A thin film, solid sate amperometric detector for mac oxide is provided based upon a mobile cation electrolyte that selectively transmits nitrosonium cations (NO.sup.+) therethrough. The presently most preferred embodiment employs NO-.beta.-alumina as the mobile cation electrolyte. The electrodes of the detector are preferably arranged in a bipotentiostat arrangement. The first and second working electrodes share a common reference electrode and a common counter electrode, which are positioned such that the potentials of the first and second working electrodes can be independently controlled. The first working electrode is exposed to a fluid (liquid or gaseous), whereas the second working electrode is normally isolated from the fluid. The first working electrode is set at a potential capable of oxidizing NO to NO.sup.+, the NO.sup.+ moves through the mobile cation solid electrolyte to the second electrode, and the second working electrode is set at a potential capable of reducing the NO.sup.+ back to NO. The detector has a diffusion barrier for the nitric oxide so that the voltage-current characteristics of the detector under diffusion limiting conditions are proportional to the concentration of nitric oxide in a fluid.
Charles K. Baker;Mohan R. A. Ram;Stephen T. Wellinghoff