The correct use and maintenance of PH meter

The pH meter is abbreviated as a pH meter and consists of an electrode and an electricity meter. If the electrode can be properly maintained during use, the standard buffer can be prepared as required and the electricity meter can be operated correctly, the pH indication error can be greatly reduced, thereby improving the reliability of the chemical experiment and medical test data.

First, the correct use and maintenance of the electrode

At present, the electrodes used in the laboratory are all composite electrodes. The advantages are that they are easy to use, free from oxidizing or reducing substances, and have a faster balance. In use, the rubber sleeve and the rubber sleeve at the bottom of the electrode filling port are completely removed to maintain the hydraulic pressure difference of the potassium chloride solution in the electrode. Here's a simple introduction to the use and maintenance of the electrode:

1. When the composite electrode is not used, it can be fully immersed in 3M potassium chloride solution. Never wash with wash solution or other absorbent agents.

2. Before use, check the bulb at the front of the glass electrode. Under normal conditions, the electrode should be transparent and free from cracks; the bulb should be filled with a solution and no bubbles should be present.

3. When measuring a solution with a large concentration, try to shorten the measurement time as much as possible and carefully clean it after use to prevent the measured liquid from adhering to the electrode and contaminating the electrode.

4. After cleaning the electrode, do not wipe the glass film with filter paper, but use filter paper to dry it to avoid damage to the glass film and prevent cross-contamination, affecting the measurement accuracy.

5. The silver-silver chloride internal reference electrode of the measurement electrode should be immersed in the chloride buffer solution in the bulb to avoid the phenomenon of digital chattering in the display part of the electricity meter. When using, pay attention to gently swing the electrode.

6. The electrode cannot be used for strong acids, alkalis or other corrosive solutions.

7. Is strictly prohibited in dehydrating medium such as anhydrous ethanol, potassium dichromate æˆŽæƒºè¤‚è°©o:p>

Second, the standard buffer preparation and preservation

1. The pH standard substance should be stored in a dry place. For example, the mixed phosphate pH standard substance will deliquesce when the humidity is high. Once the deliquescence occurs, the pH reference substance cannot be used.

2. The preparation of pH standard solution should use double distilled or deionized water. If you are using a 0.1 pH meter, use distilled water.

3. The pH standard solution should be diluted with a smaller beaker to reduce the pH standard solution on the beaker wall. Plastic bags or other containers for storage of the pH standard substance should be rinsed with distilled water several times in addition to the plastic bags or other containers, and then poured into the formulated pH standard solution to ensure that the prepared pH standard solution is accurate.

4. The prepared standard buffer solution can generally be preserved for 2-3 months. If turbidity, mildew or sedimentation is found, it cannot be used.

5. Alkaline standard solution should be sealed in a polyethylene bottle. Prevent carbon dioxide from entering the standard solution to form carbonic acid and reduce its pH.

Third, the correct calibration of the pH meter

There are many different types of pH meters due to the different design of the electricity meter, and the operation steps are different. Therefore, the operation of the pH meter should be carried out in strict accordance with its instructions. In a specific operation, calibration is an important step in the use of a pH meter. The data in Table 1 shows the accuracy of a 0.01-level, pH meter that has been qualified for metrological verification and the measured values â€‹â€‹after calibration, from which the importance of calibration can be seen.

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Standard pH â”„â”„â”„ Error before calibration (pH) è¯¯å·® Error after calibration (pH)

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13.000â”…â”…â”…00.0600â”…â”…â”…â”…00.0000

12.000â”…â”…â”…00.0450â”…â”…â”…â”…00.0005

11.000â”…â”…â”…00.0500â”…â”…â”…â”…00.0010

10.000â”…â”…â”…00.0300â”…â”…â”…â”…00.0000

9.000â”…â”…â”…00.0200â”…â”…â”…â”…00.0005

8.000â”…â”…â”…00.010â”…â”…â”…â”…00.0005

7.000â”…â”…â”…00.0015â”…â”…â”…â”…00.0000

6.000â”…â”…â”…-00.0100â”…â”…â”…â”…-00.0005

5.000â”…â”…â”…-00.0105â”…â”…â”…â”…00.0005

4.000â”…â”…â”…00.0150â”…â”…â”…â”…00.0000

3.000â”…â”…â”…-00.0300â”…â”…â”…â”…00.0000

2.000â”…â”…â”…-00.0200â”…â”…â”…â”…-00.0003

1.000â”…â”…â”…-00.0350â”…â”…â”…â”…-00.0001

Although there are many types of pH meters, the calibration method uses a two-point calibration method, which is to choose two standard buffers: one is a pH 7 standard buffer, and the second is a pH 9 standard buffer or a pH 4 standard buffer. The pH meter standard buffer was used to locate the electricity meter, and a second standard buffer was selected according to the acidity and alkalinity of the solution to be tested. If the test solution is acidic, use pH4 standard buffer; if the test solution is alkaline, use pH9 standard buffer. If the pH meter is manually adjusted, it should be repeated several times between the two standard buffers until there is no need to adjust its zero and position (slope) knobs. The pH meter can accurately display the two standard buffer pH values. The calibration process ends. After this, the zero point and positioning knob should not be moved again during the measurement. If it is a smart pH meter, it does not need to be adjusted repeatedly, because the pH value of several standard buffers has been stored in the inside, and it can be automatically identified and automatically calibrated. But pay attention to the standard buffer selection and the accuracy of its preparation. The intelligent 0.01-level pH meter typically has three to five standard buffer pH values, such as the KL-016 pH meter from Colecron.

Second, special attention should be paid to the temperature of the solution to be tested before calibrating. In order to correctly select the standard buffer, and adjust the temperature compensation knob on the power meter panel to make it consistent with the temperature of the solution to be tested. The pH of the standard buffer solution is different at different temperatures. As shown in table 2:

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Temperature (Â°C) â”„â”„ pH7 â”„â”„ pH4 â”„â”„ pH9.2

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10â”„â”„â”„â”„â”„â”„6.92â”„â”„4.00â”„â”„9.33

15â”„â”„â”„â”„â”„â”„6.90â”„â”„4.00â”„â”„9.28

20â”„â”„â”„â”„â”„â”„6.88â”„â”„4.00â”„â”„9.23

25â”„â”„â”„â”„â”„â”„6.86â”„â”„4.00â”„â”„9.18

30â”„â”„â”„â”„â”„â”„6.85â”„â”„4.01â”„â”„9.14

40â”„â”„â”„â”„â”„â”„6.84â”„â”„4.03â”„â”„9.01

50â”„â”„â”„â”„â”„â”„6.83â”„â”„4.06â”„â”„9.02

50â”„â”„â”„â”„â”„â”„6.83â”„â”„4.06â”„â”„9.02

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After calibration is completed, the instrument does not need to be calibrated again within 48 hours for frequently used pH meters. If one of the following conditions is encountered, the instrument needs to be recalibrated:

(1) When there is a big difference between the solution temperature and the calibration temperature.

(2) The electrode is exposed to the air for too long, such as more than half an hour.

(3) The positioning or slope regulator is mis-operated;

(4) Measurement of peracid (pH<2) or overbase (pH>2)

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