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An online method combining a thermal conversion elemental analyzer with isotope ratio mass spectrometry for the determination of hydrogen isotope composition and water concentration in geological samples
Author(s) -
Gong Bing,
Zheng YongFei,
Chen RenXu
Publication year - 2007
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.2973
Subject(s) - chemistry , isotope , mass spectrometry , hydrogen isotope , analytical chemistry (journal) , composition (language) , isotope ratio mass spectrometry , hydrogen , chromatography , physics , organic chemistry , quantum mechanics , linguistics , philosophy
An online continuous‐flow method, combining a thermal conversion elemental analyzer (TC/EA) with isotope ratio mass spectrometry (MS), is evaluated for the determination of both the hydrogen isotope composition and the water concentration of hydrous and nominally anhydrous minerals. The technique involves reduction of hydrous minerals or nominally anhydrous minerals by reaction with glassy carbon at 1450°C in a helium stream. The product gases, H 2 and CO, are separated on a gas chromatographic column prior to analysis in the mass spectrometer. Calibration curves for the H concentration analysis were generated from a standard of benzoic acid (C 7 H 6 O 2 ) that has an H concentration of 5.0 wt%; the analytical uncertainties were better than ±0.05% in our runs. Two standards of material with given δ D values, polyethylene IAEA‐CH‐7 and biotite NBS‐30, were tested for the purpose of calibrating a natural garnet 04BXL02 representing nominally anhydrous minerals. Preheating at 90°C for 12 h was found to be suitable for removing adsorption water on the sample surface. This results in constant δ D values and total H 2 O contents for the garnet, with weighted means of −94 ± 1‰ and 522 ± 11 ppm (wt), respectively. The TC/EA‐MS technique allows routine analysis of sample sizes as small as 0.01 µL H 2 O. For natural minerals, absolute reproducibilities for δ D values are ±0.5‰ to ±2‰ (1 σ ) and relative uncertainties for total H 2 O concentrations are at levels of ±1% to ±3% (1 σ ). Therefore, this online method can be used for the quantitative determination of H isotope composition and H 2 O concentration of either hydrous or anhydrous minerals. Copyright © 2007 John Wiley & Sons, Ltd.