Analysis of Naphthenic Acids in Filtered Oil Sands Process Water (OSPW) using LC/TOF with No Sample Preparation (original) (raw)
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Introduction Naphthenic acids (NAs) are water soluble weak acids, with the general chemical formula C n H 2n+z O 2 , where n is the carbon number, z is referred to as hydrogen deficiency, is a negative even integer and is the number of hydrogen atoms that are lost as the number of rings in naphthenic acid increases. More than one isomer will exist for a given z homolog and the molecular weights differ by 2 mass units (H 2) between z-series and by 14 mass units (CH 2) between n-series. The number of possible naphthenic acids, with the same molecular composition, are 134 with n ranging from 6 to 30 and the number of saturated rings ranging from 0 to 6. Fig.1 shows examples of the general structures of naphthenic acids which have a different number of rings 1 .
A statistical comparison of naphthenic acids characterized by gas chromatography–mass spectrometry
Chemosphere, 2003
Naphthenic acids are complex mixtures of alkyl-substituted acyclic and cycloaliphatic carboxylic acids, with the general chemical formula C n H 2nþz O 2 , where n is the carbon number and Z specifies a homologous family. These acids have a variety of commercial uses, including being used as wood preservatives. They are found in conventional and heavy oils, and in the oil sands of northeastern Alberta, Canada. Naphthenic acids are major contributors to the toxicity of tailings waters that result from the oil sands extraction process. Eight naphthenic acids preparations (four from commercial sources and four from the oil sands operations) were derivatized and analyzed by gas chromatography-mass spectrometry. The composition of each mixture was summarized as a three-dimensional plot of the abundance of specific ions (corresponding to naphthenic acids) versus carbon number (ranging from 5 to 33) and Z family (ranging from 0 to )12). The data in these plots were divided into three groups according to carbon number (group 1 contained carbon numbers 5-14, group 2 contained carbon numbers 15-21, and group 3 contained carbon numbers 22-33). A t-test, using arcsine-transformed data, was applied to compare corresponding groups in samples from various sources. Results of the statistical analyses showed differences between various commercial naphthenic acids preparations, and between naphthenic acids from different oil sands ores and tailings ponds. This statistical approach can be applied to data collected by other mass spectrometry methods.
2018
Concerns over the toxicity associated with 'naphthenic' acids (NA) within oil produced waters and oil sands process waters (OSPW), whether justified or not, have increased the need for the structural elucidation of NA. Certainly, oil sands mining operations, such as those in Alberta, Canada, result in the production of large volumes of OSPW contaminated with NA. Monitoring NA, predicting the toxicities and accounting for the toxicity of residual NA after clean-up treatments, have all been hindered by the lack of NA identifications. Recently, a method involving the conversion of the esters of petroleum NA to the corresponding hydrocarbons before analysis by comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS), resulted in the most comprehensive study of bicyclic NA from petroleum to date. Here, we present results of the analysis by GC×GC-MS of NA extracted from OSPW after conversion of the acids or ester derivatives to the corresponding hydrocarbons. The identifications presented include novel alicyclic, aromatic and sulphur-containing hydrocarbons and thus, by inference, of the corresponding acids. This supports and significantly extends, previous identifications of OSPW NA as their methyl esters and can now be used to better inform environmental monitoring programs and toxicity studies.
Journal of chromatography. A, 2015
Although bicyclic acids have been reported to be the major naphthenic acids in oil sands process-affected water (OSPW) and a well-accepted screening assay indicated that some bicyclics were the most acutely toxic acids tested, none have yet been identified. Here we show by comprehensive multidimensional gas chromatography-mass spectrometry (GC×GC-MS), that >100 C8-15 bicyclic acids are typically present in OSPW. Synthesis or purchase allowed us to establish the GC×GC retention times of methyl esters of numerous of these and the mass spectra and published spectra of some additional types, allowed us to identify bicyclo[2.2.1]heptane, bicyclo[3.2.1]octane, bicyclo[4.3.0]nonane, bicyclo[3.3.1]nonane and bicyclo[4.4.0]decane acids in OSPW and a bicyclo[2.2.2]octane acid in a commercial acid mixture. The retention positions of authentic bicyclo[3.3.0]octane and bicyclo[4.2.0]octane carboxylic acid methyl esters and published retention indices, showed these were also possibilities, as ...
Journal of Chromatography A, 2013
This study details the development of a routine method for quantitative analysis of oil sands naphthenic acids, which are a complex class of compounds found naturally and as contaminants in oil sands process waters from Alberta's Athabasca region. Expanding beyond classical naphthenic acids (C n H 2n−z O 2 ), those compounds conforming to the formula C n H 2n−z O x (where 2 ≥ x ≤ 4) were examined in commercial naphthenic acid and environmental water samples. HPLC facilitated a five-fold reduction in ion suppression when compared to the more commonly used flow injection analysis. A comparison of 39 model naphthenic acids revealed significant variability in response factors, demonstrating the necessity of using naphthenic acid mixtures for quantitation, rather than model compounds. It was also demonstrated that naphthenic acidic heterogeneity (commercial and environmental) necessitates establishing a single NA mix as the standard against which all quantitation is performed. The authors present the first ISO17025 accredited method for the analysis of naphthenic acids in water using HPLC high resolution accurate mass time-of-flight mass spectrometry. The method detection limit was 1 mg/L total oxy-naphthenic acids (Sigma technical mix).
