isotopically unmodified

https://doi.org/10.1351/goldbook.I03339
Describes a compound that has a macroscopic composition such that its constituent nuclides are present in the proportions occurring in nature.
Sources:
Blue Book, p. 514 (http://www.acdlabs.com/iupac/nomenclature/)
PAC, 1981, 53, 1887. 'Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds' on page 1889 (https://doi.org/10.1351/pac198153101887)