Three Spectrophotometric Methods for Quantitative Analysis of Duloxetine in Presence of its Toxic Impurity: 1-Naphthol

Background: Duloxetine hydrochloride (DUL) is a drug used to treat depression and anxiety. 1-Naphthol is a potential toxic impurity of DUL, as it causes hepatotoxicity in humans, and it is harmful to aquatic life. Objective: Three simple, selective, rapid, accurate and precise methods were developed and validated according to International Conference on Harmonization (ICH) guidelines with respect to linearity, accuracy, precision and selectivity for analysis of duloxetine hydrochloride (DUL) in the presence of its potential toxic impurity 1-Naphthol in different laboratory-prepared mixtures and pharmaceutical formulations. Methods: Method (A) is the first derivative of the ratio spectra spectrophotometric (1DD) method which allows determination of DUL at 251 nm and 1-Naphthol at 305.2 nm without interference from each other. Method B (dual wavelength) means that two different wavelengths were chosen to each drug, where the absorbance difference at these two wavelengths is equal to zero to the second drug. The chosen two wavelengths for DUL were 221.4 nm and 235.6, where the absorbance difference for 1-naphthol at these two wavelengths was equal to zero. While the chosen wavelengths for 1-naphthol were 247.8 nm and 297 nm, where the absorbance difference for DUL at these two wavelengths was equal to zero. Method (C) is the mean centering of ratio spectra spectrophotometric (MCR) method, which depends on measuring the mean centered values of ratio spectra of both DUL and 1-Naphthol at 226 nm. Results: These methods were validated and agreed with the requirements of ICH guidelines with respect to linearity, accuracy, precision and selectivity. Conclusions: The results indicate the ability of developed methods to be used for routine quality control analysis of DUL in bulk and pharmaceutical formulations in the presence of its potential impurity 1-Naphthol.