Ionode IJ pH V5.1 - Manual (Page 8)

Ionode IJ Instruction Manual 8
Part of the circuit is electronic (heavy lines) (see
Figure 6). The remainder is ionic. Unlike other
pH electrode measuring systems which rely on
electron transfer such as antimony and
quinhydrone, the pH glass electrode is
insensitive to ORP.
pH glass is modified lithium silica which is a
lithium ion conductor at room temperature.
Hydrous glass ion exchange layers exist on
both sides of the membrane (see Figure 7 -
Figure 9). These allow reversible exchange
between hydrogen and lithium ions.
Equal concentrations of H
+
on either side of the
membrane causes no potential to develop
across the membrane (see Figure 7).
H
+
Li
+
H
+
Si
O
-
O
-
O
O
-
O O
-
Si
H
+
Li
+
H
+
Li
+
H
+
H
+
Cl
-
Cl
-
Cl
-
H
+
H
+
Cl
-
Li
+
Figure 7