Gregory J. Hall

Oxygenated weathering products of Deepwater Horizon oil come from surprising precursors

Following the release of crude oil from the Macondo well in 2010, a wide range of weathering processes acted on the spilled oil. A recent study revealed that samples from this spill were oxidized into oxygenated hydrocarbons (OxHC) comprising more than 50% of the extracted hydrocarbons. The precursors of these compounds were not identified despite using a wide range of analytical tools, including gas chromatography (GC). To search for these precursors, over 40 samples were analyzed by comprehensive two-dimensional gas chromatography (GC×GC), one of the largest studies of its kind to date. Partial least squares regression was employed to elucidate the GC×GC peaks that could be the precursors of OxHC in our samples. We found that the formation of OxHC correlated with the disappearance of saturated hydrocarbons, including alkylcyclopentanes, alkyl cyclohexanes, alkylated bicyclic saturated compounds, tricyclic terpanpoids, and alkylbenzenes. These results indicate a previously under-reported chemodynamic process in oil spill weathering.

Analysis of petroleum compositional similarity using multiway principal components analysis (MPCA) with comprehensive two-dimensional gas chromatographic data

The accurate establishment of oil similarity is a longstanding problem in petroleum geochemistry and a necessary component for resolving the architecture of an oil reservoir. Past limitations have included the excessive reliance on a relatively small number of biomarkers to characterize such complex fluids as crude oils. Here we use multiway principal components analysis (MPCA) on large numbers of specific chemical components resolved with comprehensive two-dimensional gas chromatography-flame ionization detection (GC×GC-FID) to determine the molecular relatedness of eight different maltene fractions of crude oils. MPCA works such that every compound eluting within the same first and second dimension retention time is quantitatively compared with what elutes at that same retention times within the other maltene fractions. Each maltene fraction and corresponding MPCA analysis contains upwards of 3500 quantified components. Reservoir analysis included crude oil sample pairs from around the world that were collected sequentially at depth within a single well, collected from multiple depths in the same well, and from different depths and different wells but thought to be intersected by the same permeable strata. Furthermore, three different regions of each GC×GC-FID chromatograms were analysed to evaluate the effectiveness of MPCA to resolve compositional changes related to the source of the oil generating sediments and its exposure to biological and/or physical weathering processes. Compositional and instrumental artefacts introduced during sampling and processing were also quantitatively evaluated. We demonstrate that MPCA can resolve multi-molecular differences between oil samples as well as provide insight into the overall molecular relatedness between various crude oils.

Chemometric Determination of Target Compounds Used to Fingerprint Unweathered Diesel Fuels

Existing oil fingerprinting standard methods target mostly high-molecular-weight biomarkers for discrimination between samples. Fingerprinting of light petroleum distillates like diesel fuel is problematic with these methods because many of the target analytes are not present. To address this problem, 14 diesel fuel samples from refineries throughout the United States and Canada were analyzed by GC/MS. For each sample, peaks were integrated in 62 different extracted ion chromatograms that represented 22 classes of petroleum constituents. Over 300 individual peak ratios were calculated per sample. Principle components analysis (PCA) was used to reduce the number of ratios needed to differentiate the samples. Nine significant peak ratios were identified by PCA. The ratios included compounds in alkylbenzene, alkylphenanthrene, and sesquiterpane petroleum classes. The PCA model removed peak ratios that contributed to instrument replicate variability, which improved differentiation among samples. Real-world spill samples not subjected to evaporative or other weathering processes were used to test the robustness of the model with excellent results. The spill samples were readily seen to be significantly different. Additional studies such as the effects of weathering on these peak ratios are needed before this approach can be evaluated as a useful spill fingerprinting method.

Tracking and Modeling the Degradation of a 30 Year Old Fuel Oil Spill with Comprehensive Two-Dimensional Gas Chromatography

ABSTRACT On October 9, 1974, the barge Bouchard 65, carrying 12 million liters of No. 2 fuel oil, spilled an undetermined amount of oil off the west entrance of the Cape Cod Canal in Buzzards Bay, Massachusetts, USA. Wind patterns and currents caused significant oiling of the nearby Winsor Cove salt marsh. Fortunately, an original Bouchard 65 cargo oil sample was retained from the spill which offers a unique opportunity to compare in vitro weathering experiments with petroleum that has been weathered naturally for over thirty years. Samples of the original product were bio-weathered in the lab over a period of days, and then these samples, plus a contemporary sample from Winsor Cove, were analyzed by Comprehensive two-dimensional gas chromatography with Time of Flight Mass Spectrometry detection (GC×GC-MS). The data from the laboratory experiment was used to create a Principal Components Regression model to predict amount of weathering. The environmental sample was projected onto the regression model and ...

