Effect of mobile phase additive on chiral separation

Cellulose tris(3,5-dimethylphenylcarbamate) (OD) and amylose tris(3,5-dimethylphenylcarbamate) (AD) exhibit high chiral recognition and have been extensively used to resolve a broad range of racemates, which appear to be the most practically useful chiral stationary phases (CSPs). Cyclodextrin CSPs demonstrate unusual selectivity under either reversed- or normal-phase modes mainly attributable to inclusion complex properties and hydrogen bonding interaction, respectively. In this study the influence of the presence of heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD) in mobile phase on the enantioseparations is described. Three chiral stationary phases including cellulose tris(3,5-dimethylphenylcarbamate), amylose tris(3,5-dimethylphenylcarbamate) and their mixture are employed, with hexane/isopropanol (90:10) as mobile phase. The separation behaviour of 10 racemates when TM-β-CD are added as mobile phase additive provided information concerning the interaction of the enantiomer with the TM-β-CD, OD and AD. The increase in the selectivity of separation for some racemates is a favourable consequence of the presence of the TM-β-CD mobile phase additive.