Natural Thymol– <i>tert</i> ‐Butylhydroquinone–Based Deep Eutectic Solvent/Vortex‐Assisted Dispersive Liquid–Liquid Microextraction for Organophosphorus Pesticide Extraction in Water Samples
Elham Salehi, Kamine Dehghan, Hamid Najarzadekan, Sajad Karami, Parham Joolaei Ahranjani
Abstract
ABSTRACT Monitoring trace levels of pesticide residues in water remains a major global analytical challenge. We synthesized a bio‐derived hydrophobic deep eutectic solvent (DES), [thymol: tert ‐butylhydroquinone] (Thy:TBHQ), and coupled it with vortex‐assisted dispersive liquid–liquid microextraction (DLLME) prior to gas chromatography (GC) with micro electron capture detection (µECD) for pre‐concentration of organophosphorus pesticides (OPPs) (phosphamidon, diazinon, chlorpyrifos). DES formation and stability were confirmed by Fourier transform infrared spectroscopy (O–H red shift) and 1 H‐NMR (deshielded phenolic signals). Univariate optimization identified acetonitrile (ACN) as a disperser and ACN/DES = 1:1 (v/v), 100 mL sample, 3 min extraction, and pH 2–6 as optimal. The method showed excellent linearity (coefficients of determination = 0.991–0.997), limits of detection (LODs) of 3.44–15.43 ng L −1 and limits of quantification (LOQs) of 10.32–51.38 ng L −1 , all well below the EU 100 ng L −1 per‐pesticide limit, with enrichment factors of 13–27. Precision supported routine application (intra‐day relative standard deviation [RSD] 1.67%–3.79%; inter‐day 5.25%–9.66%). Spiked real samples across environmental waters: tap (≈90%–100% relative recovery), river (≈60%–82%), and seawater (≈54%–66%), each with RSD < 10% and no background residues detected. The DES retained >85% of its extraction performance over ≥9 adsorption–desorption cycles. Satisfactory extraction efficiency is probably due to the synergistic π–π, hydrogen bonding, van der Waals, and hydrophobic interactions between aromatic OPPs and the DES. Overall, the [Thy:TBHQ]‐based vortex‐assisted DLLME/GC with µECD platform delivers sensitive, precise, and reusable trace analysis with reduced solvent use, offering a green alternative for monitoring pesticides in diverse water matrices.