Use and maintenance of acidity meter （ = PH meter )

The commonly used and economical test method for laboratory routine determination of PH value is to use PH test paper, and the PH test paper only provides the range value of the pH value, which is useless for the need to accurately know the pH value. A pH meter is a testing instrument that can provide an accurate pH value. Due to the high price of acidity meters and sensitive consumables, it is particularly necessary to correctly grasp the use and maintenance of acidity meters.

The use of acidity meter pH electrode
At present, most of the pH meter electrodes used in laboratories are composite electrodes. Its advantages are that it is easy to use, not affected by oxidation-reduction substances, and the equilibrium speed is fast. Pay attention to the following when using:

(1) When using the pH electrode, the rubber sleeve and the lower end rubber sleeve should be removed to maintain the pressure difference of the potassium chloride solution in the electrode. Check the bulb at the front of the glass electrode before use. Under normal conditions, the electrode should be transparent without cracks, and the bulb should be filled with solution without air bubbles.
(2) Two-point calibration is generally used, 6.86pH (25°C) as the first point, 4.00pH (25°C) or 9.18 (25°C)pH as the second point (note that the calibration value should be the same as the standard solution measured in actual consistent with the standard value at temperature). Make the pH value as stable as possible during the calibration process and then press the confirm key.
(3) Generally, when the performance of the pH electrode is good, the slope after calibration is above 98%, and if the performance drops slightly, it should be above 95%. If it is lower than 90%, it is recommended to replace the electrode.
(4) In the calibration state, the reaction is slow and unstable, which is a reflection of the performance degradation of the pH electrode.
(5) The pH compound electrode is not suitable for measuring organic matter, oil, viscous and other substances.
(6) The external reference is the most prone to problems in the use of pH composite electrodes. At the liquid junction of the electrode, the blockage at the liquid junction is the main cause of error.
(7) When measuring the value of the solution with a pH electrode, it should be fully stirred or the reaction will be slow.
(8) In winter, when the ambient temperature reaches freezing point, the pH electrode cannot be used, and it is prone to cold blast. It is recommended to use it above 15°C.

The maintenance of the acidity meter mainly focuses on the use and maintenance of the electrodes. The precautions for use are as follows:
1) The acidity meter must be kept clean and dry to prevent the entry of dust and moisture. When using it, pay attention to avoid using the environment with too high humidity, which will lead to inaccurate testing. During the measurement, the lead-in wire of the electrode must remain stationary. Otherwise it will cause unstable measurement.
2) Before using the glass electrode for the first time, it needs to be soaked in distilled water for more than one day and night. There must be a proper electrode soaking solution in the protective bottle at the front end of the pH electrode, and the electrode tip needs to be soaked in it. If the soaking solution in the protective bottle is found to be turbid, moldy, etc., it is necessary to clean the electrode and the protective bottle in time and replace it with a new soaking solution.
3) The bulb film of the glass electrode is very thin, so as to prevent the glass bulb from contacting with hard objects, any damage or scratching will cause the electrode to fail. Avoid long-term contact with strong water-absorbing solvents, strong alkali solutions, pure water, protein solutions, acidic fluoride solutions, and protein-containing solutions for the electrode. Even if it is measured, it needs to be cleaned in time to ensure the accuracy of the test.
4), the accuracy of pH determination depends on the accuracy of the standard buffer. The standard buffer solution for pH meter requires greater stability and less temperature dependence.