How to calibrate pH sensors for measuring pH in water
Katarzyna Szczepocka-Kus, courtesy of Mettler Toledo | July 05, 2024Maintaining water quality involves monitoring its pH levels. A pH sensor is a vital tool in measuring acidity or alkalinity, but how do we ensure that we are using it correctly to achieve measurement precision? Calibration is the answer!
This article will show users how to calibrate a pH sensor in a few simple steps. This will ensure that the sensor is functioning optimally and providing reliable results.
1. Preparing for calibration
Turn on the pH meter:
The first step in calibrating a pH sensor is to plug in power supply and turn on the pH meter. Make sure the electrode is well attached. As the second step, connect the pH sensor. If the sensor is ISM (intelligent sensor management) enabled, it will be automatically recognized.
Rinse the electrode, dab it dry: The electrode should be rinsed thoroughly with distilled water to remove any residue from storage solution. Dab the electrode dry with a clean tissue paper.
Buffer preparation: A three-point calibration is recommended. Buffer solutions with three different pH values (pH 4.01, 7.00 and 9.21) should be available for calibration to bracket the expected pH, which is around 7.00 in this case. The first buffer should have a pH of 4.01, which is considered acidic, the second buffer should be 7, neutral and then a pH buffer of 9.21.
It is essential to ensure that the buffers are at the same temperature as the pH meter since pH readings are temperature-dependent. To calibrate the pH meter, pour each buffer into separate beakers or use single use sachets. Buffers should not be kept in a beaker for more than two hours and should be discarded after use. It is not recommended that they be returned to their original container.
Source: Mettler Toledo
2. Calibration process
1. First calibration point (4.01): Dip the electrode into the pH 4.01 buffer solution and start calibration. Allow the reading to stabilize. Rinse the electrode with distilled water and dab it dry.
2. Second calibration point (7.00): Dip the electrode into the pH 7.00 buffer solution. Allow the reading to stabilize and take the second calibration point. Rinse the electrode with distilled water and dab it dry.
3. Third calibration point (9.21): Dip the electrode into the pH 9.21 buffer solution and start the calibration. Allow the reading to stabilize.
When three calibration points are taken, the meter will calculate raw values to calibration curve data: slope and offset. If the slope is in the range of 90% to 105% and the offset is +/-15 mV - the sensor is in excellent condition.
Source: Mettler Toledo
3. Measurement
Calibration data: Using the values obtained from the three calibration points. The meter will use automatically calibrated data from the segment where the pH value of the sample lies.
Source: Mettler Toledo
Measure the sample: Dip the electrode into the water sample and start measurement. Allow the reading to stabilize.
Show measurement data: The pH measurement data will be saved automatically.
Calibrating a pH sensor is an essential step in ensuring accurate pH measurement in water. The steps outlined above should be followed precisely, and the calibration data should be entered into the pH meter according to the manufacturer’s instructions. By following these steps, you can ensure the accuracy and reliability of your pH measurements in water.
Download our free calibration poster for a quick and easy guide on how to perform pH calibration. Also, click here to learn more about the buffers and solution selection to perfectly match your specific application.
To contact the author of this article, email pHmatters@mt.com