Size-exclusion and the void volume of HPLC column

Abstract

Size-exclusion chromatography (SEC) is the main technique for determination of polymer molecular weight distribution. SEC elution volumes are limited by column void volume and interparticle volume. Measurements of these volumes at actual size-exclusion conditions is discussed together with the relationship of polymer retention to its hydrodynamic volume. We studied the retention of 32 polystyrene standards with polydispersity below 1.05 on 10 different commercial columns. Nine columns had silica based C18 modified packings, and one, polymer-based packing. Pore sizes of packing materials varied from 8 to 35 nm, and 3 packings were poroshell type. Propagation of the retention dependence on the cubic root of the polymer molecular weight to zero mass value was shown to correspond to the column void volume; and was consistent with other methods of void volume measurement. Observed linear dependencies of retention volumes on for low molecular weight polymers on all studied columns suggests a correlation between the product of the polymer hydrodynamic radius and the adsorbent surface area. This correlation is thoroughly discussed.