Enantioselective ion-exclusion chromatography on teicoplanin aglycone and (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid stationary phases

Ion-exclusion chromatography is a well established technique for the analysis of achiral ionic species, but it has rarely been applied to chiral analytes. In this paper enantioselective ion-exclusion separations were developed on two commercially available HPLC phases: Chirobiotic TAG, based on teicoplanin aglycone, and Opticrown RCA (+), based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid. Chirobiotic TAG columns have a carboxylic acid group on the chiral ligand, which can be partially ionized to exclude anionic analytes by ionic repulsion. Under acidic conditions Opticrown columns have a cationic sublayer generated from the aminopropyl base silica that excludes cationic analytes. Both columns demonstrate a large dependence of efficiency on flow-rate, with the highest efficiencies at 0.1 ml/min on a 4.6 mm inner diameter column.