Enantiomeric resolution of quinolones on crown ether CSP: Thermodynamics, chiral discrimination mechanism and application in biological samples

The enantiomers of quinolone racemates were resolved using chiral crown ether within 8 min. Thermodynamics data and modeling results were used to determine chiral recognition mechanism. The column used was (+)-Crownpack column (250 mm × 4.6 mm, 5 µm) with three mobile phases I: ACN:Water (80:20) + 10 mM H₂SO₄ and 10 mM CH₃COONH₄, II: ACN:Water (80:20) + 20 mM perchloric acid and III: EtOH:Water (80:20) + 20 mM perchloric acid. The flow rate of the mobile phases was 1.0 mL/min with UV detection at different wavelengths. The ranges of retention (k), separation (α), and resolution (Rs) factors were 1.00-5.40, 1.37-2.00 and 1.50-3.30. The tailing factor was 1.o for all peaks with 900-2325 as the number of theoretical plates were 8.0-10.0 and 32.4-22.1 µg. The difference in enthalpy, entropy and free energy varied in the range of -0.350 to -0.024, 18.74 × 10^-4 to 3.94 × 10^-4 and -0.918 to -0.143, respectively. The thermodynamic and docking results showed chiral discrimination due to physical forces of amnio group cations penetration into the chiral cavity of the chiral selector following hydrogen bindings. The binding energy of S-enantiomers was higher than R-enantiomers; confirming stronger binding of S-enantiomers with CSP than R-enantiomers. The described chiral-HPLC method was used for the analysis of the quinolone enantiomers in urine samples and the results were quite satisfactory. Therefore, the reported method may be used for the enantiomeric separation of quinolone enantiomers in urine samples.