Syringic acid

The reference compounds of ferulic acid and 3,4-dihydroxybenzoic acid were purchased from Ark Pharm (Chicago, IL, USA), caffeic acid was purchased from Aladdin Chemistry Company (Shanghai, China), and syringic acid, vanillic acid, 4-hydroxybenzoic acid and p-coumaric acid were supplied by Adamas Reagent Company (Basel, Switzerland). All standard substance purities were determined to be higher than 98%. Butylparaben was used as an internal standard (IS) which was provided by Guangfu Fine Chemical Research Institute (Tianjin, China). Methanol of HPLC-grade was obtained from Amethyst Chemicals (Beijing, China). HPLC-grade acetic acid was bought from ANPEL Scientific Instrument Company (Shanghai, China). Ultra-pure water for the UHPLC mobile phase was prepared by a Milli-Qwater purification system (Millipore, Molsheim, France).
E. purpurea was purchased from Xi’an Ruibo Biological Technology Co. Ltd. (Xi’an, China) in October, 2016 and identified by Prof. Li Yao in Harbin Medical University.

Epicatechin, kaempferol, quercetin, rutin, isoquercitrin, syringic acid, p-coumaric acid, chlorogenic acid, cryptochlorogenic acid, caffeic acid, ferulic acid and gallic acid were purchased from Adamas Reagent, Ltd. (Shanghai, China). Other standard reference materials including 4-methoxysalicylic acid, p-hydroxycinnamic acid, isoferulic acid, 1,3-dicaffeoylquinic acid, gentiopicrin, grosvenorine, diosmin, isorhamnetin and baicalein were obtained from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). 2,4,6-tri(pyridin-2-yl)-1,3,5-triazine (TPTZ), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 4-nitrophenyl α-D-glucopyranoside (p-NPG) were all obtained from Adamas Reagent, Ltd. (Shanghai, China). Acetonitrile and formic acid (99.9%, HPLC grade) were obtained from Thermo Fisher Scientific (Waltham, MA, USA). Cellulase (400 u/mg) from Trichoderma Vride G, hemiCellulase (20,000 u/g) and pectinase (500 u/mg) from Aspergillus niger were all supplied from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). All other reagents and chemicals used in this study are analytical grade.