17.3.3 Temperature Compensation
The slope of a pH electrode is affected by temperature. This effect is compensated for either by
using an Automatic Temperature Compensation (ATC) probe. Figure 17-3 shows the slope of a pH
electrode at various temperatures.
-600
-400
-200
0
200
400
600
0 7 14
Electrode
Potential (mV) at
0 oC (54mV/pH)
Electrode
Potential (mV) at
50 oC (64mV/pH)
Electrode
Potential (mV) at
100 oC
(74mV/pH)
pH Electrode Response, as a Function of Temperature
pH
Figure 17-3
17.3.4 Checking the reference junction of a pH electrode
If pH readings are inaccurate or unstable, the reference junction of the electrode may be blocked.
The following test can be performed to determine if the reference junction of a pH electrode is
making adequate contact with the sample solution.
1. Calibrate the 90-FL, as per section 6.2.
2. Dilute 1 part of pH6.88 buffer with 9 parts of distilled water.
3. Measure the pH of the diluted buffer. The result should be 7.06 +/-0.05 pH.
4. If the value obtained is outside of these limits, then clean the reference junction as per the
instructions supplied with the pH electrode.
5. Re-calibrate the 90-FL and repeat the test.
6. If the value obtained is still outside 7.06 +/-0.05 pH, then the electrode should be replaced.
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