Anal. Chem. 1998, 70, 5213-5221
Determination of a Wide Range of Volatile Organic Compounds in Ambient Air Using Multisorbent Adsorption/Thermal Desorption and Gas Chromatography/Mass Spectrometry James F. Pankow,*,† Wentai Luo,† Lorne M. Isabelle,† David A. Bender,‡ and Ronald J. Baker§
Department of Environmental Science and Engineering, Oregon Graduate Institute, P.O. Box 91000, Portland, Oregon 97291-1000, U.S. Geological Survey, Water Resources Division, 1608 Mountain View Road, Rapid City, South Dakota 57702, and U.S. Geological Survey, Water Resources Division, 810 Bear Tavern Road, West Trenton, New Jersey 08628
Adsorption/thermal desorption with multisorbent airsampling cartridges was developed for the determination of 87 method analytes including halogenated alkanes, halogenated alkenes, ethers, alcohols, nitriles, esters, ketones, aromatics, a disulfide, and a furan. The volatilities of the compounds ranged from that of dichlorofluoromethane (CFC12) to that of 1,2,3-trichlorobenzene. The eight most volatile compounds were determined using a 1.5-L air sample and a sample cartridge containing 50 mg of Carbotrap B and 280 mg of Carboxen 1000; the remaining 79 compounds were determined using a 5-L air sample and a cartridge containing 180 mg of Carbotrap B and 70 mg of Carboxen 1000. Analysis and detection were by gas chromatography/mass spectrometry. The minimum detectable level (MDL) concentration values ranged from 0.01 parts per billion by volume (ppbv) for chlorobenzene to 0.4 ppbv for bromomethane; most of the MDL values were in the range 0.02-0.06 ppbv. No breakthrough was detected with the prescribed sample volumes. Analyte stability on the cartridges was very good. Excellent recoveries were obtained with independent check standards. Travel spike recoveries ranged from 90 to 110% for 72 of the 87 compounds. The recoveries were less than 70% for bromomethane and chloroethene and for a few compounds such as methyl acetate that are subject to losses by hydrolysis; the lowest travel spike recovery was obtained for bromomethane (62%). Blank values for all compounds were either below detection or very low. Ambient atmospheric sampling was conducted in New Jersey from April to December, 1997. Three sites characterized by low, moderate, and high densities of urbanization/traffic were sampled. The median detected concentrations of the compounds were either similar at all three sites (as with the chlorofluorocarbon compounds) or increased with the density of urbanization/traffic (as with dichloromethane, MTBE, benzene, and toluene). For toluene, the median detected concentrations were 0.23, 0.42, and 0.70 ppbv at the three sites. Analytical precision was measured using duplicate sampling. As ex10.1021/ac980481t CCC: $15.00 Published on Web 11/13/1998
© 1998 American Chemical Society
pected, the precision deteriorated with decreasing concentration. At concentrations greater than 0.2 ppbv, most duplicates differed by less than 20%; below the MDL values, the differences between the duplicates were larger, but they were still typically less than 40%. Interest in determining volatile organic compounds (VOCs) in air has increased over the last several decades. In the United States, the Clean Air Act Amendments (CAAA) of 19901 now require monitoring for 55 VOC “ozone precursors” and 189 chemicals and chemical groups defined as “hazardous air pollutants” (HAPs). Nearly 100 of the HAPs have vapor pressures greater than 0.1 Torr and as such have been classified as VOCs.2,3 The work presented here in determining VOCs in air is part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) program. NAWQA seeks a comprehensive understanding of the levels of