Fluorescence EEMs and PARAFAC Techniques in the Analysis of Petroleum Components in the Water Column

Abstract

Fluorescence excitation–emission matrix (EEM) techniques coupled with parallel factor (PARAFAC) modeling have been used in the diagnosis and identification of petroleum and hydrocarbon components in aquatic environments. Here, we provide detailed protocols for the use of UV–Vis spectroscopy and fluorescence spectroscopy and for data acquisition and processing. UV absorbance at different wavelengths is used to derive optical properties, such as absorption coefficient at 254 nm (a254), specific UV absorbance (SUVA254), and spectral slopes at different wavelength intervals (e.g., S275–295) or slope ratio, and data of fluorescence EEMs are used to identify major fluorescence components. In addition, SUVA254 and spectral slope values are related to aromaticity and molecular weights of dissolved organic matter (DOM). Oil-related fluorescent components and specific polycyclic aromatic hydrocarbon (PAH) compounds could be readily identified using fluorescence EEMs, especially when combined with PARAFAC analysis. During and after the Deepwater Horizon oil spill in the Gulf of Mexico, three oil components were found in the water column with maximum Ex/Em at 224–226/328–340, 232–244/346–366, and 264–252/311–324 nm, respectively. Major PAH compounds identified include naphthalene, fluorene, phenanthrene, and others. Oil component ratios can also serve as an indicator for oil degradation status. Optical properties especially fluorescence signatures and fluorescence component ratios serve as a complement to other chemical and molecular analyses of petroleum and hydrocarbon components in seawater.