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Anal. Chem. 1983, 55,2229-2231
Determination of Aromatic Hydrocarbons in Particulate Samples by High-Temperature Extraction and Shpol'skii Spectrometry Gordon D. Renkes,' Sandra N. Walters, Ching S. Woo: Malvern K. Iles, Arthur P. D'Silva, and Velmer A. Fassel* Ames Laboratory, Iowa State University and Department of Chemistry, Ames, Iowa 50011
A rapid high-temperature (240 "C) extraction with ~2 mL of dlphenylmethane Is utilized for the determination of polynuclear aromatic hydrocarbons in particulate samples. Direct quantltation Is accomplished by laser excited Shpol'skll spectrometry (LESS) after an aliquot of the extract Is diluted with n-octane.
Finely divided, airborne particulate matter with adsorbed organic, organometallic, and inorganic compounds are emitted extensively from the combustion or processing of solid and liquid fossil fuels. A variety of compounds found on these particles have been identified as potentially toxic or mutagenic. One class of compounds of particular interest are polynuclear aromatic hydrocarbons (PAHs). Because this class of compounds contains many mutagenic and carcinogenic compounds, there is a serious concern about the environmental impact resulting from the widespread dispersal of airborne particulate matter, especially those particles in the respirable size range. Analytical methods for the determination of PAHs in particulate matter invariably have involved extraction of the PAHs into an appropriate solvent prior to analysis. The most widely utilized procedures have been Soxhlet or ultrasonic extraction of 1-10 g samples with 50-250 mL of low boiling solvents (250 "C) that are directly compatible for the direct determination of the PAHs with laser-excited Shpol'skii spectrometry.
EXPERIMENTAL SECTION The high boiling point solvents utilized in this study were diphenylmethane (Ph,CHJ, and phenyl ether (Ph,O), which have boiling points of 265 and 259 "C, respectively. These compounds were obtained from Aldrich Chemical Co. (Milwaukee, WI). The solvents were purified by distillation under vacuum and checked for purity with reference to potential fluorescent impurities. The samples analyzed consisted of (a) size fractionated stack particulate matter and electrostatic precipitator ash, collected at the City of Ames municipal power plant, (b) animal charcoal powder, and (c) a reference material "Urban Particulate Matter" (SRM 1649) obtained from the National Bureau of Standards (NBS) Washington, DC. The high-temperatureextractions were accomplished as follows. To particulate samples weighing between 50 mg and 150 mg contained in a 10-mL test tube, 1 to 2 mL of either PhzO or Ph2CH2was added and the mixture was heated for 5 min in a molten salt bath maintained at 240 "C. The salt bath consisted of an equimolar mixture of NaN03 and KNOP The hot extract was immediately filtered through a glass microfiber filter (Whatman 934-AH) fitted to a small Buchner funnel set in a test tube with a side arm attached to a vacuum filtration system. The extract was separated from the particulate matter in less than 1 min after extraction to prevent readsorbtion of analyte on cooling. The extracts were immediately frozen and kept frozen until analyzed to preserve the compositional integrity. Solvent blanks were also obtained under the above conditions. Stack particulate matter and animal charcoal samples weighing 100 mg were subjected to Soxhlet extraction with 10 mL of toluene for 8 h in a micro Soxhlet apparatus. The extract was filtered and taken to dryness in a rotary evaporator and the residue dissolved in 2.0 mL of n-heptane. The integrated, room temperature luminescencemeasurements were made with a fluorometerassembled in this laboratory (6). 0 1983 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
Table I. Extraction Efficiencies as Indicated by Relative Integrated Fluorescence Intensities of Various Extracts
sample type
solvent (temp, "C)
integrated intens (400560 nm), Ex 365 nm
toluene (95) Ph,O (95) Ph,O (240) toluene (95) Ph,O (95) Ph,O (240) toluene (95) Ph,O (95) Ph,O (240) toluene (95) Ph,O (95) Ph,O (240)
0.26 0.99 47.53 0.64 2.16 35.20 0 2.75 11.50 59.9 91.5 176.0
PYRENE
I )I
stack particulate matter (> 1 0 size) stack particulate matter ( 3- 1 0 size) electrostatic precipitator ash animal charcoal (Fisher)
The integrated luminescence in the 400-600 nm region on excitation at 365 nm was assumed to indicate the amount of PAHs extracted. This assumption is supported by the fact that most five- to seven-ringPAHs, including B[a]P and coronene, exhibit their most characteristic spectra in this region. The basic laser-excited Shpol'skii spectrometry (LESS) facility has been described (7). In the current version of the instrumentation, optical detection and data acquisition are accomplished via an optical multichannel analyzer (OMA) system (1412 diode array detector, 1215 console, and 1218controller,EG&G Princeton Applied Research, Princeton, NJ). The 0.64-m spectrometer (Model HR-640, Instruments SA, Inc., Metuchen, NJ) is fitted with both the photomultiplier tube and the diode array detectors. The selection of either detector is achieved by a simple change in the position of a beam directing mirror. With the OMA system, a typical, integrated-intensity, spectral scan within the 10-nm window of the detector can be obtained in less than 10 s. For the quantitative determination of B[a]P, benzo[k]fluoranthene (B[k]F), and benzo[ghi]perylene (B[ghi]P), the deuterated analogue of B[a]P was used as the internal reference compound (8). The extracts were diluted 10- to 100-fold with n-octane or n-heptane. For the determination of B[a]P in power plant stack ash, the excitation wavelength was 379.3 nm with deuterated B[a]P as the internal reference compound. For the determination of the three PAHs in NBS-SRM 1649, the compromise excitation wavelength of 386.88 nm allowed us to observe and measure a major fluorescence emission line for each of the PAHs and the internal reference compound, B[a]P-d12,from a single spectrum. Both Ph20and PhzCH2were used as extracting solvents during the initial comparison experiments. Due to its greater stability and for safety considerations(explosion hazard for Ph20),PhzCHz is the preferred solvent for routine analytical purposes.
