A novel flow-injection (FIA) system, for the rapid and direct determination of both total ammonia and total
carbon dioxide in clinical blood samples, has been developed. Samples were injected into a carrier stream of H2O, then emerged with a reagent stream, where the analyte was converted into a gaseous species and diffused across PTFE gas-permeable membrane into an acceptor stream. The trapped NH3/CO2 in the acceptor was determined on line by a bulk acoustic wave (BAW) impedance sensor. At a through-put of 20 and 65 h the proposed system exhibited a linear frequency response up to 200 mmol/l ammonium and 20 mmol/l bicarbonate with a detection limit of 1.0 and 10 mmol/l , respectively. Results obtained for TNH3 in serum and TCO2 in plasma were in agreement with those obtained by the conventional glutamate dehydrogenase (GDH) method and gas-sensing electrode method, respectively. The effects of composition of acceptor stream, cell constant of conductivity electrode, sample volume,flow rate and potential interferents on the FIA signals were also discussed.