Preparation and application of a chiral stationary phase based on (+)-(1 8-crown-6)-2,3,11,12-tetracarboxylic acid without extra free aminopropyl groups on silica surface

A crown ether-based chiral stationary phase (CSP) without extra aminopropyl groups on the surface of silica gel was newly prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel. The new CSP was applied to the resolution of various racemic alpha-amino acids, amines, and amino alcohols. The chiral recognition efficiency of the new CSP was generally superior to that of the original CSP containing unreacted residual aminopropyl groups on the surface of silica gel in terms of the separation (alpha) and the resolution factors (Rs). The retention behaviors of analytes on the new CSP with the variation of the content of organic and acidic modifiers in aqueous mobile phase were consistent with those on the original CSP in the resolution of alpha-amino acids, but somewhat different in the resolution of racemic amines and amino alcohols from those on the original CSP and the difference was rationalized by the lipophilicity difference of the two CSPs. The effect of the column temperature on the chromatographic resolution behaviors on the new CSP was consistent with that on the original CSP.