65
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
mV
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.