BREATH-BY-BREATH MEASUREMENT OF CARBON-DIOXIDE USING A PLASTIC FILM OPTICAL SENSOR

An optical sensor has been developed for breath-by-breath gaseous CO2 analysis. The detector is based on a general formulation described in previous work where a phase-transfer agent, tetraoctyl ammonium hydrox ide, is used to incorporate a hydrophilic pH-sensitive dye into a hydr ophobic plastic film to create an effectively solid-state colorimetric sensor. In this work the formulation has been modified to yield a sen sor which is capable of responding to clinically important levels of C O2 (0.1-5%) in less than 200 ms. This is comparable with the response of commercially available capnometers based on infrared sensing of CO2 , which are currently widely used for clinical analysis. These films h ave good stability under the hot humid conditions involved in respirat ory gas monitoring (37 degrees C gas temperature, 100% humidity) and, when stored in a freezer, show no deterioration in performance over an 80 day period.