CHIRAL SEPARATION RETENTION MECHANISMS IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING BARE SILICA STATIONARY-PHASE AND BETA-CYCLODEXTRIN AS A MOBILE-PHASE ADDITIVE

This report describes a novel approach to direct chiral separations us ing bare silica stationary phase with an aqueous mobile phase containi ng sodium phosphate, beta-cyclodextrin (beta-CD), and 2-methyl-2-propa nol. Two racemic cycloheptaindole derivatives were used as model compo unds for the study. Both enantiomer pairs were resolved in a single ch romatographic run. Analyte retention mechanisms were consistent with i on-exchange, beta-CD inclusion, and hydrophobic modes of interaction. Adding triethylamine to the mobile phase improved peak symmetry and re duced retention. Consistent separations were obtained with different l ots of beta-CD and different analytical columns. The technique has a n umber of attractive features that may broaden the use of chiral mobile phase additives for direct enantioseparations.