Spreading Phenomena in Chromatographic Columns

It is well known that all elution curves, obtained by diverse chromatographic techniques, show the following common feature They cannot be reduced to a vertical straight line1 even if a strictly monodisperse sample is injected into the column, but always show a bell-shaped curve with a finite width, evidently not originating in the MWD of the injected sample. This experimental result can be explained by an axial acceleration of the injected species by the stream of the column liquid, leading 

1 More exactly to an infinitesimally narrow Gaussian curve of infinite height, having unit area, namely Dirac s delta functional 5(V — V0), where V0 is related to the molecular weight of the injected sample, according to the calibration curve of the column used 

In the usual chromatographic techniques applied to polymers, the spreading of the concentration profile cannot be measured exactly because it is always overlapped by the broadening of the profile due to the column resolution. This is typical for gel permeation chromatography (GPC), as is well known. A quite different situation arises in PDC. 

It was already pointed out that the PDC-resolution completely vanishes at the theta point, so that practically the spreading phenomena alone can be exactly measured in a PDC-column kept at a constant temperature closely below the theta temperature of the system investigated (cf. below). The results of these measurements can then be taken as a basis for a common theory of spreading phenomena in chromatographic columns. 

A simple one-dimensional model7) including both the hydrodynamic interactions, 

---