The Clark electrode was invented by Leland Clark after criticism that his bubble oxygenator, which he had invented for use in cardiac surgery, was unable to measure the oxygen tension of the blood returning to the patient from the bypass circuit. The electrode has several components: a platinum cathode (electron receiver), silver anode (electron donor), electrolyte solution (typically KCl), impermeable membrane and a voltage source. The silver anode is submersed in the electrolyte solution, which is typically KCl. The silver interacts with the KCl to produce the following reaction: 2KCl + 2Ag → AgCl + 2K+ + 2e-. The platinum cathode utilizes the electrons produced from this reaction to reduce the oxygen from the sample being tested via the following equation: ½ O2 + 2e- + H2O → 2 OH-. The more oxygen that is available to carry out the reaction, the greater the flow of electrons (i.e. a higher current). Therefore, the Clark electrode uses amperometry to determine the oxygen tension of the sample being tested.
It is important to commit the following to memory:
- pO2 is measured via the Clark electrode (as per above)
- pCO2 is measured via the Severinghouse electrode
- pH is measured via the Sanz electrode