Hydrogen Stable Isotopes of Organic Reference Materials

The element hydrogen (H) and its stable isotopes (protium:1H and deuterium: 2H) make up ca. 6-8% of the total dry mass of Earths organic materials like plants, animals and food. The amount of deuterium in organic matter is very small, ranging only between 120-150 parts per million. The concentration of 2H usually matches that of Earths rainfall where the plant or animal grows, and this varies both predictably and spatially around the world. As a result, there tremendous interest by scientists to use deuterium as a natural tracer and source signal to track the origins of plants, animals, food, and for environmental crimes like the animal parts and the drug trade. Because the amount of deuterium and its natural variations relative to protium are so tiny it is very challenging to measure using techniques like isotope-ratio mass spectrometry. Even worse, up to 20% of the hydrogen in organic matter is easily exchangeable, meaning that any vapor in the laboratory air or moisture left in the sample can quickly contaminate and mask the original deuterium signal of the sample during handling. This isotope exchange can now be corrected by using temperature controlled vapor exchange methods. Moreover, to ensure that laboratories can produce accurate and comparable deuterium analyses, new certified organic hydrogen isotope reference materials are needed. To date, because the problem of H isotope exchange was largely unrecognized, most laboratories are unable to reproduce each others H isotope results, which has now become the major obstacle for reliable use of H isotopes in forensic applications. Recently a suite of new organic reference materials (e.g., wood, hair, flour, honey, amino acids, collagen keratins) were produced with aim to firmly establish the 2H/1H ratios of their non-exchangeable H source signal. These new reference materials will be a first step to ensure that isotope data produced are traceable and comparable amongst laboratories. In this project, we will establish reproducible new procedures to determine 2H/1H ratios for the non-exchangeable H of these new organic reference materials, thereby leading to their widespread adoption by the global scientific community and to enable hydrogen isotope biogeochemistry to track plants and animals and advance the science of ecology, paleoecology, drug authentication, environmental crime, and food traceability.

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