Deep eutectic solvent-based rapid extraction for multielement analysis of onion pulp and peel by ICP-MS/MS: a green...

The development of greener and faster sample preparation strategies is essential to reduce the environmental and time costs associated with conventional digestion-based protocols for multielement analysis. In this work, a hydrophilic deep eutectic solvent (DES) based on choline chloride, urea and water (ChCl:U:H₂O = 1:2:4) was evaluated as an alternative extraction medium for the determination of metals and metalloids in onion tissues by ICP-MS/MS. Onion pulp and peel were selected as a model heterogeneous food matrix. Extraction conditions were systematically optimised with respect to solid-to-solvent ratio, extraction technique and extraction time. A 1:10 (w w^-1) ratio combined with short extraction times provided an effective compromise between extraction efficiency and analyte enrichment. Under these optimised conditions, vortex-assisted extraction (3 min) and ultrasound-assisted extraction in a bath (5 min) afforded quantitative recoveries for the target elements and procedural limits of quantification lower than those obtained after microwave-assisted acid digestion, mainly due to the reduced overall dilution. Method accuracy was assessed by benchmarking the DES-based procedures against microwave digestion used as a reference; for most elements and both tissues, no statistically significant differences were observed. The greenness of the evaluated strategies was quantified using the AGREEprep metric, revealing a clear improvement when replacing acid digestion with DES-based extraction, with the vortex-assisted and ultra-sound protocols providing the highest score (0.65 and 0.64, respectively). Application to white and red onions from different geographical origins demonstrated the suitability of the method for resolving tissue and origin-dependent elemental distributions, establishing DES-based vortex extraction as a fast, reliable and greener alternative to conventional digestion for multielement analysis of plant-derived food matrices.