isotopically substituted

https://doi.org/10.1351/goldbook.I03338
Describes a compound that has a composition such that essentially all the molecules of the compound have only the indicated @N04257@ at each designated position. For all other positions, the absence of @N04257@ indication means that the @N04257@ composition is the natural one.
Sources:
Blue Book, p. 514 [Terms] [Book]
PAC, 1981, 53, 1887. (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1890 [Terms] [Paper]