Stable isotope natural abundance measurements application

Elements in nature come in forms called isotopes that differ only in the number of their neutrons. Most isotopes are stable and can be distinguished from their counterparts simply by their masses. Remarkably, isotopes are associated with a few simple and mass-dependent traits that result in a wide range of useful isotopic signals in natural processes. Coupled with the invention of the isotope ratio mass spectrometer in 1940s (McKinney et al., 1950 Nier, 1947) stable isotope signals provide the basis for application of stable isotopes to environmental sciences. Stable isotopes are denoted by their atomic mass such as and for the two stable isotopes of carbon, and 0, and for the stable isotopes of oxygen. Because the heavy isotope is normally rare (e.g., -1.1% for i c, 0.2% for 0, and 0.04% for O), routine measurements of the absolute isotopic concentrations is difficult and not reliable. Alternatively, the ratio, R, of the rare to the abundant isotopes is measured, such as... 

This study described the application of a common analytical procedure adapted for compound-specific stable carbon isotope analyses of riverine contaminants. To evaluate the sensitivity of the analytical method and the precision of the isotopic data obtained a set of numerous substances at different concentration levels were measured. For most of the anthropogenic contaminants investigated (including chlorinated aliphatics and aromatics, musk fragrances, phthalate based plasticizers and tetrabutyl tin) acceptable carbon isotope analyses could be obtained down to amounts of approx. 5 ng. These amounts correspond to concentrations in water samples at a natural abundance level of low to medium contaminated river systems. However, it has to be considered that the accuracy as well as the sensitivity of the analytical method depend partially on the chemical properties of the substances measured. 

Relative measurements are most commonly used to express small variations in the natural abundance of light stable isotopes and find applications in areas such as the geosciences and ecological research. No consensus exists on the appropriate units in which isotope ratios are reported, especially in the biomedical field. Most isotope ratio mass spectrometers (IRMS) report isotopic abundance in terms of delta notation ( parts per thousand or per mil ), which is a convention determined by geochemistry, because most of the original IRMS instruments were developed in isotope geochemistry laboratories. Delta units are not SI units. The SI base unit for quantity is the mole, from which atom fraction and mole fraction are derived. The units of stable isotope abundance, at.% and mol.%, are the atom and mole... 

The first ever application of a radiotracer in a biological experiment dates back to 1923 when George de Hevesy used Pb to study plant uptake of lead from solution [5]. His seminal work was honored by the Nobel Prize in Chemistry in 1943 and made him the father of isotope tracing, a tool that is still indispensable in virtually any area of scientific research. The first use of a stable isotope to study mineral metabolism was reported in 1963, when Lowman and Krivit injected stable Fe together with radioactive Fe into a human subject to compare the plasma clearance of the two isotopes [6]. However, it was not until the 1980s that stable isotope techniques were explored systematically to study mineral and trace element metabolism in humans. This was not only due to the increasing recognition of health hazards associated with the use of radioisotopes. Mass spectro-metric techniques had to be refined to measure isotope ratios of the heavier elements at a precision suitable for the exploitation of isotopically enriched elements as tracers. Stable isotopic labels are made up from the same isotopes as the natural element, from which they differ only in terms of composition, that is, in the relative abundances of their isotopes. 

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