Identification and quantification of free radical scavengers in the flower buds of Lonicera species by online HPLC-DPPH assay coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

Flos Lonicerae, derived from the flower buds of several medicinal Lonicera species, is a commonly used herbal medicine with multiple pharmacological activities, one of the major ones being antioxidant activity. In this study, free radical scavengers in the flower buds of six Lonicera species were screened, identified and quantified by online HPLC-DPPH (1,1-diphenyl-2-picrylhydrazyl) assay coupled with LC quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). The antioxidants were firstly screened from the complex plant matrix by the online HPLC-DPPH assay. Then the active compounds were identified by LC Q-TOF MS/MS, and the possible fragmentation pathways were proposed. The reactivity of antioxidants available was investigated using an internal standard method by online LC assay. The contents of 12 antioxidants were also determined or estimated by HPLC coupled with diode array detector. The total antioxidant capability determined by the online method was used as the marker to evaluate the quality of Flos Lonicerae. The results were important to clarify the material basis and therapeutic mechanism of Flos Lonicerae.