ABSTRACT
The performance of microparticulate GPC packings having narrow particle size distributions has been investigated with short columns and high speed liquid chromatography instrumentation. Reliable and reproducible data for polydispersity and molecular weight distribution of polystyrenes have been obtained by optimising the injection procedure, by using a constant flow pump, and by incorporating an internal standard into each injected solution. Column efficiency measurements for a series of polystyrene standards having narrow molecular weight distributions have given extimates of the chromatogram broadening contributions due to solute dispersion in the mobile and stationary phases. The experimental results have been compared with a theoretical expres sion for polydispersity in terms of eluent flow rate, column pack ing diameter and solute diffusion coefficient. It is shown that, for low polymers, mobile phase dispersion is the most important effect, so that efficient separations may be performed at high flow rates, whereas for high polymers dispersion owing to mass transfer into the stationary phase becomes important and it is no longer possible to achieve efficient separations for high polymers at fast flow rates. The results for a polydisperse poly styrene demonstrate that the smallest column packings should be preferred for fast and precise determinations of polydispersity. The mast accurate determination of molecular weight distribution is performed at a low flow rate.
