(Often incorrectly referred to as sensitivity). Smallest amount of material detectable (3σ-criterion) in a matrix relative to the amount of material analysed — given in atomic, mole or weight fractions.
Source:
PAC, 1979, 51, 2243. 'General aspects of trace analytical methods—IV. Recommendations for nomenclature, standard procedures and reporting of experimental data for surface analysis techniques' on page 2247 (https://doi.org/10.1351/pac197951112243)