Rapid and greener vortex-assisted deep eutectic solvent-based dispersive liquid-liquid microextraction for spectroscopic determination of Hg in fuels

Mercury is considered a global pollutant and occurs naturally at trace levels in fuel oils such as crude oil and its derivatives. The former is released into the environment during the processing of these energy sources. Due to its high toxicity, there is a global concern regarding human exposure to this element. Three distinct deep eutectic solvents (choline chloride + ethylene glycol, choline chloride + levulinic acid, and betaine + levulinic acid) were synthesized and characterized using Fourier Transform infra-red spectroscopy (FT-IR), Thermogravimetric analysis (TGA), and ¹³C nuclear magnetic resonance (NMR) for the preconcentration of Hg in fuel oils prior to quantification using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Multivariate optimization tools were used for the optimization of the vortex-assisted deep eutectic solvent based dispersive liquid-liquid microextraction (VA-DES-DLLME) procedure. The optimum conditions for the newly developed method were 4.5 pH, 5 mins extraction time, 164 µL extractant volume and 665 µL disperser solvent. The optimized method was validated using NIST SRM 2778 with certified mercury concentration of 38.98 µg/kg ± 1.10 µg/kg. The method provided enrichment factor (EF), precision (%RSD), and limit of detection (LOD) of 234, 2.3 %, and 0.025 µg/L, respectively. Additionally, the newly developed method demonstrated good accuracy 97–99.9 %. The newly developed method was successfully applied in real crude oil, kerosene, diesel, and gasoline. The concentrations obtained were 0.390 ± 0.01–0.510 ± 0.09 µg/g for crude oil samples, 0.308 ± 0.05–0.402 ± 0.05 µg/g for gasoline samples, 0.370 ± 0.35–0.510 ± 0.080 µg/g for diesel oil samples and 0.09 ± 0.09–0.098 ± 0.02 µg/g for kerosene samples. The environmental impact of the newly developed method was assessed using AGREEprep software and a score of 0.72 was obtained.