Laser-induced Fluorescence Coupled with Solid-Phase Microextraction for In Situ Determination of PAHs in Sediment Pore Water

In situ sampling with solid-phase microextraction (SPME) was coupled with laser-induced fluorescence (LIF) in an effort to develop a simple field-portable method to determine total dissolved PAH (polycyclic aromatic hydrocarbon) concentrations in sediment pore water. Glass fiber rods with a 50 mu m coating of optically clear polydimethylsiloxane (PDMS) were inserted directly into sediment/water slurries. After 1-140 h (typically 18 h), the coated rods were recovered, rinsed with water, and their LIF response was measured with excitation wavelength (308 nm) and emission wavelengths (350-500 nm) chosen to monitor 2- to 6-ring PAHs. SPME-LIF response was independent of sediment sample size, as is required for equilibrium sampling methods to be used in situ in the field. Potential interferences from high and variable background fluorescence from dissolved organic matter were eliminated by the use of the nonpolar PDMS sorbent. The detection limit in pore water was ca. 2 ng/mL (as total PAH-34), which corresponds to ca. 0.2 EPA PAH toxic units. Good quantitative agreement (r(2) = 0.96) for total PAH-34 pore water concentrations with conventional GC/MS determinations was obtained for 33 surface sediments collected from former manufactured gas plant (MGP) and related sites. Quantitative agreement between SPME-LIF and GC/MS total PAH-34 concentrations was also good for 11 sediment cores (r(2) = 0.87), but the predominance of 2-ring PAHs (compared to the other sites) resulted in a lower relative SPME-LIF response compared to the surface sediment samples. The method is very simple to perform, and should be directly applicable to field surveys.