15
109118-1 Rev. A,10/96
3.3
Maintenance
3.3.1
Meter Maintenance
The Model 440 needs no maintenance except for an occasional
wipe with a damp cloth. The front panel is made of polyester and
is not affected by most solvents. Polyester is known to be affected
by some organic solvents, including toluene, xylene and methyl-
ethyl-ketone. It is good laboratory practice to wipe away any
spillages as soon as they occur.
3.3.2
Electrode Maintenance
CAUTION
Solutions used to clean electrodes must be handled
with the care accorded to toxic or corrosive
substances.
•
Do not allow the reference chamber of the electrode to dry
out. Always keep it filled with the proper fill solution.
•
Formation of KCl salt at the tip and side of the electrode is
normal and should be rinsed off with warm water.
•
Leave the tip of the electrode in an inch (25 mm) of pH 7.0
or 4.0 buffer when it is not being used. Do not leave it in
distilled water. For long term storage follow the electrode
manufacturer's instructions.
•
If the electrode slope is off or the electrode response has
become sluggish or inaccurate, change the fill solution. If
that does not improve the response then the pH sensing
glass and the junction have probably become coated with
some of the samples being tested.
•
Test the junction for flow - rinse the tip of the electrode,
blot dry and let the electrode hang in the air for 15
minutes. A proper flowing junction should have KCl salt
crystals forming on it. If none appear, review the following
suggestions for cleaning.
Protein contamination - soak the tip of the electrode for
1-2 hours in a solution of 10% Pepsin and water with
enough Hydrochloric acid added to bring the pH of the
solution to 1.0. Rinse the electrode and soak in pH 7.0
buffer until stable.
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