The Synthesis Of A New Type Of Covalent Organic Framework Material And Its Application In Sample Pretreatment

Covalent Organic Frameworks（COFs）are an exciting new type of crystalline porous materials with ordered structure,which are constructed by covalent bonds.COFs have been widely applied in gas storage,optoelectricity,catalysis and sensing because of their characteristics of low density,large specific surface area,outstanding stability and adjustable pore structure,etc.In recent years,magnetic solid phase extraction（MSPE）is recognized as a revolutionary technology in the field of separation and enrichment.The main advantages of MSPE are that it does not need to be filled,the adsorbent is easily recovered by external magnetic field by suspending in the sample solution and transfer is very convenient.In this work,COFs were chosen as a functional group to encapsulate the surface of Fe₃O₄ and the synthesized magnetic COFs as an adsorbent were applied in the extraction of organic pollutants.The magnetic COFs could be rapidly collected by using an external magnet,which made sample pretreatment simple and fast.In this research,two magnetic COFs with great stability and excellent adsorption performance were synthesized by precipitation polymerization and solvothermal method,and applied them as MSPE adsorbent for the determination of organic pollutants in food samples.The specific research contents are as follows:1.Fe₃O₄@COF（TpBD）were synthesized by precipitation polymerization according to schiff base reaction and applied it as MSPE adsorbent for extraction of polycyclic aromatic hydrocarbons（PAHs）in food samples.The synthesized materials were characterized by transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Fourier transform infrared（FT-IR）spectra,N₂ adsorption-desorption isotherms and magnetic properties measurement.Fe₃O₄@COF（TpBD）adsorbed target analytes by hydrophobic interaction andπ-πstacking interaction.High performance liquid chromatography with diode array detection（HPLC-DAD）was used to quantify PAHs and good linearity was obtained in the range of 1-100 ng/mL with the correlation coefficent（R²）being above 0.9990 for all analytes.The limit of detection（LOD,based on the S/N=3）and limit of quantitation（LOQ,based on S/N=10）for PAHs were in the range of 0.83-11.70 ng/L and 2.76-39.00 ng/L,respectively.The recoveries of the proposed method ranged from 84.3 to 107.1%.2.Fe₃O₄@COF（TpBD）was synthesized by a solvothermal method according to read related literature and applied it as MSPE adsorbent for enrichment of endocrine disrupting chemicals（EDCs）in different meat samples（chicken,pork and shrimp）.Due to the presence of-OH in EDCs and C=O in Fe₃O₄@COF（TpBD）,Fe₃O₄@COF（TpBD）could adsord the target analytes by hydrogen bonding in addition to hydrophobic interaction andπ-πstacking interaction.Pre-column derivatization was required to transform EDCs into their derivatives with fluorescent property prior to high performance liquid chromatography with fluorescence detection（HPLC-FLD）analysis due to low ultraviolet absorbance and no significant fluorescence for most EDCs.The results indicated that the adsorption equilibrium was achieved within 5 min.The obtained Fe₃O₄@COF（TpBD）materials showed good linearity（R≥0.9986）in the range of 30-1000μg/L for all analytes and excellent extraction performance for EDCs with high sensitivity（1.4-8.7μg/L）.Finally,the developed method was successfully applied to the determination of EDCs in meats.Furthermore,the method,validated on spiked meats,showed satisfactory accuracy with average recovery in the 89.6-108.9%range.3.A novel type of magnetic COFs（Fe₃O₄@COF（TpDA））was synthesized by a solvothermal method and successfully applied to the extraction of plant growth regulators（PGRs）from fruits and vegetables.In order to obtain excellent extraction performance,the main experimental conditions affecting the extraction performance were optimized systematically,including type of eluent,formic acid content,amount of sorbent,adsorption time and desorption time.Under the optimized conditions,the proposed method exhibited good linearity（R≥0.9990）in the range of 50-2000μg/L and low LOD（S/N=3,4.68-7.51μg/L）.What’s more,satisfactory recoveries were calculated to be 83.0-105.0%with relative standard deviation（RSD）lower than 4.5%.Finally,the proposed method was successfully applied to the determination of PGRs in fruits and vegetables.