Principles and Practice of Chromatography - Factors Controlling Retention > Page 14

or  V'r = KVS (1)

 

where
(Vm) is the volume of mobile phase in the column
(VS) is the volume of stationary phase in the column,
(K) is the distribution coefficient of the solute between the phases,
and (V'r) is the corrected retention volume i.e., (Vr - Vm)

 

From equation (1) it is seen that the corrected retention volume is controlled by two parameters: firstly the distribution coefficient of the solute between the two phases and secondly, the amount of stationary phase that is available to the solute.

Consequently, the magnitude of (V'r) is determined by (K) or (Vs) or both.

From equation (1) the conditions necessary to separate two solutes (A) and (B) can be deduced.

To separate solutes (A) and (B), V'r(A) <>  V'r(B),

which can be achieved by making either K(A) <> K(B)

or VS(A) <> VS(B) or an appropriate combination of both.

Thus, to separate a mixture, either the values of (K) for all components, or the amount of stationary phase (VS), available to each component, must be made to differ or, again, appropriate adjustments must be made to both.