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Chapter 5 Maintenance
Page 5-8 MAN 0318
As buffers are typically low cost items, it will be more economical to source from a
local supplier. If finding a convenient source proves difficult, contact the local Mal-
vern representative who will be able to give advice.
Common Problems
pH electrodes are versatile but their performance is dependent on the sample being
tested. For example, pH measurement of high purity water or liquids containing
sulphur ions will require special electrodes.

Slow response can often be caused by the build-up of deposits on the glass
membrane or frit. Initially, try cleaning the probe by dipping into concentrated
Nitric Acid for 10 seconds. If this is unsuccessful, repeat for one minute. If still
unsuccessful then regeneration may be possible by dipping the membrane for
one minute into a solution of 2% HF and 5% HCl whilst stirring. Should the
frit be blocked by proteins then try soaking the electrode in an appropriate
organic solvent, or a solution of 10% pepsin in 1M HCl. As such actions usu-
ally dehydrate the glass membrane, it will be necessary to soak overnight in 3M
KCl solution. If these actions are unsuccessful then the electrode will need to
be replaced.

Always ensure that the level of the electrode's electrolyte is above that of the
liquid under test. This will prevent electrolyte contamination, and ensure a
good electrical contact. With the blue rubber cover removed, the electrode uses
a small amount of electrolyte per day. When in continuous use, weekly top-ups
are recommended.
Replacing the dispensing syringes and o-ring
It is recommended that all three dispensing syringes and o-rings are replaced at
least every 12 months or sooner if leaks develop. Replacement syringes and o-rings
are available through the Malvern representative (see
User consumable and
spares at the end of this section).
To remove a syringe and o-ring:
1.
Turn off the accessory and remove the side cover.
2.
Manually push down the syringe mount.
3.
Pull the base of the syringe

out of the syringe mount, and then out from the
o-ring.
4.
Using a small screwdriver push the o-ring out of the manifold assembly

.
The o-ring will fall out the back of the manifold onto the base of the dispensing
area.
MAN0318-4.0 - MPT-2 Autotitrator-Degasser.book Page 8 Tuesday, September 4, 2012 12:15 PM