Optimized Chiral Separation of 20 Amino Acids Derivatized with 9-Fluorenylmethyl Chloroformate Using Cyclodextrins as Chiral Selectors in Capillary Electrophoresis

Abstract

Direct chiral separation of DL-amino acids derivatized with 9-fluorenylmethyl chloroformate (FMOC-amino acids) is accomplished with micellar electrokinetic capillary chromatography. Separation parameters such as sodium dodecyl sulfate (SDS) and cyclodextrin concentrations are optimized by factorial designs. The interaction and effect of these variables on chiral recognition of FMOC-amino acids are presented in optimization charts. The enantioseparations are performed under optimized conditions by using γ-cyclodextrin (γ-CD) or β-cyclodextrin (β-CD) as chiral selectors. By using β-CD as a chiral selector, baseline separation of 20 FMOC-amino acids is achieved under some different conditions ; 17 of the amino acids could be separated under the same conditions (50 mM phosphate, 50 mM SDS, 12 mM β-CD, and 15% 2-propanol). Application of γ-CD resulted in chiral separation of 12 FMOC-amino acids. For all FMOC-amino acids tested, the presence of 2-propanol was a prerequisite for a chiral separation when using β-CD as a chiral selector. Similarly, 2-propanol was needed in the majority of cases in which γ-CD was employed. Separation efficiencies are in the range of 10.7-0.9 x 10 5 theoretical plates per meter.