The development of new microelectrode gas sensors: An odyssey

The simultaneous electrochemical reduction of oxygen, carbon dioxide and nitrous oxide was investigated at Au microelectrodes (5 μm, diam.) in dimethyl sulfoxide (DMSO) solvent, using both voltammetric and potential step chronoamperometric techniques. In agreement with previous voltammetric studies, carbon dioxide is shown to react with the superoxide anion radical, formed from the electro-reduction of oxygen (−1.3 V vs. Ag). This cross-interference reaction complicates the simultaneous detection of all three gases. The presence of nitrous oxide, however, appears to give rise to no deleterious cross-interference reactions with either oxygen or carbon dioxide. By contrast, the use of potential step, chronoamperometric techniques are shown to effectively collapse the deleterious cross-interference reaction between superoxide and carbon dioxide (current enhancement <2%). In addition, potential step interrogation of the carbon dioxide reduction signal indicates a linear dependence on the concentrations of both oxygen and nitrous oxide. Meanwhile, interrogation of the nitrous oxide reduction signal reveals a proportional current enhancement with the stepwise addition of oxygen but no dependence on the concentration of carbon dioxide. In addition, a “proof of principle” practical sensor design incorporating a polytetrafluoroethylene (PTFE, Teflon®) membrane-covered gold microelectrode is described for the simultaneous measurement of oxygen, carbon dioxide and nitrous oxide over a wide concentration range.