Oxygen eletrode
(aka Clark electrode)
Form of polarographic electrode
Setup
Cathode: platinum
Anode: Silver/silver chloride (silver wire in silver chloride gel)
Solution: KCl
Voltage: 0.6V applied
Current flow depends on oxygen concentration
At cathode,
O2 + 4e + 2H2O
--> 4OH-
Temperature kept at 37C
NB:
- Voltage applied vs current produced curve is not linear
- 0.6V is used because it is the middle of the plateau (from 0.4 to 0.8V)
* Minimise any error
* Current vs pO2 is linear at 0.6V
Method
- Clark electrode has a thin plastic membrane which separates the electrolyte solution from blood sample.
- Oxygen diffuses across the membrane into the electrolyte solution.
Disadvantage
- False high readings with some oxygen electrode when halothane is present, because it is also reduced
- Low readings may result from presence of microorganisms on the electrode
Other points
- Calibration is by zeroing in humidified nitrogen gas.
- Accuracy: +/- 2mmHg