Characterization of different reversed phase systems in liquid adsorption chromatography of polymer homologous series.

The interaction parameter of a given repeat unit in liquid adsorption chromatography (LAC) can be determined from the slope in a plot of the elution volumes versus the difference in elution volumes of subsequent monomers. In such a plot, the intercept represents the void volume, and from the slope the adsorption interaction parameter can be calculated. This parameter is independent of column dimensions and pore diameter and can thus be used as a measure of the interaction of a given repeat unit with the surface of a stationary phase in a given mobile phase composition. The interaction parameter can also be obtained from the slope in a plot of the logarithmic retention factors k versus the number of repeat units n or from the slope in a plot of the logarithmic difference in elution volumes of subsequent monomers versus n. The values obtained by the three different approaches are in good agreement. In a given mobile phase, the interaction parameter of a given repeat unit was found to be almost the same for various alkyl bonded columns from different producers. The retention of a given oligomer depends as well on the interaction parameter as on the pore dimensions (and thus the internal pore surface) of the stationary phase. The pore surface can be determined from the intercept in a plot of the logarithmic difference in elution volumes of (subsequent) nonfunctional monomers as a function of n. As the interaction parameter of a given repeat unit in a given mobile phase is the same for stationary phases with the same chemical nature, retention can be adjusted by selection of the pore surface. On a given stationary phase, there is a linear dependence between interaction parameter and mobile phase composition.