Spectrofluorimetric determination of naltrexone by a kinetic method using the stopped-flow technique Original Research Article

A simple, sensitive, selective, fast and inexpensive assay for the determination of naltrexone is proposed. The method is based on the rapid oxidation of naltrexone by hexacyanoferrate(III) in an alkaline aqueous medium to form a highly fluorescent product. A kinetic study of the reaction was realized by measuring the initial rate of change of the fluorescence intensity of the first oxidized product at 361 and 459 nm excitation and emission wavelengths, respectively. The optimum concentration of the alkaline medium, oxidant concentration and instrumental variables were determined. The method permits the determination of naltrexone over the range 0.3–2.0 μg ml−1 with high precision (the relative standard error based on the calibration graph was 1.6% and the relative standard deviation of replicates was 3.3% for 1.4 μg ml−1), selectivity and sample throughput (60 h−1). The method was applied to the determination of naltrexone in pharmaceutical preparations and was found to be satisfactory. The effect of same possible interferences has been studied.