Green chemistry-driven RP-HPLC method for diltiazem and lidocaine hydrochloride in bulk and gel formulations using AQbD

In this work, a simple, specific, accurate, and precise Reverse-Phase High-Performance Liquid Chromatography (RP-HPLC) method for estimating lidocaine hydrochloride and diltiazem hydrochloride in bulk and pharmaceutical dosage forms is developed and validated. The method uses an isocratic RP-HPLC approach for the separation and quantification of these compounds. Chromatographic analysis was performed on a Waters HPLC system that was fitted with a Thermo Scientific C₁₈ ODS column (250 mm × 4.6 mm, 5 μm). The mobile phase was supplied at a flow rate of 1.0 mL/min and consisted of methanol, acetonitrile, and buffer (orthophosphoric acid) in a 70:20:10 ratio. At 233 nm, a sharp, symmetrical peak with retention periods of 2.5 and 4.4 min was obtained through detection. Many parameters, such as linearity, accuracy, precision, specificity, and robustness, were evaluated for the method's validation. The method showed linearity throughout a concentration range of 20–100 µg/mL with correlation coefficients (r²) of 0.999 and 0.998, respectively, and the recovery of diltiazem hydrochloride varied from 99 to 100 %. Method optimization was accomplished through the use of a Box–Behnken design with desirability functions, and the validation parameters satisfied the requirements specified in the ICH Q2 (R1) recommendations. The AGREE assessment of the proposed RP-HPLC technique resulted in a score of 0.68, indicating a good balance between analytical performance and environmental sustainability. This confirms its environmental sustainability and suitability as an eco-friendly analytical method.