Estimation of the Interference in Multi-Gas Measurements Using Infrared Photoacoustic Analyzers

Abstract: Two methods were described to estimate interference in the measurements of infrared (IR) photoacoustic multi-gas analyzer (PAMGA). One is IR spectroscopic analysis (IRSA) and the other is mathematical simulation. An Innova 1412 analyzer (AirTech Instruments, Ballerup, Denmark) with two different filter configurations was used to provide examples that demonstrate the two methods. The filter configuration in Example #1 consists of methane (CH₄), methanol (MeOH), ethanol (EtOH), nitrous oxide (N₂O), carbon dioxide (CO₂), and water vapor (H₂O), and in Example #2 of ammonia (NH₃), MeOH, EtOH, N₂O, CO₂, and H₂O. The interferences of NH₃ as a non-target gas in Example #1 were measured to validate the two methods. The interferences of H₂O and NH₃ as target gases in Example #2 were also measured to evaluate the analyzer’s internal cross compensation algorithm. Both simulation and experimental results showed that the interference between the target gases could be eliminated by the internal cross compensation algorithm. But the interferences of non-target gases on target gases could not be addressed by the internal cross compensation, while they could be assessed by the IRSA and mathematical simulation methods. If the IR spectrum of a non-target gas overlaps with that of target gas A at filter A, it could affect not only gas A (primary interference), but also other target gases by secondary interference (because the IR spectrum of gas A overlaps with gas B at filter B and thus affects gas B measurements). The IRSA and mathematical simulation methods can be used to estimate the interference in IR PAMGA measurements prior to purchase or calibration of the unit.