Anal. Chem. 1981, 53, 253-258
LITERATURE CITED Greenfield, S.; Jones, I.V.; Beny, C. T. Analyst (London) 1964, 8 9 , 713. Wendt, R.; Fassel, V. A. Anal. Chem. 1965, 37, 920. Kirkbright, G. F. Analyst (London) 1971, 96, 609. Fassel, V. A.; Kniseley, R. N. Anal. Chem. 1974, 46, lllOA, 1155A. Boumans, P. W. J. M. Phlllps Tech. Rev. 1974, 34, 305. Winefordner. J. D.: FitzaeraM, J. J.: Omeretto, N. A.m . / . Smctrosc. . 1975, 29, 369. Barnes, R. M. Anal. Chem. Fund. Rev. 1976, 48, 106R. Boumans. P. W. J. M. Opt. Pura Apl. 1978, 1 1 , 143. Locke, J. Anal. Chlm. Acta 1980, 113, 3. Dahlquist, R. L.; Knoll, J. W. Appl. Spectrosc. 1976, 32, 1. Barnes. R. M.. Ed. “ADDliCatiOnS of Inductiielv Cou~ledPlasmas to Emission Spectroscopy’:; Franklin Institute Priss: kiladelphla, PA,
1978. Abercrombie, F. N.; Silvester, M. D.; Cruz, R. B. A&. Chem. Ser. 1979, No. 172, 10. b a s , W. J.; Fassel, V.; Grabau, F.; Kniseley, R. N.; Sutherbnd, W. L. Adv. Chem. Ser. 1979, No. 172, 91. Gunn, A. M.; Millard, D. L.; Kirkbright, G. F. Analyst (London) 1976, 103, 1066. Nixon, D. E.; Fassel, V. A.; Kniseley, R. N. Anal. Chem. 1974, 46,
253
(18) Guichon, G.;Pommier, C. “Gas Chromatography in Inorganics and Organometallics”; Ann Arbor Science Publlshers: Ann Arbor, MI, 1973. (19) Ross, W. D.; Sievers, R. E. Sixth International Symposium on Gas Chromatography, Rome, Italy, 1966. (20) E h t r a u t , K. J.; &!est, D. J.; Ross, W. D.; Slevers, R. E. Anal. Chem. 1971, 43, 2003. (21) Black, M. S.;Slevers, R. E. Anal. Chem. 1973, 45. 1733. (22) Sievers, R. E.; Conndly, J. W.; Ross, W. D. J. Gas Chromatogr. 1967 5,241. (23) Hansen, L. C.; Scribner, W. 0.;Gilbert, T. W.; Sievers, R. E. Anal. Chem. 1971, 43, 349. (24) Black, M. S.;Slevers, R. E. Anal. Chem. 1976. 48, 1872. (25) Wolf, W. R. Anal. Chem. 1976, 48, 1717. (26) Wolf W. R. J. Chrornatogr. 1977, 134, 159. (27) Wolf, W. R.; Mertz, W.; Masirmi, R. J. Agric. FocdChem. 1974, 22, 1037. US. (28) Carter, Richard J. “Summary Report: Trace Metals S w e y I”; Department of Health, Education, and Welfare, Center for Disease Control: Atlanta, GA.Jan 1977. (29) Fassel, V. A; Kniseley, R. N. Anal. Chem. 1974, 46, lllOA. (30) “The Guide to Techniques and Applications of Atomic Spectroscopy”; Perkin-Elmer Corp: Norwak. CT.
210. Salin, E. D.; Horlick, G. Anal. Chem. 1979, 51, 2284. Moshier, R. W.; Sievers, R. E. “Gas Chromatography of Metal Chelates”; Pergamon Press: New York, 1965.
RECEIVED for review April 30, 1980. Accepted October 27, 1980.
