Hydrophobic deep eutectic solvent-based ferrofluid for the multi-residue analysis of pyrethroid insecticides in agricultural products: Facile pretreatment and MS-friendly detection.

Pyrethroid insecticides (PYs) overuse poses ecological and health risks, leading to tightened restrictions on maximum residue limits (MRLs) by regulatory bodies like the European Union and China's National Food Safety Standards. It is important to develop multi-residue analytical methods for PYs residues. In present work, oleic acid-coated FeO nanoparticles (FeO-OA) were dispersed in hydrophobic deep eutectic solvents (HDES) to prepare ferrofluids (FFs), with the HDES synthesized from coumarin and thymol at a 1:2 molar ratio. And the HDES-FF was subsequently utilized as a vortex-assisted liquid-phase microextraction sorbent for the enrichment of 16 PYs, combined with GC-MS/MS analysis. HDES-FF could effectively enrich PYs within merely 3.5 min according to π-π stacking interactions and hydrophobic effects, while FeO-OA nanoparticles were responsible for magnetic separation. It could successfully solve the problem of separation difficulty after liquid-liquid microextraction based on DES. Simultaneously, thermogravimetric analysis confirmed that the HDES could decompose at injection port of GC-MS/MS instrument, and mass spectrometry signals of the decomposed HDES could not be collected by adjusting the solvent delay time. Thus, it could effectively protect the ion source from contamination, making DES compatible with GC-MS methods. The detection limit (LOD) of the proposed method is 0.41-7.91 ng/mL, with the recoveries of 83.33-106.02 %. The intra-day and inter-day relative standard deviations (RSDs) are less than 4.20 % and 6.94 %, respectively. The method successfully detected 16 PYs in various real fruit and vegetable samples.