Environ. Sci. Technol. 1982, 16, 410-413
Shrader, S. R. “IntroductoryMass Spectrometry”;Allyn and Bacon: Boston, 1971. Silverstein,R. M.; Bassler, G. C. “SpectrometricIdentification of Organic Compounds”; Wiley: New York, 1974. Kovats, E. Adu. Chromatogr. 1965, 1, 229. Fieser, M.; Fieser, L. “Reagents for Organic Synthesis”; Wiley Interscience: New York, 1967; Vol. 1. Graebe, C.; Trumpy, F. Chem. Ber. 1898, 31, 369-375. Elderfield, R. C.; Wythe, S. L. J. Org. Chem. 1954, 19, 683-692.
Acheson, R. M. “An Introduction to the Chemistry of Heterocyclic Compounds”;Interscience: New York, 1967; p 93.
(22) Christman, R. F.; Ghassemi,M. J. Am. Water Works Assoc. 1966,58, 723-741. (23) Sarkanen, K. V. In “The Chemistry of Wood”; Browning, B. L., Ed.; Interscience: New York, 1963; Chapter 6. (24) Wershaw, R. L.; Pinckney, D. J.; Booker, S. E. J. Res. U.S. Geol. Surv. 1977,5, 565-569. (25) Stevens, A. A.; Millington, D. S., unpublished data.
Received September 8, 1981. Accepted March 15, 1982. This research was supported in part by EPA Research Grant No. R804430 from the Municipal Environmental Research Laboratory, Cincinnati, OH, Alan A. Stevens, Project Officer.
Applicability of Passive Dosimeters for Ambient Air Monitoring of Toxic Organic Compounds Robert W. Coutant * Battelle Columbus Laboratories, Columbus, Ohio 43201
Donald R. Scott Environmental Monitoring Systems Laboratory, U S . Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1
rn Three commercially available (3M, DuPont, Abcor) diffusion-based personal monitors were evaluated for possible use for toxic organics in ambient air. Test compounds were benzene, chlorobenzene, and six chlorinated hydrocarbons. An in-series EC-PID GC method was used to quantitate pollutants collected on the charcoal collecton. Tests of detection limits, blank levels, and desorption efficiencies were performed. All three badges were contaminated with several chlorinated hydrocarbons at levels that could impair their use for ambient sampling. Comparison of calculated lower useful limits for the DuPont device with ambient concentrations showed that only benzene, carbon tetrachloride, l,l,l-trichloroethane, and trichloroethylene could be detected at representative ambient levels in a 24-h sampling time. Reasonable improvements in blank levels and detection limits would allow the detection of all other tested compounds except 1,2-dichloroethane and chlorobenzene. Introduction
Over the past decade, pollutant sampling methodology has undergone a natural development from generalized stationary-source monitoring procedures to specialized techniques for mobile and stationary monitoring of large areas or regions to the use of portable monitoring equipment. While all phases of pollution monitoring remain important, there has recently been increased emphasis on the need for direct determination of personal exposure to toxic pollutants in different environments. Portable, pump-based (active) systems have been used for monitoring toxic organic compounds in industrial environments for some time. More recently, several more convenient, passive (no pump) personal monitors have become available commercially and have been evaluated for specialized applications in the workplace (1-7). These passive devices depend upon well-characterized diffusion or permeationlimited sampling of the air rather than pump sampling. The pollutants are collected on a suitable sorbent, normally charcoal. Because of their small size (generally less than 30 cm3),low weight, low cost, and the absence of pumps, 410
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batteries, and tubing, they should be ideally suited for considerations as personal monitors for toxic organic compounds in ambient air. Although these devices have been tested to a limited extent for monitoring of relatively high organic pollutant concentrations (ppm/V) in the workplace, there has been no evaluation of their applicability to sampling at much lower concentrations (ppt-ppb/V) in ambient air. The purpose of the current work was to examine this applicability with respect to a selected group of toxic hydrocarbons and chlorinated hydrocarbons. The compounds chosen were benzene, chlorobenzene, carbon tetrachloride, chloroform, 1,2-dichloroethane, l,l,l-trichloroethane, trichloroethylene, and tetrachloroethylene. The devices investigated were manufactured by DuPont (Pro Tek organic vapor air monitoring badge), 3M (3500 organic vapor monitor), and Abcor (Gasbadge organic vapor dosimeter). The REAL personal monitor (7), which was designed for vinyl chloride, was not considered since each individual device must be calibrated for each compound. Critical laboratory tests were applied to the devices to determine potential analytical problems in ambient air applications, e.g., detection limitations, low desorption efficiencies, and high and variable blanks. Significant differences in blank levels were found among the various personal monitors. A gas chromatographic technique using an in-series combination of electron-capture and photoionization detectors was developed to determine the test compounds at the low concentrations required. Experimental Section
Analytical Methods. The target compounds were desorbed from the charcoal strips and quantitated by gas chromatography with an in-series electron-capture (ECD) photoionization detection (PID) system. A Varian 3700 GC equipped with Hewlett-Packard 3380 integrators was used. The analytical column was a commerical8 ft X ‘ / g in. 0.d. stainless steel column packed with Carbopack-B and 1% SP-1000. Nitrogen at a flow rate of 30 mL/min was used as the carrier gas. A temperature program of 10
