A novel gas-diffusion/flow-injection system coupled with a bulk acoustic wave impedance sensor for total inorganic carbonate and its application to determination of total inorganic and total organic carbon in waters

A novel flow-injection analysis (FIA) system has been developed for the rapid and selective determination of total inorganic carbonate (TIC). The method is based on the diffusion of CO2 across a PTFE gas-permeable membrane from a stream of 0.5 mol 1−1 H2SO4 (0.50 ml min−1) and H2O (0.50 ml min−1) merging into a stream of 10 mM tris(hydroxymethylamino)methane containing 0.5 mM KCl (1.00 min min−1). The CO2 trapped in the acceptor solution is determined on-line by a bulk acoustic wave impedance sensor and the signal is proportional to the concentration of TIC present in the original samples. The proposed system was applied to the direct determination of TIC in natural and waste waters and the indirect determination of the total organic carbon content based on wet chemical oxidation of the samples, it exhibited a linear frequency response up to 20 mM bicarbonate with a detection limit of 10 μM, and the precision was better than 1% (RSD) at a throughput of 45 samples per hour. The effects of composition of acceptor stream, cell constant of the conductivity sensor, sample volume, flow rates and potential interferents on the FIA signals were discussed in detail.