Application of Direct Infusion Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry in Qualitative Analysis of Sixteen Compounds From Traditional Chinese Medicine

Direct infusion (DI) electrospray ionization quadrupole time-of-flight (Q-TOF) mass spectrometry was applied to analysis sixteen compounds from traditional Chinese medicines (TCMs). Characteristics of these compounds in electrospray ionization mass spectrometry (ESI-MS) and in MS/MS were observed to know the differences of ionization capacity and dissociation characteristics of structurally different compounds. The observation indicated that in order to maximize numbers of constituents detected, it is necessary to analyze sample in both positive and negative mode. The existence of carbonyl group in structure seems to be a factor that favors the formation of quasi-molecular ion (QMI) or other adduct molecular ion (OAMI) in positive mode. When cone voltage was 30V, most compounds could form mass spectral peaks of QMIs or OAMIs. However, in-source collision-induced dissociation (CID) seemed unable to be completely avoided by altering cone voltage. Analysis was recommended at three different cone voltages of 10V, 30V and 50V. MS/MS was proved to be an effective way to obtain additional structural information because fragment ions were observed for all QMIs and OAMIs in MS/MS. The developed method has been successfully applied in our study on Si-Wu-Tang. The method is useful for quick qualitative analysis of constituents in mixture samples of TCM.