Method development for forensic oil identification by direct analysis in real time time-of-flight mass spectrometry.

The current well-established chromatography and mass spectrometry based oil spill identification procedures, such as those outlined by the European Committee for Standardization, are highly reliable as methods, highly defensible in the court of law, and widely applicable to the majority of oil spill situations. Nevertheless, the methodology is time consuming and labour intensive, which may not be ideal when dealing with an emergency oil spill situation. In this study, direct analysis in real time time-of-flight mass spectrometry (DART/TOFMS) was used to successfully develop an efficient oil identification method. To confirm the accuracy of this method spilled oil samples were tested from five previous years of blind round robin testing organized by the oil spill identification network of experts (OSINET) under the Bonn Agreement. Heatmap inspection, principal component analysis and finally discriminant analysis of principal components were used to arrive at final predictions regarding the identities of the spilled oil samples. The results were compared with the results of previous gas chromatography flame ionization detection (GC/FID) and gas chromatography triple quadrupole mass spectrometry (GC/MS/MS) analyses of the same oils. While taking only about a tenth of the time, the DART/TOFMS analysis produced results similar to those of classical GC/FID and GC/MS/MS (EI+) procedures. The ability of DART/TOFMS to display this level of validity exemplifies its potential to be a new tool for supplementing classical analyses for oil spill forensics.

Enhancement of oil forensic methodology through the addition of polycyclic aromatic nitrogen heterocycle biomarkers for diagnostic ratios.

Current oil spill forensic identification of source oils relies upon hydrocarbon biomarkers resistant to weathering. This international technique was developed by the European Committee for Standardization (CEN), under EN 15522-2 Oil Spill Identification guidelines. The number of biomarkers have expanded at pace with technological advances, while distinguishing new biomarkers becomes more challenging due to interference of isobaric compounds, matrix effects, and high cost of weathering experiments. Application of high-resolution mass spectrometry enabled exploration of potential polycyclic aromatic nitrogen heterocycle (PANH) oil biomarkers. The instrumentation showed reduction in isobaric and matrix interferences, allowing for identification of low-level PANH and alkylated PANHs (APANHs). Weathered oil samples, obtained from a marine microcosm weathering experiment, enabled comparison with source oils to identify new, stable forensic biomarkers. This study highlighted eight new APANH diagnostic ratios that expanded the biomarker suite, increasing the confidence for identifying highly weathered oils back to their source oil.

Advancement in oil forensics through the addition of polycyclic aromatic sulfur heterocycles as biomarkers in diagnostic ratios.

In current oil spill forensics, diagnostic ratios of hydrocarbon biomarker responses are commonly used to compare oil spill samples to source materials in order to determine the identity of the oil. This well recognized procedure was developed by the European Committee for Standardization (CEN) with corresponding published EN 15522-2 Oil Spill Identification guidelines. However, it is further recognized that weathering can have a negative effect on some of the biomarkers used in the analysis, leading to decreased confidence in the result. In this study, polycyclic aromatic sulfur heterocycles (PASHs) and their alkylated forms (APASHs) were assessed for their potential as additional biomarkers. With the aim of identifying stable PASHs and APASHs useful as weathered oil biomarkers, the superior specificity of gas chromatography with high resolution mass spectrometry was exploited to determine chromatographic peak responses for sixteen petroleum oil samples. Extensive study, involving microcosm extreme weathering and spreadsheet development, led to the identification of 19 new diagnostic ratios based on newly discovered stable PASH and APASH biomarkers. Application of the extended diagnostic ratio suite showed high potential to improve the forensic attribution of post-spill weathered oil back to its original source.

A rapid gas chromatography quadrupole time-of-flight mass spectrometry method for the determination of polycyclic aromatic hydrocarbons and sulfur heterocycles in spilled crude oils.

