DEVELOPMENT AND VALIDATION OF ANALYTICAL METHODS FOR SIMULTANEOUS ESTIMATION OF DEXTROMETHORPHAN AND QUINIDINE BY RP-HPLC AND UV-SPECTROMETRY

Objectives of study: To develop and validate new, rapid, selective, precise, accurate and economical, isocratic RP-HPLC and UV spectrophotometric method for simultaneous estimation of Dextromethorphan and Quinidine in bulk and in tablet formulations. Methods: A RP-HPLC was developed for the simultaneous estimation of Dextromethorphan and Quinidine on Phenomenex C-8 column with the mobile phase of methanol and phosphate buffer (pH 2.5) in the ratio 60:40 v/v at flow rate of 1ml/min and detection at 230nm was used for the study. In UV spectrometry, simultaneous equation method was based on measurement of absorbances at two selected wavelengths 278nm and 331nm for Dextromethorphan hydrobromide and Quinidine Sulfate respectively. Absorbance ratio method based on the measurement of absorbances at isobestic point and wavelength maxima of one drug, selected wavelengths were 278nm (λmax of DMH) and 289nm (isobestic point). The developed methods were validated and recovery studies were carried according to ICH guidelines. Results: The peaks of Dextromethorphan and Quinidine were found to be well resolved with retention time of 4.3min and 2.8min respectively, indicating the shorter analysis time. The proposed method was found to be accurate, precise and reproducible. The linearity was established in the concentration range of 1-30µg/ml. Limit of Detection (LOD) and Limit of Quantification (LOQ) were found to be within limits for both Dextromethorphan and Quinidine.  In UV-spectrometry, both methods obey the Beer Lambert’s law in the concentration range of 30-150μg/ml for Dextromethorphan Hydrobromide and 10-70μg/ml for Quinidine Sulfate respectively. Conclusion: The methods can be used for routine analysis of formulations containing any of the above drugs or combinations without any alteration in the chromatographic conditions.