Collection and Analysis of Trace Organic Vapor Pollutantsin Ambient Atmospheres Technique for Evaluating Concentration of Vapors by Sorbent Media Edo D. Pellizzari," John E. Bunch, and Ben H. Carpenter
Chemistry and Life Sciences Division and Environmental Studies Division, Research Triangle Institute, Research Triangle Park, N.C. 27709 Eugene Sawicki
Chemistry and Physics Laboratory, National Environmental Research Center, Environmental Protection Agency, Research Triangle Park, N.C. 2771 1
w An analytical technique is described for evaluating collection efficiencies of sorbents during the concentration of hazardous vapors from a flowing stream. The polymeric beads-Tenax GC. Porapak Q. Chromosorb 101, and Chromosorb 104-were 290% efficient in trapping vapors of epoxides. 3-lactones, sulfonates. sultones, .V-nitrosamines. chloroalkyl ethers, aldehydes. and nitro compgunds from s n t h e t i c air-vapor mixtures a t 0.23 Ijmin. Tenax and Chromosorb 101 were evaluated a t sampling rates up to 9 limin and maintained efficiencies of 290%. Carbowax 600 and 400. and oxypropionitrile coated or chemically bonded to supports were also highly efficient (>go%). Because unsaturated hydrocarbons constitute a large fraction of organic air pollutants, it is anticipated that their oxidation products and their products of reaction with NO, and SO,, whether spontaneously or photochemically induced, may be also present in ambient atmosphere. Epoxides. peroxides, aldehydes. ketones, lactones, sulfonates, sultones. nitroso. and nitro compounds have been isolated in laboratory experiments during such processes as olefin oxidation, ozonization. and sulfonation ( 1 ) . Some of these compounds have been shown to cause cancer in animals (2-7). Furthermore. many types of alkylating and arylating agents are being introduced directly at a continually increasing rate into our environment --e.g.. as industrial intermediates in organic synthesis. solvents from various chemical processes. as cross-linking agents in manufacturing processes, medicines, and as antibacterial and fungistatic agents. The characterization and measurement of extremely minute amounts (ppb) of these hazardous compounds in ambient air have been seriously hampered by the lack of a reliable sampling system and sensitive instrumentation for direct analysis. Special systems have been developed for concentrating trace organic vapors from large volumes of atmosphere and transferring the collected vapors to an analytical system (8-2.5),, Many collection devices and sorbents have been employed by investigators in air pollution. In general. the concentrating techniques have utilized cryogenic ( 19-24). absorptive (1.3. 13. 2.5) or adsorptive (9-12, 1*5-24, 26. 27) trapping methods. Cryogenic (freeze-out) methods are particularly suitable for analysis of highly volatile substances; however. if liquid nitrogen. oxygen. or solid carbon dioxide-acetone is used as coolant, large quantities of water may accumulate. which is a major problem during chromatographic analysis. Aerosol formation may be also experienced with this technique. reducing the trapping 552
Environmental Science & Technology
efficiency. D q i n g the gas by passing the air over desiccants prior to cryogenic trapping is not feasible since some solutes may also be scrubbed ( 1 3 . 28. 29). Nevertheless, the major advantage of this approach is that it is the only technique that permits the collection of low-molecularweight air pollutants. A h . oxidation or polymerization of constituents is minimized during their concentration. A number of solid materials and liquids coated on supports acting as stationary phases have been recently demonstrated to have physical properties suitable for collection of trace organic vapors. The chemical nature of sorbents that adsorb compounds is important since the process may be irreversible and/or artifacts may arise through decomposition of the organics during thermal desorption. Of the adsorbent materials used in air pollution studies. activated carbon has been extensively characterized ( 1 I ) . It may also give rise t o many artifacts. Application of chemically bonded stationary phases (H. 2.5. 30, 3 1 ) to sampling of air pollutants appears to be potentially promising because selectivity can be incorporated by choosing the appropriate phase. In addition. they are essentially nonextractable and exhibit lower background during thermal desorption than the conventional support -coated liquid phases. Nonetheless the choice of a technique for concentrating organic vapors from ambient atmosphere depends upon the chemical properties of the constituents of interest. Evaluation of sorbents for a particular air-sampling task should include the following criteria: quantitative collection efficiencies and recovery of trapped vapors. high break-through volumes. minimal decomposition of polymerization of sample constituents during collection and recovery. low background contribution from the sorhent. and little or no affinity by the sorbent for water. The performance of many sorbents as to their ability to extract and retain hazardous vapors from a moving air stream has pot been adequately studied. The parameters involved in determining the performance o f sorbents can be divided into two categories. There are those related to sampling environment such as f'low rate. air temperature. and humidity. and those related to the physicochemical properties of the sorbent such as surface area. particle size and porosity. solute capacity. sorption mechanism. and degree of solute affinity. Furthermore. some of these lactors which influence sorbent performance are not independent ofeach other. Because the collection and analysis of' volatile hazardous suhstances in nanogram per cubic meter amounts from ambient atmosphere require the selection of' a w r bent that is eft'icient under a variety of sampling conditions. we designed an instrumental technique for evaluat -
ing the collection efficiency of sorbents. This paper presents the performance of a number of candidate trapping agents for the concentration of substances such as epoxides, @-lactones, sulfonates, sultones, nitrosamines, chloroalkyl ethers, aldehydes, and nitro compounds from air.