Analysis of a Workplace Air Particulate Sample by Synchronous Luminescence and Room-Temperature Phosphorescence Tuan Vo-Dinh,’ R. 8. Gammage, and P. R. Martinez’ Health and Safety Research Division, Oak RUge National Laboratory, Oak Ridge, Tennessee 37830
An analysis of a XAD-2 resin extract of a particulate air sample collected at an industrial environment was conducted by use of two simple spectroscopic methods performed at ambient temperature, the synchronous luminescence and room-temperature phosphorescence techniques. Results of the anaiyds of 13 polynuclear aromatic compounds including anthracene, benzo[ a Ipyrene, benzo[8 Ipyrene, 2,3-benzofluorene, chrysene, 1,2,5,&dlbenzanthracene, dibenzthiophene, fiuoranthene, fluorene, phenanthrene, peryiene, pyrene, and tetracene were reported.
The identification and quantification of polynuclear aromatic (PNA) compounds are of extreme importance because many of these compounds are potentially carcinogenic and occur frequently in the environment (1). The development of practical and cost-effective analytical techniques is necessary in order to monitor these compounds routinely. Recently, we have investigated the potential of two relatively new techniques for the analysis of complexes mixtures. These two techniques are the synchronous excitation method (2) and the room-temperature phosphorescence technique (3). This paper reports the analysis of an environmental sample, an air particulate extract from an industrial site, by use of these two analytical techniques. The synchronous luminescence (SL) excitation method is a methodology that can be applied to either fluorescence, e.g., synchronous fluorimetry (SF),or phosphorescence, e.g., synchronous phosphorimetry (SP). On the other hand, the room-temperature phosphorescence (RTP) Present address: A l u m i n u m Company of America, Alcoa,
TN.
0003-2700/81/0353-0253$01 .OO/O
technique is based exclusively on the detection of phosphorescence emission. The SL method, first suggested as a fingerprinting tool (4), gained interest among analytical spectroscopists as a technique for multicomponent analysis (2-9). Recent development of the technique has been reviewed (10). The advantages as well as the limitations of this method have been the topic of several reports (11,12). One of the goals of this study was to evaluate the capabilities as well as the limitations of the SL method practically and realistically by analyzing a complex environmental sample. Since most real-life samples are extremely complex systems,this assay represents a most demanding test for an analytical technique. The analysis deals with a liquid chromatographic (LC) fraction of XAD-2 resin extracts from a particulate air sample collected a t a workplace environment according to the scheme developed for the source assessment sampling system (SASS). The SASS scheme with its associated analytical procedures is a sampling and analytical approach developed by the U.S. Environmental Protection Agency (EPA) for conducting environmental source assessments of the feed, product, and waste streams associated with industrial and energy-related processes (13). Our main emphasis was to gauge how effectively a rapid, easy-to-use and cost-effectivetechnique can be applied for the characterization of PNA compounds. The second method employed in this study is the R T P technique. This technique is also relatively new and is presently under investigation by many workers (14-24 and other references herein). A review of the RTP method is given in ref 24. Recently, the RTP technique was applied to the analysis of a Synthoil sample (25). In this work, the RTP data are given to compare the results with those obtained by the synchronous fluorescence method. Due to the complementary 0 1981 American Chemical Society
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FEBRUARY 1981
nature of fluorescence and phosphorescence, the RTP technique serves also to provide additional information on the components of the air particulate sample. After completion of both SL and RTP analysis, the results were compared with data obtained by an independent study of the same LC fraction by another laboratory using low-resolution mass spectrometry (LRMS). The results of the analysis for 13 PNA compounds in the SASS sample by SL and R T P are reported. All but four (benzo[e]pyrene, dibenzothiophene, perylene, and tetracene) are on the EPA Priority Pollutant List (anthracene, benzo[alpyrene, chrysene, fluoranthene, fluorene, phenanthrene, pyrene, 2,3-benzofluorene, and 1,2,5,6-dibenzanthracene). METHODS AND INSTRUMENTATION The Synchronous Excitation Method. The SL methodology has been described in detail previously (2). Only the main basic features of this technique are repeated here. In conventional luminescence spectroscopy, either the excitation (Aex) or the emission wavelength (Aem) is scanned. With synchronous excitation spectroscopy,the luminescence signal is recorded while both A,, and A,, are scanned simultaneously with a fixed wavelength interval (AX) between them. The principal advantage of this approach is improved selectivity produced by a narrowing of the spectral band, a decrease of spectral interference from other luminescing species that would otherwise interfere with the emission being monitored. In addition, the