Synthesis Of Magnetic Nanomaterials And Its Application In The Determination Of Food Additives

In recent years,various food safety problems emerged and have attracted consumer’s extensive attention,such as environmental pollution,pesticide residues,microbial contamination,illegal use of chemical raw materials.Food additives are a kind of compounds that usurally have added to food to preserve flavor or enhance its taste,appearance,or other qualities.However,if these food addities are excessively consumed,they would pose potential risks to human health.Therefore,various analytical methods and detection techniques have been developed for determination of food additives.As one of the most important step of analytical method,sample prparation attracted considerable attention becuase about 60%time was spend on sample preparation and 30%data error comes from sample preparation.Due to large surface area,good chemical stability,and easily modified with other compounds,nanomaterials has been paid more and more attention in sample preparation.In this thesis,the Fe₃O₄ nanoparticles,magnetic nanocomposites（GO@Fe₃O₄）and polyethyleneimine modified GO@Fe₃O₄ nanocomposites were prepared and used as the sorbents of solid-phase microextraction for clean and preconcentration of food additives prior to high-performance liquid chromatography analysis.In chapter 1:the definition and the types of food additives were generally introduced,some pre-treatment methods and detection technology for food additives analysis were brifly described.And the purpose and signification of this thesis were described,too.In chapter 2:a magnetic solid-phase extraction（MSPE）protocol followed with HPLC analysis was developed for the determination of maltol and ethyl maltol in food samples.The Fe₃O₄ nanoparticles were prepared by one-step solvothermal method and firstly used as the adsorbent for clean and preconcentration of maltol and ethyl maltol in food samples.The as-prepared Fe₃O₄ nanoparticles were characterized by transmission electron microscope,Fourier transform-infrared spectroscopy,X-ray diffraction and vibrating sample magnetometer.The extraction conditions including the amount of material,extraction time,pH,temperature,and desorption solvents were investigated,respectively.Under the optimized conditions,the liner range was in the range of 0.25-800μg/mL,the correlation coefficients（R²）were 0.9996 and0.9998,the detection limits of 0.04 and 0.05μg/mL could be achieved for maltol and ethyl maltol.The recoveries between 84.2%and 103.4%,with RSDs lower than 3.01%were obtained for the analysis of spiked pulm candy sample.The developed method was successfully applied to the analysis of real samples,such as juice,chocolate and pulm candy.In chapter 3:the magnetic graphene oxide nanocomposite（GO@Fe₃O₄）was prepared by one-step solvthermal method.The as-prepared GO@Fe₃O₄ nanocomposite was characterized by TEM,XRD,IR,VSM,BET.The results show that the material has large specific surface area,uniform size,and good dispersibility.It can be used as an adsorbent for solid-phase extraction.Betwen the surface of the graphene oxide and the target analytes,they were interacted byπ-πconjugates,electrostatic adsorption,and hydrogen bonding.The extraction and desorption conditions including the amount of material,extraction time,pH of the solution,desorption temperature,and desorption solvents were investigated,respectively.Under the optimized conditions,the linear range of lemon yellow,sunset yellow,and allura red is 0.25-1000μg/mL,the linear range of amaranth and carmine is 0.25-500μg/mL,and the correlation coefficient is R²≥0.9993.The detection limits was ranged from 0.032 to 0.061μg/mL.The recoveries between73.2%and 107.7%with RSDs（n=5）lower than 1.34%were obtained for the analysis of spiked jelly sample.The developed method was successfully applied to the analysis of real samples including jelly,candy and plum candy.In chapter 4:the GO@Fe₃O₄ nanocomposites modified with polyethyleneimine（GO@Fe₃O₄@PEI）were prepared by a solvthermal method and used as a solid phase extraction adsorbent to clean and preconcentration of various kinds of food colorants in food samples.In order to achieve the best adsorption efficiency,the experimental conditions including the amount of adsorbents,adsorption time adsorption temperature,extraction pH,elution solvents and elution temperature were systematically investigated.Under the optimized conditions,the recovery rate was achieved between 80.1%and 108.2%with RSDs≤3.5%.Compared with GO@Fe₃O₄nanocomposites,the as-prepred GO@Fe₃O₄@PEI nanocomposites provide higher adsorption ability for food colorants.