Caution on the use of NBS 30 biotite for hydrogen-isotope measurements with on-line high-temperature conversion systems

Rapid Communications in Mass Spectrometry
By: , and 

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Abstract

RATIONALE

The supply of NBS 30 biotite is nearly exhausted. During measurements of NBS 30 and potential replacements, reproducible δ2HVSMOW-SLAP values could not be obtained by three laboratories using high-temperature conversion (HTC) systems. The cause of this issue has been investigated using the silver-tube technique for hydrogen-isotope measurements of water.

METHODS

The δ2HVSMOW-SLAP values of NBS 30 biotite, other biotites, muscovites, and kaolinite with different particle sizes, along with IAEA-CH-7 polyethylene, and reference waters and NBS 22 oil that were sealed in silver-tube segments, were measured. The effect of absorbed water on mineral surfaces was investigated with waters both enriched and depleted in 2H. The quantitative conversion of hydrogen from biotite into gaseous hydrogen as a function of mass and particle size was also investigated.

RESULTS

The δ2HVSMOW-SLAP values of NBS 30 obtained by three laboratories were as much as 21 ‰ too high compared with the accepted value of −65.7 ‰, determined by conventional off-line measurements. The experiments showed a strong correlation between grain size and the δ2HVSMOW-SLAP value of NBS 30 biotite, but not of biotites with lower iron content. The δ2HVSMOW-SLAP values of NBS 30 as a function of particle size show a clear trend toward −65.7 ‰ with finer grain size.

CONCLUSIONS

Determination of the δ2HVSMOW-SLAP values of hydrous minerals and of NBS 30 biotite by on-line HTC systems coupled to isotope-ratio mass spectrometers may be unreliable because hydrogen in this biotite may not be converted quantitatively into molecular hydrogen. Extreme caution in the use and interpretation of δ2HVSMOW-SLAP on-line measurements of hydrous minerals is recommended.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Caution on the use of NBS 30 biotite for hydrogen-isotope measurements with on-line high-temperature conversion systems
Series title Rapid Communications in Mass Spectrometry
DOI 10.1002/rcm.6983
Volume 28
Issue 18
Year Published 2014
Language English
Publisher Wiley
Contributing office(s) National Research Program - Eastern Branch
Description 8 p.
First page 1987
Last page 1994