TUNING COLOURIMETRIC AND FLUOROMETRIC GAS SENSORS FOR CARBON-DIOXIDE

The basic theory behind conventional colourimetric and fluorimetric optical sensors for CO2 is examined and special attention is given to the effect on sensor response of the key parameters of initial base concentration and dye acid dissociation constant, K(D). Experimental results obtained in aqueous solution using a variety of different dyes and initial base concentrations are consistent with the predictions made by the theoretical model. A series of model-generated pK(D) versus %CO2 curves for different initial base concentrations allow those interested in constructing an optical CO2 sensor to readily identify the optimum dye/initial base combination for their sensor; the response of the sensor can be subsequently fine-tuned through a minor variation in the initial base concentration. The model and all its predictions appear also to apply to the new generation of plastic film CO2 sensors which have just been developed.