A comprehensive approach to green and robust UPLC method for combined antihypertensive drugs

A green, robust, and stability-indicating UPLC method was developed for the simultaneous quantification of Methyldopa and Hydrochlorothiazide in a combined tablet dosage form. Method optimization was achieved using a Quality by Design (QbD) approach employing a 2 3 full factorial design, with flow rate, pH, and buffer composition as critical method parameters. Chromatographic separation was performed on an HSS C18 column (100 × 2.1 mm, 2 μm) using a mobile phase of acetonitrile and 0.01 N KH₂PO₄ buffer (pH 3.5) in a 60:40 ratio at a flow rate of 0.3 mL/min, with detection at 219 nm. The method was validated as per ICH Q2(R1) guidelines and showed excellent specificity, linearity (r 2 > 0.999), precision (RSD < 2 %), accuracy (recoveries between 98 and 102 %), and solution stability. Forced degradation studies under acid, base, oxidative, thermal, photolytic, and neutral conditions confirmed the method's stability-indicating nature. Method robustness evaluated via QbD indicated that flow rate was the only significant factor affecting resolution and tailing, while pH and buffer ratio had negligible impact. RAPI tool assessed the method validation. Greenness was assessed using multiple analytical metrics: CASI (70), Analytical Eco-Scale (score of 75), AGREE (0.75), AGSA (76.39) and MoGAPI (76), confirming the method's environmental sustainability. This study demonstrates a reliable, environmentally friendly, and regulatory-compliant UPLC method suitable for routine analysis of Methyldopa and Hydrochlorothiazide in pharmaceutical formulations. • A green and stability-indicating UPLC method for simultaneous estimation of Methyldopa and Hydrochlorothiazide was developed using a QbD approach, ensuring robustness and reproducibility. • Greenness was confirmed by CASI, Eco-Scale, AGREE, AGSA, and MoGAPI metrics, all showing favorable scores with minimal solvent use and low energy demand. • The method was validated for accuracy, precision, and stability-indicating ability, while RAPI assessment confirmed its balanced performance, eco-friendliness, and suitability for regulatory and routine applications.