This paper reports absorption-based CO2 sensing of the pH-active Schiff base 2-[(2-hydroxymethylphenylimino) methyl]-5-bromo-phenol (SB) in an ethyl cellulose (EC) matrix with and without Teflon coating. The CO2 sensitivity of the SB dye in the EC matrix was evaluated in the presence of nonadecafluorodecanoic acid and tetrabutyl ammonium hydroxide. When exposed to CO2, the sensing films exhibited 76% of overall relative signal change and responded to CO2 over a wide range: 1%-100 % (v/v). However, the slope of the spectral response between 1% and 5% (v/v) is more significant. The response time (tau(90)) was 15 s, and limit of detection (LOD) was 0.3% (v/v) CO2. The stability of SB in the EC matrix was excellent, and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 6 months. Our stability tests are still in progress.