New Analytical Methods For Amino Compounds In Food Contact Materials

In recent years, food safety has become the focus of public attention. Food safety not only depends on the safety of the food but also depends on the food contact materials that used in production, processing, packaging, transport or cooking. Amine substances including aromatic amine and melamine are harmful for human body. They are also the research hotspot in recent years. Traditional methods used for detecting aromatic amine and melamine mainly include gas chromatography, liquid chromatography, mass spectrometry and so on. However, these methods have complicated detection process and high detection limit. Therefore, we need to search new methods for sensing aromatic amine and melamine migrated from food contact materials.In our work, we applied graphene, graphene quantum dots, Molecularly imprinted polymer and gold nanoparticles for electrochemical or fluorescent sensing aromatic amine and melamine.Chapter 1:IntroductionIntroduce the research purpose, present situation and significance for food contact materials. Two kinds of amine tableware including nylon tableware and melamine tableware were discussed. The preparation and applications of graphene and graphene quantum dots are also included.Chapter 2:Molecularly imprinted polymer grafted graphene for simultaneous electrochemical sensing of 4,4-methylene diphenylamine and aniline by differential pulse voltammetryA sensitive and selective electrochemical sensor based on molecular imprinting polymers grafted graphene (MIPs-G) was developed for simultaneous measurement of 4,4-methylene diphenylamine (MDA) and aniline by differential pulse voltammetry (DPV). MIPs-G was synthesized via free radical polymerization reaction using MDA and 4-vinyl pyridine as template molecule and functional monomer respectively. The obtained nanocomposites were characterized by transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometry, Raman spectroscopy and thermal gravimetric analysis. After removal template molecules, MIPs-G was used as electrode material for aromatic amines measurements. Due to the high binding affinity towards MDA and the ∏-∏ interaction with aniline, the MIPs-G based electrochemical sensor can be used for simultaneous detection of MDA and aniline by DPV. Under the optimized condition, the oxidation potentials for MDA and aniline were observed at 0.62 V and 0.72V, respectively. Moreover, MIPs-G modified glassy carbon electrode shows linear response towards MDA and aniline simultaneously over the range of 1.0 to 15 μM. The MIPs-G based electrochemical sensor has been applied for simultaneous measurement of MDA and aniline in plastic tableware.Chapter 3:Determination of melamine in food contact materials using an electrode modified with gold nanoparticles and reduced graphene oxideWe describe an electrochemical sensor for melamine based on a glassy carbon electrode (GCE) modified with reduced graphene oxide (AuNPs/rGO) that were decorated with gold nanoparticles. The AuNPs/rGO nanocomposite was synthesized by co-reduction of Au(III) and graphene oxide and characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The response of the modified GCE to melamine was investigated by using ferricyanide as an electrochemical reporters. It is found that the electrochemical response to ferricyanide is increasingly suppressed by increasing concentration of melamine. This is attributed to competitive adsorption of melamine at the AuNPs/rGO composite through the interaction between its amino groups and the AuNPs. The presence of rGO, in turn, provides a platform for a more uniform distribution of the AuNPs and enhances the electron transfer rate of the redox reaction. The findings were used to develop a sensitive method for the determination of melamine. Under optimized conditions, the redox peak current of ferricyanide at a working voltage of 171 mV (vs. SCE) is linearly related to the concentration of melamine in 5.0 to 50 nM range. The method was successfully applied to the determination of melamine in food contact materials.Chapter 4:Fluorescent detection of melamine based on the quenching ability of gold nanoparticles for graphene quantum dotsWe here report a fluorescent turn-on sensor for sensitive sensing melamine based on the fluorescence quenching between gold nanoparticles and graphene quantum dots (GQD). In the present study, upon addition of melamine, the fluorescence of AuNPs-GQD system is enhanced due to the strong interaction between the amino group of melamine and the gold nanoparticles, leading to the release of AuNPs from the surfaces of GQD. We observed that the fluorescence of GQD gradually increased with the increase of melamine concentration. Under optimum condition, the fluorescence of GQD shows a linear function against the melamine concentration ranging from 0.1μM to 1.4μM.