Evaluation of the chiral recognition properties and the column performances of three chiral stationary phases based on cellulose for the enantioseparation of six dihydropyridines by high-performance liquid chromatography

Separations of six dihydropyridine enantiomers on three commercially available cellulose-based chiral stationary phases (Chiralcel OD-RH, Chiralpak IB, and Chiralpak IC) were evaluated with high-performance liquid chromatography (HPLC). The best enantioseparation of the six chiral drugs was obtained with a Chiralpak IC (250x4.6mm i.d., 5m) column. Then the influence of the mobile phase including an alcohol-modifying agent and alkaline additive on the enantioseparation were investigated and optimized. The optimal mobile phase conditions and maximum resolution for every analyte were as follows respectively: n-hexane/isopropanol (85:15, v/v) for nimodipine (R=5.80) and cinildilpine (R=5.65); n-hexane/isopropanol (92:8, v/v) for nicardipine (R=1.76) and nisoldipine (R=1.92); and n-hexane/isopropanol/ethanol (97:2:1, v/v/v) for felodipine (R=1.84) and lercanidipine (R=1.47). Relative separation mechanisms are discussed based on the separation results, and indicate that the achiral parts in the analytes' structure showed an important influence on the separation of the chiral column.