Spectra grade methanol and acetonitrile were purchased from Tedia (Fairfeild, USA). HPLC-grade formic acid was purchased from Kermel Chemical Reagent Co., Ltd. (Tianjin, China). Purified water was purchased from Wahaha (Zhejiang, Hangzhou, China). The reference standards triptolide, triptonide, triptophenolide, tripterifordin, wilforgine, wilforine, celastrol, demethylzeylasteral, wilforlide A, and pristimerin were purchased from Sichuan Weikeqi Biological Technology Co., Ltd. (Sichuan, China), and their purity was greater than 98%. Commercial Tripterygium glycosides tablets (TGT) were purchased from 13 factories (A-J), three batches of commercial Tripterygium wilfordii tablets (TWT) were from one factory (K), six different batches of commercial Tripterygium hypoglaucum hutch tablets (THHT) were purchased from two factories (L and M).

Formic acid was HPLC grade obtained from Fisher (Fair Lawn, NJ, USA). Triptolide (Batch No. wkq18062706, purity?≥?98%), triptonide (Batch No. wkq18030812, purity?≥?98%), triptophenolide (Batch No. wkq18031301), wilforgine (Batch No. wkq18051009, purity?≥?98%), wilforine (Batch No. wkq18080604, purity?≥?98%), demethylzeylasteral (Batch No. wkq18031201, purity?≥?98%), and celastrol (Batch No. wkq18042604, purity?≥?98%) were purchased from Sichuan Weikeqi Biological Technology, Co., Ltd. (Sichuan, P.R. China).

Triptolide (HPLC purity 99.49%), triptophenolide (HPLC purity 99.29%), celastrol (HPLC purity 98.33%), wilforgine (HPLC purity 99.53%), wilforine (HPLC purity 99.32%) and wilfortrine (HPLC purity 99.09%) were supplied by Weikeqi Biological Technology Co., Ltd (Sichuan, China). Wilfordine (HPLC purity 98%) was purchased from ChemFaces Biochemical Co., Ltd (Wuhan, China) and irbesartan (HPLC purity 99.8%) was used as internal standard (IS) and was obtained from National Institute for Food and Drug Control (Beijing, China).