Potentiometric oxygen sensor based on mixed potential of cobalt wire electrode

A novel and simple potentiometric oxygen sensor suitable for the measurement of partial pressure of oxygen (Po2) in flowing blood is described. The sensor is based on measuring a steady-state mixed potential that originates at the surface of a cobalt wire electrode. This mixed or corrosion potential arises from the slow oxidation of cobalt and simultaneous reduction of oxygen at the electrode surface, and changes as a function of sample Po2 levels. The probe is fabricated with an outer gas permeable silicone rubber tubing (1.06 mm o.d.), which contains an internal buffer solution (25.0 mM potassium hydrogen phthalate, pH 4.0, containing 1.0 mM KCl), a cobalt wire (0.1 mm o.d.) as the working electrode and an Ag/AgCl wire as the reference electrode. The sensor characteristics (slope, detection limits, linear range, drift rates, etc.) along with the response mechanism based on mixed potential are discussed in detail. In vitro evaluation of catheter forms of the sensors performed in a blood loop indicate that the proposed sensor design can closely follow Po2 changes induced in blood during 2–3 h of continuous monitoring.