Determination of some organothiophosphate pesticides in fruit juice and vegetable samples using solidification of floating organic drops homogeneous liquid–liquid microextraction followed by gas chromatography–mass spectrometry

Pesticides are a part of chemical compounds which are broadly used in agriculture all over the world in order to control diseases. In spite of many merits of the pesticides in the agricultural activities such as increase production volume, extend shelf life, and improve the appearance of grown foods, majority of them own highly persistent properties and are found in agriculture products, soil, and natural waters in many regions of the world [1, 2]. They can show a serious risk to human health because of either direct exposure or residues in food and drinking water. So, it is necessary to develop convenient analytical methods for the survey of pesticides residue in foods. In this study, a new approach of homogeneous liquid–liquid microextraction based on solidification of organic droplets has been developed in a home–made extraction device for the extraction and preconcentration of some organothiophosphate pesticides from different fruit juice and vegetable samples prior to gas chromatography–mass spectrometry determination. In the present work, two parallel glass tubes with different lengths and diameters were connected with a stopcock and used as an extraction device. Firstly, a homogeneous solution containing the sample solution and an extraction solvent (cyclohexanol) was filled into the wide diameter side of the device. Then sodium sulfate solution was filled into the other side of the device and was flowed into the homogeneous solution to release the extraction solvent from the solution. By passing the produced droplets of the extraction solvent through the solution, the analytes were extracted and the organic phase was collected on surface of the aqueous phase. Afterward the device was placed into an ice bath and the solidified droplets were used for analysis. Under the optimum conditions, limits of detection and quantification were obtained in the ranges of 0.026–0.076, and 0.091–0.28 ng mL–1, respectively. The extraction recoveries and enrichment factors of the selected pesticides ranged from 216-273 and 65-82%, respectively. The relative standard deviations were lower than 8% for intra– (n=6) and inter-day (n=4) precisions at a concentration of 3 ng mL-1 of each analyte. Finally, some vegetable and fruit juice samples were successively analyzed by the proposed method.