Siemens Rapidlab 1200 Operator's Manual page 57

Rapidlab 1200 Operator's Guide: System Overview and Intended Use
pCO
2
The pCO
Bradley.
measuring electrode and an internal reference electrode. The measuring electrode,
which is a pH electrode, is surrounded by a chloride bicarbonate solution. A
membrane permeable to gaseous CO
internal reference electrode, which contains a silver/silver chloride electrode
surrounded by the chloride-bicarbonate solution, provides a fixed potential.
1
2
3
Figure 1-31
As the sample comes in contact with the membrane, CO
chloride-bicarbonate solution, which causes a change in the hydrogen ion activity:
+
CO
2
The internal pH electrode detects the change in hydrogen concentration occurring
in the chloride bicarbonate solution and generates a half-cell potential. This
potential, when compared to the fixed potential of the reference electrode, results
in a measurement that reflects pH change in the chloride bicarbonate solution. The
change in pH is related to the log of the partial pressure of CO
Sensor
sensor is based upon the electrode described by Severinghaus and
2
8
The pCO sensor is a complete electrochemical cell that consists of a
2
Measuring electrode contact
Internal reference electrode contact (Ag/AgCl)
Sample path
pCO Sensor
2
↔ − + +
H O HCO H
2 3
separates this solution from the sample. The
2
diffuses into the
2
1-37
.
2
02087462 Rev. V