Characterization of Naphthenic Acids from Athabasca Oil Sands Using Electrospray Ionization: The Significant Influence of Solvents

Abstract

There is a need to develop routine and rugged methods for the characterization of oil sands naphthenic acids present in natural waters and contaminated soils. Mass spectra of naphthenic acids, obtained using a variant of electrospray ionization coupled with a Fourier transform ion cyclotron resonance mass spectrometer, are shown here to vary greatly, reflecting their dependence on solubilities of the acids in organic solvents. The solubilities of components in, for example, 1-octanol (similar solvent to fatty tissue) compared to polar solvents such as methanol or acetonitrile are used here as a surrogate to indicate the more bioavailable or toxic components of naphthenic acids in natural waters. Monocarboxylic compounds (C_nH_2n+zO₂) in the z = −4, −6, and −12 (2-, 3-, and 6-ring naphthenic acids, respectively) family in the carbon number range of 13−19 were prevalent in all solvent systems. The surrogate method is intended to serve as a guide in the isolation of principle toxic components, which in turn supports efforts to remediate oil sands contaminated soils and groundwater.