Experimental Tenax-GC (60/80 mesh), Chromosorb 101 (100/120), Chromosorb 104 (100/120), and Chromosorb W-HP (100/120) were purchased from Applied Science, State College, Pa. A series of stationary phases chemically bonded to supports, including Carbowax 400/Poracil C (100/120), oxopropionitrile/Poracil C (80/100), and phenylisocyanate/Poracil C (80/100), were also obtained from Applied Science. Stationary phases consisting of Carbowax 600, didecyl phthalate, and tricresyl phosphate and the sorbent Porapak Q were from Supelco, Inc., Bellefonte, Pa. Carbon derived from coke (PCB and BPL, 12/30) was acquired from Pittsburgh Activated Carbon Division of Calgon Corp., Pittsburgh, Pa. Cocoanut-derived carbons (SAL19190 and 580-26) were purchased from Barneby Cheney, Columbus, Ohio. Ethyl methanesulfonate, @-propiolactone, N-nitrosodiethylamine, 1,2-dichloroethyl ethyl ether, nitromethane, methyl ethyl ketone, and aniline were from Fisher Chemicals, Pittsburgh, Pa. Glycidaldehyde and sulfolane were obtained from Aldrich Chemicals, Milwaukee, Wis. From Eastman Organic Chemicals, Rochester, N.Y ., 1,3-propane sultone, maleic anhydride, butadiene diepoxide, and propylene oxide were purchased. Styrene epoxide, bis(chloromethy1)ether and bis-(2-~hloroethyl)ether were from K&K Labs., Plainview, N.Y. The monitoring system shown in Figure 1 was designed and assembled for measuring collection efficiencies. Air (breathing quality, Linde Div. Union Carbide, East Brunswick, N.J.) from a pressurized reservoir was passed through a scrubbing tower (5 cm i.d. x 30 cm) which contained layers of CaClz desicccant and BPL-activated carbon (12 x 30 mesh, Calgon Corp., Pittsburgh, Pa.) to remove trace contaminants. Purified air entered the monitoring system a t point A as shown in the schematic where the flow rate was controlled with a Sho-Rate 250 flow meter (Model 1357-12FlBAA Brooks Instruments Div., Emerson Electric Co., Hatfield, Pa.) equipped with a Teflon diaphragm regulator for compensating downstream pressure changes. The air stream passed through a 2-1 cylindrical chamber (point B) fitted with an injection port where known quantities of organic vapors were introduced. The chamber delivered synthetic air-vapor mixtures (assuming complete and rapid mixing) to the cartridge sampler that contained the sorbent under study (point C) according to the following relationship (32):
were 35 and 250 ml/min, respectively. The detector output signal was amplified (Varian Model 520) and recorded with an Omniscribe strip chart recorder (Houston Instruments, Houston, Tex.). This apparatus monitored total organic vapor in the cartridge sampler effluent. Sorbents were packed in glass tubes (1.056 cm i.d. x 10 cm in length) using 1 cm of silanized glass wool plugs for support. The cartridge samplers were inserted in canisters constructed from tube L Yd-in. copper fitted with 3h-in. Swagelock unions. The entrance and exit lines at point C in the monitoring system were 3h-in. i.d. Teflon ( C o r '0 Plastics Corp., Raleigh, N.C.). T o synthesize known concentrations of air-solute vapor mixtures (Table I), microliter quantities of each organic compound were added to a 2-1 cylindrical flask. The flask was heated to 50°C and the air-vapor mixture was continuously stirred. An aliquot from this stock reservoir was transferred to the chamber (point B) in the monitoring system. By continuously monitoring the cartridge sampler effluent with a flame ionization detector, the collection efficiency of each sorbent was determined. A decay curve (Figure 2 ) , which represented the concentration of the airvapor mixture leaving the chamber per unit time, was established for each mixture and a t each purging rate by
:Recorder
