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Memory Effects in Compound-Specific D/H Analysis by Gas Chromatography/Pyrolysis/Isotope-Ratio Mass Spectrometry

Wang, Ying and Sessions, Alex L. (2008) Memory Effects in Compound-Specific D/H Analysis by Gas Chromatography/Pyrolysis/Isotope-Ratio Mass Spectrometry. Analytical Chemistry, 80 (23). pp. 9162-9170. ISSN 0003-2700. doi:10.1021/ac801170v.

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Compound-specific analyses of lipid D/H ratios often encounter ranges of 300‰ or more, and experiments using D-enriched water to study fractionations often extend the range up to 1000‰. Here we show that for such large dynamic ranges in D/H ratio, isotopic “memory” between adjacent peaks can be significant. Memory effects have not been previously reported for GC/P/IRMS systems but can have a significant impact on many measurements, even those exploring only natural-abundance variations in D/H. To quantitatively evaluate these effects, we synthesized two series of organic standards with δD values varying from −230 to +800‰. We then analyzed chromatograms in which analyte δD values, retention times, or relative abundances were independently varied. For two sequential GC peaks, isotopic memory is measured to be typically 2−4% of the difference in δD values between the two. Roughly half of this effect can be attributed to unknown processes within the GC itself, and the other half to surface adsorption processes in the pyrolytic conversion of analytes to H2. Isotopic memory increases with decreasing time separation between peaks, with decreasing analyte abundance, and with increasing age of pyrolysis reactors. A simple numerical model that simulates dynamic adsorption of H2 on pyrolytic carbon can reproduce many aspects of the experimental data, suggesting that this is likely to be an important mechanism in isotopic memory. Several steps to mitigate memory effects in routine analyses are suggested.

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Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2008 American Chemical Society. Received for review June 9, 2008. Accepted September 29, 2008. Publication Date (Web): October 30, 2008. The authors acknowledge Magnus Eek and Chao Li for experimental assistance and helpful discussions and Arndt Schimmelmann for analyses of D-enriched standards by dual-inlet IRMS. We thank George Rossman for access to the Raman spectrometer and Nathan Dalleska for assistance analyzing D-enriched standards by GC/MS. This work was supported by grants to A.L.S. from the Petroleum Research Fund of the ACS (PRF Grant 43746-G2) and from NSF (Grant EAR-0645502).
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American Chemical Society Petroleum Research Fund43746-G2
Issue or Number:23
Record Number:CaltechAUTHORS:WANac08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12757
Deposited By: Archive Administrator
Deposited On:22 Dec 2008 22:29
Last Modified:08 Nov 2021 22:32

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