Orion Benchtop pH/ISE Meter Instruction Manual
Determining Isopotential Points
124
Determining an Isopotential Point
1. Prepare several standards with concentration ranges over the
measuring range of the electrode.
2. Measure the millivolt value of the standards at room temperature,
i.e. 20-25°C.
3. Measure the millivolt value of each standard at 75°C.
4. Measure the millivolt value of each standard at 10°C.
5. On semi-logarithmic graph paper, plot the concentration values on
the log axis versus the millivolt values on the linear axis, as any
calibration curve would be drawn (see Figure on previous page).
6. The lines will intersect at the isopotential point. Read the
concentration off the graph for this point from the log axis. This
value is the isopotential point.
7. See previous instructions on how to adjust the isopotential point on
the Orion 920Aplus.
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