Richard B. Gaines

Comprehensive Two-Dimensional Gas Chromatography with Mass Spectrometric Detection (GC × GC/MS) Applied to the Analysis of Petroleum

Comprehensive two-dimensional gas chromatography coupled with mass spectrometric detection (GC × GC/MS) is a three-dimensional analytical method. In its application to petroleum analysis, the high peak capacity of GC × GC produced chromatographic resolution of over 750 peaks from a marine diesel fuel. The MS detector provided a full-scan mass spectrum for each resolved peak. The integration of an MS detector with GC × GC provides increased capability to identify minor components, determine members of homologous series, and characterize ordered peak patterns of related components that are visible in the GC × GC chromatogram.

Separation and identification of petroleum biomarkers by comprehensive two‐dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC×GC) has been used to separate and identify biomarker molecules in crude oil. The biomarkers examined include alkylated aromatics (naphthalenes, biphenyls, fluorenes, phenanthrenes, chrysenes), sulfur-containing aromatics (dibenzothiophenes, benzonaphthothiophenes), steranes, triterpanes, and triaromatic steranes. These biomarkers, which are frequently used in forensic oil spill analysis and petroleum exploration, were separated into easily recognizable bands in the GC×GC chromatogram. Methods used to identify the bands included peak matching with chemical standards, comparison with GC/MS extracted ion chromatograms, and the application of chemical logic based on the known volatility and polarity properties of the biomarkers.

Quantitative Determination of BTEX and Total Aromatic Compounds in Gasoline by Comprehensive Two‐Dimensional Gas Chromatography (GC×GC)

Comprehensive two-dimensional gas chromatography (GC×GC) has been applied to the quantitative analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and all heavier aromatic compounds in gasoline. The two-dimensional chromatographic separation used volatility selection on the first-dimension column and polarity selection on the second-dimension column. In the resulting GC×GC chromatogram, aromatic species were resolved from other compound classes. Moreover, structurally related aromatics were grouped in a manner that facilitated identification and integration. The response of a flame ionization detector to each major aromatic group in gasoline was calibrated using internal standards. Quantitation produced results directly comparable with ASTM standard methods. The present GC×GC method can be expanded to analyze other gasoline components.

Tracking the Weathering of an Oil Spill with Comprehensive Two-Dimensional Gas Chromatography

Comprehensive two-dimensional gas chromatography (GC × GC) was used to investigate the Bouchard 120 oil spill. The latter occurred on April 25, 2003, when the barge Bouchard 120 spilled ∼ 375,000 liters of No. 6 fuel oil into Buzzards Bay, Massachusetts. In order to gain a better understanding of the natural processes affecting the fate of the spilled product, we collected and analyzed oil-covered rocks from Nyes Neck beach in North Falmouth, Massachusetts. Here we discuss the data from samples collected on May 9, 2003, and six months later, on November 23, 2003. Along with standard two-dimensional gas chromatographic analysis, we employed unique data-visualization techniques such as difference, ratio, and addition chromatograms to highlight how evaporation, water washing, and biodegradation weathered the spilled oil. These approaches provide a new perspective to studying oil spills and aid attempts to remediate them.

Identification of a novel alkenone in Black Sea sediments

Abstract We report the identification of a novel long-chain ketone in Holocene Black Sea sediments. Based on chemical properties, and chromatographic and mass spectrometric characteristics, this compound has been identified as a di-unsaturated C36 ethyl ketone. Further analyses indicated the position and configuration of the double bonds, and the novel alkenone was determined to be hexatriaconta-(16E,21E)-dien-3-one. While this compound is present in only trace quantities in Unit I sediments, it is the most abundant alkenone in portions of Unit II. Its presence thus apparently pre-dates the invasion of Emiliania huxleyi in the Black Sea. The down-core profiles and isotopic compositions suggest that the precursor for the C36:2 alkenone may be distinct from that of the C37-39 alkenones, however the biological origin of this novel compound is presently unknown.

