@[email protected] 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 @[email protected] by also reacting with the ligand and producing a coloured compound absorbing at the same @[email protected] as the compound produced by the analyte or in an atomic spectrochemical analysis by absorbing or emitting at the same @[email protected] as the analyte.