A simple ultraperformance liquid chromatography mass spectrometry method for the determination of cortisol level in sea bass plasma

A simple, precise, and rapid ultra-performance liquid chromatography method for cortisol quantification in sea bass plasma, based on LC-ESI-UHR-QqTOF-MS, was optimised using tolperisone as internal standard. Sea bass plasma samples containing cortisol were spiked with tolperisone as internal standard and extracted with acetonitrile. Samples were vortexed and centrifuged at 15,000g for 10 min at 4 °C. The final extract, diluted in ammonium formate (1:1), was injected in the LC-ESI-UHR-QqTOF-MS system for analysis. Mass spectrometry acquisition parameters were set using positive ionisation mode over a m/z range from 150 to 2200. Cortisol and tolperisone were detected and quantified at m/z 363.21 and 246.18, respectively, in an Auto MS (MS/MS) mode. The detection and quantification limits of cortisol in sea bass plasma were 0.01 and 0.02 μg/mL, respectively. The mean extraction recovery of cortisol was of 99.1 ± 4.0 %. The within- and between-day precision presents a relative standard deviation (RSD) below 2.9 % and 5.3, respectively. Furthermore, the effect of four different diets (fish feed 1–4) in the basal and stress-induced plasma cortisol levels of sea bass was also assessed.