Chemical fingerprinting of naphthenic acids by comprehensive two-dimensional gas chromatography mass spectrometry at reclamation sites in the Alberta oil sands

Abstract

The processing of bitumen in the Athabasca oil sands region (AOSR) produces extensive volumes of oil sands process-affected water (OSPW) and tailings, which are stored within tailings ponds and settling basins to promote the consolidation of solids and the recycling of water. Oil sands operators are actively investigating dry and wet reclamation strategies in order to reduce their inventory of tailings and return disturbed land back to its original state. An important component of the reclamation of tailings is understanding the environmental fate of naphthenic acids (NAs), which are considered the most toxic constituents of OSPW and tailings. However, since NAs exist as a complex mixture comprised of thousands of compounds from dozens of chemical classes, the characterization of NAs within environmental samples poses significant challenges to analytical chemists.

This dissertation is focused on the characterization of naphthenic acids by comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC/MS). GC×GC/MS offers unparalleled chromatographic separation and peak capacity and has been used in recent years to resolve individual constituents within complex mixtures, including structural isomers. Since the biodegradation and toxicity of NAs is structure-specific and can vary between structural isomers, the profiling of individual NAs by GC×GC/MS is expected to enhance the monitoring of NAs within environmental samples impacted by oil sands activity. In this thesis, GC×GC coupled with time-of-flight mass spectrometry (TOFMS) was used to structurally elucidate a number of ‘unknown’ classical and sulfur-containing naphthenic acids by interpretation of their electron ionization (EI) mass spectra and, if available, confirmed by comparison with the spectra of references standards. GC×GC/TOFMS was also utilized as a fingerprinting tool to assess the temporal and spatial variability at two reclamation sites in the AOSR: Syncrude’s Sandhill Fen reclamation site and Base Mine Lake. Lastly, a methodology was developed which coupled GC×GC with a high resolution quadrupole time-of-flight mass spectrometer (QTOFMS) for the improved profiling of NAs. GC×GC/QTOFMS is advantageous for the monitoring of NAs since it can provide useful fingerprints via isomer distributions, differentiate NAs from several chemical classes, and provide a global overview of the elemental compositions (assigned by mass accuracy) within NA mixtures.