SEPARATIONS OF HIGH-MOLECULAR-MASS POLYSTYRENES ON DIFFERENT PORE-SIZE AND PARTICLE-SIZE REVERSED-PHASE COLUMNS IN DICHLOROMETHANE-ACETONITRILE

The effect of pore size and particle size of the silica support on the retention and resolution of high-molecular-mass polystyrenes was investigated in reversed-phase gradient elution high-performance liquid chromatography using a dichloromethane-acetonitrile mobile phase. An increase in pore size was found to increase retention slightly. A decrease in particle size was found to increase retention of all molecular masses. Both pore size and particle size had effects on resolution between polystyrenes of different molecular masses. Unretained polystyrene eluted at the solvent front for some of the conditions used but, this effect decreased with an increase in pore size and a decrease in particle size. A possible explanation for the greater effect on retention of particle size compared with pore size, is that the polystyrene molecules in a gradient elution experiment do not have access to the same number of pores as they do in an isocratic or size-exclusion experiment. It is proposed that this is due to a lag in the mobile phase composition in the pores compared with interstitial composition in the gradient experiment.