# Plate Theory and Extensions - The Capacity Ratio of a Solute > The Separation Ratio of Two Solutes > Page 18

## The Separation Ratio of Two Solutes

The separation
ratio of two solutes (A) and (B), (a_{A/B}), is taken as the ratio of
their corrected retention volumes, i.e.,

* *

The *separation
ratio* is simply the ratio of the solute distribution coefficients which
depends only on the operating temperature and the chosen phase system. Most
importantly, they are independent of both the mobile phase flow rate and the
phase ratio of the column. Thus, the same separation ratio for two
solutes would be obtained from either a packed column or a capillary column if
the same temperature and the same phase system is used (at this time no
exclusion effects from the support or stationary phase is assumed).

To identify a solute, a standard substance is added to the sample mixture and the separation ratio of the solutes of interest to the standard is measured. The ratios are then compared with those obtained for reference substances chromatographed under the same conditions. The ratios are calculated as the ratio of the distances in centimeters between the dead point and the maximum of each peak. If the flow rate is constant and data processing is employed, then the corresponding retention times can be used.