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18.1.5 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 smartCHEM-Titro, as per section 4.4.
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 smartCHEM-Titro and repeat the test.
6. If the value obtained is still outside 7.06 +/-0.05 pH, then the electrode should be replaced.
18.1.6 Determining if an instrument or electrode is faulty
The following test can be performed to help determine if the smartCHEM-Titro or the pH or
Redox electrode is faulty.
1. Initialise the smartCHEM-Titro (see section 15).
2. Disconnect the pH or Redox electrode from the main pH/mV/Ion BNC connector.
3. Connect the centre pin of the main pH/mV/Ion BNC connector with the outside frame of the
connector, using a short piece of wire or a paper clip etc.
4. The meter should display approximately pH7.00, depending on the current calibration settings.
5. If the smartCHEM-Titro is operating correctly, the reading should be totally stable with the
wire firmly in place. If not, the meter requires servicing.
6. Now carefully disconnect the wire from the centre pin only (make sure the other end of the
wire remains connected to the outside frame of the connector).
7. The reading should steadily drift away from 7.00 (either up or down) at a rate of approximately
1 pH or less every 3 seconds. If the drift rate is faster than this, then input circuitry of the
smartCHEM-Titro is faulty and requires servicing.
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