Stability Indicating RP-HPLC-PDA Method for Simultaneous Estimation of Olmesartan Cilnidipine and Chlorthalidone with Forced Degradation Behavior Study in Bulk and in Its Tablet Dosage Form

An accurate, efficient Stability indicating reversed-phase high-perfomance liquid chromatographic (RP-HPLC) method has been developed and validated for the simultaneous estimation of Olmesartan, Cilnidipine and Chlorthalidone. All the drugs were separated on a KROMASIL 250 x 4.6 mm, column packed with 5 µm particles. The mobile phase, optimized through an experimental design, was a 45:55 (v/v) mixture of acetonitrile and Ortho phosphoric acid buffer(0.1%OPA), pumped at a flow rate of 1 ml/min. UV detection was performed at 230 nm. The retention time of Olmesartan, Cilnidipine and Chlorthalidone was found to be 2.280min, 8.356 min and 2.804min respectively. The method was validated in the sample concentration ranges of 20-120 µg/ml for Olmesartan and 5-30 µg/ml for Cilnidipine, and Chlorthalidone 6.25-37.5µg/ml.  The method demonstrated to be robust, resisting to small deliberate changes in pH and flow rate of the mobile phase. The LOD values were 0.08µg/ml, 0.04µg/ml and 0.05 µg/ml, while the LOQ values were 0.24µg/ml, 0.12µg/ml and 0.16µg/ml for Olmesartan, Cilnidipine and Chlorthalidone respectively.