Enantioseparation of esbiothrin by cyclodextrin-modified microemulsion and micellar electrokinetic chromatography

A comparison between chiral cyclodextrin-modified microemulsion electrokinetic chromatography (CD-MEEKC) and cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) for the enantiomeric separation of esbiothrin was carried out. For both methods, the separation conditions were optimized by varying CD types and concentration, running buffer pH and compositions, organic modifiers, and temperature. The optimal CD-MEEKC conditions were 0.8% n-heptane, 2.3% SDS, 6.6% n-butanol, 90.3% 10 mM sodium tetraborate containing 3% (w/v, the ratio of CD mass to microemulsion volume) methyl-beta-cyclodextrin, pH 10, 25 degrees C. The optimized CD-MEKC conditions were 3.3% SDS, 96.7% 10 mM sodium tetraborate containing 5% (w/v) beta-CD, pH 10, 25 degrees C. The difference in physicochemical properties of the buffer and CDs resulted in different optimal CD type. The competitive distribution between the microemulsion (or micelle) and chiral CD contributed to the chiral separation. Both methods provided excellent separation (R(s) approximately 3) with similar migration time (ca. 15 min). CD-MEEKC provided higher separation efficiencies (>300000) than CD-MEKC (>200000). The LODs for CD-MEEKC and CD-MEKC were 4.7 microg/mL and 3.2 microg/mL, respectively. The RSDs of migration time and peak area for CD-MEEKC were slightly higher than for CD-MEKC. Both the demonstrated CD-MEEKC and CD-MEKC methods provided high efficiencies, low LODs, and reproducible enantioseparations of esbiothrin.