After the calibration of the acid meter is in compliance with the requirements, correct the electrode section and prepare the distilled water or deionized water and filter paper used for calibration. At present, there are 7 kinds of standard solutions. In China, the following three kinds of solutions are generally used: 1) potassium hydrogen phthalate (KHC8H4O4) 4.003pH; 2) mixed phosphoric acid pot (Na2HPO4) 6.864 pH; 3) borax (Na2B4O7·l0H2O) 9.182 pH (the above pH is at 25 ° C). The electrode was washed with distilled water at a constant temperature, and distilled water was placed in a beaker, and the electrode portion was soaked to sufficiently dissolve the residual impurities in the electrode portion.
1. When calibrating, adjust the slope of the instrument to the maximum, and open the rubber plug on the top of the electrode to expose the small hole. Otherwise, when the calibration is performed, a negative pressure will be generated, causing the solution to fail to perform normal ion exchange. Measurement data is not accurate. The electrode was taken out from the beaker containing distilled water, and the residual distilled water on the electrode was blotted with a filter paper. Place the electrode in a beaker with a mixed phosphoric acid pot and wait for more than 15 minutes. Then adjust the positioning knob on the instrument to make the instrument display 6.86 pH. This is the first reference point for the instrument. After setting the reference point, the electrode was taken out from the 1hm, _ beaker containing the mixed phosphoric acid, and the electrode was washed with distilled water and placed in a beaker containing distilled water. Wait for about 3 minutes to dissolve the residual portion of the mixed phosphoric acid 1hm, _. The electrode was later taken out of the beaker containing distilled water, and the residual distilled water on the electrode was blotted with filter paper. The electrode is then placed in a solution containing potassium hydrogen phthalate or borax, waiting for more than 15 minutes, and the instrument is shown to be 4.00 or 9.18 pH. If it is not necessary to adjust the slope knob on the instrument to make the instrument display 4.00 or 9.18 pH, this is the commonly used two-point calibration. If you need a three-point calibration, you can use another solution and follow the steps above. This is the calibration method for the acidity meter.
2. After the calibration is completed, the rubber plug is plugged back. If it is not used for a while, remember to install a 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. The electrode has a service life and is fragile. Therefore, each laboratory needs to change the electrode frequently. Do not think that the electrode in use is not broken. Before using the composite electrode, first check whether the glass bulb is cracked or broken. If not, use the pH buffer solution to perform two-point calibration. When the positioning and slope knobs can be adjusted to the corresponding pH value, it is generally considered to be usable. Otherwise, press Use the instructions for electrode activation. The activation method is immersed in a 4% hydrogen fluoride solution for about 3 to 5 s, and is taken out and rinsed with distilled water; then, after soaking for several hours in a 0.1 mol/L pot acid solution, it is rinsed with distilled water and then calibrated. For non-closed composite electrodes, if the solution is inside
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