simplification of the spectra from the individual components present results in a more resolved structure of the composite system. Room-Temperature Phosphorimetry. The RTP technique is based upon the detection of phosphorescence from organic compounds adsorbed on solid substrates at room temperature. The RTP method is being developed into a versatile and practical method of trace organic analysis. Although several types of substrates may be used, the solid substrate in this work is filter paper. A description of the method is available in previous reports (17, 25). The simplicity of the experimental procedures is a distinct figure of merit. A 3-rL sample solution is spotted on the filter paper and, after a 5-min drying period, phosphorescence is measured. Prior to sample delivery, the filter paper is spotted with a heavy atom salt solution in order to increase the phosphorescence signal. During the measurements, warm, dry air is passed through the sample compartment since moisture can quench the phosphorescence emission (24). Apparatus. All the spectrometric measurements were conducted with a Perkin-Elmer spectrofluorimeter (Model 43A, Perkin-Elmer). The spectrometer used a 150-W xenon arc lamp as the excitation light source and a R777 photomultiplier (Hamamatsu Co.) as the detector. For synchronous excitation measurements, both excitation and emission monochromators were locked together and scanned simultaneously. Standard 1 X 1 cm quartz cells were used for fluorescence measurements of liquid samples. Most fluorescence spectra were recorded with 1-nm spectral resolution whereas phosphorimetric measurementswere conducted with 5-nmspectral resolution. The small spectral band width used for SF measurements was necessary to prevent excessive scattered light from the excitation because of the usually small interval AA = 3 nm between A,, and iem*
Phosphorimetric measurements were conducted with the same spectrofluorimeter equipped with a rotating phosphoroscope. The paper fiiter circles were mounted on laboratory-comtmd sample holders. Materials and Reagents. All the PNA compounds were purchased from Aldrich Chemical Co. and used as received. Their purity was checked by UV absorption and fluorescence measurements. As a part of the interlaboratory study to evaluate EPA Level 1organic analysis, we were provided with the SASS sample by Arthur D. Little, Inc. The purpose of level 1 procedures is to obtain preliminary environmental assessment information, identify problem areas, and provide the data for the prioritization of streams for further consideration in the overall assessment (13). This sample, prepared by Arthur D. Little, is the LC fraction 3 of pooled XAD-2 resin extracts from three SASS train runs. The LC preparation produced seven fractions. Fraction 1 contains
F L U O R E S C E N C E S P E C T R U M OF A W O R K P L A C E AIR S A M P L E E X T R A C T
F I X E D EXCITATION 4
.Ae, = 2 80 nm
1
4
3
2
i
i
0
l
l
l 300
1
1
l
l
l
l
l
400 WAVELENGTH
l
l
l
l
l
l
500 inml
Flgwe 1. Fixed-excttationfluorescence spectrum (a)and synchronous fluorescence spectrum (b) of the SASS sample.
only aliphatic hydrocarbons. Fractions 2, 3, and 4 contain polyaromatic hydrocarbons (PAH) and sulfur-containing heterocyclic compounds. Fractions 5,6,and 7 mostly contain nitrogen and oxygen-heterocyclic compounds, phenols, esters, and carboxylic acids. Fraction 3 is the main PAH fraction with sulfur heterocyclics as the only non-PAH species found in this fraction. This fraction is referred to in this work as the SASS sample. Composition of the fraction and details for the preparation of this sample were given previously (26). All samples were dissolved in ethanol (spectral grade) for fluorescence and phosphorescence measurements. The heavy-atom salts for RTP analysis were commercially available and used in ethanol-water mixtures (volume ratio 1:O. Schleicher and Schnell paper filters (Type 2040A) were used as sample support in RTP measurements. RESULTS AND DISCUSSIONS Analysis by Synchronous Fluorescence. Figure la,b compares the conventional fixed excitation fluorescence and the synchronous fluorescence spectra of the SASS sample. With an excitation at 280 nm, the fluorescence spectrum exhibits a number of small peaks emerging from a relatively broad background centered a t approximately 340 nm. The fluorescence spectrum, extending from 300 nm to approximately 500 nm, indicates the presence of PNA compounds having various ring sizes. The use of other excitation wavelengths a t 320 and 340 nm did not produce any better resolution. The profiie of the fluorescence spectra produced with the excitation a t longer wavelengths depicted the general red-shift trend as expected when PNA compounds of larger size are excited. Although the small emission bands could be assigned to certain compounds, such a spectral assignment is highly ambiguous due to the severe spectral overlap and the limitless number of combinations of vibronic bands from
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
WORKPLACE AIR 2 , 3 -8ENZOFLUORENE
@@@
255
PYRENE SAMPLE AX= 30 nm
A X 1 3 8 nm
oc I
I
I
1
300
I
I
I 1
I
I
I
I
400 WAVELENGTH l n m l
1
I 1
I
L
t u
500
300
340
380 340 WAVELENGTH ( n m )
380
420
Figure 2. Synchronous fluorescence spectra of the PNA compounds Identified in one scan.
