5. Target Identification in Methods

Target identification is considered in detail. A qualitative analysis of this type is mostly performed according to validated methods which are screening and confirmatory. An identification result is the conclusion based on criteria. Those for screening identification are not very rigorous and not numerous. An example is the presence of a particular mass chromatographic peak in a rather wide range of the retention parameter. Most chromatographic techniques are suitable for screening. For confirmation of identity, more analytical data are required, e.g., three or four mass peaks and matching tolerance/range criteria for peak intensities. Any such value is named an identification point. An analyst should gather the required number of points. Chromatography and mass spectrometry and their combinations are the most appropriate techniques for the purpose. Different versions of the techniques, as well as other types of spectroscopy, are considered. The requirements and guidelines for setting up identification criteria presented in a number of laboratory guidances which have been issued by various organizations and agencies are outlined in detail. These are not the same in different documents; that is the reason for criticizing them. The system of identification points itself and the evident or suspected invalidity of tolerance criteria has also been criticized. The criticism is partly accepted, and some objections are also presented here. In general, the guidelines are regularly tested through a global analytical practice, and new improvements of identification criteria are reported.