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R9 Laboratory SOP 310
Analysis of VOCs in Air Collected in Canister or Tedlar Bags
Summary
This Standard Operating Procedure (SOP) is applicable to analysis of air samples collected in specially prepared stainless steel canisters or Tedlar bags. Canisters included are SUMMA® polished interior canisters and SilcoSteel⁜ silica coated interior canisters. Air samples may originate from soil pores, the ambient environment, the indoor environment, or air pollution source emissions. This method is appropriate for a variety of applications including ambient air monitoring, soil vapor analysis, and indoor air analysis in support of EPA, Superfund, RCRA, Water, and Air programs.
This Standard Operating Procedure (SOP) describes the procedures used at the Region 9 Laboratory for the analysis of volatile organic compounds in air samples collected in specially prepared stainless steel canisters or Tedlar bags. The procedures are based on EPA methodologies, specifically Compendium Method TO15, titled "The Determination of Volatile Organic Compounds (VOCs) in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS)". A known volume of sample is directed from the sample container to a three-stage preconcentration process called Microscale Purge and Trap.
The first stage of preconcentration by Microscale Purge and Trap involves concentrating an aliquot of the air sample in a cryogenic glass-bead trap cooled to a temperature below the freezing point of the VOCs of interest. This first stage eliminates N2 and O2 from the air sample while retaining VOCs, water and CO2. The glass-bead trap is then heated while slowly passing helium through the trap to transfer the sample to a second trap. The second trap in the process contains Tenax which has also been cooled. This second trap removes much of the water and CO2 in the air sample with minimal loss of VOCs. The Tenax trap is then heated and the VOCs are swept to a third trap with a minimal volume of helium. The third and final trap is cooled and focuses the VOCs into a small volume. Upon heating, the VOCs are swept from the final trap with helium and rapidly injected into the analytical system. The analytical system consists of a high resolution gas chromatograph (GC) coupled to a mass spectrometer (MS).
The samples are spiked with internal standards (IS) during the pre-concentration process. The target volatile organic compounds are identified in the sample by analyzing standards under the exact same conditions employed for samples, and comparing the resulting mass spectra and GC retention times. A response factor is established for each target compound during the initial and continuing calibrations by comparing the MS response of the primary ion produced by the target compounds to the MS response for the primary ion produced by the associated internal standard. Each target compound is quantitated by comparing the responses of the target compound responses to the internal standard responses, using the response factors from the most recent continuing calibration.