Flow injection analysis with amperometric detection of naltrexone in pharmaceuticals

Flow injection analysis (FIA) with amperometric detection using a carbon paste electrode is applied to the determination of naltrexone. The sample solution was injected into the carrier stream of 0.1 M perchloric acid, being determined by oxidation at +1.0 V vs. Ag/AgCl/sat. KCl using a flow rate of 4 ml min-1. A relative standard deviation of 1.5% was calculated for a concentration level of 10(-5) M (n = 17) without carrying out a carbon paste electrode pretreatment. Calibration curves were found to be linear between 2 x 10(-8) and 10(-5) M (almost three orders of magnitude) and the method has a detection limit of 2 x 10(-8) M. A simple and reproducible procedure is proposed for the determination of naltrexone in pharmaceuticals. The results compared favourably with those obtained by an HPLC-UV method.