Colorimetric and refractometric measurements of carbon dioxide

摘要

In this work, a polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative p-nitro-phenol is presented for carbon dioxide measurements. Thin films casted on glass slides were tested, using a LED source (λc at 410 nm) and an Ocean Optics USB4000 spectrometer, in the 0% to 15.25% CO_2 concentrations range, showing a 40% maximum transmittance variation with a 51s response time and a 0.15% resolution. Preliminary results indicate that CO_2 also induces refractive index changes in the sensitive layer. Using a fiber based interferometric setup, a CO_2 dependent refractive index change of ～0.045 RIU was observed, in the 0%-90% CO_2 concentration range.