Synthesis Of Novel Cross-linked Chitosan Microspheres And The Application In Analysis Of Heavy Metals In Food

As the acceleration of modern industrialization progress in China,as well as many unscrupulous businessmen's blind pursuit of economic interests,heavy metals contamination in food safety has intensified.It has become one of the greatest problems,which has threatened human health.With the development of the determination of heavy metals in food safety,the modem instrument analysis methods achieve higher sensitivity and selectivity than the traditional methods.However,they also have the problems of high cost,complexity of operation,which limit the popularization of determination of heavy metals in food businesses in China.The spectrophotometers owning to be economic and easy for operation become the main and economic instrument for determination of heavy metals.However,it's impossible to detect heavy metals in low concentration accurately because of the high detection limit of spectrophotometers.The good absorbents possess the great property such as high selectivity,adsorption capacity,elution rate and so on.Therefore,if the absorbents can be synthesized successfully and the heavy metals in low concentration are separated and enriched by the absorbents in advance,the problem may be solved.There is no doubt that it lays the foundations of the application of spectrophotometers in the determination of heavy metals in food business.Chitosan?CTS?results from deacetylation of chitin which is the second abundant polymer in nature next to cellulose.It is well known that chitosan is effective in the adsorption of heavy metals because the large number of -NH₂ groups and -OH groups on CTS chains serve as the coordination sites.In this study,on basis of the overview of CTS and the adsorption behavior of heavy metals,for the purpose of establishing a new method of selective separation and enrichment of heavy metals,the cross-linked chitosan microspheres?CCTS?which is stable in the acidic solution was synthesized.Then chemical modified CCTS has been prepared by grafting ligands into CCTS.The synthesis conditions have been studied.Besides,the adsorption behaviors to metal ions were also studied.Then,a new method of the determination of heavy metals by spectrophotometry was proposed for chemical modified CCTS in pork liver,which may broaden the application areas of spectrophotometry.The main contents are as follows:1.On the condition of chitosan powder as raw materials,formaldehyde as the amino protective agent and Epichlorohydrin as the cross-linking agent,CCTS which is stable in acidic solution was synthesized.The conditions impacting the preparation of CCTS,such as the concentration of chitosan solution,the amount of cross-linking agent and the stirring speed were discussed to determine the optimal synthesis conditions.CCTS has been characterized by elemental analysis,infrared spectra analysis and thermogravimetry analysis,and the possible synthetic route has been inferred.2.Although the CCTS is stable in acidic solution,the adsorption capacity of metal ions is very low.To solve this problem,chemical modification was performed.Then,according to the change of nitrogen content by elemental analysis and the nitrogen content in ligands,the optimum conditions such as the solvent,temperature and mass ratio,have been investigated.Three chemical modified CCTS with new property have been chose from the five which were modified by five different ligands.They have also been characterized by elemental analysis,infrared spectra analysis and thermogravimetry analysis.The possible synthetic routes have been deduced.3.The adsorption properties of two chemical modified CCTS for heavy metals were systematically investigated.The experimental results showed that CCTS-g-CBM possessed the selective adsorption of Hg²⁺,and adsorption capacity is 243.7mg/g;CCTS-g-ED possessed the selective adsorption of Cu²⁺,and adsorption capacity is 113.9mg/g.Two isotherm,Langmuir model and Freundlich models,have been fitted at different temperatures.What's more,adsorption kinetics and thermodynamics were studied.The result showed that the adsorption of Hg²⁺ onto CCTS-g-CBM and that of Cu²⁺ onto CCTS-g-ED met Langmuir models and Second-order kinetics well;and the adsorption process is endothermic.The elution ratio of those two chemical modified CCTS can reach 100%.Dynamic studies have indicated that adsorption capacity of Hg²⁺ onto CCTS-g-CBM is 257.8mg/g;and that of Hg²⁺ onto CCTS-g-ED is 115.4mg/g.The elution ratio is 100%.4.Two methods of determination of Cu²⁺ in pork liver by ICP-AES and spectrophotometry using the CCTS-g-ED in preconcentration and separation are proposed.The study demonstrated that through the absorbent separation and enrichment,the data of above two methods are basically the same in the determination of Cu²⁺.