Electrospray Ionization Quadrupole Time-of-flight Tandem Mass Spectrometry of Iridoid Glucosides in Positive Ion Mode

The mass spectral fragmentation behaviors of iridoid glucosides(IGs) was studied via electrospray ionization(ESI) quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS) in the positive ion mode. The homogeneous IGs, such as 7,8-cyclopentene-type and cyclopentane-type IGs, the main and typical losses of these classes of compounds are the H2O, CO2, CH3OH, CH3COOH and a glucosidic unit, which indicate the presence of OH, COOH, COOCH3, CH3COO and glucosidic groups on the aglycone moiety. The common fragment ion [Glc+Na](+) (m/z 185. 0) was detected, due to the existence of glucosidic unit. In addition, the cleavages of the dihydro-pyranoid ring were observed in the different sub-classes, but no cleavages were observed in other parts of the aglycone moieties and glucosidic units. The mass spectral fragmentation patterns of IGs in positive ion mode were less characteristic than those in negative ion mode, and the ion intensities were also weaker than those in negative ion mode.