40 CFR § 1065.366 - Interference verification for FTIR analyzers.
(a) Scope and frequency. If you measure CH4, C2H6, NMHC, or NMNEHC using an FTIR analyzer, verify the amount of interference after initial analyzer installation and after major maintenance.
(b) Measurement principles. Interference gases can interfere with certain analyzers by causing a response similar to the target analyte. If the 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. An FTIR analyzer must have combined interference that is within ±2% of the flow-weighted mean concentration of CH4, NMHC, or NMNEHC expected at the standard, though we strongly recommend a lower interference that is within ±1%.
(d) Procedure. Perform the interference verification for an FTIR analyzer using the same procedure that applies for N2O analyzers in § 1065.375(d).