Method 26A: Hydrogen Halide and Halogen - Isokinetic Method
Method 26A is the isokinetic alternative to Method 26. This method is particularly suited for sampling sources controlled by wet scrubbers emitting acid droplets. The method requires a Method 5 sampling train with the use of additional impingers, reagents, and PTFE-coated glass fiber filter media.
Gaseous and particulate pollutants are withdrawn isokinetically from the source
and collected in an optional cyclone, on a filter, and in absorbing solutions. The cyclone collects
any liquid droplets and is not necessary if the source emissions do not contain them; however, it
is preferable to include the cyclone in the sampling train to protect the filter from any liquid
present. The filter collects particulate matter including halide salts but is not routinely recovered
or analyzed. Acidic and alkaline absorbing solutions collect the gaseous hydrogen halides and
halogens, respectively. Following sampling of emissions containing liquid droplets, any halides/halogens dissolved in the liquid in the cyclone and on the filter are vaporized to gas and
collected in the impingers by pulling conditioned ambient air through the sampling train. The
hydrogen halides are solubilized in the acidic solution and form chloride (Cl−), bromide (Br−),
and fluoride (F−) ions. The halogens have a very low solubility in the acidic solution and pass
through to the alkaline solution where they are hydrolyzed to form a proton (H +), the halide ion,
and the hypohalous acid (HClO or HBrO). Sodium thiosulfate is added to the alkaline solution to
assure reaction with the hypohalous acid to form a second halide ion such that 2 halide ions are
formed for each molecule of halogen gas. The halide ions in the separate solutions are measured
by ion chromatography (IC). If desired, the particulate matter recovered from the filter and the
probe is analyzed following the procedures in Method 5.
NOTE: If the tester intends to use this sampling arrangement to sample concurrently for
particulate matter, the alternative Teflon probe liner, cyclone, and filter holder should not be
used. The Teflon filter support must be used. The tester must also meet the probe and filter
temperature requirements of both sampling trains.
For more information and documents about Method 25A, please consult the EPA's Method 25A webpage.
Apex Instruments offers a Method 25A Sampling Train. If interested in Method 25A sampling, Apex Instruments works with our customers to make sure we are providing the correct products for your project and will provide you with a price quote. For any questions about our sampling train, please contact sales@apexinst.com.