IMPROVED ONE-STEP SOLID-PHASE EXTRACTION METHOD FOR MORPHINE, MORPHINE-3-GLUCURONIDE, AND MORPHINE-6-GLUCURONIDE FROM PLASMA AND QUANTITATION USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

This communication describes an improved one-step solid-phase extracti on method for the recovery of morphine (M), morphine-3-glucuronide (M3 G), and morphine-6-glucuronide (M6G) from human plasma with reduced co extraction of endogenous plasma constituents, compared to that of the authors' previously reported method. The magnitude of the peak caused by endogenous plasma components in the chromatogram that eluted immedi ately before the retention time of M3G has been reduced (similar to 80 %) significantly (p < 0.01) while achieving high extraction efficienci es for the compounds of interest, viz morphine, M6G, and M3G (93.8 +/- 2.5, 91.7 +/- 1.7, and 93.1 +/- 2.2%, respectively). Furthermore, whe n the improved solid-phase extraction method was used, the extraction cartridge-derived late-eluting peak (retention time 90 to 100 minutes) reported in our previous method, was no longer present in the plasma extracts. Therefore the combined effect of reducing the recovery of th e endogenous components of plasma that chromatographed just before the retention time of M3G and the removal of the late-eluting, extraction cartridge-derived peak has resulted in a decrease in the chromatograp hic run-time to 20 minutes, thereby increasing the sample throughput b y up to 100%.