Isotope fractionation

Isotope fractionation is the separation of isotopes through physical or chemical processes that affect them differently, changing their relative abundances between substances.

Rayleigh fractionation: A model describing isotope changes as a fractionating reservoir is progressively consumed or removed. It predicts how residual material shifts as evaporation, crystallization, or reaction proceeds.
Stable isotope analysis: The measurement and interpretation of stable-isotope ratios in natural or engineered materials. It uses fractionation patterns to infer processes that shaped a sample.
Isotope: One of two or more atoms of the same element with different numbers of neutrons. Fractionation changes the relative abundance of an element’s isotopes.
Mass-independent fractionation: Isotope fractionation that does not follow the usual systematic relationship with isotope mass differences. Its departures from mass-dependent trends can signal distinct chemical or atmospheric pathways.
Mass-dependent fractionation: Isotope fractionation in which the magnitude of the effect varies systematically with isotope mass differences. Most natural fractionation follows mass-dependent relationships among isotopes.
Paleoclimatology: The study of past climates using evidence preserved in natural archives. Oxygen-isotope fractionation in archives records past temperature and hydrological change.
Delta notation: A convention expressing an isotope ratio’s deviation from a reference standard, usually in parts per thousand. It is the common way to report small fractionation-related isotope shifts.
Kinetic isotope effect: A change in reaction rate caused by replacing an atom with one of its isotopes. It contrasts rate-controlled separation with equilibrium-controlled partitioning.
Isotope ratio: The abundance of one isotope of an element divided by the abundance of another isotope. Fractionation is observed as a change in isotope ratios between materials.
Isotope hydrology: The use of isotopes to investigate water sources, movement, and residence times. Evaporation and condensation fractionate water isotopes along the hydrological cycle.

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