Spilled crude oil samples contain various toxic compounds including polycyclic aromatic hydrocarbons (PAHs) as well as sulfur heterocycles (PASHs) and their related alkylated forms (APAHs and APASHs). In this study, a method was successfully developed employing a gas chromatography quadrupole time-of-flight (GC-QToF) mass spectrometer to quantitatively analyze both PAHs/APAHs and PASHs/APASHs in these samples. With GC-QToF, the monoisotopic mass of the compounds is distinguished, allowing the PASHs/APASHs to be extracted separately from the PAHs/APAHs in crude oil. A gas chromatography triple quadrupole (GC-MS/MS) mass spectrometer was also used to confirm that a GC-QToF is the preferred instrument for analyzing these compounds. With the use of PASH/APASH standards to determine response correction factors (RCFs) in relation to PAH standards, the developed method is capable of analyzing PAHs, APAHs, PASHs, and APASHs in a single injection. The use of RCFs allowed for the development of a practical polycyclic aromatic carbon (PAC) method for analyzing a total of 77 compounds of the 2 groups in crude oil. This newly developed method was applied to spilled crude oils, demonstrating its potential in toxicological study as well as oil spill forensic investigation.

Enhanced analysis of weathered crude oils by gas chromatography-flame ionization detection, gas chromatography-mass spectrometry diagnostic ratios, and multivariate statistics.

Artificially weathered crude oil "spill" samples were matched to unweathered suspect "source" oils through a three-tiered approach as follows: Tier 1 gas chromatography-flame ionization detection (GC/FID), Tier 2 gas chromatography-mass spectrometry (GC/MS) diagnostic ratios, and Tier 3 multivariate statistics. This study served as proof of concept for a promising and new method of crude oil forensics that applies principal component analysis (PCA) and partial least squares discriminant analysis (PLSDA) in tandem with traditional forensic oil fingerprinting tools to confer additional confidence in challenging oil spill cases. In this study, weathering resulted in physical and chemical changes to the spilled oils, thereby decreasing the reliability of GC/FID and GC/MS diagnostic ratios in source attribution. The shortcomings of these traditional methods were overcome by applying multivariate statistical tools that enabled accurate characterization of the crude oil spill samples in an efficient and defensible manner.

Tiered approach to long-term weathered lubricating oil analysis: GC/FID, GC/MS diagnostic ratios, and multivariate statistics.

Frequent small-scale environmental releases of lubricating (lube) oils have deleterious effects on aquatic ecosystems. In the event of a spill, oil fingerprinting is critical to source attribution, clean-up procedures, and liability assignment. Oil forensic investigations are particularly challenging when oils are weathered over an extended period of time, as a large number of biomarkers become lost and the chemical composition changes significantly from its source. This study simulated an environmental case in which long-term weathered lube oil "spill" samples were matched to unweathered suspect "source" oils. While traditional oil fingerprinting techniques including GC/FID and GC/MS diagnostic ratios were insufficient for reliably attributing the source, a comprehensive and systematically tiered approach proved successful. The proposed methodology featured three tiers: Tier 1 GC/FID, Tier 2 GC/MS diagnostic ratios, and Tier 3 multivariate statistics. This novel approach provided environmental chemists with a powerful tool for dealing with an otherwise extremely challenging lube oil forensic investigation.

Enhanced marine monitoring and toxicity study of oil spill dispersants including Corexit EC9500A in the presence of diluted bitumen.

Observations made for the analysis of the oil spill dispersant tracer dioctyl sulfosuccinate (DOSS) during LC50 toxicity testing, highlighted a stability issue for this tracer compound in seawater. A liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (LC/QToF) was used to confirm monooctyl sulfosuccinate (MOSS) as the only significant DOSS breakdown product, and not the related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate. Combined analysis of DOSS and MOSS was shown to be applicable to monitoring of spill dispersants Corexit® EC9500A, Finasol OSR52, Slickgone NS, and Slickgone EW. The unassisted conversion of DOSS to MOSS occurred in all four oil spill dispersants solubilized in seawater, although differences were noted in the rate of MOSS formation. A marine microcosm study of Corexit EC9500A, the formulation most rapid to form MOSS, provided further evidence of the stoichiometric conversion of DOSS to MOSS under conditions relevant to real world dilbit spill. Results supported combined DOSS and MOSS analysis for the monitoring of spill dispersant in a marine environment, with a significant extension of sample collection time by 10 days or longer in cooler conditions. Implications of the unassisted formation of MOSS and combined DOSS:MOSS analysis are discussed in relation to improving dispersant LC50 toxicity studies.

