Hydrophobic Eutectic Solvents Based on Perfluorinated Hydrogen Bond Donors as Extractants for Dispersive Liquid–Liquid Microextraction

Abstract

In this work, six hydrophobic eutectic solvents composed of menthol, tetrabutylammonium chloride, and tetrahexylammonium chloride as hydrogen-bond acceptors and trifluoroacetic acid and hexafluoroisopropanol as hydrogen-bond donors were prepared. All solvents exhibit a higher than water densities ranging from 1.094 to 1.237 g mL⁻¹. The quaternary ammonium salt-based solvents have moderate viscosities varying between 46.4 and 70.6 mPa s. The viscosities of both menthol-based liquids were over an order of magnitude lower. The extraction properties of the solvents were evaluated employing phthalates, parabens and flavonoids as model analytes. Four solvents demonstrated considerably better overall extraction efficiency than conventional chlorinated solvents (CH₂Cl₂, CHCl₃, and CCl₄). The developed solvents were examined as sample diluents for RP-HPLC separations. Finally, solvent consisting of tetrahexylammonium chloride and trifluoroacetic acid was applied for dispersive liquid–liquid micro-extraction of four parabens from wastewater samples prior to HPLC analysis. Under optimized extraction conditions, the enrichment factors ranged from 66 to 72. Calibration curves were linear (R² ≥ 0.9970) for a concentration level between 1.00 and 500 μg L⁻¹ and the detection limits were in the range 0.44–0.58 μg L⁻¹. The recoveries of the parabens of the developed method for the spiked wastewater samples were 84–104%, with the coefficients of variation less than 7.5%.