Stability-Indicating HPLC Method for Simultaneous Determination of Captopril, Indapamide, and Their Related Compounds

A validated stability-indicating HPLC method was developed for simultaneous determination of Captopril (CP), Indapamide (ID), and their related compounds in tablets using a 250 × 4.6 mm Xterra RP8 column, 5 µm particle size with UV detection at 210 nm. Isocratic elution was employed using mobile phase consisting of a mixture of 26 mM pentane-1-sulfonic acid sodium salt in 30 mM potassium dihydrogen phosphate (pH 2.8, adjusted by phosphoric acid):methanol:acetonitril (6:2:2) v/v/v. The described method was linear over the range of 0.25–150 µg/mL with (r = 0.9999) for CP and 0.2–100 µg/mL with (r = 0.9999) for ID. The stability of CP and ID was studied under accelerated acidic, alkaline, and oxidative conditions. The proposed method was used to investigate the kinetics of acidic and alkaline degradation process of CP and ID at different temperatures and the apparent pseudo first-order rate constant, half-life, and activation energy were calculated. The pH rate profiles of degradation of CP and ID in Britton-Robinson buffer solutions within the pH range 1.8–12.0 were studied. The developed method was validated with respect to linearity, accuracy, precision, selectivity, and robustness. The forced degradation studies prove the stability indicating power of the developed method.