IC. CONTROLS. Concerns in pH # 4: Reference Contamination. PROBLEM. pH electrodes have porous reference junctions which allows KCl to migrate through the junction to complete the electrochemical connection and cause a mV signal to be produced.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Concerns in pH # 4:
pH electrodes have porous reference junctions which
allows KCl to migrate through the junction to
complete the electrochemical connection and
cause a mV signal to be produced.
Since the junction is porous the process can also
migrate into the reference causing reference
contamination and premature failure of the pH
As the process migrates into the reference it attacks the
Silver/Silver Chloride wire changing the chemistry
which results in the electrode drifting. This is seen as an
offset from zero mV during calibration.
Potassium Chloride (KCl)
Internal Fill Solution
Solid Spool Piece
With no protection in the reference the KCl and Silver/Silver Chloride wire becomes contaminated very quickly.
By adding the Double Junction, the path length is increased and the rate of contamination is decreased.
By adding the Plasticized Reference, which is solid up to 150oC, the migration is slower because it will take longer to migrate through a solid in comparison to a liquid.
and Plasticized Internal
By combining the Double Junction and the plasticized Reference, the path length is increased and the rate of contamination is decreased which will give maximum life in applications where reference contamination is a problem. Life expectancy can be months longer when this combination is used.
Longer Path Length
Solid up to 150oC
Longer Sensor Life