Utilization of deep eutectic solvents in chemically recycled polymeric resins for multielement determination

The search for greener methodologies has challenged analytical chemists, leading to the development of methods that minimize environmental impact and risks to analysts. Green Analytical Chemistry, composed of 12 principles, has been a guide for these innovations, with recent emphasis on deep eutectic solvents (DES). These mixtures formed by intermolecular interactions provide unique physicochemical properties, such as melting point, viscosity, density and solubility, making them attractive for extractions and solubilizations. Among DES, natural deep eutectic solvents (NADES), composed of substances of primary metabolic origin, are even more sustainable, being formed by compounds with low toxic potential. Despite their advantages, DES are still rarely applied to certain samples, such as polymers, which have been the focus of growing concern due to the presence of microplastics and contamination by trace elements. Given this scenario, this study aims to determine trace elements (Al, Ba, Cr, Cu, Fe, Mn, Ni, Pb, Sn, Sb, Ti and Zn) in chemically recycled polymeric resin, developed in partnership between UFES and Vale, using DES as a greener alternative to conventional methods. Four DES were prepared based on choline chloride and water, combined with malic acid, oxalic acid, phenol and urea, of which three are NADES. The polymeric samples were subjected to ultrasound-assisted extraction (UAE-DES) and analyzed by ICP-MS. The characterization of the DES by FTIR and NMR confirmed their adequate formation, and the Hansen solubility parameters (HSP) were used to understand the solvent-sample interactions - wich allowed the unprecedented determination of the sample’s Hansen solubility parameters itself. The results showed that DES were effective in recovering elements such as antimony (Sb), barium (Ba), and manganese (Mn), although the recovery efficiency varied: Sb was determined in all DES, Ba in NADES, and Mn only in solvents formed with acids. The AGREEprep metric demonstrated the environmental advantage of DES over the traditional microwave-assisted acid decomposition (MW-AD) method, with the highest score of 0.61 for NADES. However, elements such as aluminum (Al) and iron (Fe) showed unsatisfactory recoveries, suggesting the need for method optimization. The use of DES is a viable alternative for the preparation of recycled polymeric samples, with promising results for multielement determination and considerable environmental advantages. Additional adjustments may improve the recoveries of some elements and expand the use of the methodology to other matrices