Study On Seperation,Concentration And Determination Of Heavy Metals In Food

Heavy metal pollution has become one of the factors that affect food safety,which requires great attention of the consumer.The heavy metals in aquatic products,crops,animals and poultry are accumulated by bioconcentration,and finally harm to human health with the effect of food chain.Traditional methods are mostly for qualitative and quantitative detection of heavy metal in food,but it is hard to remove or recover from the food.Most heavy metals in food are difficult to analyze by conventional detection methods as the concentration is usually at trace or ultratrace level.Chelating resin can be effectively used in removing and concentrating trace metals from food and detect by UV and ICP techniques with some advantages,such as easy to operate,low cost,excellent separation performance,etc.,which provides a novel method with a wide application in heavy metal removal and detection from food.In this paper,four kinds of chelating resins were prepared by the synthesis of crosslinked chloromethylated polystyrene microsphere(PS-Cl)and four ligand compounds.The structure of chelating resins were characterized by element analysis,FTIR and TGA.Two kinds of chelating resins were screened for the determination of heavy metals in food as the excellent selective adsorption performance.Results manifested as follows:(1)The effect of reaction solvent,reaction temperature and reaction molar ratio were discussed,and the optimum synthesis conditions were determined.Element analysis was used to determine nitrogen content of chelating resin to calculate the percentage of functional group conversion,and the percentage of functional group conversion of MTZR,ATPR,DMTUR and METR were 94.80%,91.57%,96.94%and 73.08%,respectively.The FTIR and TGA results characterized the four chelating resins and assisted us to hypothesize their possible synthesis,possible structure,and thermal stability.(2)The adsorption properties of four chelating resins for six heavy metal ions were investigated.Static adsorption results showed that the saturated adsorption capacities of DMTUR for Hg(Ⅱ)was 347 mg/g at pH=4,and that of MTZR for Cd(Ⅱ)was 189 mg/g at pH=5.5.Kinetics adsorption process of DMTUR and MTZR followed pseudo-second-order kinetics,and isotherm adsorption followed Langmuir model,which suggested that chemical reaction kept control of the whole adsorption,and both of them were monolayer preferential adsorption.Thermodynamic functions indicated that the adsorption process of DMTUR for Hg(Ⅱ)and MTZR for Cd(Ⅱ)were endothermic and spontaneous chemisorption.4 mol/L HNO3 could eluted Hg(Ⅱ)from DMTUR completely,and 0.5 mol/L HCl with 2.5%thiourea mixture solution could eluted Cd(Ⅱ)from MTZR completely.The favorable regeneration performance and repetitive properties of DMTUR and MTZR was beneficial to save cost and increase efficiency.Dynamic adsorption process of DMTUR for Hg(Ⅱ)and MTZR for Cd(Ⅱ)were in agreement with Thomas model for the saturated adsorption capacities of 476.8 mg/g and 370.3 mg/g,respectively.SEM showed that there was much granular substance on the surface of DMTUR and MTZR after adsorption.The coordinated bond of nitrogen atom with chelating resins with heavy metal ions was probably the main reason for adsorption,which was deduced by FTIR.TGA results showed that the adsorption process that led to the thermal stability of DMTUR decreased,while that of MTZR increased.Besides,the adsorption and desorption of DMTUR and MTZR were apt to carried out under 125℃ and 175℃.(3)A novel technique for heavy metal from food was investigated based on chelating resin and UV.In this paper,heavy metals of Hg and Cd from seafood,rice and liquor were successfully detected with some advantages,such as excellent separation effect and anti-interference ability,low cost,and many more.DMTUR and MTZR were used to concentrate Hg(Ⅱ)and Cd(Ⅱ)ions under optimum conditions,respectively,and detected by UV and ICP.Results showed that the data of above detection methods were almost the same,which demonstrated that UV can applied in the detection of trace elements in food with low cost and high detection limit in our method.