The Plate theory established that the retention volume of a solute is proportional to its distribution coefficient that in turn is exponentially related to the standard energy of transfer. Thus, a graph relating log retention volume to molar volume (to which the magnitude of the dispersive forces and thus the potential energy of interaction has been shown to be linearly related) should give a straight line for a given homologous series separated on a dispersive stationary phase. Employing GC, Desty et al, made some very accurate measurements of the retention volume of a series of hydrocarbons on pure squalane (a hydrocarbon stationary phase). They actually measured the capacity ratio of each solute that (for the purposes of this discussion and as will be seen later) is equivalent to the corrected retention volume (V_r'). Curves for three n-alkanes, three 2-methyl alkanes and two cyclo-alkanes are shown in figure 35. It is seen that the curves are precisely linear for the n-alkane and 2-methyl alkane values and almost exactly parallel to the line drawn through the two points for the cyclo-alkanes. These curves confirm the correlation between retention and molar volume and substantiates that the interactions of the solute with the stationary phase were indeed dispersive in nature.

Figure 35. Graph of Ln(Capacity Factor) against Molar Volume