A method for continuous measurement of ammonia in respiratory airways

A method has been developed that can continuously measure respiratory NH3 with a detection limit of 30 parts per billion by volume (ppbv) at an averaging time of 1 s. The method is based on the chemiluminescent detection of NO, which is produced by oxidizing NH3 at 850 degrees C. A polyethylene sampling probe, incorporating a heated capillary tip bathed in dry, NH3-free diluent air, minimizes NH3 losses due to absorption in breath condensate. In one subject, flow and tidal volume were monitored during quiet mouth breathing while NH3 and CO2 were sampled at the lips. In 10 subjects, NH3, and CO2 were sampled at the lips during quiet mouth breathing ranged from 280 to 1,280 ppbv (mean plus or minus SE, 540 PLUS OR MINUS 85 PPBV).