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Precautions for PH Meter Use in Laboratory

The pH meter is a commonly used instrument, which is mainly used to accurately measure the pH value of liquid media. According to the volume of the instrument, it is divided into pen type (mini type), portable type, desktop type and online connection monitoring and measurement type. According to the measurement accuracy, it is divided into 0.2, 0.1, 0.01 and 0.001 degrees, and he smaller the number, the higher the accuracy. According to the reading indication method, it is divided into pointer type and digital type.
In order to prolong the service life, the following items must be noted when using the pH meter:
I. Before use 
1. Under normal circumstances, the pH meter should be calibrated once a day when it is used continuously. Generally, the instrument does not need to be calibrated again within 24 hours. The calibrated buffer solution generally uses a pH 6.86 solution for the first time, and use a buffer close to the pH value of the tested solution for the second time. If the tested solution is acidic, the buffer should be pH 4.00, and if the tested solution is alkaline, choose pH 9.18 buffer.
2. The water used to prepare pH 6.86 and pH 9.18 buffers should be boiled for 15 to 30 minutes in advance to remove dissolved carbon dioxide. Try to avoid contact with air during the cooling process to prevent carbon dioxide pollution.
II. In use 
1. When measuring the pH value with the pH meter, ensure that the bulb of the electrode is completely immersed in the medium to be measured, so as to obtain more accurate measurement results.
2. After adding acid or alkali to the solution to be tested, it must be mixed evenly before measurement.
3. The temperature should not be too high during the measurement. If the measurement result is inaccurate when the temperature exceeds 40℃, take it out with a beaker and cool it slightly.
III. Maintenance after use 
1. If the electrode used by the pH meter is a new electrode or an electrode that has not been used for a long time, it must be soaked in distilled water for several hours before use, so that the asymmetric potential of the pH meter electrode can be reduced to a stable level, thereby reducing the internal resistance of the electrode.
2. Keep the electrode bulb moist. If it is found to be dry, it should be soaked in a 3mol/L potassium chloride solution or a slightly acidic solution for several hours before use to reduce the asymmetric potential of the electrode.
3. The composite electrode should avoid contact with organic matter. Once it is contacted or contaminated, clean it with absolute ethanol.
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