Chiral separations in capillary electrophoresis with betaine: Urea as a major component of a mixed aqueous-deep eutectic solvent

This work reports the first investigation of chiral separations in capillary electrophoresis (CE) using a deep eutectic solvent (DES) as the major component of the background electrolyte solvent (DES/water (70:30, v /v)). With sulfobutylether-β-cyclodextrin (SBE-β-CD) serving as the chiral selector, the effects of key parameters—including the type and concentration of the BGE (apparent pH ⁎ ), SBE-β-CD concentration, and the separation voltage—were examined. The results showed that the DES, betaine:urea (BU) system exhibited superior enantioseparation performance compared with conventional aqueous media in certain cases. All six chiral drugs with diverse structures were baseline-resolved in BU under optimized conditions (25 mM NH₄OAc at pH ⁎ 8.9, 2.0–3.0% (m/v) SBE-β-CD, and a separation voltage of 30 kV). Preliminary insights into the recognition mechanism were obtained by fluorescence spectroscopy, which revealed opposite fluorescence responses of drug enantiomers upon SBE-β-CD addition in BU and aqueous phases (quenching versus enhancement), suggesting distinct binding modes in the two solvents. Molecular docking analysis suggested that the presence of DES components modifies the host–guest interactions between SBE-β-CD and enantiomers, which is consistent with the experimentally observed enantioselectivity. The newly developed separation system was further validated, and its environmental sustainability and practical applicability were quantitatively assessed using the ComplexMoGAPI and BAGI tools. These findings demonstrate the potential of DESs as more efficient and sustainable separation media for addressing complex enantioseparation challenges encountered in conventional CE systems. They also highlight the broader applicability of DESs as eco-friendly, cost-effective alternatives to traditional organic solvents in separation science.