The Application Of Covalent Organic Polymers In The Analysis Of Food Safety

In recent years,food safety related accidents occur frequently,and food safety has become a widespread concern.The monitoring of food contaminations is of great significance.Usually,food samples cannot be analyzed directly by analytical instruments because of the complex matrix and low concentration of target analytes.An appropriate sample pretreatment technique is usually necessary to enrich the target analytes and remove the complex matrix prior to instrumental analysis.Magnetic solid phase extraction(MSPE)has the advantages of fast separation,simple operation,and low organic solvent consumption,exhibiting a good application prospect in trace analysis.Extraction adsorbent is the key factor which determines the selectivity and kinetics of MSPE-based methodologies.In MSPE,the ideal adsorbents should possess good dispersibility,stability,magnetic separation ability and good extraction properties for target analytes.Covalent organic polymers(COPs)are a kind of good adsorbents for SPE due to their unique properties of low densities,high surface area and good chemical stability.While,when COPs are directly used for dispersive solid phase extraction,they are easy to agglomerate and float on water surface due to the poor dispersibility,causing serious difficulty in the separation from sample solution.Doping the magnetic particles into the COPs would increase the density of COPs composites and improve their dispersibility in aqueous solution,benefiting the extraction and magnetic separation.The purpose of this dissertation is to prepare magnetic COPs,and establish MSPE-gas chromatography(GC)method for the analysis of trace organic pollutants in food samples.The main contents of this dissertation are described as follows:(1)Magnetic CTFs/Ni composite was prepared by in situ reduction of nickel ions on CTFs matrix with a solvothermal method.The magnetic CTFs/Ni composite was characterized by transmission electron micrograph,powder X-ray diffraction and saturation magnetizations,and the stability and preparation reproducibility were investigated.The results demonstrate that Ni particles are well dispersed in the composite,and CTFs/Ni has good magnetic property,chemical stability and preparation reproducibility.By using the prepared CTFs/Ni as the sorbents,a novel method of MSPE combined with GC-flame ionization detector(FID)was developed for the analysis of trace phthalate esters(PAEs)in plastic packaging materials.The extraction efficiencies for target PAEs were 44.4-66.2%.Under the optimal conditions,the limits of detection(LODs,S/N=3)for six PAEs(dimethyl phthalate,diethyl phthalate,di-n-butyl phthalate,benzyl butyl phthalate,di(2-ethyl hexyl)phthalate,di-n-octyl phthalate)were found to be in the range of 24-85 ?g/g,with relative standard deviations(RSDs)of 0.35-1.01%(n=7,c=800 ?g/g).The proposed CTFs/Ni-MSPE-GC-FID method was successfully applied to the analysis of PAEs in various plastic packaging materials.Di-n-butyl phthalate(110-530 ?g/g)and di(2?ethyl hexyl)phthalate(590-137 ?g/g)were detected in all tested samples,and benzyl butyl phthalate(230 ?g/g)and di-n-octyl phthalate(460 ?g/g)were detected in disposable plastic cup.The developed method has the advantage of rapid and simple operation,high enrichment factor and low consumption of harmful organic solvents.(2)In consideration of the relatively high temperature(180 °C)and long time(13 h)employed in the synthesis procedure for CTFs/Ni,magnetic CTFs/Co composite was prepared by reducing cobalt ions on the CTFs with hydrazine hydrate.The synthesis process is simple and time-saving with only 60 0C for 4 h.By using the prepared CTFs/Co as the sorbents,a novel method of MSPE combined with GC-FID was developed for the analysis of five pyrethroids,including bifenthrin,fenpropathrin,cypermethrin,permethrin and fenvalerate,in fruit juice,honey and vegetable samples.Under the optimal conditions,the extraction efficiencies for target pyrethroids were 52.0-67.0%,and the LODs(S/N=3)were found to be in the range of 0.34-0.84 ?g/L,with RSDs of 2.3-4.2%(n=5,c=5 ?g/L).The proposed CTFs/Co-MSPE-GC-FID method was applied to the analysis of target pyrethroids in fruit juice,honey and vegetable samples,and the recoveries of 73.0-118%were obtained,indicating a good application potential of the developed method in analysis of real sample with relatively complex matrix.(3)The schiff-base networks(SNWs)was synthesized by using melamine and 1,4-phthalaldehyde.Magnetic SNWs/Ni composite was prepared by a simple hydrazine hydrate reduction of nickel ions on the SNWs.The obtained SNWs/Ni composites presented good dispersibility and chemical stability.Based on it,a novel method of MSPE combined with GC-flame photometric detector(FPD)was developed for the analysis of trace phenothiazines(promethazine,chlorpromazine,trifluoperazine)in milk and milk powder samples.Compared with other reported materials for trace phenothiazines analysis,the home-made SNWs/Ni materials showed faster adsorption/desorption kinetics(20 min)and higher extraction efficiencies(64.5-69.6%).Under the optimized conditions,the analytical performance of SNWs/Ni-MSPE-GC-FPD for the determination of phenothiazines was evaluated.The LODs(S/N=3)for phenothiazines were found to be in the range of 0.31-0.46?g/L,with RSDs of 9.7-12.6%(n=7,c=3.6 ?g/L).The proposed SNWs/Ni-MSPE-GC-FPD method was successfully applied to the analysis of trace phenothiazines in milk and milk powder samples,with the recoveries of 86.6-110%and 78.0-116%,respectively.