This study integrated a Membrane Contactor (MC) with a Tedlar Bag Reactor (TBR) for continuous, real-time monitoring of dissolved CO₂ and its carbon isotope (δ¹³C) in deionized water (DIW). Experiments were conducted in two stages across three CO₂ concentrations (437, 7,940 ppmv, and 100%). Baseline CO₂ (437 ppmv) and δ¹³C levels were measured in the first stage, while the second stage involved observing changes after injecting 7,940 ppmv or 100% of CO₂ into the TBR. CO₂ and δ¹³C levels were tracked using Cavity Ring-Down Spectroscopy (CRDS) on gas samples extracted through the MC. CO₂ dissolution led to a significant pH decrease and an increase in electrical conductivity (EC), reflecting CO₂’s chemical interactions with water. δ¹³C values showed substantial variation at lower CO₂ concentrations, while higher CO₂ levels resulted in more stable δ¹³C values with clearer shifts. The findings suggest that the MC system is particularly effective for monitoring environments characterized by rapid and dynamic chemical changes, such as geological CO₂ storage, volcanic gas emissions, earthquake-related gas dynamics, and CO₂-rich waters. This research demonstrates that MC-based systems can enhance field applications by supporting continuous sampling and real-time dissolved gas analysis.

Keywords: Membrane Contactor (MC), Tedlar Bag Reactor (TBR), dissolved gas extraction sampling, dissolved CO₂ monitoring, dissolved carbon isotope