2.7 Sample extraction method
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After the sample was slowly thawed at 4°C, an appropriate amount of the sample was added with precooled methanol/acetonitrile/water solution (2:2:1, v/v), vortex mixed, sonicated at low temperature for 30 min, allowed to stand at -20°C for 10 min, centrifuged at 14,000 g for 20 min at 4°C, the supernatant was vacuum-dried, and 100 μL of acetonitrile aqueous solution (acetonitrile: water = 1:1, v/v) was added for reconstitution during mass spectrometry, vortex, centrifuged at 14000 g for 15 min at 4°C, and the supernatant was injected for analysis.