Figure 1. Monitoring system for determining collection efficiency of sorbents
Table I. Synthetic Air-Vapor Mixtures for Cartridge Sampler Eva Iuation Mixture
C = C,,e-"
I
where
C,
= initial concentration in chamber C = concentration in chamber after time, t , has elapsed F = purging rate (ml/min or l/hr) V = volume of chamber
The effluent stream from the sampler was split and a flow of 50-100 ml/min was directed to a flame ionization detector (Model 1200, Varian Instruments, Corp., Walnut Creek, Calif). Because the organic vapors under study were toxic, the apparatus between points A and D was contained in a glove box (Kewaunee Scientific Equipment, Adrian, Mich.) evacuated by vacuum through cryogenic safety traps. Hydrogen and air flow to the detector
Ii
Ill
Test compound
Ethyl methanesulfonate p-Propiolactone N.nitrosodiethy1arnine 1,2-Dichloroethylethyl ether Nitromethane Methyl ethyl ketone Styrene epoxide N -n i t rosod i et h y I a mine Butadiene diepoxide Glycidaldehyde Sulfolane Propylene oxide Aniline Bis-(2.~hloroethyl)ether
N-nitrosodiethylarnine
Bis-(chlorornethy1)ether
Maleic anhydride 1,3-Propanesultone
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using empty cartridge samplers. The percent collection efficiency was estimated by comparing the areas under curves obtained for samplers with and without sorbent (Figure 2).
Results and Discussion At a sampling rate of 0.25 l/min, over 90% of the airvapor mixture is purged through the cartridge sampler in less than 20 min. Since the decay process for moderate concentrations of vapor (0.05 ng/sec) can be monitored with a flame ionization detector, the ability of a sorbent to extract vapors from a flowing gas stream can be determined. We have defined this phenomenon as collection ef-
1.4-
h
U
0.4
-
0.2-
I 0
2
4
0
2
4
TIME ( M I N . )
Figure 2. Flame ionization detection of cartridge effluent Profile A represents n o sorbent in cartridge sampler, B with Tenax GC (packing was 1.0 cm i.d. X 3.0 c m in length). Sampling rate through cartridge was 6 I/rnin. Text mixture I I I was used for obtaining profiles
ficiency-i.e., the fraction of solute vapor in the polluted gas retained by the sorbent bed. The collection efficiencies for several sorbent media are given in Table 11. All of the polymeric sorbents were relatively effective in extracting vapors from a flowing stream of 0.25 l/min. In separate experiments we discovered that propylene oxide and butadiene diepoxide were not efficiently trapped by cocoanut-type carbons and thus accounted for the observed low efficiencies for air-vapor mixture 11. Efficiencies decreased substantially when the polarity of liquid phases coated on supports were increased; tricresyl phosphate was least effective in extracting vapors from a flowing gas stream. On the basis of these preliminary observations, two polymers, Tenax GC (33) and Chromosorb 101, were selected and further tested using higher flow rates. The results depicted in Tables III and IV indicate that high collection efficiencies can be expected even when flow rates up to 9 l/min are employed. The described monitoring system can also be used to determine the effects of continuous sampling when no additional solute vapors are present in the air stream. This represents the extreme case encountered during field sampling. When polluted gas enters a sorbent bed, an equilibrium zone is established near the point of entry. As more pollutant is introduced this zone may expand through the packing length until the capacity of the sorbent is exceeded. However, if after an initial period of time no additional polluted vapors are introduced and purging of the packing bed continues, the zone of vapors may move through the packing bed. When the mass zone moves to the end of the available