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Performance audit results of two different ambient air monitoring projects for volatile organic compounds (VOCs) are presented. A National Institute of Standards and Technology (NIST) traceable gas cylinder containing several VOCs in dry nitrogen at parts per billion (ppb) concentration levels was used at the field sampling site to evaluate performance of the sampling and analytical systems. Both Tenax cartridges and evacuated stainless steel canisters (6 L) were used to sample the air. Sample media exposed to the audit gas were returned to the laboratory for analysis.
The data indicate that a mean percent bias of 30% or less was achieved for most of the audit compounds sampled by Tenax. The results also show that the canister sampler cannot be adequately evaluated using volatile organics in dry nitrogen because of absorption losses of certain compounds. Several of the less volatile compounds in the audit gas exhibited significantly reduced recovery or were not detected after being sampled by the canister. Recovery of highly volatile compounds in the gas was quantitative. Further investigation showed that the use of humidified audit gas resulted in the quantitative recovery of all the VOCs that were sampled by the canister.
toxics, air monitoring, volatile organics, canister, audit standards, performance audits, Tenax
Chemist, Atmospheric Research and Exposure Assessment Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC