Impedance sensor for dissolved nitrogen oxide using a series piezoelectric crystal device

Abstract

An impedance sensor for the determination of nitrogen oxide in aqueous solution is presented. The sensor is realized by using a series piezoelectric crystal (SPC) device, which is constructed by connecting an AT-cut piezoelectric crystal with a probe in series. The probe is filled with an internal electrolyte solution that is separated from sample solutions by a gas-permeable membrane. Such a gas sensor based on the SPC device can overcome the influence of water vapour efficiently and can be used in the determination of nitrite in aqueous solutions. The proposed sensor exhibits a favourable frequency response to 5 × 10–7–1 × 10–3 mol l–1 nitrite. The limit of detection is 1 × 10–7 mol l–1. Aspects of the sensor preparation are considered. The dynamic range, reproducibility, response time and selectivity of the sensor are also discussed. The proposed sensor was used successfully for the determination of nitrite in smoked pork samples; the results obtained were comparable to those obtained by the official first action AOAC method. The technique described here should find wider application in the development of other gas and enzyme sensors.