The pH sensor should be cleaned if fouling reduces response time and prior to any calibration. Cleaning with sharp objects or abrasive material should be avoided due to the potential for damage. Basic guidelines for cleaning sensors are listed below:
Process-related cleaning procedures
pH fouling in basic processes
Consider cleaning the sensor with a strong acid such as 4% HCl. Submerge the tip of the sensor in the solution for 5 to 10 minutes to dissolve or loosen and build-up on the pH sensitive membrane glass. Rinse the sensor with potable water then submerge in storage solution for another 10 minutes prior to using the sensor.
pH fouling in acidic processes
A strong base solution such as 4% NaOH should be used to clean coatings that occur in acidic processes. Soak the sensor for 5 to 10 minutes in the solution. Rinse the pH sensor with potable water then submerge in storage solution for another 10 minutes to allow the pH sensor to recover prior to use.
pH fouling due to proteins
Proteins are well known to coat the pH sensitive glass and diaphragm. Submerge the sensor in 0.4% HCl with 5 g/L pepsin for several hours to remove the proteins. Rinse with potable water and submerge in storage solution for a final 10 minutes prior to usage.
Fats and Oils
These types of coatings can often be removed using isopropyl alchohol, detergent, or acetone. Gently wipe the sensor tip with a clean cotton cloth soaked in these solvents. Clean off any residual solvent with potable water and let the sensor soak in storage solution for 10 minutes prior to usage.
ORP sensor cleaning
The platinum metal band around the tip of the ORP electrode can oxidize over time. When this occurs the platinum will appear grey with no metallic shine. Light scrubbing with a mild abrasive such as toothpaste will remove the oxidization. Rinse with potable water and store in storage solution prior to usage.
Hamilton cleaning solution set (Ref 238290) includes both acidic and basic cleaning solutions as well as storage solution
After cleaning it is important that the sensor tip remain wetted. Sensors should be stored in the original watering cap supplied with the sensor. The liquid in the cap is a 3M KCl solution which can be purchased from Hamilton (Ref 238931)