DETERMINATION OF DIHYDROETORPHINE IN BIOLOGICAL-FLUIDS BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY USING SELECTED-ION MONITORING

A method for the determination of dihydroetorphine hydrochloride, a po werful anaesthetic and analgesic drug, in biological fluids by GC-MS w ith selected-ion monitoring using etorphine as internal standard was e stablished. Dihydroetorphine was extracted from human blood and urine with dichloromethane and then derivatized with N-heptafluorobutyrylimi dazole after concentration to dryness. A dihydroetorphine monoheptaflu orobutyl derivative was formed which showed good behavior on GC-MS wit h electronic-impact ionization. The main fragment, m/z 522, which is t he base peak, was selected as the ion for quantitation and the corresp onding ion, m/z 520, was selected for monitoring the internal standard , etorphine. The recoveries and coefficients of variation of the whole procedure were determined with five controlled dihydroetorphine-free urine and plasma samples spiked with different concentrations of dihyd roetorphine. The concentration of dihydroetorphine for quantitation wa s in the range 1-20 ng/ml for urine and 2.5-250 ng/ml for plasma. The correlation coefficients of the standard curves are sufficient to dete rmine the dihydroetorphine. The accuracy for quantitation of dihydroet orphine in urine and plasma is less than 10.6%.