A rapid and green vortex-assisted liquid–liquid microextraction of the radionuclide 137Cs using deep eutectic solvents

In the present study, a hydrophobic deep eutectic solvent (DES) composed of lauric acid, thymol, and camphor at a molar ratio of 1:4:1 was proposed as a versatile and green extractant for ¹³⁷Cs, achieving extraction yields of 92.5 %. Bis(2-ethylhexyl) hydrogen phosphate (DEHPA) and 18-crown-6 ether were used as additives to the DES and thus boosted extraction efficiency to above 95 %. A fast and reliable procedure for the determination of ¹³⁷Cs in water samples based on liquid-liquid microextraction using a DES prior to the gamma spectrometry measurement was developed. The DES-based extraction solvent containing 10 % DEHPA could ensure excellent yields of 96 % by just vortexing for 1 min. The applicability of the proposed procedure was demonstrated by analyses of industrial water, wastewater, and dam water preliminarily spiked with ¹³⁷Cs. Recoveries ranged from 95 % to 98 %, with relative standard deviations (RSD) below 6 %, indicating the absence of significant matrix effects, as well as very good precision. Enabling 20-fold preconcentration, the limits of detection (LOD) and quantitation (LOQ) of the method were 0.40 Bq mL^-1 and 0.62 Bq mL^-1, respectively. The greenness assessment using the AGREE and ComplexMoGAPI metric tools showed that the method complies with the principles of Green Analytical Chemistry. The Click Analytical Chemistry Index (CACI) evaluated the practical utility of the method as acceptable.