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Maintenance Chapter 5
MPT-2 & Degasser Page 5-5
If the probe has become dry, then it may be possible to recover the performance by
soaking the probe overnight in a solution of 0.1M hydrochloric acid. However, the
performance may never fully recover and there may be no alternative except to
replace the pH probe.
Cleaning the pH probe
The probe should be periodically cleaned. The calibration procedure detailed
below will indicate whether the probe requires cleaning.
Chemical cleaning is usually sufficient. To chemically clean, soak the probe over-
night in a solution of 0.1M hydrochloric acid, then use a soft tissue soaked in iso-
propanol and wipe over the end of the probe. Once cleaned, re-calibrate the probe
to see if its performance has recovered.
Some probes have a PTFE 'wick' which is fibrous. This is more easily wetted than
the ceramic junction but can become clogged by very fine particles in the disper-
sion.
When this happens, the pH probe will not respond to pH changes in the sample.
Carefully brushing this wick can recover performance.
This effect is reduced by using more dilute samples.
Calibrating the pH probe
The performance of the titrator relies on the pH probe being correctly calibrated. If
the pH probe has not been calibrated then the pH values will be incorrect.
It is recommended that the pH probe is calibrated before each titration session.
To calibrate the pH probe the following is needed:

At least two pH buffers. The default buffers are pH 4 and pH 9 (these are sup-
plied with the probe). See
Choosing the buffers when calibrating later in
this section for advice on selecting buffers. A maximum of four buffers can be
used for the calibration.

A container of clean deionised water to rinse the probe between measurements.
Ideally, the pH probe should be calibrated while fitted to the system and using the
standard sample containers.
Note
The pH probe should be recalibrated if the room temperature changes by
more than 5°C.
MAN0318-4.0 - MPT-2 Autotitrator-Degasser.book Page 5 Tuesday, September 4, 2012 12:15 PM