Division 3.1.1.1 Specificity

For analytical methods, the power of discrimination between the analyte and closely related substances (isomers, metabolites, degradation products, endogenous substances, matrix constituents, etc) is important. Two approaches are necessary to check for interferences.

Therefore, potentially interfering substances shall be chosen and relevant blank samples shall be analysed to detect the presence of possible interferences and to estimate the effect of the interferences:

• select a range of chemically related compounds (metabolites, derivatives, etc.) or other substances likely to be encountered with the compound of interest that may be present in the samples;

• analyse an appropriate number of representative blank samples (n ≥ 20) and check for any interferences (signals, peaks, ion traces) in the region of interest where the target analyte is expected to elute;

• additionally, representative blank samples shall be fortified at a relevant concentration with substances that are likely to interfere with the identification and/or quantification of the analyte;

• after analysis, investigate whether:

  • the presence may lead to a false identification,

  • the identification of the target analyte is hindered by the presence of one or more of the interferences, or

  • the quantification is influenced notably.