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IĆ14 800 Series Operator's Manual
Potassium, Chloride, and
Calcium Sensor
Sample Path
Silver/Silver Chloride
Wire
Electrolyte
Solution
Silver/Silver Chloride
Wire
Electrolyte Solution
Sample Path
Sodium Sensor
The recognition mechanism in the ISE is the membrane. Each sensor has a
membrane selective for the specific substance that it measures. To understand this
concept more clearly, take the case of the potassium sensor. The potassium sensor
membrane is designed as a charge separator. As shown in Figure I-9, the
positively-charged potassium ions selectively interact with the membrane when the
sample interfaces with the membrane. The negatively-charged chloride ions do not
interact with the membrane. The charge separation causes the membrane potential
that is measured by the electrochemical cell.
Electrolyte
Solution
Membrane
Electrode
Cl
-
Cl
-
Cl
-
Cl
-
Cl
-
Cl
-
Cl
-
Cl
-
Na
+
Na
+
Na
+
Cl
-
Cl
-
Cl
-
Cl
-
K
+
Cl
-
K
+
Na
+
Cl
-
Randomly
Oriented Ions
Internal Electrolyte
Solution
K
+
K
+
K
+
K
+
K
+
K
+
K
+
K
+
K
+
K
+
K
+