1, commonly used laboratory PH meter instrument calibration, the slope of the instrument should be adjusted to the maximum, and set aside the electrode on the upper part of the rubber plug, so that the small holes are exposed, otherwise in the calibration, it will produce a negative pressure, muddy to the solution can not be normal ion exchange, it will make the measurement data inaccurate.
Take the electrode out of the beaker containing distilled water, and use filter paper to absorb the residual distilled water on the electrode. Then put the electrode into the beaker containing the mixed phosphate basin, wait for more than 15 min, and then adjust the positioning knob on the instrument so that the instrument displays 6.86pH, which is the first to set the reference point for the instrument. Set a good reference point after the electrode from the beaker containing mixed phosphoric acid solution out, with distilled water to wash the electrode, and placed in the beaker containing distilled water, wait for about 3 min, so that the residual part of the mixed phosphoric acid solution dissolved.
2. Take the electrode out of the beaker with distilled water later and dry the residual distilled water on the electrode with filter paper. Then put the electrode into the solution containing potassium hydrogen phthalate or borax, wait for more than 15 min, observe whether the instrument display is 4.00 or 9.18 pH. If not, we have to adjust the slope knob on the instrument, so that the instrument displays 4.00 or 9.18 pH, which is commonly used two-point calibration. If you need three-point calibration, another solution, according to the steps above and operate more than once on the line. This is the calibration method of acidity meter.
3, after correction, after plugging back to the rubber plug, if not used temporarily, remember to install the electrode in the protective sleeve of the saturated solution to keep the electrode wet, which can extend the life of the electrode and reduce the electrode's asymmetric potential. Electrodes have a period of use, and are fragile, therefore, each laboratory needs to replace the electrode often, do not think that the use of the electrode is not bad on the replacement.
4, composite electrode before use, first check the glass bulb whether there are cracks, broken, if not, with pH buffer solution for two-point calibration, positioning and slope knob can be adjusted to the corresponding pH value, it is generally considered to be able to use, otherwise you can use the electrode according to the instructions for activation treatment. Activation method is in 4% hydrogen fluoride solution immersed in about 3 ~ 5 s, remove the distilled water for rinsing clean; then in 0.1 mol / L of potentiometric acid solution soaked for several hours, rinsed with distilled water, and then calibration. For the non-closed composite electrode, if the solution is "1/3", it is necessary to add the external reference solution, i.e. 3 mol/L potassium fluoride solution. If the potassium fluoride solution exceeds the position of the small hole, shake off the excess potassium fluoride solution and check whether there are air bubbles in the solution, if there are air bubbles, we need to flick the electrode to drive out the air bubbles completely. To avoid causing inaccurate measurement data.
5, pen PH meter calibration method:
Test pen electrode immersed in PH value of 6.86 (25 degree ) of the mixed phosphate standard buffer, and gently shake; with a small screwdriver to adjust the calibration potentiometer until the display value and the standard buffer solution in the ambient temperature of the PH value match; electrode inserted into the PH4.01 of the phosphorus of the potassium hydrogen dicarboxylate or PH9.18 of the standard buffer solution of borax; the display value of the buffer solution with the PH value compared to the display value should be in the The displayed value should be within the permissible range of error when compared with the pH value of the buffer solution.
