Enantiomeric separations of cationic and neutral compounds by capillary electrochromatography with monolithic chiral stationary phases of β-cyclodextrin-bonded negatively charged polyacrylamide gels

Enantiomeric separation by capillary electrochromatography with β-cyclodextrin-bonded negatively charged polyacrylamide gels was examined. The columns used are capillaries filled with a negatively charged polyacrylamide gel, a so-called monolithic stationary phase, to which allyl carbamoylated β-CD (AC-β-CD) derivatives covalently bind. The capillary wall is activated first with a bifunctional reagent to make the resulting gel bind covalently to the inner surface of the fused-silica tubing. Enantiomeric separations of 15 cationic compounds were achieved using the above-mentioned columns and mobile phases of 200 mmol l−1 Tris–300 mmol l−1 boric acid buffer (pH 7.0 or 9.0) or 200 mmol l−1 Tris–300 mmol l−1 boric acid buffer (pH 7.0) containing an achiral crown ether (18-crown-6). Enantiomeric separations of two neutral compounds were also achieved using 200 mmol l−1 Tris–300 mmol l−1 boric acid buffer (pH 9.0) as a mobile phase. High efficiencies of up to 150 000 plates m−1 were obtained. Both the within- and between-run reproducibilities of retention time and separation factor were good. The reproducibilities of retention time and separation factor for three different columns prepared from a different batch of monomers were acceptable. The gel-filled capillaries were stable for at least 3 months with intermittent use, utilizing the mobile phase of 200 mmol l−1 Tris–300 mmol l−1 boric acid buffer (pH 9.0).