13
109117-1 Rev. A, 10/96
3
3.3.2 Electrode Maintenance (cont)
• 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 (25mm) 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.
Oil contamination - Carefully clean the tip of the
electrode using a cotton swab soaked with alcohol or
acetone. The tip of glass body electrodes can be put
directly into organic cleaners but do not put plastic or
epoxy body electrodes into organic solvents. Rinse the
electrode and soak in pH 7.0 buffer until stable.
All others - Soak tip of the electrode in 0.1 M
Hydrochloric acid for one hour. Rinse the electrode and
soak in pH 7.0 buffer until stable.
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