nonselectively labelled

An isotopically labelled compound is designated as nonselectively labelled when the position(s) and the number of the labellingnuclide(s) are both undefined.
Source:
Blue Book, p. 517
PAC, 1981, 53, 1887 (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1896