Aqueous gel permeation chromatographic methods for technical lignins

The molecular weights and molecular weight distributions of lignosulfonates and soda lignins were determined by aqueous gel permeation chromatography (GPC). The elution behavior of the samples, was investigated in detail to evaluate the non-size-exclusive effect in the aqueous GPC system. The ionic strength and pH are thought to be the main factors influencing the accuracy and the reliability of measurements. Solutions of 0.1M NaNO3 with pH 7 or 0.1 M NaNO3 with pH 12 were shown to be optimum for determining the molecular weight of lignosulfonate and alkali lignin. Accuracy of the method was checked by comparing the data obtained by aqueous GPC with that from vapor pressure osmometry (VPO).