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LOSS/GAIN OF VOCS FROM TEDLAR BAGS AND OTHER SAMPLING EQUIPMENT
Citation:
PAUL, C. LOSS/GAIN OF VOCS FROM TEDLAR BAGS AND OTHER SAMPLING EQUIPMENT. Presented at The 17th Annual Association for Environmental Health and Sciences Meeting, San Diego, CA, March 21 - 22, 2007.
Impact/Purpose:
To inform the public.
Description:
Soil gas samples are collected to evaluate human health risk from vapor intrusion into homes and other buildings. In order to meet risk assessment goals, the analytical reporting limit for many compounds of concern are down to part per billion ranges. The appropriate sampling tubing, sample containers and leak check compounds should be selected in order to ensure data quality objectives. Mechanisms which can impact sample integrity include adsorption of volatile organic compounds (VOCs) onto the sampling media and diffusion of VOCs through the sampling media which may result in artificially low values, and desorption of compounds from the sampling media into the sample which may results in artificially high values. A literature search was conducted to compile published results of impacts on soil gas samples from sampling equipment (i.e., tubing) and containers (i.e., Tedlar® bags). The literature search revealed that the recommended holding time for samples stored in Tedlar® bags not exceed 48 hours. A laboratory study was conducted to evaluate the holding times for certain VOCs in 1 L Tedlar® bags stored at two different temperatures. VOCs used in this experiment include 1,1,1-trichloroethane (1,1,1-TCA), trichloroethylene (TCE), benzene, and toluene that were combined in a gas mixture with nitrogen. Bags were filled with the gas mixture and then stored for different times and temperatures. Two incubators were set at two temperatures, 15C and 25C to simulate field temperatures and the bags were stored from 8 hours to 2 weeks. Results of this study show that 1,1,1-TCA, TCE, and benzene can be stored up to one week without significant impact on concentrations. Results for toluene are less conclusive. However, soil gas samples collected in Tedlar® bags should be analyzed as quickly as practical or samples can be transferred to another container with longer holding times (i.e., Summa canister).