selectively labelled

https://doi.org/10.1351/goldbook.S05556
An @I03336@ compound is designated as selectively labelled when a mixture of @I03338@ compounds is formally added to the analogous @I03339@ compound in such a way that the position(s) but not necessarily the number of each @L03425@@N04257@ is defined. A selectively labelled compound may be considered as a mixture of @S05793@ compounds.
Sources:
Blue Book, p. 515 [Terms] [Book]
PAC, 1981, 53, 1887. (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1893 [Terms] [Paper]