A Robust and Sustainable HPLC Refractive Index Method Using Box–Behnken Design for Simultaneous Determination of Glycerin and Propylene Glycol

Glycerin (Gly) and propylene glycol (PG) are widely used excipients in pharmaceutical formulations, and their accurate and reliable quantification is essential for quality control (QC). The present study describes the development, optimization, and validation of a robust, sustainable, and environmentally conscious high‐performance liquid chromatography (HPLC) refractive index method for the simultaneous determination of glycerin and PG using a quality‐by‐design (QbD) approach. The optimized chromatographic conditions employed an Inertsil ODS‐3, 5 µm, 4.6 mm × 250 mm column with a mobile phase of water and methanol (90:10, v/v), flow rate of 0.5 mL/min, and column temperature of 40°C. The method was validated in accordance with International Council for Harmonization (ICH) guidelines. Accuracy results were found to be 99.1%–99.9% for Gly and 99.7%–99.9% for PG. Precision results were found Gly 0.3% and PG 0.4% relative standard deviation. Correlation coefficient ( r 2 ) was obtained >0.998 for two components. Analytical solutions are stable for 67 h at ambient conditions. The environmental sustainability of the method was assessed using AGREE, AGREEprep, Green Analytical Procedure Index (GAPI), ComplexGAPI, and Blue Applicability Grade Index (BAGI) tools, indicating a favorable greenness profile due to low organic solvent usage and simple sample preparation. The proposed method is reliable, cost‐effective, and suitable for routine QC applications while aligning with green analytical chemistry principles.