title: Measurement of compound-specific carbon isotope ratios (δ(13) C values) via direct injection of whole crude oil samples.
abstract: BACKGROUND
  Stable isotope analysis is a powerful tool in understanding the generation, history and correlation of hydrocarbons. Compound-specific δ(13) C measurements of oils allow detailed comparison of individual compound groupings; however, most studies of these sample materials separate and isolate individual fractions based on the chemistries of particular compound groups, potentially losing considerable valuable isotopic data. Even if all fractions are analyzed, this represents a large increase in the data-processing burden, effectively multiplying data evaluation time and effort by the number of fractions produced. Gas chromatography/isotope ratio mass spectrometry (GC/IRMS) of untreated, whole crude oils allows the immediate collection of a larger suite of valuable isotopic data for these studies.
  
  
  METHODS
  Untreated ('neat', undiluted), whole crude oils were directly injected and measured on a GC/IRMS system, using split (40:1) injections and a 50 m HP-PONA column. The GC method, 97 min in duration, was designed to maximize baseline separation of target analyte peaks, while an additional oxygen flow was admitted into the combustion reactor to maximize the lifetime of the combustion chemicals.
  
  
  RESULTS
  The method and setup utilized allow the measurement of a much greater range of the n-alkanes (n-C4 to n-C25+ ) than traditional methods, while also retaining important cycloalkane, aromatic and isoprenoid peaks within the same analysis. Carbon isotope (δ(13) C) evaluation of these additional compound classes reveals trends in maturity and origins which are not identifiable when exclusively assessing the traditional n-alkane package (>n-C12 ).
  
  
  CONCLUSIONS
  The described setup and method open up new possibilities for assessing the origins and histories of crude oil samples. The data generated for the whole oil n-alkanes by this method is equivalent to that reported for isolated n-alkane studies, while also providing valuable additional data on many other important compounds. The end result of this method is a more complete assessment of the carbon isotopic composition of crude oils. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: GeoMark Research, 9748 Whithorn Dr., Houston, TX, 77095, USA.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Barrie
authors.affiliation: Isoprime Ltd, Earl Road, Cheadle Hulme, SK8 6PT, UK.
authors.forename: Kyle W R
authors.initials: KW
authors.lastname: Taylor
authors.affiliation: GeoMark Research, 9748 Whithorn Dr., Houston, TX, 77095, USA.
authors.forename: John
authors.initials: J
authors.lastname: Zumberge
mesh_terms: D000473:Alkanes / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis*; D004867:Equipment Design; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry; D010578:Petroleum / Q000032:analysis*; D013781:Texas
chemical_list: D000473:Alkanes; D002247:Carbon Isotopes; D006841:Hydrocarbons, Aromatic; D010578:Petroleum