TPS MC-81 - Page 35

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12.6.2 The Slope of a pH Electrode
As mentioned above, a pH electrode produces 0 mV output at around 7.00 pH.
As the pH goes up, an “ideal” pH electrode produces -59mV/pH unit at 25
o
C As
the pH goes down, an ideal pH electrode produces +59mV/pH unit. In practice,
pH electrodes usually produce slightly less than this. The output of a pH
electrode is expressed as a percentage of an ideal electrode. For example, an ideal
electrode that produces 59mV/pH unit has “100% Slope”. An electrode that
produces 50.15mV/pH unit has “85% Slope” (see Figure 12-2).
-600
-400
-200
0
200
400
600
0 7 14
85% Slope at 25 oC
(50.15mV/pH)
100% Slope at 25 oC
(59mV/pH)
Response of pH Electrode, as a Function of Slope
Electrode Response (mV)
pH
Figure 12-2