IMPROVEMENTS IN A CHEMILUMINESCENT OZONE ANALYZER FOR RESPIRATORY APPLICATIONS

The performance characteristics of a previously developed analyzer utilizing the homogeneous chemiluminescent reaction of ozone (O3) with a stoichiometric excess of 2-methyl-2-butene were improved with the eventual goal of measuring the distribution of O3 in a single human breath. By increasing the sampling flow from 200 to 400 ml/min and utilizing a combination of analog and digital filtering, it was possible to improve the signal-to-noise ratio at 0.5 ppm O3 from 5.5 to 28, the minimum detection limit from 0.02 to 0.01 ppm, the sensitivity from 1.5 to 2.3 na/ppm, and the 10%-90% step-response time from 200 to 100 ms. Humidity, temperature, and inlet gas composition interferences were also evaluated. While temperature and humidity have no influence on the analyzer output, the substitution of carbon dioxide for oxygen increased the analyzer sensitivity by 3.8% for each percent of CO2 that was present. Thus, provided that an appropriate correction for carbon dioxide is made, these improvements allow the instrument to monitor inhaled and exhaled O3 concentrations with a rapid dynamic response and over a broad range of physiologically relevant values.