The Preparation Of Magnetic Carbon Nanotubes Solid Phase Extraction Agent,and Its Application In Determination Of Chlorpyrifos And 3,5,6-trichloro-2-pyridinol In Water

As one of the worldly most widely used organophosphate pesticides,chlorpyrifos is indispensable in the analysis of pesticide residue.However,the biological toxicity of its degradation products is larger than chlorpyrifos.Therefore,it is very necessary for the simultaneous determination of chlorpyrifos and its degradation products 3,5,6-trichloro-2-pyridinol（TCP）However,the solubility of TCP and chlorpyrifos is 49.1 g/L and 2 mg/L,respectively,which has tens thousand time of discrepancy,so traditional liquid-liquid extraction was extremely hard to extract both of them from water at the same time.The main work of this dissertation focuses on the application of multi-walled carbon nanotubes（MWCNTs）for the adsorption of chlorpyrifos and TCP in water,which was used as a magnetic solid phase extraction agent.Meanwhile,a novel method was established for the analysis of the chlorpyrifos and TCP with a magnetic solid phase extraction by high performance liquid chromatography.And the details are as follows（1）We developed a novel method for the synthesis of magnetic solid phase extracting agent in the first part.MWCNTs with strong hydrophobicity,π-π,hydrogen bond affinity were magnetically modified by solvent thermal reaction,and making the generated Fe₃O₄ nanoparticles be loaded in bundles of MWCNTs,which can make MWCNTs/Fe₃O₄ magnetic adsorption material in one step.The reaction temperature,reaction time,material’s magnetic property,the adsorption performance of MWCNTs and iron source quality were investigated carefully.XRD,SEM,BET and VSM were used to characterize the crystal structure of material,microstructure,specific surface area,magnetic properties.The results show that the crystal structure of Fe₃O₄ nanoparticles in the material is single,its crystal grain size is small.And we find the Fe₃O₄ nanoparticles was successfully loaded in MWCNTs bundles.Its material saturation magnetization intensity was 28.29 emu/g,and the specific surface area is 208.45 m2/g,which exhibits well performance of the magnetic materials.（2）The second part of this paper is to investigate the adsorption characteristics of the MWCNTs/Fe₃O₄ for chlorpyrifos and TCP analysis.The experiment explored the factors including temperature,pH,initial concentration of organic compounds on the absorption target of MWCNTs/Fe₃O₄,adsorption kinetics,adsorption isotherm and adsorption thermodynamic parameters.And we also study the related analysis and explanation of the adsorption rate and adsorption mechanism of MWCNTs/Fe₃O_4.It can be concluded that the MWCNTs/Fe₃O₄ adsorption of the chlorpyrifos and TCP is in equilibrium within 30 minutes,and satisfy the quasi secondary rate equation,and the adsorption isotherm of both types are more in line with the Freundlich adsorption model,whose thermodynamics parameters,ΔH,ΔG,ΔS are negative,which showed that adsorption reaction auxiliary surface physical adsorption,spontaneous,and exothermic process.The MWCNTs/Fe₃O₄ nanoparticles show a good adsorption ability for chlorpyrifos and TCP,this may due to the factors includingπ-πfunction’s difference,hydrogen bonding.And we find the adsorption of TCP is stronger than chlorpyrifos.Moreover,repeated material recycling test was also showed by the materia’s property of recycling.It provides the theory and practice basis of MWCNTs/Fe₃O₄’s magnetic solid phase extraction for trace chlorpyrifos and TCP.（3）The third part of this paper is focused on the analysis of chlorpyrifos and TCP of MWCNTs/Fe₃O₄ with magnetic solid-phase extraction by HPLC in the water.The condition of high performance liquid chromatography（HPLC）was optimized,combining with the optimized adsorption conditions MWCNTs/Fe₃O₄ to chlorpyrifos and TCP in the second chapter.Solid-phase extraction conditions were further optimizd,including solid phase extraction agent quality,the type of eluent,eluent volume,elution times and elution temperature;combining with the optimal chromatographic conditions and the conditions of solid phase extraction,methodology validation.Under the optimized experimental conditions,the detection limit of chlorpyrifos and TCP is respectively 0.8μg/L,0.5μg/L,method quantification limit is 2.5μg/L and 1.5μg/L.Method of chlorpyrifos and TCP’s recovery in different dosage range is from 83.2%to91.7%and from 93.5%to 97.1%,respectively and their relative standard deviation range is from 3.2%to 7.4%and from 1.1%to 4.6%,respectively,which also showed good precision and precision.The accuracy of the proposed method was validated by analyzing two certified reference sample with a satisfactory analytical result.The recovery are greater than 85%,RSD<10%.Compared with the traditional liquid-liquid extraction and solid-phase extraction,the magnetic solid phase extraction have a lot of advantags including less organic reagent used,short time-consuming and excellent material adsorption performance,etc.The method can be used for chlorpyrifos and TCP’s simultaneous determination in actual water in the future.