Ultra-trace detection of organochlorine pesticides in food and water samples using magnetic graphene oxide and methyl trichloroacetate in solid phase extraction/dispersive liquid-liquid microextraction/GC-µECD.

This work presents a combined magnetic solid-phase extraction (MSPE) and dispersive liquid-liquid microextraction (DLLME) method for the determination of four organochlorine pesticides lindane (LIN), alachlor (ALA), heptachlor (HEP), and endrin (END) in food and water samples using gas chromatography with micro-electron capture detection (GC-µECD). Magnetic graphene oxide (Fe3O4@GO) nanoparticles were synthesized, characterized, and employed as the MSPE sorbent, while methyl trichloroacetate (MTCA) was evaluated as a relatively safer extraction solvent compared to conventional carbon tetrachloride in the DLLME step. A central composite design (CCD) was used to optimize the MSPE parameters (pH, GO loading, and sorbent dosage). Under optimal conditions, the method provided limits of detection (LODs) ranging from 0.12 to 0.58 ng L-1, linear dynamic ranges of 1-1000 ng L-1 for LIN and 3-1000 ng L-1 for ALA, HEP, and END (R2 ≥ 0.9977), and enrichment factors between 1109 and 1547. Intra and inter-day relative standard deviations (RSDs) were below 7.2% and 9.5%, respectively. The method was applied to river water, milk, honey, and apple juice samples, yielding relative recoveries from 87.6% to 104.9%. A comparative toxicity assessment confirmed that MTCA lacks the carcinogenicity and ozone-depleting hazards associated with carbon tetrachloride, supporting its selection as a more environmentally acceptable alternative. These results demonstrate that the MSPE-DLLME-GC-µECD method offers a sensitive, reproducible, and relatively safer analytical platform for ultra-trace monitoring of organochlorine pesticides in complex matrices.