Enantiomeric separation of flavonoid compounds using capillary electrokinetic chromatography

Abstract

Simultaneous separation of 2'- 4'- and 7-hydroxyflavanone enantiomers was investigated using cyclodextrin-electrokinetic chromatography (CD-EKC) with single or dual highly sulfated-CD (HS-β-CD and/or HS-γ-CD in a pH 2.5 phosphate buffer. Enantioselectivity (к) defined as the ratio of the binding constant к for enantiomers to CD, was obtained in order 2'- > 4'- ≈ 7- with HS-β-CD (3.16, 1.04 and 1.02, respectively) while 4'- > 2'- > 7- with HS-y-CD (1.40, 1.17, and 1.09 respectively). The optimum enantiomeric resolution (Rs) was found to be consistent with the к scale: very high Rs, up to 19 for 2'- with HS-β-CD, partial Rs for 4'- and 7- with HS-β-CD, and achieved baseline Rs ≥ 1.5 for simultaneous separation of these three enantiomers with HSγ-CD. In dual CDs using the fixed concentration of CD1 (4 or 8 mM HS-β-CD) and varying the concentration of CD2 (2 to 47 mM HS-γ-CD), a change in separation selectivity (α), defined as the ratio of the electrophoretic mobilities for enantiomers, with an increase in the CD2 concentration was found to be consistent with the concept of dual enantioselectivities for dual CDs: an increase in α for 7- due to the same order of enantiomers in CD2 and CD2 with к2 > α1, a decrease in α for 2'- due to the same order of enantiomers in CD2 and CD1 with к2 < к1, while a decrease in α to 1.0 and then an increase in α at higher CD2 for 4'- due to the reversed migration order of enantiomers in CD2 and CD1 with к2 > к1.