Direct Detection of Aqueous CO₂ by Infrared Waveguide Spectroscopy with an Amorphous Fluoropolymer Coating Rod

Infrared waveguide spectroscopy using a sapphire rod coated with an amorphous fluoropolymer (Cytop, Asahi Glass Co., ltd, Japan) has been developed in order to directly observe CO₂ in aqueous solutions. Since the amorphous fluoropolymer has a relatively high gas-permeability and hydrophobic feature, the aqueous CO₂ transmits into the amorphous fluoropolymer coating film, but water cannot penetrate into the film. Good linearity of calibration curves for CO₂ in the gas and the aqueous solution were obtained.