ABSTRACT
Size exclusion chromatography (SEC) is currently the most widely used method for determining the molecular weight (MW) and molecular weight distributions (MWD) of polymers. What is less known is that during a SEC run another chromatographic separation mechanism, hydrodynamic chromatography (HdC), is also taking place. Figure 1 shows polystyrene standards that were separated by these two mechanisms in a single injection (1) using small-pore columns. The calibration curve for the chromatogram in Fig. 1 is plotted in Fig. 2. It shows that standards larger than MW 5×105 are separated by HdC. Those smaller than 5×104 are separated by SEC. In a larger poresize column, the MW ranges separated by these two mechanisms overlap and it becomes difficult to distinguish from the calibration curve. HdC is currently used more for particle size distribution studies. It has also been investigated for MW studies (2, 3). This chapter discusses the combination of these two mechanisms, whereby an analysis benefits from the separation abilities of both.
