Cleaning pH Electrodes
Published with permission from Georg Fischer Signet LLC
pH electrodes should be cleaned on a regular basis and prior to calibration. The build-up of material on the electrode can cause incorrect readings, and shorten the electrode?s life.
Regardless of the cleaning schedule, the pH electrode should be cleaned and conditioned prior to each calibration. Failure to clean the electrode prior to calibration can result in an incorrect calibration, the incorrect determination of the health of the electrode, or an increase in frequency of calibration. The material coating the pH sensitive glass or the reference junction can cause offset in the measured values affecting the calibration and leading to incorrect or drifting calibrations.The frequency of cleaning is dependent on the application. Applications with high levels of oils, fats, grease or other contaminants may coat or clog the electrode and require daily cleaning. Applications that encourage biological growth on the electrode, such as aquaculture, may require weekly cleaning. Applications in clean water may require cleaning as part of the monthly maintenance of the electrode.
![]() | Prior to cleaning, examine the electrode for any signs of damage such as cracked glass or damaged reference junctions. If any physical damage is observed replace the electrode. |
Hard coatings on electrodes, such as scale, can be removed with a mild acid or base solution. If the application?s pH is greater than 7 pH, soak the pH electrode for 2 to 5 minutes in a dilute HCl solution (less than 5%). If the application?s pH is less than 7 pH, soak the electrode for 2 to 5 minutes in a dilute NaOH solution (less than 5%). After soaking the electrode in the solution rinse in DI water and then soak for 5 to 10 minutes in 4 pH buffer.
Soft coatings, oils, fats, grease, or organic materials can be cleaned with dish detergent. Make a solution of dish detergent and soak the probe for 5 to 10 minutes. For stubborn materials gently scrub the reference junction and glass with a soft toothbrush. For difficult organic fouling a 5 percent solution of bleach can be substituted for the dish detergent. After cleaning the electrode rinse with DI water and then soak for 5 to 10 minutes in 4 pH buffer.
The final step in each of the cleaning procedures is soaking the electrode in 4 pH buffer. This step rehydrates the pH sensitive glass. Failure to soak the electrode will cause the electrode to drift for a time after the cleaning procedure.
After cleaning reexamine the pH electrode for damage that may have been hidden from view. Replace any physically damaged electrodes.
By following a regular cleaning and maintenance schedule, calibrations and system readings will be more accurate and reliable, and the service life of the electrode can be increased.
