Dispersive liquid-liquid extraction of Cr(III) by using choline chloride-thymol deep eutectic solvent and its application for chromium speciation analysis

This work utilized dispersive liquid-liquid extraction as a non-chromatographic separation technique for chromium speciation employing choline chloride-thymol hydrophobic deep eutectic solvent (DES) coupled with inductively coupled plasma optical emission spectroscopy (ICP-OES). The successful separation of chromium species was achieved with the use of a complexing agent, triethanolamine, which facilitated the migration of Cr (III) from the aqueous phase to the DES phase. Optimal conditions for Cr(III) extraction were determined, including a vortex time of 1 min, pH 9.0, triethanolamine concentration of 0.5 mM, and an aqueous-to-extractant volume ratio of 10. These conditions resulted in the extraction efficiency exceeding 95 %. Similarly, stripping of the extracted Cr(III) was accomplished with 90 % efficiency using 0.2 M nitric acid and a contact time of 12 min at room temperature. The consistently high extraction and stripping efficiencies (80-100 %) throughout the five consecutive cycles via this approach indicate the sustainability and ability to reuse choline chloride-thymol DES. The application of the proposed method was also demonstrated through the analysis of various samples with excellent accuracy and precision.