Research On Detection Of N-nitrosamines Based On Molecularly Imprinted Hybrid Materials

N-nitrosamines are a class of compounds with high toxicity and widely found in nature.In recent years,N-nitrosamines have been frequently detected in foods,mainly in processed foods,environmental waters and aquatic products,posing potential health hazards（carcinogenicity and mutagenicity,etc.）to humans.Since N-nitrosamines are present in food at trace levels and the composition of food matrices is complex,the existing pretreatment methods cannot effectively enrich for the target and exclude interfering substances,resulting in serious matrix interference in instrumental detection,and therefore it is necessary to develop efficient and convenient analytical methods for N-nitrosamines to monitor their contents in the environment and food.The solid-phase extraction technique has been widely used in the enrichment and detection of trace substances because of its advantages of high extraction efficiency,low consumption of organic reagents and simple operation method.In this process,the sorbent material used is a decisive factor in determining the extraction performance.In this study,to achieve efficient enrichment and detection of trace N-nitrosamines,based on molecular imprinting technology and metal-organic frameworks,the dummy-template magnetic molecularly imprinted hybrid materials were firstly prepared and used for rapid enrichment of N-nitrosamines in environmental water samples.Subsequently,metal-organic framework@molecularly imprinted hybrid materials were prepared for complex food matrices and applied to the enrichment of N-nitrosamines in pickled foods.Finally,a（magnetic）solid-phase extraction technique based on molecularly imprinted hybrid materials combined with high performance liquid chromatography was established for the simultaneous detection of various N-nitrosamines.The main findings of this thesis are as follows:（1）Magnetic nanoparticles（Fe₃O₄）were synthesized by co-precipitation method,vinyl-modified on their surface,using benzhydrol and 5-nonanol as dummy template molecules,the dummy-template magnetic molecularly imprinted hybrid materials（DMMIPs）were prepared with polymerizing molecularly imprinted layers by surface imprinting method.The synthesis conditions of the polymers were optimized and determined experimentally（vinyl modified magnetic nanoparticles,methacrylic acid as functional monomer,acetonitrile-H₂O（9:1,v/v）as porogen solvent,trimethylolpropane trimethacrylate as cross-linker,molar ratio of template molecules,functional monomer and cross-linker is 1:4:20）.The composites were characterized by a series of techniques,and the polymers were microspherical and roughly folded on the surface,the imprinted polymerization layer was uniformly encapsulated on the surface of magnetic nanoparticles with a typical core-shell structure.The adsorption properties of the materials were investigated by dynamic and static adsorption experiments.The results showed that the magnetic imprinted polymers have high adsorption capacity（11.543 mg/g）and fast adsorption performance with a saturation time of only 5 min.The obtained DMMIPs were applied to the magnetic solid phase extraction process,and the extraction conditions（sample volume of 50 m L,100 mg of materials,p H 7,adsorption time of 15 min,and methanol as elution solvent）were optimized and determined.Finally,an MSPE-HPLC-UV method based on DMMIPs was developed for the enrichment and detection of NAs in environmental water samples.The method showed good linearity in the range of 0.1～20（?）g/m L with R² from 0.9964 to 0.9998.The recoveries of three concentration levels（30,50and 100 ng/m L）added to environmental water samples ranged from 69.4%to 101.6%and RSDs were 0.1%～5.2%.The experimental results demonstrated that the established method has the advantages of high accuracy,simple operation,good reproducibility and easy to recycle materials,which provides a new strategy for rapid enrichment and detection of N-nitrosamines in environmental samples.（2）The metal-organic framework material MIL-101（Fe）was firstly prepared by the solvothermal method based on the coordination of Fe³⁺with terephthalic acid.On this basis,metal-organic framework@molecularly imprinted hybrid materials（MIL-101@DMIPs）were prepared using surface imprinting technique with benzhydrol,5-nonanol and N-formylpyrrolidine as dummy template molecules.By a series of characterization techniques,the material has a typical core-shell structure and the surface is clearly folded.The diameter of MIL-101（Fe）is about 0.5～1μm,and the diameter of the hybrid materials is significantly larger（about 2～2.5μm）,indicating that the imprinted layer was successfully polymerized onto the surface of MIL-101（Fe）.The adsorption experiments showed that the material has higher adsorption capacity（73.407 mg/g）and faster adsorption rate.An SPE-HPLC-UV method based on MIL-101@DMIPs was developed for the enrichment and detection of N-nitrosamines in pickled vegetables under optimal adsorption and desorption conditions（40 mg of materials,p H 7,2 m L of H₂O as the washing solvent and 2 m L of methanol as the eluent solvent）.The results showed that the method exhibited good linearity in the range of 0.2～10μg/g with R² of 0.9941～0.9999.The recoveries ranged from 66.0%to 100.5%and RSDs were 0.1%～3.4%for the addition of three different concentration levels in six kinds of pickled vegetables.In this study,the hybrid imprinted materials were prepared by combining a metal-organic framework and molecularly imprinted polymers,which conferred the molecular imprint with higher mass transfer rate and larger adsorption capacity;based on this,the established method exhibited higher accuracy,better selectivity and reproducibility,which provided a novel adsorbent material for the detection of trace N-nitrosamines in complex matrices.