Real-time detection of PAH mixtures in the vapor phase at high temperatures

Abstract

Laser-induced fluorescence (LIF) spectroscopy can serve as a rapid analytical method for the quantitative analysis of polycyclic aromatic hydrocarbons (PAHs). The high quantum yields of this class of compounds, along with large absorption cross-sections, make fluorescence a very attractive technique for trace analysis determination of PAHs. Furthermore, fluorescence can provide in situ and online information regarding the composition and concentration of PAHs formed during combustion or pyrolysis processes. In this paper, we utilize a fiber-optic probe coupled to a spectrometer to collect fluorescence spectra of several PAH vapors at elevated temperatures using excitation at 337 nm. We have collected the fluorescence of standards as well as complex mixtures of PAHs at 300°C. The expected band broadening induced by temperature effects was observed, but did not compromise the spectrum signature for each PAH studied. We have measured fluorescence spectra of benzo[a]pyrene, pyrene, anthracene, and phenanthrene vapors. Determination of trace amounts of the toxicologically important benzo[a]pyrene has been shown to be feasible. Experimental results show that at 337 nm, benzo[a]pyrene is the most quantum efficient fluorophore among the PAHs studied. Furthermore, fluorescence lifetime measurements were found to be helpful in the characterization of PAH mixtures.