VOCs, pesticides, metals, and other contaminants in the natural waters of the United States.4 For VOCs, this requires an understanding of the extent to which VOCs move between the atmosphere and natural waters. Depending on the activity gradient between the two phases, VOCs can either enter natural waters from the atmosphere or volatilize from natural waters to the atmosphere. Predicting the direction and magnitude of such VOC fluxes requires the application of appropriately sensitive and specific analytical methods for VOCs in air. The majority of the methods that have been developed for VOCs in air have been either canister-based5-15 or sorbent†
Oregon Graduate Institute. U.S. Geological Survey, South Dakota. § U.S. Geological Survey, New Jersey. (1) Stenvaag, J. M. Clean Air Act 1990 Amendments Law and Practices; Wiley: New York, 1991. (2) Kelly, T. J.; Mukund, R.; Gordon, S. M.; Hays, M. J. Ambient Measurement Methods and Properties of the 189 Title III Hazardous Air Pollutants; EPA600/R-94-098, Final Report, NTIS PB95-123923; U.S. Government Printing Office: Washington, DC, 1994. (3) Mukund, R.; Kelly, T. J.; Gordon, S. M.; Hays, M. J.; McClenny, W. A. Environ. Sci. Technol. 1995, 29, 183A-187A. (4) Gilliom, R. J.; Alley, W. M.; Gurtz, M. E. Design of the National Water-Quality Assessment Program: Occurrence and Distribution of Water-Quality Conditions; U.S. Geological Survey Circular 1112; U.S. Geological Survey: Sacramento, CA, 1995; 33 pp. (5) Jayanty, R. K. M. Atmos. Environ. 1989, 23, 777-782. ‡
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based.11,16-29 In the former, a whole air sample is drawn (or pumped) into a metal (usually surface-treated stainless steel) canister; a portion of that air is then analyzed using methods that involve passing the air through either a cryotrap or a sorbent bed, thereby focusing the VOCs prior to their determination using gas chromatography (GC). In sorbent-based methods, an air sample is pulled directly through a glass or metal tube that is packed with an appropriate sorbent material. When thermal desorption is used to transfer the analytes to the GC column, the resulting method is referred to as “adsorption/thermal desorption” (ATD). Both canister- and sorbent-based methods have been used with a variety of GC detectors, including the mass spectrometer (MS). Both types of methods can provide detection limits of ∼0.5 parts per billion by volume (ppbv) or lower for a variety of compounds.10,18,27,30 The relative merits of canister and sorbent methods have been discussed in the literature.5-29 Recently, a new type of steel canister has become available from Restek (Bellefonte, PA) that is lined with fused silica and which may offer increased inertness toward sampled analytes. We chose to develop a sorbent method for our studies because (1) NAWQA is interested in a very broad range of VOCs, some of which (e.g., polar and lower volatility VOCs) can be difficult to recover quantitatively from canisters; (6) Gholson, A. R.; Jayanty, R. K. M.; Storm, J. F. Anal. Chem. 1990, 62, 18991902. (7) McClenny, W. A.; Pleil, J. D.; Evans, G. F.; Oliver, K. D.; Holdren, M. W.; Winberry, W. T. J. Air Waste Manage. Assoc. 1991, 41, 1308-1318. (8) Hsu, J. P.; Miller, G.; Moran, V. J. Chromatogr. Sci. 1991, 29, 83-88. (9) Pate, B.; Jayanty, R. K. M.; Peterson, M. R.; Evans, G. F. J. Air Waste Manage. Assoc. 1992, 42, 460-462. (10) Kelly, T. J.; Callahan, P. J.; Pleil, J.; Evans, G. F. Environ. Sci. Technol. 1993, 27, 1146-1153. (11) Seeley, I.; Broadway, G. Fresenius Environ. Bull. 1994, 3, 158-163. (12) Kelly, T. J.; Holdren, M. W. Atmos. Environ. 1995, 29, 2595-2608. (13) Brymer, D. A.; Ogle, L. D.; Jones, C. J.; Lewis, D. L. Environ. Sci. Technol. 