Acation Of Electrochemical Coprecipitation In Separation And Determination Of Trace Amounts Of Heavy Metals

Electrochemical coprecipitation is a combination of the coprecipitated separationmethod and electrochemical analysis. Coprecipitation separation, enrichment andanalytical determination were carried through simultaneously. The method ofelectrochemical coprecipitation modified with nanotechnology has become anextremely important direction of applied research in the analysis and detection of traceheavy metal ions. It has important significance of fundamental research and a widerange of applications. In this paper, the superiority of the nanomaterials and thecomplexation and coprecipitation carrier of organic ligands on the metal ions werecombined. The electrode was prepared with ion-association complex, chelate or aninert precipitant by self-assembly, electrochemical deposition or drop coating method,with the helping of modification and doping of nanomaterials. Separation,preconcentration and determination for heavy metal ions were achieved. The mainworks are summarized as follows:1. Modification of ion-association complex coprecipitation carrierCV⁺I-/MWCNTs/GCE was prepared by nanomaterials self-assembledmonolayers with the helping of electrostatic adsorption. CV⁺and I-formed ionassociation complex （CV⁺I^-）, which was modified on the surface of the electrode as acarrier. What’s more, excess I-was adsorbed on the surface of theCV⁺I-/MWCNTs/GCE because of the residual field. Then, Hg²⁺and I-formed HgI₄^2-,CV⁺was organic coprecipitator and it formed HgI₄^2-·2CV⁺with HgI4^2-by electrostaticadsorption. Last, the HgI₄^2-·2CV⁺was induced adsorbed by the carrier CV⁺I-on thesurface of modified electrode by the principle of organic co-precipitation.Simultaneously the trace mercury was detected on the CV⁺I-/MWCNTs/GCE. Underthe optimum conditions, The CV⁺I^-/MWCNTs modified electrode has a low detection limit of0.1nM, wide linear range of0.005to1.9μM, good stability andreproducibility, high sensitivity and excellent selectivity. Satisfyingly, theCV⁺I-/MWCNTs/GCE could effectively avoid the interferences from other heavymetal ions that might also form complexes with I-.2. Modification of metal chelate coprecipitation carrier2.1Co-poly （cupferron and β-naphthol）/GNPs/GCECupferron is an important chelating agent because of its unique structure whichcontains electron donor atoms such as oxygen atom. It has adsorption andelectrochemical activity. β-naphthol can be used as an inert coprecipitation carrier incoprecipitative preconcentration and separation of trace copper ion. In this paper,based on nano-doping technology, the co-poly （cupferron and β-naphthol） waselectrochemically deposited on the prepared gold nanoparticles/GCE by CV scanningin order to obtain co-poly （cupferron and β-naphthol）/gold nanoparticles/GCE. Theelectrochemical behavior of copper ion at the modified electrode was studied and anew method was proposed for the detection of copper ion. It is thatpreconcentration-separation and electrochemical detection of trace copper aresimultaneously and synchronously carried through. First, the chelating ligandcupferron on the surface of the modified electrode and copper ion in the solution formthe chelate complex （Cu（Ⅱ）-Cpf）. At the same time, the Cu（Ⅱ）-Cpf was induced tobe adsorbed by the carrier β-naphthol on the surface of modified electrode by theprinciple of organic co-precipitation, in order to achieve the separation andenrichment of trace copper. Thus, the Cu²⁺of the coprecipitated complexation can bedetected at the co-poly （cupferron and β-naphthol）/GNPs/GCE. After optimization,two linear responses were obtained in the concentration range from9.0×10^-10to5.0×10^-8M and5.0×10^-8to1.5×10^-6M, with a correlation coefficient of0.9865,0.9948, respectively and with a low detection limit of5.0×1011M （S/N=3）. Thismodified GCE does not present any significant interference from Cd²⁺（100）, Ag⁺（500）,Fe³⁺（200）, Pb²⁺（100）, Cr³⁺（100）, Zn²⁺（500）, NO₃^-（500）, Cl^-（500）, SO₄^2-（500） andEDTA（500）.2.2CPf/MWCNTs/GCE CPf/MWCNTs/GCE was prepared by casting method, and the morphologicalcharacterization of CPf/MWCNTs flims were examined by scanning electronmicroscopy （SEM）. Electrochemical behavior of trace molybdenum ion was studiedat the modified electrode based on complexation, adsorption and electro-catalyticactivity of the organic ligand cupferron. Under the optimum conditions, theexperiments of DPV showed that the oxidation current of molybdenum ion versus itsconcentration had good linearity in the range of5.0×10^-11–1.6×10^-8M with acorrelation coefficient of0.9969and1.6×10^-8–1.42×10^-6M with a correlationcoefficient of0.9978. The limit detection was found to be1.6×10^-11M （S/N=3）.Satisfyingly, the CPf/MWCNTs/GCE could effectively avoid the interferences fromother heavy metal ion and organic ligand. The experiment result showed that the CPf/MWCNTs modified electrode shows high selectivity, sensitivity and stability for tracemolybdenum ion.