Matters needing attention in PH meter measurement
Before proceeding, the integrity of the electrode should be checked first. At present, most of the electrodes used in acidity meters (PH meters) are composite electrodes, and the older generation of acidity meters still use glass electrodes and calomel electrodes. Since composite electrodes are widely used, the composite electrodes are mainly discussed below.
At present, the composite electrodes used in the laboratory mainly include fully enclosed and non-enclosed types, and the fully enclosed type is relatively small, mainly produced by foreign companies. Before using the composite electrode, first check whether the glass bulb is cracked or broken. If not, when the pH buffer solution is used for two-point calibration, the positioning and slope buttons can be adjusted to the corresponding pH value. Use the manual for electrode activation treatment. The activation method is to soak in 4% hydrogen fluoride solution for about 3-5 seconds, take it out and rinse it with distilled water, then soak it in 0.1mol/L hydrochloric acid solution for several hours, rinse it with distilled water, and then calibrate it, that is, use the pH value 6.86 (25°C) buffer solution for positioning. After adjustment, choose another pH buffer solution for slope adjustment. If it cannot be adjusted, the electrode needs to be replaced. For non-closed composite electrodes, an external reference solution, namely 3mol/L potassium chloride solution, must be added inside, so it is necessary to check whether the potassium chloride solution in the electrode is more than 1/3, if not, add 3mol/L potassium chloride solution Potassium solution. If the potassium chloride solution exceeds the position of the small hole, shake off the excess potassium chloride solution so that the solution is below the small hole, and check whether there are bubbles in the solution. If there are bubbles, flick the electrode to drive out the bubbles completely.
During use, the rubber on the electrode should be peeled off to expose the small hole, otherwise, a negative pressure will be generated during the analysis, resulting in the potassium chloride solution not being able to pass through the glass bulb for ion exchange with the measured solution. will make the measurement data inaccurate. After the measurement is completed, the rubber should be restored to seal the small hole. After the electrode is cleaned with distilled water, it should be soaked in 3mol/L potassium chloride solution to keep the electrode bulb moist. If the electrode is found to have lost the protective solution before use, it should be soaked in 3mol/L potassium chloride solution for several hours. , so that the electrode reaches the best measurement state. In actual use, it is found that some analysts treat the composite electrode as a glass electrode and soak it in distilled water for a long time. This is incorrect, which will greatly reduce the concentration of potassium chloride solution in the composite electrode, resulting in The electrode reaction is not sensitive during measurement, which will eventually lead to inaccurate measurement data, so the composite electrode should not be soaked in distilled water for a long time.
