RESUMO
Objective:To establish an LC–MS/MS method for the determination of the active metabolite(SN-38) and secondary metabolite(SN-38G) of irinotecan in rat liver microsomes incubation system, and optimize the incubation conditions. Methods:Meth-anol was selected to precipitate protein in the samples, and then the concentrations were analyzed by LC–MS/MS. All the separation was carried out on a ZORBAX Eclipse XDB-C18 column(2. 1 mm × 50 mm, 3. 5 μm) with the mobile phase of acetonitrile – water (containing 0. 1% formic acid) (23 :77) at a flow rate of 0. 3 ml·min-1. The mass spectrometer was operated with multiple reac-tions monitoring ( MRM) using electrospray ionization ( ESI) . The incubation conditions were optimized by single factor design. Re-sults:SN-38 and SN-38G showed a good linearity ( r≥0. 9972) respectively within the range of 2. 3-920 ng·ml-1 and 2. 5-1000 ng ·ml-1. The intra-and inter-day RSD was below 14. 6%(n=6). The average recovery was within the range of 74. 1%-123. 4% with RSD below 13. 5% (n=6). The optimal incubation conditions were as follows:the concentration of liver microsomal protein was 0. 3 mg·ml-1 and the incubation time was 30 min. Conclusion:The method is rapid, sensitive and accurate in the quantification of SN-38 and SN-38G in the incubation system,which provides methodological basis for the activity determination of UGT1A1 enzyme in vitro.