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Cd2+ detection in water by voltammetry stripping method
Source：Corrtest
Time：2021-12-22
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Cd2+ detection in water by voltammetry stripping method
Principle
Stripping voltammetry includes two processes- electrolytic deposition and electrolytic stripping.
In electrolytic deposition process, the working electrode (eg. glassy carbon electrode) is fixed at a relatively negative potential. Under solution stirring, reduction reaction occurs for metal ions at the limit current. The tested metal ions are deposited on the electrode.
After a period of Quiet time, the reverse stripping process is started. A positive potential is applied on the working electrode to create anode stripping and form a corresponding anodic current peak. Qualitative and quantitative analysis of metal ions can be performed according to the potential and peak current during stripping.
Process
1. Instrument and solution
CS350 potentiostat
Glassy carbon working electrode
Ag/AgCl reference electrode
Pt wire counter electrode
Cell: beaker
Magnetic stirrer; Cadmium standard solution 1mg/L; pH=5.0, 0.2M acetate buffer.
All reagents are of analytical grade or above, and the experimental water is ultrapure water.
2. Procedures
2.1 To polish the glassy carbon electrode on the polishing cloth with 0.3mm and then 0.05mm Alpha alumina powder. Clean it with absolute alcohol and finally with ultrapure water(15min).
2.2 Standard curve testing
- Preparation of the Cd2+ solution(eg:100mg/L)：Into the 100ml measuring cylinder, please add 25ml pH=5.0, 0.2M acetate buffer, and 10ml 1mg/L Cadmium standard solution, dilute it with ultrapure water to get 100ml solution. This is 100mg/L Cd2+ solution. Use the similar method to get 5~90mg/L Cd2+ solution.
- Take 50ml 100mg/L Cd2+ solution into the beaker with a pipette. Set up the three electrodes. Connect the cell system with the CS350 potentiostat.
Choose “Differential Pulse Voltammetry Stripping”. Set parameters as follows:
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- Click OK and start the magnetic stirring. Fix the stirring rate and ensure there is no contact of stir bar to the electrodes. When deposition period reaches 30s, shut down the stirrer immediately. After 15s of quiet time, it goes to stripping period. The anode stripping peak of Cd2+ can be observed.
.png)
Similarly, test the anode stripping curves for 5mg/L, 10mg/L, …90mg/L Cd2+ anode stripping.
2.3 Testing of solution of unknown Cd2+ concentration
Use a pipette to take 50ml of the Cd2+ solution whose concentrations is to be measured and put it into the electrolytic cell. Insert the electrodes, connect the system with the CS350 potentiostat. Follow the steps and parameter setting as 2.2.2 ~ 2.2.3. Obtain the anodic stripping curve of the solution.
Firstly plot the original voltammetry stripping curve, then plot the peak current vs. concentration curve. See below picture.
.png)
From (a) it can be seen that the peak current fluctuated with the increasing concentrations of Cd2+. Apparent shift occurred for peak current when the concentration was 90mg/L,100mg/L. Obtain the current value at -780mV for each curve, and regard it to be the peak current. Then we fit the peak current vs. concentration in Origin to get a line and its standard expression: Current = slope * concentration + intercept. The slope and intercept value can be obtained by Origin fitting.
3.2 Determination of Cd2+ concentration
Based on the anodic stripping curve in 2.3, take the current value at -780mV, and according to the standard curve expression in 3.1 we can obtain the concentration of Cd2+ solution.
Principle
Stripping voltammetry includes two processes- electrolytic deposition and electrolytic stripping.
In electrolytic deposition process, the working electrode (eg. glassy carbon electrode) is fixed at a relatively negative potential. Under solution stirring, reduction reaction occurs for metal ions at the limit current. The tested metal ions are deposited on the electrode.
After a period of Quiet time, the reverse stripping process is started. A positive potential is applied on the working electrode to create anode stripping and form a corresponding anodic current peak. Qualitative and quantitative analysis of metal ions can be performed according to the potential and peak current during stripping.
Process
1. Instrument and solution
CS350 potentiostat
Glassy carbon working electrode
Ag/AgCl reference electrode
Pt wire counter electrode
Cell: beaker
Magnetic stirrer; Cadmium standard solution 1mg/L; pH=5.0, 0.2M acetate buffer.
All reagents are of analytical grade or above, and the experimental water is ultrapure water.
2. Procedures
2.1 To polish the glassy carbon electrode on the polishing cloth with 0.3mm and then 0.05mm Alpha alumina powder. Clean it with absolute alcohol and finally with ultrapure water(15min).
2.2 Standard curve testing
- Preparation of the Cd2+ solution(eg:100mg/L)：Into the 100ml measuring cylinder, please add 25ml pH=5.0, 0.2M acetate buffer, and 10ml 1mg/L Cadmium standard solution, dilute it with ultrapure water to get 100ml solution. This is 100mg/L Cd2+ solution. Use the similar method to get 5~90mg/L Cd2+ solution.
- Take 50ml 100mg/L Cd2+ solution into the beaker with a pipette. Set up the three electrodes. Connect the cell system with the CS350 potentiostat.
Choose “Differential Pulse Voltammetry Stripping”. Set parameters as follows:
- Click OK and start the magnetic stirring. Fix the stirring rate and ensure there is no contact of stir bar to the electrodes. When deposition period reaches 30s, shut down the stirrer immediately. After 15s of quiet time, it goes to stripping period. The anode stripping peak of Cd2+ can be observed.
Similarly, test the anode stripping curves for 5mg/L, 10mg/L, …90mg/L Cd2+ anode stripping.
2.3 Testing of solution of unknown Cd2+ concentration
Use a pipette to take 50ml of the Cd2+ solution whose concentrations is to be measured and put it into the electrolytic cell. Insert the electrodes, connect the system with the CS350 potentiostat. Follow the steps and parameter setting as 2.2.2 ~ 2.2.3. Obtain the anodic stripping curve of the solution.
3.Results
3.1 Standard curves plotting
Firstly plot the original voltammetry stripping curve, then plot the peak current vs. concentration curve. See below picture.
Voltammetry stripping curves(a) Linear curve of concentration vs. peak current(b)
From (a) it can be seen that the peak current fluctuated with the increasing concentrations of Cd2+. Apparent shift occurred for peak current when the concentration was 90mg/L,100mg/L. Obtain the current value at -780mV for each curve, and regard it to be the peak current. Then we fit the peak current vs. concentration in Origin to get a line and its standard expression: Current = slope * concentration + intercept. The slope and intercept value can be obtained by Origin fitting.
3.2 Determination of Cd2+ concentration
Based on the anodic stripping curve in 2.3, take the current value at -780mV, and according to the standard curve expression in 3.1 we can obtain the concentration of Cd2+ solution.
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