NO, N2O, and O2 reaction kinetics: scope and limitations of the Clark electrode.

The Clark electrode, which has been commercially available for more than 50 years, is a robust first-generation sensor originally used to determine the concentration of dissolved oxygen. This paper describes a simple experimental setup employing the Clark electrode to measure low concentrations of aqueous solutions of dissolved nitric oxide (NO) (>5nM) and nitrous oxide (N2O) (>50nM) in addition to oxygen (>5nM). The Clark electrode is connected to a low-noise (home-built) amplifier interfaced via a 16-bit AD converter to a computer providing increased signal-to-noise performance. Owing to the robustness of the Clark electrode, experiments can be performed routinely and repeatedly even to 90-95 degrees, aiding, for example, in enzyme purification. The low noise enables determination of K M values for O2, NO, or N2O from a single trace. Analyses can be conveniently performed on pure enzymes or on membranes from psychrophilic, mesophilic, and (hyper)thermophilic microorganisms. The sensitivity for O2 and NO of the current apparatus approaches that of commercially available microelectrodes, while that for N2O is superior.