Three-way analysis of fluorescence spectra of polycyclic aromatic hydrocarbons with quenching by nitromethane

The application of trilinear decomposition (TLD) to the analysis of fluores cence excitation-emission matrices of mixtures of polycyclic aromatic hydro carbons (PAHs) is described. The variables constituting the third-order ten ser are excitation wavelength, emission wavelength, and concentration of a fluorescence quencher (nitromethane), The addition of a quencher to PAH mix tures selectively reduces the fluorescence intensity of mixture components according to the Stern-Volmer equation. TLD allows the three-way matrix to be decomposed to give unique solutions for the excitation spectrum, emissio n spectrum, and quenching pro files for each component. The availability of spectra and calculated Stern-Volmer constants can aid in the identificatio n of unknown components. Preprocessing of the data to correct for Rayleigh/ Raman scatter and primary absorption by the quencher is necessary. Both thr ee-component (anthracene, pyrene, l-methylpyrene) and four-component (fluor anthene, anthracene, pyrene, 2,3-benzofluorene) synthetic mixtures are succ essfully resolved by TLD using quencher concentrations up to 100 mM, Result s are compared using both alternating least-squares and direct trilinear de composition algorithms. The reproducibility of extracted Stern-Volmer const ants is determined from replicate experiments. To illustrate the applicatio n of TLD to a real sample, a chromatographic cut from the analysis of a lig ht gas oil sample was used. Analysis of the TLD extracted spectra and quenc hing constants suggests the presence of three classes of polycyclic aromati c hydrocarbons consistent with data from a second dimension of chromatograp hy and mass spectrometry.