Facile Colorimetric Determination of Duloxetine in Formulations Using Methyl Orange as Ion-Pairing Agent

Purpose: To develop a new and fully validated ion-pair spectrophotometric method for the determination of duloxetine hydrochloride (DX). Methods: Ion-pair spectrophotometric method was employed for the determination of duloxetine hydrochloride (DX) in bulk and pharmaceutical formulations using acidic dye methyl orange (MO) as ion-pairing agent at pH 4 (phthalate buffer). The yellow ion-pair complex was extracted with chloroform and spectrophotometrically estimated at 420 nm. The developed method was validated according to ICH and USP guidelines. Results: The ion-pair complex of DX and MO obeyed Beer’s law in the range of 2 - 20 g mL-1 of DX with a correlation coefficient of 0.998. Recovery was good, with a relative standard deviation (%RSD) of 0.88 - 1.02; precision (inter-day, 0.878 and intra-day, 0.921) was also within validation limits. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.25 and 4 g mL-1, respectively. The method developed was successfully applied to determine DX in a formulation. Conclusion: The developed method is accurate, precise, rugged, robust and reproducible. It is also sensitive and specific for the determination of DX in bulk and formulation.