Direct resolution of chiral 'pineno' fused terpyridyl ligands on amylose based chiral stationary phase using long chain alcohol modifiers

Chiral separation of novel pineno fused terpyridyl ligands have been investigated on a silica-based amylose tris(3,5-dimethylphenyl carbamate) stationary phase (Chiralpak AD), using normal phase conditions. The chromatographic parameters investigated include retention factor (k), separation factor (α), column efficiency (N) and resolution (R_S) of the analytes. In addition, the effect of alcohol modifiers on the enantioselectivity of the column has been discussed. The chiral resolution of the ligands was significantly improved by using 1-pentanol as alcohol modifier in the mobile phase. The reversal of the elution order achieved in this study allows a lower detection limit (<0.1%) of the minor enantiomer and the chromatographic system described is suitable for assessing the enantiomeric excess (ee) of the ctpy ≥ 99.9%. The method is selective and sensitive with a limit of detection (LOD) and quantification (LOQ) of 0.2 μg/ml and 0.6 μg/ml for ctpy, 0.6 μg/ml and 1.2 μg/ml for ctpy-x-ctpy, respectively. This study suggests that superior enantioseparation may be obtained for certain analytes using the same column by simply changing the type of alcohol modifier in the mobile phase instead of choosing another expensive chiral stationary phase for the same purpose.