Cyclodextrin-electrokinetic chromatography using Betaine:Urea, a deep eutectic solvent as the separation medium

While deep eutectic solvents (DESs) are emerging as greener alternatives to conventional separation media for capillary electromigration techniques (CE), their compatibility with cyclodextrins (CDs), a key group of pseudo-stationary phases (PSPs) in CE, remains unexplored. In this study, we present the first systematic investigation of CD functionality in a DES-based electrokinetic chromatography (EKC) system. Eight CDs-including three native forms (α-, β-, γ-CD) and five derivatives-were evaluated for their solubility and separation performance toward three groups of complex analytes. The results demonstrated that the DES, Betaine:Urea (BU), exhibited excellent solubility for all tested CDs, with native CDs showing a particularly significant enhancement (2 to 20-fold increase) in solubility compared to water. More importantly, the host-guest properties of these CDs, primarily mediated by hydrophobic effects, remained effective in the DES, and even exhibited markedly enhanced hydrophobic selectivity compared to aqueous systems. This enabled successful separations of three groups of highly hydrophobic polycyclic aromatic hydrocarbons (PAHs), covering both charged and neutral ones. In contrast, none of these separations were achieved in conventional aqueous CD-EKC systems, highlighting the potential of DESs as more efficient and sustainable separation media for addressing specific challenges in traditional CE.