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from a practical point of view. The fundamental aspect concerns the fact that the kinetics of O2scavenging from the micelle interior and the dynamics of the entry and exit of a luminescent probe within the micellar core (to be quenched by oxygen) could be studied by the MS-RTP technique. Studies of oxygen diffusion into or out of biomembranes and liposomes could be envisaged by this technique. The practical point of view concerns its application to facilitate convenient RTP analysis of a variety of organic compounds (including argricultural, pharmaceutical, petroleum, and biological-related samples) and extend the technique to facile metal ion determinations in solution, a field completely unexploited so far (23) and which is being intensely investigated in our laboratory (24). Moreover, this chemical deoxygenation procedure should extend the applicability of phosphorescence in fluid solutions as a detection mode (25, 26) for flow injection analysis or HPLC. Also, the technique proposed here can be extended to chemically deoxygenate other organized media in which it is also possible to observe RTP (e.g., cyclodextrins (27,28)). In fact, our preliminary experiments in this area have shown that the phosphorescence signal from 1-bromonaphthalene in a @-cyclodextrinsolution is enhanced more than 3 times when sodium sulfite is added.
ACKNOWLEDGMENT Thanks are due to J. N. Miller (Loughborough University of Technology, UK) for helpful comments during the early stages of this research and to W. L. Hinze (Wake Forest University, NC) for his suggestions.
Registry No. Oxygen, 7782-44-7; sodium sulfite, 7757-83-7.
LITERATURE CITED (1) Parker, C. “Photoluminescence of Solutions”; Elsevier: Amsterdam, The Netherlands, 1968. (2) Aaron, J. J.; Wlnefordner, J. D. Talanta 1975, 2 2 , 707. (3) Bower, L. Y.; Winefordner, J. D. Anal. Chlm. Acta 1978, 702, 1. (4) Schulrnan, E. M.; Walling, C. J. Phys. Chem. 1973, 77, 902. (5) Miller, J. N. Trends Anal. Chem. 1981, 1 , 31. (6) Parker, C. A.; Hatchard, C. G. J. Phys. Chem. 1962, 66, 2506. (7) Parker, C. A.; Joyce, T. A. Trans. Faraday SOC. 1969, 65, 2823. (8) Turro, N. J.; Liu, K. Ch.; Chow, M. F.; Lee, P. Photochem. fhotobiol. 1978, 27, 523. (9) Thomas, J. K. Acc. Chem. Res. 1877, 70, 133. (10) Cline Love, L. J.; Skrilec, M.; Habarta, J. G. Anal. Chem. 1980, 5 2 , 754. (11) Cline Love, L. J.; Habarta, J. G.; Dorsey, J. G. Anal. Chem. 1984, 56, 1132A. (12) Rollle, M. E.; Ho, C.-N; Warner, J. M. Anal. Chem. 1983, 55, 2445. (13) Turro, N. J.; Sidney Cox, G.; Xin, Li fhofochem. fhotobiol. 1983, 37, 149. (14) Cline Love, L. J.; Weinberger, R. Spectrochim. Acta, Part B 1983, 368,1421. (15) Hohn, H. “Chemische Analysen mit dem Polarographen”; Berllo, 1937. (16) Kilthoff, I. M.; Llngane, J. J. “Polarography”; Interscience: New York, 1952; Vol. 1. (17) Israel, Y.; Vromen, A.; Paschkes, B. Talanta 1967, 14, 1967. (18) Almgren, M.; Grieser, F.; Thomas, J. K. J. Am. Chem. SOC. 1974, 101, 279. (19) Escabi-PBrez, J. R.; Nome, F.; Fendler, J. H. J. Am. Chem. SOC. 1977, 99, 7749. (20) Turro, N. J.; Aikawa, M.; Yekta, A. Chem. Phys. Lett. 1979, 64, 473. (21) Thomas, J. K. Chern. Rev. 1880, 80, 283. (22) Matheson, I. B. C.; Massoudi, R. J. Am. Chem. SOC. 1980, 102, 1942. (23) Holzbecher, 2.; HeJtmanek, M.; Sobalik, 2 . Collect. Czech. Chem. Commun. 1978, 43, 3325. (24) Dlaz Garcia, M. E.; Marthenez Garcia, P. L.; Sanz-Medel, A. X V I I European Congress on Molecular Spectroscopy, Madrid, Spain, Sept 1985. (25) Gooijer, G.; Velthorst, N. H.; Frei, R. W. Trends Anal. Chem. 1984, 3, 259. (26) Frei, R. W.; Blrks, J. W. Eur. Spectrosc. News 1984, 57, 15. (27) Scypinski, S.; Cline Love, L. J. Anal. Chem. 1984, 56, 322. (28) Scypinski, S.; Cline Love, L. J. Anal. Chem. 1984, 56, 331.
