Non-Severinghaus Potentiometric Dissolved CO2 Sensor with Improved Characteristics

Abstract

A new type of carbon dioxide sensor comprising a pH glass electrode measured against a carbonate-selective membrane electrode based on a tweezer type carbonate ionophore is presented here for the first time. No cumbersome liquid junction based reference element is utilized in this measurement. The sensor shows an expected Nernstian divalent response slope to dissolved CO₂ over a wide range covering the routine environmental and physiological PCO₂ levels. Unlike the conventional Severinghaus CO₂ probe for which the response is substantially delayed to up to 10 min due to diffusion of carbon dioxide into the internal compartment, the ion-selective CO₂ sensor proposed here shows a response time (t_95%) of 5 s. When used together with a traditional reference electrode, the sensor system is confirmed to also monitor sample pH and carbonate along with carbon dioxide. A selectivity analysis suggests that Cl^– does not interfere even at high concentrations, allowing one to explore this type of sensor probe for use in seawater or undiluted blood samples. The CO₂ probe has been used in an aquarium to monitor the CO₂ levels caused by the diurnal cycles caused by the metabolism of the aquatic plants and shows stable and reproducible results.