Preparation Of Novel Chelating Resins And Determination Of Heavy Metals In Food

In recent years,with human activities and the development of industry,food polluted with heavy metals(such as mercury,cadmium,lead,arsenic)has been paid more attention, and heavy metals must be determined in food safety inspection, so it is very important to analyze and detect the trace heavy metals of food, which is helpful to human health and useful to evaluate harmness to people. Recently, many analytical methods such as ICP-MS, ICP-AES,HG-AFS possess high sensitivity and selectivity, still expensive and difficulty to apply in small and medium-sized enterprises. Spectrophotometer is regarded as low-cost instrument in analysis of heavy metals, and UV-Vis spectrophotometry has been widely used with its advantages of simple operation and low cost; its limit lies in the narrow instrument detection, and easy to be interfered by coexisting ions. Because of low-concentration and high complexity of heavy metals in food, it is difficult to analyze by conventional methods, so food samples must be separation and preconcentration before determination.In this paper, research on the chelating resins and their adsorption to heavy metals were reviewed, and novel chelating resins were prepared by anchoring heterocyclic into crosslinked polystyrene.The adsorption behaviors to heavy metals were studied by static and dynamic adsorption,and excellent resin was selected for separation and preconcentration of mercury in food.Subsequently, method of determination of mercury by spectrophotometry combined with separation and preconcentration by chelating resins was established. It is mainly manifested as follows:1.Eight heterocyclic organic ligands,containing nitrogen, sulfur,which had an excellent chelating properties to heavy metals were used to react with chloromethylated polystyrene beads in preparing chelating resins,and five kinds of resins were screened out.Effect of reaction solvent, reaction temperature and molar ratio of reagents on functional group conversation was studied,and optimum conditions were found. The N atom content of the resins,functional group capacity and functional group conversion were determined by elemental analysis. The resin structures were characterized by IR. The thermal decomposition of the resin by TGA instrument was used to study their synthetic scheme and thermal stability.2.The adsorption properties of five kinds of resins for seven kinds of common heavy metal ions were researched, three kinds of resins were selected on the basis of large adsorption capacity,good selectivity and easy elution, focusing on the adsorption behavior for Hg (II).Static experiment showed that AR,APR and MTR have high adsorption selectivity for Hg(II),maximum adsorption capacity is384.4mg/g(pH=4),304.1mg/g(pH=5),343.6mg/g(pH=6).And they have good selectivity for Hg (II) in binary mixture system composed of Hg (II) and other metal ions.The statically saturated adsorption capacities of ABTR for Cd(II) was201.8mg/g(pH=4),and has good selectivity for Cd(II) in binary mixture system composed of Cd(II) and other metal ions. Respectively,it was found that Hg (II) adsorbed on AR,APR and MTR could be eluted completely by1.0mol/L HCl-5%thiourea solutions,1.5mol/L HCl-5%thiourea solution,2mol/L HCl-5%thiourea solutions.And resins had favorable regeneration performance and repetitive property. No satisfying eluent had been found for ABTR under the experimental conditions,maybe ABTR and Cd(II) formed strong chemical bond which made elution hard.Through the study of the adsorption isotherms in different temperature,the isotherms adsorption data was in good agreement with Langmuir model.Kinetics functions showed the adsorption behavior followed with second-order kinetics. Thermodynamic functions indicated that Hg(II) adsorption by three kinds of resins was endothermic and spontaneous chemisorption.Dynamic adsorption studies showed that the dynamic saturated adsorption capacities of AR and MTR were417.0mg/g and471.5mg/g, respectively. The Thomas model was successfully coincided with dynamic adsorption.Dynamic desorption ratio of two kinds of resins can achieve100%; during the three-time repeated adsorption-desorption experiment,dynamic adsorption rate was not less than95%of initial adsorption, AR exhibited a better regeneration performance compared with MTR. 3.Method of determination of trace mercury by UV-Vis spectrophotometry was proposed by using AR in separation and preconcentration in edible fungi,aquatic product,animal food and vegetables. Experimental results showed that, through AR resin separation and enrichment, the data was in accordance with ICP-AES,which suggested that this method can be applied to determine trace mercury in food and other simples.