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Concerns in pH # 4: Reference Contamination

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.

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Concerns in pH # 4: Reference Contamination

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  1. IC CONTROLS Concerns in pH # 4: Reference Contamination

  2. 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. Since the junction is porous the process can also migrate into the reference causing reference contamination and premature failure of the pH electrode

  3. CAUSE 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.

  4. Typical pH Electrode Internal Silver/Silver Chloride Wire Potassium Chloride (KCl) Internal Fill Solution Porous Frit Solid Spool Piece Porous Reference Junction

  5. Contamination with Standard Internal With no protection in the reference the KCl and Silver/Silver Chloride wire becomes contaminated very quickly. Process

  6. Contamination with Double Junction Internal By adding the Double Junction, the path length is increased and the rate of contamination is decreased. Process

  7. Contamination with Plasticized Internal 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. Process

  8. Contamination with Double Junction 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. Process

  9. IC Controls Plasticized, Double Junction Reference Longer Path Length Slower Migration Solid up to 150oC Longer Sensor Life Proven Technology Superior Design Better Results

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