isotopically enriched ions
When the abundance of a particular nuclide is increased above the level at which it occurs in nature and is incorporated in a molecule, the term 'isotopically enriched ion' is used to describe any ion enriched in the isotope.
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1549 (