Energy & Fuels 1990, 4, 307-319 1 psi reduction in RVP is achieved essentially independent of methanol content. These results are encouraging, but, again, the reader is cautioned that the test fuel used as a poor model of the actual RVP of commercial gasolines; it is possible that the RVP lowering demonstrated would not be as effective in commercial fuels. Further work to clarify this point is required.
Conclusions Significant improvement in PST and RVP can be achieved by the use of virtually any of the surfactant/ cosurfactant pairs examined in this work, especially at high methanol content. The Igepal C0-530/ 1-pentanol combination demonstrated the most methanol-independent performance. This behavior could be useful in formulating a versatile additive system for methanol/gasoline blends. A number of difficulties remain, however, including cost, determination of octane effects, potential corrosion effects, potential intake system and combustion chamber deposition difficulties, and driveability. The cost of Igepal CO-530/l-pentanol in a ratio of 1:2 has been roughly estimated at $0.12/gal of methanol/gasoline blend treated
307
with 3 vol 70 surfactant/c~surfactant.'~ Also, further studies are needed on more realistic gasolines (the 50/50 isooctane/toluene system, though commonly employed for studies of this sort, is highly idealized particularly with respect to RVP) with somewhat higher water contents. Naturally, careful characterization to verify that any modified motor fuels conformed to ASTM standards for spark-ignition engine fuels would have to be undertaken prior to marketing. However, surfactant/cosurfactant combinations appear promising for stabilizing methanol/gasoline mixtures against phase separation and for reducing the Reid vapor pressure.
Acknowledgment. We gratefully acknowledge the support of the State of Ohio and the Ohio Board of Regents through the 1986-88 Research Challenge program. Registry No. Igepal CO, 9016-45-9; methanol, 67-56-1;water, 7732-18-5; oleic acid, 112-80-1; heptanoic acid, 111-14-81-pentanol, 71-41-0; 2-pentanol, 6032-29-7; isooctane, 540-84-1; toluene, 108-88-3. (13) Nitirahardjo, S. Master's Thesis, The University of Akron, 1989.
Chemical Characterizatian and Bacterial Mutagenicity Testing of Ethylene Combustion Products from a Jet-Stirred/Plug-Flow Reactor Arthur L. Laflew,* John P. Longwell, Lata Shirnam6-More, Peter A. Monchamp, William A. Peters, and Elaine F. Plummer Center for Environmental Health Sciences and Energy Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 Received October 10, 1989. Revised Manuscript Received March 15, 1990
Ethylene combustion products from a jet-stirred/plug-flow reactor were characterized by gas chromatography/mass spectrometry, gas chromatography/Fourier transform infrared spectrometry, and high-performance liquid chromatography with UV spectrophotometric detection. Samples were also tested for mutagenicity both in the presence and in the absence of an exogenous metabolizing enzyme system (PMS) using a forward mutation assay based on Salmonella typhimurium. By correlating chemical analysis findings with PMS-dependent (+PMS) mutagenicity data, it was determined that cyclopenta[cd]pyrene (CPP) and fluoranthene (FLA) accounted for the bulk of the mutagenicity at high dose levels (300 pg/mL). However, at low dose (30 pg/mL) the observed mutagenicity of the sample was from 1.5 to 7 times greater than the sum of the mutagenic contributions of known components. HPLC fractionation and bioassay results showed that a fraction composed mainly of CPP was responsible for 50% of the +PMS mutagenicity of the plug-flow sample while a second fraction containing FLA accounted for an additional 8%. However, three other mutagenic fractions were also obtained and were found to be composed of C20-C30 (five to nine fused rings) polycyclic aromatic hydrocarbons (PAH). Together these three fractions accounted for 42% of the total +PMS activity. Nine ethynyl-substituted aromatics were identified including three ethynylacenaphthylene isomers, one of which was among the 10 most abundant species. Also, nitrogencontaining organics were detected at trace levels by GC with nitrogen-specific detection.
Introduction The formation, molecular structureand biological effect of polycyclic aromatic hydrocarbons (PAH) have been the studies primarily because of the subjects of potential health hazard posed by many PAH when they * T o whom correspondence should be directed.
0887-0624/90/2504-0307$02.50/0
are introduced to humans.' PAH have long been associated with the combustion of fossil fuels aiid are known animal carcinogens.' Furthermore, PAH as a class have been implicated as the most important mutagens derived (1)Grimmer, G.; Misfeld, J. In Enuironmental Carcinogens: Polycyclic Aromatic Hydrocarbons; Grimmer, G., Ed.; CRC: Boca Raton,FL, 1983;pp 1-25.
0 1990 American Chemical Society
308 Energy & Fuels, Vol. 4, No. 3, 1990
Lafleur et al.
Table I. Jet-Stirred/Plua-Flow Reactor: Samolina Parameters
sampling location jet-stirred reactor plug-flow region
total gas throughput, mol/s 0.3166 0.3166
total sampling effluent vol effluent time, s sampled,' m3 vol,' m3 4680 0.800 35.76 6600 1.090 50.43
f,b 2.224 X 2.161 X
total fuel consumed, kg 5.808 8.191
final sample vel: mL 99 233
QT$ mg
YT,Cmg/kg
146 358
1130 2022
aVolumes measured at 21 "C. *Defined as the volumetric fraction of the combustor effluent diverted through the sampling train. CVolumeof CHzClzconcentrate of sampled organic material. dObtained gravimetrically. See ref 21 for details. e YT (total emission yield) = mass (mg) of material emitted per unit mass (kg) of fuel consumed
from combustion. A large fraction of the bacterial mutagenic activity of typical combustion samples, expressed in the presence of an exogenous metabolizing enzyme system (postmitochondrial supernatant or PMS), can be traced to neutral PAH-containing fractions. The mutagenic prominence of PAH has been demonstrated for many typical soots including kerosene soot and furnace black2" as well as for automotive diesel soot.3 When particulate extracts from automotive diesels were tested directly (without PMS), the bulk of the bacterial mutagenicity was traceable to nitroarenes and other polar component^.^ Likewise, for other combustion samples a significant fraction of the bacterial mutagenicity (measured variably with or without PMS) has also been traced to polar fractions devoid of neutral PAH. This has been demonstrated for particle extracts from heavy-duty dies e l ~extractable , ~ ~ ~ organics from rice straw smoke,7wood stove emissions,8p9exhaust samples from gasoline-powered motor vehicles,'O dichloromethane extractables from a domestic oil furnace,11J2and extractables from airborne particulate^.'^-'^ Although combustion-derived polar mutagens have not been exhaustively characterized, some observations can be made: (1)in contrast to PAH, many are mutagenic in the absence of an exogenous metabolizing system and (2) many are known to contain nitro groups. It remains to be determined whether polar mutagens are produced by inflame reactions, by postflame oxidative pyrolysis, or by artifactual reactions in sampling systems. In order to shed light on the nature of both neutral and (2)Kaden, D. A.; Hites, R. A,; Thilly, W. G. Cancer Res. 1979,39, 4152-4159. (3)Thilly, W. G.; Longwell, J. P.; Andon, B. A. Enuiron. Health Perspect. 1989,48,129-136. (4)Salmeen, I. T.; Pero, A. M.; Zator, R.; Schuetzle, D.; Riley, T. L. Enuiron. Sci. Technol. 1984,18, 375-382. (5)Schuetzle, D.; Jensen, T. E.; Ball, J. C. Enuiron. Int. 1985,11, 169-181. (6)Peterson, B. N.; Chuang, C. C. In Toxicological Effects of Emissions from Diesel Engines; Lewtas, J., Ed.; Elsevier Biomedical: New York, 1982;pp 51-68. (7)Mast, T. J.; Hsieh, D. P. H.; Seiber, J. N. Enuiron. Sci. Technol. 1984,18,338-348. (8)Alfheim, I.; Becher, G.; Hongslo, J. K.; Ramdahl, T. Enuiron. Mutagen. 1984,6, 91-102. (9)Kamens, R. M.; Rives, G. D.; Perry, J. M.; Bell, D. A,; Paylor, Jr., R. F.; Goodman, R. G.; Claxton, L. D. Enuiron. Sci. Technol. 1984,18, 523-530. (10)Alfheim, I.; Ramdahl, T. MIL-2, Mutagenic and Carcinogenic Compounds From Energy Generation; Final Report; Center for Industrial Research: Oslo, Norway, 1986;p 18. (11)Leary, J. A.; Lafleur, A. L.; Longwell, J. P.; Peters, W. A.; Kruzel, E. L.; Biemann, K. In Polynuclear Aromatic Hydrocarbons: Formation Metabolism and Measurement; Cook, M., Dennis, A. J.; Eds.; Battelle Press: Columbus, OH, 1983;pp 799-808. (12)Leary. J. A.; Biemann, K.; Lafleur, A. L.; Kruzel, E. L.; Prado, G. P.; Longwell, J. P.; Peters, W. A. Enuiron. Health Perspect. 1987,73, 223-234. -- - -- -. (13)Alfheim, I.; Lofroth, G.; Maller, M. Enuiron. Health Perspect. 1983,47,227-238. (14)AUheim, I. Mutagens in Our Environment: Liss: New York. 1983: pp 235-248. (15)Lofroth, G.; Lazaridis, G.; Agurell, E. Enuiron. Int. 1985, 11, 161-167.
polar mutagens formed during combustion, we have focused on characterizing products of ethylene combustion in a jet-stirred/plug-flow reactor.1618 This combustor is specially designed to provide well-defined combustion conditions, and its use is part of an ongoing program aimed at understanding and controlling the combustion chemistry responsible for mutagen formation. Sample preparation methods were chosen to permit the collection and characterization of components encompassing wide polarity and volatility ranges. Cyanopropyl (CN) columns were selected for chromatographic separation because of their demonstrated efficiency in preserving bioactivity during f r a c t i o n a t i ~ n . ' ~ *Mutagenicity ~~ was determined both in the presence (+PMS) and in the absence (-PMS) of an exogenous metabolizing enzyme system (PMS). Samples and fractions were characterized by gas chromatography/mass spectrometry (GC/MS), gas chromatography/Fourier transform infrared spectrometry (GC/FTIR), and high-performance liquid chromatography with spectrophotometric diode-array detection (HPLC/ DAD).
