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Ultra-performance liquid chromatography ion mobility time-of-flight mass spectrometry (UPLC-IM-TOFMS) was utilized for the analysis of naphthenic acids (NAs) in fractions of pH-dependent sequential liquid-liquid extractions from oil sands process-affected water. Ion-mobility separation technique allowed the differentiation of O y S−NAs (2 ≤ y ≤ 4) from O x −NAs (2 ≤ x ≤ 5) via drift time versus retention time separations. The results indicated that the addition of S atom to the O 2 −NA molecule led to a lower increase in the dissociation constant (pK a ) compared to that caused by the addition of O atom. Because additional O is present as OH while the S atom is present as the C S C structure, the latter does not involve into the deprotonation process directly. The pK a value decreased along with increasing carbon number and |Z| number for O 2 −, O 3 −, O 4 −, and O 2 S−NA species, except for O 5 −, O 3 S−, and O 4 S−NA species, each of which are comprised of chemical structures with distinct functional groups. A calculation model was developed to estimate pK a values for individual and total NA species via nonlinear regression curve fitting, utilizing the relative abundances of detected NA species. pK a values were calculated as 3.9 for total NAs, 3.3 for O 2 −NAs, 4.4 for O 3 −NAs, 7.3 for O 4 −NAs, and 4.1 for O 2 S−NAs. Knowledge of NAs pK a is crucially important for the comprehensive understanding of their potential transformation route and toxicity as well as for the development of water remediation applications. Both the ion-mobility separation technique and the new calculation model could be widely applied for the investigation of other complicated pollutants present in water and wastewater. [ABSTRACT FROM AUTHOR]

Naphthenic acids (NAs) are a highly complex mixture of organic compounds naturally present in bitumen and identified as the primary toxic constituent of oil sands process-affected water (OSPW). This work investigated the degradation of cyclohexanoic acid (CHA), a model NA compound, and natural occurring NAs during the UV photolysis of Fe(III)-nitrilotriacetic acid (UV-Fe(III)NTA) and UV-NTA-Fenton processes. The results indicated that in the UV-Fe(III)NTA process at pH 8, the CHA removal increased with increasing NTA dose (0.18, 0.36 and 0.72 mM), while it was independent of the Fe(III) dose (0.09, 0.18 and 0.36 mM). Moreover, the three Fe concentrations had no influence on the photolysis of the Fe(III)NTA complex. The main responsible species for the CHA degradation was hydroxyl radical ( OH), and the role of dissolved O 2 in the OH generation was found to be negligible. Real OSPW was treated with the UV-Fe(III)NTA and UV-NTA-Fenton advanced oxidation processes (AOPs). The removals of classical NAs (O 2 -NAs), oxidized NAs with one additional oxygen atom (O 3 -NAs) and with two additional oxygen atoms (O 4 -NAs) were 44.5%, 21.3%, and 25.2% in the UV-Fe(III)NTA process, respectively, and 98.4%, 86.0%, and 81.0% in the UV-NTA-Fenton process, respectively. There was no influence of O 2 on the NA removal in these two processes. The results also confirmed the high reactivity of the O 2 -NA species with more carbons and increasing number of rings or double bond equivalents. This work opens a new window for the possible treatment of OSPW at natural pH using these AOPs. [ABSTRACT FROM AUTHOR]

The fractionation of oil sands process-affected water (OSPW) via pH-dependent extractions was performed to quantitatively investigate naphthenic acids (NAs, C n H 2 n + Z O 2 ) and oxidized NAs (O x -NAs) species (C n H 2 n + Z O 3 and C n H 2 n + Z O 4 ) using ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOFMS). A mathematical model was also developed to estimate the dissociation constant p K a for NAs species, considering the liquid–liquid extraction process and the aqueous layer acid-base equilibrium. This model provides estimated dissociation constants for compounds in water samples based on fractionation extraction and relative quantification. Overall, the sum of O 2 -, O 3 -, and O 4 -NAs species accounted for 33.6% of total extracted organic matter. Accumulative extracted masses at different pHs revealed that every oxygen atom added to NAs increases the p K a (i.e., O 2 -NAs < O 3 -NAs < O 4 -NAs), indicating that the additional O atoms exist as –OH in O 3 - and O 4 -NAs. Molecule electron-withdrawing groups such as double bonds and aromatic groups, as indicated by higher carbon and − Z number, may be responsible for the lower p K a of O 2 -, O 3 -, and O 4 -NAs. The model obtained estimated p K a values of 3.5 for O 2 -NAs, 4.8 for O 3 -NAs, and 6.8 for O 4 -NAs via nonlinear regression curve fittings. These p K a values are valuable physicochemical parameters for environmental engineering applications targeting OSPW NAs treatment. [ABSTRACT FROM AUTHOR]

There are several established methods for the determination of naphthenic acids (NAs) in waters associated with oil sands mining operations. Due to their highly complex nature, measured concentration and composition of NAs vary depending on the method used. This study compared different common sample preparation techniques, analytical instrument methods, and analytical standards to measure NAs in groundwater and process water samples collected from an active oil sands operation. In general, the high- and ultrahigh-resolution methods, namely high performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) and Orbitrap mass spectrometry (Orbitrap-MS), were within an order of magnitude of the Fourier transform infrared spectroscopy (FTIR) methods. The gas chromatography mass spectrometry (GC-MS) methods consistently had the highest NA concentrations and greatest standard error. Total NAs concentration was not statistically different between sample preparation of solid phase extraction and liquid-liquid extraction. Calibration standards influenced quantitation results. This work provided a comprehensive understanding of the inherent differences in the various techniques available to measure NAs and hence the potential differences in measured amounts of NAs in samples. Results from this study will contribute to the analytical method standardization for NA analysis in oil sands related water samples. [ABSTRACT FROM AUTHOR]

This work investigated the oxidative transformation of the organic species in oil sands process-affected water (OSPW) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) in both negative and positive electrospray ionization (ESI) modes. This is the first time to apply FTICR-MS to investigate species transformation in OSPW treatments by ferrate (VI), UV/H 2 O 2 , and molecular ozone, and also this is the first preliminary study to use positive ESI to investigate organic species in addition to naphthenic acids (NAs) in these treatment processes. The oxidation processes with potassium ferrate (VI), UV/H 2 O 2 , and ozone transformed the distribution profiles of O x , O x S y , and O x N y organic fractions (i.e., species containing oxygen, sulfur, and nitrogen, with x, y specifying the oxygen number and sulfur/nitrogen number, respectively), with O x S y distribution profiles showing the most sensitive responses to the oxidation extent and can be used as a signature fraction to evaluate the oxidation effectiveness. Negative mode UPLC-TOF-MS confirmed the transformation pattern of O x species observed with FTICR-MS, but positive mode UPLC-TOF-MS results showed severe discrepancies with FTICR-MS results and should be subjected for future further investigation, regarding the relatively low mass resolution of UPLC-TOF-MS. The investigation of the transformation patterns of different organic species using two ionization modes was a preliminary study to enhance the understanding of the efficiency, selectivity, and mechanism of different oxidation processes in OSPW remediation for both NAs and non-NA species. [ABSTRACT FROM AUTHOR]