A new highly sensitive and versatile optical sensing film for controlling CO2 in gaseous and aqueous media

We describe a CO2-selective sensing film based on the incorporation of a phase-transfer agent, tetraoctylammonium hydroxide (TONOH), into a fluorescence pH-sensitive functionalized polymer. This film can be used for CO2 determination in gaseous and aqueous media. We have investigated the effect of the concentration of TONOH, and the influence of external parameters such as flow rate, humidity and interfering gases (O2, CO and NO2). The sensing films respond to CO2 concentrations in the gas phase between 7.7 and 40% CO2 (v/v) and between 4.4 and 60% CO2 (v/v) in aqueous media, with detection limits of 2.3 and 1.3% CO2 (v/v), respectively. The covalent immobilization of the fluorescence pH-indicator on the polymer chains provides lower probability of aggregation and no leaching of the optical pH-sensitive dye. In addition, the developed sensing film quick response time (t95 = 5 s from 0 to 20% CO2 (v/v) in gas phase), good opto-thermal stability and high versatility. In order to demonstrate this claim, we have developed an optical fiber sensor. It shows good analytical properties (linear dynamic rage of 1.4–40% CO2 (v/v) with a detection limit of 0.4% CO2 (v/v).