Impact of triethylamine as a mobile phase additive on the resolution of racemic amino acids on an (+)-18-crown-6-tetracarboxylic acid-derived chiral stationary phase

Recently, a new HPLC chiral stationary phase (CSP) prepared by covalently b onding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid on silica gel was su ccessfully employed in resolving various racemic natural and unnatural amin o acids containing a primary amino group. Current work details on-going eff orts to improve the effectiveness of this type of material. The analytes us ed in this study included various substituted phenylalanines, phenylglycine homologues and other primary amino acids. In an attempt to increase enanti oselectivity, the effect of methanol and triethylamine modifiers was evalua ted in an aqueous mobile phase containing sulfuric acid. In general, retent ion time increased with increasing methanol and triethylamine concentration . In addition, highest enantioselectivities were obtained with high methano l and high triethylamine; however, these conditions produced excessively lo ng retention. All of the analytes were well resolved on the CSP with a mobi le phase of 20% methanol containing 14.3 mM triethylamine and 10.0 mM sulfu ric acid. (C) 2001 Elsevier Science B.V. All rights reserved.