Spectrophotometric and Fluorimetric Methods for Determination of Naltrexone in Urine, Serum and Tablets by Oxidation with Cerium (iv)

This paper proposes new methods for simple and sensitive spectrophotometric and fluorimetric determination of naltrexone (NALT) in tablet and biological fluids. The spectrophotometric method involve addition of a known excess of Ce(IV) to NALT in acid medium, followed by determination of residual Ce(IV) by reacting with a fixed amount of methyl orange, and measuring the absorbance at 510 nm. Fluorimetric method was based on the oxidation of NALT with Ce(IV) to produce Ce(III) and its fluorescence was monitored at 350 nm after excitation at 250 nm. In both methods, the amount of Ce(IV) reacted corresponds to the amount of NALT and the measured absorbance or fluorescence were found to increase linearly with the concentration of NALT, which are corroborated by the correlation coefficients of 0.9999 and 0.9996 for spectrophotometric and fluorimetric methods, respectively. Different variables affecting the reaction conditions such as the concentrations of Ce(IV), type and concentration of acid medium, reaction time, temperature, and the diluting solvents were carefully studied and optimized. The accuracy and precision of the methods were evaluated on intra-day and inter-day basis. The proposed methods were successfully applied for the determination of NALT in pharmaceutical formulation and biological samples with good recoveries.