Study On Analysis Of Lead Iron With Preconcentration And Stripping Of Electrodeposition

As the preconcentration of lead in food and its harm to human, it is significant to determine lead in food and in environment, as well as to find a sensitive and accurative analysis method on trace amounts of lead and a technique for the removal of lead in food. The main purpose of the paper is to study the mechanism of preconcentration and stripping of electrodeposition of lead on the platinum electrode. On this basis, this paper explores experimental parameter of lead analyzed with anodic stripping voltammetry.Firstly, cyclic voltammetry is used to the electrochemical behavior of lead iron on the platinum electrode. The scanning begins from positive Pb²⁺/Pb electrode potential to the increasing negative direction. When it reaches -0.5V, there appears an apparent reduction peak. The scanning continues to -0.8V and then turns back. When it reaches -0.47V, a crossed loop of current appears. This indicates that lead has a behavior of crystallization nucleation during the process of electrodeposition on the platinum electrode. The scanning of positive direction reaches an apparent oxidation peak at -0.46V, meanwhile the lead deposited on platinum electrode begins to strip with a anodic peek at -0.12V. To know more about the electrodeposition behavior of lead, another scanning begins from 0.2V to -0.55V,-0.6V,-0.8V,and turns back at these points respectively. Therefore different cyclic voltammetry curves, which in turns indicate that crystal nucleus formed and the behaviors of the diffusion-controlled step, the secondary nucleation and growing up happened. Then the scanning begins from 0.10V to -0.8V at different speeds which are from 2mV/s～50mV/s. The results show the current of cathodic reduction peak of lead increases regularly as the scanning speed increases, that is to say, increases with the increase of the extraction of the speed. However, there is no apparent linear relationship between them. And this indicates the electrodeposition process of lead is quasi_reversible within the potential range of the cathodic peak. Also, linearity scanning anodic stripping voltammetry is applied to study the efficiency of the electrodeposition of lead on the platinum electrode. Although different potentials correspond to different efficiencies of the electrodepositions, the efficiencies of the electrodepositions are far less than 100%。This is because crystallizing needs certain overpotential, the lower potential of electrodeposition influences the rate of nucleation. The competing reaction of the released hydron is the other factor which results the reduction of the efficiency of the electrodeposition. This paper explores the choices of experimental conditions in anodic stripping voltammetry. Experiments show that when 10mmol/LKNO₃ solution with pH=3 is chosen to be the supporting electrolyte, the stripping peak is fine and the peak current is high. The deposition efficiency and the peak current climax when the preconcentration protential is -0.6V. Square wave voltammetry favors the reduction of detection limit of the analysis. Results from orthogonal experiment for choosing square wave parameter show a better can be got when amplitude is 0.025V,frequency is 15Hz,increment is 0.004V.experiments show proper stirring velocity favors getting the biggest peak current. Both the alcohol and 2-propanol affect the peak current. With the rising of their concentration, the peak current decreases, while the influence of alcohol grows. Lastly, standard curves with different concentration are got from the experiments.