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| Titel |
Stable oxygen and hydrogen isotopes of brines - comparing isotope ratio mass spectrometry and isotope ratio infrared spectroscopy |
| VerfasserIn |
Christian Ahrens, Paul Koeniger, Robert van Geldern, Susanne Stadler |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074667
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| Zusammenfassung |
| Today’s standard analytical methods for high precision stable isotope analysis of fluids are
gas-water equilibration and high temperature pyrolysis coupled to isotope ratio mass
spectrometers (IRMS). In recent years, relatively new laser-based analytical instruments
entered the market that are said to allow high isotope precision data on nearly every media.
This optical technique is referred to as isotope ratio infrared spectroscopy (IRIS). The
objective of this study is to evaluate the capability of this new instrument type for highly
saline solutions and a comparison of the analytical results with traditional IRMS
analysis.
It has been shown for the equilibration method that the presence of salts influences the
measured isotope values depending on the salt concentration (see Lécuyer et al, 2009;
Martineau, 2012). This so-called ‘isotope salt effect’ depends on the salt type and salt
concentration. These factors change the activity in the fluid and therefore shift the isotope
ratios measured by the equilibration method. Consequently, correction factors have to be
applied to these analytical data. Direct conversion techniques like pyrolysis or the new laser
instruments allow the measurement of the water molecule from the sample directly and
should therefore not suffer from the salt effect, i.e. no corrections of raw values are necessary.
However, due to high salt concentrations this might cause technical problems with the
analytical hardware and may require labor-intensive sample preparation (e.g. vacuum
distillation).
This study evaluates the salt isotope effect for the IRMS equilibration technique (Thermo
Gasbench II coupled to Delta Plus XP) and the laser-based IRIS instruments with liquid
injection (Picarro L2120-i). Synthetic salt solutions (NaCl, KCl, CaCl2, MgCl2, MgSO4,
CaSO4) and natural brines collected from the Stassfurt Salt Anticline (Germany; Stadler et
al., 2012) were analysed with both techniques. Salt concentrations ranged from seawater
salinity up to full saturation.
References
Lécuyer, C. et al. (2009). Chem. Geol., 264, 122–126. [doi:10.1016/j.chemgeo.2009.02.017]
Martineau, F. et al. (2012). Chem. Geol., 291, 236–240. [doi:10.1016/j.chemgeo.2011.10.017]
Stadler, S. et al. (2012). Chem. Geol., 294–295, 226–242. [doi:10.1016/j.chemgeo.2011.12.006] |
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