1-(o-Tolyl)thiourea-based deep eutectic solvent as a stationary phase in flow injection analysis system for mercury and copper determination in edible oils

In this work, a novel deep eutectic solvent (DES) composed of thymol and 1-(o Tolyl)thiourea 9/1 (mol) is presented for the first time. This DES has not been described in the literature. This DES was first used as a stationary phase in an extraction column integrated into a flow injection analysis system for the simultaneous determination of mercury and copper in edible oils. The automated approach involves passing an aqueous sample solution obtained after microwave mineralization through a microcolumn of DES retained on polytetrafluoroethylene. This leading to the extraction and concentration of the analytes. The metals are then eluted with an aqueous thiourea solution for subsequent analysis by inductively coupled plasma-optical emission spectrometry. The limits of detection (LODs) for mercury and copper were 3 μg L⁻¹ and 2.5 μg L⁻¹, respectively. The approach demonstrated high accuracy. Relative standard deviations (RSD) for repeatability and inter-day reproducibility ranged from 3 % to 11 %. Extraction recovery of both metals exceeded 95 %, indicating the high efficiency of the DES-based extraction process. Environmental assessment using the AGREEprep method yielded a favorable environmental index of 0.54, highlighting the robustness of the approach. This novel use of DES as a stationary phase in flow injection analysis system provides a robust, efficient and environmentally friendly approach to the determination of trace metals in edible oils. This method can also be applied to the analysis of other samples.