The reference standards of stachydrine, scopoletin, hesperidin, 5,7-dimethoxycoumarin, limonin, nomilin, nobiletin, and tangeretin were obtained from Weikeqi (Sichuan, China). The compounds had purities higher than 98%. High-performance liquid chromatography (HPLC)-grade formic acid was purchased from Thermo Fisher Scientific (USA). HPLC-grade acetonitrile and n-hexane were obtained from Merck (Germany). Deionized water was prepared by a Milli-Q system (Millipore, USA).

The other reagents were of analytical grade and purity and commercially available. The reference standards (gallic acid, synephrine, hesperidin, nobiletin, tangeretin, ferulic acid, narirutin, and limonin) were obtained from Must Biotechnology. The other reference standards (3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF), isoscopoletin, scopoletin, scoparone, stachydrine) were purchased from Weikeqi Biological Technology Co., Ltd. and 5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone (5-HPMF) was obtained from Spring & Autumn Biological Engineering Co., Ltd. The purity of these reference standards was above 98%.

Reference standards of stachydrine, scopoletin, 5,7-dimethoxycoumarin, and nomilin were obtained from Sichuan Weikeqi Biotechnology (China), and hesperiden, ferulic acid, nobliletin, limonin, and tangeretin were purchased from Chengdu Mansite Biotechnology (China).