Concentration Dependence in Gel Permeation Chromatography

Abstract

Four narrow distribution polystyrene samples with molecular weights from 3.5 × 10⁴ to 2.7 × 10⁶ and six linear or branched polyvinyl acetate samples were used in the study. GPC experiments were performed in two solvents (THF and MEK), three column sets (different permeation limits) and five different concentrations ranging from 0.05% to 3%. The elution curves were normalized while average retention volumes and peak width were calculated. The data of the same sample with different concentrations can thus be compared on the same graph. The following conclusions were drawn. (1) At very low concentration, elution curves were independent of the concentration. On increasing the concentration, peak positions were first moved to longer retention volumes and then the whole curves broaden appreciably. (2) Concentration dependence increases with the increase in molecular weight and goodness of the solvent power. (3) The it lots of the retention volume vs concentration deviate from linearity. Extrapolation at higher concentrations is not reliable. (4) The peak widths of the elution curves expressed by the variance σ increase with the increase of concentration. (5) The initial slopes of the peak-concentration plot of the branched PVAc samples are proportional to the hydrodynamic volumes expressed as [η] M of the samples.