Separation of achiral anti-diabetic drugs using sub/supercritical fluid chromatography with a polysaccharide stationary phase: Thermodynamic considerations and molecular docking study.

A simple, fast and environmental friendly supercritical fluid chromatography-photodiode array (SFC-PDA) method was developed for the simultaneous determination of metformin and three sodium-glucose co-transporter 2 (SGLT-2) inhibitors (canagliflozin, dapagliflozin and empagliflozin). The impact of different stationary phases, co-solvents, column temperature and outlet pressure was extensively evaluated for selective separation and quantitation of the drugs. Amongst several achiral and chiral stationary phases tested, the best results were obtained on amylose based Chiralpak IG column using CO and 0.1 % diethylamine in methanol and isopropanol 50:50 (v/v) in 60:40 ratios as the mobile phase. The separation efficiency was mainly dependent on the nature of stationary phase and the mobile phase composition. The limit of detection (LOD) and quantitation (LOQ) of the method were 0.155 and 0.469, 0.062 and 0.187, 0.015 and 0.045, 0.028 and 0.084 μg/mL for metformin, canagliflozin, dapagliflozin and empagliflozin, respectively. The chromatographic resolution between metformin-canagliflozin, metformin-dapagliflozin and metformin-empagliflozin pairs was 6.87, 3.44 and 6.47, respectively. The intra-batch and inter-batch precision of the method was ≤1.64 % while the accuracy was in the range of 96.2-103.3 %. The method was used to analyze metformin and SGLT-2 inhibitors in their binary fixed-dose formulations with acceptable accuracy (recovery) and precision. To support the experimental results, molecular docking was performed on Schrodinger software to provide a deeper insight into the interactions between the analytes and the chiral stationary phase and to understand their elution orders under optimized conditions.