Validated stability-indicating RP-HPLC method for simultaneous estimation of cilnidipine and chlorthalidone in tablet dosage form

A novel, simple, specific, accurate & precise stability-indicating Gradient reverse-phase high-performance liquid chromatography (RP-HPLC) method was developed for simultaneous estimation of Cilnidipine & Chlorthalidone in tablet dosage form, validated as per ICH guideline. The separation was achieved on Inertsil ODS column (250 mm x 4.6 mm, 5 μm) in a gradient mode.  The mobile phase consisted of Methanol, 0.025 M Potassium dihydrogen phosphate Buffer pH 5.5 adjusted by 10% v/v Ortho Phosphoric Acid (50:50 v/v) (Solution A) and Acetonitrile, 0.025 M Potassium dihydrogen phosphate Buffer pH 5.5 adjusted by 10%v/v Ortho Phosphoric Acid (75:25 v/v) (Solution B), gradient programming for 20 min at 1 ml/min rate of flow and response was detected at 225 nm. The retention time was found to be 3.580 min and 12.606 mins for Chlorthalidone and Cilnidipine, respectively. The method is validated according to ICH guideline, which includes linearity, specificity, accuracy, precision and robustness. Linearity was obtained over the concentration range of 10-60 μg/ml for Cilnidipine and 6.25-37.5 μg/ml for Chlorthalidone, had a regression coefficient (r2) almost 0.9966. The % Recovery was found to be 99.63-100.59 % and 100.24-100.51 % for Cilnidipine and Chlorthalidone, respectively. The method was found to be specific enough to separate all degradation products from the active compound. Drug samples were exposed to various stress conditions like photolysis, oxidation, heat conditions, and hydrolysis (acidic and alkaline), there was no interference of any degradants and excipient in the determination of drugs so that methods can be successfully applied for routine QC analysis.