RESULTS AND DISCUSSION A comparison of the extraction efficiencies of conventional Soxhlet extraction with toluene at 95 O C for 8 h and extraction with PhzO for 5 min at 95 OC and 240 "C are shown in Table 1. The large difference in fluorescence intensity is due to a difference in extraction efficiency rather than a solvent effect, based on the results on a separate experiment in which the integrated fluorescence intensity of a complex PAH mixture dissolved in toluene, Ph20,or Ph2CHzwas shown to differ by leas than 10%. The data indicate that extraction with PhzO at 240 OC is definitely superior to extraction with PhzO or toluene a t 95 OC. Similar results were also obtained with Ph2CHp The quasi-line luminescence spectrum obtained by nonselective excitation at 308 nm of the PhzCHzextract of a stack ash sample diluted 100-fold with n-hepane is shown in Figure 1. The characteristic line at 372 nm of pyrene and the multiple lines of B[a]P normally observed in a n-heptane matrix are readily seen in this spectrum (7). The quasi-line
I
I
370
1
I
380 390 WAVELENGTH ! n m )
I
410
400
Flgure 1. Fluorescence spectra of PAHs observed on nonselective excitation at 308 nm of Ph,CH2 extract of stack particulate sample 60242 (see Table IV) diluted with n-heptane and cooled to 10 K.
40 0
402 404 406 W A V E L E N G T H !n rn )
408
Figure 2. Fluorescence spectra observed on a photodiode at'ray detector of a Ph,CH, extract of SRM 1649 diluted 1 to 100 with n octane Shpol'skii host and cooled to 10 K. Selective excitation was at 379.3 nm.
Table 11. Quantitative Data (pglg) for Several Polynuclear Aromatic Hydrocarbons in Urban Dust
NBS Standard Reference Material 1649 LESS procedure NBS benzo[a]pyrene benzo [k]fluoran thene benzo [ghilperylene
3.2 i: 0.2' 2.5 i: 0.3' 6.3 i: 0.4'
2.9 i: 0.5b 2.1 ?: 0.1c 4.5 i: l . l b
a Range for three difference extractions each at two dilutions. Certified values. Information value.
character of the spectral lines is a clear indication that the presence of PhzCH2solvent in the n-heptane host does not destroy the Shpol'skii effect (9). The Shpol'skii effect spectrum of the NBS-SRM 1649 extract diluted in an octane host is shown in Figure 2. The quantitative data derived from this and similar spectra, via the deuterated B[a]P approach, are shown in Table 11. There is a consistent pattern of slightly higher analytical results obtained by the rapid, high-temperature extraction procedure, particularly so for the six-ring B[ghi]P compound. Whether this pattern of results can indeed be completely attributable to higher extraction efficiency by the high-temperature procedure requires a far more detailed data base, as noted at the end of the paper. Several critical factors control the efficacy of the hightemperature extraction procedure. One of these is extraction
ANALYTICAL CHEMISTRY, VOL. 55, NO. 14, DECEMBER 1983
Table 111. Effect of Extraction Time on PAH Recoverya extraction time, min 5 10 30
concentration, pg/g B[a]P BkIP B[ghi]P 2.9 i 0.2 2.4 i 0.4 1 . 5 + 0.2
2.1
i
0.1
1.9 f 0.2 1.7 i 0.3
Table IV. Quantitative Data for B[a]P in Size Fractionated Stack Particulate Matter (SPM) sample SPM-601
6.3 f 0.7 7.3 i 0.7 5.9 It 0.9
SPM-602
Duplicate 100-mg samples of NBS-SRM 1649 were extracted in 1mL of Ph,CH,. Each sample was diluted 1/10 and 1/20 with n-octane. Determinations were by LESS. a
SPM-603 SPM-6 0 4
size fraction'
c1 c2 c1 c2 c1 c2 c1
B[a]P content, nglg 36 163 16 82 3 6 15
c2
SPM-605 time, which is demonstrated in Table 111. Similar data were obtained by integrated room temperature luminescence measurementsof other particulate matter extracts. Prolonging the extraction time from 5 to 10 min caused a decrease in fluorescence intensity of approximately lo%, The decrease approached 50% with an extraction time of 30 min. Different compounds appear to be affected to varying extents. For other than two-ring compounds, loss due to volatilization is unlikely because the boiling points of compounds having three or more rings are above 300 "C. Thermal decomposition reactions occurring in the hot solvent and at the surface of the inorganic particulate matter are more likely causes