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UC Davis Plant Sciences


Oxygen (18O) and Hydrogen (D/H) Analysis of Solids by TC/EA-IRMS

The SIF provides 18O or D/H isotope analyses of solid samples using a TC/EA system interfaced to IRMS.

Analyses

18O and D/H are analyzed separately. If both analyses are needed, duplicate sets of samples must be sent.

 

 

18O Analysis

Solids are analyzed for 18O isotopes using an elementar PyroCube (Elementar Analysensysteme GmbH, Hanau, Germany) interfaced to a Isoprime VisION (Isoprime Ltd., Stockport, UK, a unit of Elementar Analysensysteme GmbH, Hanau, Germany). Samples are thermally decomposed to CO in a glassy carbon reactor filled with glassy carbon, graphite felt, and lamp black at 1400°C. An adsorption trap isolates CO from any interfering N2.  We continue to validate methods for 18O in salts and inorganic matrices (such as bone apatite). We do not analyze mineral samples (including soils). Please email with specific interests. For 18O in carbonate samples, please refer to our carbonates page.

 

During analysis, samples are interspersed with several replicates of at least four different laboratory reference materials. These reference materials have been previously calibrated against international reference materials, including: IAEA-V9, IAEA-600, USGS-42, USGS-43, USGS-35. A sample's provisional isotope ratio is measured relative to a reference gas peak analyzed with each sample. These provisional values are finalized by correcting the values for the entire batch based on the known values of the included laboratory reference materials.


The final 18O delta values, delivered to the customer, are expressed relative to international standard VSMOW (Vienna Standard Mean Ocean Water). For information on delta notation and the international standards, please refer to a stable isotope reference such as Sharp, Z. (2005) Principles of Stable Isotope Geochemistry (Prentice Hall).

 

 

DH Analysis

Solids are analyzed for D/H isotopes using an elementar PyroCube (Elementar Analysensysteme GmbH, Hanau, Germany) interfaced to a Isoprime VisION (Isoprime Ltd., Stockport, UK, a unit of Elementar Analysensysteme GmbH, Hanau, Germany). Samples are thermally decomposed to H2 in a glassy carbon reactor filled with glassy carbon and graphite felt at 1450°C.

 

During analysis, samples are interspersed with several replicates of at least four different laboratory reference materials. These laboratory reference materials, have been previously calibrated against international reference materials, including: IAEA-CH7, USGS-42, USGS-43, CBS and KHS (developed by Len Wassenaar and Keith Hobson, Environment Canada, Science and Technology Branch, Saskatoon, Canada). A sample’s provisional isotope ratio is measured relative to a reference gas peak analyzed with each sample. These provisional values are finalized by correcting the values for the entire batch based on the known values of the included laboratory reference materials.

The final D/Hdelta values, delivered to the customer, are expressed relative to international standard VSMOW (Vienna Standard Mean Ocean Water). For information on delta notation and the international standards, please refer to a stable isotope reference such as Sharp, Z. (2005) Principles of Stable Isotope Geochemistry (Prentice Hall).

 

 

Exchangeable Hydrogen

Hydrogen in solid samples is susceptible to exchange with ambient water vapor. This fraction can be substantial - up to 30%. The desire is to determine the D/H for the non-exchangeable fraction of a given sample. For keratin samples (such as feather and hair), this exchange is well understood. Keratin samples are allowed to equilibrate with keratin reference materials for at least 96 hours before analysis, as described by Wassenaar and Hobson, 20031. Following analysis the laboratory keratin standards are used to establish the D/H for the non-exchangeable hydrogen fraction of the customer's samples.

 

For hydrogen samples other than keratin, the only reliable method to determine D/H for the non-exchangeable fraction is to equilibrate the samples and standards with two waters with different D/H values. From the two datasets, the fraction of exchangeable hydrogen and the D/H for the non-exchangeable fraction can be calculated (see Chesson 20092). SIF is finalizing its implementation of the dual equilibration method for non-keratin solid hydrogen samples. Please contact us prior to sample preparation to confirm if we can accept your non-keratin samples.

 

1Wassenaar, L.I., and Hobson, K.A. (2003). Comparative equilibration and online technique for determination of non-exchangeable hydrogen of keratins for use in animal migration studies. Isotopes in Environmental and Health Studies, 39(3): 211-217.

 

2Chesson, L.A., Podlesak, D.W., Cerling, T.E., and Ehleringer, J.R. (2009). Evaluating uncertainty in the calculation of nonexchangeable hydrogen fractions within organic materials. Rapid Commun. Mass Spectrom, 23: 1275–1280.




 
e-mail: sif@ucdavis.edu | phone: 530-752-8100 | fax: 530-752-4361
UC Davis Stable Isotope Facility | Department of Plant Sciences
One Shields Avenue | Davis, California, 95616 | USA