Steps and methods of calibrating pH meter
1. Calibration of pH meter and pH meter used in the laboratory:
When calibrating the commonly used laboratory pH meter instruments, the slope of the instrument should be adjusted to the maximum, and the rubber plug on the upper part of the electrode should be opened to expose the small hole. Otherwise, negative pressure will be generated during calibration, which will make the solution unable to exchange ions normally and make the measurement data inaccurate.
Take the electrode out of the beaker filled with distilled water, and suck up the residual distilled water on the electrode with filter paper. Then put the electrode into a beaker with a mixed phosphoric acid basin, wait for more than 15 min, and then adjust the positioning knob on the instrument to make the instrument display 6.86pH, which is to set the reference point for the instrument first. After setting the reference point, take the electrode out of the beaker containing mixed phosphoric acid solution, wash the electrode with distilled water, put it in the beaker containing distilled water, and wait for about 3 min to dissolve the residual part of mixed phosphoric acid solution.
2. Later, take the electrode out of the beaker filled with distilled water, and suck up the residual distilled water on the electrode with filter paper. Then put the electrode into a solution containing potassium hydrogen phthalate or borax, wait for more than 15 min, and observe whether the instrument shows a pH of 4.00 or 9.18. If not, adjust the slope knob on the instrument to make the instrument display 4.00 or 9.18 pH, which is the commonly used two-point correction. If three-point correction is needed, just repeat the operation of another solution according to the above steps. This is the calibration method of acidity meter.
3. After calibration, plug the rubber plug back. If it is not used for a while, remember to put saturated solution in the protective sleeve of the electrode to keep the electrode moist, which can prolong 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. Don't think that electrodes will not be replaced if 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 two-point calibration is carried out with pH buffer solution, the positioning and slope knobs can be adjusted to the corresponding pH value, which is generally considered to be usable. Otherwise, the electrode can be activated according to the instruction manual. The activation method is to soak in 4% hydrogen fluoride solution for about 3 ~ 5 s, take it out and rinse it with distilled water; Then soak in 0.1 mol/L pan acid solution for several hours, rinse with distilled water, and then calibrate. For the non-closed composite electrode, if the internal solution is less than 1/3, an external reference solution, namely 3mol/L potassium fluoride solution, should be added. If the potassium fluoride solution exceeds the position of the small hole, throw 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, so as to avoid inaccurate measurement data.
5, pen pH meter calibration method:
Immerse the electrode of the test pen in the mixed phosphate standard buffer with pH value of 6.86 (at 25℃) and gently shake it; Adjust the calibration potentiometer with a small screwdriver until the displayed value is consistent with the pH value of the standard buffer solution at ambient temperature; The electrode is inserted into the standard buffer solution of potassium hydrogen phosphate with pH4.01 or borax with PH9.18; The displayed value should be within the allowable error range compared with the PH value of the buffer solution.
