The simultaneous separation of o-, m-, and p-fluoro-DL-phenylalanine and o-, m-, and p-hydroxy-DL-phenylalanine (tyrosine) by ligand-exchange micellar electrokinetic capillary chromatography (LE-MEKC) was carried out. A copper(II) complex of L-4-hydroxyproline was used as the chiral selector. The influence of the concentration of the chiral additive, organic modifiers such as methanol or acetonitrile, field strength and pH value on the selectivity was investigated The relationship of electroosmotic flow with sodium dodecyl sulfate (SDS) concentration as well as the pH of electrolyte was discussed. The addition of SDS resulted in a significant improvement in the separation. It was interestingly observed that the migration order of D,L-enantiomers as well as o-, m-, p-enantiomers was reversed when the concentration of SDS exceeded a certain concentration. A possible mechanism of LE-MEKC was discussed. (C) 1998 Elsevier Science BN. All rights reserved.