From Tech Trends March 1995

Field Portable Monitor for PAHs

By William H. Engelmann, EPA's Environmental Monitoring System Laboratory, Las Vegas

The Field-Portable Scanning Spectrofluorometer (FPSS) has tackled the difficult task of providing immediate in situ screening for polyaromatic hydrocarbons (PAHs) in complex mixtures such as oils, creosotes and tars. The FPSS, developed by Tuan Vo-Dinh and co-workers at Oak Ridge National Laboratory for EPA's Environmental Monitoring Systems Laboratory in Las Vegas, Nevada (EMSL-LV), has overcome the challenge presented by the high molecular weight of these compounds since spectrofluorometry can readily measure their relatively high luminescence yields. Heretofore these heavy compounds have been troublesome to analyze with traditional gas chromatography.

Additionally, the FPSS can provide measurements into the low part-per-billion (ppb) range, or even lower, for not only PAHs but also oils, polychlorinated biphenyls, phenols, dioxins and most pesticides.

The FPSS performs in either emission or synchronous wavelength scan modes. The latter mode scans both excitation and emission monochromators simultaneously with a small, constant wavelength offset. The result is a simplified synchronous spectrum with more spectral resolution.

Advantages of the synchronous mode include: (1) spectral peaks are simplified and sharpened; (2) mixed PAHs with differing numbers of fused rings are spaced out spectrally with no overlap, allowing unambiguous assignment to individual PAHs; and (3) the relative amounts of the various PAHs in a mixture are easily estimated. The emission mode has a slightly higher sensitivity and is useful for determining the total PAHs in a mixture, or in identifying spectral classes of PAHs, oils or tars. In the synchronous scanning mode, it can detect anthracene --a typical PAH -- at about 3.5 ng/mL (nanograms per milliliter). In the emission mode, anthracene can be detected at about 0.5 ng/mL. The FPSS consists of three parts: a small suitcase-sized instrument that houses the optics and electronics; a battery pack; and a laptop computer used for instrument control, data storage and analysis. The spectral coverage of the instrument is 210 to 650 nanometers. The instrument parameters are chosen by the operator through computer control.

The FPSS can be operated two ways: using a standard fluorescence cuvette cell or a bifurcated optical fiber. The cuvette can be used with liquid samples or extracts of soils. The optical fiber attachment allows direct screening of water samples. The prototype of the FPSS has been demonstrated at Region 4's American Creosote Works Superfund site near Jackson, Tennessee. These results have been so promising that they have merited the presentation at two recent technical symposia; these findings are being published in the Proceedings. The FPSS will be further demonstrated at sites in Regions 6 and 8. The prototype FPSS currently is available for performance comparison at sites by Remedial Project Managers and On Scene Coordinators. If you think that your site may be a candidate, contact Ken Brown at EMSL-LV at 702-798-2270.

The prototype is ready for commercial manufacturing; and, EMSL-LV and Oak Ridge National Laboratory will transfer the technology to a commercial manufacturer.

For more information, call Bill Engelmann at EMSL-LV at 702-798-2664 by phone or at 702-798-2107 by FAX.