Cleaning pH Sensors
Basic Steps
- Rinse electrode in clean water
- Clean by immersing the electrodes in a cleaning solution (see below).
- Rinse Again
- Check with buffers
Cleaning Solutions:
If you know a specific way to clean the sensors for your process use that method. Often Hot Water is sufficient. In many cases 5 - 10% Hydrochloric acid (HCl) in water will work for stubborn deposits. If you have trouble finding 5 - 10% HCL you can buy muriatic acid at a building supply house and it is usually 20 - 35% HCL. Check the label. Dilute it with tap water to get something close to 10%.
BE VERY CAREFUL WHEN DILUTING THE ACID. USE PROTECTIVE CLOTHING (GLOVES, FACE SHIELD ETC.) ALWAYS ADD ACID TO WATER, NEVER ADD WATER TO ACID (this can cause the water to boil and splash acid out of the container).
Cleaning Process:
First, rinse off the electrodes/sensor in just plain water. To remove any heavy process coating use a soft brush, taking care not to damage the electrodes. Greasy or sticky deposits may respond to a mild detergent, but limit the time the sensor is exposed to keep the detergent from penetrating the reference junction. Rinse well after using detergent.
Most process deposits will be removed if you immerse the electrodes in an acid cleaning solution for 5 - 10 minutes, agitating them regularly. Use a soft brush to clean off any remaining coating deposits. If the coating is extreme this could take longer.
Now rinse the electrodes thoroughly again with clean water to remove any detergent or acid that would contaminate the buffer solution used.
Dry and place the electrodes in a new clean pH buffer solution and allow it to stabilize. If the displayed value is within ±0.03 pH of the buffer value, the electrodes are clean and do not require calibration. Put the system back on line. If the value is outside the tolerance (± 0.03 pH), then a two point buffer calibration is required.