TITLE: Calibration of glass electrode half-cells
AUTHORS: Agnes Heering, Ivo Leito, Markus Lahe, Martin Vilbaste

[DESCRIPTION]
<div class = "text-blocks"><div class = "text-block">The purpose of this document is give glass-electrode half-cell calibration procedure with aqueous buffers.</div></div>

[STEPS]
?. [Software]
Start Quick IV Measurement Software.
Computer cannot go to sleep during measurements or the communication between computer and instruments is lost and data collection stops.
?. [Software]
On the left hand pick Function “Source & Sampling”.
Alternatively, open previously saved QIVM file with measurement settings.
?. [Software]
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.
This must be done every time the program is started.
?. [Software]
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.
Range is "Fixed 20V" in case of EST-0601 calibration, otherwise it is "Fixed 2V".
?. [Filling the cell]
25 °C
The side ports must be open.
A beaker can also be used if temperature is controlled.
?. [Filling the cell]
Fill capillary with standard aqueous buffer with pH 7.00.
50 mL
?. [Filling the cell]
Insert a glass electrode and a reference electrode.
?. [Filling the cell]
Electrode is rinsed with water, gently dried, and then rinsed with solution to be measured.
?. [Filling the cell]
Connect electrodes to the instrument.
?. [Filling the cell]
Crocodile clips are as following:red is signal and connects to the glass electrode,black is shield and is connected to reference electrode andgreen is guard. Green stays unused.
Cable goes through the port in Faraday cage. Electrometer is not in the Faraday cage.
?. [Measurement]
Start the measurement by clicking on the "Measure" button on the upper panel.
?. [Measurement]
Data collection. Point is taken at 10 s interval.
Calibration duration must be the same as later used in pH measurements.
?. [Measurement]
Save data. Files are named as Date_GE_vs_ref_pHx.
SAVE THE FILE BEFORE NEW MEASUREMENT! Otherwise, data is lost. Data is given in volts and seconds.
?. [Measurement]
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.
?. [Washing]
Remove the solution.
?. [Washing]
Rinse three times with plenty of water
[each]
?. [Washing]
Rinse once with acetone to ease the drying.
5 mL
?. [Washing]
Dry cell with compressed air.
?. [Measurement]
Repeat measurements with standard buffers pH 4 and pH 10.
?. [Data analysis]
Points from 30 min to 60 min are used for analysis.
?. [Data analysis]
Take the average of the chosen data points.
?. [Data analysis]
Plot ΔE vs pH.
?. [Data analysis]
Obtain the slope and intercept of the glass electrode-half cell.