Simple liquid chromatographic method for the determination of naltrexone in human plasma using amperometric detection

A simple liquid chromatographic method using amperometric detection was developed for the determination of naltrexone in human plasma. Prior to analysis, naltrexone and the internal standard (naloxone) were extracted from plasma samples using a 9:1 mixture of chloroform and isopropyl alcohol. The mobile phase comprised 0.1 M disodium hydrogen orthophosphate (pH 3.5) and acetonitrile (85.5:14.5, v/v). Analysis was run at a flow-rate of 0.8 ml/min with the detector operating under oxidative mode at an applied potential of +0.95 V. The method is specific and sensitive with a detection limit of approximately 1 ng/ml at a signal-to-noise ratio of 3:1. Mean recovery value of the extraction procedure was about 93%, while the within day and between day coefficient of variation and percent error values of the assay method were all less than 10%. The calibration curve was linear over a concentration range of 1.5-100 ng/ml.