Study On The Application Of Magnetic Graphene Composites In The Determination Of Vegetable Preservatives

Preservatives were usually used to prevent the vegetables from rotting.However,most of the chemical preservatives were pesticides.The phenomena of indiscriminate use,abuse,exceeded residues were emerged gradually when they were widely used,which caused a serious threat to the health of consumers.So it is very important to find a more effective adsorbent to improve the sample pretreatment technology so as to ensure the food safety that has been paid more and more attention.Magnetic nanoparticles（Fe₃O₄）have superparamagnetism,which can be quickly separated from the solution by external magnetic field.In the analysis of the detection process,the advantages of a large specific surface area and low toxicity of Fe₃O₄ could be utilized.Besides,it could be combined with other materials to improve the extraction efficiency and separation rate.Graphene（G）was composed of carbon atoms in the sp2 hybrid orbital with only one atom thick two-dimensional crystal.It had large specific surface area,large conjugate system,excellent acid and alkali resistance,and thermal stability.The surface of G could be modified to produce different effects.The ionic liquid（IL）was an organic salt composed of organic cations and inorganic or organic anions at room temperature.IL has excellent physical and chemical properties,such as good thermal stability,high solubility and volatility,which has been widely used in organic synthesis,catalysis,separation and analysis.In this work,the new magnetic graphene composites was prepared and used as purification adsorption material for the detection of the preservatives in vegetables.Part Ⅰ Magnetic graphene composites applied for the determination of 16 preservatives in vegetablesObjective: Based on mechanism of QuEChERS method,a novel magnetic graphene composites（Fe₃O₄@SiO2@G）was synthesized and applied as the efficient MSPE adsorbent for rapid clean-up of vegetable samples prior to analysing 16 preservatives residues by gas chromatography–mass spectrometry（GC-MS）.Methods: The compound material of Fe₃O₄@SiO2@G was synthesized by chemical bonding method.The proportion of synthesis was optimized.The vegetables were used as raw materials,which were extracted with acetonitrile.The extracts was purified by Fe₃O₄@SiO2@G,and detected by GC-MS with external standard method.Results: 16 preservatives showed good linearity over the range of 0.02-2.00 mg/L with correlation coefficients（R2）of 0.9946-0.9998.The limits of detections（LOD）were in the range of 0.21-11.50 μg/kg.The recoveries of 16 preservatives ranged from 78.3% to 116.7% and the relative standard deviations（RSDs）ranged from 1.4% to 11.9%.Conclusion: The Fe₃O₄@SiO2@G had the merits of the excellent adsorption capacity,superparamagnetic properties,which greatly improved the speed of separation.The results showed that the method was rapid,accurate and sensitive,and could be applied to the determination of 16 kinds of preservatives in the actual vegetable samples.Part Ⅱ Magnetic graphene polymeric ionic liquid composites applied for the determination of 20 preservatives in vegetablesObjective: Magnetite nanoparticles（Fe₃O₄）with 200-1000 nm were synthesized.Then Fe₃O₄@SiO2@G@PIL was synthesized and used as modified QuEChERS adsorbent.And a method for rapid determination of 20 kinds of preservatives in vegetables by GC-MS was established.Methods: By controlling the synthesis conditions for chemical precipitation method,Fe₃O₄ with different particle sizes were prepared.Then the Fe₃O₄@SiO2@G@PIL composites with different particle sizes also were prepared.The vegetables were used as raw materials,which were extracted with hexane saturated acetonitrile.The extracts were purified by Fe₃O₄@SiO2@G@PIL composites with different particle sizes.The different effects were compared in detail by GC-MS with external standard method.Results: The good linearity with correlation coefficients（R2）of 0.9972-0.9999 was obtained over the range of 0.02-2.00 mg/L for 20 preservatives.The detection limits of the proposed method for 20 preservatives ranged from 0.82 to 6.64 μg/kg.Conclusion: The prepared Fe₃O₄@SiO2@G@PIL composites had good adsorption properties and could be applied to the efficient detection of 20 kinds of preservatives in vegetable samples.