Malvern MPT-2, User Manual, Page: 60 / 85

Chapter 5 Maintenance
Page 5-4 MAN 0318
Preparation before first use
1.
Remove the screw end-cap and connect to the cable supplied.
2.
Remove the membrane protection teat. This teat contains a small amount of
saturated KCl solution (3.8M).
3.
To allow air pressure equalization in the reference junction part of the probe,
remove the rubber cover, or sleeve that covers the reference junction vent.
4.
Check that the reference electrolyte is about 1cm below the level of the open-
ing. Top up with the electrolyte supplied if necessary.
5.
Check that there are no air bubbles within the inner glass membrane. Bubbles
may be removed by shaking the electrode using a similar action used with a
clinical thermometer.
Keeping the pH probe wet
If the pH probe is allowed to dry out, even for short periods, the performance of
the probe can be severely affected. It may not be possible to recover a degraded pH
probe.
Typically, when the probe is immersed in a buffer solution, the pH should be
attained (to within 0.1 of the pH) within 10 seconds. If this time exceeds 30 sec-
onds, and the probe cannot be recovered, then the probe should be replaced.
When changing the sample container, do not allow the probe to be exposed to air
for more than 20 seconds. Make sure that the next sample container is ready to
attach, or alternatively have a spare container of storage solution available.
pH probe storage
The pH probe can be stored in water or a soaking solution. A soaking solution is a
liquid that the probe can be immersed in to prevent it from drying out. The follow-
ing guidelines should be followed when using a pH probe:

The probe can be immersed in the sample solution for short periods (a few
hours).

The probe can be immersed in tap water for the up to a day. (Do not use de-
ionised water as it will destroy the charge equilibrium of the glass electrode).

For long periods (more than a day) the probe should be immersed in either a
dilute acid solution (pH 2 to pH 4) or an acidic buffer such as pH 4.

If the electrode is not being used for a period of, say, more than a week, then it
is advisable to protect the glass membrane by replacing the protective rubber
teat containing a small quantity of the electrolyte solution. It is best to squeeze
the end of the teat first to make it easier to slide on and also to prevent electro-
lyte being forced back into the probe.
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