Research On Liquid Chromatographic Detection Of Neonicotinoid Pesticides Based On Metal Organic Frameworks And Molybdenum Disulfide

Neonicotinoid pesticides are widely used in agricultural production as a class of highly effective pesticides,but residues in the environment pose a potential hazard to human health.The development of efficient,easy-to-use and highly sensitive methods for the detection of neonicotinoid pesticide residues is of great importance for monitoring their residue levels in the environment.Current pre-treatment methods for neonicotinoid pesticides have disadvantages such as cumbersome and complicated processes and high consumption of organic solvents.In order to solve these problems,this thesis developed a novel solid phase extraction（SPE）and magnetic solid phase extraction（MSPE）technique based on metal organic framework（ZIF-8）and molybdenum disulfide（Mo S₂）,combined with high performance liquid chromatography（HPLC）,for the enrichment and detection of neonicotinoid pesticides in environmental samples.The details of the research in this thesis are as follows:（1）The metal-organic framework（ZIF-8）was prepared by a water bath stirring method and was shown to exhibit a regular cubic shape by a series of characterization means.ZIF-8 was prepared as a solid phase extractant into a solid phase extraction column and applied to the extraction and enrichment of neonicotinoid pesticides.A method for the enrichment and detection of neonicotinoid pesticides in environmental water samples was developed by optimizing the solid phase extraction conditions and combining high performance liquid chromatography（HPLC）with optimal conditions（20 m L loading volume,3 m L hexane as the eluent,p H 7 and 3m L acetone as the resolving solvent）.The four neonicotinoid pesticides showed good linearity in the range of 0.02-10μg m L^-1with good recoveries（72.5%-98.7%）at three different spiked levels(50,80 and 100 ng m L^-1)and RSD values of 1.9%-5.6%.These data indicate that the developed SPE-HPLC-UV method has high sensitivity,good repeatability and low consumption of organic reagents.These data indicate that the SPE-HPLC-UV method has the advantages of high sensitivity,good repeatability and low consumption of organic reagents.（2）The magnetic ZIF-8（Fe₃O₄@ZIF-8）was prepared by modifying sodium polystyrene sulfonate onto the surface of Fe₃O₄using an ambient stirring method and adsorbing Zn²⁺using electrostatic interactions.By means of SEM,TEM and XRD characterization,it was demonstrated that the complex has a typical core-shell structure,ZIF-8 was successfully wrapped on the surface of Fe₃O₄and possessed strong magnetic properties.The composites were applied to magnetic solid-phase extraction of neonicotinoid pesticides in environmental water samples.Under optimal extraction conditions（sample volume of 30 m L,p H 7,elution solvent of 0.1%FA-methanol,elution volume of 3 m L）,combined with high performance liquid chromatography,the four neonicotinoid pesticides showed good linearity in the range of 0.02-10μg m L^-1,with R~2above 0.9991.The LODs and LOQs ranged from 0.48 to0.63 ng m L^-1and 1.45 to 1.89 ng m L^-1,respectively;the RSD values were 2.6%to4.6%.Good recoveries（71.5%-98.1%）were obtained at three different spiked levels(50,80,100 ng m L^-1).The MSPE-HPLC-UV method based on Fe₃O₄@ZIF-8composites is sensitive,easy to operate and has high extraction efficiency,and also provides a reference for the detection of other trace contaminants in environmental water samples.（3）Flower-like molybdenum disulfide was prepared by the solvothermal method,on the basis of which positively charged trivalent iron ions were adsorbed onto the surface of the molybdenum disulfide by coordination,and magnetic molybdenum disulfide hybrid materials（Fe₃O₄/Mo S₂）were successfully prepared under certain experimental conditions（vigorous stirring in a constant temperature water bath at80°C for 1 h）.The nanocomposites were characterized using FT-IR,XRD,SEM and VSM,and Fe₃O₄was attached to the surface of Mo S₂,which has a strong magnetic property.It was used as a magnetic solid phase extraction（MSPE）sorbent to optimize the sorption and resolution conditions and to determine the optimum MSPE conditions（40 mg sorbent material,30 m L water sample,10 min sorption time,p H 7,acetone/ethyl acetate（1:1 v/v）as eluent）.An MSPE-HPLC-UV method was developed for the rapid enrichment and detection of neonicotinoid pesticides in environmental water samples based on Fe₃O₄/Mo S₂.The results showed that the four neonicotinoid pesticides showed good linearity in the range of 0.02-10μg m L^-1with R~2greater than 0.9997,and the LODs and LOQs were 0.48-0.67 ng m L^-1and 1.44-2.02 ng m L^-1,respectively;at three different spiked levels(50,80,100 ng m L^-1),the recoveries were good（71.0%-83.8%）.The above data demonstrate that the developed method is not only sensitive and reproducible,but also introduces a new solid phase extraction agent for the detection of neonicotinoid pesticides.