Anal. Chem. 1983, 55, 1893-1896 (6) Su, S. Y.; Jurgensen, A.; Bolton, D.; Wlnefordner, J. D. Anal. Lett.
1981, 14, A l , 1-6. (7) Su, S. Y., Lai, E. P. C.; Wlnefordner, J. D. Anal. Lett. 1982, 15, A5, 439-450. (8) Donkerbroek, J. J.; Veltkamp, A. C.; Praat, A. J. J.; Gooijer, C.; Frel, R. W.; Velthorst, N. H. Appl. Spectrosc. 1983, 37, 188-192. (9) Almgren, M. Photochem. Photoblol. 1967, 6 , 829-840. (10) Donkerbroek, J. J.; Elzas, J. J.; Gooijer, C.; Frel, R. W.; Velthorst, N. H. Talanta 1981, 28, 717-723. (11) Donkerbroek, J. J.; Gooijer, C.; Velthorst, N. H.; Frei, R. W. Anal. Chem. 1982, 5 4 , 891-895. (12) Turro, N, J. “Modern MoUecular Photochemistry”, 1st ed.; The BenjaminlCummings Publishing Co.: Menlo Park, CA, 1978; Chapter 5. (13) Turro, N. J. “Modern Molecular Photochemistry”, 1st ed.; The BenJamin/Cummings Publishing Co.: Menlo Park, CA, 1978; Chapter 9. (14) “Handbook of Chemistry and Physics”, 55th ed.; Chemical Rubber Co: Cleveland, OH, 1974-19’75; pp E74-E78. (15) Goodman, L. S.; Gilrrian, A. The Pharmacological Basis of Therapeutlcs”, 4th ed.; MacMillan: London, 1979; Chapter 2. (16) Burger, A. “Medicinal Chemistry”, 2nd ed.; Interscience: New York, 1960; Chapter 6. (17) Fulton, A.; Lyons, L. E. h s f . J . Chem. 1968, 2 1 , 873-889.
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(18) Fulimori, E. Mol. Photochem. 1974, 6 , 91-93. (19) Lepri, L.; Deslderl, P. G.; Helmler, D. J . Chromatogr. 1980, 19-5, 339-348. (20) Bortolus, P.; Delontei, S. J . Chem. Soc., Faraday Trans. 2 1975, 71, 1338-1342. (21) Rehm, D.; Weller, A. Ber. Bunsenges. Phys. Chem 1969, 7 9 , 834-839. (22) “Handbook of Chernlstry and Physics”, 50th ed.; Chemlcal Rubber Co.: Cleveland, OH, 1969-1970; pp D 1 0 9 - D l l l . (23) Wlnefordner, J. D.; Schulman, S. G.; O’Haver, T. C. “Luminescence Spectrometry in Anialytical Chemistry”, Vol. 38; Wiley-Interscience: London, 1978; p 213-215. (24) Werkhoven-Goewie, C. E.; Nlessen, W. M. A,; Brinkman, U. A. Th; Frei, R. W. J . Chrornatogr. 1981, 203, 165-172. ’ (25) Hanekamp, H. B.; 130% P.; Frei, R. W. J . Chromatogr. 1979, 186, 489-496.
RECEIVED for review March 7,1983. Accepted June 1, 1983. Presented in part art the Pittsburgh Conference (ASTILI Symposium), Atlantic City, NJ, March 7-12, 1983.
Determination of Polycyclic Aromatic Hydrocarbons in Unfractianated Solid Solvent-Refined Coal by Matrix Isolation Fluorescence Spectrometry Mildred B. Perry, E. IL. Wehry,* and Gleb Mamantov* Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996
An untreated solid solvent-reflned coal sample yields matrix Isolation fluorescence spectra suitable for identlflcatlon and determinatlon of polycyclllc aromatic hydrocarbons. Selectlve excitation of fluorescence in Shpol’skll matrlces and background suppresslon usinig the time resolutlon capabllltles of a dye-laser spectrometer permit the unambiguous Identlflcation of PAHs includlng be!nro[a Ipyrene. Determinatlon of four polycyclic aromatic hydrocarbons (benzo[a Ipyrene, perylene, benr[a]anthracene, and benro[bYluorene) in Solvent Reflned Coal I Is reported, as Is the determlnation, by Identical spectrometric technique, of the benzo[a]pyrene content of a NBS shale oil standard reference material.
