Applications of laser-induced fluorescence excitation emission matrix spectroscopy for the analysis of PAHs

An optical fiber laser induced fluorescence (LIF) excitation emission matrix (EEM) instrument for polycyclic aromatic hydrocarbons (PAH) measurement has been developed. The system has been applied to in situ contamination monitoring via cone penetrometer technology (CPT) deployment and has been successfully field-tested. The instrument has also been modified to allow the detection of fluorescent species in flowing streams within a capillary. This version of the instrument has been applied to high performance liquid chromatography (HPLC) and flow injection analysis (FIA) of PAHs. The system employs a neodyimiun: yittrium aluminum garnet (Nd:YAG) laser and Raman shifter (RS) as a rugged field portable excitation source. This excitation source simultaneously produces {dollar}>{dollar}20 beams of differing wavelength in the UV that can be selectively chosen for launch into optical fibers. The system uses two sets of silica-clad-silica optical fibers: one for the delivery of excitation light from the multi-wavelength laser excitation source to the sample and the other to collect fluorescence and deliver it to the imaging spectrograph and charge coupled device (CCD) detection system.; The in situ monitoring system has been installed in a CPT vehicle and has successfully undergone three field tests at two different sites. The matrix-formatted field data are displayed as three-dimensional fingerprints of contamination at given push locations and depths; they are also reduced in dimension by summing over one or both wavelength axes and plotting summed fluorescence vs. depth to facilitate visualization of the approximate extent of the contaminant plume. The summed fluorescence data have been photon-normalized to the incident excitation intensity during the push in which they were measured. Selected EEMs from each push location are examined for characteristic patterns and are qualitatively compared to standard EEMs of pure compounds and fuels. Rank annihilation factor analysis (RAFA) was performed on selected in situ measured EEMs and naphthalene concentrations reported. The summed fluorescence intensities at selected push locations in North Carolina were compared with laboratory determined naphthalene concentrations. Normalized plots of naphthalene concentration versus summed fluorescence were linear with correlation coefficients between 0.6 and 0.9. The trends were generally linear, indicating a reasonable correlation between the in situ LIF-probe and lab measurements.; For HPLC and FIA, the data are analyzed by examining the summed fluorescence plots and qualitatively comparing the EEMs with standard measurements made with the same system. Species are qualitatively identified and quantitated by RAFA using pure component EEMs as standards and the EEMs measured during an analysis as the unknowns. RAFA calculated PAH concentrations in HPLC and FIA were in the near-quantitative regime, typically within a factor of 2 of the known concentration for laboratory-prepared mixtures. Several real world samples were analyzed and the results were generally acceptable: for HPLC all components were identified and all except two were quantitated to within a factor of 2. Analysis of lab mixtures by FIA yielded good agreement with known concentrations. The analysis of complex real world samples with many components provided reasonable qualitative identification of species and estimates of concentration.