nominally labelled tracer

https://doi.org/10.1351/goldbook.N04178
A tracer in which the label is present mainly in a specified position.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2526 (https://doi.org/10.1351/pac199466122513)