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A test of comparative equilibration for determining non-exchangeable stable hydrogen isotope values in complex organic materials

Oklahoma Biological Survey and Department of Zoology, 111 East Chesapeake St., University of Oklahoma, Norman, OK, USA.
Rapid Communications in Mass Spectrometry (Impact Factor: 2.64). 08/2009; 23(15):2316-20. DOI: 10.1002/rcm.4150
Source: PubMed

ABSTRACT Comparative equilibration has been proposed as a methodological approach for determining the hydrogen isotopic composition (deltaD) of non-exchangeable hydrogen in complex organic materials, from feathers to blood and soils. This method depends on using homogenized standards that have been previously calibrated for their deltaD values of non-exchangeable H, that are compositionally similar to unknown samples, and that span an appropriate isotopic range. Currently no certified organic reference materials with exchangeable H exist, and so isotope laboratories have been required to develop provisional internal calibration standards, such as the keratin standards currently used in animal migration studies. Unfortunately, the isotope ratios of some samples fall outside the range of keratin standards currently used for comparative equilibration. Here we tested a set of five homogenized keratin powders as well as feathers from Painted Buntings and Dark-eyed Juncos to determine the effects of extrapolating comparative equilibration normalization equations outside the isotopic range of keratin standards. We found that (1) comparative equilibration gave precise results within the range of the calibration standards; (2) linear extrapolation of normalization equations produced accurate deltaD results to approximately 40 per thousand outside the range of the keratins standards used (-187 to -108); and (3) for both homogenized keratin powders and heterogeneous unknown samples there was no difference in variance between samples within and outside the range of keratin standards. This suggested that comparative equilibration is a robust and practical method for determining the deltaD of complex organic matrices, although caution is required for samples that fall far outside the calibration range.

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    • "H value. CE proved to be a very effective means of analyzing large numbers of ecological keratin samples by CF-IRMS by many ecologists, with demonstrated excellent comparability of results between labs for δ 2 H n values. [18] "
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    ABSTRACT: RATIONALE: Measurement of δ2H values in non-exchangeable-H (δ2Hn) and δ18O values in organic environmental samples are inconsistent among laboratories worldwide due to varied and lengthy approaches in controlling for H isotope exchange (for δ2Hn values) and removal of trace moisture (δ2Hn and δ18O values), which undermines the comparability of organic δ2H and δ18O data produced among different laboratories. METHODS: An online preparation system was developed for the measurement of the δ2Hn and δ18O values of organic samples, coupled to isotope-ratio mass spectrometers. The system features a 50-position autosampler and isolation valve where (1) the samples are held isothermal between ambient to 40–120 ± 0.1 °C for H isotopic exchange experiments (δ2Hn) and drying of hygroscopic samples (δ2Hn and δ18O), (2) the samples are evacuated to <5 mbar and flushed with helium for moisture and N2 removal, and (3) injection of up to 500 μL of H2O is possible for controlled vapour exchangeable-H experiments. RESULTS: The system provides highly reproducible and precise δ2Hn isotope estimates for a range of organic keratinous standard powders over a wide range of experimental temperatures. A reproducible sample processing regimen can now be applied to a wider range of organics and hygroscopic samples that are currently hampered by poorly controlled preparative methods amongst laboratories. CONCLUSIONS: Rapid and reproducible online vacuum equilibration of samples and standards for the routine measurement of δ2Hn and δ18O values is now possible using the online equilibration system, with the added benefit that sample processing times for organic δ2H values are reduced from weeks to hours.
    Rapid Communications in Mass Spectrometry 03/2015; 29:397-407. · 2.64 Impact Factor
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    • "H value. CE proved to be a very effective means of analyzing large numbers of ecological keratin samples by CF-IRMS by many ecologists, with demonstrated excellent comparability of results between labs for δ 2 H n values. [18] "
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    ABSTRACT: RationaleMeasurement of δ2H values in non-exchangeable-H (δ2Hn) and δ18O values in organic environmental samples are inconsistent among laboratories worldwide due to varied and lengthy approaches in controlling for H isotope exchange (for δ2Hn values) and removal of trace moisture (δ2Hn and δ18O values), which undermines the comparability of organic δ2H and δ18O data produced among different laboratories.Methods An online preparation system was developed for the measurement of the δ2Hn and δ18O values of organic samples, coupled to isotope-ratio mass spectrometers. The system features a 50-position autosampler and isolation valve where (1) the samples are held isothermal between ambient to 40–120 ± 0.1 °C for H isotopic exchange experiments (δ2Hn) and drying of hygroscopic samples (δ2Hn and δ18O), (2) the samples are evacuated to <5 mbar and flushed with helium for moisture and N2 removal, and (3) injection of up to 500 μL of H2O is possible for controlled vapour exchangeable-H experiments.ResultsThe system provides highly reproducible and precise δ2Hn isotope estimates for a range of organic keratinous standard powders over a wide range of experimental temperatures. A reproducible sample processing regimen can now be applied to a wider range of organics and hygroscopic samples that are currently hampered by poorly controlled preparative methods amongst laboratories.Conclusions Rapid and reproducible online vacuum equilibration of samples and standards for the routine measurement of δ2Hn and δ18O values is now possible using the online equilibration system, with the added benefit that sample processing times for organic δ2H values are reduced from weeks to hours. Copyright © 2015 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 03/2015; 29(5). DOI:10.1002/rcm.7118 · 2.64 Impact Factor
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    • "Our results indicate that the method has the potential to make significant contributions to disease modeling efforts. However, our findings also imply that there is a need for detailed ground-truthing and the generation of continental-scale feather-based isoscapes for isotope-tracking to attain its full potential (see Kelly and Finch, 1998; Sellick et al., 2009). Feather isoscapes have been generated for some regions (e.g. "
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    ABSTRACT: Satellite-based tracking of migratory waterfowl is an important tool for understanding the potential role of wild birds in the long-distance transmission of highly pathogenic avian influenza. However, employing this technique on a continental scale is prohibitively expensive. This study explores the utility of stable isotope ratios in feathers in examining both the distances traveled by migratory birds and variation in migration behavior. We compared the satellite-derived movement data of 22 ducks from 8 species captured at wintering areas in Bangladesh, Turkey, and Hong Kong with deuterium ratios (δD) in the feathers of these and other individuals captured at the same locations. We derived likely molting locations from the satellite tracking data and generated expected isotope ratios based on an interpolated map of δD in rainwater. Although δD was correlated with the distance between wintering and molting locations, surprisingly, measured δD values were not correlated with either expected values or latitudes of molting sites. However, population-level parameters derived from the satellite-tracking data, such as mean distance between wintering and molting locations and variation in migration distance, were reflected by means and variation of the stable isotope values. Our findings call into question the relevance of the rainfall isotope map for Asia for linking feather isotopes to molting locations, and underscore the need for extensive ground truthing in the form of feather-based isoscapes. Nevertheless, stable isotopes from feathers could inform disease models by characterizing the degree to which regional breeding populations interact at common wintering locations. Feather isotopes also could aid in surveying wintering locations to determine where high-resolution tracking techniques (e.g. satellite tracking) could most effectively be employed. Moreover, intrinsic markers such as stable isotopes offer the only means of inferring movement information from birds that have died as a result of infection. In the absence of feather based-isoscapes, we recommend a combination of isotope analysis and satellite-tracking as the best means of generating aggregate movement data for informing disease models.
    Ecological Indicators 10/2014; 45:266–273. DOI:10.1016/j.ecolind.2014.04.027 · 3.23 Impact Factor
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