Natural deep eutectic solvents as sustainable alternative for the Ultrasound-Assisted extraction of triazines from agricultural soils

Natural deep eutectic solvents (NADES) have gained much attention as a viable and sustainable alternative to traditional organic solvents in multiple areas of analytical chemistry, including extraction of contaminants from samples of environmental concern. In this work, a total of 68 potential NADES have been assayed and further evaluated as sustainable solvents in the development of an ultrasound (US)-assisted extraction method for triazinic herbicides from agricultural soil samples and final determination by HPLC-UV. Choline chloride (ChCl) was used as hydrogen bond acceptor (HBA), and different carboxylic acids, alcohols and amines were tested as hydrogen bond donors (HBDs) in different molar ratios in order to find the optimum combination able to form appropriated NADES for the extraction of triazines. Among the different ChCl:carboxylic acids mixtures tested, those consisting of ChCl:formic acid and ChCl:acetic acid, both in a molar ratio 1:2, presented the better physicochemical properties (pH, stability at room temperature, water miscibility, etc.). Concerning amines, NADES could not be obtained at any of the combination assayed whereas, among the alcohols tested, 2,3-butanediol was found to be the most appropriated for NADES formation. A three-level factorial design was then used to further evaluate the effect of time and temperature on the ability of these selected optimum NADES for the US-assisted extraction of triazines from agricultural soil samples. Under optimal conditions, the developed US-assisted extraction method provided quantitative recoveries (from 87 to 104 %) with good reproducibility (RSDs lower than 12 %) and limits of detection (LODs) lower than 0.05 mu g g-1 for all target triazines.