isotopically labelled

https://doi.org/10.1351/goldbook.I03336
Describes a mixture of an isotopically unmodified compound with one or more analogous isotopically substituted compound(s).
Sources:
Blue Book, p. 514 (https://www.acdlabs.com/iupac/nomenclature/)
PAC, 1981, 53, 1887. 'Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds' on page 1891 (https://doi.org/10.1351/pac198153101887)