Continuing interest in fossil fuel alternatives to petroleum has placed increasing deimands upon analytical methodologies for the characterization of highly complex samples, such as coal-derived liquids and solids. Some products of coal conversion are believed to contain significant quantities of polycyclic aromatic hydrocarbons (PAHs), many of which are carcinogens. Most procedures for characterization of these “real” samples require elaborate separation schemes which are time-consuming and subject to losses of sample constituents and/or introduction of contaminants (1-4). Most PAHs absorb strongly in the UV and/or visible spectral regions and are highly fluorescent. At cryogenic temperatures, electronic spectral bands of most PAHs are narrow and distinctive (5). If a sample is frozen in certain n-alkanes, either from solution or by codeposition with the alkane in the gas phase (“matrix isolation”, MI), absorption and emission bands of some PAHs are reduced to “quasi-lines” (the Shpol’skii effect); energy transfer is minimized, and conditions are nearly optimal for observation of highly resolved
fluorescence or phosphorescence spectra (5-16). In an MI experiment, analytes are sublimed or distilled from the sample and then mixed with the matrix solvent in the gas phase (5, 17,18); therefore, NU is not subject to solubility limitations which may be encountered in frozen-solution experiments. Even under cryogenic conditions, unfractionated complex samples tend to yield spectra with severely overlapping bands and a broad background when continuum excitation sources are used. Continuously tunable dye-laser spectrometers permit exploitation of the narrow absorption features of solute species in low-temperature samples (11, 12, 19-21). This work evaluates the utility of MI fluorescence spectrometry for the identification and determination of PAHs in an intractable solid solvent-refined coal (SRC I) sample without any prior fractionation. Continuum-source (xenon lamp) excitation wa!3 used when possible for a general survey of PAH content, and narrow-band (dye-laser) excitation was used for selective excitation of PAH fluorescence.
EXPERIMENTAL SECTION A solid SRC I sample, prepared in a Southern Company Services, Inc., pilot plant in Wilsonville, AL, operated by Catalytic, Inc., was obtained from Peter W. Jones (Electric Power Research Institute, Palo Alto, CAI; the feedstock was an Illinois No. 6 coal. The elemental composition of the sample was as follows: C, 85.89%; H, 6.02%; Pi, 2.07%; and S, 0.90%. Small portions of the sample were pulverized with a mortar and pestle and sieved (245 ,urn), and then stored in the dark under dry nitrogen until used. For deposits o€SRC I, 200-7OO-wg portions were weighed by difference with a Cahn Model 7000 Electrobalance. A shale oil standard reference material (SRM 1580), obtained from the National Bureau of Standards, Washington, DC, was transferred, immediately after opening each vial, to a sample container made by modifying a two-part in-line valve (Fisher 14-630-7A)which permitted the sample to be frozen while the air above it was evacuated. The sample was stored under vacuum
0003-2700/83/0355-1893$01.50/00 1983 Amerlcan Chemlcal Soclety
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 12,OCTOBER 1983 Heptane
Octane
B I
,
Aexc:389.4nm
400
,
410
I
420
l
:389.2 nm
,A,
80ns Delay
100ns Delay
l
4ao
l
400
l
l
120
,
,
440
,
,
L
460
nm
Flgure 1. Laser-excited fluorescence spectra of benzo[a Ipyrene In SRC I at 15 K in vapor-deposited n-heptane (A) and n-octane (B) matrices. in this container in the dark until use. For MI sample preparation, a conventional Knudsen cell (22) was modified to accommodate solid samples by enlargingthe front orifice from 0.5 mm to 4 mm diameter. Samples were codeposited by vacuum sublimation with matrix gas as described previously (17). Upon completion of deposition, samples in n-heptane and n-octane matrices were annealed (23) at 150 K and 155 K, respectively, for 5 min before viewing spectra at 15 K. Matrix solvents including “distilled in glass” n-heptane (Burdick and Jackson) and 99.8% (GC) n-octane (Tridom Chemical, Inc.) were used as received. The total time required for the complete deposition procedure (cool-down, deposition, and annealing) was