Fast Analysis of PAH in Complex Organic Carbon Mixtures by Reconstruction of UV-Visible Spectra

Polycyclic aromatic hydrocarbons (PAH) are components of complex organic mixtures featuring liquid and solid fossil fuels as well as tars derived from combustion and/or pyrolysis of coal and hydrocarbon fuels. PAH can also be detected at the exhaust of combustion systems, often associated to carbon particulate matter emissions. Due to their high toxicological potential the concentration levels of PAH detection should be very low (order of ppm) to meet the limits provided by the regulation on combustion emissions and atmosphere quality control. The PAH detection is mainly achieved by conventional, mainly chromatographic, analytical techniques applied to the fuel or to the organic carbon extracted from carbon particulate matter. Preliminary extraction, purification and pre-separation methods are the time-consuming methods necessary to isolate the PAH-rich mixtures from whichever organic matrix for further analysis with liquid or gas-chromatography. In this paper an alternative method based on the UV-Visible spectroscopic technique has been used for the qualification of PAH into the organic carbon associated to particulate matter sampled in fuel-rich sooting flames. In particular, a computing methodology able to solve nonlinearly constrained problems has been implemented on the UV-Visible absorption spectra of the organic material sampled in the soot-forming region of a laminar premixed rich ethylene-oxygen flame. The procedure allowed the good fitting of measured spectra with the spectra reconstructed by a suitable composition of PAH spectra. The methodology considers and evaluates the contribution of individual PAH which altogether better reproduces the fine structure overcoming the absorption background typically observed in the UV-Visible spectra of complex organic mixtures.