Green dispersive liquid–liquid microextraction of copper and nickel using a dual-function hydrophobic natural deep eutectic solvent for the analysis of water samples

Abstract

An environmentally friendly and simple dispersive liquid–liquid microextraction method based on a hydrophobic natural deep eutectic solvent (NADES) was developed for the simultaneous preconcentration of Cu and Ni from water samples. The NADES composed of a 1:1 molar ratio of menthol and decanoic acid, presents hydrophobic characteristics and allows to simultaneously extract both analytes avoiding the addition of ligands or emulsifier agents. The extraction was performed in 1.0 min using 0.500 mL of NADES and a sample volume up to 25.0 mL in 0.5 M ammonium chloride-ammonia buffer solution at pH 8.2. The content of Ni and Cu in the NADES phase was determined using Flame Atomic Absorption Spectroscopy. Under optimal conditions, limits of detection of 1.9 µg L−1 for Cu and 4.6 µg L−1 for Ni were obtained, with precision (expressed as RSD% value) better than 5 % for both metals (n = 3). The method was applied to extract and determine Cu and Ni in water samples with different characteristics: tap water, bottled water, river water, dam water, and seawater. The recoveries for spiked water samples ranged between 97 and 110 % for Cu and 92–98 % for Ni, demonstrating the suitability of the method. The environmental impact of the method was assessed using the AGREE, AGREEprep, and ChlorTox metric tools, resulting in scores of 0.58, 0.61, and 0.48 g, respectively.