Isotope fractionation become enriched in the liquid phase while the lighter isotopes (O and H) tend toward the vapor phase. Isotope fractionation Isotope fractionation describes processes that affect the relative abundance of isotopes, often used in isotope geochemistry. Normally, the focus is on stable isotopes of the same element. Isotopic fractionation in the natural environment can be measured by isotope analysis, using isotope-ratio mass spectrometry, to separate different element isotopes on the basis of their mass-to-charge ratio, an important tool to understand natural systems. For example, in biochemistry processes cause a fluctuation in the amount of isotopes of carbon ratios incorporated into
Standard atomic weight uncertainties are accumulative. The published value is a result of all these. Modern relative atomic masses (a term specific to a given element sample) are calculated from measured values of atomic mass (for each nuclide) and isotopic composition of a sample. Highly accurate atomic masses are available for virtually all non-radioactive nuclides, but isotopic compositions are both harder to measure to high precision and more subject to variation between samples. For this reason, the relative atomic masses of the 22 mononuclidic elements (which are the same as the isotopic masses for each of the single naturally occurring nuclides of these