Chemotyping and identification of protected Dalbergiatimber using gas chromatography quadrupole time of flight mass spectrometry.

The international trade in illegally logged and environmentally endangered timber has spurred enforcement agencies to seek additional technical procedures for the identification of wood species. All Dalbergia species are listed under the Convention on International Trade in Endangered Species (CITES) which is the reason this genus was chosen for study. Multiple sources of the heartwood from different Dalbergia species were extracted and chromatographic profiles collected by gas chromatography with high resolution quadrupole Time of Flight mass spectrometry (GC/QToF). The collected data was mined to select peaks and mass ions representative of the investigated Dalbergia species, and used to develop a Microsoft Excel® template offering immediate graphical representation of the results. Using wood specimens sourced from different xylaria, this graphical fingerprint proved adept at definitive identification of Dalbergia species. The CITES Appendix I species, D. nigra, was easily distinguished from D. melanoxylon and look-alike species of other genera. Similarly, a number of other Dalbergia species were differentiated using this current approach. Kernel discrimination analysis (KDA) was applied to increase the confidence of the species identification. The mislabeling of specimens appears to be common, and the emerging technique of GC/QToF in combination with other techniques, offers improved confidence in identification. GC/QToF further provides automation, the dimension of chromatography to avoid interferences, and production of reproducible electron impact positive (EI+) spectra. The prospect of building an EI+ spectral database for future wood identification is an important feature considering the limited accessibility of authenticated wood species specimens.

Improved oil spill dispersant monitoring in seawater using dual tracers: Dioctyl and monoctyl sulfosuccinates sourced from corexit EC9500A.

A high resolution mass spectrometry method was developed for the environmental impact monitoring of oil spill dispersants. Previously reported instability of dioctyl sulfosuccinate (DOSS) dispersant tracer was addressed by the new procedure. The method monitors both DOSS and its degradation product, monooctyl sulfosuccinate (MOSS), by liquid chromatography time-of-flight mass spectrometry. The related isomer, 4-(2-ethylhexyl) 2-sulfobutanedioate, was chromatographically resolved from MOSS but was not a product of DOSS degradation. Using this direct injection method (10 µL), the practical lower limit of quantitation was 0.5 nM for each analyte, a concentration equivalent to 0.22 ng mL-1, or 0.30 ng mL-1 including initial dilution factor with acetonitrile. The method was shown applicable to analysis of the dispersants Corexit® EC9500 A, Finasol OSR 52, Slickgone NS, and Slickgone EW for which DOSS is an active ingredient. A marine microcosm study of Corexit EC9500A, together with diluted bitumen (dilbit), at 15 ± 1 °C, provided evidence of the stoichiometric conversion of DOSS to MOSS under conditions reflecting a western Canadian marine environment. The advantage of the developed method is in its ability to extend environmental seawater sample collection time from 4 days for DOSS alone, to 14 days when both DOSS and MOSS are simultaneously analysed and results combined. The collection time is likely extended beyond the 14 day period with cooler temperatures. Preservation of collected seawater samples using sodium hydroxide, converting DOSS into MOSS in situ, was rejected due to stability issues. Addition of disodium ethylenediaminetetraacetic acid did not improve hold times, thus eliminating the theory of cation induced micelle effects causing DOSS loss.

Colorimetric method for determining Pb2+ ions in water enhanced with non-precious-metal nanoparticles.

Sulfur anions and their derivatives have long been recognized for their high selectivity and reactivity toward Pb(2+) ions and formation of highly absorptive yet water-insoluble compounds with both acid and base media. This phenomenon has been used for qualitative analysis of lead ions in water. We demonstrate a new method to quantitatively determine the Pb(2+) concentration in the range of 0.5-500 ppm in water using colorimetric measurement, based on forming "soluble" lead sulfide in water enhanced with non-precious-metal nanoparticles. This method has inherent high selectivity for lead over other alkali-metal and alkaline-earth-metal ions. The colorimetric measurements of the absorptive solutions provide accurate determination of the lead concentration in water comparable to that measured using inductively coupled plasma mass spectrometry. To our knowledge, this is the simplest, lowest cost, and easiest-to-use method for detecting and determining the lead concentration in water.