Colorimetric polymer film sensors for dissolved carbon dioxide

Plasticized and unplasticized polymer colorimetric film sensors for gaseous CO2, containing the dye m-cresol purple, are tested as sensor for dissolved CO2. The plasticized polymer m-cresol purple film sensor develops a measurable degree of opacity when exposed to aqueous solution, especially in netural, compared with alkaline, solution. However, it is shown that a presoaked, fogged plasticized polymer m-cresol purple film does function as a quantitative sensor for dissolved CO2 over the range 0–4% CO2. An unplasticized polymer m-cresol purple film remains largely clear upon exposure to aqueous solution and also function as a quantitative sensor for dissolved Co2 over the range 0–4% CO2. However, in both of films the dye interacts with electrolytes present in solution; invariably the dye appears to be converted from its initial deprotonated form (blue) to its protonated form (yellow) and the rate of this process appears to increase with increasing ionic strength, anionic charge and decreasing pH. The 90% response and recovery times for an unplasticized film are determined as 19 s (CO2:O→5%) and 21 s (CO2:5→3.6%), respectively.