1996, 30, 188-195. (14) Hagerman, L. M.; Aneja, V. P.; Lonneman, W. A. Atmos. Environ. 1997, 31, 4017-4038. (15) U.S. EPA. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Method TO-14; Center for Environmental Research Information, Office of Research and Development, U.S. EPA.: Cincinnati, OH, March 1989. (16) Chan, C. C.; Vainer, L.; Martin, J. W.; Williams, D. T. J. Air Waste Manage. Assoc. 1990, 40, 62-67. (17) Rothweiler, H.; Wa¨ger, P. A.; Schlatter, C. Atmos. Environ. 1991, 25B, 231235. (18) Heavner, D. L.; Ogden, M. W.; Nelson, P. R. Environ. Sci. Technol. 1992, 26, 1737-1746. (19) Sturges, W. T.; Elkins, J. W. J. Chromatogr. 1993, 642, 123-134. (20) Cao, X.-L.; Hewitt, C. N. Chemosphere 1993, 27, 695-705. (21) Cao, X.-L.; Hewitt, C. N. J. Chromatogr. 1994, 688, 368-374. (22) Helmig, D.; Greenburg, J. P. J. Chromatogr. 1994, 688, 123-132. (23) Jaouen, P.; Gonzalez-Flesca, N.; Carlier, P. Environ. Sci. Technol. 1995, 29, 2718-2724. (24) Helmig, D.; Vierling, L. Anal. Chem. 1995, 67, 4380-4386. (25) McClenny, W. A.; Oliver, K. D.; Daughtrey, E. H. J. Air Waste Manage. Assoc. 1995, 45, 792-800. (26) Sunesson, A.-L.; Nilsson, C.-A.; Andersson, B. J. Chromatogr. 1995, 699, 203-214. (27) Oliver, K. D.; Adams, J. R.; Daughtrey, E. H.; McClenny, W. A.; Yoong, M. J.; Pardee, M. A.; Almasi, E. B.; Kirshen, N. A. Environ. Sci. Technol. 1996, 30, 1939-1945. (28) Woolfenden, E. J. Air Waste Manage. Assoc. 1997, 47, 20-36. (29) U.S. EPA. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Method TO-17; Center for Environmental Research Information, Office of Research and Development, U.S. EPA.: Cincinnati, OH, January 1997. (30) Chan, C. C.; Vainer, L.; Martin, J. W.; Williams, D. T. J. Air Waste Manage. Assoc. 1990, 40, 62-67.
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(2) canisters require careful cleaning, and conventional steel canisters also require a complicating humidification step during analysis to ensure reproducible and quantitative recoveries of many common analytes of interest; and (3) large numbers of samples were anticipated, and the cost-effectiveness of sorbentbased methods argued strongly for the utilization of ATD. This paper describes the development and evaluation of ATD for the determination of a wide variety of VOCs in ambient air. The 87 method analytes include halogenated alkanes, halogenated alkenes, ethers, alcohols, nitriles, esters, ketones, aromatics, a disulfide, and a furan. EXPERIMENTAL SECTION Method Development. The analytes for the method are given in Table 1. Compounds 1-8 were collected using a very retentive sorbent bed and a relatively low volume (LV) air sample of 1.5 L. Compounds 9-87 were collected by passing a separate, higher volume (HV) air sample of 5 L through a second, less retentive cartridge. The overall list of 87 analytes is similar to the target analytes for USGS Method 2020 for VOCs in water31 except that (1) the Method 2020 analytes 2-propenal, vinyl acetate, and iodomethane were excluded as air analytes here because of stability problems and (2) the compounds tert-butyl alcohol (TBA), tert-amyl alcohol, and methyl acetate were included here because they are degradation products of the alkyl ether compounds currently used as fuel oxygenates to reduce carbon monoxide and ozone in urban air. Sorbent Cartridges. The length and diameter of the glass cartridges were 8.9 and 0.64 cm, respectively. Each LV cartridge contained 50 mg of Carbotrap B followed by 280 mg of Carboxen 1000 (Supelco Inc., Bellefonte, PA). Carbotrap B is a moderately strongly sorbing graphitic carbon material with a specific surface area of 100 m2/g. It exhibits a low capacity for water (
