Application Of Triphenylamine-based Covalent Organic Polymers In Food Pretreatment And Analysis

In recent years,food safety incidents have emerged one after another,and food safety has become a major issue related to the health of residents.A variety of hazardous substances can be introduced into food during production,packaging,storage and transportation.Accurate analysis of hazardous substances in food was an important factor in food quality control,and control of food processing and storage conditions was an important method to reduce food contaminants.The analysis of harmful substances in food was a great challenge because of the complex food matrix,many interfering components,and the presence of most target substances at trace level.Sample pretreatment technology was an important method to eliminate impurities and enrich the target substances.Dispersive solid phase extraction（DSPE）has become an important pretreatment method for liquid samples because of its good repeatability,high enrichment efficiency,simplicity and high efficiency.The adsorbent was an important factor in the success of dispersive solid phase extraction.Covalent organic frameworks（COFs）have become ideal adsorbents for dispersive solid phase extraction due to their low density,good stability,large specific surface area and adjustable pore size.In this study,tris（4-formylphenyl）amine with three-dimensional structure reacted with other materials to synthesize a series of triphenylamine COFs.Then,it was used for the pretreatment of aldehydes,phthalates and polychlorinated biphenyls.The quantitative analysis of the above-mentioned target substances can be accomplished through the combination of pre-processing methods in this study and chromatography or chromatography-mass spectrometry.The COFs with excellent fluorescence performance was selected.The COFs with good fluorescence characteristics was used as fluorescence sensor to establish a fluorescence quantitative detection method for water in food.This method provides a rapid basis for judging the storage conditions of food.The specific work completed was as follows:Chapter 1:The food pretreatment technologies were introduced in brief.Next the dispersed solid phase extraction pretreatment technology and covalent organic polymer were briefly introduced and summarized.Then the purpose and significance of this paper was explained.Chapter 2:COF（TFPA-OT）was synthesized from tris（4-formylphenyl）amine and o-tolidine under ultrasound conditions in DMSO at room temperature for 5 min.Then it was used as an adsorbent in dispersive solid phase extraction technology.The aldehydes were extracted and enriched by COF（TFPA-OT）.Moreover,dansyl hydrazide was sensitive to mass spectrometry response and was used as a labeling reagent for aldehyde compounds to improve their sensitivity.A liquid chromatography coupled to tandem mass spectrometry（LC-MS/MS）was used for quantitative analysis of aldehydes.The established method has been evaluated for linearity,accuracy and precision.The results show that the method was feasible.The detection limit of this method was in the range of 19.7–32.2 ng/L,and the recovery rate was 89.1–101.4%.This method can be regarded as an efficient and sensitive choice for the detection of aldehyde compounds in fried foods.Chapter 3:Tris（4-formylphenyl）amine reacted with o-tolidine and methyl iodide to form the positively charged COF（TFPA-OT）.Then,the modified COFs was used to enrich plasticizers in plastic packaging materials.Moreover,phthalate esters can be adsorbed on the modified COF（TFPA-OT）by electrostatic interaction,hydrophobic interaction andπ-πinteraction.Gas chromatography coupled to tandem mass spectrometry（GC-MS/MS）was used for quantitative analysis of samples.The detection limit of this method was between 0.011–0.33μg/m L,and the recovery rate was between 89.5–102%.The results show that COF（TFPA-OT）was an ideal adsorbent for extracting plasticizers from plastic packaging materials.Chapter 4:Tris（4-formylphenyl）amine reacted with amines with different spatial structures to produce a series of COFs.The relationship between the structure of amine and the porosity of COFs was explored by means of N₂ adsorption desorption isotherms.The results showd that COFs synthesized with 3D tetrakis（4-aminophenyl）methane has the largest adsorption capacity.It can be used as adsorbent in the pretreatment method developed in this study to enrich PCBs in aquatic products.Under the optimal conditions,the method has good performance.The detection limit of PCBs in aquatic products was 0.56–2.81 ng/L.The recovery rate of this method was 90.9–101.3%.Chapter5:Tris（4-formylphenyl）aminereactedwith4,4’,4”-（1,3,5-triazine-2,4,6-triyl）triphenylamine to synthesize COF（TFPA-TTA）.Due to COF（TFPA-TTA）hasπ-conjugated,electron-rich and electron-deficient units,it exhibited good fluorescence in organic solvents such as acetonitrile.Hydrogen bonds were formed between water molecules and N atoms in COFs,which blocked intramolecular charge transfer（ICT）and caused fluorescence quenching.The response curve of water in organic solvents was established with water content as the abscissa and fluorescence intensity as the ordinate.The detection limit of this method was 0.056wt%,and the linear range was 0.5–4.5wt%.The phenomenon of fluorescence quenching caused by water was used in the fluorescence analysis of food moisture.