18-crown-6-tetracarboxylic acid as a chiral additive for the simultaneous separation of o-, m- and p-enantiomers of phenylalanine family by capillaryelectrophoresis

Simultaneous separation of 12 o-, m- and p-positional enantiomers of tyrosi ne and fluorophenylalanine has been achieved by the use of optically active 18-crown-6-tetracarboxylic acid (18C6H(4)) as an additive in the backgroun d electrolyte. It has been investigated that the separation conditions such as pH, electroosmotic flow, the concentration of 18C6H(4) and applied volt ages have critical influence on the simultaneous separation. Based on the i nformation of electropherograms obtained, the interaction between the chira l selector and positional enantiomers has been discussed. It was shown that a-methyl group in the amino acid enantiomers make the resolution be reduce d, and that o-, m- and p-substituents have an influence on the resolution.