Method 18
Measurement of Gaseous Organic Compound Emissions By Gas Chromatography
40 CFR Part 60, Appendix A-6
From the method — regulatory text
Sections 1.0 and 2.0 of Method 18—Measurement of Gaseous Organic Compound Emissions By Gas Chromatography, as published at 40 CFR Part 60, Appendix A-6. Retrieved 10/07/2026. The full method is on the eCFR.
1.0 Scope and Application
1.1 Analyte. Total gaseous organic compounds.
1.2 Applicability.
1.2.1 This method is designed to measure gaseous organics emitted from an industrial source. While designed for ppm level sources, some detectors are quite capable of detecting compounds at ambient levels, e.g., ECD, ELCD, and helium ionization detectors. Some other types of detectors are evolving such that the sensitivity and applicability may well be in the ppb range in only a few years.
1.2.2 This method will not determine compounds that (1) are polymeric (high molecular weight), (2) can polymerize before analysis, or (3) have very low vapor pressures at stack or instrument conditions.
1.3 Range. The lower range of this method is determined by the sampling system; adsorbents may be used to concentrate the sample, thus lowering the limit of detection below the 1 part per million (ppm) typically achievable with direct interface or bag sampling. The upper limit is governed by GC detector saturation or column overloading; the upper range can be extended by dilution of sample with an inert gas or by using smaller volume gas sampling loops. The upper limit can also be governed by condensation of higher boiling compounds.
1.4 Sensitivity. The sensitivity limit for a compound is defined as the minimum detectable concentration of that compound, or the concentration that produces a signal-to-noise ratio of three to one. The minimum detectable concentration is determined during the presurvey calibration for each compound.
2.0 Summary of Method
The major organic components of a gas mixture are separated by gas chromatography (GC) and individually quantified by flame ionization, photoionization, electron capture, or other appropriate detection principles. The retention times of each separated component are compared with those of known compounds under identical conditions. Therefore, the analyst confirms the identity and approximate concentrations of the organic emission components beforehand. With this information, the analyst then prepares or purchases commercially available standard mixtures to calibrate the GC under conditions identical to those of the samples. The analyst also determines the need for sample dilution to avoid detector saturation, gas stream filtration to eliminate particulate matter, and prevention of moisture condensation.
EssentialRegs notes
Our plain-English reading of Method 18. Not the method text.
What it measures
The concentrations of individual gaseous organic compounds in an exhaust gas or process stream, identified and measured by gas chromatography.
How it works
A gas sample is separated into its component compounds in a gas chromatograph, and a detector measures each compound as it emerges. The method lets the tester choose how the sample is collected, such as by direct connection to the instrument, by dilution, in a sample bag, or on adsorption tubes, depending on the compounds and the source. The tester identifies the compounds present and shows that the chosen sampling and analysis approach works for them.
Equipment
A gas chromatograph with a detector suited to the compounds, such as a flame ionization detector (FID), plus a sample collection system and calibration standards for each compound measured.
When a rule cites it
Performance tests of control devices and process vents that need the amount of particular organic compounds, such as individual hydrocarbons or hazardous air pollutants. It is also used where a rule requires methane or ethane to be measured separately from the other organics.
Notes for compliance staff
Method 18 is a framework in which the tester selects and validates the sampling and analysis approach, so the test plan and the validation data matter when reviewing a report. It reports compounds individually. Where only a total hydrocarbon concentration is needed, the rule cites a total-organics method such as Method 25A instead.
Cited by
Provisions in the corpus whose text cites Method 18. Subscribers land on the provision in the regulation reader; visitors see a preview of it (the GP05 sample opens in full).
Regulation 7
40 CFR Part 60 Subpart JJJJ
- § 60.4244(g)
- § 60.4245(d)
- Table 2 to Subpart JJJJ of Part 60 — Requirements for Performance Tests
40 CFR Part 60 Subpart OOOOa
40 CFR Part 60 Subpart OOOOb
40 CFR Part 60 Subpart OOOOc
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.