Extraction, Enrichment, and Quantification of Main AntioxidantAglycones of Flavonoids
and Tannins from Melastoma Dodecandrum Lour.: Guided by UPLC-ESI-MS/MS

2.2. Chemicals. /e reference substances including p-coumaric acid, gallic acid, 
ellagic acid, apigenin, naringenin, luteolin, kaempferol, quercetin, vitexin, and
 isovitexin were obtained from Chengdu Alfa Biotechnology Co., Ltd.
(Chengdu, China). /eir purity was all greater than 98% (w/
w). Trolox and 1,1-diphenyl-2-picrylhydrazyl radical 2,2-
diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH), 2.2′-
azino-bis(3-ethylbenzenothiazoline6-sulfonic acid) (ABST),
and 2,4,6-tripyridyl-s-triazine (TPTZ)