Validated Spectrophotometric Method for Determination of Some Benzimidazole Derivatives in Pharmaceutical Formulations Using 1,2-naphthoquinone-4-sulphonate

Aim: To develop and validate a sensitive method for the determination of rapeprazole (RPZ) and omeprazole (OPZ) in bulk and formulations based on nucleophilic substitution reaction of RPZ and OPZ with sodium 1,2-naphthoquinone-4-sulphonate (NQS) in an alkaline medium. Study Design: All variables were studied to optimize the reaction conditions and the reaction mechanism was postulated. Place and Duration of Study: Department of Chemistry, Faculty of Science, Aleppo University, Aleppo, Syria between December 2011 and December 2012. Methodology: The colored products were measured spectrophotometrically at 453 nm using double beam UVD-2960 (Labomed, INC., U.S.A) ultraviolet-visible spectrophotometer with matched 1-cm quartz cells. The reaction time and temperature were 20 min and 25oC for RPZ and OPZ. As per ICH guidelines, the proposed method was validated. The developed method was successfully applied for the estimation of RPZ and OPZ in tablets and capsules and results were compared statistically with the official methods. Research Article International Research Journal of Pure & Applied Chemistry, 3(2): 118-132, 2013 119 Results: The developed method showed a linear Beer's law range from 0.26 to 12.0 and from 0.49 to 12.0 μg mL with limit of detection values of 0.181 and 0.187 μg mL for RPZ and OPZ, respectively. The calculated molar absorptivity values are 7.7×10 and 3.8×10 L mol cm for RPZ-NQS and OPZ-NQS, respectively. The proposed methods were successfully applied to the determination of RPZ and OPZ in formulations and the results tallied well with the label claim. Conclusion: The developed method was linear, sensitive, selective, precise, accurate and robust, being suitable for routine quality control analyses of RPZ and OPZ.