Box 17-1 Oxygen Sensors

02 in solution is measured amperometrically with a Clark electrode, in which a Pt cathode is held at —0.6 V with respect to a Ag AgCl anode. The cell is covered by a semipermeable membrane. across which 02 can diffuse in a few seconds. The current is proportional to the dissolved 02 concentration. 

The electrode must be calibrated in solutions of known 02 concentration. 

Clark oxygen electrode. [D. t. Sawyer, A. Sobkowiak, and J. L. Roberts, Jr., Electrochemistry for Chemists, 2nd eel. (New York Wiley. 1995).] A modern, commercial oxygen electrode is a three-electrode design with a Au cathode, a Ag anode, a Ag I AgBr reference electrode, and a 50-(im-thick fluorinated ethylene-propylene polymer membrane. Leland Clark, who invented the Clark oxygen electrode, also invented the glucose monitor and the heart-lung machine. 

Gradient of dissolved 02 near a cluster of cells measured by micro oxygen electrode. [S.-K. Jung. J. R. Trimarchi. R. H. Sanger, and PJ. S. Smith. Development and Application of a Self-Referencing Glucose Microsensor lor the Measurement of Glucose Consumption by Pancreatic i Cells, Anat. Chem. 

Carbon working electrode 2 coated with mediator but no enzyme 

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