Lebouf, RF; Burns, DA; Ranpara, A; Rossner, A
Sorbent tubes are typically used for occupational exposure monitoring of volatile organic compounds in many different industrial environments. To choose an appropriate sorbent, the user must have some prior knowledge of the target analytes as well as environmental conditions (humidity and temperature) and approximate concentrations to effectively sample exposures. Whole-air sampling into evacuated canisters requires no prior knowledge of air concentrations since breakthrough (the loss of sample that occurs when chemicals are not effectively trapped by sampling media) is not an issue. Canisters can handle chemical air concentrations ranging from sub-part per billion to part per million, and the technique is amenable to a wide range of compounds, such as alcohols, ketones, alkanes, aromatics, and terpenes. EPA has been using evacuated canisters for decades to sample VOCs in ambient air via the agency's TO-15 method. Why not use canisters for occupational exposure monitoring? One challenge is the size of the canisters. Traditional whole-air sampling uses 6L canisters, but who wants a volleyball-sized canister strapped to their back? Smaller canister sizes (400 or 450 mL) are now available. Analytical instruments are more sensitive and no longer need the large injection volumes to reach sub-ppb concentrations of VOCs. Using sample injection volumes of 250 mL, the canister method can easily achieve 0.2 ppb detection limits for most analytes using gas chromatography-mass spectrometry (GC-MS). The second challenge is controlling the sampling flow rate. Metal diaphragm flow controllers are heavy (approximately 1 lb.), but researchers at Clarkson University have addressed this issue through the use of capillary flow controllers. NIOSH continued this work with capillary flow controllers and applied a canister sampling method in a field survey to characterize healthcare workers' exposures to cleaning and disinfecting products. Canisters coupled with restrictive flow controllers make sampling easier for the field industrial hygienist because the flow controllers require no onsite pre- or post-sampling calibration. The focus of NIOSH's canister method development was to evaluate an evacuated canister-based (passive) sampling approach followed by preconcentration of samples into a gas chromatograph/mass spectrometer. The agency recently added a new method for sampling and analysis of VOCs using personal evacuated canisters to the NIOSH Manual of Analytical Methods. In NIOSH method 3900, samples are analyzed using a pre-concentrator/gas chromatograph-mass spectrometer system. The NIOSH Respiratory Health Division Organic Laboratory in Morgantown, W. Va., evaluated this method for 17 VOCs: ethanol, acetone, 2-propanol, dichloromethane, hexane, trichloromethane, 2,3-butanedione, 2,3-pentanedione, 2,3-hexanedione, benzene, methyl methacrylate, toluene, ethylbenzene, m,p-xylene, o-xylene, a-pinene, and d-limonene. This article describes the canister method.