Liquid chromatographic direct resolution of β-amino acids on a chiral crown ether stationary phase

A chiral stationary phase (CSP) prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel was used for the direct resolution of β-amino acids. To determine the optimum mobile phase composition, two β-amino acids were selected and their resolutions on the CSP were performed with variation of the types and contents of organic and acidic modifiers in the aqueous mobile phase. The chromatographic resolution behaviors were found to be dependent on the types and contents of organic and acidic modifiers in the aqueous mobile phase. From the results of these experiments, a possible optimum mobile phase composition was proposed to be a mixed solvent of 50% methanol in water containing acetic acid (10 mM). The chromatographic resolution behaviors were also found to be dependent on the column temperature, the retention (k1) and the separation factors (α) being greater at lower temperatures. At the optimum mobile phase composition, all β-amino acids tested in this study were resolved quite well on the CSP with baseline separation.