High-performance gel permeation chromatography of polystyrene with silica microspheres

Abstract

Gel permeation chromatography separations have been performed with short low capacity columns containing silica microspheres (particle diameter ≈ 20 μm) having narrow particle size distributions and mean pore diameters in the range 8–120 nm. Plate height data for non-permeating polystyrene standards permitted an evaluation of chromatogram broadening due to mobile phase dispersion. These results together with plate height data for permeating polystyrene standards, tetraphenylethylene and toulene gave an assessment of chromatogram broadening due to mass transfer dispersion as a function of eluent flow-rate and solute molecular weight. It was found that mass transfer dispersion increased at higher flow-rates, the flow-rate dependence increasing as the diffusion coefficient of permeating polystyrene decreased. At very low flow-rates (0.05 cm 3 min −1, mobile phase dispersion is the major contributor to the chromatogram broadening,of permeating polystyrene. From theoretical considerations of chromatogram broadening, a relation is derived permitting the approximate determination of the true polydispersity of a permeating polymer at very low eluent flow-rates from the plate height for that polymer and from the plate height arising from mobile phase dispersion. The results show that fast separations may be accomplished in several minutes and that the most precise determinations of polydispersity are obtained at slow eluent flow-rates with separation times of about 1 h.