Kinetic response of an oxygen-selective electrode evaluated for the quantification of oxygen

An evaluation of the transient response of a membrane-based amperometric electrode for the quantification of oxygen in aqueous and gaseous phases is described. Data collected during the early part of the responses are used to compute the steady-state signals that would be measured if the responses were monitored to steady state. Both first-order and variable-order models were used successfully to fit data for aqueous samples; only the variable-order model worked successfully with data for gaseous samples. Because the shapes of response curves did not permit steady-state signals to be measured, comparisons are based on measured values of current at fixed times in each response. The slopes of computed vs. measured signals varied from 0.90 to 1.03 for fits of data over 3–5 half-lives with both models. Calibration graphs of computed current vs. concentrations were linear for similar fitting ranges and the least-squares parameters were similar to those for current measured at different fixed points in time.