MiloÅ¡ NetopilÃk
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Czech Republic
Title: Size exclusion chromatography models and its comparison with experiment
Biography
Biography: MiloÅ¡ NetopilÃk
Abstract
Size exclusion chromatography (SEC) is a method generally used of the separation and analysis of polymers with respect to molecular wight. The benefits of the method are exploited by additional detectors (light scattering, viscometer, UV detector) which give maximum information about the sample. The basic functioning of chromatographic separation was described by the Martin and Synge model of relatively simple mechanism of establishing an equilibrium on each of theoretical plates followed by a shift of the mobile phase by the size of the plate. The model was further developed and for SEC it applies with some constraints. The results of the chromatographic models is the band broadening function. The basic mechanism of separation is accompanied by numerous side effects and mechanisms which depend on conditions of analyzes, as flow-rate, influencing the establishing the equilibrium, the detector-cell volume, etc. The systematic experimental investigation of analyzes of polystyrene standards by size exclusion chromatography evaluated on the background of the plate-height model of separation provides the insight into the mechanism and its efficiency, a measure of reaching equilibrium. The model gives results which can be transformed into those given by the Giddings and Eyring model. The separation being improved with decreasing flow-rate is in accord with Giddings observation of transversal diffusion as a factor decreasing the broadening of the band broadening function. The efficiency of the separation is judged on the basisi of the shape of the elution curves, which depends on the experimental conditions. This suggests that it reflects rather properties of the band broadening function than the molecular weight distribution of the polymer sample. The elution curves obtained by SEC of polystyrene standards in tetrahydrofuran using pumps and UV detector Deltachrome, and one column PL gel mixed D are depicted in Figure 1. The decrease in broadness of the elution curves is obvious. The curve obtained at lowest flow-rate of 0.01 ml/ min fits the theoretical model best.