Preparation Of Novel Functional Chelating Fibers And Determination Of Hexavalent Chromium In Food

With the intensification of human material production activities,food pollution is becoming more and more serious,in which heavy metals is one of the most main pollutants.Therefore,we need to assess and detect the safety of heavy metals in food.The basic characteristics of detection of heavy metals in food:the large number of samples,the detection threshold is low,Therefore,the establishment of a low-cost,high sensitivity,easy operation of the detection method for the correct evaluation of the real level of heavy metals in food and protect human health is great significance.In this paper,the damage of common heavy metals in food and its detection-methods were introduced,and the application scope of various methods was discussed.On the other hand,the preparation of polyurethane fiber,the optimization of synthesis conditions and its chelating effect on heavy metal were introduced,and a new method for the simultaneous determination of heavy metals in foods by separation and enrichment column-spectrophotometry was established.In this paper,a novel functional chelate fiber was synthesized by the reaction of polyurethane fibers with the organic ligands,and the synthesis conditions were optimized by response surface methodology.The adsorption properties of the chelate fibers were studied.The chelating fiber with high specificity and adsorption ability to heavy metals was screened and combined with spectrophotometry for the analysis and detection of heavy metals in food.The main contents are as follows:1.Using citric acid grafted Polyurethane fibers(PU-CA)as substrate materials to modify chemically and grafting eight kinds of organic ligands containing different functional groups,we could screen out four chelating fiber AAPF?AHPF?AMIF and DAPF with high conversion rate according to the size of the conversion rate from 8 synthetic fibers.Using EA to explore further how the three factors of solvent varieties,synthetic temperature and molar ratio had influence on the AAPF?AHPF?AMIF and DAPF conversion rate,we could determine the optimal synthesis process.The conversion rate of chelating fiber AAPF?AHPF?AMIF and DAPF were respectively 68.71%,83.01%,71.63%,and 66.55%under the optimal conditions.Using FT-IR and SEM to analyze the synthetic route of chelating fibers,Using FT-IR to analyze the synthetic route of chelating fibers,we could reckon that PU-CA fibers can go on condensation reaction by carboxyl functional groups on its molecular structure and organic heterocyclic ligand which carries amino group.2.Chelating fiber adsorption capacity to six common heavy metal ions in food was studied,and the adsorption capacity of two chelating fiber AHPF and AMIF to Cr(VI)were further screened out,and the focus were adsorption and desorption processes.The experiments of Static adsorption and desorption showed that AHPF and AMIF possess a strong selective adsorption capacity to Cr(VI),and optimum adsorption pH were respectively 5.0 and 5.0,and adsorption capability were 196.2mg/g and 201.5mg/g.The experiments also indicated that 5%thiourea solution was able to completely desorbed chelating fiber AHPF which adsorbed Cr(VI),and 4%thiourea solution could completely desorb chelating fiber AMIF which adsorbed metal ions Cr(VI).The kinetic adsorption process and isothermal adsorption process of the two chelating fibers are in accordance with the second-order reaction kinetics model and the Langmuir model,respectively,indicating that the two fibers are adsorbed by the monolayer.Thermodynamics results show that the adsorption process of AHPF and AMIF fibers is spontaneous endothermic reaction.Adsorption kinetics and fiber re-use experiments fully demonstrated that the chelating fibers AHPF and AMIF have a faster adsorption rate and better regeneration ability.Adsorption of Cr(VI)on chelating fibers was confirmed by thermogravimetric analysis(TGA)and scanning electron microscopy(SEM).The thermogravimetric analysis also showed that the chelating fibers AMIF and AHPF had good thermal stability.3.A novel technique for heavy metal from food was investigated based on chelating fibers and UV.This method has the advantages of good separation effect,strong anti-interference ability and low cost.Firstly,AMIF were used to concentrate Cr(VI)ions under optimum conditions,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 limitinour method.