Flgue 3. Identification of pyrene using synchronous fluorescence (AA
various species in a complex mixture. Unless the presence of a specific compound is known and the appropriate excitation used, strong overlaps between spectra from various components often produce ambiguous results. The synchronous excitation spectrum (AX = 3 nm) given in Figure l b shows a series of narrow and well-resolved peaks. Comparing with the library of SF data, one can identify eight PNA compounds in this synchronous scan. The peaks labeled 1 , 3 , 6 , 7 , 8 , and 9 correspond to fluorene, 2,3-benzofluorene, anthracene, benzo[a]pyrene, perylene, and tetracene, respectively. For example, peak 1at 302 nm corresponds to the SF spectrum of fluorene. The synchronous fluorescence profiles of other individual PNA compounds are given in Figure 2. The use of AA = 3 nm permits the characterization of eight compounds in one single synchronous scan. We have suggested 3 nm as the average AA value because many polyaromatic hydrocarbons (PAH) with t w e to five-ring sizes have a Stokes shift value (SA,) between 2 and 5 nm in organic solvents such as ethanol and cyclohexane. Whenever possible, it is advantageous to use a AA value that matches SX, because this condition produces a single SF peak with the most intense signal and the narrowest half-width (2). It should be emphasized that the 3-nm value is selected because use of this AA permits identification in a single scan of most of the PAH compounds with strong 0-0 band overlaps in absorption and emission. The use of this AA value does not require an “a priori“ knowledge of the components in a mixture. Exceptions to the general rule requiring matching of the 0-0bands are those situations where the compounds exhibit nonoverlapping or weak emissions and/or absorption bands. The detection of pyrene is a typical example of the latter situation. The fluorescence emission of pyrene in ethanol shows an intense 0-0 band at 372 nm but the excitation (or absorption) spectrum exhibits a very weak 0-0 band at approximately 370 nm. Only the second electronic absorption S2 shows a strong band at 334 nm, in agreement with the theoretical ab initio calculations based upon the Pariser-Parr-Pople calculations (27). Two possibilities exist for identifying pyrene when using the SF method. If the concentration of pyrene is sufficiently high M), the use of AA = 3 nm produces a peak at 372 nm. At lower concentrations of pyrene, this band
is often too weak to be observed and a larger value of AA = 38 nm, matching the 0-0fluorescence (372 nm) and the Sz band at 334 nm, also produces a narrow peak at 372 nm. Figure 3 shows the SF spectrum of pyrene assigned to the SASS sample and that of a sample of pure pyrene using AA = 38 nm. Fluoranthene is also detected by SF using a large value of AA = 80 nm. Because fluoranthene has a broad fluorescence spectrum with a weak shoulder as the 0-0band, it is necessary to match the more intense band at 440 nm with the absorption peak at 360 nm. The use of AA = 80 nm (440-360 nm) produces a band at 438 nm for fluoranthene. Peak 2 in Figure 1at about 325 nm appears as a weakly resolved doublet (323 nm/325 nm). This band might correspond to acenapthene (323 nm) and/or dibenzothiophene (326 nm). Because of the proximity of the emission band from these two compounds, it is not possible to obtain a more conclusive assignment. It is noteworthy to mention that the use of fixed excitation did not provide a more precise determination. Peak 3 in Figure 1 at 342 nm corresponds to 2,3-benzofluorene which has a sharp band at this wavelength. The doublet (peaks 4 at 374 nm and peak 5 at 388 nm) can be assigned to chrysene which exhibits two similar bands. The identification of other peaks (6-9) in Figure 1did not present any problem. The SF spectrum of 1,2,5,6-dibenzanthracene (DBA) consists of a peak at 395 nm with AX = 3 nm. Because benzo[a]pyrene (BaP) exhibits an intense SF band at 404 nm with a smaller peak at 390 nm, spectral overlap prevents an accurate quantitative determination of 1,2,5,6-DBA. Table I gives the experimental conditions used in the identification of the PNA compounds by SF analysis. Spectral interferences caused by the filter effect have been the subject of several previous studies (3, 11, 12). These interferences, however, are inherent to all luminescence methods of liquid solutions either conventional or synchronous. Figures 4 and 5 compare synchronous spectra of two solutions of the same SASS sample diluted 100-fold (10 mL/L) and 1000-fold (1 mL/L), respectively. Spectra in these two figures were produced under identical experimental conditions by using conventional 1 cm X 1 cm quartz cells and a right angle excitation-emission geometry. It is clear that the filter
= 38 nm).