for the observed loss of analyte species during prolongations of the extraction time. Such losses should be more serious for reactive PAH derivatives, such as phenolic compounds. A second critical factor involves the separation of the extract from the particles, which must be accomplished rapidly to prevent reabsorption of the extracted PAHs on the particulate matter. To investigate this experimental parameter, extracts were allowed to remain in contact with the particulate matter for periods from 5 to 60 min before separation by filtration. The integrated roomtemperature fluorescence of the extracts decreased as contact time with the particles increased. The individual PAHs adsorbed on stack particulate samples collected from the City of Ames power plant could not be determined by conventional extraction and detection techniques because the sample size was very small and the PAH concentrationwas below the detection limits of other analytical techniques. When the rapid high-temperature extraction method was combined with the LESS determination, the concentration of the target PAH compound, B[a]P, on these particulate samples, could be determined (Table IV). Samples SPM-601 to SPM-603 were obtained when refuse derived fuel (20%) was coburned with coal. The data summarized in Table IV demonstrate the utility of the method with real samples and its advantages over other conventional extraction, separation, and detection techniques. The rapid, high-temperature extraction procedure described above combined with the LESS determination of the extraded PAH has several advantages over conventional Soxhlet extraction-chromatographic techniques. The small sample size required minimizes the long sampling periods needed to obtain adequate size-fractionated samples for conventional Soxhlet extraction procedures. The direct analyses of the extract
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SPM-606
c1 c2 c1 c2
a
4 1
4 1
5
C1. >10 um. C2.3 to 10 pm.
reduces potential errors incurred during processing of the extract prior to analysis by chromatographic-mass spectroscopic techniques. The extraction and LESS analysis can be performed in a short time period, thus facilitating the routine processing of many samples. Although all of the data obtained to date have followed a consistent pattern of higher extraction efficiencies of PAHs by the rapid, high-temperature procedure than is obtained by conventional, lower temperature Soxhlet extraction, a far more extensive data base on a broader variety of adsorbed and/or occluded PAHs and other polynuclear materials on a wider range of particulate matter is needed to verify the general utility of the procedure. Registry No. Ph20, 101-84-8; Ph2CH2,101-81-5;tduene, 108-88-3;benzo[a]pyrene,50-32-8;benzo[k]fluoranthrene,20708-9; benzo[ghi]perylene, 191-24-2.
LITERATURE CITED (1) Bjorseth, A. Anal. Chlm. Acta 1977, 9 4 , 21. (2) Broddin, G.; Van Vaeck, L.; Van Cauwenberghe, K. Atmos. Environ. 1977, 1 7 , 1060. (3) Wlse, S. A.; Eowie, S. L.; Chesler, S. N.; Cuthrell, W.F.; May, W. E.; Rebbert, R. E. "Proceedings of the Sixth International Symposium an Polynuclear Aromatic Hydrocarbons"; Cooke, M.. Dennis, A. J., Fisher, G. L., Eds.; Battelle Press: Columbus, OH, 1982; p 919. (4) Griest, W. H.; Yeatts, L. B., Jr.; Caton, J. E. Anal. Chem. 1980, 52, 199. (5) Griest, W. H.; Caton, J. E.; Guerin, M. R.; Yeatts, L, El,, Jr ; Higgins, C. E. "Polynuclear Aromatic Hydrocarbons: Chemistry and Biological Effects"; Bjorseth, A., Dennls, A. J. Eds.; Eatteiie Press: Columbus, OH, 1980;p 819. ( 6 ) Walters, S. N.; D'Silva, A. P.; Fassel, V. A. Anal. Chem. 1982, 54. 2571. (7) Yang, Y.; D'Silva, A. P.; Iles, M.; Fassel, V. A. Roc. SOC.Photo-Opt Instrum. Eng. 1981, 286, 126. (8) Yang, Y.; D'Sllva, A. P.; Fassel, V. A. Anal. Chem. 1881, 53, 2187 (9) Nurmukhametov, R. N.; Gobov, G. V. Opt. Spectrosc. (Engl. Trans/.) 1965, 78, 126.
RECEIVED for review July 5, 1983. Accepted Augnst 29, 1983. This research was supported by the U.S. Department of Energy, Contract No. W-7405-Eng-82, Office of Health and Environmental Research, Physical and Technological Studies, Budget Code GK-01-02-04-3.
