Analytical Validation and Stability Indicating Studies for Simultaneous Estimation of Benidepine and Metoprolol by Strong Cation Exchange (SCX) Chromatography

Introduction: Polar anti-hypertensive drugs like benidepine and metoprolol often suffer from peak fronting and peak tailing effects in RP-HPLC. SCX chromatography which is alternative and complimentary to this RP-HPLC also has the capability to separate benidepine and metoprolol. Considering these aspects, SCX method was developed with performing stability indicating studies for the simultaneous quantification of benidepine (BEN) and metoprolol (MET) in bulk and tablet formulation. Methods: This investigation was performed on the Phenomenex Luna SCX column (100 × 2.1 mm, ID, particle size 5 μm) where both BEN and MET were eluted with ammonium formate (15mM) buffer: MeOH in ratio of 75:25 v/v for 12 min with isocratic elution at the flow rate of 1.2 ml/min; performed at 28°C and monitored at 226 nm wavelength. Results: The average retention time of BEN and MET were 1.290 and 3.520 min, respectively. The validation studies revealed good linearity over different concentration ranging between 7.5-250 μg/ml for BEN and 15.5-250 μg/ml for MET with R2 values were 0.999 recorded for both drugs. Average drug recoveries of BEN and MET were ranging between 99.36±0.83% and 100.51±1.03%, respectively. The acid (0.1N HCl; 50°C), dry heat (50°C) and alkali (0.1N NaOH; 50°C) have not made any significant changes in both BEN and MET but peroxide (3% H2O2; 28°C) have degraded the BEN but MET was unaffected. Conclusion: The present SCX method represented the shortest run time for the investigation of benidipine and metoprolol where the results of linearity, accuracy, precision, robustness and specificity were under the obligation of ICH guidelines.