Novel Magnetic Porous Materials Based Magnetic Solid Phase Extraction Coupled With Gas Chromatography For Trace Analysis Of Organic Pollutants

Magnetic solid phase extraction(MSPE)has attracted extensive attention in the field of sample pretreatment due to its advantages of high efficiency and simplicity.In MSPE,the employed adsorbents are the key factors determining the analytical selectivity and sensitivity of the method.Novel porous materials are good alternative for MSPE adsorbents due to their specific pore structure and excellent physical/chemical properties,such as large specific surface area,good chemical stability,and easy to be functionalized.However,traditional preparation method for porous materials usually consumes a large quantity of harmful organic reagents,requires high temperature/pressure reaction conditions and precious metal catalysts.It limits wide application of porous materials in trace analysis to some extent.Moreover,systematical investigation on the adsorption behavior of analytes with different structure on magnetic porous adsorbents are expected,along with the exploration on the relationship between the size of interest analytes and the pore structure of adsorbents.The purpose of this paper is to prepare magnetic porous adsorbents by simple and mild methods,investigate the adsorption performance of them for interest organic pollutants with different structure,and establish new MSPE-gas chromatography(GC)methods for the efficient analysis of trace organic pollutants in real samples.The main contents of the dissertation include:(1)Magnetic nanoporous carbons(MNPCs)based on metal organic frameworks(Zn/Co-MOFs)was synthesized via a facial one-step carbonization method.The prepared MNPCs exhibited high specific surface area,good chemical stability and high extraction efficiency for interest organophosphorus pesticides(OPPs).The good extraction performance of the MNPCs for interest OPPs can be primarily attributed toπ-π interaction and hydrophobic interaction between MNPCs and OPPs.Based on it,a method of MNPCs-based MSPE-GC-flame photometric detection(FPD)was established for the quantification of five interest OPPs in fruit samples.The main experimental conditions for MSPE of five target OPPs were investigated systematically,such as the desorption solvent and volume,sample volume,ionic strength,extraction time and desorption time.Under the optimal conditions,the limits of detection(LODs,S/N=3)were found to be in the range of 0.018(ethion)-0.045(malathion)μg/L.The linear range was 0.05-100 μg/L for phorate,diazinon,ethionand 0.1-10 μg/L for malathion,fenthion respectively.The relative standard deviations(RSDs)of the method were in the range of 3.5-9.7%(c=0.5 μg/L).The recovery test was carried out by spiking target OPPs into the homogenated fruit samples at three concentration levels to validate the accuracy of the proposed method,and the recoveries for target OPPs were 84.4-116%.The results show that the proposed method can be successfully used to analyze trace OPPs residue in fruit samples.(2)Magnetic porous organic polymers(MOPs)was synthesized by a simple azo reaction.The preparation process was mild,green and environmental-friendly,avoiding the use of high temperature,metal catalyst and harmful organic reagent.The obtained MOPs was characterized in terms of morphology,pore structure,and magnetism;they represented high surface area,good stability/dispersibility,and excellent extraction performance for interest triazole fungicides(TFs).Based on the prepared MOPs,a method of MSPE-GC-flame ionization detection(FID)was proposed for the analysis of target TFs in vegetables.Different operating conditions affecting the extraction efficiency of TFs,such as extraction time,pH,ionic strength,sorbent dosage,and sample volume as well as eluent were carefully optimized.Under the optimized experimental conditions,quantitative extraction could be achieved for target TFs(extraction efficiency of 84.5-90.3%),and the LODs(S/N=3)were0.12-0.19 μg/L,which is the lowest among the reported methods based on GC-FID detection for target TFs analysis presently.The method was assessed by the analysis of trace TFs in vegetables,and the recovery for the spiked cucumber and cabbage was86.9-117% and 84.7-114%,respectively.(3)Simple amide reaction was adopted to prepare amide bonded MOPs(Am-MOPs)under mild conditions,and the as-synthesized materials had good preparation reproducibility.Taking seven organophosphorus esters(OPEs)with different structure as analyte models,the adsorption performance of the Am-MOPs was investigated.It was found that Am-MOPs exhibited relatively high extraction efficiency for OPEs containing aromatic rings in the structure,possibly due to the π-πinteraction between aromatic OPEs and abundant benzene ring in the Am-MOPs structure.Based on this,a new MSPE-GC-FPD method was established to analyze seven OPEs in plastic samples.Experiment conditions that may affect the extraction of OPEs were systematically optimized.Under the optimal conditions,the LODs were in the range of 0.054-0.280 μg/L,and the RSDs were 3.9-9.2%(n=7,c=2 μg/L).The application potential of the method was assessed by the analysis of OPEs in plasticsamples,and the recovery of target OPEs in beverage bottle and medical plastic bottle samples were 85.9-115% and 84.8-118%,respectively.The established MSPE-GC-FPD method is simple,rapid,sensitive and selective,which has a good prospect for the analysis of trace OPEs in plastic samples.