Forensic Analysis of Ignitable Liquids in Fire Debris by Comprehensive Two-Dimensional Gas Chromatography

The application of comprehensive two-dimensional gas chromatography (GC x GC) for the forensic analysis of ignitable liquids in fire debris is reported. GC x GC is a high resolution, multidimensional gas chromatographic method in which each component of a complex mixture is subjected to two independent chromatographic separations. The high resolving power of GC x GC can separate hundreds of chemical components from a complex fire debris extract. The GC x GC chromatogram is a multicolor plot of two-dimensional retention time and detector signal intensity that is well suited for rapid identification and fingerprinting of ignitable liquids. GC x GC chromatograms were used to identify and classify ignitable liquids, detect minor differences between similar ignitable liquids, track the chemical changes associated with weathering, characterize the chemical composition of fire debris pyrolysates, and detect weathered ignitable liquids against a background of fire debris pyrolysates.

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere.

Highly cracked and isomerized archaeal lipids and bacterial lipids, structurally changed by thermal stress, are present in solvent extracts of 2,707- to 2,685-million-year-old (Ma) metasedimentary rocks from Timmins, ON, Canada. These lipids appear in conventional gas chromatograms as unresolved complex mixtures and include cyclic and acyclic biphytanes, C36–C39 derivatives of the biphytanes, and C31–C35 extended hopanes. Biphytane and extended hopanes are also found in high-pressure catalytic hydrogenation products released from solvent-extracted sediments, indicating that archaea and bacteria were present in Late Archean sedimentary environments. Postdepositional, hydrothermal gold mineralization and graphite precipitation occurred before metamorphism (≈2,665 Ma). Late Archean metamorphism significantly reduced the kerogens adsorptive capacity and severely restricted sediment porosity, limiting the potential for post-Archean additions of organic matter to the samples. Argillites exposed to hydrothermal gold mineralization have disproportionately high concentrations of extractable archaeal and bacterial lipids relative to what is releasable from their respective high-pressure catalytic hydrogenation product and what is observed for argillites deposited away from these hydrothermal settings. The addition of these lipids to the sediments likely results from a Late Archean subsurface hydrothermal biosphere of archaea and bacteria.

Determination of Oxygenates in Gasoline by GC×GC

Comprehensive two-dimensional gas chromatography (GC × GC) has been applied to the quantitation of oxygenates in reformulated gasoline. Target oxygenates were C 1 -C 4 alcohols, tert-pentanol, methyl tert-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). These were separated from the gasoline matrix using a volatility-based selectivity in the first chromatographic dimension, followed by a mixed-phase polarity/shape selectivity in the second dimension. The high resolving power of this stationary phase combination completely separated all oxygenates except DIPE, ETBE, and TAME, which exhibited coelution with other nonpolar gasoline components. Oxygenates quantitation was achieved with the use of an internal standard, an FID detector, and calibration curves. Quantitation results are in good agreement with ASTM and EPA standard methods. When coupled with our previous method for BTEX and aromatics, a single GC × GC method can now quantitate MTBE, alcohols, BTEX, and aromatics in a one-hour analysis.

Isomer-specific determination of 4-nonylphenols using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry.

Technical nonylphenol (tNP), used for industrial production of nonylphenol polyethoxylate surfactants, is a complex mixture of C(3-10)-phenols. The major components, 4-nonylphenols, are weak endocrine disruptors whose estrogenicities vary according to the structure of the branched nonyl group. Thus, accurate risk assessment requires isomer-specific determination of 4-NPs. Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC x GC/ToFMS) was used to characterize tNP samples obtained from seven commercial suppliers. Under optimal chromatographic conditions, 153-204 alkylphenol peaks, 59-66 of which were identified as 4-NPs, were detected. The 4-NPs comprised approximately 86-94% of tNP, with 2-NPs and decylphenols making up approximately 2-9% and approximately 2-5%, respectively. The tNP products were analyzed for eight synthetic 4-NP isomers, and results were compared with published data based on GC/MS analysis. Significant differences were found among the products and between two samples from a single supplier. The enhanced resolution of GC x GC coupled with fast mass spectral data acquisition by ToFMS facilitated identification of all major 4-NP isomers and a number of previously unrecognized components. Analysis of tNP altered by the bacterium, Sphingobium xenophagum Bayram, revealed several persistent 4-NPs whose structures and estrogenicities are presently unknown. The potential of this technology for isomer-specific determination of 4-NP isomers in environmental matrices is demonstrated using samples of wastewater-contaminated groundwater and municipal wastewater.

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.