| Vegetables and fruits are one of the essential food in our daily life. In recent years, food safety and environmental protection issues have attracted international attention. Many countries in the world attach great importance to the issue of pesticide residues and have imposed stringent limits on pesticide residues in agricultural products. Therefore, a more efficient, accurate and easier extraction and detection method is required imminently.Magnetic nanoparticles(MNPs), a novel and interesting material, have attracted enormous scientific attention in the past few years on account of their special magnetic, adsorption, optical, and mechanical properties and extremely large specific surface area. Due to the unique magnetic of MNPs, they can easily be separated out of sample solution by an external magnetic field and avoid an additional step of centrifugation or filtration. Therefore, sample pre-treatment using MNPs can be simple and quick.Currently, traditional and commonly used pesticide sample preparation technologies include solid-phase extraction(SPE), solid phase micro extraction(SPME), gel permeation chromatography(GPC), supercritical fluid extraction(SFE), accelerated solvent extraction(ASE) and so on. However, these methods each have their own shortcomings, such as being time consuming and/or labour intensive, exposing workers to hazardous solvents, and for some of them it is difficult to easily and simultaneously achieve high quality for the vast majority of pesticide extraction and analysis. In 2003, quick, easy, cheap, effective, rugged and safe(QuEChERS) is a type of sample preparation method that was first reported by Anastassiades et al.. This method has many advantages, including high recovery for a wide scope of pesticides with different polarity and volatility in different matrices, meeting low detection limits, use of smaller volumes of organic solvents and simple operation. Therefore, this method and modified versions of it are widely used in food analysis and serve as a template for the determination of pesticide residues.In this study, based on a modified QuEChERS sample preparation method with MNPs as the adsorbing material and gas chromatography–tandem mass spectrometry(GC–MS/MS) determination in multiple reaction monitoring(MRM) mode, we established a new method for the determination of multiple pesticides in vegetables and fruits. The results are as follows:(1) We choose cucumber as sample. We modified traditional QuEChERS method by adding MNPs in the purification steps. MNPs were prepared by co-precipitation method, and characterized by transmission electron microscopy(TEM); Eight kinds of pesticides were choosen to use in optimizing purification conditions. After optimaization, primary and secondary amine(PSA), graphitised carbon black(GCB), MNPs mixed purification system were choosen. The amount of GCB, MNPs and PSA was 10 mg, 40 mg and 50 mg, respectively, while the purification time is 60 s. Samples after purified were almost colorless.(2) The study compared purification system by adding MNPs or not. Through the sample photos, the pigment content of adding MNPs samples was less than not adding MNPs samples. Meanwhile, through the chromatogram, the number of impurity peak was obviously reduced by adding MNPs. Compared with traditional Qu EChERS method, this modified QuEChERS method in addition to MNPs used for purification improved the speed of sample pre-treatment and exhibited an enhanced performance and purifying effect.(3) The research established gas chromatography tandem mass spectrometric method for 101 kinds of pesticides in vegetables and fruits. The mass spectrometry was performed in electron ionisation(EI) mode with an ionising energy of 70 eV. Aliquots of 1 μL of the sample extract were injected into the gas chromatograph. The colum of HP-5 ms capillary column(methyl phenyl siloxane, 30 m × 0.25 mm × 0.25 μm) was used. The oven temperature programme was as follows: starting temperature 95 °C held 1.5 min, increased at 7 °C/min to 165 °C, then increased to 210 °C at 5 °C/min and finally increased to 280 °C and held for 8 min. The detector interface was set at 250 °C, and the ion source temperature was set at 230 °C. The analysis was performed in multi reaction monitoring(MRM) mode. Under the MRM mode, 101 kinds of pesticides can be separated. The linear correlation coefficients(r2) are higher than 0.99 in the range from 5 to 500 μg kg-1.(4) Recoveries were evaluated in four representative matrices(tomato, cucumber, orange and apple) with the spiked concentrations of 10 μg kg-1, 50 μg kg-1and 200 μg kg-1 in all cases. The results showed that the recovery of 101 pesticides ranged between 71.5 and 111.7%, and the relative standard deviation was less than 10.5%. Based on the results presented above, the modified methodology meets the requirements for multiple pesticide determination in fruits and vegetables and will have broad applications in food analysis. |
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