A kind of isotope dilution analysis in which the final isotopic abundance is estimated from the amount of the nuclide present in a known quantity of the relevant element separated from the test portion, where this quantity is smaller than the total amount of that element present in the test portion.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2521 (https://doi.org/10.1351/pac199466122513)