Why are 4 pH and 7 pH buffers recommended over a 10 pH buffer for calibration of process pH sensors?

Document ID

Document ID TE2057

Published Date

Published Date 01/05/2022
Question
Why are 4 pH and 7 pH buffers recommended over a 10 pH buffer for calibration of process pH sensors?
Summary
process pH sensor calibration
Answer
A 2 point calibration is recommended for process pH sensors.  When deciding which 2 buffers to use we generally recommend choosing 4 and 7 pH buffers.
A 10 pH buffer solution will become unstable when it absorbs carbon dioxide (CO2) from the air. When CO2 is absorbed in water, it forms carbonic acid, which lowers the pH of the buffer.
To prevent potential problems from calibrating with inaccurate pH 10 buffer solutions, we recommend calibrating with 4 pH and 7 pH buffers. This establishes a slope value that will carry over to the high pH readings as well. 
If a 10 pH buffer is required or preferred we recommend using newly opened 10 pH buffer to avoid any change in pH and ensure accurate results.

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