Humidity-Independent Solid-State Amperometric Sensor for Carbon Monoxide Based on an Electrolyte Prepared by Sol−Gel Chemistry

An amperometric sensor consisting of a film of silica gel over an interdigitated microsensor electrode provided a humidity-independent response to CO over the range of 9%-76% humidity. The residual solvent contents were in the 20%-50% range, depending on the age of the gels and the humidity. Variations in this range did not change the sensitivity. Gaseous CO was quantified in the absence of a contacting liquid phase using either linear scan voltammetry (LSV) or flow injection amperometry (FIamp) at constant applied potential. With LSV after a 2-min exposure to the sample, sensors with gels aged for 28-40 days yielded sensitivities of 0.38, 0.41, and 0.38 nA/ppmv for measurements at 9%, 33%, and 76% humidity, respectively; the corresponding correlation coefficients were 0.992, 0.995, and 0.999. The detection limit with FIamp was 5 ppmv.