Stability-indicating reversed-phase HPLC method for the separation and estimation of related impurities of Cilnidipine in pharmaceutical formulations

A novel HPLC method was developed and validated for the determination of cilnidipine (CLDP) along with its related impurities A and B in pharmaceutical formulations. The chromatographic separation was carried out by isocratic elution using an X Terra C18 column (250×4.6mm; 5μ). The mobile phase was composed of methanol and phosphate buffer at a pH of 5.8 in the ratio of 10:90 (V/V) at a flow rate of 1.0 mL/min. The eluents were detected and quantified at a UV detection wavelength of 229 nm. Calibration curves of all analytes in the range of 2-12μg/mL showed a good correlation linearly (r ≥ 0.999) with recovery rate of more than 98% for each analyte. The percentage RSD in intraday, interday precision and ruggedness were found to be less than 2. Small variations in the developed conditions like mobile phase ratio, flow rate, pH and UV wavelength do not influence the results. This proves the precise and robust nature of the developed method. Stress degradation studies were conducted for standard drug and high amount of degradation was observed under UV light exposure. After 24hours, the molecules degraded up to 9.967%. In base hydrolysis, the CLDP molecule degrades up to 6.223%. In other stress conditions like acidic (5.347%), oxidative (4.916%) and thermal (4.319%) conditions, CLDP was found to be highly labile. In stress degradation study, there is no interference of both known impurities and other degradation products formed and were separated from CLDP. Therefore, this method was found to be selective and specific. The method development and validation result confirms that this method is suitable for determination and quantification of process impurities (A and B) of CLDP in pharmaceutical formulations.