Liquid-liquid microextraction with hydrophobic deep eutectic solvent followed by magnetic phase separation for preconcentration of antibiotics.

This study describes a miniaturized approach for liquid-liquid microextraction based on mass transfer into low volume of deep eutectic solvent and magnetic phase separation, using specially produced magnetic chromium dioxide nanoparticles with a hydrophobic surface layer of fatty acids. The nanoparticles modified with fatty acid helped to recover low volumes of viscous hydrophobic deep eutectic solvent-based extract reproducibly and easily (up to 10 μL) in a microextraction procedure with the application of magnetic forces. It was demonstrated that the collector properties depend on nanoparticles' surface and magnetic characteristics. The developed approach was implemented for the separation and preconcentration of trace fluoroquinolone antibiotics from environmental waters prior to their determination by high-performance liquid chromatography with fluorometric detection as a model analytical task. The limits of detection, calculated from a blank test based on 3σ, were 0.01 μg L for ofloxacin, 0.02 μg L for lomefloxacin and fleroxacin, and 0.04 μg L for norfloxacin. The procedure provides significant solvent reduction and high enrichment factors. The approach is green, which is proved by the analytical eco-scale assessment tool with the total score equal to 85 out of 100.