Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GCXGC)

University of Illinois at Chicago, Department of Earth and Environmental Sciences, M/C 186, 845 West Taylor Street, Chicago, IL 60607-7059, USA
Organic Geochemistry (Impact Factor: 3.07). 07/2008; 39(7):846-867. DOI: 10.1016/j.orggeochem.2008.03.006
Source: OAI


Hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatography display gas chromatograms with dramatically rising baselines or “humps” of coeluting compounds that are termed unresolved complex mixtures (UCMs). Because the constituents of UCMs are not ordinarily identified, a large amount of geochemical information is never explored. Gas chromatograms of saturated/unsaturated hydrocarbons extracted from Late Archean argillites and greywackes of the southern Abitibi Province of Ontario, Canada contain UCMs with different appearances or “topologies” relating to the intensity and retention time of the compounds comprising the UCMs. These topologies appear to have some level of stratigraphic organization, such that samples collected at any stratigraphic formation collectively are dominated by UCMs that either elute early- (within a window of C15–C20n-alkanes), early- to mid- (C15–C30n-alkanes), or have a broad UCM that extends through the entire retention time of the sample (from C15–C42n-alkanes). Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC–MS) was used to resolve the constituents forming these various UCMs. Early- to mid-eluting UCMs are dominated by configurational isomers of alkyl-substituted and non-substituted polycyclic compounds that contain up to six rings. Late eluting UCMs are composed of C36–C40 mono-, bi-, and tricyclic archaeal isoprenoid diastereomers. Broad UCMs spanning the retention time of compound elution contain nearly the same compounds observed in the early-, mid-, and late-retention time UCMs. Although the origin of the polycyclic compounds is unclear, the variations in the UCM topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized. Isomerization of these constituents may have resulted from hydrothermal alteration of organic matter.

Download full-text


Available from: Robert K Nelson
  • Source
    • "In addition, the composition of crude oils is susceptible to physical (e.g. evaporation , emulsification, natural dispersion, dissolution and sorption), chemical (photo degradation) and biological (mainly microbial degradation) weathering processes [1]. As one of the most complex fluids, both advanced separation tools and high efficient methods of data processing are essential in order to achieve accurate molecular fingerprints of crude oils with different origin or geochemical history and find potential marker compounds. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC/TOFMS), volatile and semi-volatile organic compounds in crude oil samples from different reservoirs or regions were analyzed for the development of a molecular fingerprint database. Based on the GC × GC/TOFMS fingerprints of crude oils, principal component analysis (PCA) and cluster analysis were used to distinguish the oil sources and find biomarkers. As a supervised technique, the geological characteristics of crude oils, such as thermal maturity and sedimentary environment etc., are assigned to the principal components. The results show that tri-aromatic steroid (TAS) series are the suitable marker compounds in crude oils for the oil screening, and the relative abundances of individual TAS compounds have excellent correlation with oil sources. In order to correct the effects of some other external factors except oil sources, the variables were defined as the content ratio of some target compounds and 13 parameters were proposed for the screening of oil sources. With the developed model, the crude oils were easily discriminated, and the result is in good agreement with the practical geological setting
    Full-text · Article · Jan 2015 · Journal of Chromatography A
  • Source
    • "Because intact polar membrane lipids (IPLs) are rapidly degraded upon cell death, they can be used to quantify live microbial biomass (White et al., 1979; Lipp et al., 2008). For studies that extend to the geological record, lipid classes that contain highly branched and polycyclic compounds result in fossil hydrocarbons that can survive for billions of years (Brocks et al., 2003b; Brocks and Summons, 2004; Marshall et al., 2007; Ventura et al., 2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract The bicarbonate-buffered anoxic vent waters at Chocolate Pots hot springs in Yellowstone National Park are 51-54°C, pH 5.5-6.0, and are very high in dissolved Fe(II) at 5.8-5.9 mg/L. The aqueous Fe(II) is oxidized by a combination of biotic and abiotic mechanisms and precipitated as primary siliceous nanophase iron oxyhydroxides (ferrihydrite). Four distinct prokaryotic photosynthetic microbial mat types grow on top of these iron deposits. Lipids were used to characterize the community composition of the microbial mats, link source organisms to geologically significant biomarkers, and investigate how iron mineralization degrades the lipid signature of the community. The phospholipid and glycolipid fatty acid profiles of the highest-temperature mats indicate that they are dominated by cyanobacteria and green nonsulfur filamentous anoxygenic phototrophs (FAPs). Diagnostic lipid biomarkers of the cyanobacteria include midchain branched mono- and dimethylalkanes and, most notably, 2-methylbacteriohopanepolyol. Diagnostic lipid biomarkers of the FAPs (Chloroflexus and Roseiflexus spp.) include wax esters and a long-chain tri-unsaturated alkene. Surprisingly, the lipid biomarkers resisted the earliest stages of microbial degradation and diagenesis to survive in the iron oxides beneath the mats. Understanding the potential of particular sedimentary environments to capture and preserve fossil biosignatures is of vital importance in the selection of the best landing sites for future astrobiological missions to Mars. This study explores the nature of organic degradation processes in moderately thermal Fe(II)-rich groundwater springs-environmental conditions that have been previously identified as highly relevant for Mars exploration. Key Words: Lipid biomarkers-Photosynthesis-Iron-Hot springs-Mars. Astrobiology 14, xxx-xxx.
    Full-text · Article · Jun 2014 · Astrobiology
  • Source
    • "The UCM can account for more than 80% of semivolatile emissions from diesel [Schauer et al., 1999] and gasoline engines [Schauer et al., 2002], representing a major fraction of SVOCs in urban areas [Williams et al., 2010b]. Furthermore, the UCM is ubiquitous in environmental chemistry, often found in samples associated with fossil fuel use [Frysinger et al., 2003; Nelson et al., 2006; Ventura et al., 2008]. [4] The UCM is thought to contain a large number of constitutional isomers, most of which are linear (also termed straight-chained or normal), branched, and/or cyclic alkanes [Mao et al., 2009]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: [1] Recent studies suggest that semivolatile organic compounds (SVOCs) are important precursors to secondary organic aerosol (SOA) in urban atmospheres. However, knowledge of the chemical composition of SVOCs is limited by current analytical techniques, which are typically unable to resolve a large number of constitutional isomers. Using a combination of gas chromatography and soft photoionization mass spectrometry, we characterize the unresolved complex mixture (UCM) of semivolatile aliphatic hydrocarbons observed in Pasadena, California (~16 km NE of downtown Los Angeles), and Bakersfield, California, during the California Research at the Nexus of Air Quality and Climate Change 2010. To the authors' knowledge, this work represents the most detailed characterization of the UCM in atmospheric samples to date. Knowledge of molecular structures, including carbon number, alkyl branching, and number of rings, provides important constraints on the rate of atmospheric processing, as the relative amounts of branched and linear alkanes are shown to be a function of integrated exposure to hydroxyl radicals. Emissions of semivolatile branched alkanes from fossil fuel-related sources are up to an order of magnitude higher than those of linear alkanes, and the gas-phase OH rate constants of branched alkanes are ~30% higher than their linear isomers. Based on a box model considering gas/particle partitioning, emissions, and reaction rates, semivolatile branched alkanes are expected to play a more important role than linear alkanes in the photooxidation of the UCM and subsequent transformations into SOA. Detailed speciation of semivolatile compounds therefore provides essential understanding of SOA sources and formation processes in urban areas.
    Full-text · Article · Jun 2013
Show more