FEATURE
New Instrument Brings PAH Analysis to the Field A field-portable scanning spectrofluorometer has completed site tests and is nearing commercialization. C L A R E L. G E R L A C H
T
he need for rugged, portable instruments for field use at hazardous waste sites has led to development of a new generation of c o m p a c t gas c h r o m a t o g r a p h s , fieldportable X-ray fluorescence (FPXRF) units, and even portable mass spectrometers. These instruments bring the laboratory to the field for most environmental analyses, especially at the screening and semiquantitative levels. Tests that once required t r a n s p o r t i n g samples back to a fully equipped laboratory now can be done without delay in the field. Portable gas chromatographs have made on-site analysis of volatile organic compounds easier, and FPXRF has expedited analysis of inorganic compounds. But the analysis of high molecular weight organic compounds, such as polyaromatic hydrocarbons (PAHs), has remained a difficult problem for scientists engaged in site characterization. PAHs occur in oils, creosotes, tars, and other complex mixtures in many hazardous waste sites. Sites contaminated with creosotes from wood preservation operations, for example, are especially widespread in the southeastern United States. Substances such as tars, oils, and creosotes can pyrolize and plug up costly gas chromatography (GC) columns and detectors. Yet GC is currently the most rnmmon methofi for field analysis of higher molecular weight compounds Until now analysts could only modify sample preparation procedures which risks compromising the sample integrity
In the 1980s, environmental scientists began developing an alternate method for analyzing PAHs, oils, and creosotes. The work led to a new instrument— the field-portable scanning spectrofluorometer (FPSS)—for on-site determination of PAHs and other high molecular weight compounds. The U.S. Department of Energy (DOE) and EPA have evaluated a prototype instrument developed at Oak Ridge National Laboratory under EPA sponsorship. Manufacture of the second generation of instruments is about to begin. DOE researchers at Oak Ridge have developed various portable instruments for monitoring workers' exposure and environmental contamination (1-3). Recently, they tested a prototype instrument in the laboratory that met the specifications for on-site analysis of PAHs creosotes and polychlorinated biphenyls (PCBs) (3) The instrument then was used at several Superfund sites by EPA and its contractors through EPA's Technology Support Project (4 5) EPA regional personnel charged with the characterization of multiple sites containing PAHs and PCBs worked with the project to demonstrate the prototype FPSS instrument at their sites One of those test sites was the Atlantic Wood Industries wood-treating facility in Portsmouth, Va., 2 5 2 A • VOL. 30, NO. 6, 1996/ ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
0013-936X/96/0930-252A$12.00/0 © 1996 American Chemical Society
which opened in 1926 and is now a Superfund site. FIGURE 1 It typifies a class of sites where PAH and creosote conComparison with GC-MS results tamination of soil, sediment, and groundwater is an Total polyaromatic hydrocarbon (PAH) measurements environmental concern. At this site, PAH concentra(mg/kg) by the field-portable scanning spectrofluorometer tions ranged from 500 mg/kg to 38,000 mg/kg. Ex(FPSS), taken on site at the Atlantic Wood Industries cavation of sediment at a nearby river inlet was unSuperfund site in Portsmouth, Va., showed significant correlation (least-squares regression in log-log units) with der way, and scientists needed to monitor the extent GC-MS laboratory data for samples from the site. of contamination as work progressed. The leastsquares regression in Figure 1 summarizes results from this study. The FPSS (alternately called the synchronous luminescence monitor) results are comparable to GC-mass spectrometry (MS) results, but the FPSS has less resolution for individual analytes. Unlike GC-MS, which provides results for each PAH present the FPSS provides results by PAH class, such as phenanthrenes. The wavelength at which a PAH fluoresces usucillv depends on its molecular weight with lighter molecules fluorescing at lower wavelengths Luminescence spectrometry is an especially good technique for analyzing PAHs, PCBs [when used with an indicator (6)], and creosotes. When excited with light at a certain wavelength, the contaminants' resulting luminescence (Figure 2) is measurable by spectrometers. Thus, they can be measured by optical methods, such as spectrofluorometry. Wellequipped environmental laboratories long have used spectrofluorometFIGURE 2 ric instruments and methods (7). But the challenge was to develop a porAnalyzing contamination sources table instrument that could provide Atypical 3-ditnensionatfield-portable scanning spectrofluorometer spectrum from the Atlantic good results in a field survey. Wood Industries site allows fingerprinting of molecules from a specific source, a benefit in tracing the source(s) of an oil spill, for example. The FPSS employs a synchronous scanning capability that takes advantage of the overlap between the emission and absorption spectra of a particular compound (Figure 3). Synchronous luminescence was first used as a qualitative tool for oil spill identification (7) but was further developed as a qualitative tool for multicomponent analysis (8, 9). The portable instrument fits inside a suitcase-size carrying case and has a battery pack. A laptop or notebook computer provides instrument control, data analysis, spectral display, and data storage Several instrument models will be produced by Environmental Systems Corp. (Knoxville, Tenn.) in collaboration with Oak Ridge National Laboratory in 1996. It is expected that these will be available for researchers to lease or buy in 1997. In early field studies {10), modifications were made VOL.30, NO. 6, 1996 /ENVIRONMENTAL SCIENCE S TECHNOLOGY / NEWS • 2 5 3 A
FIGURE 3 How synchronous luminescence works First used as a qualitative tool for oil spill identification, synchronous luminescence takes advantage of the overlap between the emission and absorption spectra of a particular compound. Light from a flashlarnp (right) is focused onto the entrance slit of the excitation monochromator. The light from the monochromator is then focused at the center of the cuvette with two lenses. The resulting fluorescence is collected and focused onto the entrance slit of the emission monochromator (3).
