Development of high sensitivity potentiometric NOx sensor and its application to breath analysis

Using a combination of similar potentiometric sensors connected in series, a strategy for measuring NO at ppb concentrations has been demonstrated. Sensors numbering from 2 to 20 were fabricated, with each sensor based on YSZ electrolyte with WO3 sensing electrode and Pt-zeolite/Pt as the reference electrode. Use of a catalytic filter allows for the cancellation of interferences due to oxidizable gases, such as CO. The optimum operating temperature of the filter and sensor was determined to be 250 and 425 °C, respectively. For human breath samples, the interference from water was acute enough that only scrubbing through a dry ice/acetone bath led to adequate performance for detection of NO in the 5–80 ppb range with a 20-sensor array. A more practical strategy suitable for clinical analysis was demonstrated by using water saturated air as the background gas. A linear calibration curve in the range suitable for use in clinical analysis is demonstrated.