When maintaining a pH probe, which solution should be checked for proper level and condition?

• A. Electrolyte
• B. Calibration solution
• C. Reference solution
• D. Deionized water

Answer: (A)

Maintaining the pH probe hinges on keeping the reference system properly supplied with its electrolyte. The reference electrode contains an electrolyte solution (typically KCl) that provides the conductive path and a stable reference potential. If this electrolyte is low or becomes contaminated, the reference potential can drift and the readings will wander. So, when you check the probe, you inspect the electrolyte level and its condition—look for the correct level, clear solution without crystallization or cloudiness. Refill with the same electrolyte up to the recommended mark. Do not top up with deionized water, as diluting the electrolyte destabilizes the reference. Calibration solutions have their own role, used for calibration, not for maintaining the electrolyte level.