ISL – January 2021 Page 82 of 160 b) Validation of Confirmation Procedures  for Non-Threshold Substances  Factors to be investigated in the method validation procedure to demonstrate that a Confirma tion Procedure for Non-Threshold Substances  is Fit-for-Purpose  include, but are not limited to:  - Selectivity : The ability of the Confirmation Procedure  to detect and identify the Analyte  of interest, taking into account  interference(s) from the matrix or from other substance(s) present in the Sample .