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Maintenance of pH electrodes
A pH electrode is active and stable only after wetting!
For this purpose it must
be immersed for
at least ten hours
in a 3...4 M KCl solution. During short inter-
ruptions (e.g. storage) the electrode should be immersed in a 3...4 M KCl solution.
In doing this it is always kept ready for use. When the interruption is longer than
a month, refill the closing cap with 3...4 M KCl and plug it on the electrode tip in
order to protect the glass bulb. Before use, ensure that the reference part of the
electrode is topped up with a 3...4 M KCl solution.
Avoid a low pressure inside the electrode!
Therefore always remove the closure
from the refilling aperture during the measurements as well as during the calibra-
tion. This allows the saltbridge solution to flow through the ceramic liquid junction
and prevents contamination of the electrolyte. For the same reason, the inside
level should always be higher than the outside level of the measuring solution.
Close the refilling aperture again when storing the electrode.
A polluted electrode may be cleaned with a soft detergent or 0.1 M HCl. Greasy
substances may be removed with acetone or alcohol
(never do this with plastic
electrodes!)
.
If the electrode is polluted by proteinaceous materials (such as blood), it should
stand in a cleaning solution overnight and then be cleaned with distilled water
before use. The pH electrode wears away by being used. If the electrode tends to
respond slower and calibration becomes difficult, even after cleaning, it should be
replaced by a new one.
Maintenance of metal electrodes
Metal electrodes (Pt, Ag, Au):
Metal electrodes are always ready for use. During
short interruptions they are immersed in distilled water.
They should be cleaned
regularly:
• Silver electrodes are immersed in a concentrated ammonia solution during one
hour.
• Platinum or gold electrodes are immersed in concentrated nitric acid during
one hour.
Maintenance of conductivity electrodes
A conductivity cell is active and stable only after wetting!
For this purpose it
must be immersed for
at least one hour
in distilled water. Rinse the cell always
after use and store it in distilled water (add some detergent to keep the spongy
platinum surface in perfect condition).
A polluted cell may be cleaned with a soft detergent or diluted nitric acid. Greasy
substances may be removed with acetone or alcohol (never do this with plastic
electrodes!).
