Kaempferol

Chromatographic grade acetonitrile was purchased from Avantor Performance Materials, Inc. (Center Valley, PA, USA). Chromatographic grade methanol was purchased from Tianjin Shield Fine Chemicals Co., Ltd. (Tianjin, China) Analytical grade glacial acetic acid was purchased from Tianjin Fuyu Fine Chemical Co., Ltd. (Tianjin, China) The water was Wahaha pure water. Coomassie brilliant blue was purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China). The isoquercitrin, astragalin, quercetin and kaempferol with purity greater than 98% were purchased from Chengdu Pufei De Biotech Co., Ltd. (Sichuan, China). The 4-nitrocatechol and 4-nitrophenol were purchased from A Johnson Matthey Company (Royston, UK). Phenacetin and 6β-Hydroxytestosterone and clomethiazolewere purchased from Sigma (St. Louis, MO, USA). Testosterone was purchased from Beijing J & K Technology Co., Ltd. (Beijing, China). NADPH was purchased from Blue Chemical Technology Co., Ltd. (Shanghai, China). Ketoconazole was purchased from Tokyo Chemical Industry (Tokyo, Japan).

Quercetin coarse powder (purity > 95%) was purchased from Shaanxi Ci Yuan Biotechnology Co., Ltd. (Xi’an, China); QT reference standard (purity > 98%) and kaempferol (internal standard, purity > 98%) were purchased from Chengdu Pufei De Biotech Co., Ltd. (Chengdu, China); Labrafac Lipophile WL 1349 was obtained from Beijing Fengli Jingqiu Pharmaceutical Co., Ltd. (Beijing, China). HPLC-grade methanol was purchased from Fisher Scientific (Waltham, MA, USA). Other chemicals were analytical grade.