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Isotope fractionation occurs during a phase transition, when the ratio of light to heavy isotopes in the involved molecules changes. When water vapor condenses (an equilibrium fractionation), the heavier water isotopes (18 O and 2 H) become enriched in the liquid phase while the lighter isotopes (16 O and 1 H) tend toward the vapor phase. [1]
The stable isotope composition of amino acids refers to the abundance of heavy and light non-radioactive isotopes of carbon (13 C and 12 C), nitrogen (15 N and 14 N), and other elements within these molecules. Amino acids are the building blocks of proteins.
Equilibrium isotope fractionation is the partial separation of isotopes between two or more substances in chemical equilibrium. Equilibrium fractionation is strongest at low temperatures, and (along with kinetic isotope effects) forms the basis of the most widely used isotopic paleothermometers (or climate proxies): D/H and 18 O/ 16 O records from ice cores, and 18 O/ 16 O records from calcium ...
The equations can be used to describe an isotope fractionation process if: (1) material is continuously removed from a mixed system containing molecules of two or more isotopic species (e.g., water with 18 O and 16 O, or sulfate with 34 S and 32 S), (2) the fractionation accompanying the removal process at any instance is described by the ...
Nitrogen-15 is a rare stable isotope of nitrogen. Two sources of nitrogen-15 are the positron emission of oxygen-15 [8] and the beta decay of carbon-15. Nitrogen-15 presents one of the lowest thermal neutron capture cross sections of all isotopes. [9] Nitrogen-15 is frequently used in NMR (Nitrogen-15 NMR spectroscopy).
Fractionation makes it possible to isolate more than two components in a mixture in a single run. This property sets it apart from other separation techniques. Fractionation is widely employed in many branches of science and technology. Mixtures of liquids and gasses are separated by fractional distillation by difference in boiling point.
Nitrogen-15 (15 N) tracing is a technique to study the nitrogen cycle using the heavier, stable nitrogen isotope 15 N.Despite the different weights, 15 N is involved in the same chemical reactions as the more abundant 14 N and is therefore used to trace and quantify conversions of one nitrogen compound to another.
The most notable examples of mass-independent fractionation in nature are found in the isotopes of oxygen and sulfur.The first example was discovered by Robert N. Clayton, Toshiko Mayeda, and Lawrence Grossman in 1973, [2] in the oxygen isotopic composition of refractory calcium–aluminium-rich inclusions in the Allende meteorite.