Abstract: Objective To develop a column-switching high-performance liquid chromatographic method for the determination of morphine and O 6 -monoacetylmorphine in urine.Methods Urine samples1.0mlwere spiked with1.0ml borate buffer,after centrifugation,1.0ml of supernate were injected directly into an extraction columnYWG C 18 33mm×5.0mm,10 μ m.After a washing step with the extraction mobile phase,the retained morphine and O 6 -monoacetylmorphine were flushed into the analytical columnLichrospher R 100CN125mm×4.0mm,5 μ mwith the mobile phase CH 3 OH-H 2 O60∶40.The analytical mobile phase is CH 3 OH-phosphate bufferpH6.8622∶78.The UV detector was set at λ 286nm.Results The method shows excellent linearity from50to1600ng/ml for morphine and from100to1600ng/ml for O 6 -monoacetylmorphine.The linear correlation coefficients were>0.999.The relative standard deviations were<4%.The limits of detection were40ng/ml for both morphine and O 6 -monoacetylmorphine.Conclusion The method described is sensitive,rapid,reproducible,and simple.

Key words: morphine, O 6-monoacetylmorphine, CSHPLC, urine