A solidified floating organic drop-dispersive liquid–liquid microextraction based on in situ formed fatty acid-based deep eutectic solvents for the extraction of benzophenone-UV filters from water samples

Abstract

A solidified floating organic drop-dispersive liquid–liquid microextraction (SFOD-DLLME) was established for the extraction of four benzophenone-ultraviolet filters (BP-UV filters) from water samples using a fatty acid deep eutectic solvent (DES) as the extractant. The extracted UV filters were determined by high-performance liquid chromatography with UV detection (HPLC-UVD). In this method, tributyl(dodecyl)phosphonium bromide (P_4,4,4,12Br) and sodium decanoate (DecA-Na) were first dissolved in a solution as precursors of DES components. Then they were converted into tributyl(dodecyl)phosphonium tetrafluoroborate (P_4,4,4,12BF₄) and decanoic acid (DecA) through an anion-exchange reaction and acid–base reaction, respectively. During this period, P_4,4,4,12BF₄ and DecA formed a DES extraction phase dispersed throughout the solution and the extraction of the analytes was carried out simultaneously. The extraction conditions, including the type and volume of fatty acids, the type and volume of the proton agent, the temperature of the P_4,4,4,12Br and NaBF₄, solution, salt addition, sample volume and solution pH, were investigated in detail. Under optimal conditions, the method was validated providing correlation coefficients greater than 0.999 for all analytes, limits of detection (LODs) from 0.600 to 1.50 μg L⁻¹, limits of quantification (LOQs) from 2.00 to 5.00 μg L⁻¹, extraction recoveries of 73.1 to 99.8%, intra-day precision from 2.0 to 6.1%, inter-day precision from 3.9 to 7.7%, and enrichment factors from 34 to 42. Finally, the proposed method was applied for the determination of BP-UV filters in different water samples (including tap, river, bottled mineral, bottled vitamin, face-washing and bathing water) with acceptable results.