Continuous Conductometric Sensor for Carbon Dioxide

A continuous conductometric sensor is described for the determination of carbon dioxide in the atmosphere and innonacidic and nonbasic gases. Gaseous carbon dioxide diffuses through a hydrophobic, gas-porous membrane into a thin layer of pure water. The back wall of the thin water layer is a porous screen that separates the water layer from a mixed-bed ion exchanger column. The ion exchanger continuously removes ionic species from the water layer including the products from the dissociation of CO₂(aq). Conductivity electrodes positioned in the thin water layer measure its conductance. The diffusion of carbon dioxide through the membrane into the thin water layer and the removal of ionic species through the screen by the mixed-bed ion exchanger establish a steady-state concentration gradient of CO₂. This gradient is proportional to the partial pressure of CO₂ In the gas phase, and cell conductance is proportional to Pco₂^1/2-This device was evaluated for use in the determination of carbon dioxide levels up to -1% and conformed to the theoretical predictions.