How do You Calibrate pH Meter?

In order to ensure the accuracy of the detection value, we will calibrate the pH meter before using it. There are generally three calibration methods, let us understand the calibration method of the pH meter together.

The calibration method of the pH meter

Any pH meter must be calibrated with a pH standard solution before measuring the pH value of the sample. For samples whose measurement accuracy is below 0.1pH, a one-point calibration method can be used to adjust the instrument. Generally, we choose pH 6.86 or pH 7.00 standard buffer. Some instruments have an accuracy of only 0.2pH or 0.1pH, so the instrument only has a positioning adjustment knob. The specific operation steps are as follows:

1. Measure the temperature of the standard buffer solution, determine the pH value at this temperature, and adjust the temperature compensation knob to below this temperature.
2. Rinse the electrode with pure water and dry it.
3. Immerse the electrode in the buffer solution, shake it, and place it still. After the value is stable, adjust the positioning knob to make the instrument display the pH value of the standard solution.
4. Take out the electrode, rinse, and dry it.
5. Measure the sample temperature, and adjust the temperature compensation knob of the pH meter to the temperature value.

The calibration method of pH meter two

The precision grade pH meter, in addition to the adjustment of positioning and temperature compensation, also has the adjustment of electrode and slope, which needs to be calibrated with two kinds of standard buffer solutions. Generally, pH6.86 or pH7.00 is used for positioning calibration first, and then according to the acid-base condition of the test solution, pH4.00 (acidic) or pH9.18 and pHI0.0l (alkaline) buffer solutions are selected for slope calibration. The specific operation steps are:

1. Wash and dry the electrode, immerse it in pH 6.86 or pH 7.00 standard solution, and place the temperature compensation knob of the instrument at the temperature of the solution. After the displayed value is stable, adjust the positioning knob to make the displayed value of the instrument the pH value of the standard solution.
2. Take out the electrode, wash and dry it, and immerse it in the second standard solution. After the displayed value is stable, adjust the slope knob of the instrument so that the displayed value of the instrument is the pH value of the second standard solution.
3. Take out the electrode, wash it and dry it, and then immerse it in pH6.86 or pH7.00 buffer solution. If the error exceeds 0.02pH, repeat steps (1) and (2) until the correct pH value can be displayed in the two standard solutions without adjusting the knob.
4. Take out the electrode and shake it dry, adjust the temperature compensation knob of the pH meter to the temperature of the sample solution, then immerse the electrode in the sample solution, shake it and place it still, and display a stable reading.

The calibration method of pH meter three

No matter what kind of digital pH meter, the point of pH=7 must be calibrated and the pH=7 must be calibrated first when the two points are calibrated at this point. When doing the calibration, start from 7.0. The selected standard solution is related to the pH value of the solution to be measured, which can make the pH value of the solution fall within the pH range of the calibration. Generally, two points can meet the requirements. If the requirements are very high, only consider the third point. Some instruments can calibrate three points, and there is an optional mode, which can be used directly. For some that don't, two-point two point proofreading is generally used, that is to say, proofreading twice.

When calibrating, pay attention to:

1. Clean with pure water before and after the pH test/calibration, and then use absorbent paper to absorb the liquid before performing the calibration operation.
2. The calibration solution is easily contaminated after opening the cap, and the calibration data will have slight deviations after contamination. Therefore, it is necessary to cover the lid in time and store it away from light. It can be reused for about 3 months.
3. After the first calibration, gently wipe off the liquid on the electrode with a paper towel before proceeding to the next step of calibration to avoid contamination of the calibration solution, thereby greatly improving the shelf life of the solution.
4. If it is a 2-point calibration, please select a standard buffer liquid that is closer to the pH value of the solution to be tested. At the same time, the temperature of the standard buffer solution should be as close as possible to the temperature of the measured solution.

   

A pH buffer is a solution that keeps the pH stable and is used to check the accuracy of the pH controller as a reference value. After the pH meter is calibrated and used, it may drift or change, so insert the electrode into the solution to be tested before the test, and determine whether it needs to be re-calibrated according to the size of the error.

The positioning standard buffer solution should be as close as possible to the pH value of the solution to be measured. Or two-point calibration, try to make the pH value of the measured solution within the interval of the two standard buffer solutions. After calibration, the electrode immersed in the standard buffer solution should be specially rinsed with water.

Precautions for use of pH meter

1. In general, when the pH meter is used continuously, it should be calibrated once a day. Generally, this instrument does not need to be recalibrated within 24 hours.
2. Before use, pull off the rubber sleeve on the upper end of the electrode of the pH meter to expose the small hole on the upper end.
3. For the calibration buffer solution, the pH=6.86 solution is generally used for the first time, and the buffer solution close to the pH value of the measured solution is used for the second time. If the solution to be tested is acidic, the buffer should be pH=4.00. If the solution to be tested is alkaline, the buffer should be pH=9.18.
4. When measuring, the leading wire of the electrode should keep still, otherwise, it will cause unstable measurement.
5. 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.
6. When the pH meter is measuring the pH value, it is necessary to ensure that the detection port of the electrode is completely inserted into the medium to be measured, so as to obtain more accurate measurement results.