Determination Of Copper In Aqueous By Anodic Stripping Voltammetry

With the rapid development of industry, the heavy metal pollution has become one of themost serious environmental problems. The heavy metals are not biodegradable and tend toaccumulate in living organisms resulting in heavy metal poisoning. Therefore, thedetermination of heavy metal is particularly important. The traditional methods of detectionheavy metal include atomic absorption spectrometry, atomic emission spectrometry,inductively coupled plasma mass spectrometry and so on. However, most of these methodsneed not only expensive equipments but also time-consuming pretreatments. And a few ofthem need the operator to be professional. Electrochemical analysis based on anodic strippingvoltammetry （ASV） is a proper method for the trace analysis of heavy metals. ASV measurementis based on relatively cheap and portable equipment. ASV measurement also allows to monitorlow concentration of metals by electrochemical accumulation of the metal on the electrode surface.The working electrode plays an important role in the voltammetric analysis. In this thesis,different working electrodes were used to detect copper ion by differential pulse anodicstripping voltammetry with high sensitivity.1. Determination of trace copper by anodic stripping voltammetry atnano-TiO₂/Nafion modified gold electrodeA nano-TiO₂/Nafion modified gold electrode was developed to detect copper utilizingthe properties of nano-TiO₂. The electrochemical behavior of Cu²⁺at the nano-TiO₂/Nafionmodified gold electrode was studied by differential pulse stripping voltammetry. Theexperimental parameters such as the amount of nano-TiO₂/Nafion suspension, the pH value ofthe supporting electrolyte, the accumulation potential and the accumulation time wereoptimized. The results indicated that a remarkable anodic peak appeared at 0.25 V whenaccumulating for 240 s at -0.50 V in HNO₃（pH =2.0） solution with stirring. Compared to thebare gold electrode, the peak current enhanced greatly indicating the strong preconcentrationof Cu²⁺at the nano-TiO₂/Nafion composite film. Under the optimized working conditions, thestripping peak currents were linear with concentrations of Cu²⁺over the range from 0.010 to0.90μmol/L. The detection limit was 3.2 nmol/L. The electrode possesses some anti-interference abilities for the determination of Cu²⁺. The proposed electrode was applied to thedetermination of Cu²⁺in the National Standard Substance and tap water samples withsatisfactory results. 2. Determination of trace copper in water samples by differential pulseanodic stripping voltammetry at gold microelectrodeThe applicability of gold microelectrode of 25μm diameter for electrochemicaldetermination of trace copper ion (Cu²⁺) in water samples by anodic stripping voltammetry（ASV） has been demonstrated. The analysis of Cu²⁺at gold microelectrode includes two steps.Cu²⁺ions are firstly reduced and accumulated on the microelectrode surface during anaccumulation step, then oxidized during the positive potential sweep. The experimentalparameters such as the pH value of the supporting electrolyte, the accumulation potential andthe accumulation time were optimized. The results indicated that a remarkable anodic peakappeared at 0.28 V when accumulating for 210 s at -0.40 V in HNO₃（pH =2.0） solution. Dueto the rapid mass transporting and low background current of gold microelectrode, lowdetection limit （0.30 nmol/L） and wide linear range （1.0⁹0 nmol/L） can be obtained. Thepractical application of gold microelectrode was verified by determination of trace level ofCu²⁺in tap water, lake water and commercial drinking water samples.3. Determination of trace copper in aqueous by anodic strippingvoltammetric at rotating-disk gold electrodeA home made rotating-disk gold electrode was used to detect copper in aqueous byanodic stripping voltammetry （ASV）. Compared to conventional electrode, rotating-diskelectrode has many advantages such as analysis without stirring and fast mass transport. Theexperimental parameters such as the accumulation potential and the accumulation time wereoptimized. After accumulating at -0.30 V for 40 s, a remarkable anodic peak appeared at 0.35V in HNO₃（pH =2.0） solution. The result demonstrated that the rotating-disk gold electrodereached a low limit detection （0.10 pmol/L） of copper. And the linear concentration was from10 pmol/L to 90 pmol/L. This method has great develop potential in trace metal analysis.4. Monitor adsorption of polyvinyl alcohol on quartz surface bypiezoelectric sensorThe adsorption process of polyvinyl alcohol on quartz surface was monitored in real timeby a piezoelectric sensor. It was shown that the adsorption kinetics followed thepseudo-first-order kinetic model and the adsorption isotherm obeyed the Langmuir isothermmodel. With increasing pH, the adsorption equilibrium constant and saturation amountadsorbed were decreased.