Glycyrrhizic acid

Standard compounds of albiflorin, paeoniflorin, ferulic acid, senkyunolide I, quercetin, isoliquiritigenin, atractylenolide III, ligustilide, atractylenolide II, liquiritin, liquiritigenin, saikosaponin c, glycyrrhizic acid, saikosaponin a and naringenin as an internal standard (IS) (≥98% purity) were purchased from Chengdu Herbpurify Co., Ltd. (Chengdu, China). The structures of these compounds are shown in Figure 3.
Acetonitrile (HPLC grade) was purchased from Fisher (Fair Lawn, NJ, USA). Ultrapure water with a sensitivity of 18.2 W was prepared from a Milli-Q water purification system (Millipore, Billerica, MA, USA). All other chemicals were analytical grade.

Paeoniflorin, baicalin, scutellarein, liquiritigenin, baicalein, glycyrrhizic acid, wogonin, and oroxylin A were purchased from Chengdu Herbpurify Co., Ltd. (Sichuan, China). glycyrrhizic acid ammonium salt and norwogonin were purchased from ChemFaces (China). All other reagents and solvents were of high performance liquid chromatography (HPLC) grade. Deionized water was purified using a Milli-Q system (Millipore, Bedford, MA, United States). Scutellaria baicalensis Georgi (Hebei Province), Glycyrrhiza uralensis Fisch (Inner Mongolia of China), Paeonia lactiflora Pall (Anhui Province), and Ziziphus jujuba Mill (Henan Province) were authenticated by Dr. Ehu Liu (State Key Laboratory of Natural Medicines, China Pharmaceutical University, China).