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Calibration
If an ion meter is used e.g. PHM250 Ion Analyzer, the electrode
can be calibrated to display the lead ion concentration directly. The
PHM250 can perform a calibration on up to 9 calibration points. In
other cases, calibration can be based upon mV readings and on a
manually drawn calibration curve.
mV
-90
-120
-150
-180
-6
10
Shown above is an example of a calibration curve obtained with
ISE25Pb. The measured potentials are drawn on semi-logarithmic
paper against the lead ion concentration of the calibration stand-
ards used. To obtain the highest accuracy, the concentration
values of the standards must lie on either side of the concentration
values of the samples to be measured. Furthermore, the same
temperature should be used during the calibration and sample
measurement.
Note: due to the fact that the electrode sensitivity (slope) remains
relatively stable with time, it is normally only necessary to check
one point on the calibration curve e.g. by immersing the electrode
in a standard solution and comparing the measured potential with a
previous measurement.
-5
-4
-3
10
10
10
7
c
Pb
-2
-1
10
10
2+
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