What is a pH calibration slope, and what value should it be?

Document ID

Document ID TE486

Published Date

Published Date 08/18/2020
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Question
What is a pH calibration slope, and what value should it be?
Summary
pH Calibration Slope
Answer
The calibration slope is a conversion that the pH meter uses to convert the electrode signal in mV to pH. The meter determines the slope by measuring the difference in the mV reading of two different buffers and divides it by the difference in pH of the buffers.

For example:

If the electrode reads 2 mV in the 7 buffer, and 182 mV in the 4 buffer, the slope is (2-182)/(7-4) or -60 mV per pH unit. The theoretical slope value is -58 (+/- 3) mV per pH unit, so typically any value between -55 and -61 mv is acceptable for calibration.

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