Figures of Merit for Full Validation

As discussed previously in Section 6.2.1, the selectivity of an analytical method can be summarized as the ability of the method to measure and differentiate the analytes in the presence of components that may be expected to be present, e.g. metabohtes, impurities, degradants or matrix components. The terminology specificity is sometimes used in the hterature as a synonym for selectivity but more properly describes the property of an analytical method for which only the target analyte gives any response whatsoever, i.e. the extreme case of selectivity. (It seems unlikely that a truly specific method exists for any analyte.) One of 

Basic Components Selectivity Sensitivity Range of reliable response Accuracy Precision Reproducibility 

Additional Components Analyte recovery (extraction efficiency) Stock stability Matrix stability Post process stability (extract) Integrity of dilution Carryover and contamination Matrix effects Incurred sample reproducibility Incurred sample stability 

The best assessment for selectivity of a method is achieved with the use of matrix extracted blanks that are prepared from control matrix that is representative of the sample matrix. This allows checking that ions with mJz values characteristic of analyte or SIS are not observed at the crucial retention times in chromatograms for the blank. A detailed account of how blanks of this type are used in method development to ensure selectivity is given in Section 9.4.7b. 

Depending on the apphcation, one or more source of control matrix may be available for selectivity screening. For instance, when testing for herbicides in a soil dissipation study the control matrix may come from the actual field where the study is to take place prior to application of the herbicide or from an adjacent control plot For bioanalytical analysis several lots of control matrix may be screened independently and as a pool (Section 10.4.1c), and additional selectivity data may be obtained from actual subjects prior to dosing (pre-dose samples). When a representative control matrix is not available or if additional confidence is required for analyte identification additional measures such as the inclusion of multiple 

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