Introduction to the steps and methods for calibrating pH meters
1. PH meter used in the laboratory | Acidity meter calibration:
When calibrating commonly used laboratory pH meters, 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, during calibration, negative pressure will be generated, causing the solution to be unable to exchange ions normally and resulting in inaccurate measurement data.
Remove the electrode from the beaker containing distilled water and use filter paper to absorb any remaining distilled water from the electrode. Then put the electrode into the beaker with the mixing phosphoric acid basin, wait for more than 15 min, and then adjust the positioning knob on the instrument to make the instrument display 6.86 pH. This is the first time to set the reference point for the instrument. After setting the reference point, remove the electrode from the beaker containing the mixed phosphoric acid solution, wash the electrode with distilled water, and place it in the beaker containing distilled water. Wait for about 3 minutes to dissolve the residual part of the mixed phosphoric acid solution.
2. Later, remove the electrode from the beaker containing distilled water and use filter paper to absorb the remaining distilled water on the electrode. Then place the electrode in a solution containing potassium hydrogen phthalate or borax, wait for more than 15 minutes, and observe whether the instrument displays a pH of 4.00 or 9.18. If not, adjust the slope knob on the instrument to display 4.00 or 9.18 pH, which is a commonly used two-point correction. If three point correction is required, simply repeat the steps above for another solution. This is the calibration method for acidity meters.
3. After calibration, plug the rubber plug back in. If not in use temporarily, remember to install a saturated solution in the protective sleeve of the electrode to keep the electrode moist. This can extend the lifespan of the electrode and reduce the asymmetric potential of the electrode. Electrodes have a lifespan and are considered fragile. Therefore, various laboratories need to frequently replace the electrodes, and do not assume that the electrodes are not damaged during use.
4. Before using the composite electrode, first check the glass bulb for cracks and breakage. If not, use a pH buffer solution for two point calibration. When the positioning and slope knobs can be adjusted to the corresponding pH value, it is generally considered usable. Otherwise, electrode activation treatment can be carried out according to the user manual. The activation method is to immerse in a 4% hydrogen fluoride solution for about 3-5 seconds, then remove and rinse thoroughly with distilled water; Then soak in a 0.1 mol/L basin acid solution for several hours, rinse thoroughly with distilled water, and then calibrate. For non enclosed composite electrodes, if the internal solution is less than 1/3, an external reference solution of 3mol/L potassium fluoride solution needs to be added. If the potassium fluoride solution exceeds the small hole position, shake off the excess potassium fluoride solution and check if there are any bubbles in the solution. If there are bubbles, gently flick the electrode to completely drive them out to avoid inaccurate measurement data.
5. Calibration method for pen pH meter:
Immerse the test pen electrode in a mixed phosphate standard buffer with a pH value of 6.86 (at 25 ℃) and gently shake it; 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; Insert the electrode into a standard buffer solution of potassium hydrogen phosphobenzoate at pH 4.01 or borax at pH 9.18;
