A green HPLC-UV method for the simultaneous analysis of enalapril, enalaprilat and diketopiperazine in pharmaceutical formulations

An analytical method today should be both statistically reliable and enviromentally sustainable, following the principles of Green Analytical Chemistry. The official analytical method for assay and impurities in enalapril maleate tablets, as described in pharmacopoeial monographs, relies on HPLC-UV with a C8 column (250 × 4.6 mm; 5 μm) and a mobile phase consisting of acetonitrile and phosphate buffer (pH 2.2, 25 : 75 v/v). In order to reduce analysis time, cost, and environmental impact, an optimised method was developed. The chromatographic column was replaced with a C18 (100 × 4.6 mm; 3.5 μm), as the reduced particle size and shorter column length allowed for faster separations while maintaining efficiency. In addition, the mobile phase was modified to ethanol and phosphate buffer (pH 2.2, 30 : 70 v/v), since ethanol has a lower environmental impact compared with acetonitrile. Relative to the official method, the optimised procedure shortened the chromatographic run by approximately 8 minutes, reduced organic solvent consumption by 17.1 mL (equivalent to US$ 0.40) per run, and achieved better scores in the NEMI, GAPI, Eco-Scale (84 <i>vs.</i> 89), and AGREE (0.57 <i>vs.</i> 0.78) assessment tools. During validation, the linear range for enalapril was established as 140-260 μg mL^-1, and the method proved capable of simultaneously quantifying enalapril, enalaprilat, and diketopiperazine with BAGI and RAPI scores of 80.0 and 67.5, respectively.