FLOW-INJECTION DETERMINATION OF TOTAL AMMONIA AND TOTAL CARBON-DIOXIDE IN BLOOD BASED ON GAS-DIFFUSION SEPARATION AND WITH A BULK ACOUSTIC-WAVE IMPEDANCE SENSOR

A novel flow-injection (FIA) system, for the rapid and direct determin ation of both total ammonia (T-NH3) and total carbon dioxide (T-CO2) i n clinical blood samples, has been developed. Samples were injected in to a carrier stream of H2O, then emerged with a reagent stream, where the analyte was converted into a gaseous species and diffused across a PTFE gas-permeable membrane into an acceptor stream. The trapped NH3/ CO2 in the acceptor was determined on line by a bulk acoustic wave (BA W) impedance sensor. At a through-put of 20 and 65 h(-1), the proposed system exhibited a linear frequency response up to 200 mu mol l(-1) a mmonium and 20 mmol l(-1) bicarbonate with a detection limit of 1.0 an d 10 mu mol l(-1), respectively. Results obtained for T-NH3 in serum a nd T-CO2 in plasma were in agreement with those obtained by the conven tional glutamate dehydrogenase (GDH) method and gas-sensing electrode method, respectively. The effects of composition of acceptor stream, c ell constant of conductivity electrode, sample volume, flow rate and p otential interferents on the FIA signals were also discussed. (C) 1998 Elsevier Science B.V.