MEASUREMENT OF NALOXONE IN PLASMA USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

A new sample preparation technique, solid-phase extraction employing t he ion-pair reagent octyl sodium sulfate (OSS), was developed for the selective isolation of nanogram quantities of naloxone from human plas ma. Plasma samples containing naloxone, OSS, buffer, and naltrexone (i nternal standard) were applied to octyldecylsilane (C18) cartridges, a nd the opiates were eluted with 100% methanol. An extraction efficienc y of 90% was achieved. Extracts were then examined by reversed-phase h igh-performance liquid chromatography with electrochemical detection, with mobile phase composition adjusted to optimize separation and quan titation. An oxidizing potential of +0.93 V resulted in an assay sensi tivity of 1.0 ng. Thus, plasma naloxone levels of ca. 20 ng/ml could b e readily detected and quantified. The intra-assay coefficient of vari ation at plasma levels of 80 ng/ml was 7.2%. Plasma naloxone values ob tained during a 5-h infusion of the drug (0.24 mg/min) in two normal h uman subjects were stable and reproducible. Thus, the method herein de scribed is applicable to human studies employing naloxone infusion.