To establish a method for determining the concentration of contezolid in human cerebro spinal fluid (CSF) using ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS).

Linezolid as the internal standard (IS) and acetonitrile as the protein precipitant. Waters ACQUITY UPLC^® BEH C₁₈ (2.1 mm×50.0 mm, 1.7 μm) chromatographic column was used for separation, with a mobile phase of 0.1% formic acid aqueous solution-0.1% formic acid acetonitrile solution, gradient elution method, flow rate was 0.4 mL·min^-1, column temperature was 40 ℃, automatic sampler temperature was 10 ℃, the analysis time was 4 minutes. Electrospray ion source, positive ion mode, and multi-reaction monitoring scanning mode were used. The monitoring and analysis ion pairs for contezolid were m/z 409.15→269.14, and the monitoring ion pairs for linezolid were m/z 338.14→195.10. The specificity, standard curve and lower limit of quantification (LLOQ), precision and recovery rate, matrix effect, residual effect, dilution effect and stability of the method were investigated.

The endogenous substances in CSF do not interfere with the determination of the analyte contezolid and the internal standard linezolid, and the method has good specificity. Satisfactory linearity was observed within the concentration range of 20-5 000 ng·mL^-1 for contezolid in CSF, the calibration curve was y=8.97×10^-4x+1.95×10^-2 (r=0.999 1), and the LLOQ was 20 ng·mL^-1. Precision of the intra-batch and inter-batch relative standard deviation (RSD)<15%, and the extraction recovery were 90.96%-98.71%. The average normalized matrix effect factor of the quality control CSF sample were 94.39%-100.25%. The RSD of dilution effect<15%. The CSF samples of contezolid were stored at room temperature, in the automatic sampler for 72 hours, -20 ℃ and -80 ℃ for 90 days, and subjected to repeated freezing and thawing three times, were stable with all of which the RSD<10%.

This method is high sensitivity, rapid, simple and accurate, which is very suitable for the therapeutic drug monitoring of contezolid in human CSF.