packing bed and the vapors begin to leave, breakthrough has occurred. Furthermore, the elution volume ( E V ) can be calculated if the time required for the zone to traverse and elute from the sorbent bed and sampling rate are known. In an ideal system, EV has an infinite value. Displacement chromatography may occur during sampling of polluted air leading to early breakthrough. Because each substance has a specific affinity for the sorbent, the quantity absorbed is characteristic for each substance; furthermore one compound can be displaced by another, if the latter has a higher adsorption affinity. Thus, breakthrough studies should be performed in the field under the full complexity of polluted air rather than in the laboratory. The capacity of Tenax GC for various compounds such as alkanes, alcohols, and amines has been reported to be
Table II. Collection Efficiencies of Candidate Sorbents Percent efficiencyn Sorbent
Polymer beads Carbons
Liquid
phases
Tenax GC Porapok Q
Chromosorb 101 Chromosorb 104 Activated carbons
Chemical type
2,6-Diphenyl-p-phenylene oxide
Polyalkyl styrene
Styrene-divinyl benzene Acrylonitrile-divinyl benzene PCB cocoanut (Pittsburgh Act.) BPL coal (Pittsburgh Act.) SA L19190 cocoa nut (Barne by-Cheney) 580-26 Cocoanut/pecan (BarnebyGheney) 20% Carbowax 600 on Chromosorb W(HP) 100/120 mesh Carbowax 400/Poracil C 100/120h
Oxypropionitrile/Poracil C 80/100* 25% Didecyl phthalate on Chrom P 100/120 20% Tricresyl phosphate on Chrom W(HP) 100/120
Mixture
Mixture
Mixture Ill
95 90 95 98 90 90 90 95 90 90 98 50
90 95 95 90 95 90 30
80 90 95 80 90
I
20
II
30
-
90 90 96 80 20
90 95 90 50 20
S a m p l i n g rate was 0.25 I / m i n , p a c k i n g b e d d i m e n s i o n s were 1.056 c m i.d. X 3.0 c m in l e n g t h . T h e exponential dilution flask was m a i n t a i n e d a t 50OC. b Chemically b o n d e d phases.
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Environmental Science 8 Technology
Table 111. Approximate Collection Efficiency of Tenax-GC at Various Sampling Rates
Table IV. Approximate Collection Efficiency of Chromosorb 101 at Various Sampling Rates
Sampling rate, I / m i n Test mixtu rea
I II Ill
Sampling rate, I/min
4
6
a
9
Test mixture”
4
6
a
9
95b 95 >95
90 95 95
90 90 95
90 90 95
I II Ill
95b >95 >95
95 95 95
90 95 90
95 90 80
a A,pproxirnately 1500,ng/co,mponent/rnixture was used to determine efficiencies. Packing dimensions were: 10.5 X 60 rnrn. mesh 60/80. T h e exponential dilution flask was maintained at 50°C. b All values are average of duplicate runs.
a Approximately1500 n g of component mixture was used to determine efficiencies. Packing dimensions were: 10.5 X 30 m m , 100/120. T h e exponential flask was maintained at 50°C. b All values are average of duplicate runs.
higher than aldehydes, ketones, and phenols ( I 7). Bertsch et al. (17) also reported that all sulfur compounds examined were trapped in a narrow zone a t the cartridge entrance. Volatile hydrocarbon compounds containing less than five carbon atoms are not efficiently trapped by Tenax GC ( I 7) while aromatics were ( I 7). Since adsorption affinity constants were strongly temperature dependent, the effects of temperature should be considered in any collection efficiency and breakthrough study. We are currently examining the influence of temperature and humidity on the collection efficiency of Tenax GC and Chromosorb 101 using the monitoring system described here. With respect to packing bed dimensions (length and i.d.) and particle size, it has been suggested that they play a major role in breakthrough (1.7); however, our preliminary studies have shown that an increase in both collection efficiency and EV can be expected. We are presently defining more precisely these relationships.
