GC018 Selectivity


The selectivity (α) of a separation is calculated as the ratio of the adjusted retention times of two adjacent peaks:

Alpha = t’R(2) / t’R(1)

The numbers 1 and 2 are for the earlier (1) and later (2) eluting peaks.

Selectivity can also be written as the equality between the ratio of the retention factors (k1 and k2) and equal to the two partition coefficients (K1 and K2).

The selectivity is a consequence of the differences on intermolecular interactions between the compounds and the stationary phases. Selectivity increases as the differences in those interactions increase. In GC capillary columns, the selectivity required to perform a separation can be as low as 1.02 or less.

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