Preliminary fingerprinting of Athabasca oil sands polar organics in environmental samples using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract

There is a growing need to develop analytical methods that can distinguish compounds found within industrially derived oil sands process water (OSPW) from those derived from natural weathering of oil sands deposits. This is a difficult challenge as possible leakage beyond tailings pond containments will probably be in the form of mixtures of water-soluble organics that may be similar to those leaching naturally into aquatic environments. We have evaluated the potential of negative ion electrospray ionization high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) for comparing oil sands polar organics from tailing ponds, interceptor wells, groundwater, river and lake surface waters. Principal component analysis was performed for all species observed. which included the O(2) class (often assumed to be monocarbxoylic naphthenic acids) along with a wide range of other species including humic substances in the river and lake samples: O(n) where n=1-16; NO(n) and N(2)O(n) where n=1-13; and O(n)S and O(n)S(2) where n=1-10 and 1-8, respectively. A broad range of species was investigated because classical naphthenic acids can be a small fraction of the 'organics' detected in the polar fraction of OSPW, river water and groundwater. Aquatic toxicity and environmental chemistry are attributed to the total organics (not only the classical naphthenic acids). The distributions of the oil sands polar organics, particularly the sulfur-containing species, O(n)S and O(n)S(2), may have potential for distinguishing sources of OSPW. The ratios of species containing O(n) along with nitrogen-containing species: NO(n), and N(2)O(n), were useful for differentiating organic components derived from OSPW from those found in river and lake waters. Further application of the FTICRMS technique for a diverse range of OSPW of varying ages and composition, as well as the surrounding groundwater wells, may be critical in assessing whether leakage from industrial sources to natural waters is occurring.

Beyond Naphthenic Acids: Environmental Screening of Water from Natural Sources and the Athabasca Oil Sands Industry Using Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…APPI thus gives accessibility to a greater range of compounds that would not have been ionized under ESI conditions. When characterizing OSPW samples by negative-ion ESI, it could be expected that~1900 elemental compositions could be assigned to monoisotopic peaks (i.e., not including the multiple, associated isotopologues for each case) [17]. By comparison, we determined~3600 elemental compositions could be assigned by APPI, representing a doubling in the amount of potentially useful information obtained.…”

“…Zooming in further (Figure2d), to a window with a width of approximately 0.5Dapercharge, highlights the fact that a number of peaks are present at this nominal m/z, similar to nominal m/z windows throughout the mass spectrum. Sulfur is commonly present in OSPW samples [15,17,35], and Figure2e illustrates the need for ultrahigh resolving power in order to separate ions that differ in mass by approximately 3.4mDa (0.003371Da), due to the difference in composition between C 3 and SH 4 [42]. Figure2f provides a histogram of mass errors associated with the assignments for the positive-ion groundwater mass spectrum; the RMS error was calculated to be 0.17ppm in this example.…”

“…Organics were eluted with methanol, evaporated to dryness under nitrogen, redissolved in 1mL of acetonitrile/Milli-Q water (1:1) that also contained 0.1% ammonium hydroxide solution. Prior to analysis by an FT-ICR mass spectrometer, the concentrates were diluted 20× in acetonitrile/Milli-Q water (1:1), to ensure the sample preparation conditions were the same as for analysis by ESI [17]. A dopant was not used to optimize the detection of components for the APPI studies presented here, as the intent was to analyze the same sample solutions by APPI as previously investigated by ESI.…”

“…It has been hypothesized that polar, organic components will have the greatest potential to migrate [17], making negative-ion ESI the methodology of choice as it has been for the study of naphthenic acids in general over the past decade (reviewed in [2]). Preliminary work has demonstrated the differences in profiles between river and lake waters and OSPW by negative-ion ESI FT-ICR-MS [17]; however, ESI can be prone to matrix-derived signal effects [38]. An alternate approach is to utilize APPI, which is less sensitive to matrix effects than ESI [12,39].…”

“…Naphthenic acids have traditionally been defined as carboxylic acids containing one or more saturated rings, but this definition has broadened as new compound classes have recently been elucidated. They have been amongst the most studied of the OSPW components [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and their remediation from the oil sands industry has attracted attention [19][20][21].…”