Calibration of glass electrode half-cells
Agnes Heering, Ivo Leito
Abstract
The purpose of this document is give glass-electrode calibration procedure with aqueous buffers.
Before start
Turn on the thermostat and electrometer at least half an hour before starting the work.
Steps
Software
Start Quick IV Measurement Software.
On the left hand pick Function “Source & Sampling”.
Right hand side click on tab “Channel Communication”. Click on “Search Channels”, which opens a new window. Select USB interface and search for the channel. After the search click on the channel and close the window.
Settings can be saved as QIVM file, which can be used for measurements. The saved file can be opened under tab “File”. The settings will remain the same between the measurements if the program is not closed.
Filling the cell
25.0°C
Equipment
| Value | Label |
|---|---|
| VistaShield | NAME |
| Faraday cage | TYPE |
| Gamry | BRAND |
| VistaShield | SKU |
| https://www.gamry.com/ | LINK |
Fill capillary with standard aqueous buffer with pH 7.00.50mL
Insert glass electrode and a reference electrode.
Equipment
| Value | Label |
|---|---|
| K401 | NAME |
| Calomel reference electrode | TYPE |
| Radiometer | BRAND |
| K401 | SKU |
Electrode is rinsed with water, gently dried, and then rinsed with solution to be measured.
Connect electrodes to the instrument.
Equipment
| Value | Label |
|---|---|
| B2987A Electrometer / High Resistance Meter | NAME |
| Electrometer | TYPE |
| Keysight | BRAND |
| B2987A | SKU |
Crocodile clips are as following:
red is signal and connects to the glass electrode,
black is shield and is connected to reference electrode and
green is guard. Green stays unused.
Equipment
| Value | Label |
|---|---|
| N1415A Triax to Alligator Cable | NAME |
| Cable | TYPE |
| Keysight Technologies | BRAND |
| N1415A | SKU |
Measurement
Start the measurement by clicking on the "Measure" button on the upper panel.
Data collection. Point is taken at 10 s interval.
Save data. Files are named as Date_GE_vs_ref_pHx.
Go to table view, right click on the table, choose “Export as CSV…” and save the results. The data can be automatically imported into excel file while measuring or after (both under “Excel Navigation”), but this causes constant shift in the comma position.
Washing
Remove the electrodes.
Remove the solution.
Rinse three times with plenty of water20mL
Rinse once with acetone to ease the drying. 2mL
Dry cell with compressed air.
Repeat measurements with standard buffers pH 4 and pH 10.
Data analysis
Points from 30 min to 60 min are used for analysis.
Take the average of the chosen data points.
Plot Δ E vs pH.
Obtain the slope and intercept of the glass electrode-half cell.
