Research in our group has shown that a multiple channel laser-induced fluorescence (LIF) system is an effective tool for in situ monitoring of polyaromatic hydrocarbons (PAHs). The system delivers ten laser beams to a samples and simultaneously detects the fluorescence signals from the individual channels, generating an excitation-emission matrix (EEM) of the sample. Speciation of chemical present in a mixture EEM is conducted by target factor analysis. To determine the capability of the technique for speciation, various aromatic compounds were measured with the LIF system. The pure-component EEMs were analyzed against each other as targets to separate the compounds into classes with the target factor analysis method. Then EEMs of mixtures containing 2-5 components were analyzed using the pure- component EEMs as standards. In this preliminary study of eleven target aromatic compounds, nine were successfully identified individually, while two spectroscopically very similar compounds, naphthalene and 2-methylnaphthalene, could be differentiated from the other nine but not from each other. In such cases, the technique can correctly identify the presence of the class, e.g., naphthalenes, instead of an individual components, and the quantitative results for the class must be interpreted accordingly.
We have recently developed instrumentation capable of quickly characterizing or monitoring a site using laser-induced fluorescence (LIF) measurements made through a sapphire window near the tip of a cone penetrometer (CPT) probe as it advances through the subsurface. By incorporating ten laser wavelengths simultaneously and collecting a full three-dimensional fingerprint of the soil sample at a vertical resolution of approximately 2 cm, we have made advances in site characterization using this technique, which enjoys all the advantages of in situ measurements: no exposure to, handling, custody or generation of hazardous waste is involved, and results are available in near real time. This report presents the results of recent work at Otis Air National Guard Base. First, a simple one-dimensional measure of the fluorescence fingerprints was correlated with laboratory results for total petroleum hydrocarbons (TPH), as a potentially convenient way for an operator of our instrument to monitor the results of the LIF measurements in real time, as the probe advances. Second, and more importantly, results are presented to demonstrate the potential of the instrumentation to identify individual target species and to quantify their concentrations approximately. The samples collected on site for conventional laboratory analysis were also measured by LIF and the resulting excitation-emission matrices (EEMs) were analyzed for ten target polycyclic aromatic hydrocarbons (PAHs). Qualitative and semi-quantitative agreement between these two sets of results was obtained. The agreements were extended to the in situ LIF data taken 2 - 3 feet away.