Speciation of nitrogen-containing polycyclic aromatic compounds via Raman spectroscopy and entropy minimization

Abstract

Following a previously developed approach of identifying PAH in a mixture, Raman spectroscopy was used to analyze nitrogen-containing polycyclic aromatic compounds (NPAC)-mixture solutions by determining the pure component spectra of the constituent species without recourse to any library or any a priori knowledge. The mixture solutions consisted of 1 PAH and 5 NPAC, naphthalene, 3-cyanoquinoline, 3-methylquinoline, 3-cyanoisoquinoline, 3-methylisoquinoline and acridine, and were prepared using solvent carbon tetrachloride. The individual mixture samples were scanned using a laser operating at a wavelength of 1064 nm and the Raman sampling compartment incorporated 180° collection optics. An advanced spectral reconstruction algorithm, Band-Target Entropy Minimization (BTEM), successfully recovered the pure component spectra of all PAC, based on information entropy minimization. The recovered spectrum of individual constitutes showed satisfactory authenticity, overcoming the challenge of ambiguous signals and complexity exhibited by the mixture samples. This demonstrated the great potential of the BTEM techniques to better identify and understand the composition of PAC in various environmental samples. This is an abstract of a paper presented at the 229th ACS National Meeting (San Diego, CA 3/13-17/2005).