The analysis of the C1–C5 components of natural gas samples using gas chromatography-combustion-isotope ratio mass spectrometry

Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: A northern Appalachian Basin case study

“…Carbon Isotopic Composition of Natural Gases Natural gas samples are typically characterized as either being derived from biogenic or thermogenic sources or processes based on the carbon isotopic composition d 13 C (‰) = ð½ 13 C= 12 C sample À 13 C = 12 C PDB = 13 C= 12 C PDB Ã 1000Þ (where the PDB is the standard for a belemnite from the Pee Dee Formation) of the hydrocarbon constituents (C 1 -C 5 ) (e.g., Baylis et al, 1994). Biogenic gas is generated at low temperatures (<<100°C) by anaerobic bacteria and is characterized by a dominance of methane gas (∼99%) with a light d 13 C less than -60‰ isotopic composition (Schoell, 1980(Schoell, , 1983Coleman et al, 1981;Woltemate et al, 1984;Whiticar et al, 1985;Elliot et al, 1993).…”

High-precision continuous-flow isotope ratio mass spectrometry

“…The start of a peak is identified in the highest abundance mass channel trace (m/z 44 for CO 2 ) by comrithms, as discussed above. Isotopic calibration can be accomplished if one of the peaks in the chromatograms is paring the slope from a rolling five-point regression to a user-defined threshold, and the end of a peak is determined an internal standard (Caimi, Houghton, & Brenna, 1994). More commonly and conveniently, a pulse of calibrated as the first point after the apex that drops below some fixed percentage of the apex maximum.…”

“…Methane is often observed to be the isotopically lightest hydrocarbon in nature. Progressively larger hydrocarbon chains increase in 13 C content up to C 3 or so (Baylis, Hall, & Jumeau, 1994). MS for structure analysis of pyrolysis products to verify 247 rior for purified small molecules, where fragmentation is known or is relatively simple; and the more complex system is appropriate for complex mixtures and larger, uncharacterized molecules.…”

“…The inconvenience of the off-line static sample preparation for less abundant isotope, this depletion requires additional measurement time to yield precisions that are equivalent to water analysis using the chemical reduction routine particularly for D/H measurements can be reduced by the use samples that are less fractionated during their preparation. SO 2 is the most common gas employed for S isotopic of batch processing (Kendall & Coplen, 1985) but off-line preparation continues to demand high operator skill and analysis; however, SF 6 has been used and has the advantage that F is monoisotopic so that there are no isobaric stamina to produce acceptable results. Electrolytic conversion of water to molecular O 2 and H 2 (Kirshenbaum, 1996) interferences with S isotopes.…”

A new application of headspace single-drop microextraction technique for compound specific carbon isotopic determination of gasoline range hydrocarbons

“…In addition to varying the injection volume, changing the split ratio of the GC injector is a simple method for adjusting the amount of individual gasoline range hydrocarbons. Some studies indicated that the split ratio could cause isotopic fractionation in light gases (Baylis et al, 1994). However, Harris et al (1999) …”