Two-chiral-component microemulsion electrokinetic chromatography-chiral surfactant and chiral oil: part 1. dibutyl tartrate.
The first simultaneous use of a chiral surfactant and a chiral oil for microemulsion EKC (MEEKC) is reported. Six stereochemical combinations of dodecoxycarbonylvaline (DDCV: R, S, or racemic, 2.00% w/v), racemic 2-hexanol (1.65% v/v), and dibutyl tartrate (D, L, or racemic, 1.23% v/v) were examined as chiral pseudostationary phases (PSPs) for the separation of six pairs of pharmaceutical enantiomers: pseudoephedrine, ephedrine, N-methyl ephedrine, metoprolol, synephrine, and atenolol. Subtle differences were observed for three chromatographic figures of merit (alpha(enant), alpha(meth), k) among the chiral microemulsions; a moderate difference was observed for efficiency (N) and elution range. Dual-chirality microemulsions provided both the largest and smallest enantioselectivities, due to small positive and negative synergies between the chiral microemulsion components. For the ephedrine family of compounds, dual-chiral microemulsions with surfactant and oil in opposite stereochemical configurations provided higher enantioselectivities than the single-chiral component microemulsion (RXX), whereas dual-chiral microemulsions with surfactant and oil in the same stereochemical configurations provided lower enantioselectivities than RXX. Slight to moderate enantioselective synergies were confirmed using a thermodynamic model. Efficiencies observed with microemulsions comprised of racemic dibutyl tartrate or dibutyl-D-tartrate were significantly higher than those obtained with dibutyl-L-tartrate, with an average difference in plate count of about 25 000. Finally, one two-chiral-component microemulsion (RXS) provided significantly better resolution than the remaining one- and two-chiral-component microemulsions for the ephedrine-based compounds, but only slightly better or equivalent resolution for non-ephedrine compounds.
Kahle
Kimberly A
KA
Department of Chemistry, Drexel University, Philadelphia, PA 19104, USA.
Foley
Joe P
JP
D001262:Atenolol / Q000302:isolation & purification; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D004655:Emulsions / Q000737:chemistry; D004809:Ephedrine / Q000031:analogs & derivatives / Q000302:isolation & purification; D000441:Hexanols / Q000302:isolation & purification; D008790:Metoprolol / Q000302:isolation & purification; D009821:Oils / Q000737:chemistry; D013237:Stereoisomerism; D013501:Surface-Active Agents / Q000737:chemistry; D013578:Synephrine / Q000302:isolation & purification; D013644:Tartrates / Q000737:chemistry*; D013816:Thermodynamics; D014633:Valine / Q000031:analogs & derivatives / Q000737:chemistry
D004655:Emulsions; D000441:Hexanols; D009821:Oils; D013501:Surface-Active Agents; D013644:Tartrates; C104188:N-dodecoxycarbonylvaline; C522497:dibutyl tartrate; D001262:Atenolol; C041707:N-methylephedrine; C037076:2-hexanol; D008790:Metoprolol; D004809:Ephedrine; D014633:Valine; D013578:Synephrine