| As the industrialization progresses, the problem of heavy metal contamination in food intensifies day after day. The concentration of heavy metals, especially in the food, is usually at trace or ultra-trace levels. And generally several kinds of heavy metals are contained in a particalar system, so before detection the pre-concentration step of the samples is needed. Magnetic chitosan Microspheres, which is one kind of magnetic polymer microspheres, not only have the features of chitosan, but also can be separated quickly by using external magnetic field. So magnetic chitosan microspheres may achieve dramatic application prospect due to its significant properties of separation for heavy metals.In this paper, researches about magnetic polymer microspheres, chitosan, synthesis and modification of Magnetic chitosan Microspheres and their adsorption capacity for heavy metals had been reviewed. For the purpose of establishing a new method of heavy metals determination by spectrophotometry for pork liver, the magnetic chitosan microspheres(MCTS) was synthesized and modified by six kinds of anchoring heterocyclic ligands, respectively. Their structure, morphology, chemical composition and performance of adsorption for heavy metals were investigated in order to selecte excellent microspheres that can be applied in analysis of heavy metals in food. The main contents are as follows:1. The magnetic chitosan microspheres(MCTS) was synthesized, using chitosan powder and Fe3O4nanoparticles as raw materials. The structure, morphology and chemical composition of MCTS were characterized by SEM, EDS, XRD, VSM, EA, FI-IR and TGA. Results showed that Fe3O4particles were embedded by chitosan, MCTS were spherical and paramagnetic, their surface was flat and smooth relatively. The process of synthesis did not change the polymorphs of Fe3O4and the mass fraction of Fe3O4was7.3%.2. The six heterocyclic organic ligands were chosen to react with MCTS after activated by epichlorohydrin. Then, according to the results of elemental analysis, three kinds of modified MCTS were screened out and the optimum conditions of different ligands were investigated, such as the solvent, temperature and mass ratio. The structure, morphology and chemical composition of modified MCTS were characterized. The process of modification practically did not change the structure, morphology and paramagnetic of modified MCTS and the polymorphs of Fe3O4.3. The adsorption properties of two chemical modified MCTS for Hg(â…¡) were systematically investigated by static and dynamic methods.Batch studies showed that both MCTS-g-AT and MCTS-g-BIT had high adsorption capacities for Hg(â…¡). The statically saturated adsorption capacities were228.2and194.4mg/g, for pH=5.0and5.5respectively.Maximum recovery of Hg(â…¡) absorbed by MCTS-g-AT and MCTS-g-BIT achieved100%with4mol/L HCl,3mol/L HNO3and4mol/L HCl, and4mol/L HNO3eluent solutions,. Kinetics studies showed that the adsorption kinetics data of Hg(â…¡) onto these two kinds of modified MCTS obeyed pseudo-second-order kinetics. Thermodynamics studies suggested that the isotherms adsorption followed the Langmuir model, the adsorption process of two kinds of microspheres was endothermic and spontaneous. The adsorption was chemisorption mainly, along with the physisorption. Column studies showed that the Thomas model was successfully applied to predicte the experimental breakthrough curves. In the conditions of dynamic desorption process, the desorption rate can achieve100%. The results of EDS proved that the eluted substance was mercury. 4. MCTS-g-AT, as a new material for microcolumn pre-concentration was synthesised, and its working conditions were optimized. The method was applied to detect mercury in oyster samples. |
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