Infrared CO2 analyzer error: an effect of background gas (N-2 and O-2)

Three infrared CO2 analyzers were tested for the effect of background gases : the Ametek CD-3A (Ametek, Thermox Instruments Division, Pittsburgh, PA), the Drager Multiwarn P CO2 (Drager, Lubeck, Germany), and the Servomex 1440 (Servomex, Crowborough, East Sussex, UK). Various CO2 concentrations were prepared with Wosthoff precision pumps (H. Wosthoff, Bochum, Germany). Cali bration with a different background gas (O-2 or N-2) caused a similar but s ystematic error in the CO2 readings of all three analyzers. When the CO2 an alyzers were calibrated with N-2 as the background gas, the CO2 reading in an O-2-enriched atmosphere was 8% lower than the true value. Conversely, ca libration with O-2 as the background gas resulted in a 10% overestimation o f CO2 levels when N-2 was the background gas. This error may be important i n a few fields of respiratory physiology.