| Food is necessity for people's daily life.With the improvement of people's living,the food consumption is increasing year by year.To achieve high yield,pesticides are usually used to increase yields by protecting oil crops from weeds,diseases,and pests,which results in a high risk of pesticide contamination of food.The presence of pesticides in food is harmful to human health.During the 13th Five Year Plan period,food safety has risen to a major national issue.And food safety is listed as livelihood issue in Central Conference on Rural Work.As we all know,food contains a lot of organic acids,sugars,pigments,fat and other complex interfering substances,so it is a great challenge and task to develop a method that can effectively minimize the matrix effect while maintains superior sensitivity for the determination of pesticides in foods.And,it is significant to develop a sensitive and effective method to detect the pesticide residues in food.Considering this,three kinds of regular food(vegetables,freshly squeezed fruit juices and edible oils)are selected as the research objects in the current works.The modern pretreatment technology and gas chromatography-mass spectrometry were selected and used to construct efficient and sensitive new technology for the determination of organophosphorus and pyrethroid pesticides in the above foods.These developed methods have been successfully applied to the analysis of real food samples and achieved good results.We introduce our works as follows:1.A sensitive,efficient,and environmentally friendly method was developed to determine malathion,chlorpyrifos,parathion,bifenthrin,cyhalothrin,permethrin,fenvalerate and deltamethrin in organic and conventional vegetables.Samples were extracted,purified and concentrated using QuEChERS and dispersive liquid-liquid microextraction based on solidification of floating organic droplet(DLLME-SFO).The key parameters were optimized through orthogonal array experimental design and statistical analysis.Determination of target compounds in the final extract was performed using gas chromatography-mass spectrometry.The optimized method demonstrated good recovery(61.6-119.4%)with relative standard deviations<16.1%for all pesticides.The linearity of the calibration curves is satisfied in matrix-matched standard solution with R2?0.99.The limits of detection and limits of quantification were 0.3-1.5 ng/g and 0.9-4.7 ng/g,respectively.The method was applied successfully to analyze 15 pairs of organic and conventional vegetables,reflecting the robustness of this method to determine organophosphorus and pyrethroid pesticide residues.2.A novel dispersive solid-phase extraction method using microporous UiO-66 as the sorbent was developed to trace the amount of parathion,isocarbophos,triazophos,bifenthrin,permethrin and fenvalerate in commonly consumed vegetables.The UiO-66 was prepared and characterized by X-ray diffraction pattern,fourier transform infrared spectra,scanning electron microscope and N2 sorption-desorption isotherm.Prior to gas chromatography-mass spectrometry analysis,UiO-66 was used to directly extract target pesticides and exclude interfering matrix compounds.The important experimental parameters were optimized through orthogonal array experimental design.In optimized conditions,good linearity with coefficient R2?0.99 is achieved for the target pesticides.The limits of detection are 0.4-2.0 ng/g.The recoveries range from 60.9 to 117.5%with relative standard deviations below 14.6%.The established method significantly reduces the matrix effect.Moreover,the proposed method is applied to detect the pesticides in ten pairs of organic and conventional vegetables and the sorbent UiO-66 can be reused at least 25 times,demonstrating to be a robust way for screening the harmful residues in vegetables.3.A new method was designed and developed to determine bifenthrin,cyhalothrin,permethrin and fenvalerate in freshly squeezed fruit juices,based on dispersive solid phase extraction using UiO-66 as sorbent.The results revealed that microporous UiO-66 can directly and selectively adsorbed pyrethroid pesticides and excluded interfering compounds.Clean analytes were obtained.Under optimized conditions,the linearity of the calibration curves is satisfied,and the limits of detection and limits of quantitation of the pesticides in freshly squeezed fruit juices were 0.8-1.5 ng/g and 2.9-4.6 ng/g,respectively.The average pesticide recoveries were 68.1-119.7%.The intra-day and inter-day relative standard deviations for analyte recovery were<14.8%.Thus,the method is successfully applied to determine pyrethroid pesticides in six freshly squeezed fruit juices.4.A QuEChERS-type method without matrix interference was designed and developed to determine dichlorovos,dimethoate,malathion and methidathion in edible vegetable oils,based on dispersive solid phase extraction using UiO-66 as sorbent.Microporous UiO-66 directly and selectively adsorbed organophosphorus pesticides and excluded interfering compounds.Clean analytes were obtained by elution and analyzed using gas chromatography-tandem mass spectrometry.The dispersive solid phase extraction conditions(amount of adsorbent,extraction time,desorption solvent volume,and elution time)were optimized.Under optimized conditions,the linearity of the calibration curves is satisfied,and the limits of detection of the pesticides in vegetable oils were 0.16-1.56 ng/g.The average pesticide recoveries were 81.1-1 13.5%.The intra-day and inter-day relative standard deviations for analyte recovery were<8.2%and<13.9%,respectively.Thus,the method is reliable,and could detect organophosphorus pesticide residues in edible vegetable oils.Furthermore,UiO-66 can be easily recycled and reused at least 10 times,reducing the cost of analysis.5.In this study,the mechanism study of the pesticides can be selected by metal organic framework materials UiO-66 and interfering compounds can be excluded by UiO-66 was studied in detail.the theoretical basis for the sieving action of UiO-66 was obtained by using the quantum chemical calculation method.It was confirmed that the ordered micropores of UiO-66 can exclude the matrix compounds with large molecular size,while allows the analytes with relatively small size to enter.At the same time,the mechanism of the adsorption of pesticides on UiO-66 was studied by means of fourier transform infrared spectroscopy,ultraviolet visible spectroscopy,thermogravimetry and X-ray photoelectron spectroscopy.The reason why the pretreatment method can directly suppress the matrix effect in these developed methods was summarized. |
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