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A pH meter measures the pH or acidity/alkalinity of a substance. Most pH meters rely on glass electrodes that measure the amount of hydrogen ions in the solution. Normally, pH meters need to be calibrated once a day or once a week.

This is a key step in calibrating a pH meter, because the pH value changes with temperature. Some pH meters have a built-in temperature measurement probe, while in other cases an external temperature probe may be required.

To use external or internal measurement, the temperature value needs to be entered into the pH meter. It should be noted that the temperature of the buffer pH value will also cause the pH value to change.

Use approximately 30 mL of three different calibration buffer solutions-one with a pH of 10.00, another with a pH of 7.00, and the third with a pH of 4.01.

After pouring these solutions into a 50 mL beaker, they can be covered with watch glass or parafilm before the calibration process. The temperature of all these buffers should be the same, because the pH value depends on the temperature.

The sample solution can be prepared as needed. Then, 30 mL of this solution can be poured into a 50 mL beaker. As mentioned above, the solution should also reach the same temperature as the calibration buffer, because the pH value changes with temperature.

Electrodes and meters can be prepared and set up according to the user guide, because these conditions may vary for each instrument and company.

Before the calibration process, all buffers should reach the same temperature. If the temperature of the buffer is not 25°C, temperature compensation can be performed. A thermometer can be used to manually calculate the temperature of the buffer, and these values ​​can be manually added to the meter to transfer these values ​​to the pH meter.

The calibration buffer prepared as described above does not need to be capped. The pH electrode should be rinsed carefully in deionized water to avoid contamination of the buffer solution. It should be noted that the pH electrode should not be cleaned with the same buffer that is subsequently used for calibration.

First, you can keep the pH electrode in a calibration buffer with a pH of 10.01 so that the electrode tip and connector are completely immersed in the calibration buffer. After starting the calibration on the meter, it is best to wait 1-2 minutes until the reading on the meter stabilizes.

If the temperature of the buffer cannot be automatically identified, the value should be manually entered to obtain the temperature, so as to obtain the correct pH value. After completing this operation, the electrode should be rinsed with deionized water before the next buffer calibration to prevent contamination.

The electrode can now be placed in the pH 7.00 calibration buffer. After waiting for the reading to stabilize for 1-2 minutes, you can record the temperature-corrected reading.

If the temperature values ​​are not detected automatically, they must be added manually to obtain an appropriate reading. After calibration, the electrode should be rinsed again with deionized water to avoid contamination in the next step.

The electrode can now be placed in the pH 4.01 calibration buffer. Allow the reading to stabilize for 1-2 minutes before recording. Similarly, if the temperature value is not automatically detected, you can manually enter the temperature value, and the electrode should be rinsed with deionized water.

The sample should be at the same temperature as the calibration buffer, because the pH reading depends on the temperature mentioned above. If the sample is not at 25°C, the temperature can be corrected.

The sample can be prepared appropriately, and the electrode should be cleaned with deionized water. After that, you can start reading. After putting the electrode into the sample solution, you can gently stir the sample at a steady and moderate speed.

After waiting for the reading to stabilize for 1-2 minutes, the reading can be recorded. If necessary, you can repeat these steps. Before each reading, rinse the electrode with deionized water.

Dr. Surat graduated with a doctorate degree. In 2016, he received a PhD in Cell Biology and Mechanical Biology from the Tata Institute of Basic Research (Mumbai, India). Before pursuing her Ph.D. degree, Surat studied for a Bachelor of Science in Zoology (B.Sc.), during which time she was a recipient of a summer scholarship from the Indian Academy of Sciences to study AIDS-related proteins. She has authored feature articles on a wide range of topics, such as medical ethics, data processing, pseudoscience and superstition, education, and human evolution. She is passionate about science communication and writes articles covering all fields of life sciences.  

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