Optimal electrode cleaning procedures are dependent upon the type and the thickness of the coating. The glass membrane should only in extreme cases be mechanically cleaned as abrasion can lead to permanent damage. Even wiping or drying the glass membrane can lead to faults in the measurement function. Hard coatings should be chemically removed.
A good advice is to clean the pH sensor regularly.
In most cases, rinsing the electrode after measurement with clean water is just enough.
If, after rinsing in water, your pH electrode still not works properly, you need to use a cleaning agent. The cleaning agent used basically depends on the type of contamination. For cleaning agents, check with your pH electrode supplier.
Your pH electrode can be cleaned with whatever chemical that can dissolve the coating, provided the chemical will not attack the electrode's materials of construction.
However, a good rule is to minimize the exposure of the pH sensor to the cleaning solution and only immerse the glass membrane or the glass membrane and the diaphragm.
Soak in 0.1M HCl for half an hour.
• Oil and grease
Warm water with some detergent solution is probably sufficient. An alternative is to rinse with an ethanol solution.
Soak in 1% pepsin and 0.1M HCl solution for about 1 hour.
For most pH electrodes a measuring solution containing sulfides will result in silver sulfide contamination of the diaphragm that is difficult to dissolve.
Soak in 0.1M Thiourea/HCl solution for 15 min to 1 hour or until the diaphragm is totally bleached.
Soak in 0.1M tetrasodium EDTA solution for 15 minutes. An alternative is to use commercial glass cleaning solution (not strongly acidic).
• Acid or alkaline deposits
Alkaline deposits can be removed with weak acid solutions (0.1 molar HCl) or vinegar. Acidic deposits can be removed with mild alkaline solutions (0.1 molar NaOH.)
Soak the glass membrane for a few minutes.
Keep the acid or alkaline solvent away from the liquid junction. If not, hydrogen ions (acid solvent) or hydroxide ions (alkaline solvent) will diffuse into the junction and causing the liquid junction potential and the pH reading to drift. It may take hours or days for the reading to stabilize.
After any of these electrode cleaning procedures, rinse thoroughly with water and soak the electrode in storage solution overnight. If the electrode is refillable, drain and refill the reference solution.
Always recalibrate the pH electrode after cleaning. If the electrode response is slow or the electrode does not calibrate correctly, you maybe need to restore the hydrated glass layer.
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