Separation behavior of amino acid enantiomers in ligand exchange micellar electrokinetic chromatography

The separation of amino acid enantiomers using a Cu(II) complex with L-hydr oxyproline as a chiral selector has been investigated by ligand exchange mi cellar electrokinetic chromatography. It was found that anionic surfactants like sodium dodecyl sulfate (SDS), sodium n-decyl sulfate, and sodium n-te tradecyl sulfate can not only improve the resolution of D,L-enantiomers, bu t also can change their migration orders. The migration order of o-, m-, an d p-positional isomers of fluorophenylalanine and tyrosine was reversed whe n the concentration of SDS exceeded a certain concentration. Tween 20 impro ved the separation efficiency, but the migration time became longer. Cetylt rimethylammonium bromide can change the direction of electroosmotic flow, b ut it has no significant improvement on resolution. Organic modifiers cause the decline of resolution, but not the reversal of enantiomer migration or der (EMO). A possible mechanism of the reversal of EMO is presented. (C) 19 99 John Wiley & Sons, Inc.