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An evaluation of alumina reaction tube conditioning for high‐precision 2 H/ 1 H isotope measurements via gas chromatography/thermal conversion/isotope ratio mass spectrometry
Author(s) -
Cao Yunning,
Liu Weiguo,
Sauer Peter E.,
Wang Zheng,
Li Zhenghua
Publication year - 2012
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6378
Subject(s) - chemistry , pyrolysis , hydrogen , deuterium , isotope ratio mass spectrometry , analytical chemistry (journal) , hexane , methane , isotopes of carbon , gas chromatography , mass spectrometry , hydrocarbon , carbon fibers , isotope , chromatography , radiochemistry , organic chemistry , total organic carbon , materials science , physics , quantum mechanics , composite number , composite material
RATIONALE The condition of the pyrolysis reactor is very important for obtaining stable, precise hydrogen isotopic ratios using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC/TC/IRMS). However, few studies of the conditioning process have been conducted, and little is known about the best methods for high‐precision hydrogen isotope analysis. METHODS We investigated δ 2 H variations and observed the changes in carbon coating using six different conditioning methods for the pyrolysis alumina tube: (i) no treatment; (ii) conditioning with 4 μL hexane; (iii) conditioning with 2 μL hexane; (iv) conditioning with 2 μL hexane followed by backflushing overnight; (v) conditioning with 10 s of backflushing with methane; (vi) conditioning with 3 s of backflushing with methane. RESULTS Conditioning the alumina tube can improve the pyrolysis efficiency of organic compounds because a moderate amount of carbon acts as a catalyst in high‐temperature regions of the alumina tube. Carbon actually flows in the tube and is difficult to confine to the high‐temperature region. Insufficient amounts of carbon in the high‐temperature regions lead to incomplete pyrolysis of organic compounds and lower δ 2 H values due to kinetic fractionation of hydrogen isotopes. In contrast, excess hexane or methane can lead to higher δ 2 H values, probably due to enrichment of deuterium in the hydrocarbon residue. CONCLUSIONS The δ 2 H values obtained by Method 6 are closest to the TC/EA δ 2 H values and are more precise than those obtained by other methods, perhaps because this method introduces a moderate, consistent amount of carbon with each sample injection. Copyright © 2012 John Wiley & Sons, Ltd.