Effect of deep eutectic solvents on the chiral separation of pesticides by cyclodextrin-electrokinetic chromatography and quantitation of ethofumesate enantiomers

The effect of deep eutectic solvents (DES) on the chiral discrimination of a group of pesticides (prothioconazole, dimethenamid-P, metalaxyl, ethofumesate, malathion, dichlorprop-P, mecoprop) in Cyclodextrin-Electrokinetic Chromatography (CD-EKC) was investigated in this work. A screening of 21 neutral and anionic cyclodextrins (CDs) was carried out and TM-β-CD, CE-β-CD, CM-γ-CD, and P-γ-CD were initially selected for further optimization due to their superior chiral recognition ability for the studied compounds although the resolution achieved was insufficient for some of them. Then, the effect of adding hydrophilic and hydrophobic DES as additives to the separation medium was studied. While hydrophilic DES hindered separation, hydrophobic DES, specifically menthol–octanoic acid and eucalyptol–octanoic acid, improved the chiral resolution for selected pesticides. The influence of the DES percentage, temperature, and voltage, on enantioresolution and analysis time was evaluated. Under optimized conditions, the enantiomers of prothioconazole and metalaxyl were baseline-separated with TM-β-CD and P-γ-CD, respectively, while only a partial separation was possible for ethofumesate with CM-γ-CD. However, using SBE-β-CD, a resolution >1.5 was achieved for ethofumesate. The best results were obtained using 5 mM TM-β-CD-0.5% eucalyptol–octanoic acid for prothioconazole (Rs = 3.13, analysis time = 5.20 min), 10 mM P-γ-CD-0.25% menthol–octanoic acid for metalaxyl (Rs = 1.55, 9.77 min), and 5 mM SBE-β-CD-0.25% eucalyptol–octanoic acid for ethofumesate (Rs = 2.00, 9.45 min). The analytical characteristics of the developed method for ethofumesate were evaluated showing its adequate performance for the enantiomeric determination of this herbicide in herbal infusions.