Experimental Section 1. Sampling Procedure. Detailed descriptions of the jetstirred/plug-flow combustor are available.'"18 In this study, the fuel was ethylene. Other conditions are fuel equivalence ratio, 2.37; residence time, 5.69 ms; and reactor temperature, 1628 "C. Samples were obtained from the jet-stirred and plug-flow regions of the combustor by use of an aspirated probe connected to a high-yield combustion sampler consisting of four refrigerated traps filled with a total of 4 L of CH,Cl,. The first trap was maintained a t -30 "C while the final three were a t -68 "C. Sampling parameters are given in Table I. The soluble material was concentrated in a 1-L Kuderna-Danish evaporative concentrator to the dissolution limit. Final concentrate volumes were 99 mL for the toroid sample and 233 mL for the plug-flow sample. Samples were filtered through a 0.2-pm fluorocarbon filter to remove particulates. The weight of nonvolatile (bp > 200 "C) material was determined by a microscale evaporation technique described previously.21 Chemical characterization of components too volatile for bioassay has been reported e l s e ~ h e r e . " J * * ~ ~ 2. Column Chromatography Fractionation. Gravity-flow fractionation columns used in this study were commercial products based on 6-mL polypropylene syringe bodies fitted with polyethylene filters and were packed with 1 g of cyanopropyl-bonded silica (CN) packing material. The column was cleaned and (16)Nenniger, J. E. Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA, 1983. (17)Vaughn, C. B. Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA, 1988. (18)Lam, F. W. Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA, 1988. (19)Lafleur, A. L.; Braun, A. G.; Monchamp, P. A.; Plummer, E. F., Anal. Chem. 1986,58,568-572. (20)Lafleur, A. L.; Monchamp, P. A.; Chang, N. T.; Plummer, E. F.; Wornat, M. J. J. Chromatogr. Sci. 1988,26,337-344. (21)Lafleur, A. L.; Monchamp, P. A.; Plummer, E. F.; Kruzel, E. L. Anal. Lett. 1986,19(A22),2103-2119. (22)Lafleur, A. L.; Gagel, J. J.; Longwell, J. P.; Monchamp, P. A. Energy Fuels 1988,2,709-715.
Characterization of Ethylene Combustion Products conditioned by washing with 10 mL of dichloromethane followed by 10-mL volumes of methanol, dichloromethane, benzene, and hexane, in that order. An empty column (filtration column) was charged with 2-3 g of clean sand. The Luer end of the filtration column was connected to a source of clean nitrogen, and the gas was allowed to flow a t a rate that caused the sand to fluidize. The sample, totaling 18.5 mg of dichloromethane-soluble material, was added to the fluidized sand in small portions enabling the solvent to evaporate completely and permitting the sample to be wholly contained in the sand. The sand column was then coupled to a CN column, and the sample was eluted with mobile phases of increasing polarity and collected in V-bottom vials. Four fractions were eluted with the following mobile-phase volumes: (1)hexane, 3.5 mL; benzene, 10 mL; dichloromethane, 2.0 mL; and methanol, 5.0 mL. Additional details including expected fraction compositions have been reported.20 3. High-Performance Liquid Chromatography. Instrumentation. The apparatus used for preparative-scale HPLC fractionation consisted of a Varian Model 5060 ternary gradient pumping system coupled with a Hewlett-Packard 8450A diodearray UV-vis spectrophotometer through a quartz flow cell with a 3.0-mm aperture and a 2.0-mm path length. A 7225B graphics plotter and a HP9121 disk drive completed the system. Injections were made with a Rheodyne injector using either a 0.1-mL or 1.0-mL sample loop. The HPLC column was 50 cm in length and had a 10-mm i.d. It was packed with 10-pm RSIL-CN material. (Alltech Associates; Deerfield, IL). The HPLC system used for chemical analysis consisted of the following: Hewlett-Packard Model 1090 ternary gradient pumping system with 190-600-nm diode-array detector and HPLC operating software running on a Model 7994 analytical workstation. Injection volumes ranging from 1 to 25 pL could be selected. A wide-band diode-array detection scheme was employed for peak q u a n t i t a t i ~ n . ~Complete ~ UV-vis spectra (200-600 nm) were obtained at 0.10-s intervals. The three Alltech-CN columns used for separation had an inside diameter of 4.6 mm and were 250 mm in length (Alltech Associates; Deerfield, IL). The packing was irregular, 5-pm cyanopropyl material having a 60-A average pore diameter and a surface area of 400 m2/g. Sample Preparation for HPLC. A single fraction (mutagen concentrate) containing all of the bacterial mutagenic activity of the sample was obtained by passing a volume of the sample (in CH&) containing 15 mg of dissoluble material through the CN gravity-flow column and eluting with 2 mL of additional CH2C12. The CN column stripped the sample of highly polar inactive components while the eluate in CH,Cl, contained all of the bioactive components. The amount of material in the CH2C1, eluate ranged from 61% to 72% of the total mass. This procedure had the additional benefit of removing undesirable components that could bind irreversibly to the HPLC column. For HPLC separation of the neutral +PMS mutagens, 8 mL (12 mg) of the plug-flow sample dissolved in CHzClz was concentrated and exchanged into 1.0 mL of decahydronaphthalene by evaporation under a stream of nitrogen. This step is necessary because a large injection of CH,Cl, drastically alters retention of neutral species in normal-phase HPLC. For the isolation of the polar -PMS mutagens, a &fold increase in sample was necessary and this requirement led to the use of a different concentration technique: A 40-mL portion of the sample dissolved in CHZCl2was eluted through a gravity-flow CN column. The eluate was concentrated in a microscale Kuderna-Danish concentrator (Wheaton Scientific) and exchanged into 1.0 mL of cyclohexane. HPLC Separation of Neutral Species. Injection volume was 1.0 mL and the flow rate was 4 mL/min. The following mobile-phase program was used: (1) Initial composition of 100% hexane was maintained for 25 min. (2) CH,Cl, increased linearly to 100% in 10 min and held a t 100% for an additional 10 min. Five neutral fractions were collected during the isocratic phase with hexane as mobile phase and one fraction was collected with CH2Cl,. Collection volumes were N1,17 mL; N,, 10 mL; N3, 21 mL; N4, 20 mL; N,, 48 mL; and Ne, 27 mL. (23) Lafleur, A. L.; Monchamp, P. A.; Plummer, E. F.; Wornat, M. J. Anal. Lett. 1987, 20(8), 1171-1192.
