RESUMO
In this work, the surface nature-dependent behaviors of magnetic deep eutectic solvents (MDES) and magnetic low-transition-temperature mixtures (MLTTM) are reported for the first time. It has been observed that the surface of material where the MDES or the MLTTM is placed could considerably affect the dispersion and the magnetic and structural properties of these magnetic mixtures. Several experiments have been carried out in order to point out the differences observed in the properties depending on the material on which these magnetic mixtures are placed. As a result, it has been shown that the MDESs or MLTTMs are retained and adhered to glass surfaces, resulting in a loss of magnetism in addition to a loss in the performance of synthesis carried out on the closeness of glass materials as the interaction between the glass and the mixture modify the composition and therefore the properties. As a preliminary result, when using these magnetic mixtures as extractant solvents in dispersive liquid-liquid microextraction, the MDES or MLTTM is retained on the walls of the glass tubes reducing the extraction efficiency, repeatability and the extraction recovery using an external magnetic field. For all these reasons, polypropylene materials should be recommended when handling MDES and MLTTMs.
RESUMO
A new simple, fast and environmentally friendly deep eutectic solvent based dispersive liquid-liquid microextraction (DES-based DLLME) methodology assisted by vortex is presented for the separation and preconcentration of three elements (i.e., Fe, Cu and Pb) from edible oil samples (i.e., soybean, sunflower, rapeseed, sesame, and olive oil) prior to the determination by microwave-induced plasma optical emission spectrometry (MIP-OES). The deep eutectic solvent selected as extractant (i.e., choline chloride and ethylene glycol, 1:2) is synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC), and the extraction conditions are optimized by a two steps experimental design. Under the optimum extraction conditions (i.e., diluted sample weight: 8.6 g; DES volume: 100 µL; extraction time: 1 min; centrifugation time and speed: 3 min and 3000 rpm; and dispersion system: vortex) the analytical method presents excellent linearity (i.e., R2 values higher than 0.99) in the range 10-500 µg kg-1, repeatability (i.e., CV values lower than 9.2%), and limits of detection (LOD) values of 3, 2 and 0.7 µg kg-1 for Pb, Fe and Cu, respectively. None of the analytes displayed amounts over the upper limit permitted by law, and recovery values of all analytes evaluated in the different samples using external standard calibration were close to 100%, which excludes significant matrix effects. Finally, AGREEprep metric has been used to evaluate the method greenness (final score of 0.47) and it has been compared successfully with previous publications for the same type of analytes and matrices.