Development of an efficient method for extraction of some widely used pesticides in fruit and vegetable samples prior to their determination by GC-FID

Pesticides are chemical compounds with a wide range of physico–chemical characteristics that their consumption in agriculture is increased day by day aiming to combat weeds, fruit diseases, and any other agents that can affect crop quality and yield [1]. Although the use of pesticides has many advantages, however, they can enter the crop matrices and alter them to products that are toxic for human health [2, 3]. These products can cause long–lasting cancer, endocrine disruptors, chronic poisoning, and genetic variation [4]. Therefore, the monitoring of pesticide residues in various food products, especially in fresh fruits and fruit juices is of great importance, because they are unprocessed and consumed by people of all ages, especially children. So, it is critically important to devise facile and highly sensitive analytical methods, which are capable of detecting their trace residue concentrations in food and environmental samples. In this study, a combination of Quick Easy Cheap Effective Rugged and Safe extraction and dispersive liquid–liquid microextraction has been proposed for the extraction and preconcentration of some extensively used pesticides (diazinon, chlorpyrifos, penconazole, oxadiazon, and diniconazole) from fruit and vegetable samples prior to their determination by gas chromatography–flame ionization detection. In the proposed method, firstly, an aliquant of sample is crushed and its refuse and juice are separated by centrifuging. The juice is transferred to a conical glass test tube. Then acetonitrile as an extraction/disperser solvent is added into the tube containing the refuse. The analyte residues are extracted into acetonitrile after vortexing. The obtained acetonitrile is mixed with an extraction solvent (1, 2–dibromoethane) at µL level and rapidly injected into the juice. As a result, a cloudy state is formed and the tiny droplets of the extractant containing the extracted analytes are collected at the bottom of the tube after centrifugation. Finally, an aliquot of the sedimented organic phase is removed and injected into the separation system for quantitative analysis. In this study, several significant factors affecting the performance of the introduced method were investigated and optimized. Under the optimum experimental conditions, enrichment factors ranged from 240-375. The relative standard deviations were ≤ 7% for intra– (n=6) and inter–day (n=4) precisions at a concentration of 100 µg L–1 of each analyte. Limits of detection were in the range of 0.27– 0.48 µg L–1 in solution and 0.68 ¬¬–1.2 µg Kg-1 in the samples. Finally, several fruit and vegetable samples were analyzed by the proposed method and penconazole was found in grape at µg Kg–1 level.