ABSTRACT
The mechanism of retention, which arises largely from molecular interactions and molecular restraint, is quite different from the mechanism that causes band spreading, which is mainly the result of molecular kinetics. In order to derive an expression for the retention volume, it is necessary to obtain the equation for the elution curve of a solute; that is, an equation that will relate the concentration of the solute in the system eluent to the volume of mobile phase that has passed through it. The plate theory assumes that the solute is, at all times, in equilibrium with the two phases. Classical thermodynamics provides an expression that relates the change in free energy of a solute when transferring from one phase to the other as a function of the equilibrium constant that, in the case of chromatographic retention, will be the distribution coefficient.
