Chiral microemulsion electrokinetic chromatography with two chiral components: Improved separations via synergies between a chiral surfactant and a chiral cosurfactant

Abstract

In this study, the combination of two chiral components in a microemulsion formulation for the separation of enantiomers via microemulsion EKC (MEEKC) was successfully accomplished. Previous publications of chiral microemulsions have utilized only one chiral entity; the surfactant, cosurfactant, or oil was chiral. This is the first study, to date, of the effects of using two chiral species in a single pseudostationary phase (PSP). The chiral surfactant dodecoxycarbonylvaline (DDCV) was used in conjunction with the chiral cosurfactant S-2-hexanol. Ethyl acetate was incorporated as the oil core of the microemulsion and the buffer was 50 mM phosphate at a pH of 7. Additionally, a microemulsion prepared with racemic 2-hexanol was used for comparison to a previous DDCV microemulsion and as a baseline for the newly formulated dual chiral microemulsion. The efficiencies, resolutions, and enantioselectivities for the S-2-hexanol, racemic 2-hexanol, and original 1-butanol DDCV microemulsions are compared. The hexanol-based PSPs provide improved efficiencies and resolutions. To evaluate the combination of each DDCV enantiomer (R and S) with S-2-hexanol, changes in Gibb's free energy were calculated. A synergistic effect was found when two chiral components were combined to form a microemulsion.

(S)-(+)-2-Octanol as a Chiral Oil Core for the Microemulsion Electrokinetic Chromatographic Separation of Chiral Basic Drugs

“…In addition to the use of a chiral surfactant [17][18][19][20][21][22] or a chiral cosurfactant 23 as the enantioselective element within the microemulsion droplets in MEEKC, the present study was demonstrated for a novel chiral-MEEKC system employing optically active (S)-(+)-2-octanol as a chiral oil for effecting the enantioseparation of basic drugs in MEEKC.…”

“…17,19,23 In addition, it is also recognized that organic modifiers can have an effect on the electroosmotic flow (EOF), the viscosity, the dielectric constant, the conductivity of the background electrolyte, and the solubility of the analytes. 27 Consequently, the effect of the 1-butanol concentration (4.4 to 8.8% (w/w)) on the enantioseparation of (±)-norephedrine was studied; and the obtained results can be seen in Fig.…”

“…Recently, many works have come up with a new kind of chiral emulsion in which a chiral surfactant (dodecoxycarbonylvaline) is incorporated in the microemulsion. [17][18][19][20][21][22] In addition, Zheng et al presented another novel chiral microemulsion for achieving chiral separations based on the use of chiral alcohol as a cosurfactant. 23 In this work, a new chiral-MEEKC system using (S)-(+)-2-octanol as an oil core was employed for the enantioseparation of basic drugs.…”

Capillary Electrophoresis in Bioanalysis

“…A combination of two chiral components in microemulsion electrokinetic chromatography was investigated (170). By using an S-dodecoxycarbonylvaline with the cosurfactant S-2-hexanol, an increased resolution of 3.7 was achieved in the separation of pseudoephedrine enantiomers.…”

Review of aqueous chiral electrokinetic chromatography (EKC) with an emphasis on chiral microemulsion EKC

“…The next DDCV publication was the first to describe the simultaneous incorporation of two chiral selectors into one microemulsion; it was subsequently employed for the separation of N-methyl ephedrine and pseudoephedrine enantiomers [66]. Each chiral surfactant enantiomer (R-and S-DDCV) was combined with one enantiomer of a chiral cosurfactant (S-2-hexanol).…”