Visually check electrode for cracks or other abnormalities. A cracked or damaged electrode should be
2. Visually check electrode for low filling solution or excess KCI crystals. Filling solution should be at least
2/3 full, bulb and filling hole should be free of excess KCI crystals.
If no defects are seen, go to next step.
Clean the electrode to eliminate a clogged reference junction.
Immerse the tip of the electrode into concentrated NH40H for 10 15 minutes.
NH40H is very caustic and should be used in a hood.
Rinse the electrode.
Soak in pH 4.0 buffer for 10-15 minutes.
If cleaning does not result in improved performance, the meter could be at fault. Go to Section 9.1-c.
Symptom pH readings are unstable, slow, erratic, or drift.
a. Check the sample.
A changing sample temperature Allow sufficient time for a sample temperature to stabilize.
Vigorous stirring on an uninsulated stirring motor can lead to small but significant sample temperature
A non-uniform sample pH "zones" which result in erratic or drifting readings can be eliminated by gentle
stirring using an insulated stirring motor.
A very low or very high ionic strength sample These readings can take a long time to stabilize.
A sample that is incompatible with the pH electrode When measuring pH of special solutions such as HF,
strong oxidizing solutions, or solutions that contain elements that can poison an electrode be certain that you
are using the correct electrode. If you have questions, your electrode supplier can usually help.
b. Check electrode for physical defects. (See Section 9.2-c).
c. Clean the electrode. (See Section 9.2-d).