Chemically Modified Electrodes In The Research And Application Of Heavy Metal Ions Detection

In recent years, the local pollution incidents have been reported frequently, especially in the field of heavy metal pollution, which has caused the wide social attention. Therefore,before the monitoring and control of heavy metal pollution, it is of importance that heavy metal ionscan be determinated efficiently and fast. Because of the advantages of real-time and on-line detection, the method of electrochemical analysis has been used by researchers, but the key point is to research and develop a working electrode which is highly sensitive,non-toxic harmless, low cost and easy to be made. In this paper, it was mainly studied that the chemical-modified working electrode on the heavy metal ions in the water environment of anodic stripping voltammetry test. The main contents are as followed:（1） It was realized that the heavy metal ions(Pb²⁺、Cd²⁺、Cu²⁺) were determianted in water at the same time with the help of carbon paste electrode by the method of differential pulse stripping voltammetry. The results showed that, at the condition of p H=2, 0.1 mol/L KCl electrolyte solution, mass ratio of graphite and paraffin=2.12:1, scanning speed=100mv/s, and-1.0 V potential preliminary enrichment of heavy metal ions in the 480 s, the method were high sensitivity, selectivity and repeatability. When the conditions were optimized, carbon paste electrode as working electrode at the same time detection of Pb²⁺、Cd²⁺、Cu²⁺, linear range 150-400 μg/Land 100-300 μg/L respectively, which detection limit were 3.0525 μg/L and 6.2273 μg/L.The artificial samples wereused to determinate recovery rateof Pb²⁺, Cd²⁺and Cu²⁺, which were 97.387%, 97.103%, and 95.312%.（2） This chapter was prepared by hydrothermal synthesis method of nanometer hydroxyapatite（HAP）, then go to HAP modified carbon paste electrode in the preparation of the nanometer hydroxyapatite modified carbon paste electrode, and the differential pulse stripping voltammetry determination of Pb²⁺and Cd²⁺ heavy metal elements.In the condition of p H=3, 0.1 mol/L KCl electrolyte solution, the quality percentage of HAP/graphite powder=10%, to 1.0 V potential preliminary enrichment of heavy metal ions in the 300 s. This method has high sensitivity, selectivity and repeatability. When the conditions were optimized,it was realizedthat Pb²⁺ and Cd²⁺ was determinate separately and simultaneously. The separatedetermination linear range of Pb²⁺ and Cd²⁺were 10-350 μg/L and 5-400 μg/L, respectively.And determination limit of Pb²⁺ and Cd²⁺at the same timewas 1.0451 μg/L and 1.667 μg/L,linear range 10-500 μg/L and 10-420 μg/L, while determination limit was 1.3313 μg/L and1.612 μg/L. The artificial samples wereused to determinate the recovery rate of Pb²⁺ and Cd²⁺,which were 98.056%, and 98.003%.（3） The preparation of the nanometer hydroxyapatite and bismuth film modified carbon paste electrode, based on the differential pulse voltammetry for lead and cadmium test at the same time.The experimental results showed that bismuth film modified nano hydroxyapatite carbon paste electrodes on Pb²⁺ and Cd²⁺was of better adsorption ability. When conditions were optimized, in the solution of 200 μg/L Bi3+,it was realizedthat Pb²⁺ and Cd²⁺ was determinatedseparately and simultaneously by the bismuth film modified nano hydroxyapatite carbon paste electrode.The separate determination linear range of Pb²⁺ and Cd²⁺ was 20-280μg/L and 5-400 μg/L respectively, while the determination limit was 1.252 μg/L and 1.2445μg/L. And determinationrange of Pb²⁺ and Cd²⁺at the same timewas 5-250 μg/L and 30-350μg/L, and determination limit were 1.2582 μg/L and 1.2476 μg/L.The artificial samples wereused to determinate the recovery rate of Pb²⁺ and Cd²⁺, which was 99.4224% and97.8838%.（4） Carbon paste electrode modified by（Bi O）2CO₃ was prepared, which was made by the method of hydrothermal synthesis. Through electrochemical behavior characteristics analysis,it was found that（Bi O）2CO₃ could improve the determination sensitivity of heavy metal ions and by using cyclic voltammetry, heavy metal element Pb²⁺, Cd²⁺ and Cu²⁺ could be determinated. Through the optimized experimental conditions, such as scanning speed and the carbon powder mixed with（Bi O）2CO₃ content, the heavy metal ions(Pb²⁺, Cd²⁺ and Cu²⁺)in water were determinated. And the experimental results showed that（Bi O）2CO₃ modified carbon paste electrode by cyclic voltammetry test could improve the response to metal ions detection sensitivity.Under optimized conditions, the scanning speed was 100 mv/s, with the quality ratio of（Bi O）2CO₃ to the graphite was 0.5%. Anddetermination concentration range of Cu²⁺, Pb²⁺ and Cd²⁺ was 100-1000 μg/L, 200-5000 μg/L, and 200-5000 μg/L, while determiantion limit was 0.1048 mg/L, 0.269 mg/L, and 0.498 mg/L.Parallel determination could get the good reproducibility, but there were some interference.