The rule parameters in liquid adsorption chromatography of polymer homologous series and their determination

The separation of polymer homologous series is governed by two rule parameters: the interaction parameter c of the repeat unit and the sorbent surface S (relation of pore volume to pore diameter). The interaction parameter is independent on column dimensions and pore diameter. In a plot of elution volumes Vn versus the difference ΔV = Vn − Vn−1 in elution volumes of consecutive oligomers, straight lines are obtained, the intercept of which yields the accessible volume. Using the accessible volume as the hold-up volume in the calculation of the retention factor k, a strictly linear dependence of ln k versus the number of the repeat units n is observed (Martinʹs plot). The interaction parameter c can be determined experimentally by three different approaches: from the slope in a plot of V versus ΔV, from the slope in Martinʹs plot (ln k versus n), and from the intercept in a plot of ln(ΔV) versus n. The pore surface is obtained from the intercept in Martinʹs plot (ln k versus n) or the intercept in a plot of ln(ΔV) versus n. The results obtained by the different approaches agree very well. The theoretical predictions are verified by comparison with the experimental data obtained on columns with different pore diameter and pore volume and thus, different pore surface at conditions corresponding to the same interaction parameter.