256
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
Table I. Experimental Conditions and Spectral Positions of the Synchronous Fluorescence Bands of the PNA Compounds Identified in the SASS Samples A A , peak A,, compound nm nm peak no.a acenaphthene 3 323 (2) anthracene 3 378 6 benzo[a]pyrene 3 404 7 2,3-benzofluorene 3 342 3 chrysene 3 3741388 415 172,5,6-dibenzanthracene 3 395 not shownb dibenzothiophene 3 325 (2) fluoranthene 80 438 not shown fluorene 3 304 1 phenanthrene 3 347 not shown perylene 3 438 8 pyrene 38 372 not shown tetracene 3 474 9 a Peaks are labeled in Figure l b . These emission bands are not shown in Figure l b because different experimental conditions and/or different sensitivity scales must be used.
(6
-
I
z
,
1
1
1
1
1
I
I
I
I
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WORKPLACE AIR SAMPLE EXTRACT FIXED EXCITATION FLUORESCENCE
14
,
I
300
I
I
I
I
I
I
I
400 WAVELENGTH inml
l
l
1
500
Flgure 5. Effect of sample concentration on fixed-excitation fiuorescence. SELECTIVITY OF THE EXCITATION
-
A*, '330 nm
kex6 365 nm
(6
-
WORKPLACE AIR SAMPLE EXTRACT SL SPECTRA (CONCENTRATION EFFECT) A x = 3 nm
nII
4
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6 -
6 t.
5 -
,
>
2
4 -
c 3 r
2 f -
0 -
400
500 600 WAVELENGTH l n m l
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Figure 6. Specificity of the excitation in room-temperature phosphorescence.
300
400 WAVELENGTH (nrnl
500
Flgure 4. Effect of sample concentration on synchronous fluorescence. effects cause spectral distortion in synchronous and conventional luminescence spectra. These effects decrease the relative intensities of the peaks labeled 1, 2, and 3 in the SF spectrum in Figure l b and also cause an almost complete suppression of the emission at short wavelengths between 300 and 400 nm in the conventional spectrum of the more concentrated solution. Room-Temperature Phosphorescence Analysis. The use of heavy-atom (HA) perturber is essential in the detection of nonpolar or weakly polar PNA compounds (17,18,28-31). The HA effect offers an additional factor of selectivity for multicomponent analysis (17). In this study, four major heavy-atom salts including cesium iodide, lead acetate (PbOAc), sodium bromide, and lead thallium acetate (TlOAc), were used. Among these four substances, thallium and lead acetate were found to be the most efficient HA perturbers. Cesium iodide and sodium bromide induced less enhancement of the phosphorescence but were useful to verify the compound identification by the specificity of their effect.