typically 2 h. Continuum-sourceinstrumentation (7 nm h h m ) (24)and laser fluorometric instrumentation (19,ZO) have been described previously. Angle-tuned KDP crystals were used for frequency doubling the output of the dye laser. All quantitative determinations were performed with a dye-laser spectrometer. Deposits of SRC I (360 pg/deposit) in n-octane were used to obtain a quantitative “standard addition” plot for each analyte; three different spikes were used. Internal standards and spikes of analyte were injected into the Knudsen cell from solutions of pure compounds and the solvent was evaporated before adding the sample to the cell. For each determination, one deposit also was prepared for the unspiked sample. Thus, each “standard addition plot” contained four points. For each point, the ratio of the fluorescence intensity of the analyte to that of the internal standard was measured and plotted (24). For each analyte, an internal standard was chosen that could be excited at a wavelength at which the analyte absorbed strongly, but did not exhibit a fluorescence spectrum that overlapped that of the analyte. The purpose of this procedure was to compensate for drift in laser power (a self-correcting fluorometer was not used) and irreproducibility in amount or spatial distribution of the matrix-isolated sample on the deposition surface (24). Care was exercised to ensure that all standard additions occurred on the linear portion of the analytical calibration curve for the analyte. The accuracy of the method for SRC I was evaluated by performing a determination of benzo[a]pyrene in SRM 1580. The presence of benzo[a]pyrene was confirmed in SRM 1580 by preparing deposita of 1.5 pL of shale oil in heptane and octane. A density of 0.895 mg/pL for the shale oil sample was used to convert weight/volume measurements to a weight/weight basis (pg/g or P P d .
RESULTS AND DISCUSSION Shpol’skii matrices were found t o be optimum media for identification of PAHs in SRC I because of the very narrow but intense “quasi-lines” produced for PAHs in annealed MI deposits. Because the fluorescence spectra of several PAHs of interest (e.g., benzo[a]pyrene, benz[a]anthracene, and benzo[b]fluorene) exhibit complex multiplet structure in n-heptane but singlets in n-octane, these two Shpol’skii solvents were chosen for the characterization of SRC I and SRM 1580. The multiplets served as excellent “fingerprints” for identification of individual compounds (Figure lA), while the singlets (Figure 1B) were considered more useful for quantification.
320
340
380
400
380
440
420
460
~480
nm
Flgure 2. Lamp-excited fluorescenceand phosphorescence spectrum (A,,, = 300 nm) of SRC I in a heptane matrix at 15 K: BbF, benzo[blfluorene; Ph, phenanthrene; BaA, benz[a ]anthracene; Py, pyrene; BaP, benzo[a Ipyrene. 8
7, IO-DM-BtalP
SRC I
l
1
400
l
420
l
nm
I
440
407.1
l
l
460
u 420 nm
400
Flgure 3. Laser-excited fluorescence spectra (A,, = 365.0nm, 60 ns delay)of pure 7,10dimethylbenzo[a]pyrene (B) and SRC I (A), both in n-octane matrices at 15 K.
u u 350 330 350 330 35 0
330
nrn Flgure 4. Variation of relative fluorescence signals from benzo[a 3fluorene and benzo[b]fluorene in n-heptane matrices at 15 K as a function of the delay time between the laser-pulse and measurement of fluorescence. Several PAHs were identified in SRC I by using xenon-lamp excitation of fluorescence (e.g., Figure 2); such spectra are useful for preliminary “rapid screening” of complex samples. However, deposits of SRM 1580 yielded no distinct spectral bands which could be assigned to PAHs when lamp excitation was employed. SRM 1580 is known to contain appreciable quantities of polar compounds which exhibit broad absorption and emission bands even a t low temperatures (20). In Shpol’skii matrices, use of dye-laser excitation enabled fluorescence spectra of a number of PAH constituents to be excited selectively. Example fluorescence spectra are shown for BaP (Figure 1) and 7,10-dimethylbenzo[a]pyrene(7,lODMBaP) (Figure 3) in SRC I. The time-resolution capability of the dye-laser spectrometer was highly effective in reducing background in spectra of SRC I as well as in confirming the identities of specific PAH constituents (e.g., benzo[a]fluorene, and benzo[b]fluorene; Figure 4) in SRC I.
