Selectivity factor expresses the separability of two consecutive eluting peaks; thus measures the chromatographic system to differentiate solute peaks.

For two peaks A and B, A with the shorter retention time the selectivity factor is defined as;

Magnitude of the selectivity factor (greater than 1) give the ability to tell peaks from each other. It can be seen from above that the selectivity factor is an intensive property, i. e. it does not depend on the geometrical parameters of the system, neither the mobile phase velocity. It depends on K's and is only a function of temperature and the nature of the stationary phase/mobile phase system.

If the selectivity factors are defined with respect to a reference compound, such values can be used for qualitative analysis.

Back to Contents