RECEIVED for review October 15,1985.
Accepted January 3,
1986.
Gasoline Engine Exhaust Analysis Using Constant Energy Synchronous Luminescence Spectrometry Leigh Ann Files, Bradley T. Jones, Shigeki Hanamura, and James D. Winefordner* Department of Chemistry, university of Florida, Gainesville, Florida 3261 1
Constant energy synchronous luminescence spectrometry at low temperature (77 K) Is applled to environmental analysis Involving flngerprlntlng gasollne exhaust samples containing pdyaromatlc hydrocarbons (PAHs). Comblnlng this technique with a system that allows a crude sample separation based on temperature provldes Increased selectivlty and sample Informatlon. I t also conflrms previous results demonstrating the effect sampllng methodology can have on the number and quantlty of PAHs found In engine exhaust.
Polyaromatic hydrocarbons (PAHs) are formed during incomplete combustion of organic material. Concern over possible health hazards associated with PAHs has led to a search for a method capable of identifying and quantitating these compounds. Luminescence techniques are very sensitive for PAH determination (1-5). However, the broad overlapping
bands obtained with conventional excitation and emission scans result in limited applications to complex mixture analysis. Constant energy synchronous luminescence spectrometry (CESLS) was developed in 1982 by Inman and Winefordner and involves obtaining luminescence signals while scanning both the excitation and emission monochromators keeping a constant energy difference between them (6, 7). In CESLS the sensitivity associated with luminescence techniques is maintained while offering several additional advantages: (i) spectral profile simplification, (ii) spectral bandwidth reduction, and (iii) reduction of Rayleigh, Raman, and T p d a l l scatter. CESLS also allows the scan to be optimized for a specific absorption-fluorescence transition. The theory behind this method and its advantages have been described previously (6, 7). Further improvement in spectral resolution is obtained through analysis of samples at low temperature (77 K). Inman
0003-2700/86/0358-1440$01.50/00 1986 American Chemical Society
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E X C l T ATION WAVELENGTH Figure 2. CESLS scan of 16-component PAH mixture at 4800 cm-'.
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and Winefordner (6) demonstrated the advantages of LTCESLS over CESLS at 298 K, and Kerkhoff et al. (8) applied LTCESLS to synthetic PAH mixture analysis.
EXPERIMENTAL SECTION Instrumentation. The experimental setup used for this study is similar to the one shown previously (9). Changes were made and described in a more recent publication (8). Two monochromators of moderate resolution were used with 1.2-nm spectral bandpasses. The scan rate was approximately 50 nm/min allowing a constant-energy scan with an excitation range from 200 to 500 nm to be collected in less than 6 min. The excitation monochromator was pulsed at a constant rate, while the emission monochromator was pulsed at a variable and faster rate to maintain the desired constant energy difference. Scan rates were controlled by an Apple 11+ microcomputer through a versatile interface adapter (VIA, SY622). PAH Mixture Analysis. To determine the suitability of CESLS for PAH mixture analysis, a 16-component mixture (Chem Service, Westchester, PA) was used. All of these compounds are PAHs on the EPA priority pollutant list. The mixture was first scanned at a variety of constant energy differences (ADvalues). The AD values were chosen based on preliminary work determining optimum AD values for each compound calculated from excitation and emission scans (9). The values used for this study included AD = 1400, 2800,4800, and 5300 cm-*. The small number of AD values necessary for multicomponent identification agrees with molecular luminescence theory, which shows that compounds within a class (such as PAHs) generally exhibit similar vibrational energy level separations and consequently comparable AD values. After the mixture was scanned, a library of scans was established containing each of the 16 compounds (obtained from Foxboro Analabs, North Haven, CT, and the EPA Repository, Cincinnati, OH) at the different AD values. This library was used to identify the peaks in the scans
