Dual-function deep eutectic solvent for the sustained determination of chromium in water and food samples

A sensitive, selective, and environmentally friendly method for the preconcentration and speciation of trace levels of hexavalent chromium in aqueous solutions is described. The method depends on using a dual-functional DES, consisting of 1,5-diphenylcarbazide as a H-bond donor, and oleic acid as a H-bond acceptor. The prepared DES that combines the coordination property (through the ligand) with the ability to separate Cr(VI) from aqueous media (due to the nonpolar nature of oleic acid), allowing for efficient extraction without the need for conventional organic solvents or a complexation step. The novelty of this work lies in the integration of the extraction and complexation functions into a single solvent component, simplifying the process and increasing its efficiency. Furthermore, the solvent can be recycled multiple times without significant loss of performance, enhancing its environmental and economic value in analytical applications. The calibration graphs were linear across the concentration ranges under ideal conditions, from 10 to 300 µg L^-1 for Cr(VI). The limit of detection and limit of quantification of the developed method were 3.1 and 10.9 µg L^-1, respectively. The relative standard deviations for 6 replicate determinations were less than 4.0%. Chromium species were successfully determined and speciated in water and tea samples using the proposed approach. Several tools were used to assess the greenness, and applicability of the proposed strategy.