Hydrophobic eutectic solvent with antioxidant properties: application for the dispersive liquid-liquid microextraction of fat-soluble micronutrients from fruit juices

Despite the great interest devoted to eutectic solvents with significant negative deviations from ideality (namely, deep eutectic solvents), many hydrophobic liquid mixtures are ideal or quasi-ideal systems. In this regard, we propose the introduction of a hydrophobic eutectic solvent based on l-menthol and butylated hydroxytoluene, blended in a molar ratio of 3:1. The physicochemical characterization by means of differential scanning calorimetry and infrared spectroscopy has identified that it is an ideal eutectic solvent. Compared to other hydrophobic mixtures, this one represents an advanced solvent system due to its intrinsic antioxidant activity, which makes it an ideal green choice for the extraction and preservation of easily oxidizable lipophilic compounds. In order to evaluate its efficiency, it was applied for the first time as an extractant for the dispersive liquid-liquid microextraction of carotenoids and fat-soluble vitamins from fruit juices, carried out at 298 K. All extracts were analyzed by high-performance liquid chromatography-tandem mass spectrometry. The developed method was then validated, providing precise (4-8%) and accurate (4-6%) results on a commercial fruit juice containing declared values of β-carotene and α-tocopherol acetate. Recoveries were ≥70%, while the detection limits were 0.05 μg L-1 for β-carotene and 0.28 μg L-1 for α-tocopherol acetate. Here, we also propose an original approach to properly determine the antioxidant activity of eutectic mixtures since the available commercial kits cannot be applied to such systems without altering their nature. Last but not least, a circular process of reuse of this ideal eutectic solvent has been developed using a low-cost activated carbon material obtained from coconut shells.