Rapid Communications in Mass Spectrometry, 2013
The large volumes of 'supercomplex' mixtures of reputedly toxic organic compounds in acidic extracts of oil sands process-affected waters (OSPW) represent a challenging goal for complete characterisation. To date, comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCxGC/TOFMS) has allowed the acquisition and interpretation of numerous electron ionisation mass spectra including many of those confirmed to be tricyclic and pentacyclic carboxylic acids by reference to the spectra and retention positions of authentic or synthetic compounds. This has allowed the toxicities of some of the identified acids to be determined and their environmental significance to be better assessed. METHODS: Synthesis, derivatisation (methyl, trideuteriomethyl and trimethylsilyl esters) and GCxGC/TOFMS with nominal mass and higher mass accuracy (ca. 5 ppm) were used to study three abundant unknown acids present in OSPW samples from two different industrial suppliers. RESULTS: GCxGC/TOFMS with nominal mass accuracy, of methyl, trideuteriomethyl and trimethylsilyl esters of three abundant acids in two OSPW samples, produced mass spectra consistent with their assignment as either C 16 tetracyclic acids or as isobaric pentacyclic C 15 hydroxy acids ('O 3 ') or sulfur-containing ('SO 2 ') species. The synthesis of several isomeric pentacyclic C 15 hydroxy acids and examination of the GCxGC retention times and mass spectra (nominal mass) of their derivatives suggested that the unknown OSPW acids were not hydroxy acids, and GCxGC/TOFMS with higher mass accuracy ruled out the possibility. The possibility that they were isobaric 'SO 2 ' species could also be dismissed as this was inconsistent with accurate masses, the derivatisation reactions observed, the fragmentation patterns and the isotope distributions, which excluded the presence of sulphur. CONCLUSIONS: The data support the contention that the three abundant unknowns were indeed C 16 tetracyclic acids. An equally rigorous approach will be necessary to characterise further acids in such mixtures. This is important so that chemistry can be used to guide the search for toxic modes of action.
Water Research, 2002
The water produced during the extraction of bitumen from oil sands is toxic to aquatic organisms due largely to a group of naturally occurring organic acids, naphthenic acids (NAs), that are solubilized from the bitumen during processing. NAs are a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids, with the general chemical formula C n H 2n+Z O 2 , where n is the carbon number and Z specifies a homologous family. Gas chromatography-electron impact mass spectrometry was used to characterize NAs in nine water samples derived from oil sands extraction processes. For each sample, the analysis provided the relative abundances for up to 156 base peaks, with each representing at least one NA structure. Plotting the relative abundances of NAs as three-dimensional bar graphs showed differences among samples. The relative abundance of NAs with carbon numbers p21 to those in the ''C22+cluster'' (sum of all NAs with carbon numbers X22 in Z families 0 to À12) proved useful for comparing the water samples that had a range of toxicities. A decrease in toxicity of process-affected waters accompanied an increase in the proportion of NAs in the ''C22+cluster'', likely caused by biodegradation of NAs with carbon numbers of p21. In addition, an increase in the proportion of NAs in the ''C22+cluster'' accompanied a decrease in the total NAs in the process-affected waters, again suggesting the selective removal of NAs with carbon numbers of p21. This is the first investigation in which changes in the fingerprint of the NA fraction of process-affected waters from the oil sands operations has corresponded with measured toxicity in these waters. r
Journal of Chromatography A, 2012
The naphthenic acids of oil sands process-affected water (OSPW) are said to be important toxicants. The major acids are stated to have alicyclic structures and recently, numerous of these have been identified, but some evidence suggests 'aromatic' acids are also present. The proportions of such acids have not been reported because they exist in so-called supercomplex mixtures with the alicyclic species. Their contribution to the toxicity of OSPW, if any, is therefore unknown. Here we report the use of multidimensional comprehensive gas chromatography-mass spectrometry (GC × GC-MS) with polar first dimension and non-polar second dimension GC columns and argentation solid phase extraction, to separate methyl esters of the acids of an OSPW supercomplex, into distinct fractions. A major fraction (ca 70%) was shown to contain acids (methyl esters) previously identified as alicyclic species. Authentic adamantane acid methyl esters were shown to chromatograph in this fraction. This fraction was isolated by argentation solid phase extraction (SPE) by elution with hexane. GC-MS and GC × GC-MS confirmed this to be the major fraction in the original supercomplex containing alicyclic acids (methyl esters). A second fraction shown to contain monoaromatic acids (methyl esters) by GC × GC-MS was unexpectedly abundant (ca 30% relative to the acyclic acids). The naphtheno-aromatic dehydroabietic acid was confirmed by co-injection with an authentic compound and several acids previously tentatively identified as naphtheno-monoaromatics were present. This fraction was isolated by argentation SPE by elution with more polar 5% diethyl ether in hexane. GC-MS and GC × GC-MS confirmed that the fraction represented a significant proportion of the original supercomplex. A further fraction, eluting from the argentation SPE column with more 5% diethyl ether in hexane in the same retention volume as authentic methyl naphthoate, contained, in addition to some of the second fraction, a third, much more minor complex. This had somewhat similar GC × GC retention characteristics to that of methyl naphthoate and the methyl ester of authentic fluorene-9-carboxylic acid. Spectra are reported. Non-alicyclic, mono-and possibly diaromatic acids are a much more quantitatively significant proportion of OSPW than previously realised. The individual acids need to be better identified and the toxicity of these and other SPE fractions studied in order to assess any possible environmental effects of OSPW.