Energy & Fuels, Vol. 4, No. 3, 1990 309
HPLC Separation of Polar Species. Injection volume (1 mL) and flow rate (4 mL/min) were the same as above. The following mobile-phase program was used: (1)90% hexane 10% CHzClz maintained for 20 min; (2) CHzClzincreased linearly to 100% in 10 min and held a t 100% for 10 min; (3) composition changed linearly from 100% CH,Cl, to 100% CH30H 10 min and held at 100% CH30H for 10 min. Selection of fractions was made on the basis of retention behavior of reference compounds and was guided by previous work." Fraction collection intervals and probable eluates were as follows: (1)0-800 s, neutral PAH; (2) 800-1300 s, mononitro-PAH; (3) 1300-1800 s, dinitro-PAH; polycyclic aromatic aldehydes, quinones, or ketones; (4) 1800-2400 s, polynitrated PAH, azaarenes; (5) 2400-3000 s, hydroxy-PAH, amino-PAH; (6) 3000-3600 s, highly polar compounds. 4. Gas Chromatography with Flame Ionization Detection. A methyl (5% phenyl) silicone fused-silica open tubular column (FSOT) was used for GC/FID analyses (Quadrex, Inc.). It was 50 m long and had an internal diameter of 0.32 mm and a film thickness of 1.0 Nm. The helium carrier gas pressure at the column head was maintained at 126 kPa (18 psi). The GC/FID consisted of a Perkin-Elmer Model 8320 capillary gas chromatograph equipped with flame ionization detector (FID), Model AS-300 autosampler, and a heated injector operated in a split mode. Data acquisition was accomplished with a Perkin-Elmer Model 7500 computer running Chromatographics-I11 software. A 2 0 1 split ratio was employed for these analyses. The GC oven temperature was programmed to hold a t 40 "C for the first 10 min, to ramp linearly to 280 "C at 10 OC/min, and to maintain 280 "C for 16 min. 5. GC/MS and GC/FTIR. The GC/MS consisted of an H P 5890 GC connected to a Model 5970 mass-selectivedetector. Data acquisition and analysis were accomplished by use of a Model 59970C MS ChemStation. The GC/FTIR consisted of an H P 5890 GC coupled with a Model 5965A infrared detector. A Model 59965 IRD ChemStation was used for data processing. Both instruments were obtained from Hewlett-Packard Corp., Palo Alto, CA. The GC column was a methyl (5%) phenyl FSOT column (Quadrex, Inc.) having a length of 25 m, an inside diameter of 0.25 mm, and a film thickness of 0.25 pm. Head pressures of helium carrier gas were 6.0 psi for the GC/MS and 21 psi for the GC/FTIR. The difference in pressures served to equalize GC retention characteristics between instruments. Column temperature programming was from 40 to 280 "C a t 10 "C/min. Injector and transfer lines were at 280 "C. Injection volume was 1.0 pL. 6. Gas Chromatography with Nitrogen-SpecificDetection. The gas chromatograph was a Perkin-Elmer Model 990 modified to accept 0.53-mm FSOT columns and fitted with an on-column injector (SGE, Ltd.) and an electronic flowmeter. The column was a 15-m RTX-5 methyl (5%) phenyl silicone FSOT column (Restek, Inc.) having a film thickness of 1.5 pm and an inside diameter of 0.53 mm. The GC was coupled to a Model 610 nitrogen detector (Thermedics, Inc.; Woburn, MA). The GC column exited through the GC interface (300 "C) and the nitrogen detector pyrolyzer interface (310 "C) and was inserted directly into the nitrogen detector pyrolyzer region. The pyrolyzer consisted of a 6 mm 0.d. X 2 mm i.d. quartz tube 40 cm in length. A 10 cm x 1.0 mm platinum wire catalyst was fitted into the tube's heated zone. The pyrolyzer was maintained at 950 "C. Applications of the GC/CLND to the detection of n i t r o a r e n e ~ and ~~-~~ azaarenes= have been reported. Two different modes of detection were used: In the totalnitrogen mode, selective for all N-containing compounds, the GC effluent enters the pyrolyzer tube and undergoes rapid catalytic pyrolysis in the presence of oxygen. This process converts the fixed nitrogen in the sample to NO, which is then oxidized by
+
(24) Lafleur, A. L.; Mills, K. M. Anal. Chem. 1981, 53, 1202-1205. (25) Phillips, J. H.; Coraor, R. J.; Prescott, S. R. Anal. Chem. 1983,
55, 889-892. ( 2 6 ) Tomkins, B. A. In Nitrated Polycyclic Aromatic Hydrocarbons; White, C. M., Ed.; Huethig: Heidelberg, 1985; pp 87-120. (27) Yu, W. C.; Fine, D. H.; Chiu, K. S.; Biemann, K. Anal. Chem. 1984.56. ~ . - -. ,1158-1162. ~ ~ ~ -
-
(28) Wornat, M. J.; Sarofim, A. F.; Longwell, J. P.; Lafleur, A. L.; Energy Fuels 1988, 2, 775-782.
310 Energy & Fuels, Vol. 4, No. 3, 1990 ozone to form electronically excited NOz*. The chemiluminescence signal of this product passes through a selective filter and is detected by a cooled photomultiplier. In the NO, mode, highly selective for organic nitro and nitroso compounds, the instrument operation is similar except that the pyrolyzer is operated without oxygen so that NO will be produced only if R-NO, or R-NO species are present in the sample. In addition, a trap cooled to -80 "C is placed between the pyrolyzer and the NO detector to remove organic pyrolysis products. 7. Bacterial Mutation Assay. Forward mutation assay to 8-maguanine resistance in Salmonella typhimurium strain TM677 was used as the principal means of measuring the mutagenicity. Detailed protocols for measurement of forward mutation have been described p r e v i o u ~ l y . Briefly, ~ ~ ~ ~ ~exponentially growing bacteria were suspended in medium in the presence of test sample for 2 h. Samples a t concentrations of 30, 100, and 300 pg/mL were exposed to the bacteria in the absence and in the presence of 5% (v/v) Aroclor induced postmitochondrial supernatant (PMS). Cultures containing PMS had a reduced nicotinamide adenine dinucleotide (NADPH) generating system. After 2 h the cells were resuspended in fresh medium. Aliquots were plated in the presence and in the absence of the selective agent (8azaguanine; 50 pg/mL). Two independent cultures were used for each treatment point. Colonies were counted a t 48 h and the mutant fraction (MF) was determined as the number of colonies formed under selective conditions divided by the number of colonies formed under nonselective conditions multiplied by the dilution factor. If this ratio was greater than that found for untreated control cultures with greater than 99% confidence and if that ratio also exceeded the 95% upper confidence limit of the mutant fraction for the cumulative historical control, the test was considered positive. The induced mutant fraction (IMF) is calculated by subtracting the background mutant fraction from the measured values. The samples, dissolved in CH2C12,were prepared for bioassay by adding a measured amount of dimethyl sulfoxide in a V-bottom vial. The CH2Clzwas evaporated with a gentle stream of nitrogen until the total volume was reduced to that of the original dimethyl sulfoxide. Final sample concentrations in (CH,),$O were typically 30 mg/mL. 8. Materials. Dichloromethane, acetonitrile, decahydronaphthalene, cyclohexane, methanol, and hexane were Caledon glass-distilled solvents obtained from American Bioanalytical, Natick, MA. Reference mixtures of PAH were obtained from the US.National Institute for Standards and Technology (SRM 1647) and from Supelco Inc. (EPA 16 PAH standard). They included the following 16 PAH: naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[ 1,2,3-cd]pyrene, dibenz[a,h]anthracene,benzo[ghi]perylene. A reference quantity of naphtho[8,1,2-abc]coronenewas generously provided by Dr. John Fetzer.
Results and Discussion The jet-stirred/plug-flow combustion apparatus used in this study (Figure 1)incorporates two major combustion chambers: (1) a toroidal, jet-stirred chamber where reactants and products undergo rapid mixing and are effectively at uniform concentration throughout the reactor volume and (2) a plug-flow section where species formed in the jet-stirred chamber can further react for a fixed period of time before sampling. One large sample was taken from each region, and each was worked up as detailed in the Experimental Section. Our approach to bioassay-coupled chemical characterization of complex mixtures has been described p r e v i o u ~ l y . ~ J ~ ~ ~ ~ 1. Total Emission Yield of Organic Material. Because of the relatively small capacity of the sampling (29) Skopek, T. R.; Liber, H. L.; Krolewski, J. J.; Thilly, W. G. Proc. Natl. Acad. Sci. U.S.A. 1978, 75, 410-414. (30)Skopek, T. R.; Liber, H. L.; Kaden, D. A.; Thilly, W. G. Proc. Natl. Acad. Sci. U.S.A. 1978, 75, 4470-4473.
Lafleur e t al. PFR Probe
--
F 1
I
Pro-Heat
I ,To
Exhourl
Flow Straightener
Fuel /Air Feed Burner
Pro-Mixed FueliOxidizer
JSR P r o b e d
II
Injechn Port
-
FLAT F LA M E
JET-STIRRED / PLUG-FLOW REACTOR Figure 1. Schematic cross section of the jet-stirred/plug-flow reactor and its comparison with a laminar flat flame. The two circular jet-stirred flame zones are sections of the toroid-shaped combustor. Samples were collected by use of water-cooled probes as indicated.
system relative to the combustor output and because of the need to minimize perturbations in the sampling regions, only a small fraction of the total combustor effluent can be sampled. The fraction of the total combustor output that is continuously sampled by the sampling system is called the sampling fraction VJ. It is determined by measuring the ratio of the amount of effluent collected by the sampler to the total combustor effluent. Dividing the total amount of material collected (QT) by the sampling fraction (f,)gives the total amount of CH,Cl,-soluble organic material emitted, and this divided by the amount of fuel consumed gives the total emission yield ( Y T )as in eq 1. QT ( m d YT = (1) /,[fuel consumed (kg)] Calculations of total output yield for the jet-stirred reactor and the plug-flow region samples are listed in Table I. These values are based on gravimetric measurementsz1 of the total collected material (QT) and are later compared with results obtained by gas chromatography (Table 111) and by high-performance liquid chromatography. (Table VII). It is seen from Table I that nearly twice as much dichloromethane-soluble material is emitted from the plug-flow region (2022 mg/kg) than from the jet-stirred reactor (1130 mg/kg). 2. Bacterial Mutagenicity Testing. Measured amounts of the samples were dissolved in dimethyl sulfoxide by solvent exchange and tested for mutagenicity by use of a S. typhimurium forward mutation awsay. Samples were tested both in the presence (+PMS) and absence (-PMS) of an exogenous metabolizing enzyme system. Additional portions of the sample were fractionated by CN gravity-flow column chromatography into four increasingly polar fractions. Individual fractions as well as reconstituted samples (obtained by combining fractions) were also assayed for bacterial mutagenicity. Figure 2 shows results obtained for the jet-stirred reactor sample. Without added PMS, the sample was too toxic to 5'. typhimurium for reliable mutagenicity determination; however, fractionation resulted in the removal of some toxic components so that the fractions as well as the reconstituted sample could be tested for -PMS mutagenicity. This result is seen in Table 11. Figure 3 shows the corresponding data for the plug-flow sample. Toxicity in the
Energy &Fuels, Vol. 4, No. 3, 1990 311
Characterization of Ethylene Combustion Products
Table 11. Bacterial Mutagenicity Data for Samples and Fractions mutagenicity contribn' sample description
wt, mg
wt contribn, %
1.1 14.1 2.1 1.2 18.5
6 76 11 7
fractions hexane benzene dichloromethane methanol/residue sum of fractions reconstituted sample original sample
effective dose, pg/mL Jet-Stirred Reactor 6 76 11 7 100 100 100
+PMSb
-PMS'
5f2 73 f 12
0 87 f 50
0 0
0 0 87 f 50 67 f 14 (indeterminate)d
78 f 14 58 f 7 84f 11
Plug-Flow Region fractions hexane benzene dichloromethane methanol/residue sum of fractions reconstituted sample original sample
0 11.3 0.3 7.5 19.2
0 59 2 39
0 59 2 11 100 100 100
0
0 170 f 30 0 0 170 f 30 98 i 22 125 f 14
34 f 4 0 0
34 f 4 17 f 3 48 f 14
Induced mutant fraction ( ~ 1 0followed ~) by 99% confidence limits. b+PMS: measured in the presence of PMS (exogenous metabolizing enzyme system). -PMS: no PMS added. Sample toxic to bacteria. 2w
0
50
Mo
150
200
250
300
0
50
Do
150
200
250
300
~.:""""""""""""""
L h12
w-'
0-' 0 Llutogenicity-
50
XK)
1 5 0 2 0 0 2 5 0 3 0 0 Dose h/dI
_ _ _ _ Toxicity
Dose [ig/mLI
Mutogenicity-
_ _ _ _ Toxicity
Figure 2. Bacterial mutagenicity assay results for the jet-stirred reactor sample obtained in the presence (+PMS) and in the absence (-PMS) of an exogenous metabolizing enzyme system using a S. typhimurium forward mutation assay. The mutagenicity dose-response curve is drawn with a solid line and the corresponding toxicity curve with a dotted line.
