Identification of Flavonoid Aglycones in Ethyl Acetate Multi-Components of Scutellaria barbata D. Don by HPLC/ESI-MS

The flavonoid aglycones in ethyl acetate multi-components of Scutellaria barbata D.Don were identified by high performance liquid chromatography/positive electrospray ionization-mass spectrometry (HPLC/ESI-MS). Because the fragmentation behaviors of the flavonoid aglycones were crucial for the identification of unknown flavonoid aglycones, the characteristic MS fragments of five subclasses of flavonoid aglycones were initially studied using positive ion ESI-MS. The results indicate that the consequential loss of two CO molecules can be regarded as the diagnostic fragmentation pathway of isoflavone. ^0,2A⁺ and ^2，3B⁺ fragments originated from the cleavage of C—C bonds of C-ring at positions 0/2 and 2/3 are the characteristic fragments of flavonol and isoflavanone respectively, and ^0,4B-H₂O+H⁺ can be used to identify the flavanones. Based on these characteristic fragments, six flavonoids including isocarthamidin, scutellarin, luteolin, naringenin, 4’hydroxy-wogonin and apigenin are identified unambiguously. Then, combined with the chromatographic retention time and UV spectra, another six compounds are identified tentatively.