Chiral separation of amino acid esters by micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC) was used for the chiral separation of uncharged analytes (C- and N-protected amino acids). Sodium dodecyl sulfate (SDS) was the micelle forming agent, and different cyclodextrin (CD) derivatives were added as chiral selectors. Suitable conditions for the enantioseparation were found by variation of the separation conditions. The influence of addition of organic solvents like acetonitrile or methanol, and other chiral additives (camphor-10-sulfonic acid, malic acid) was examined. The addition of an organic modifier resulted in different effects on micelle formation, and thereby on the separation. The used chiral additives did not improve the selectivity. Furthermore, dependence of the electroosmotic flow (EOF), and the capacity factors on the concentration of CDs was investigated. Increasing the CD concentration, both the EOF to a smaller extent as well as the capacity factors decrease. Nevertheless, the enantioseparation is improved with a CD-concentration up to 30 mM. Higher CD-concentrations reduce the separation of the analytes.