Characterization and identification of isomeric flavonoid O-diglycosides from genus Citrus in negative electrospray ionization by ion trap mass spectrometry and time-of-flight mass, spectrometry

Flavonoid O-diglycosides are important bioactive compounds from genus Citrus. They often occur as isomers, which makes the structural elucidation difficult. In the present study, the fragmentation behavior of six flavonoid 0-diglycosides from genus Citrus was investigated using ion trap mass spectrometry in negative electrospray ionization (ESI) with loop injection. For the flavonoid O-rutinosides, [M - H - 308](-) ion was typically observed in the MS' spectrum, suggesting the loss of a rutinose. The fragmentation patterns of flavonoid O-neohesperidosides were more complicated in comparison with their rutinoside analogues. A major difference was found in the [M - H - 120](-) ion in the MS2 spectrum, which was a common feature of all the flavonoid O-neohesperidosides. The previous literature for naringin located the loss of 120 Da to the glycan part, whereas the present study for naringin had shown that the [M - H - 120](-) ion was produced by a retro-Diels-Alder reaction in ring C, and this fragmentation pattern was confirmed by the accurate mass measurement using an orthogonal time-of-flight mass spectrometer. Combined with high performance liquid chromatography (HPLC) and diode array detection (DAD), the established approach to the structural identification of flavonoid O-diglycosides by ion trap mass spectrometry was applied to the analysis of extracts of two Chinese medicines derived from genus Citrus, namely Fructus aurantii and E aurantii immaturus. According to the HPLC retention behavior, the diagnostic UV spectra and the molecular structural information provided by multistage mass spectrometry (W) spectra, 13 flavonoid O-glycosides in F aurantii and 12 flavonoid O-glycosides in F a. immaturus were identified rapidly. (C) 2007 Elsevier B.V. All rights reserved.