Extractive FTIR Method for the Measurement of Emissions from the Mineral Wool and Wool Fiberglass Industries – USEPA Method 318

USEPA Method 318 is used for the determination of formaldehyde, phenol, methanol, carbonyl sulfide (COS) and carbon monoxide (CO) concentrations in emissions from manufacturing processes using phenolic resins.  The compounds are analyzed in the mid-infrared spectral region (about 400 to 4000 cm-1 or 25 to 2.5 µm). 
 
The analytical range is a function of instrumental design and composition of the gas stream.  Theoretical detection limits depend on:

• the absorption coefficient of the compound in the analytical frequency region;
• the spectral resolution;
• interferometer sampling time;
• detector sensitivity and response;
• absorption pathlength.

Practically, there is no upper limit to the range.  The practical lower detection limit is usually higher than the theoretical value, and depends on:

• moisture content of the flue gas;
• presence of interferants;
• losses in the sampling system.

In general, a 22 meter pathlength cell in a suitable sampling system achieves practical detection limits of 1.5 ppm for three compounds (formaldehyde, phenol, and methanol) at moisture levels up to 15 percent by volume.  Sources with uncontrolled emissions of CO and COS require a 4 meter pathlength cell due to high concentration levels.
 
This method does not apply when:

• polymerization of formaldehyde occurs;
• moisture condenses in either the sampling system or the instrumentation;
• when moisture content of the gas stream is so high relative to the analyte concentrations that it causes severe spectral interference.