Determination of organophosphorus pesticide residues in vegetables using solid phase micro-extraction coupled with gas chromatography-flame photometric detector

An adequate and simple analytical method based on solid-phase microextraction (SPME) followed by gas chromatography-flame photometric detection (GC-FPD) for the determination of eleven organophosphorus pesticide residues (i.e., ethoprophos, sulfotep, diazinon, tolclofos-methyl, fenitrothion, chlorpyrifos, isofenphos, methidathion, ethion, triazophos, leptophos) in vegetables samples (cabbage, kale and mustard) was developed. Important parameters that influence the extraction efficiency (i.e., fibre type, extraction modes, extraction time, salt addition, desorption time and temperature) were systematically investigated. Four types of commercially available fibres (i.e., 50/30 mu m divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS), 65 mu m polydimethylsiloxane/divinylbenzene (PDMS/DVB), 100 lm polydimethylsiloxane (PDMS), and 85 mu m polyacrylate (PA)) were evaluated. PA fibre exhibited the best performance and was used for the rest of the studies. The optimised extraction conditions were: extraction time, 30 min at room temperature; stirring speed, 1275 rpm; salt content, 10% NaCl; desorption time and temperature, 11 min at 260 degrees C; and no pH adjustment of the sample extract. The method was validated over the range 0.1-100 mu g/L. Repeatabilities were satisfactory, ranging between 2.44% and 17.9% for all analytes. The limits of detection and quantitation ranged from 0.01 to 0.14 and 0.03 to 0.42 mu g/L, respectively. The method was applied to twenty local vegetable (cabbage, kale and mustard) products. Chlorpyrifos (0.22-1.68 mu g/kg) was the most detected pesticide in the tested samples. The obtained values are however lower than the Maximum Residue Limits (MRLs) as stipulated in the Food Act & Regulations of Malaysia. (C) 2014 The Authors. Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).