PULSED TITRATION SENSORS .1. A BREATH-BY-BREATH CO2 SENSOR

A novel electrochemical sensor for the determination Of CO2 in expired breath is described. The sensor works by generating O2.- from the reduction Of O2 in dimethyl sulphoxide (DMSO) in a generating pulse. There is a rapid titration reaction between the O2.- and any CO2 present. In the recovery pulse the amount of unreacted O2.- is determined. The larger the concentration Of CO2 the less O2.- is found in the recovery pulse. The solubilities and diffusion coefficients of O2 and CO2 in DMSO have been determined using rotating disc voltammetry and rotation speed step experiments. The stoichiometry, the product, and the rate constant of the titration reaction have been determined using ring-disc voltammetry and laser Raman spectroscopy. The operation and the effect of adventitious water on the sensor are described. Results are presented which show that the sensor can indeed measure the breath-by-breath rhythm of expired CO2 from a human subject.