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Simultaneous analysis of 17 O/ 16 O, 18 O/ 16 O and 2 H/ 1 H of gypsum hydration water by cavity ring‐down laser spectroscopy
Author(s) -
Gázquez Fernando,
Mather Ian,
Rolfe James,
Evans Nicholas P.,
Herwartz Daniel,
Staubwasser Michael,
Hodell David A.
Publication year - 2015
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.7312
Subject(s) - chemistry , analytical chemistry (journal) , deuterium , oxygen 18 , isotope , hydrogen , stable isotope ratio , mass spectrometry , extraction (chemistry) , isotopes of oxygen , nuclear chemistry , chromatography , atomic physics , quantum mechanics , physics , organic chemistry
Rationale The recent development of cavity ring‐down laser spectroscopy (CRDS) instruments capable of measuring 17 O‐excess in water has created new opportunities for studying the hydrologic cycle. Here we apply this new method to studying the triple oxygen ( 17 O/ 16 O, 18 O/ 16 O) and hydrogen ( 2 H/ 1 H) isotope ratios of gypsum hydration water (GHW), which can provide information about the conditions under which the mineral formed and subsequent post‐depositional interaction with other fluids. Methods We developed a semi‐automated procedure for extracting GHW by slowly heating the sample to 400°C in vacuo and cryogenically trapping the evolved water. The isotopic composition (δ 17 O, δ 18 O and δ 2 H values) of the GHW is subsequently measured by CRDS. The extraction apparatus allows the dehydration of five samples and one standard simultaneously, thereby increasing the long‐term precision and sample throughput compared with previous methods. The apparatus is also useful for distilling brines prior to isotopic analysis. A direct comparison is made between results of 17 O‐excess in GHW obtained by CRDS and fluorination followed by isotope ratio mass spectrometry (IRMS) of O 2 . Results The long‐term analytical precision of our method of extraction and isotopic analysis of GHW by CRDS is ±0.07‰ for δ 17 O values, ±0.13‰ for δ 18 O values and ±0.49‰ for δ 2 H values (all ±1SD), and ±1.1‰ and ±8 per meg for the deuterium‐excess and 17 O‐excess, respectively. Accurate measurement of the 17 O‐excess values of GHW, of both synthetic and natural samples, requires the use of a micro‐combustion module (MCM). This accessory removes contaminants (VOCs, H 2 S, etc.) from the water vapour stream that interfere with the wavelengths used for spectroscopic measurement of water isotopologues. CRDS/MCM and IRMS methods yield similar isotopic results for the analysis of both synthetic and natural gypsum samples within analytical error of the two methods. Conclusions We demonstrate that precise and simultaneous isotopic measurements of δ 17 O, δ 18 O and δ 2 H values, and the derived deuterium‐excess and 17 O‐excess, can be obtained from GHW and brines using a new extraction apparatus and subsequent measurement by CRDS. This method provides new opportunities for the application of water isotope tracers in hydrologic and paleoclimatologic research. © 2015 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.