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Northern Region: Regina, SK, Canada, 1979. (54) Kuntz, K. Canada Centre for Inland Waters, personal communication, 1991. (55) Anderson, R. L. Practical Statistics for Analytical Chemists; Van Nostrand Reinhold: New York, 1987; pp 35-40. (56) Karickhoff, S. W.; Brown, D. S.; Scott, T. A. Water Res. 1979, 13, 241. (57) Kenaga, E. E.; Goring, C. A. I. In Aquatic Toxicology, ASTM STP 707; Eaton, J. G., Parrish, P. R., Hendricks, A. C., Eds.; American Society for Testing Materials: Philadelphia, PA, 1980; pp 78-115.
(58) Guidelines establishing test procedures for the analysis of pollutants. Fed. Regist. 1979, 44, No. 233. (59) Prudent Practices for Handling Hazardous Chemicals in Laboratories; National Research Council; National Academy Press: Washington, DC, 1981; p 36. Received for review September 24, 1990. Revised manuscript received March 4, 1991. Accepted March 20, 1991. W e thank the New York State Department of Environmental Conservation for funding this study.
Comparison of Portable Gas Chromatographs and Passivated Canisters for Field Sampling Airborne Toxic Organic Vapors in the United States and the USSR Richard E. Berkley," Jerry L. Varns, and Joachlm Pleil
Atmospheric Research and Exposure Assessment Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1 Collection of samples in passivated canisters is widely used in analysis of trace volatile organic compounds in air because preconcentration is usually required to detect analytes. Sample integrity can be compromised by deterioration or artifact formation during storage and preconcentration. A laboratory-tested portable gas chromatograph (PGC) equipped with a highly sensitive photoionization detector (PID) offers the advantage of near real-time data without preconcentration, but its limitations as a field-portable instrument must be recognized. This paper presents data produced simultaneously by the canister/TO-ll method and by PGCs. Data were obtained in US. and overseas field studies at industrial, hazardous waste, and roadway sites. Field results suggest that a combination of canister and PGC methods offers a synergistic approach to source assessment measurements.
Introduction The low part per billion (ppb) concentrations of toxic organic compounds found in ambient air have generally eluded direct detection, and samples must undergo preconcentration prior to analysis. Sample collection may actually be a preconcentration process in which analytes are stripped from the air matrix by a cryogenic trap or a sorbent bed, or whole air samples may be collected in passivated canisters and kept for later analysis (I). Use of a portable gas chromatograph (PGC) equipped with a photoionization detector (PID) of sufficient sensitivity to detect organic compounds without preconcentration at sub-ppb levels offers a significant alternative approach to this difficult analytical problem. Reviews by Verner and Driscoll (2, 3) in 1984-1985 describe more than a decade of PID applications in gas chromatography. Several reports describe analyses of organic vapors in air with PID-equipped chromatographs that were not portable and required preconcentration (4-8).Leveson developed a 10.6-eV photoionization detector with significantly enhanced sensitivity, which was incorporated into a portable gas chromatograph (9). The photon source was an electrodeless discharge tube excited by a radio-frequency oscillator. It was claimed to detect benzene without preconcentration at 0.1 ppb (10-13). With this instrument, Berkley estimated a benzene detection limit equivalent to 0.03 ppb. The smallest sample actually analyzed, 1 pL containing 1.6 pg of benzene,
produced a 2.3-V-s peak at maximum gain. Linear response over a wide range of concentration (0.5-130 ppb benzene) could be maintained, and air injections as large as 1 mL could be made without unacceptable loss of chromatographic resolution. Comparable sensitivities to other aromatic compounds and chloroalkenes were also found (14). A portable instrument of such sensitivity would obviously be suitable for air monitoring, but relatively few reports of such use have appeared (15-17). Potential sampling errors with canisters include breakthrough of analytes from the preconcentration trap, chemical reactions between collected compounds, and sample degradation during storage. Sample integrity during storage in passivated canisters has been demonstrated in the absence of highly reactive compounds (18), but HC1, for example, was shown to cause artifact formation (19). Parallel use of a PGC method that does not store or preconcentrate samples could call attention to the occurrence of such problems. PGCs are more easily transported than a large number of canisters and can more readily obtain a large volume of data in the field. On the other hand, they are presently limited to low-resolution chromatography, they identify the limited number of compounds that they can detect at ambient levels by retention time only, and they require a skilled operator. The analytical trade-offs in field sampling between the widely used canister method and the near-real-time PGC are listed in Table I. We have operated PGCs in both laboratory and field tests, (20, 21), but those evaluations included minimal comparison with data obtained by other methods. The objective of this report was to compare PGC data with method TO-14 canister data for volatile organic compounds. Herein are data obtained in two field studies, conducted in Delaware and Lithuania.
Experimental Section Canister Analysis. Spherical 6-L electropolished canisters (SIS, Inc.) were used to collect air samples and to store PGC calibration standards. Canisters were cleaned by heating to 90 OC while they were evacuated through a liquid nitrogen trap to a final pressure below 10-pm (mercury equivalent) for 2 h. For direct comparison between canister and PGC results, a canister was held with its inlet less than 10 cm from the end of the PGC probe and the valve was opened to fill it
Not subject to U.S. Copyright. Published 1991 by the American Chemical Society
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Table I. Relative Advantages of Canister and PGC Methods for Ambient Air Sampling comparative criteria no. of compds analyzed quantitation limit specificity data delay sample integrity multiple sampling field screening critical personnel
canister portable GC typically 41" typically
