Ethyl gallate

The reference standards of chlorogenic acid, caffeic acid, ethyl gallate, 3-butyl-phthalide, benzoyloxypaeoniflorin, senkyunolide I, gallic acid, oxypaeoniflorin, vanillic acid, albiflorin, paeoniflorin, ferulic acid, 1,2,3,4,6-pentagalloylglucose, benzoylpaeoniflorin, paeonol, and ligustilide (the purities of all standards were above 98.0%) were supplied by Shanghai Yuanye Bio-Technology Co., Ltd. Appropriate amounts of the reference standards were mixed and dissolved in methanol in a 10-mL measuring flask, then filtered and set aside.

The standard compounds paeoniflorin, albiflorin, catechin, lactiflorin, benzoylpaeoniflorin, 1,2,3,4,6-O-pentagalloylglucose, ethyl gallate, 3,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid were purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Gallic acid, oxypaeoniflorin, methyl gallate, benzoic acid, and apiopaeonoside were obtained from Chengdu Push Bio-Technology Co., Ltd. (Chengdu, China). The purity of each standard was >98%. The chemical structures of the 14 reference compounds were presented in Supplementary Figure 1. A Milli-Q system (Millipore, MA, United States) was used to prepare ultra-pure water. HPLC-grade acetonitrile and methanol were procured from Tedia (Fairfield, OH, United States), and formic acid (LC-MS grade) was purchased from Aladdin (California, United States). All other reagents were of analytical grade.

Chromatographically pure acetonitrile and acetic acid was purchased from Thermo Fisher (Waltham, MA, USA). Catechins (C), epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), epigallocatechin gallate (ECG), gallocatechin gallate (GCG), epigallocatechin-3-O-gallate (EGCG), procyanidin B1, procyanidin C1, kaempferitrin, rutin, isoquercetin, myricetin-3-O-galactoside, myricetin-3-O-rutinoside, galloylglucose, gallic acid, cinnamic acid, chlorogenic acid, shikimic acid, p-coumaric acid, quinic acid, pyrogallic acid, theogallin, strictinin, theanine, theobromine, ethyl gallate, tannic acid, caffeine, L-sodium glutamate, and D-glucose were purchased from Yuanye (Shanghai, China). Quercetin, myricetin, kaempferol, and kaempferol-3-O-glucoside were purchased from Shanghai Zzstandard (Shanghai, China). Amino acid mixture standard reagent, borate buffer solution, o-phthalaldehyde (OPA), and 9-fluorene methyl chloroformate (FMOC) were purchased from Agilent Technology (Santa Clara, CA, USA). n-Hexane was purchased from Thermo Fisher (Waltham, MA, USA). 2-Methyl-3-heptanone and n-alkanes (C₇–C₃₀) were purchased from Sigma (St. Louis, MO, USA).