2.7.1. Sample preparation.
The frozen follicular fluids first were melted at 4°C. Accurately measured 100 µL was then transferred into a 1.5 mL centrifuge tube. A total of 300 µL methanol, internal standard 500 ng/mL chloramphenicol, and control were added and then vortexed for 5 minutes. The tube with the content was centrifuged at 14,000g high-speed at 4°C for 30 minutes. The supernatant was absorbed into the EP tube and 10 µL samples were taken for analysis.