ANALYTICAL CHEMISTRY, \/OL. 55, NO. 12, OCTOBER 1983
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Table I. PAHs Identified in Solvent Refined Coal compound
abbr
matrix
benz [ a ]anthracene benzo[ a ] fluorene benzo[ b ]fluorene benzo [ b ]fluorene 7,lO-dimethylbenzo [ a Ipyrene benzo[a]pyrene benzo[a]pyrene benzo[k Ifluoranthene! chrysene perylene perylene pyrene pyrene phenanthrene triphenylene
BaA BaF BbF BbF 7,lO-DMBaP BaP BaP BkF C Per Per PY
octane heptane heptane octane octane octane heptane octane heptane heptane octane octane heptane heptane heptane
PY Ph T
laser, nm 280.0 265.0 265.0 275.0 365.0 389.2 389.4 312.0 271.0 388.5 389.4 275.0
hex,,
delay, ns
SRC I, pure cmpd, hem,nm 385.1 385.1 347.1 347.1 340.3 340.3 340.5 340.5 407.1 407.1 403.9 403.9 403.7 403.7 404.3 404.3 361.5 361.5 445.9 445.9 445.6 445.6 372.9 372.9 372 372 347 347 352.6 352.6
lamp, nm
hex,,
80 30 60 20 60 80 100 4 50 10 0 120
hem,=
260, 315 300 305
31 5 300 305
I _ _
Table 11. Results of Determinations sample SRM 1580 SRC I SRC I SRC I sac I a
analyte BaP BaP perylene BaA BbF
int std perylene perylene BaP BaP pyrene
corr coeff 0.9926 0.9991 0.9997 0.9959 0.9906
certified 23. i 6
found, pglg 23 i. 4a 83 t 19 41 t 7 1.3 i 0.2 220 t 63
95% confidence interval calculated via linear regression of the analyte addition plot ( 2 6 ) . -___
Spiking the sample with a solution of a pure PAH suspected to be present in the sample also was useful in certain cases for confirming the identification of peaks in spectra of SRC I deposits. As exemplified for benz[a]anthracene (Figure 5), a peak was first noted in a spectrum of SRC I. If the ,A, of that peak matched a major peak in the spectrum of a pure PAH in the same matrix, a second deposit was prepared which was spiked with the suspected compound. If there was no detectable shift in band location, production of a spectral multiplet, or detectable chtmge in the fluorescence decay time of the spectral feature in question, then an increase in the intensity of the suspected peak was construed as verification of the identity of the suspected compound. The PAHs identified in SRC 1 (and the relevant spectral data) are compiled in Table I. The excitation wavelengths listed in Table I are compromise choices. In principle, the maximum analytical selectivity is achieved by exciting into, or as close as possible to, the 0-0 transition. However, doing so may result in decreased sensitivity, because the 0-0 bands are not necessarily the most intense absorption features for PAHs in Shpol'skii matrices (25). Moreover, for determination of PAHs, it is highly desirable to use the same excitation wavelength for the analyte and internal standard, in order to avoid retuning the laser to measure the fluorescence of the internal standard. Because absorption bands of PA& in Shpol'skii matrices are very sharp, especially in the 0-0 region, small uncertainty in retuning the laser produces serious imprecision in the analytical results (21). Each excitation wavelength listed in Table I corresponds to a wavelength at which both the PAH in question and a plausible internal standard (whose fluorescence does not overlap that of the indicated PAH) absorb strongly. Thus, fluorescence intensity ratios in "standard addition curves" can be measured without changing the excitation wavelength. Excitation in SRC I at the indicated wavelengths was sufficiently selective tci permit unambiguous identification of the indicated PAHs (see Figure 1,3,4, and 5 for examples). Clearly, the "optimum excitation wavelength" for a given PAH may vary, depending upon whether the objective of the ex-
280.0nm 8011s Delay
A,,,:
BaA
I
-
360
'
'
380
'
'
nm
'
400
I
420
Figure 5. Laser-induced fluorescence spectrum of SRC I (top) and
