Application of deep eutectic solvents for the simultaneous determination of organophosphorus and pyrethroid pesticides in aqueous matrices and the assessment of its level of whiteness

Abstract

This work presents as a novelty the development of a method for the simultaneous determination of organophosphorus and pyrethroid pesticides in aqueous samples using only deep eutectic solvents (DES) followed by a gas chromatography-mass spectrometry analysis. Combining 4 hydrogen bond acceptors and 6 hydrogen bond donors, 17 DES were prepared. Menthol:thymol in a 1:1 molar ratio presented the best extraction performance and was, therefore, characterized by Fourier transform infrared spectroscopy (FTIR), hydrogen-nuclear magnetic resonance (¹H NMR) and nuclear Overhauser effect spectroscopy (NOESY-NMR), comparing the spectra from the pure components and from the DES. In the FTIR analysis, the main shifts occurred in the CO bonds. The NMR analyses allowed a better understanding of the interactions occurring during solvent formation, which were attributed to the interaction between the hydroxyls from menthol and thymol. Vortex-assisted dispersive liquid-liquid microextraction (DLLME) required no dispersing solvents. The main variables affecting the extraction were optimized using full factorial design, including a triplicate center point. For a fixed 10-mL sample volume, the optimum ranges obtained were: 3.0 ± 0.60 g of NaCl, pH in the range from 5 to 9, a vortex stirring time of 4 ± 2 min and 150 μL of a DES composed of menthol and thymol in a 1:1 molar ratio. Satisfactory figures of merit were then obtained: coefficients of determination greater than 0.99, linear working ranges from 1 μg/L to 400 μg/L, limit of detections of 0.3 μg/L, an inter-day precision from 1.33 % to 9.86 % (n = 12), and an intra-day precision from 4.65 % to 15.52 % (n = 4). The application was carried out in six different aqueous matrices, with methyl parathion being detected in a lake sample. An excellent mean recovery of 98.0 % was obtained for the three levels evaluated and all analytes. The comparison with other methods was based on the principles of White Analytical Chemistry using Algorithm 12, by which the method proposed in this work showed a higher level of whiteness compared to the others.