40 CFR § 1065.366 - Interference verification for FTIR analyzers.

---
identifier: "/us/cfr/t40/s1065.366"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1065.366 - Interference verification for FTIR analyzers."
title_number: 40
title_name: "Protection of Environment"
section_number: "1065.366"
section_name: "Interference verification for FTIR analyzers."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "U"
subchapter_name: "AIR POLLUTION CONTROLS"
part_number: "1065"
part_name: "ENGINE-TESTING PROCEDURES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401-7671q."
regulatory_source: "70 FR 40516, July 13, 2005, unless otherwise noted."
cfr_part: "1065"
---


# 1065.366 Interference verification for FTIR analyzers.

(a) *Scope and frequency.* If you measure CH<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, NMHC, or NMNEHC using an FTIR analyzer, verify the amount of interference after initial analyzer installation and after major maintenance.

(b) *Measurement principles.* Certain species can interfere with 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, a correct result depends on simultaneously conducting 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 CH<sub>4</sub>, 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 N<sub>2</sub>O analyzers in § 1065.375(d).

[81 FR 74168, Oct. 25, 2016, as amended at 89 FR 29801, Apr. 22, 2024]