Figure 6 shows the effect of the excitation wavelength on the RTP spectra. Considering the complexity of such a sample, the spectral structure is reasonably well-resolved. The selectivity of the excitation is depicted by the change of the emission profile with the variation of the excitation wavelength. With A,, = 270 nm, the emissions from fluorene (Flu) and phenanthrene (Phe) are predominant. With A,, = 330 nm, the emissions of chrysene (Chy) fluoranthene (Fluo), and pyrene (Pyr) are apparent. Pyrene is best detected with A,, = 343 nm and fluoranthene with A,, = 365 nm. The four compounds found in the previous SF assay to be of relatively high concentration were chrysene, fluorene, phenanthrene, and pyrene. Characterization and quantification of these compounds by RTP is straightforward even with the fixed-excitation method. Figure 7, showing the RTP spectrum of the SASS sample and of pure fluoranthene, illustrates the degree of specificity of the analysis. Verification of the spectral identification and quantification for major compounds were also performed with the addition method by measuring the increased emission bands. As mentioned previously, the synchronous excitation technique can be applied to phosphorimetry whenever the conventional fixed-excitation method is uneffective in identifying a compound unambigously. In the present work the usefulness of the synchronous method in RTP analysis is demonstrated in Figures 8 and 9. With fixed excitation at 305 and 327 nm, the RTP spectra of the SASS sample show only weak shoulders at 430 and 420 nm, respectively (Figure
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
n
R T P SPECTRA
iz
---
257
IUI
Ak:93nm
SASS SAMPLE FLUORANTHENE
10
WITH LEAD ACETATE Aex = 365 nm
9
1
400 440 480 400 440 480 400 440 4 8 0 WAVELENGTH I nml
500
700
600
Figure 9. Identlflcation of fluorene and dibenzothiophene in the SASS sample by synchronous room-temperature phosphorimetry.
WAVELENGTH (nm)
Figure 7. Direct identification of fluoranthene in the SASS sample by room-temperature phosphorimetry. (Or
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,
,
(a)
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1
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~
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'
SASS SAMPLE
-k e x = 305
nm
I
~
(bl DIBENZOTHIOPHENE (Aex: 327 nm) FLUORENE (A,,=305 nm)
-
I
-
-
Table 11. Experimental Conditions Used for Quantitative Determination of the PNAk in the SASS Sample by Room Temperature Phosphorimetry compound benzo[a Ipyrene 2,3-benzofluorene chrysene 1,2,5,6-dibenzanthracene dibenzothiophene fluoranthene fluorene phenanthrene pyrene
methoda
heavy atom
hex = 392 nm A h = 181 nm hex = 330 nm A h = 250 nm A h = 93 nm A h = 365 nm A h = 125 nm hex = 297nm hex -343nm
PbOAc TlOAc CsI, TlOAc TlOAc, CsI TlOAc PbOAc TlOAc TlOAc TlOAc a k e x = fixed-excitation, A h = synchronous excitation. The conditions for synchronous excitation are given when the conventional fixed-excitation method cannot identify the emission bands unambiguously. Table 111. Concentrations of PNA Compounds in the SASS Sample Determined by SF and Room-Temperature Phosphorimetry Analyses
400
440
480 400 440 WAVELENGTH (nm)
480
500
Figure 8. Identification of fluorene and dibenzothiophene in the SASS sample by fixed-excitation room-temperature phosphorimetry.
sa). Although these two bands could be assigned to fluorene and dibenzothiophene (Figure 8b), such an assignment, based only upon fixed-excitation data, is inconclusive. The synchronous excitation technique using AA = 125 nm and AA = 93 nm allows more conclusive characterization of these two compounds. The value AA = 125 nm (93 nm) is optimal for fluorene (dibenzothiophene) because it matches the singlettriplet splitting ( A ~ T of ) this compound (7). The much narrower peaks in Figure 9 underscore the efficacy of the synchronous R T P technique. Table I1 gives the experimental conditions used in the R T P analysis of the SASS sample. Comparison of the Quantitative Results. The results of the quantitRtive analysis of the SASS sample by SF and R T P are given in Table 111. The standard deviation, measured with 15 replicate samples for various compounds, is within 5-15% for SF and 10-30% for RTP. The fluorimetric technique was used to identify 13 compounds. Results of the
compound acenaph thene anthracene benzo [a Ipyrene benzo [ e Ipyrene 2,3-benzofluorene chrysene
concentration: M SF RTP NQ 1.7 x 10-7
6.0 x 10-7