of the mixture. Standard additions were also used when identification was difficult. Results of two of the scans obtained after dilution to a concentration of 0.2 ppm in each component are shown in Figures 1 and 2. Thirteen of the compounds in the 16-component mixture are identified in the two scans used for demonstration purposes. The other three compounds were dibenz[a,h]anthracene (which was identifiable in the 2800-cm-' scan), acenaphthylene, and indeno[l,2,3-~d]pyrene.The last two were not identifiable at the sample concentration chosen for the demonstration scans. These scans were later used for comparison to unknown mixtures for preliminary identification of components. Sampling Procedure. The samples in this study were collected from the exhaust of a small 4-cycle 1975 Model 21 Toro Lawn mower. One of the first considerations in identifying and quantitating the components of the exhaust of an engine is the choice of the sampling system. The number and quantity of PAHs measured at a sampling site shows a strong dependence on the sampling methodology ( l G l 4 ) .TWO different sampling systems were used in this study. In the first system (outlined in Figure 3) the exhaust was routed through a short (20 cm) flexible metal tube into an open glass tube 120 cm long for 30 min. To determine the effect of sampling location on PAH content, sections 3 cm in length were cut from the tube. Three sections were taken: one from the end connected to the metal tube (a), one from the center (b), and one from the open end (c). Although the temperature was not calibrated along the length of the tube, it was expected that this sampling procedure would be equivalent to a crude chromatographic separation based on the volatility of the compounds. The 3-cm sections labeled a, b, and c were each extracted with 25 mL of hexane (obtained from Burdick and Jackson). The extraction process involved immersing the 3-cm sections in hexane contained in amber glass vials and placing them in an ultrasonic bath at room temperature for 30 min. Constant-energy scans were then obtained for these samples. The second system for sample collection was designed for qualitative comparison of PAHs produced by different samples. The system involved routing the exhaust into an open 120-cm glass U-tube (i.d. 8 mm, 0.d. 12 mm) placed in a Dewar containing liquid nitrogen. Samples were
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a
200
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EXCITATION
WAVELENGTH (nm
Figure 3. CESLS scan of leaded gasoline exhaust extracts obtained by uslng multiple sample collectlon system (AP = 1400 cm-I). Compounds identifled include benzo[a Ipyrene (BAP), benzo[k]fluoranthene (BKF), anthracene (A), coronene (COR), and perylene (PER).
IO EXCl TAT1ON
50 WAVE LENGTH ( n m )
Flgure 5. CESLS scan of exhaust from different gasoline samples obtained by using U-tube collection system at 1400 cm-’: samples (a) brand A super unleaded, (b) brand A unleaded, (c) brand B super unleaded with ethanol, (d) brand B unleaded with ethanol, (e) brand C regular leaded.
and one brand of regular leaded gasoline. The two brands of super and regular unleaded were chosen because, although they have comparable octane ratings, only one of them contains ethanol.
RESULTS AND DISCUSSION
a
Figures 3 and 4 show results obtained for exhaust samples collected by using the first system described. The AD values chosen for demonstration purposes were 1400 and 2800 cm-l. The exhaust samples shown here were from regular leaded gasoline, and the separation results were typical of other gasoline samples that were measured with the same sampling system. Results indicate that section a, which would be the hottest since it is closest to the engine, is too hot to allow significant condensation of any of the PAHs. (Spectra of section a are typical of the background obtained with hexane alone.) The next sections indicate condensation of PAHs in a trend that agrees with their boiling points (15). Identification of PAHs was made through comparison to standard spectra at all AD values and confirmed by standard additions. This experiment confirms previous studies which indicate that the results obtained from a particular sampling system may not be indicative of the total PAH content of an exhaust. It also demonstrates the advantage of combining CESLS with a preliminary separation, when one wishes to analyze an especially complex mixture to obtain further information about a sample. Of course, a more elegant separation technique would enhance the information content at the expense of time. Another possibility for information enhancement would be the use of mathematical techniques such as factor analysis. Figures 5 and 6 show scans of the extracts from the U-tube samples collected for the exhaust of the five different gasolines analyzed in the second system. The AV values chosen for demonstration purposes were 1400 and 4800 cm-l. No attempt was made in this study to label peaks in Figures 5 and 6 because of the confusion that would arise with the need for
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SO
E x c l T A T I O N WAVELENGTH
Flgure 4. CESLS scan of leaded gasoline exhaust extracts obtained
by using multiple sample collection system (A? = 2800 cm-I). Compounds ldentlfied include phenanthrene (PHE), chrysene (CHR), pyrene (PYR), anthracene (A), benzo[a Ipyrene (BAP), benzo[k] fluoranthene (BKF), and anthanthrene (ANT).
