specifically labelled

An @I03336@ compound is designated as specifically labelled when a unique @I03338@ compound is formally added to the analogous @I03339@ compound. In such a case, both position(s) and number of each @L03425@ @N04257@ are defined.
Blue Book, p. 514 [Terms] [Book]
PAC, 1981, 53, 1887. (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1891 [Terms] [Paper]