SRC I spiked with benzl alanthracene (bottom). The "spiking" experiment confirms assignment of the spectral band denoted * to BaA,. periment is detecting the presence of the compound or quantifying it. Determination of four PAHs (benzo[a]pyrene, perylene, benz[a]anthracene, and benzo[ blfluorene) in SRC I was performed. The results are listed in Table 11. Because this sample has not been previously characterized and no suitable solid standard reference material was available, the accurac,y of the reported values cannot be satisfactorily assessed. In a determination of BaP in SRM 1580,the present result (2:3 f 4 Fg/g) compares favorably with the NBS certified value (21 A 6 wg/g), indicating that the basic measurement techlniques are quite accurate. For a solid sample such as SRC I, the accuracy ultimately is determined by the "recovery" of analyte sublimed frorn the initial solid. The reproducibility of the results for SRC I and their lack of sensitivity to changes
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Anal. Chem. 1983. 55. 1896-1901
in deposition parameters (such as time and temperature of sublimation) strongly suggest that the removal of PAHs from SRC I by this procedure is quantitative. The precision of the quantitative results of PAHs in SRC I and the accuracy of the BaP determination in SRM 1580 indicate MIF to be a promising technique for identification and determination of PAHs in unfractionated “real” samples. While frozen-solution Shpol’skii spectrometry has been utilized with considerable success for the determination of PAHs in unfractionated coal liquids (IO), it is less likely (because of solubility requirements) that this technique could be successfully applied to the direct characterization of intractable solid samples such as SRC I. Since quantitative applications of MIF are not constrained by solubility requirements or the efficiencies of solvent-extraction procedures, the greatest success of this technique (as compared with other low-temperature fluorometric methods) should be realized for solid samples containing PAHs in the parts-per-million range.
ACKNOWLEDGMENT We thank Peter W. Jones for providing the SRC I sample used in this investigation. Registry No. Benzo[a]pyrene, 50-32-8; perylene, 198-55-0; benz[a]anthracene, 56-55-3; benzo[blfluorene, 30777-19-6; ben63104zo[a]fluorene, 30777-18-5; 7,10-dimethylbenzo[a]pyrene, 33-6; benzo[k]fluoranthene, 207-08-9; pyrene, 129-00-0;phenanthrene, 85-01-8; triphenylene, 217-59-4; chrysene, 218-01-9.
LITERATURE CITED (1) Lee, M. L.; Novotny, M. V.; Bartle, K. D. “Analytlcal Chemistry of Polycyclic Aromatic Compounds”; Academic Press: New York, 1981. (2) Futoma, D. J.; Smith, S. R.; Tanaka, J. CRC Crlt. Rev. Anal. Chem. 1982, 73, 117.
Karasek, F. W.; Clement, R. E.;Sweetman, J. A. Anal. Chem. 1981, 5 3 , 1050A. Janardan, K. G.; Schaeffer, D. J. Anal. Chem. 1979, 57,1024. Wehry, E. L.; Mamantov, G. I n “Modern Fluorescence Spectroscopy”; Wehry, E. L., Ed.; Plenum: New York, 1981; Vol. 4, p 193. Shpoi’skil, E. V.; Bolotnikova, T. N. Pure Appl. Chem. 1974, 37, 183. Klrkbrlght, G. F.; de Lima, C. G. Analyst (London) 1974, 99, 338. ColmsJo, A.; Stenberg, U. Chem. Scr. 1978, 9 , 227. Colmsjo, A.; Stenberg, U. Anal. Chem. 1979, 57, 145. Yang, Y.; D’Silva, A. P.; Fassel, V. A,; Iles, M. Anal. Chem. 1980, 52, 1350. Yang, Y.; D’Sllva, A. P.; Fassel, V. A. Anal. Chem. 1981, 53,894. Yang, Y.; D’Sllva, A. P.; Fassel, V. A. Anal. Chem. 1981, 53,2107. Lai, E. P.; Inman, E. L., Jr.; Wlnefordner, J. D. Talanta 1982, 2 9 , 601. Rima, J.; Lamotte, M.; Joussot-Dubien, J. Anal. Chem. 1982, 54, 1059. Garrlgues, P.; Ewald, M.; Lamotte, M.; Rlma, J.; Veyres, A,; Lapouyade, R.; Joussot-Dubien, J. I n t . J . Envlron. Anal. Chem. 1982, 7 7 , 305. Garrigues, P.; De Vazelhes, R.; Ewald, M.; Joussot-Dubien, J.; Schmlttar, J.