Figure 3. Bacterial mutagenicity assay results for the plug-flow region sample obtained in the presence (+PMS) and in the absence (-PMS) of an exogenous metabolizing enzyme system using a S. typhimurium forward mutation assay. The mutagenicity dose-response curve is drawn with a solid line and the corresponding toxicity curve with a dotted line.
absence of PMS was also a factor, but at higher dose. Overall, the data in Table I1 indicate that the +PMS mutagenic activities of the whole samples approximate the sum of the contributions of their individual fractions to an acceptable degree. Also, the mutagenicity of the original samples could be recovered by recombining the fractions. 3. Chemical Analysis. Gas Chromatography. The samples were quantified by GC/FID according to aromatic carbon number (C,) grouping. To compensate for nonlinear instrument response as PAH increase in size and decrease in volatility, a response calibration curve was derived as follows: First, a set of 16 reference PAH were used to obtain individual response factors (RF) as in eq 2: area response (arbitrary integration units) RF = (2) quantity (pg) Then, through the use of an iterative curve fitting process, we obtained the following expression relating R F (area units/pg) to retention time (t,) (min):
using a spreadsheet computer program. Individual RF's were calculated for each peak and individual quantities (Qi) of collected components were determined by dividing the component peak areas by the response factors: [peak areali (area units) Qi (4) [response factorli (area units/pg)
RF = 9.80 + 0.766[tr] - 9.01
X
10-3[t,]2
Each GC peak was assigned an aromatic carbon number (C,) range by correlating the GC/FID chromatogram with the GC/MS total ion plot and by identifying peak constituents from GC/MS data. The quantity of sample collected for each C, range (8,) was obtained by summing individual peaks in each range:
Q, = C(Qi) (for each C, range)
Summing all peaks yielded the total quantity of material eluting from the GC. By application of suitable conversion factors, convenient units for quantity (mg) were obtained and are listed in Table 111. Emission yields in mg/ kg were calculated as follows:
r = 0.99 (3)
All peaks in the chromatogram were then quantified by
(5)
emission yield
Qn or Qi ( m d fs[fuel consumed (kg)]
(6)
312 Energy & Fuels, Vol. 4, No. 3, 1990
Lafleur et al.
Table 111. Gas ChromatograDhic Determination of Emission Yields bv Carbon Number Grouo
C" group
C?-clO ClZ C14 C16
c 18
Go+
total GC output noneluting material nitrogen compdse
jet-stirred reactor piug-flow region emission yield" emission yield" material collected, mg mg/kg 5% YT material collected, mg mg/kg % YT GC/FID + GC/MS Survey of PAC by Aromatic Carbon Number* major ions ( m / z ) 92, 128 25.6 198 18 26.1 148 7.3 152 17.3 134 12 34.5 195 9.6 178 5.6 43 3.8 11.8 67 3.3 202 4.0 31 2.7 17.2 97 4.8 226 7.1 55 4.9 20.5 116 5.7 252, 276 4.4 34 3.0 27.7 157 7.7 64.1 495 44.0 138 780 38.0 81.9' 635d 56.0 220c 1242d 62.0 Gas Chromatography with N-Specific Detection 10.4 80 7.1
5.3
30
1.5
"Mass (mg) of sample emitted per unit mass (kg) of fuel consumed. Percent values based on total emission yield (YTin Table I). *Molecular identification performed by GC/MS; quantitation by GC/FID using eqs 2-5. cTotal GC output subtracted from the total mass of material sampled (QTin Table I). dTotal GC-based emission yield subtracted from the total emission yield (YTin Table I). eSum of all nitrogen-containing GC components. Obtained by nitrogen-specific detection. See Experimental Section for details.
Comparing relative emission yields in Table 111, we see that, in the jet-stirred reactor, light species (C7-Cio) account for 18% of the GC-based emission yield, a result that is 2 1 / 2 times larger than the corresponding value (7.3%) for the plug-flow sample. Conversely, when results are compared for the heaviest (Cz0+)species, the plug-flow emission yield at 7.7% is 2 1 / 2 times greater than the value for the jet-stirred reactor at 3.0%. The plug-flow sample, formed in a region where components can interact leading to larger molecules, was not only richer in heavier species than the jet-stirred sample but also accounted for a greater yield of emitted material (780 vs 495 mg/kg). Data in Table I11 also shown that only a fraction of either sample could be recovered by gas chromatographic methods. For example, the plug-flow sample yielded 138 mg by GC/FID compared to a total of 358 mg measured gravimetrically, giving a total GC output of 38%. The jet-stirred sample gave only a slightly better GC output of 44%. It is likely that only a small fraction of the noneluting mass represents missing analytes since some of the residue consists of soot and insoluble polymeric material. Gravity-flow CN column results for a number of different jet-stirred/plug-flow samples showed that roughly 5-2590 of the sample mass does not elute. In any case, it is clear that the GC-based analyses must be supplemented by other techniques to more completely characterize these samples. Nitrogen Compounds. In mutation assays based on S. typhimurium, as is our forward mutation assay, the observation of -PMS activity often signals the presence of nitroaromatic c o m p ~ u n d s . ~ lNitroarenes -~~ have been implicated as the components responsible for the bulk of the -PMS bacterial mutagenicity in the effluents from a number of combustors including automotive heavy-duty diesel^,^,^ wood ~ t o v e sand . ~ ~a~domestic oil furnace."J2 Other nitrogen compounds, including a number of amines and azaarenes, are also -PMS mutagens in (31) Tokiwa, H.; Kitamori,S.; Nakagawa, R.; Horikawa, K.; Matamala, L. Mutat. Res. 1983, 121, 107-116. (32) Nakagawa, R.; Kitamori, S.; Horikawa, K.;Nakashima, K.; Tokiwa, H.Mutat. Res. 1983, 124, 201-211. (33) Rosenkranz, H. S.; Mermelstein, R. Mutat. Res. 1983, 114, 217-267. (34) Rosenkranz, H. S.; Mermelstein, R. In Nitrated Polycyclic Aromatic Hydrocarbons; White, C. M., Ed.; Huethig: Heidelberg, 1985;pp 267-297. (35) Mermelstein, R.; Kiriazides, D. K.; Butler, M.; McCoy, E. C.; Rosenkranz, H. S. Mutat. Res. 1981,89, 187-196.
our assay.29 Although some oxygenated PAH also exhibit -PMS activity in our in general, the detection of -PMS mutagenicity strongly implies the presence of nitrogen compounds, especially nitroarenes. Although nitrogen compounds were not detected by GC/MS and GC/FTIR, it was possible that they might be present at levels below the detection limit of these techniques. Therefore, the samples were analyzed by gas chromatography with nitrogen-specific chemiluminescence detection (GC/CLND) as detailed in the Experimental Section. The resulting chromatogram revealed the presence of a number of nitrogen-containing components, but their low levels ruled out further characterization. Total amounts of N-containing compounds for each sample are given in Table 111. There we see that the total amount of N-containing species accounted for 7.1% of the jet-stirred reactor emission yield and 1.5% of the plug-flow output. Further GC/CLND analysis in a nitro-selective mode failed to detect nitro compounds, so it is improbable that the N species detected in the total-N mode could be nitrated because their peak signatures would have been reproduced in the nitro-selective mode. It is possible, however, that some nitro species may be present at levels below the GC/CLND detection limit (1 ng/pL). The inability to detect nitro compounds is consistent with the fact that the combustor was operated in a fuel-rich mode where the amount of thermal NO, is low. However, even at very low levels, some undetected components could still play important roles in determining the mutagenicity of the samples. For example, dinitropyrenes are extremely potent mutagens and were implicated as major mutagens in airborne particulates31 and diesel exhaust32even though present at very low levels. Dinitropyrenes and certain other nitroarenes are so strongly mutagenic that they can be bioactive at dose levels below the detection limit of common analytical technique~.~~~~~ GC/MS, GC/FID, and GC/FTIR.The intact samples were also characterized by gas chromatography/mass spectrometry (GC/MS) and by gas chromatography/ Fourier transform infrared spectrometry (GC/FTIR). Gas chromatography with flame ionization detection (GC/FID) was used in conjunction with the spectral techniques to obtain emission yields of major components. (36) Leary, J. A.; Ldeur, A. L.; Liber, H. L.; Biemann, K. Anal. Chem. 1983,55, 758-761.
