1. Potentiometric measuring principles ABL800 FLEX Reference Manual
Electrolyte electrodes
The K electrode (E722) is an ion-
selective electrode whose sensing
element is a PVC membrane containing
a potassium-neutral ion carrier. The ion-
sensitive membrane is covered with a
cellophane membrane in order to
protect it from the samples.
The electrolyte has a constant and
known concentration of potassium ions.
When a sample is brought in contact
with the electrode, a potential develops
across the PVC and cellophane
membranes. The potential depends on
the difference between the potassium
(more precisely, activity) in the
electrolyte and the sample. If the
cK
+
in
both solutions is the same, the potential
across the electrode tip will be 0 V.
The Na electrode (E755) is an ion-
selective electrode whose sensing
element is a Na
+
-sensitive ceramic pin
contained in the tip of the jacket.
The electrolyte has a constant and
known concentration of sodium ions.
When a sample is brought in contact
with the electrode, a potential develops
across the ceramic pin. The potential
depends on the difference between the
sodium (more precisely, activity) in the
electrolyte and the sample. If the
cNa
+
in both solutions is the same, the
potential across the electrode tip will be
0 V.
Electrode contact
Description
Electrode jacket
Cellophane membrane
Cellophane membrane
Electrode contact
Electrode jacket
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1-22
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