to suit the matrices and analytes. Optimization of the extraction procedure for soils and tars is difficult and site-specific. The synchronous mode has greater resolution than the emission mode and produces more specific data from each sample run. Confirmatory studies are being conducted in the laboratory at Oak Ridge and in the field by EPA. These should establish the exact reliability of FPSS and its eventual place among the analytical tools available to environmental scientists. George Peeler of Environmental Systems Corp. (ESC) believes that method optimization will pose the biggest challenge for this instrument. Peeler explained that the fluorescence technique is very sensitive, and the instrument can be affected by impurities in solvents a n d heterogeneity in sample matrices. These concerns led developers to consider packaging the instrument with a complete reagent kit and including training and technical service with every i n s t r u m e n t purchase. Research continues at ESC to develop appropriate sample preparation techniques through collaborative research with Oak Ridge. Another Technology Support Project study took place at the Rab Valley Superfund site, an abandoned wood preservation operation in Oklahoma. Researchers used the prototype FPSS to analyze 243 soil samples for pentachlorophenol and numerous PAHS (fluoranthene, benzo (a) anthracene, benzo(£>)fluoranthene, benzo(fc)fluoranthene, chrysene, and pyrene) at concentrations in the low part-per-million concentration range. Researchers at Rab Valley collected soil bore samples, split them into subsamples, and homogenized each by mixing and breaking up soil clumps. They t h e n placed 2 grams (g) of soil in a 40milliliter (mL) glass vial, added 6 g of anhydrous sodium sulfate, and mixed with a stirring rod. Next, they added 10 mL of isooctane, tightly sealed the vial, and shook it for 10 minutes (min). Centrifuging for 2 min
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separated the solvent extract from the solid phase. A second extraction with 10 mL isooctane, with similar shaking and centrifuging, followed. The first and second extracts were combined and put in a quartz cuvette for FPSS analysis (3). The exact protocol for sampling and sample preparation is still being developed. It is clear that obtaining a representative sample is as important for this method as for others. Another factor is the fluorescence-quenching effect when analytes are present in high concentrations. The use of site-specific standards can enhance the results of field analyses, especially when the matrix effects of soils, sediments, and oils can contribute to erroneous results if regressed against pure laboratory standards. With the introduction of the next-generation FPSS instruments, further site studies are expected, and the development of specialized sample preparation and instrumental customizing steps will continue.
References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Vo-Dinh, T. /. Am. Ind. Hyg. Assoc. 1987, 48, 894. Vo-Dinh, T.; White, D. A. Anal. Chem. 1986, 58, 1128. Alarie, J. P. et al. Rev. Sci. Instrum. 1993, 64(9), 2541. Amick, E. N. "Field Analysis of Sediment Samples at Atlantic Wood Industries by Synchronous Fluorescence Spectrometry," Internal report to EPA, Las Vegas, 1995. Amick, E. N. "Field Analysis of Soil Samples at Rab Valley Wood Preserving Site by Synchronous Fluorescence Spectrometry," Internal report to EPA, Las Vegas, 1995. Vo-Dinh, X; Pal, A.; Pal, T. Anal. Chem. 1994, 66, 1264. Lloyd, I.B.F. Nature 1971, 231, 64. Vo-Dinh, T. Anal. Chem. 1978, 50, 396. Vo-Dinh, T. In Modern Fluorescence Spectroscopy, Vol. 4; Wehry, E. L., Ed.; Plenum Press: New York, 1981. Amick, E. N. et al. Proceedings of Twelfth Annual Environmental Management and Technology Conference International; Advanstar Expositions Publications: Glen Ellyn, IL, 1994.
Clare L. Gerlach is the task leader for technology transfer at Lockheed Environmental Systems & Technologies Company, Las Vegas, Nev.