Plutonium Isotopes in the Terrestrial Environment at the Savannah River Site, USA. A Long-Term Study

This work presents the findings of a long-term plutonium (Pu) study at Savannah River Site (SRS) conducted between 2003 and 2013. Terrestrial environmental samples were obtained at the Savannah River National Laboratory (SRNL) in the A-Area. Plutonium content and isotopic abundances were measured over this time period by α particle and thermal ionization mass spectrometry (3STIMS). We detail the complete process of the sample collection, radiochemical separation, and measurement procedure specifically targeted to trace plutonium in bulk environmental samples. Total plutonium activities were determined to be not significantly above atmospheric global fallout. However, the (238)Pu/(239+240)Pu activity ratios attributed to SRS are substantially different than fallout due to past (238)Pu production on the site. The (240)Pu/(239)Pu atom ratios are reasonably consistent from year to year and are lower than fallout indicating an admixture of weapons-grade material, while the (242)Pu/(239)Pu atom ratios are higher than fallout values, again due to actinide production activities. Overall, the plutonium signatures obtained in this study reflect a distinctive mixture of weapons-grade, heat source, and higher burn-up plutonium with fallout material. This study provides a unique opportunity for developing and demonstrating a blue print for long-term low-level monitoring of trace plutonium in the environment.

Anthropogenic plutonium-244 in the environment: Insights into plutonium's longest-lived isotope.

Owing to the rich history of heavy element production in the unique high flux reactors that operated at the Savannah River Site, USA (SRS) decades ago, trace quantities of plutonium with highly unique isotopic characteristics still persist today in the SRS terrestrial environment. Development of an effective sampling, processing, and analysis strategy enables detailed monitoring of the SRS environment, revealing plutonium isotopic compositions, e.g., 244Pu, that reflect the unique legacy of plutonium production at SRS. This work describes the first long-term investigation of anthropogenic 244Pu occurrence in the environment. Environmental samples, consisting of collected foot borne debris, were taken at SRS over an eleven year period, from 2003 to 2014. Separation and purification of trace plutonium was carried out followed by three stage thermal ionization mass spectrometry (3STIMS) measurements for plutonium isotopic content and isotopic ratios. Significant 244Pu was measured in all of the years sampled with the highest amount observed in 2003. The 244Pu content, in femtograms (fg = 10−15 g) per gram, ranged from 0.31 fg/g to 44 fg/g in years 2006 and 2003 respectively. In all years, the 244Pu/239Pu atom ratios were significantly higher than global fallout, ranging from 0.003 to 0.698 in years 2014 and 2003 respectively.

Fiber optic laser-induced fluorescence excitation emission detector applied to flow injection analysis

A multi-channel fiber optic laser induced fluorescence (LIF) detection system has been developed for flow injection analysis (FIA). It has been applied to the detection of standard PAH mixtures and real world samples. The instrument uses a fiber optic array to deliver Raman shifter generated excitation beams (260 nm - 340 nm) to samples flowing in a fused silica capillary. An identical fluorescence collection fiber optic array was positioned perpendicular to the excitation array to collect fluorescence generated by the sample at each excitation wavelength. A spectrograph and charge coupled device (CCD) were used to spectrally discriminate and detect the fluorescence delivered by each collection fiber. Several samples were investigated including standard PAH mixtures and a fuel oil sample. Identification and quantitation were accomplished using rank annihilation factor analysis (RAFA) using pure single component standards and the EEMs of mixtures measured during FIA of the unknown samples. For all components in the standard PAH mixtures, quantitative estimates of concentration were within a factor of 2.5 from the known values with some of the components being determined to within a factor of 1.3. For the complex fuel oil sample, 6 out of 8 components were correctly identified.