Theory of HPLC retention based on the adsorption from solutions can help to establish
the relationships of measurable retention values (** V_{R}, t_{R}**,
and

Capacity factor is the ratio of the reduced retention volume to the dead volume:

(20)

From the basic retention equation we can get

(21)

For the low analyte concentration, in the absence of the analyte-analyte interactions in solution and on the surface, the equation (14) could be applied for the description of adsorption isotherm. At very low concentrations the limit of the derivative of the excess adsorption by concentration is equal to:

(22)

From equations (21) and (22) we can conclude that capacity factor may be expressed in form

*k' = K - 1*

Thermodynamic equilibrium constant is an energetical parameter. Its logarithm is equal to the difference of the free Gibbs energy of the analyte and solvent in the adsorption system,

where ** DH** is the difference of the enthalpy of
adsorption of analyte and solvent and

This is one of the experimental facts which could not be explained on the basis of
partitioning theory.