Characterization of Naphthenic Acids by Gas Chromatography-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

During the bitumen extraction from the oil sands of Alberta, large volumes of process water containing naphthenic acids are stored in tailing ponds. The naphthenic acids along with other components in the processed waters are known to be toxic in aquatic environments. In view of the complex matrix and the toxicity of the processed waters, there is a need for complementary analytical techniques for comprehensive characterization of the naphthenic acid mixtures. This study reports the online gas chromatographic separation of naphthenic acid mixtures prior to ultrahigh resolution mass spectrometry detection, using electron and chemical ionization. Two oil sands processed water samples and two groundwater samples were characterized to evaluate the performance of the instrumental technique. The high mass resolution of the system enabled visualization of the data using Kendrick mass defect plots. The addition of gas chromatographic separations enabled visualization of the data as unique compound class elution fingerprints. The technique is demonstrated to be a valuable tool for chemical fingerprinting of naphthenic acids

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Characterization of Athabasca Oil Sand Process-Affected Waters Incubated in the Presence of Wetland Plants

Naphthenic acid fraction compounds (NAFCs) are naturally present in the oil sand. These compounds become integrated into the oil sands process-affected water (OSPW) during the bitumen extraction process. NAFCs have been identified as causing toxicity in the OSPW to aquatic organisms. Water treatment technologies that are largely passive, such as constructed treatment wetlands, are a sought-after technology for the degradation of NAFCs in aquatic environments, partly because of their low energy intensity. However, it can be challenging to accurately assess the performance regarding decreased NAFC concentration and biodegradation characteristics in water samples that have been exposed to such systems. This is due to interferences of biological products such as fatty acids and humic-like materials, which may give false-positive information on NAFCs estimation with conventional analytical sample cleanup methods such as liquid–liquid extraction (LLE). It is recognized that this same issue exists when attempting to characterize NAFCs in natural wetlands for environmental monitoring purposes and, therefore, an analytical method that can remove background interferences in water samples is desirable on several fronts. Studies were thus conducted to develop and compare methods for NAFC isolation in an experimental wetland setting. A controlled greenhouse experiment was conducted with sedge (Carex aquatilis), bulrush (Schoenoplectus acutus), and cattail (Typha latifolia) grown in OSPW. Two methodsthe Isolute Biotage ENV+ SPE method and a new weak anion exchange (WAX SPE)were assessed for their ability to isolate, clean up, and concentrate NAFCs in OSPW and municipal tap water (control) that were exposed to samples of plants and associated microbes. Negative-ion-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) data revealed that WAX SPE method has better relative enhancement (5%–50%) of O₂ classes in OSPW exposed to wetland plants, compared to ENV+ SPE method. The WAX SPE method is a good candidate for the isolation of organic compounds in complex environmental matrices and supports the development of analytical protocols for isolation and characterization of NAFCs. Compound classes from negative-ion ESI-FT-ICR-MS data were further probed using principal component analysis (PCA) to evaluate the NAFCs that are potential indicators of efficiency of engineered wetlands for monitoring in future wetland studies. Given the PCA results, future wetland NAFC degradation investigations should target O₂ classes for detailed evaluation of the performance of treatment systems, or measurement of the fate and distributions of NAFCs in natural wetlands exposed to OSPW