A sensitive analytical method on cortisol in marine fish serum was established using ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry(UPLC-Q-TOF MS).The cortisol in marine fish serum was extracted with chloroform,dried under nitrogen gas,and solved in 1:1 methanol-H2O for analysis,with dexamethasone as internal standard.The mass spectrometry was performed in reflective time-of-flight using electron spraying ionization in negative mode,with m/z 407.2 for cortisol and 437.2 for dexamethasone,respectively.The results showed efficient separation of cortisol and dexamethasone are achieved on BEH C18 column.The linearity was good with the equation : Y=0.0154X+0.0451,from 0 to 200 ng/mL,with correlation coefficient of 0.999 3 and low detection limit of 1.64 pg.The average recovery was from 93.3% to 98.1%,with SD less than 10%.Using this method,corsitol in yellow croaker and Japanese sea bass collected in Ningbo China,were determined with content ranged from 0 to 15.81 ng/mL.
