results indicate the specific property of saponins that have the 11-oxo-12-ene structure to localize positive or negative charge in the mass spectrometric ionization and fragmentation process. Information obtained from the present study can be utilized for structural elucidation of triterpenoid saponins in the Glycyrrhiza radix by LC-MS.