Pulsed titration sensors: Part 1: A breath-by-breath CO 2 sensor

Abstract

A novel electrochemical sensor for the determination of CO 2 in expired breath is described. The sensor works by generating ▪ from the reduction of O 2 in dimethyl sulphoxide (DMSO) in a generating pulse. There is a rapid titration reaction between the ▪ and any CO 2 present. In the recovery pulse the amount of unreacted ▪ is determined. The larger the concentration of CO 2 the less ▪ is found in the recovery pulse. The solubilities and diffusion coefficients of O 2 and CO 2 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 CO 2 from a human subject.