Method 25A
Determination of Total Gaseous Organic Concentration Using a Flame Ionization Analyzer
40 CFR Part 60, Appendix A-7
From the method — regulatory text
Sections 1.0 and 2.0 of Method 25A—Determination of Total Gaseous Organic Concentration Using a Flame Ionization Analyzer, as published at 40 CFR Part 60, Appendix A-7. Retrieved 10/07/2026. The full method is on the eCFR.
1.0 Scope and Application
1.1 Analytes.
| Analyte | CAS No. | Sensitivity |
|---|---|---|
| Total Organic Compounds | N/A | <2% of span. |
1.2 Applicability. This method is applicable for the determination of total gaseous organic concentration of vapors consisting primarily of alkanes, alkenes, and/or arenes (aromatic hydrocarbons). The concentration is expressed in terms of propane (or other appropriate organic calibration gas) or in terms of carbon.
1.3 Data Quality Objectives. Adherence to the requirements of this method will enhance the quality of the data obtained from air pollutant sampling methods.
2.0 Summary of Method
2.1 A gas sample is extracted from the source through a heated sample line and glass fiber filter to a flame ionization analyzer (FIA). Results are reported as volume concentration equivalents of the calibration gas or as carbon equivalents.
EssentialRegs notes
Our plain-English reading of Method 25A. Not the method text.
What it measures
The total concentration of gaseous organic compounds in a gas stream, measured continuously as total hydrocarbons.
How it works
A sample of the gas is drawn continuously to a flame ionization analyzer, which burns the sample in a hydrogen flame and measures the electrical signal produced by the organic compounds. The reading is a single total, expressed as the compound used to calibrate the instrument, and it does not separate one hydrocarbon from another. The instrument is calibrated with gases of known concentration and checked for drift before and after the test.
Equipment
A flame ionization analyzer (FIA), also called a total hydrocarbon analyzer, with a sampling probe and line, a data recorder and calibration gases.
When a rule cites it
Performance tests of control devices such as enclosed flares, enclosed combustors and thermal oxidizers, where the organic concentration entering and leaving the device is measured to show a destruction efficiency or an outlet concentration limit. It is also used for total organic concentration in process vents.
Notes for compliance staff
Method 25A includes methane in its total, since the analyzer responds to it, and it identifies no individual compounds; Method 18 is used where a compound must be measured by itself. A destruction efficiency also needs the gas flow at the inlet and outlet, usually from Methods 1 through 4.
Cited by
Provisions in the corpus whose text cites Method 25A. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
Regulation 31
40 CFR Part 60 Subpart JJJJ
- § 60.4244(g)
- Table 2 to Subpart JJJJ of Part 60 — Requirements for Performance Tests
40 CFR Part 60 Subpart OOOO
40 CFR Part 60 Subpart OOOOa
40 CFR Part 60 Subpart OOOOb
40 CFR Part 60 Subpart OOOOc
40 CFR Part 63 Subpart ZZZZ
- § 63.6630(e)(4)
- § 63.6640(c)(4)
- Table 4 to Subpart ZZZZ of Part 63 — Requirements for Performance Tests
The sections marked as regulatory text above are reproduced from the CFR. Everything under ‘EssentialRegs notes’ is our reference copy, not the method. The method as published in the CFR controls.