Do you know how to calibrate the PH meter?

　　PH meter should be regularly checked and calibrated to make the precision and accuracy meet the requirements. How to calibrate a pH meter, or how to calibrate a PH meter. The following detailed steps teach you how to do it
　　1. Calibration of PH meter used in laboratory:
　　When calibrating the commonly used laboratory pH meter instrument, adjust the slope of the instrument to the maximum and set aside the rubber plug on the upper part of the electrode to expose the small hole, otherwise, when performing calibration, negative pressure will be generated and the mud will cause the solution to fail to exchange ions normally, which will make the measurement data inaccurate.
　　Take the electrode out of the beaker with distilled water, and use filter paper to absorb the distilled water left on the electrode. Then put the electrode into the beaker with mixed phosphoric acid basin, wait for more than 15 min, then adjust the positioning knob on the instrument to make the instrument display 6.86pH, which is the reference point for the instrument first. After setting the reference point, take out the electrode from the beaker with mixed phosphoric acid solution, wash the electrode with distilled water and put it in the beaker with distilled water, wait for about 3 min to make the residual part of mixed phosphoric acid solution dissolve.
　　2. Later, take the electrode out of the beaker with distilled water and use filter paper to absorb the residual distilled water on the electrode. Then put the electrode into the solution with potassium hydrogen phthalate or borax, wait for more than 15 min and observe whether the instrument shows 4.00 or 9.18 pH. If not, adjust the slope knob on the instrument to make the instrument show 4.00 or 9.18 pH, which is the common two-point calibration. If you need a three-point calibration, you can operate another solution more than once according to the above steps. This is the calibration method of PH meter. 3.
　　3. After calibration, put back the rubber plug, if not used for a while, remember to put saturated solution inside the protective sleeve of the electrode to keep the electrode wet, so as to prolong the life of the electrode and reduce the asymmetric potential of the electrode. The electrode has a service life and is fragile, therefore, each laboratory needs to replace the electrode frequently, do not think that the electrode is not broken in use.
　　4. Before using the compound electrode, first check whether the glass bulb is cracked or broken, if not, when using pH buffer solution for two-point calibration, the positioning and slope knob can be adjusted to the corresponding pH value, it is generally considered to be usable, otherwise the electrode activation process can be carried out according to the instruction. The activation method is to dip in 4% hydrogen fluoride solution for about 3~5 s, take out and rinse clean with distilled water; then dip in 0.1 mol/L basin acid solution for several hours, rinse clean with distilled water, and then calibrate. For the non-closed composite electrode, if the solution in the inside is <1/3, the external reference solution, i.e. 3 mol/L potassium fluoride solution, needs to be added. If the potassium fluoride solution exceeds the position of the small hole, dump the excess potassium fluoride solution and check whether there are bubbles in the solution, if there are bubbles, flick the electrode to drive out the bubbles*. To avoid inaccurate measurement data. 5.
　　5. Calibration method of pen pH meter:
　　Immerse the test pen electrode into the mixed phosphate standard buffer solution with pH 6.86 (at 25℃) and shake it gently; adjust the calibration potentiometer with a small screwdriver until the displayed value matches with the pH of the standard buffer solution at ambient temperature; insert the electrode into the standard buffer solution of potassium hydrogen phosphate dicarboxylate with pH 4.01 or borax with pH 9.18; the displayed value compared with the pH value of the buffer solution should be within within the allowable error range.