Steps and methods for calibrating a pH meter
1. pH meter used in laboratory | Acidity meter calibration:
When calibrating a commonly used laboratory pH meter, the slope of the instrument should be adjusted to the maximum, and the rubber plug on the upper part of the electrode should be removed to expose the small hole. Otherwise, negative pressure will be generated during calibration, causing the solution to not proceed normally. Ion exchange will cause inaccurate measurement data.
Take the electrode out of the beaker containing distilled water and use filter paper to absorb the remaining distilled water on the electrode. Then put the electrode into the beaker with the mixed phosphoric acid basin, wait for more than 15 minutes, and then adjust the positioning knob on the instrument so that the instrument displays 6.86pH. This is to first set the reference point for the instrument. After setting the reference point, take the electrode out of the beaker containing the mixed phosphoric acid solution, wash the electrode with distilled water, and place it in the beaker filled with distilled water. Wait for about 3 minutes to allow the remaining part of the mixed phosphoric acid solution to dissolve.
2. Later, take out the electrode from the beaker containing distilled water, and use filter paper to absorb the remaining distilled water on the electrode. Then put the electrode into a solution containing potassium hydrogen phthalate or borax, wait for more than 15 minutes, and observe whether the instrument displays pH 4.00 or 9.18. If not, adjust the slope knob on the instrument so that the instrument displays 4.00 or 9.18 pH. This is a commonly used two-point calibration. If three-point calibration is required, just add another solution and follow the above steps one more time. This is how to calibrate an acidometer.
3. After calibration, put the rubber plug back in. If it is not used temporarily, remember to put a saturated solution in the protective sleeve of the electrode to keep the electrode moist. This can extend the life of the electrode and reduce the asymmetric potential of the electrode. Electrodes have a service life and are fragile. Therefore, each laboratory needs to replace electrodes frequently. Do not replace the electrodes because they are not broken during use.
4. Before using the composite electrode, first check whether the glass bulb is cracked or broken. If not, when using a pH buffer solution for two-point calibration, and the positioning and slope knobs can be adjusted to the corresponding pH value, it is generally considered safe to use. Otherwise, Electrode activation can be performed according to the instruction manual. The activation method is to soak in 4% hydrogen fluoride solution for about 3 to 5 seconds, take it out and rinse it with distilled water; then soak it in 0.1 mol/L basin acid solution for several hours, rinse it with distilled water, and then calibrate. For non-sealed composite electrodes, if the inner solution is <1/3, an external reference solution, namely 3mol/L potassium fluoride solution, needs to be added. If the potassium fluoride solution exceeds the position of the small hole, shake off the excess potassium fluoride solution and check whether there are bubbles in the solution. If there are bubbles, flick the electrode to drive them out completely to avoid inaccurate measurement data.
5. Calibration method of pen pH meter:
Dip the test pen electrode into the mixed phosphate standard buffer solution with a pH value of 6.86 (at 25°C) and shake it gently; use a small screwdriver to adjust the calibration potentiometer until the displayed value matches the pH value of the standard buffer solution at ambient temperature. ; The electrode is inserted into potassium hydrogen phosphobenthate with pH 4.01 or borax standard buffer solution with pH 9.18; the displayed value should be within the allowable error range compared with the pH value of the buffer solution.
