Abstract: Objective·To investigate the influence of mobile phase in chromatographic conditions and mass spectrometry ion source parameters on the quantitative results of four common immunosuppressant drugs including cyclosporine A（CsA）, tacrolimus（TaC）, sirolimus（SiR） and everolimus（EvE）by liquid chromatography-mass spectrometry. Methods·Based on ultra-high performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS） technology, the effect on peak shape and response under different parameter settings were evaluated by changing the mobile phase and ion source parameters; the sensitivity of the method under different ion source temperatures was detected by linearity of the standard curve and limit of quantitation（LOQ）. Results·The narrower peak width was obtained when methanol was used as organic phase; the addition of ammonium formate（AF） to the aqueous phase observably improved the peak response but inhibited partly when the concentration of AF excessed; therefore, 5 mmol/L AF was chosen as the mobile phase modifier. The optimization of the ion source temperature significantly improved the chromatographic peak shape and quantitative sensitivity. The quantitative method had nice linearity（r2>0.99） and sensitivity（LOQ=0.05 ng/mL） under 250 ℃ ion source temperature. Conclusion·A simultaneous quantitative analytical method for four immunosuppressant drugs is established based on UPLC-MS/MS technology and the quantitative sensitivity has been conveniently and significantly improved by optimizing the mobile phase and ion source parameters. The addition of AF in the mobile phase and the ion source temperature are key parameters that affect the quantitative analysis and provide new ideas for the development and optimization of high-sensitivity quantitative methods for other compounds based on liquid chromatography-mass spectrometry.

Key words: immunosuppressant drug, ultra-high performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）, ion source temperature, quantitative analysis