Energy & Fuels, Vol. 4, No. 3, 1990 313
Characterization of Ethylene Combustion Products 4
Iz
8
20
16
24
28
0
32
2
6 M ) ~ & '
'
4
6
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8
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' ' 12'
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. . . . . . . . . . . . . . . . . . . . . . .
4
12
8
16
20
24
28
0
32
Retention Time [min]
Figure 4. GC/FID response curve for a standard reference mixture of 16 PAH with two to six fused rings. Nph = naphthalene; Acl = acenaphthylene; Acn = acenaphthene; Flu = fluorene; Ant = anthracene; Phe = phenanthrene; Fla = fluoranthene; Pyr = pyrene; Chr = chrysene; BaA = benz[a]anthracene; BbF = benzo[b]fluoranthene; BkF = benzo[k]fluoranthene; BaP = benzo[a]pyrene; IPy = indeno[ 1,2,3-cd]pyrene; DahA = dibenz[a,h]anthracene; BghiP = benzo[ghi]perylene.
-
80
0.0 10 TIME (min)
15
20
Figure 5. GC/MS total-ion chromatogram for the plug-flow sample. Numbered peaks refer to Table IV, where components are identified and emission yields are calculated. Peaks labeled A are common artifacts.
The GC/MS total-ion chromatogram of the plug-flow sample is shown in Figure 5. The numbers above the peaks in the GC/MS chromatogram refer to data listed in Table IV. The two peaks designated by the letter A are common plasticizer artifacts. The components making up the chromatogram in Figure 5 account for 67.7% of the GC output as shown in Table IV. The components were identified through their MS and gas-phase FTIR spectral data and often by comparison with a reference compound as indicated in Table IV. Quantification was done by comparison with a reference standard when available or by using eq 3 and 4. The resulting emission yields (mg/kg) are also listed in Table IV. Mutagenic Contribution of Components. For kerosene soot2 and diesel soot3extracts tested with PMS in the forward mutation assay, the total mutagenicity generally approximated the sum of the mutagenic contributions of individual components. The reported procedures2J for calculating mutagenic contribution of components were duplicated to permit comparison of our results. In this study, the mutagenic contribution of the components was found to approximate the mutagenicity of the sample at some dose levels but a t low dose (30 pg/mL) the mutagenicity of either sample was clearly greater than the calculated mutagenic contributions of individual components.
12
kl
14
16
I
10-1
1 8 2 0 2 2
1
O i # I # , # 5
8
6
4
Mutcqenicity Dose bg/mLl _ _ _ _ Toxicity Figure 6. Doseresponse c w e for cyclopenta[cd]pyrene obtained in the presence of an exogenous metabolizing enzyme system (+PMS) using a S. typhimurium forward mutation assay. Error bars indicate 99% confidence limits. The mutagenicity of benzo[a]pyrene a t 20 pg/mL [99% confidence interval, N = 481 is given for comparison.
9
7
2
Mutagenicity-
0.5
tPMS I
I
I
I
I
1.0
1
I
I
,
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,
I
8
!
/
2.0
Dose [pg/mLl
I
/ I I I , # I I , I I II
2.5
3.0
3.5 _ _ _ _ Toxicity
Figure 7. Low-dose +PMS bacterial mutagenicity for [ l ] cyclopenta[cd]pyrene (CPP) and [2] fluoranthene (FLA). Error bars indicate 99% confidence limits. The toxicity curves (dotted lines) are indexed to the scale on the right.
The data for the jet-stirred reactor and plug-flow samples are listed in Tables V and VI, respectively. The components used for the mutagenicity calculations were 9 of the 12 major species (Table IV) for which we could obtain reference samples for bioassay. For purposes of calculating mutagenic contributions, all other components possibly present in the sample are assumed to have no effect on the total mutagenicity of the sample. Mutagenicity data were obtained for all nine components. Dose-response curves for the components exhibiting +PMS mutagenic activity are plotted in Figures 6 and 7. Concentrations of each of the nine components were determined at each total sample dose (30,100, or 300 pg/mL), and the mutagenic contribution of each component was obtained from their dose-response curves and listed in Tables V and VI. For the jet-stirred-reactor sample (Table V), no component was abundant enough or potent enough to contribute conclusively to the +PMS mutagenicity of the sample until the 300 pg/mL dose level was reached. At that dose, the only contributor to +PMS mutagenicity among the known sample components was cyclopenta[cdlpyrene (CPP) with a contribution of 58 f 8 to the total mutagenicity of the sample which tested out at 153 f 33 (IMF X lo5). No other individual PAH could be singled out as an important +PMS mutagen even though the amount of CPP in the sample could account for less than
Lafleur et al.
314 Energy & Fuels, Vol. 4, No. 3, 1990
Table IV. Structural Identification and Emission Yields of Major ComDonents jet-stirred reactor identificationc emission yielde component MWb MS IR GCIt, quantd mg/kg GYT X X X STD 6.5 0.57 102 phenylacetylene X X NAf 98 1,3,5,7-octatetrayne NQ X X X STD 21.0 1.9 116 indene X X NA 126 1,3-diethynylbenzene NQ X X NA 126 1,4-diethynylbenzene NQ X X NA 126 1,2-diethynylbenzene NQ X X X 30.0 2.7 STD 128 naphthalene X X 152 NA 2-ethynylnaphthalene NQ X X X 36.7 3.3 152 STD acenaphthylene X X 176 NA 7.2 0.63 CRV r-ethynylacenaphthyleneB X X NA 176 y-ethynylacenaphthylend NQ X X 176 NA z-ethynylacenaphthylend NQ X X X STD 3.7 0.32 178 phenanthrene X X X 0.35 STD 190 4.0 cyclopenta[ deflphenanthrene X X X 0.31 STD 202 3.5 fluoranthene X X NA 0.33 CRV 202 3.7 acephenanthrylene X X X 0.74 STD 8.3 202 pyrene X X 0.61 STD NA 6.9 226 benzo[ghi] fluoranthene X X X 0.75 STD 226 8.5 cyclopenta[ cdlpyrene ~~
peako no. 1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19
sum of major components fraction of total GC output
140.0
12.4 (28.3)"
plug-flow region emission yielde mg/kg %Y* 7.3 0.36 30.4
1.5
121.0
6.0
199.0 17.4
9.8
12.6 10.5 17.1 11.0 29.3 16.0 56.4
0.62 0.52
528.0
26.1 (67.7)"
0.86
0.85 0.54 1.5
0.79 2.8
ORefers to peaks in GC/MS chromatogram (Figure 6). bMolecularweight in mass units obtain from mass spectra. 'MS = mass spectrum; IR = gas-phase infrared spectrum; GC/t, = same retention time as authentic standard. dSTD = quantified by comparison with reference standard; CRV = quantified using eq 3; NQ = not quantified. (Emission yield = mass (mg) of component emitted per unit mass (kg) of fuel consumed. Percent values are based on the total emission yield, YT (see Table I). f Reference standard not available for retention comparison. #Position of ethynyl substituent unknown. "Based on total GC Output (see Table 3).
Table V. Contribution of Components to +PMS Mutagenicity of Jet-Stirred Reactor Sample comDonent dose and mutagenicity at given samde dose 30 ag/mL 100 rglmL 300 rglmL concn concn,O concn: concn,O major components pg/mL % pg/mL mut,b I M P rg/mL mut,b I M P pg/mL mut,bIMP phenylacetylene 8.5 0.57 0.17 0 0.57 0 1.71 0 indene 27.4 1.89 0.57 0 1.89 0 5.67 0 39.1 2.65 0.79 0 naphthalene 2.65 0 7.95 0 acenaphthylene 48.2 3.25 0.97 0 3.25 0 9.74 0 phenanthrene 4.9 0.33 0.10 0 0.33 0 0.98 0 cyclopenta[deflphenanthrene 5.2 0.35 0.11 0 0.35 0 1.06 0 fluoranthened 4.6 0.31 0.09 0 0.31 0 0.93 0 pyrene 10.8 0.73 0.22 0 0.73 0 2.20 0 cyclopenta[ cd]pyrened 11.2 0.75 0.23 0 0.75 5*3 2.26 58 8 sum of mutagenic contributions bioassay results for jet-stirred sample
0
34
4
5*3 83 f 11
* 58 * 8 153 * 33
OConcentration of each component when overall sample concentration is at given value (30, 100, or 300 pg/mL). bMutagenicity values taken from measured doseresponse curves for individual components. CIMF= induced mutant fraction (He) followed by 99% confidence limits. Components showing statistically significant mutagenic activity.
