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), (aA/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.