METROLOGICAL CHARACTERISTICS OF THE CONVENTIONAL MEASUREMENT SCALES FOR HYDROGEN AND OXYGEN STABLE ISOTOPE AMOUNT RATIOS: THE delta-SCALES

摘要

Natural variations of stable isotope amount ratios for the elements hydrogen and oxygen areused in diverse scientific fields to delineate for example the origin of water masses, past climatic conditions, biological processes or the authenticity of food products. Here, only a brief outline is provided on measurement methods. The focus lays on discussion on properties of the measurement scale, which can be described as a conventional measurement scale based on isotope ratio properties of arbitrarily chosen artefact materials (calibrators). The traceability chain for such measurements is thus limited back to the used artifacts. Any change of those calibrators potentially induces problems in scale consistency and in any case increases the combined uncertainty of measurements. The recent efforts are described to limit the increase of uncertainty due to the necessary change of calibrators (exhaustion of used artefact material). The internationally used calibrators are pure water samples and therefore the discussion below focuses on hydrogen and oxygen stable isotopes in water. Similar arguments are valid for other substances containing hydrogen and oxygen isotopes. Furthermore similar concepts hold for measurements of isotope amount ratios of other elements like carbon, nitrogen and sulfur.