A green dispersive liquid-liquid microextraction based on deep eutectic solvents doped with β-cyclodextrin: Application for determination of tetracyclines in water samples

A hydrophilic/hydrophobic deep eutectic solvent (DES) system was developed and used as a disperser/extraction solvent mixture in dispersive liquid-liquid microextraction of tetracyclines (TCs) in water samples. Five DESs were prepared, and their applicability was evaluated. Among them, [choline chloride]:[ethylene glycol] (a hydrophilic DES) and [thymol]:[octanoic acid] (a hydrophobic DES) showed the highest efficiencies as disperser solvent and extraction solvent, respectively. The addition of beta-cyclodextrin (β-CD) to the extraction phase led to enhance extraction efficiencies, probably through the selective supramolecular host-guest inclusion of TCs. Besides, β-CD improved the dispersibility of the extraction solvent and contributed to the formation of a very stable cloudy solution. The significant parameters of the extraction process were investigated and the optimal conditions were obtained as follows: extraction solvent ([Th]:[OA]), 175 µL; disperser solvent ([ChCl]:[EG]), 750 µL; β-CD, 5 mg; pH, 5; NaCl, 1% (w/v); and sample solution, 10 mL. Under the optimized conditions, the limits of detection were 1.37–4.38 µg L−1, and the linear range was 4.6–500 µg L−1. The greenness of the developed method was assessed using Analytical Eco-Scale and Green Analytical Procedure Index (GAPI). The proposed DLLME method was coupled with HPLC-UV technique and applied to the analysis of oxytetracycline, doxycycline, and tetracycline antibiotics in environmental water samples and satisfactory recoveries (74–113%) were obtained.