half of its mutagenic activity. However, many minor sample components are not completely characterized and their bacterial mutagenic properties are unknown and could prove to be important. For the plug-flow sample (Table VI), CPP was also the most important mutagen and it became dominant at a lower sample dose level (100 pg/mL). At 300 pg/mL, the mutagenic contribution of fluoranthene (FLA) became evident as well. In Table VI it is evident that the sum of the mutagenic contributions of the plug-flow components does not equal the observed mutagenicity of the sample a t any dose and that the disparity is greatest at 30 pg/mL. An attempt was made to improve correlation by testing a purified fraction (mutagen concentrate) of the plug-flow sample. A portion of the plug-flow sample was purified according to a simple chromatographic procedure (details in Experimental Section) so that a mutagen concentrate was obtained that retained all of the mutagenic activity of the sample. With nonmutagenic material removed, the
concentrations of individual PAH were now 40% higher in the mutagen concentrate than in the original plug-flow sample. Bioassay results are also included in Table VI. At a dose of 300 pg/mL, the sum of the mutagenic contributions for the concentrate (IMF = 308 f 40)was statistically equivalent to the bioassay result for the whole mixture (IMF = 269 f 61). It is seen that CPP and FLA account very well for the total mutagenicity of the mutagen concentrate at the tested dose level. It is likely that the removal of nonmutagenic material contributed to the improved correlation observed. Regardless of the mutagenic contribution results, it is clear that CPP is a major contributor to the overall mutagenicity of the samples and that FLA is also an important mutagen. Figure 6 shows the +PMS dose response curve for CPP over the 0-20 pg/mL dose interval. Error bars reflect 99% confidence intervals for mean mutant fraction values. The 99% confidence interval for a series of benzo[a]pyrene reference measurements (N = 48) is
Energy & Fuels, Vol. 4, No. 3, 1990 315
Characterization of Ethylene Combustion Products
Table VI. Contribution of Components to +PMS Mutagenicity of Plug-Flow Sample component dose and mutagenicity at stated sample dose mutagen concentratea 300 rg/mL concn,b mut: pg/mL IMP
plug-flow sample
major components phenylacetylene indene naphthalene acenaphthylene phenanthrene cyclopenta[defl phenanthrene fluoranthenee pyrene cyclopenta[cd]pyrenee sum of mutagenic contributions bioassay results for plug-flow sample bioassay results for surrogate mixture'
concn pg/mL % 5.5 0.36 20.4 92.1 151.0 9.6 8.0 13.0 22.3 42.8
1.50 5.98 9.84 0.62 0.51 0.84 1.44 2.78
30 r d m L concn,b mut: rg/mL IMFd 0.11 0.45 1.80 2.95 0.19 0.16 0.25 0.43 0.84
0 0 0 0 0 0 0 0 12 f 3
100 r d m L
concn,b rg/mL 0.36 1.50 5.98 9.84 0.62 0.52 0.85 1.45 2.79
300 rg/mL
mut: IMFd 0 0 0 0 0 0 0 0 68
f
8
concn,b rg/mL
mut: IMFd
1.08 4.51 17.95 29.52 1.87 1.56 2.54 4.35 8.37
0 0 0 0 0 0 24 f 3 0 198 f 30
1.50 6.26 24.93 41.00 2.60 3.52 2.16
0 0 0 0 0 32 0f5
6.04 11.62
0 276 f 35
12 f 3
68 f 8
222 f 33
308 f 40
92 f 11
125 f 14
115 f 18
269 f 61
17
60
183
a CN-column fraction containing essentially all mutagenicity of sample. Concentration of component when overall sample concentration is at given value (30, 100, or 300 pg/mL). (Mutagenicity values taken from measured dose-response curves for individual components. IMF = induced mutant fraction (XIOs) followed by 99% confidence limits. e Components showing statistically significant mutagenic activity. 'Mixture of the nine components at same concentrations found in plug-flow sample. See Figure 8.
given for comparison. As seen in Figure 6, the mutagenicity is linearly related to dose in the following manner with high correlation: mutant fraction ( ~ 1 0 =~ ) 5.15 + 24.2[dose] (pg/mL) r = 0.99 (7)
A t low doses, however, the mutagenicity response for C P P is not completely linear and the simple equation in Figure 6 does not hold. The nonlinearity is evident in Figure 7 where the dose-response curve is given for the 0-3 pg/mL dose region. The low-dose curve for FLA is also seen to be similar in shape but less steep than that of CPP. It should be noted that the shape of these pure compound dose-response curves (Figure 7) is quite different from the shape of the sample curves (Figures 2 and 3), which suggests the possibility of multicomponent interaction in the case of complex mixtures. In any case, CPP is one of the most potent +PMS mutagens we have tested in our assay. In Figure 6, CPP is seen to be twice as mutagenic as benzo[a]pyrene (BaP) at 20 wg/InL, so it is not surprising that CPP was the dominant mutagen in these samples. The +PMS mutagenic potency of FLA although less than CPP is still high, approximating that of BaP. Although bacterial mutagenicity is an important parameter in estimating human health risk for exposure to PAH, the importance of CPP and FLA as health hazards is more strongly suggested by their tumorigenic behavior It is also important to note that in animal bioassay~.~'-~ bacterial mutagenic potency is not always a reliable predictor of activity in other types of bioassays. For example: although CPP tested twice as mutagenic than BaP in our +PMS bacterial mutation assay, BaP was 3-15 times more and human ~ e l l assays. ~~v~~ active than CPP in rodent97a*40 (37) Schmahl, D.; Deutsch-Wenzel, R. P.; Brune, H.; Schneider, P.; Mohr, U.; Habs, M.;Pott, F.; Steinhoff, D. In Enuironmental Carcinogens: Polycyclic Aromatic Hydrocarbons; Grimmer, G.,Ed.; CRC: Boca Raton, FL, 1983; pp 157-219. (38) Busby, W. F.; Stevens, E. K.; Kellenbach, E. R.; Cornelisse, J.; Lugtenburg, J. Carcinogenesis 1988, 9, 741-746. (39) Busby, W. F.; Goldman, M. E.; Newberne, P. M.; Wogan, G. N. Carcinogenesis 1984,5, 1311-1316. (40) Raveh, D.; Slaga, T. J.; Huberman, E. Carcinogenesis 1982, 3, 763-766.
I
- 2
o , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , 0
0
M
30
10
50
0
M
Eqlhivalent sampk Dose
hhtl Figure 8. +PMS bacterial mutagenicity data for the plug-flow surrogate mixture composed of nine components a t the same concentrations as in the plug-flow sample (Table VI). These results are compared with the mutagenicity response expected for the amounts of cyclopenta[cd]pyrene (CPP) and fluoranthene (FLA) present in the sample [ x ( C P P + FLA)]. The equivalent sample dose is the concentration of plug-flow sample needed to give the listed dose of CPP + FL.
Similarly, FLA, although equimutagenic with BaP in our bacterial assay, was 30 times less potent than BaP in a newborn mouse lung adenoma bioassay39and negative in others.37 Surrogate Mixture Testing. A surrogate mixture of the plug-flow sample was produced by combining the nine compounds listed in Table VI so as to duplicate their concentration in the sample. In an attempt a t improving mutagenic correlation between the plug-flow sample and its components, the surrogate mixture was tested at a number of dose levels in the bacterial mutation assay and these results were compared with calculated mutagenicity values. In Table VI, we see that for a 100 bg/mL sample (41) Skopek, T. R.; Liber, H. L.; Kaden, D. A,; Hites, R. A.; "hilly, W. G.J.Natl. Cancer Inst. 1979,63, 309-312. (42) Barfknecht, T. R.; Hites, R. A.; Cavalieri, E. L.; Thilly, W. G., In Toxicological Effects of Emissions from Diesel Engines; Le-, J. Ed.; Elsevier: New York, 1982, pp 277-294.
316 Energy & Fuels, Vol. 4, No. 3, 1990
Lafleur et al.
dose, the +PMS mutagenicity of the surrogate mixture (IMF = 60) compared well with the sum of the mutagenic contributions (IMF = 68); however, these values are roughly a factor of 2 less than the observed mutagenicity of the actual plug-flow sample (IMF = 125 f 14). Overall, the mutagenic contributions of the components accounted reasonably well for the mutagenicity of the surrogate mixture; however, neither result correlated well with mutagenicity of the actual sample. The disparity between predicted results and bioassay results was greatest at 30 pg/mL, so additional bioassay testing was done in this dose range. In order to learn more about the behavior of the components a t low dose, additional bioassay data for the surrogate mixture were obtained for the 040 pg/mL dose range and the data were compared with calculated mutagenic contributions of CPP + FLA [ x ( C P P + FLA)]. When the data were plotted (Figure 8), it became evident that the mutagenicity of the surrogate mixture was clearly greater than the calculated values [C(CPP + FLA)] throughout most of the dose range. Although the unexpectedly elevated mutagenicity response was not evident at dose levels approaching 60 pg/mL, below 20 pg/mL the magnitude of the effect was remarkable. For example, at 10 pg/mL the induced mutant fraction observed for the surrogate mixture was a factor of 6 greater than x ( C P P + FLA). Bioassay results for the actual sample showed an even greater elevation of predicted activity than the surrogate mixture: A t 30 pg/mL the mutagenicity of the sample (IMF = 92 f 11)was 8 times greater than C(CPP + FLA) (IMF = 12) and 5 times greater than the mutagenicity of the surrogate mixture (IMF = 17). Although the mutagenic behavior of the plug-flow sample could not be quantitatively reproduced with the surrogate mixture, the unpredictably elevated mutagenicity level observed with the sample at low doses was also observed with the surrogate mixture and was thus seen to be an important effect that deserves further investigation. 4. High-Performance Liquid Chromatography. Chemical Characterizationby HPLC/DAD. Although CPP was found to be the most important +PMS mutagen, CPP alone or combined with FLA could not account for the total +PMS mutagenicity of either jet-stirred or plug-flow samples a t every dose tested. Also, for both jet-stirred and plug-flow samples, it is likely that a number of important components remain uncharacterized because the low-dose mutagenic behavior of the sample could not be duplicated with known components. Moreover, components subject to analysis by GC (Table 111) accounted for only 44% of the jet-stirred sample and 38% of the plug-flow sample. For these reasons, the samples were further analyzed using HPLC. The HPLC chromatograms for the jet-stirred reactor (A) and the plug-flow section (B)samples are shown in Figure 9. The letters above the peaks refer to data in Table VII. Each peak is listed with its retention time, aromatic carbon number (C,) range and emission yield (mg/kg fuel consumed). Further details are given in the Experimental Section. Two calibration curves, whose use permits the quantitation of PAH for which no reference standards exist,25 were used to calculate values for C, and emission yields (Table VII). The first curve (eq 8) was derived from retention data for reference PAH (see Figure 10) similar in structure to those identified in the sample. It relates C, as a function of elution volume V , as follows:
C, = 0.7087
+ 0.577Ve - 0.00257V2
r = 0.988
(8)
I
30011 J S R
A
I I: I
B
1
3
E 208
100
18
28 Tlme
38
(mtn.)
