2.4. Plasma sample preparation
The mixtures were put into 1.5-ml microcentrifuge tubes containing 20 ml of standard solution and 100 ml of plasma. Then, 1000 μl of isopropanol:ethyl acetate (20:80, v/v) was injected into the tubes and vortexed for 60 s. The tubes were subsequently centrifuged at 8049.6×g for 10 min. Another tube was used for the organic layer, which was subsequently evaporated to dryness. After dissolving the residue in 100 μl of mobile phase, 2 μl of the extract was injected into the HPLC-MS/MS system. SYKG2003-0005 is the license number of the Animal Protection and Utilization Committee at Guangxi Medical University that approved this study.