An improperly calibrated pH sensor is detrimental to any process. During the pH calibration procedure, several key moments require careful consideration to ensure the utmost accuracy. Skipping a step or a moment of oversight can lead to various issues, both in terms of pH sensor performance and process integrity. Knowing what to avoid when conducting a calibration will contribute to the overall performance of the sensor and the accuracy of the measurement.

If you’re unfamiliar with the sensor calibration process itself, M4 Knick’s YouTube page has several helpful videos that walk through the calibrations of various different types of sensors.

1. Not Rinsing Between Buffers

Industrial pH sensors are highly sensitive to the solutions they come into contact with. When using buffer solutions to conduct a calibration, it is critical that the person performing the calibration properly rinse the sensor before transferring to another buffer. Cross-contaminating buffers can render that supply of buffer solution unusable if diluted enough. If the buffer solution is not properly cleaned from a sensor, it can alter the ionic activity around the measuring membrane, leading to inaccurate readings.

2. Not Allowing Sensors to Stabilize

When performing a calibration, you must allow the sensor to stabilize before transferring it to another buffer. Stabilization time can vary depending on the sensor’s condition, the integrity of the buffer, and temperature. These variables only account for a few minutes or seconds, but they critically impact the calibration’s accuracy and effectiveness.

3. Failing to Account for Temperature

It’s important to perform calibrations under fixed conditions to not disrupt any of the variables associated with calibration accuracy. As the sensor compensates for the different values of the buffers, it does so with a temperature compensation. Be sure to avoid moving your calibration setup from one room to another, and certainly not locations with stark differences in room temperature. If not using equipment that automatically accounts for buffer temperature, calibrators must be sure to do so manually through their meter. Refer to your buffer temperature table for accurate values at individual temperatures.

4. Improper Buffer Storage/Handling

Store buffers in tightly sealed containers and keep them at room temperature whenever possible. Cool, darkened places like supply closets or storage lockers are the recommended locations for buffer solutions. Direct UV exposure can advance the degradation of buffers, so avoiding direct sunlight is a useful tactic in extending the life of buffer solutions.  Additionally, be sure to place an adequate amount of buffer solution in a separate reservoir and discard it after the calibration. Dipping a sensor into a full bottle of buffer solution can lead to contamination of the buffer.

5. Inadvertent Static Charges

Inadvertent static charges can alter pH values. Some things that may cause this are using abrasive cloths or rags to clean the sensor between buffer solutions. Another method that may cause unwanted static charges is utilizing Styrofoam cups to dip the sensor in, whether with a buffer or as a cleaning method. We recommend plastic or glass containers to avoid the further potential for a static charge that could interfere with the calibration.

Properly calibrated sensors will contribute to extending the sensor’s service life, and maintain the integrity of your process accuracy. Avoiding the common mishaps listed above can help ensure that maximum, accurate uptime is maintained. For more helpful insights into maintaining accuracy, M4 Knick has various mindful checklists and blogs for guidance on keeping the integrity of your process’s liquid analysis needs.