Reference compounds, comprising specnuezhenide, oleuropein, nuezhenidic acid, ligustroflavone, G13, oleoside 11-methyl ester, tyrosol, hydroxytyrosol, salidroside, acteoside, protocatechuic acid, galuteolin, apigenin, quercitrin, rutin, luteolin, quercetin, oleanolic acid, ursolic acid, betulin, emodinmonomethyl ether, 3β-O-acetylpomolic acid, oleonuezhenide, 6′-O-trans-cinnamoyl-8-epikingisidic acid, ligulucidumoside A, ligulucidumoside C, oleuropeinic acid, echinacoside, 3β-O-acetylpomolic acid, oleonuezhenide, 6′-O-trans-cinnamoyl-8-epikingisidic acid, ligulucidumoside A, ligulucidumoside C and geniposide (purity ≥98%), were provided by Yifang S&T Co. Ltd (Tianjin, China), the National Institutes for Food and Drug Control and Sichuan Weikeqi Pharmaceutical Technology Co. Ltd. Methanol and acetonitrile (chromatographic purity) were obtained from Fisher Scientific (Fair Lawn, NJ, USA). The Milli-Q water purification system (Millipore, Bedford, MA, USA) was used to produce Ultrapure-water. All reagents were analytical grade. |