Sep 24, 2021
Calibration of glass electrode half-cells
- Agnes Heering1,
- Ivo Leito1,
- Markus Lahe1,
- Martin Vilbaste1
- 1University of Tartu
External link: https://analytical.chem.ut.ee/, uniphied.eu
Protocol Citation: Agnes Heering, Ivo Leito, Markus Lahe, Martin Vilbaste 2021. Calibration of glass electrode half-cells. protocols.io https://dx.doi.org/10.17504/protocols.io.byh2pt8e
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it’s working
Created: September 24, 2021
Last Modified: September 24, 2021
Protocol Integer ID: 53530
Keywords: glass electrodes, unified acidity, pHabs, calibration, unified pH
Funders Acknowledgements:
EMPIR
Grant ID: 17FUN09
Estonian Research Council
Grant ID: PRG690
Abstract
The purpose of this document is give glass-electrode half-cell calibration procedure with aqueous buffers.
Before start
Turn on the thermostat and electrometer at least half an hour before starting the work.
Software
Software
Start Quick IV Measurement Software.
Note
Computer cannot go to sleep during measurements or the communication between computer and instruments is lost and data collection stops.
On the left hand pick Function “Source & Sampling”.
Position of the Function choice “Source & Sampling”.
Note
Alternatively, open previously saved QIVM file with measurement settings.
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 name to choose the channel and close the window.
Position of the tabs “Channel Communication” and “Search Channels”.
Note
This must be done every time the program is started.
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.
Program settings.
Note
Range is "Fixed 20V" in case of EST-0601 calibration, otherwise it is "Fixed 2V".
Filling the cell
Filling the cell
8m
8m
Special water-jacketed glass cell from Gebr. Rettberg.
25 °C
Equipment
UT cell
NAME
Special water-jacketed glass cell
TYPE
Rettberg
BRAND
Glass cell
SKU
Equipment
VistaShield
NAME
Faraday cage
TYPE
Gamry
BRAND
VistaShield
SKU
Equipment
U2c
NAME
Thermostat
TYPE
MLW
BRAND
U2c
SKU
Note
The side ports must be open.
Note
A beaker can also be used if temperature is controlled.
Fill capillary with standard aqueous buffer with pH 7.00.50 mL
2m
Insert a glass electrode and a reference electrode.
Equipment
K401
NAME
Calomel reference electrode
TYPE
Radiometer
BRAND
K401
SKU
2m
Electrode is rinsed with water, gently dried, and then rinsed with solution to be measured.
2m
Connect electrodes to the instrument.
Equipment
B2987A Electrometer / High Resistance Meter
NAME
Electrometer
TYPE
Keysight
BRAND
B2987A
SKU
LINK
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.
Note
Cable goes through the port in Faraday cage. Electrometer is not in the Faraday cage.
Equipment
N1415A Triax to Alligator Cable
NAME
Cable
TYPE
Keysight Technologies
BRAND
N1415A
SKU
LINK
Measurement
Measurement
1h
1h
Start the measurement by clicking on the "Measure" button on the upper panel.
Data collection. Point is taken at 10 s interval.
Note
Calibration duration must be the same as later used in pH measurements.
1h
Save data. Files are named as Date_GE_vs_ref_pHx.
Note
SAVE THE FILE BEFORE NEW MEASUREMENT! Otherwise, data is lost. Data is given in volts and seconds.
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
Washing
Remove the electrodes.
Remove the solution.
Rinse three times with plenty of water20 mL each
Rinse once with acetone to ease the drying. 5 mL
Dry cell with compressed air.
Measurement
Measurement
Repeat measurements with standard buffers pH 4 and pH 10.
Data analysis
Data analysis
Points from 30 min to 60 min are used for analysis.
Take the average of the chosen data points.
Plot ΔE vs pH.
Calibration graph of a glass electrode half-cell.
Obtain the slope and intercept of the glass electrode-half cell.