A Tunable Colorimetric Carbon Dioxide Sensor Based on Ion‐Exchanger‐ and Chromoionophore‐Doped Hydrogel

Abstract

We report here a colorimetric carbon dioxide (CO2) optode sensor with a polypropylene microporous membrane on top of a thin layer (30 μm) of polyurethane hydrogel. The diffusion of CO2 across the polypropylene membrane induced pH changes in the hydrogel containing a lipophilic indicator, a cation exchanger, and a cationic amine. The ratio of the indicator and the cation exchanger was successfully utilized to adjust the sensitivity of the CO2 response. Increasing the relative amount of the cation exchanger made the sensor much more sensitive to CO2 in the lower concentration range. Moreover, the carbarmic formation reaction between the primary amine and CO2 was investigated. The results indicated a very small contribution of carbarmic formation to the overall pH change. With a detection limit of 0.014 % for the CO2 partial pressure, the sensor was successful applied to monitor CO2 evolution during yeast catalyzed flour fermentation.