Optochemical HCl gas detection based on tetraphenylporphine dispersed in ethylcellulose

To detect sub-ppm levels of HCl gas spectral changes of tetraphenylporphine and derivatives dispersed in ethylcellulose were examined in the visible region. For free-base tetraphenylporphyrin the absorbance of the Soret and Q-bands are sensitive to sub-ppm levels of HCl and reversibility at room temperature. The Soret and Q-bands are also sensitive to vapours from aqueous solutions of HNO3, HF or HCOOH, while they are insensitive to vapours from CH3COOH or C2H5COOH and also to 1 ppm of NH3, Cl-2, NO2 and NO. The sensitivity can be modified by substituent groups and using different concentrations of porphyrin in the composite.