An electrode assembly used to measure PO2 consists of a silver/silver chloride anode, a platinum cathode, and a selectively permeable membrane separating the sample from an electrolyte. This design is used to measure which parameter?

• A. pH
• B. PCO2
• C. PO2
• D. HCO3

Answer: (C)

This arrangement is designed to measure oxygen partial pressure (PO2) because it uses a Clark-type oxygen electrode mechanism. Oxygen from the sample diffuses through the gas-permeable membrane into the electrolyte and is electrochemically reduced at the platinum cathode. The silver/silver chloride anode maintains a stable reference potential. The current produced by the reduction of O2 is proportional to the rate of oxygen diffusion, which in turn is proportional to the PO2 in the sample. This setup is specific for PO2 and isn’t used to measure pH, PCO2, or HCO3, which require different sensing chemistries or calculations.