0013-936X/82/0916-0410$01.25/0
0 1982 American Chemical Society
Table I. GC Detection Limits and Relative Sensitivitiesa electron capture
photoionizationb
DL,C DL,C RSb ng/badge RSb ng/badge chloroform 1.0 5.0 0.0 1,2-dichloroethane 0.030 170 0.0 l,l,l-trichloroethane 3.1 1.6 0.05 200 carbon tetrachloride 14 0.36 0.0 trichloroethylene 1.4 3.6 0.34 29 benzene 0.0 1.0 10 tetrachloroethylene 7.0 0.71 0.30 33 0.0 0.55 18 chlorobenzene Mass basis; measured under conditions for detection of the complete list of chemicals, not optimized for particular compounds. Sensitivity relative to chloroform (ECD) or benzene (PID). Approximate detection limits in ng/ badge with 0.1% of sample extract for analysis. Division by 1000 gives absolute mass limits. 10.2-eV lamp. compound
min at 100 "C followed by a ramp of 4 "C/min to 180 "C was used. The photoionization detector was a HNU 10.2-eV system. Desorption. Carbon disulfide, which is usually used as the desorbing solvent, cannot be used in pure form with electron-capture detection because of the excessive response of the detector and appreciable solvent tailing on most columns. Also, even the best grade of carbon disulfide that was examined (Baker Instra-Analyzedreagent) contains appreciable impurities that are evident by both ECD and PID. Methanol yields minimal response with both ECD and PID, and there are several commercially available grades that are "clean" enough for use. The current work was performed with a mixture of 5% (V/V) carbon disulfide in Baker Resi-Analyzed methanol. Charcoal collectors were taken from the badges, placed in a glass vial with 1mL (DuPont) or 2 mL (Abcor and 3M) of the desorbing solution, and allowed to sit overnight, and then 1 pL of the resulting solution was used for GC analysis. Solvent blank corrections for this solvent mixture were found to be 2 pg/pL for l,l,l-trichloroethane, 5 pg/pL for carbon tetrachloride, and 10 pg/pL for tetrachloroethylene. Desorption Efficiencies. Preliminary experiments with chloroform were performed with a 1.9-L stainless steel canister coupled to the GC via a gas-sampling valve with graphite seats. This canister was flushed with nitrogen and then loaded to the desired concentration level. A stainless steel vial containing a test charcoal strip was then attached to the canister and allowed to adsorb the test compound for periods of time ranging from a few hours to a day. The change in concentration and the known volume of the canister were used to calculate the amount adsorbed by the charcoal strip. Comparison of this value
with the results of analysis of the strip yielded apparent desorption efficiencies. Final data were obtained by the phase-equilibrium method (8). Charcoal collectors were placed in sealed glass vials with 1 mL of the desorbing solvent containing a known loading of the test compounds and were allowed to equilibrate overnight. A similar vial containing 1 mL of the same solution was used as a reference. Comparison of the analysis data for the badge solution with those from the reference solution then gave the desorption efficiencies at each concentration level tested.
Results and Discussion Detection Limits. Conventional analysis of the charcoal sorbents used in passive devices in industrial environments involves the use of a polar solvent, usually carbon disulfide, for desorption of the pollutants, followed by gas chromatographic (GC) analysis of an aliquot (ca. 0.1%) using flame ionization detection (FID). With use of these devices at typical ambient concentractions, however, the absolute amounts of pollutants collected over an 8-24 h period would be expected to be of the order of tens of nanograms. The amount of material presented to the detector would thus be of the order of tens of picograms, which is much less than that detectable by a FID detector. Therefore, in the current work a series combination of electron-capture (ECD) and photoionization (PID) (10.2eV source) detectors was used to obtain the required detection limits. The detection limits and relative sensitivities of the ECD-PID detector system for the various compounds evaluated are shown in Table I. No attempt was made to optimize for particular compounds. The detection limits are given in units of ng/badge and are defined as the concentration that corresponds to a signal 2 standard deviations above the apparent zero level. To obtain absolute mass detection limits the values in ng/badge should be divided by 1000. The ECD responses for benzene and chlorobenzene are effectively zero, and the PID is required for these compounds. For those compounds that responded to both detectors, the ECD gave better detection limits. Even with ECD, however, the response for 1,2dichloroethane was very low in comparison to responses for other chlorinated hydrocarbons. These detection limits are representative of the particular methodology used, and modification of this methodology by the use of larger aliquots or the use of capillary column chromatography could improve the detection limits. Badge Blanks. Contamination of unused charcoal collectors was determined for each of the three types of badges. Three to seven badges were selected at random from supplies purchased from the manufacturers and were analyzed in the same manner as exposed badges. The results expressed as range and median values are shown
Table 11. Badge Blanksa (ng/badge) Abcorb
DuPontC
3Md
compound chloroform 1,2-dichloroethane 1,l,l-trichloroethane carbon tetrachloride trichloroethylene tetrachloroethylene benzene chlorobenzene
median range median range median range
