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