DETERMINATION OF 6-MONOACETYLMORPHINE AND MORPHINE IN PLASMA, WHOLE-BLOOD AND URINE USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

6-Monoacetylmorphine and morphine were determined simultaneously in plasma, whole blood and urine, after solid-phase extraction, by high-performance liquid chromatography using amperometric detection at 600 mV oxidation potential. The recoveries ranged from 92 to 99%. The reproducibility study indicated that the coefficients of variation were less than 11% for morphine and 12.4% for 6-monoacetylmorphine. The determination limits were 1 ng/ml for morphine and 4 ng/ml for 6-monoacetylmorphine. The method had a good selectivity towards opiate and nonopiate analgesics and other drugs. The stability of the analytes in methanol (standard solutions), in samples (plasma, whole blood and urine) at -20 degrees C and at 20 degrees C, and in samples after enzymatic hydrolysis at 37 degrees C, was also studied. For samples containing 6-monoacetylmorphine, inadequate storage or hydrolysis could lead to overestimation of morphine or its conjugates. The technique described can be applied for the study of the pharmacokinetics of heroin; it is also available for forensic toxicology to distinguish heroin use from medical prescription of morphine and other opiate drugs.