A green and sensitive hydrophobic deep eutectic solvent dispersive liquid-liquid microextraction coupled with gas chromatographic method for forensic pesticide analysis in necrophagous larvae.

Abstract

Conventional extraction of organophosphorus (OP) pesticides from necrophagous larvae relies on toxic chlorinated solvents, risking environmental and analyst safety. To address this, we developed a green dispersive liquid-liquid microextraction using a hydrophobic deep eutectic solvent (HDES) as a sustainable alternative. For detection, gas chromatography-electron capture detector (GC-ECD) was chosen for its moderate cost relative to gas chromatography-mass spectrometry, while maintaining robust and accurate quantification. The HDES (menthol:octanoic acid, 1:1) was characterized for its organic composition, thermal behavior, and physicochemical properties. A 150 μL aliquot of HDES dispersed in 1000 μL acetonitrile was injected into aqueous larval samples (pH 6-7), followed by GCECD. The linear ranges for dimethoate, diazinon, malathion, and chlorpyrifos were 100-1000 μg/kg, 50-500 μg/kg, 50-500 μg/kg, and 20-120 μg/kg, respectively, with coefficients of determination (R²) exceeding 0.99 for all analytes. The lower limits of quantitation were 100, 50, 50, and 20 μg/kg for dimethoate, diazinon, malathion, and chlorpyrifos, respectively. Extraction recoveries ranged from 81.5% to 95.3%, and the intra- and inter-day relative standard deviations for all analytes were below 20%. In simulated larval specimens, all the target compounds were separated within 9.0 min. The method achieved Analytical Eco-Scale and Analytical Greenness scores of 82 and 0.64, confirming excellent eco-friendliness. Thus, this HDES-DLLME-GC-ECD method offers a green, cost-effective, and sensitive tool for simultaneous determination of dimethoate, diazinon, malathion, and chlorpyrifos in necrophagous larvae, well suited for forensic entomotoxicological investigations.