Two‐chiral component microemulsion EKC – chiral surfactant and chiral oil. Part 2: Diethyl tartrate

In this second study on dual‐chirality microemulsions containing a chiral surfactant and a chiral oil, a less hydrophobic and lower interfacial tension chiral oil, diethyl tartrate, is employed (Part 1, Foley, J. P. et al.., Electrophoresis, DOI: 10.1002/elps.200600551). Six stereochemical combinations of dodecoxycarbonylvaline (DDCV: R , S , or racemic, 2.00% w/v), racemic 2‐hexanol (1.65% v/v), and diethyl tartrate ( D , L , or racemic, 0.88% v/v) were examined as pseudostationary phases (PSPs) for the enantioseparation of six chiral pharmaceutical compounds: pseudoephedrine, ephedrine, N‐ methyl ephedrine, metoprolol, synephrine, and atenolol. Average efficiencies increased with the addition of a chiral oil to R ‐DDCV PSP formulations. Modest improvements in resolution and enantioselectivity ( α enant ) were achieved with two‐chiral‐component systems over the one‐chiral‐component microemulsion. Slight enantioselective synergies were confirmed using a thermodynamic model. Results obtained in this study are compared to those obtained in Part 1 as well as those obtained with chiral MEEKC using an achiral, low‐interfacial‐tension oil (ethyl acetate). Dual‐chirality microemulsions with the more hydrophobic oil dibutyl tartrate yielded, relative to diethyl tartrate, higher efficiencies (100 000–134 000 vs. 80 800–94 300), but lower resolution (1.64–1.91 vs. 2.08–2.21) due to lower enantioselectivities (1.060–1.067 vs. 1.078–1.081). Atenolol enantiomers could not be separated with the dibutyl tartrate‐based microemulsions but were partially resolved using diethyl tartrate microemulsions. A comparable single‐chirality microemulsion based on the achiral oil ethyl acetate yielded, relative to diethyl tartrate, lower efficiency (78 300 vs. 91 600), higher resolution (1.99 vs. 1.83), and similar enantioselectivities.