Preparation Of Fe₃O₄ Magnetic Molecularly Imprinted Material For Chlorophyll Recognition And Its Application In Pesticide Residue Detection

Excess residues of pesticides in food and drinking water have been one of the most important problems that threaten the environment and human health.Monitoring of pesticide residues in food and the environment has become a necessary means for human health.In order to avoid the problem of ineffectiveness and inefficiency in detecting pesticide residues at higher than the maximum pesticide residue limit,the development of simple,rapid,reliable and effective analytical methods has aroused great interest among researchers.In the pretreatment of pesticide residues,graphitized carbon black（GCB）is often used as a strong adsorbent.However,GCB not only adsorbs pigments,but also adsorbs part of the planar structural pesticides,and affect the accuracy of pesticide residue detection.Therefore,the selective adsorption of pigment treatment method is particularly important.In this study,we have prepared a selective adsorption of chlorophyll magnetic molecular imprinting material.This material was not only good for chlorophyll specific identification with high adsorption capacity,but also no adsorb of planar structural pesticides.It makes up the shortcoming of GCB.In this paper,we specially developed a magnetic molecularly imprinted polymer with selective adsorption capacity for chlorophyll.With functionalized Fe₃O₄ as the core nanoparticles,this unique adsorbent has the practical advantages of rapid separation and optimization under the action of magnetic field.Functional monomers and crosslinkers of imprinted materials are the most common and easy-to-use methacrylic acid（MAA）and ethylene glycol dimethacrylate（EGDMA）.The preparation conditions of magnetic molecularly imprinted polymer（Fe₃O₄@MIP）were first optimized and fixed,and then a series of in-depth studies were carried out on the micro-morphology and adsorption capacity of the material.And the magnetic molecularly imprinted polymer is used as an adsorbent.The optimum conditions for the preparation of Fe₃O₄@MIP were determined by optimization,and the surface structure of the magnetic molecularly imprinted polymer was characterized by IR（FTIR）and projection electron microscopy（TEM）.The vibrational sample magnetometer（VSM）and thermogravimetric analysis（TGA）were used to analyze the magnetic and thermal stability of Fe₃O₄@MIP.The adsorption properties of the Fe₃O₄@MIP were verified by adsorption experiments（including adsorption kinetics experiments and adsorption equilibrium experiments）.The experimental results show that the magnetic molecular imprinted polymer with hematoxylin as template is characterized by rapid mass transfer and high adsorption capacity to chlorophyll,while the adsorption capacity of chlorophyll is less and the adsorption capacity is 628.9 mg/g.A combination of high performance liquid chromatography（UPLC-MS/MS）and gas chromatography（GC-MS/MS）was developed by using GCB and Fe₃O₄@MIP as adsorbents.The method was used to detect the difference in the recovery rates of pesticides using GCB and MIPs as adsorbent food.In order to verify the practicability of the magnetic molecularly imprinted polymer as adsorbent,we carried out 39 kinds of pesticides in leek sample and analyzed the recovery rate.The results show that the recovery rate of Fe₃O₄@MIP as adsorbent are 70.08%¹20.51%、57.35%¹14.3%、56.55¹15.18%,respectively.The relative standard deviations are 0.7%¹5.8%、0.2%¹4.9%、0.5%¹2.2%,respectively.The recovery rate of GCB as adsorbent are 24.08%¹17.87%、14.51%¹17.02%、20.36%¹16.00%,respectively.The relative standard deviations are 2.2%¹7.2%、3.6%²0.8%、2.8%²6.0%.Take chlorpyrifos,diazine,ethomyl,benzophos,hexachlorobenzene and pentachloronitrobenzene as an example,When GCB was used as adsorbent,the recovery rates were 61.44%,63.88%,40.01%,45.96%,20.36%and 56.27%at 100μg kg^-1.When Fe₃O₄@MIP was used as adsorbent,the recovery rates were 90.28%,93.26%,114.9%,109.04%,110.83%and 115.07%at 100μg kg^-1.All the results show that this method has good practical value.By comparing the results of the two groups,it can be seen that Fe₃O₄@MIP can selectively adsorb chlorophyll,but has little adsorption on pesticides,which improves the accuracy of pesticide residue detection.This method changes the limitations of conventional molecular imprinting materials that can only detect one or more similar structural pesticides.It can be used as an adsorbent in the pretreatment of pesticide residue detection samples.It removes the common interferon chlorophyll in pesticide residue analysis,and successfully established a pretreatment method for high pesticide samples such as leek.And it also combines the advantages of rapid adsorption of magnetic nano-materials,easy to separate.This is a good method for pretreatment of chlorophyll purification ability and high recovery rate of pesticide,matrix effect is significantly reduced,fast and reliable sample preparation.