collected for 6 min and subsequently extracted into 25 mL of hexane by repeated rinsing. The samples included exhaust collected from two different brands of super and regular unleaded
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the engine used in this study could not be optimized and reproducibly run to obtain controls and therefore prohibited the possibility of obtaining data necessary for a meaningful efficacy analysis. The difference in the appearances of spectra obtained with the two different methods (Figures 3 and 4 compared to Figures 5 and 6) can be attributed to the sampling procedures. In the second system the extracts contain all PAHs collected over the 120-cm length of tube, while in the first system each extract contains only the PAHs condensed in a 3-cm interval of the tube. Possible applications of this method included preliminary screening to evaluate systems proposed for reducing PAH emission and fingerprinting of samples to identify their origin as in the case of an oil spill or other environmental hazard. Applications to other samples including pesticides and pharmaceuticals are also being investigated. The high spectral selectivity and sensitivity of this simple technique, CESLS, for measurements involving complex matrices, such as exhaust particulates, has been demonstrated here. Registry NO.A, 120-12-7;BAP, 50-32-8;BKF,207-08-9; PHE, 85-01-8; PYR, 129-00-0; CHR, 218-01-9; fluorene, 86-73-7; acenaphthene, 83-32-9; benz[a]anthracene, 56-55-3; benzo[ghi]perylene, 191-24-2;naphthalene, 91-20-3;benzo[b]fluoranthene, 205-99-2; fluoranthene, 206-44-0.
LITERATURE CITED EXCITATION
WAVELENGTH (nm 1
Figure 6. CESLS scan of exhaust from different gasoline samples obtained by using U-tube collection system at 4800 cm-': samples (a) brand A super unleaded, (c) brand B super unleaded with ethanol, (e) brand C regular leaded.
multiple labeling of individual peaks. However, this system demonstrates the sensitivity of CESLS for PAH analysis, especially for fingerprinting and screening. The results of the study indicate comparable PAH production from different gasoline samples with slight differences in relative concentrations of particular species, such as pyrene, perylene, and acenaphthene. Tests to determine the efficacy of the extraction processes and sampling systems were not performed because the intent of this paper was to demonstrate the sensitivity and selectivity of CESLS and not to propose a new sampling method. Also
(1) Parker, C. A. Photoluminescence of Solutions; Elsevier: New York, 1968. (2) Colmsjo, A.; Stenberg, U. Anal. Chem. 1978, 57, 145. (3) Hurtubise, R. J.; Phillip, J. D. Anal. Chim. Acta 1979, 52, 159. (4) Kirkbright, G. F.; dellma, C. G. Analyst (London) 1974, 99,338. (5) Shabad, L. M.; Smirnov, G. A. Atmos. Environ. 1972, 6 , 153. (6) Inman, E. L.; Wlnefordner, J. D. Anal. Chem. 1982, 5 4 , 2018. (7) Inman, E. L.; Winefordner, J. D. Anal. Chim. Acta 1982, 747, 241. (8) Kerkhoff, M. J.; Files, L. A.; Wlnefordner, J. D. A n d . Chem. 1985, 57, 1673. (9) Kerkhoff, M. J.; Inman, E. L.; Voigtman, E.; Hart, L. P.;Winefordner, J. D. Appl. Spectrosc. 1984, 38, 239. (10) Lamb, S. I.; Petrowskl, C.; Kaplan, I. R.; Simoneit, B. R. T. J . Air Pollut. Control Assoc. 1980, 30, 1098. (11) Billings, W. N.; Bldleman, T. F. Environ. Sci. Techno/. 1980, 74, 679. (12) Turner, 8. C.; Glotfelty, D. E. Anal. Chem. 1977, 49,7. (13) Braun, T.; Farag, A. B. Anal. Chim. Acta 1978, 99, 1. (14) Cautrells, W.; Van Cauwenbergh, K. Atmos. Environ. 1978, 72, 1133. (15) Grimmer, G. Environmental Carcinogens : Polycyclic Aromatic Hydrocarbons; CRC: Boca Raton, FL, 1983; p 36.
RECEIVED for review November 12,1985. Accepted February 18,1986. This work has been supported by NIH-GM-11373-23 and DOE-DE-AS05-780R06022.