S8
40
Figure 9. Isocratic HPLC separation of jet-stirred reactor (A) and plug-flow region (B) samples using three 25-cm CN columns with a hexane mobile phase. The ordinate gives the wide-band diode-array response over the 200-400-nm wavelength interval. Component identities and emission yields are found in Table VIII. Retenth Tm i [mn]
0
20
x)
30
UJ
50
60 9
I
0
15
C, = 0.709 t 05mJ - 0.0025m$ , , , , , , , , , , , , r 1 30 45 60 75 90 oution v o h [dl
Figure 10. Correlation between HPLC elution volume (V,) and aromatic carbon number (C,) for PAH separated on a CN column with a hexane mobile phase. The scale at right gives the corresponding number of fused aromatic rings. Bzn = benzene; Nph = naphthalene; Acl = acenaphthylene; Acn = acenaphthene; Flu = fluorene; Ant = anthracene; Phe = phenanthrene; Fla = fluoranthene; Pyr = pyrene; Chr = chrysene; BaA = benz[a]anthracene; BaP = benzo[a]pyrene; BbF = benzo[b]fluoranthene; BkF = benzo[k]fluoranthene; Athn = anthanthrene; BghiP = benzo[ghi]perylene; IPy = indeno[1,2,3-cd]pyrene;Cor = coronene; NCor = naphtho[8,1,2-abc]coronene.
In Figure 10, the aromatic carbon number (C,)is plotted as a function of elution volume (VJ and is also correlated with the number of fused aromatic rings. The retention time scale at the top of Figure 10 corresponds to the one in Figure 9. Equation 8 applies for PAH with molecular shapes similar to those found in the sample and would not be generally applicable because of the effect of molecular topology on HPLC retention of PAH.& In Table VII, each (43) Wise, S.A. In Handbook of Polycyclic Aromatic Hydrocarbons; Bjarseth, A., Ed.; Marcel Dekker: New York, 1983; pp 183-256.
Energy & Fuels, Vol. 4, No. 3, 1990 317
Characterization of Ethylene Combustion Products
Table VII. Characterization of Jet-Stirred/Plug-Flow Samples by HPLC with Spectrometric Diode-Array Detection jet-stirred reactor plug-flow region emission yielde emission yielde C,* t,: min C, ranged mg/kg %YT t,: min C, ranged mg/kg %YT peak" identification 7.2 4.7-5.9 16.4 1.45 7.2 4.8-5.9 16.3 0.81 A 7.9 5.9-6.4 7.8 0.69 7.9 5.9-6.6 10.1 0.50 B 6.6-7.4 26.8 8.7 6.4-7.3 20.1 1.78 8.8 1.32 C benzenef c6 7.4-7.8 17.9 D 7.3-8.2 43.5 3.85 9.4 9.6 0.89 10.2 7.9-10.4 247.1 E 12.2 7.9-10.2 142.9 12.7 10.5 naphthalenefa Go 10.4-11.2 34.9 36.4 13.5 13.4 F 10.2-11.4 3.09 1.80 11.2-12.8 181.5 52.3 14.2 13.9 11.4-12.8 4.63 G 8.98 acenaphthylenefg c12 12.8-13.5 H 1.32 16.3 16.0 12.9-13.7 0.76 26.6 8.6 phenanthrene@ c14 13.5-14.9 21.5 17.8 13.7-15.2 3.58 72.3 17.5 I 1.90 pyrenefg c16 19.2 14.9-15.9 15.2-16.1 J 0.89 2.30 46.5 10.0 19.5 fluoranthenefg cl6 0.75 K 1.55 31.3 8.5 20.5 20.3 15.9-17.1 16.1-17.4 acephenanthrylenefa c16 1.31 14.8 17.1-18.6 22.9 22.2 17.4-19.2 L 3.73 75.4 cyclopenta[cd]pyrenefg c16 0.24 h M 0.79 15.9 2.8 25.2 24.9 18.8-19.6 18.8-19.6 0.36 0.70 14.2 h 4.1 26.2 19.6-20.2 19.6-20.6 N 26.8 13.7 27.4 20.2-21.1 20.5-21.5 0 0.30 h 0.68 3.4 28.0 2.1 21.1-21.9 21.5-22.0 0.19 P 0.84 16.9 30.2 29.6 anthanthreng (322 0.27 31.4 21.9-22.7 22.2-23.0 0.84 17.0 3.0 30.6 Q benzo[ghi]perylenefg c22 0.41 0.89 17.9 4.7 R 23.0-24.3 33.2 32.5 22.7-23.8 coroneng C24 S h 24.3-24.8 0.10 1.1 23.8-24.4 5.6 0.28 35.9 35.0 T 0.14 h 24.8-25.7 9.3 0.46 1.6 37.0 36.1 24.4-25.4 h U 25.8-26.6 0.17 10.4 0.51 1.9 39.4 38.3 25.4-26.2 V 26.6-27.9 0.36 1.14 h 4.1 41.5 40.3 26.2-27.3 23.0 28.0-28.8 0.06 W h 46.0 43.5 27.3-28.5 5.5 0.27 0.7 28.8-29.6 X h 47.2 0.08 4.3 0.21 0.9 48.6 28.5-29.3 29.7-31.1 Y 51.4 naphtho[8,1,2-abc]coronenef C m 0.19 14.3 0.71 2.1 50.2 29.3-30.7 total HPLC eluate 4.7-31.1 413.8 36.62 4.8-30.7 956.2 47.29 ~
Listed peaks are shown in Figure 9. * C, = number of aromatic carbon atoms in identified components. t, = retention time in minutes. dRange of C , values corresponding to width of peak; calculated from eq 8. eMass (mg) of effluent emitted per kg of fuel consumed. 'Identification by GC/MS. #Identified by correlation with elution volume and UV spectrum of authentic standard. UV spectrum obtained but could not be interpreted. (I
Table VIII. +PMS Mutagenicity Results for Neutral Fractions of Plug-Flow Sample sample fraction recovered injected on column N1 N2 N3 N4 N5 N6 weight, mg 8.64 0.105 1.050 0.795 0.330 0.345 1.40 weight fraction, % 100 1.2 12 9.2 4.0 4.0 16 12 12 48 tested dose, pg/mL 300 3.6 36 28 +PMS mutagenicity, IMF" mutagenic contribution, %
269 f 61
Distribution of +PMS Mutagenicity 0 24 144 78 0 9.0 54 29
32 12
13 5.0
eluate, total recovered 4.03 46.6
291 109
"IMF = induced mutant fraction (X106)followed by 99% confidence limits.
peak is given a C, range derived from eq 8. The beginning and end of the peak elution interval correspond to the lower and upper C, values of the C, range. Equation 9 gives the wide-band (200-400 nm) diodearray response factor (RF,) for PAH in units of ng/area as a function of aromatic carbon number (Cn): RF, = 22.5e-0.293Cn 0.478 r2 = 0.99 (9)
+
The response factor for each peak is computed by solving eq 8 for C, and then using this value in eq 9 to obtain the response factor (RF,). The amount of material can then be obtained as follows: Qi (ng) = [peak areali (area units) X [RF,], (ng/area units) (10) Emission yields were calculated by using eq 6. Relative emission yields are given as percent values based on the total gravimetric emission yields found in Table I. As seen in Table VII, components in peaks A-Y ranged in carbon number from C6 to Cm which corresponds to one to nine fused aromatic rings. Quantitative determinations over a range of values were roughly comparable to those obtained using GC/FID: For example, the C14 C16 species in Table VI1 (peaks H, I, J, K)give a total emission
+
yield of 48.6 mg/kg for the jet-stirred sample and 176.7 mg/kg for the plug-flow sample. Comparable CI4 + C16 emission yields obtained by GC/FID (Table 111) are 74 mg/kg and 164 mg/kg, respectively. Emission yields for individual PAH cannot generally be compared because the CN-HPLC columns used here could not resolve individual components in these samples. Many large PAH were detected by HPLC/DAD and anthanthrene, benzo[ghi]perylene, coronene, and naphtho[8,1,2-abc]coronenewere identified, but other components still eluded identification, especially those PAH in the C24-C30 range (seven to nine fused aromatic rings). Although UV spectra of good quality were obtained for these components (peaks S-X)none of the spectra could be traced to known compounds. Fractionation of Neutral PAH. Further work focused on the plug-flow sample because it was more stable than the jet-stirred sample which was known to contain larger amounts of reactive species.22 Portions of the plug-flow sample were separated by HPLC into neutral and polar fractions which were then tested for +PMS and -PMS activity by bacterial mutation assay. The plug-flow sample was fractionated on an HPLC column into six neutral PAH fractions which were tested
Lafleur et al.
