Stochastic theory of size exclusion chromatography: peak shape analysis on single columns

The stochastic theory of size exclusion chromatography (SEC) was applied to analyze the peak shape of chromatograms obtained with a wide range of polystyrene standards on various columns. The columns were packed with stationary phases of different pore sizes. The stochastic-dispersive model of SEC results in a peak shape model that fits well the symmetrical and asymmetrical peaks observed in SEC. From the peak shape parameters obtained after nonlinear parameter estimation, information can be gained regarding the fundamental characteristics of the size exclusion process. When a series of polymer standards are analyzed on one column-in a manner similar to other methods of inverse chromatography-the stationary phase can be characterized. The dependence of the ingress and the egress processes on the relative size of the macromolecule to the pore size was determined. We found that for small molecules the selectivity in SEC arises from the ingress process, while when the size of the macromolecule is comparable to that of the pore-i.e., close to the exclusion limit-the egress process will also strongly affect the selectivity.