-M.; Gulochon, G. Anal. Chem. 1983, 55, 138. Wehry, E. L.; Mamantov, G. Anal. Chem. 1979, 57,A643. Wehry, E. L. Trends Anal. Chem. 1983, 2 , 143. Maple, J. R.; Wehry, E. L.; Mamantov, G. Anal. Chem. 1980, 52, 920. Maple, J. R.; Wehry, E. L. Anal. Chem. 1981, 53,266. Conrad, V. 6.; Wehry, E. L. Appl. Spectrosc. 1983, 37,46. Hembree, D. M.; Hinton, R. E., Jr.; Kemmerer, R. R.; Mamantov, G.; Wehry, E. L. Appl. Spectrosc. 1979, 33,477. Tokousbalides, P.; Wehry, E. L.; Mamantov, G. J . Phys. Chem. 1977, 87, 1769. Stroupe, R. C.; Tokousballdes, P.; Dlckinson, R . B., Jr.; Wehry, E. L.; Mamantov, G. Anal. Chem. 1977, 4 9 , 701. Farooq, R.; Kirkbright, G. F. Analyst (London) 1976, 707,566. Larsen, I. L.; Hartmann, N. A.; Wagner, J. J. Anal. Chem. 1973, 4 5 , 1511.
RECEIVEDfor review April 25, 1983. Accepted July 15, 1983. This research was supported in part by the National Science Foundation (Grant CHE-8025282) and the Electric Power Research Institute (Contract RP-1307-1).
Spectrofluorimetric Determination of Polycyclic Aromatic Hydrocarbons in Aqueous Effluents from Generator Columns Rance A. Velapoldi,* Patricia A. White, and Willie E. May Center for Analytical Chemistry, National Bureau of Standards, Washington, D.C. 20234
Keith R. Eberhardt Center for Applied Mathematics, National Bureau of Standards, Washington, D.C. 20234
An on-stream, standards addltlon spectrofluorlmetrlc technlque has been used to determine the concentratlons of anthracene, benz[a]anthracene, and benzo[a]pyrene In the effluents of generator columns (which yield saturated solutlons) at temperatures between 10 and 30 OC. Concentratlon values for the standard solutions of PAH’s In water over thls temperature range were as follows: anthracene, 9.9 X IO-’ to 34.4 X mol/L; benz[a]anthracene, 1.5 X lo-’ to 5.7 X IO-’ mol/L; and benzo[a]pyrene, 2.4 X to 8.9 X I O T g mol/L. Confidence llmlts (99 % Worklng-Hotelling) for the values at 25 OC were approxlmately 3-8% of the concentratlon. The method provides data that agree well wlth data from dynamic coupled column hlgh-performance llquld chromatography and, together wlth these values, were used to certlfy the effluent PAH concentratlons of the Standard Reference Material generator columns. The method can be used to determlne PAH concentratlons In aqueous effluents, aqueous solubllities, and octanol-water partltlon coeff lcients In a fast, easy procedure.
The widespread presence in the environment of polycyclic aromatic hydrocarbons (PAH’s), some of which are known carcinogens, has necessitated the development of accurate methods for PAH analyses. The role of standards and more specifically Standard Reference Materials (SRM’s) in method development has been well documented (1,2) and the National Burea of Standards (NBS) has recently certified the concentration of PAH’s in a number of matrices including shale oil (SRM 1580), acetonitrile (SRM 1647), Urban Dust/Organics (SRM 1649), and Water (SRM 1644). Development of the latter was hampered because the usual procedures to produce stable aqueous standard solutions were not successful. Direct gravimetric procedures are hampered by low aqueous solubilities (3,4). Formation of saturated solutions by stirring excess PAH in an aqueous medium leads to the phenomenon of “accommodation” in which microparticles mimic the dissolved PAH (5). Dissolution of the PAH in an organic solvent followed by successive dilutions of the solution is wasteful of organic solvent and sometimes scarce chemicals. Additionally,
This article not subject to US. Copyright. Published 1983 by the Amerlcan Chemical Society