318 Energy & Fuels, Vol. 4, No. 3, 1990
for bacterial mutagenicity and were analyzed by GC/MS as detailed in the Experimental Section. In Table VIII, the +PMS mutagenicity of the sample is compared with mutagenic contributions of individual fractions. Although the recovered fractions accounted for only 46.6% of the initial sample mass, all of the mutagenic activity of the sample was recovered. The separation procedure was optimized for resolving neutral species only and did not utilize mobile phases suitable for the complete elution of the sample; therefore, the amount of eluate recovered is not expected to equal the amount injected. The fractions were subjected to GC/MS and HPLC/DAD analysis and were assayed for mutagenicity at dose levels corresponding to a whole sample dose of 300 pg/mL. The data are summarized as follows: Fraction N1 contained simple one to two ring aromatics including benzene and naphthalene and was found to be nonmutagenic. Fraction N2 contained acenaphthylene, phenanthrene, pyrene, fluoranthene, and acephenanthrylene, and it contributed 8% of the total mutagenicity. Fraction N3, containing cyclopenta[cd] pyrene, was the most active fraction and accounted for 50% of the +PMS bacterial mutagenicity of the whole sample. Fraction N4 containing only 4% of the mass was responsible for 27% of the +PMS mutagenicity at high dose. Results from GC/MS analysis indicated that benzo[ghi]perylene was the major component; however, it is only weakly mutagenic in our mutation assay and could not account for the activity of the whole fraction. The second most abundant component in fraction N4 gave an apparent molecular ion at m/z 250 and is suspected to be a novel PAH. Three different PAH with apparent molecular weight of 250 were found in the plug-flow sample. Plausible structures include isomers of di[cyclopenta]pyrene and ethynylcyclopenta[cd]pyrene,all of which would give similar mass spectra. Anthanthrene and coronene were also identified in this fraction from their UV spectra. Although fraction N5 was responsible for 11% of the total +PMS mutagenic activity, no components could be identified by gas chromatographic techniques including GC/FID, GC/MS, and GC/FTIR. HPLC/DAD data indicated that it contained C24-c30 PAH eluting between coronene and naphtho[8,1,2-abc]coronene.PAH in this molecular weight range are generally not volatile enough for analysis by GC-based methods. HPLC/DAD data showed that fraction N6 contained naphtho[8,1,2-abc]coroneneand probably other C30 PAH or some of slightly larger molecular size. As in fraction N5, components in fraction N6 were of insufficient volatility for GC-based chemical analysis. Overall, the HPLC data confirmed that CPP is the most important +PMS bacterial mutagen in the plug-flow sample, although it is clear that other important sources of +PMS mutagenicity are present in the sample and deserve further investigation. Fractionation of polar species. Combustion-derived samples and fractions reported to have -PMS activity have Likewise, comgenerally been polar in pounds exhibiting -PMS activity in our forward mutation assay have also been polar species. As stated earlier, the most common -PMS mutagens appear to be nitroa r e n e ~ ; ~however, l - ~ ~ some oxygenated polycyclic aromatic compounds are also known to be -PMS mutagens.36 Although each sample or one of its fractions exhibited -PMS mutagenic activity, initial chemical analysis failed to reveal obvious sources; therefore HPLC methods were employed for additional characterization. The plug-flow sample was fractionated by HPLC into six fractions of
I
o c
1
I
-
7
4
HPLC F R A C T I O N A T I O N A N D BIOASSAY RESULTS
i i I
i
060
w
y
I
HPLC FRACTIONS
N
II
040
I
I
i
I
I
v) 0
2 020
’
0% l 3 i ” L 0%
tPMS
13%
T-PMS
001
I
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500
I000
1 I
0% 0%
I
I I
1500
0%
75%
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I0 %
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1 3000
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Figure 11. HPLC separation of plug-flow sample into six polar fractions on a preparative CN column using a hexane/dichloromethane mobile phase. +PMS and -PMS bacterial mutagenicity results are given for each fraction. Fraction 4, containing little material, accounts for the bulk of the -PMS bacterial mutagenicity.
increasing polarity, and the fractions were subjected to bioassay and chemical analysis. The preparative HPLC chromatogram for the polar fractionation is shown in Figure 11 along with mutagenicity results. The HPLC conditions and other details are found in the Experimental Section. It is seen that all of the +PMS activity could be traced to the first neutral fraction, as anticipated, and that a single polar fraction (fraction 4 in Figure 11) was responsible for the bulk of the -PMS activity. Since wideband absorbance is proportional to concentration for PAH, the -PMS mutagens in this fraction are active at exceptionally low dose levels. Although fraction 4 is the major source of -PMS activity, a significant (13%) level of -PMS activity was also detected in the neutral fraction. This confirms similar results obtained from the HPLC fractionation of the neutral species. HPLC retention data obtained with reference compounds showed that fraction 4 eluted in the retention interval predicted for polynitrated aromatics. Although the finding of such species would be consistent with the significant -PMS mutagenicity and small mass of fraction 4, no evidence for such a finding could be obtained. Chemical analysis by all available methods proved incapable of shedding light on the identity of the compounds responsible for the -PMS mutagenicity of fraction 4. Future work will focus on characterizing the -PMS mutagens by generating larger amounts for conventional analyses and also by using HPLC with improved methods of detection such as LC/MS or LC/IR.
Summary 1. Samples taken from both the jet-stirred and plug-flow regions were active in the S . typhimurium forward mutation assay with and without the addition of an exogenous metabolizing enzyme system (PMS). 2. Cyclopenta[cd]pyrene was the most important +PMS bacterial mutagen identified followed by fluoranthene. At high sample dose levels the sum of the mutagenic contributions of CPP and FLA approximated the observed mutagenicity of the samples. 3. At low dose (30 pg/mL), the +PMS mutagenicity of the plug-flow sample was 8 times higher than would be predicted on the basis of the mutagenic contributions of known components. Similarly, an unpredictably elevated low-dose mutagenicity result was also obtained with a nine-component surrogate mixture whose composition was
Energy & Fuels 1990,4, 319-333 based on the plug-flow sample. 4. HPLC/DAD analysis revealed the presence of a number of CZo-C30 PAH not detectable by the GC-based methods. Together, the three HPLC fractions containing C20-C30 PAH accounted for 42% of the total +PMS mutagenicity when tested a t doses equivalent to a sample concentration of 300 pg/mL. 5. Nineteen major components were identified by GC/MS and GC/FTIR of which nine were ethynyl-substituted. Examples included diethynylbenzenes, 2ethynylnaphthalene, and three ethynylacenaphthylene isomers, one of which was among the 10 most abundant species.
319
6. A number of nitrogen-containing organics were detected at trace levels by GC with nitrogen-specific detection, thus implying the fixation of atmospheric nitrogen. Further analysis in a nitro-specific mode gave negative results for nitro compounds.
Acknowledgment. This investigation was supported by National Institute of Environmental Health Sciences Center Grant NIH-5P30-ES02109-10 and Health Effects of Fossil Fuels Utilization Program Grant NIH-5PO1ES01640-10. We thank Fred Lam, Craig Vaughn, and Edward Kruzel for their assistance in obtaining the combustion sample and for fruitful discussions.
Analysis of the Argonne Premium Coal Samples by Thermogravimetric Fourier Transform Infrared Spectroscopy P. R. Solomon,* M. A. Serio, R. M. Carangelo, and R. Bassilakis Advanced Fuel Research, Inc., 87 Church Street, East Hartford, Connecticut 06108
D. Gravel, M. Baillargeon, F. Baudais, and G. Vail Bomem, Inc., 450 rue S t . Baptiste, Quebec City, Quebec, Canada Received October 19, 1989. Revised Manuscript Received April 2, 1990
We have developed a TG-FTIR instrument that combines thermogravimetric analysis (TGA) with evolved product analysis by Fourier transform infrared (FT-IR) spectroscopy. FT-IR analysis of evolved products has advantages over mass spectroscopy in allowing analysis of very heavy products and over gas chromatography in speed. This paper describes the most recent improvements in the apparatus and presents its application in characterizing the Argonne premium coal samples. The TG-FTIR apparatus for pyrolysis, oxidation of pyrolysis products, and oxidation of the sample is described. To analyze coal, a sequence of drying, pyrolysis, and combustion is employed to obtain proximate analysis, volatile composition, volatile kinetics, and relative char reactivity. Pyrolysis results are presented for the eight Argonne coals, several demineralized coals, and two oxidized samples of Pittsburgh Seam coal. A kinetic analysis was applied to species evolution data collected at several different heating rates. There is a systematic variation in rate with rank. The rate for tar evolution from Pittsburgh Seam coal is in good agreement with that of Burnham et al. using a similar set of data. Analysis of the amounts of evolved products also show a systematic variation with rank consistent with the coal's elemental and functional group comositions. Postoxidation of the volatile products has been successful in providing elemental composition information on the volatile products as well as showing the evolution of HP,which is not infrared active, and H2S (in the postoxidized SO, profile), which is a weak infrared absorber. Oxidation of the char yields an ash amount as well as two measures of the char's reactivity, the oxygen absorbed by the char and the temperature a t which significant oxidation of the char occurs.
Introduction
Thermogravimetric analysis (TGA) has been employed in coal science to perform a number of characterizations 0887-0624/90/2504-0319$02.50/0
including proximate analysis,' kinetics of weight ~ O S S , ~ ~ ~ char and gas adsorption measurements.'O A complimentary technique, evolved-product analysis, has been employed to study pyrolysis product distributions 0 1990 American Chemical Society
