Sample preparation method for the analysis of some organophosphorus pesticides residues in tomato by ultrasound-assisted solvent extraction followed by dispersive liquid-liquid microextraction.

A very simple and economic method for organophosphorus pesticides (OPPs) residues analysis in tomato by means of gas chromatography-flame photometric detection (GC-FPD) has been developed. The method involves a rapid and small-scale extraction. The sample was homogenised and extraction of the OPPs with acetone was carried out assisted by sonication. No clean-up or evaporation were required after extraction. Pre-concentration of the OPPs from the acetone extract was done by using dispersive liquid-liquid microextraction (DLLME) technique. Chlorobenzene was added in micro-level volume as extraction solvent and triphenylphosphate as internal standard in DLLME procedure. The method showed good linearity over the range assayed (0.5-1000μgkg(-1)) and the detection limits for the pesticides studied varied from 0.1 to 0.5μgkg(-1). Repeatability studies resulted a relative standard deviation lower than 10% in all cases. The proposed method was used to determine pesticides levels in tomatoes grown in open field.