Precautions and Countermeasures during pH Meter Measurement
Before operation, first inspect the integrity of the electrode. Most electrodes currently supplied with acidometers (pH meters) are combination electrodes. Older acidometers still use glass electrodes and calomel electrodes. Since combination electrodes are widely used, the discussion below focuses mainly on combination electrodes.
Combination electrodes used in laboratories are mainly of two types: fully sealed and non-sealed. Fully sealed electrodes are relatively uncommon and mostly produced by foreign manufacturers. Before using a combination electrode, first check whether there are cracks or breakages on the glass bulb. If intact, calibrate it using two pH standard buffer solutions. If the positioning and slope adjustment buttons can be adjusted to the corresponding pH values, the electrode is generally considered usable; otherwise, activate the electrode following the instructions in the manual.
The activation procedure is as follows: soak the electrode in 4% hydrofluoric acid solution for about 3–5 seconds, take it out and rinse with distilled water. Then immerse it in 0.1 mol/L hydrochloric acid solution for several hours, rinse thoroughly with distilled water, and perform calibration. Use the buffer solution with a pH value of 6.86 (25°C) for positioning. After positioning, select any pH buffer solution for slope adjustment. If adjustment cannot be completed, replace the electrode.
For non-sealed combination electrodes, the internal filling solution (3 mol/L potassium chloride solution) must be checked. The liquid level shall be higher than 1/3 of the electrode. If not, add 3 mol/L potassium chloride solution. If the potassium chloride solution overflows from the small hole, drain the excess solution so that the liquid level is below the hole. Check for air bubbles in the solution. If bubbles exist, gently shake the electrode to fully expel the bubbles.
