40 CFR § 1065.369 - H2O, CO, and CO2 interference verification for photoacoustic alcohol analyzers.
(a) Scope and frequency. If you measure ethanol or methanol using a photoacoustic analyzer, verify the amount of H2O, CO, and CO2 interference after initial analyzer installation and after major maintenance.
(b) Measurement principles. H2O, CO, and CO2 can positively interfere with a photoacoustic analyzer by causing a response similar to ethanol or methanol. If the photoacoustic analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.
(c) System requirements. Photoacoustic analyzers must have combined interference that is within (0.0 ±0.5) µmol/mol. We strongly recommend a lower interference that is within (0.0 ±0.25) µmol/mol.