Hydrophobic membrane sensors for the optical determination of hydrogen chloride gas

The acid-base complexation reaction between the metal free porphyrin, H2TPP, and hydrogen chloride gas has been used as the basis for a chemical gas sensor. The porphyrin is incorporated into a thin silicone rubber membrane which provides the hydrophobic conditions needed for the operation of the sensor. Porphyrin fluorescence emission provides an optical probe for the measurement of sorbed hydrogen chloride gas. A kinetic method of operation achieves low ppm (at least 2 ppm) detection. Factors such as long term stability and humidity effects limit the use of the membranes and these are considered in detail. Good agreement has been obtained between the experimental response and the response generated by a diffusion controlled model. The membranes have also been found to show sensitivity to chlorine and nitrogen dioxide but not to sulphur dioxide.