Combining dispersive and traditional solid phase extraction using magnetic nanoparticles performed in a narrow–bore tube for extraction of some pesticides in vegetable and fruit juice samples

Most of samples are not compatible with analytical instruments for analysis. Sample preparation methods solve this problem. Actually, sample preparation influences the accuracy and precision of the method. The purpose of sample preparation is the enrichment of analytes for increasing sensitivity and selectivity by eliminating of matrix effect [1]. Among various sample preparation methods, solid phase extraction (SPE) as some advantage over the other methods. However, this method suffers from some drawbacks such as: treatment of large sample volumes is not possible, high back-pressure is observed, clogging and agglomeration of the cartridges are possible, and pumping or suction. Thus, to over the drawbacks of SPE, other SPE approaches, such as dispersive solid phase extraction and magnetic solid phase extraction (MSPE) have been reported. Among these methods; MSPE has received significant attention in last few years. In this method, an external magnetic field is used for separating the analytes adsorbed on the magnetic nanoparticles from solution [2].The main purpose of this study was to develop a solid phase extraction procedure performed in a narrow bore tube for the extraction and preconcentration of different pesticides from various vegetables and fruit juices followed by gas chromatography–flame ionization detection. In the mentioned method, a mg-level of the synthesized nanoparticles (Fe3O4@SiO2@C8) are added into an aqueous sample placed in the narrow bore tube. These sorbents move down through the tube under gravity force and are collected in the end of tube using an external magnetic field (the end of the tube is narrower and is connected to a stopcock). After a predetermined time, the stopcock is opened and the solution is passed through the bed of the sorbents maintained by the magnet. Finally target analytes are desorbed using an elution solvent. Then, to achieve a high enrichment factor, a dispersive liquid–liquid microextraction method is carried out. The Fe3O4@SiO2@C8 nanoparticles were characterized by scanning electron microscope, X-ray diffraction and Fourier transforms infrared spectrometer. Under the optimum extraction conditions limits of detection and quantification were in the ranges of 0.02–0.03 and 0.06–0.1 mg L-1, respectively. The method precision, expressed as relative of standard deviation was within the range of 4-8% (n=6, C=0.05 mg L-1 of each analyte).