Ultra performance liquid chromatography conditions
All samples were analyzed using LC-MS system (ultra performance liquid chromatography (UPLC) system (SCIEX, UK)) following the manufacturer’s instructions. The analytical conditions were as follows, UPLC: column, ACQUITY UPLC T3 (100 mm×2.1 mm, 1.8 µm, Waters, UK); solvent system, water (0.1% formic acid) as solvent A, acetonitrile (0.1% formic acid) as solvent B; gradient elution procedures: 0~0.5 min, 5% solvent B; 0.5~7 min, 5% to 100% solvent B; 7~8 min, 100% solvent B; 8~8.1 min, 100% to 5% solvent B; 8.1~10 min, 5% solvent B; the injection volume: 4 µL.