Fundamental Concepts

Abstract

Molecular size, or more precisely, molecular hydrodynamic volume governs the separation process of SEC. That is, as a mixture of solutes of different size passes through a column packed with porous particles, the molecules that are too large to penetrate the pores of the packing elute first, as shown in Fig. 2.1. Smaller molecules, however, that can penetrate or diffuse into the pores, elute at a later time or elution volume. Thus a sample is separated or fractionated by molecular size, the profile of which describes the molecular weight distribution (MWD) or size distribution of the mixture. If the SEC system is calibrated with a series of solutes of known MW, as shown in Fig. 2.2, a relationship between log MW and elution volume is obtained. This relationship can then be used as a calibration curve to determine the MWD and MW averages of samples, as explained in Chap. 7.