Multiwavelength laser-induced fluorescence spectroscopy for quantitative classification of aromatic hydrocarbons.

Time-resolved laser-induced fluorescence (LIF) spectroscopy and laser excitation at 248 nm and 337 nm are applied to investigate fuel and oil contaminations in water with respect to classify between different aromatic hydrocarbons. The quantitative interpretation of the LIF-data is difficult because petroleum products are complex mixtures of hydrocarbons in various compositions. Solvent and concentration effects like fluorescence reabsorption or excimer formation cause a red shift of the fluorescence intensity spectra and a change in time evolution of the LIF-decay spectra. In this paper these effects are discussed with respect to practical applications. A time-integrated photon counting technique applying two different time-gates in combination with fiber optics has drawn out to simplify the method, so it becomes very attractive for quantitative diagnostics of oil and fuel contaminations in water or soil samples. An example for on-line monitoring is reported.