Isotopically enriched ion

Isotopically enriched ion. Any ion containing an abundance of a particular isotope above the level at which it occurs in nature. 

If the abundance of a particular nuclide is increased above the natural level in an ion, the term isotopically enriched ion is used to describe any ion enriched in the isotope. [1] The degree of isotopic enrichment is best determined by mass spectrometry. 

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