by a substance that produces a signal by a similar mechanism to the analyte, which in the given procedure (including the apparatus used) can not be distinguished from the signal given by the analyte. For example, in a colour reaction with an organic ligand
by also reacting with the ligand and producing a coloured compound absorbing at the same wavelength
as the compound produced by the analyte or in an atomic spectrochemical analysis by absorbing or emitting at the same wavelength
as the analyte.
PAC, 1983, 55, 553
(Recommendations for the usage of selective, selectivity and related terms in analytical chemistry)
on page 554
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook