Existing guidance for system suitability was developed for pharmaceutical compounds and
may not be directly applicable for proteins which, due to their structural complexity and
inherent heterogeneity, require additional considerations beyond those typically required
for small molecules. For example, appraisal of resolution by measuring the number of
theoretical plates (commonly done for small molecules), may not be the best way to assess
the system readiness to resolve charge isoforms of a protein on an ion exchange column.
This may be due to the relatively poor resolution of protein peaks resulting from inherent
product microheterogeneity, when compared to the resolution typically seen with small
molecules. However, this methodology (the number of theoretical plates) may be a very
good indicator to measure the system performance for size exclusion chromatography
(SEC), which does not typically resolve product isoforms resulting from microheterogeneity.