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 a result of molecular kinetics. The extent to which two substances are separated will depend on their relative retention in the chromatographic system. Consequently, an expression for the retention volume of a solute will show how retention is controlled and thus how the separation can be achieved. 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 which, in the case of chromatographic retention, will be the distribution coefficient. Equation can be used to identify the type of retention mechanism that is taking place in a particular separation by measuring the retention volume of the solute over a range of temperatures.