(8) Aue, W. A., Enuiron. Health., 5, l(1971). (9) Altschuller, A. P.,J. A i r P o l l u t . Contr. Assoc., 16, 87 (1966). (10) Brooman, D. L., Edgeley, E., ibid., p 25. (11) Jones, W. M., J . A p p l . Chem., 16,345 (1966). (12) Krumperman, P. H., J . Agr. Food Chem., 20,909 (1972). (13) Williams, F. W., Umstead, M. E., A n a l . Chem., 40, 2232 (1968). (14) Williams, I. H., ibid., 37, 1723 (1965). (15) Raymond, A., Guiochan, G., Enuiron. S e i . Tech., 8, 143 (1974). (16) Hollis, D. L., A n a l . Chem., 38, 309 (1966). (17) Bertsch, W., Chang, R. C., Zlatkis, A , , J . Chromatog. Sei., 12, 175 (1974). (18) Zlatkis, A,, Lichenstein, H. A,, Tishbee, A,, Chromatograp h i a , 6,67 (1973). (19) Rasmussen, R. A,, A m e r i c a n L a b . , 4, 19 (1972). (20) Rohrschneider, L., Jaeschke, A,, Kubik, W., Chem. Ing. T e c h . , 43, 1010 (1971). (21) Kaiser, R. E., A n a l . Chem.. 45.966 (1973). (22) Bellar, T. A,, Brown, M. F., Sigsby, J . E., Jr., ibid., 35, 1924 (1963). (23) Lonneman, W. A,, Bellar, T. A,, Altschuller, A . P., Enuiron. Sei. Technol., 2, 1017 (1968). (24) Altschuller, A . P., Lonneman, W. A,, Sutlerfield, F. D., Kopczynski, S. L.. ibid., 5,1009 (1971). (25) Aue, W. A , , Teli, P. M., J . Chromatog., 62, 15 (1971). (26) Versino,. B., deGroot, M., Geiss, F., Chromatographia, 7, 302 (1974). (27) Janlk, J., Ruzickovd and Novhk, J., J . Chromatog., 99, 689 (1974). (28) McEwen, D. J., A n a l . Chem., 38, 1047 (1966). (29) Farrington, P. S., Pecsok, R. L., Meeker, R. L., Olson, T . J., ibid., 31, 1512 (1959). (30) Aue, W. A,, Hastings, C. R., J . Chromatog., 42, 319 (1960). (31) Kirkland, J. J., Destefano, J. J., J . Chromatog. .Sei., 8, 309 (1970). (32) Turk, A,, “Basic Principles of Sensory Evaluation,” A S T M S p e c . T e c h . Publ., No. 433, pp 79-83, (1968). (33) Sakodynskii, K., Panina, L., Klinskaya, N., Chromatograp h i a , 7, 339 (1974).
Acknowledgments The authors are grateful to L. Retzlaff for his assistance in the machining and construction of experimental devices used in this study and M. E. Wall for his helpful suggestions. Literature Cited (1) Calvert, J . G., Pitts, Jr., J . N., “Photochemistry,” pp 366-557, John Wiley & Sons, Inc., New York, N.Y., 1966. (2) Dunham, C. L., “Biologic Effects of Atmospheric Pollutants-Particulate Polycyclic Organic Matter,” pp 95-117, Nat. Acad. Sci., Washington, D.C., 1972. (3) Van Duuren, B. L . , J . ,Vat. CancerInst., 48,1931 (1972). (4) Van Duuren, B. L., ibid., p 1539. (5) Van Duuren, B. L., Int. J . Enuiron. A n a l . Chem., 1, 233 (1972). (6) Van Duuren, B. L., M e t h o d s Pharmacol., 2,63 (1972). (7) Van Duuren, B. L., Proc. h t . S y m p . , 149 (1968).
Received for review J u l y 11, 1974. Accepted Dee. 2, 1974. Work supported b y EPA Contract N o . 68-02-1228 f r o m the Enuironm e n t a l Protection A g e n c y , Health, Education, and Welfare.
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