Packing material base, parameters

Still, the use of the hydrodynamic volume, a size based on dynamical properties, in the interpretation of SEC data is not fully understood. This is because SEC is typically run under low flow rate conditions where hydrodynamic factor should have little effect on the separation. In fact, both theory and computer simulations assume a thermodynamic separation principle the separation process is determined by the equilibrium distribution (partitioning) of solute macromolecules between two phases — a dilute bulk solution phase located at the interstitial space and confined solution phases within the pores of column packing material. Based on this theory, it has been shown that the relevant size parameter to the partitioning of polymers in pores is the mean span dimension (mean maximal projection onto a line). Although this issue has not been fully resolved, it is likely that the mean span dimension and the hydrodynamic volume are strongly correlated. 

The mass of the packing material in the column is a largely underestimated parameter. As it was discussed in the theory chapter, the retention is proportional to the total surface area of the adsorbent in the column. External methods of the surface area measurement determine the specihc surface area (in square meters per gram of the material), and the total surface in the column is a product of the specific surface area of base material and the mass of the adsorbent in the column. 

Consider Taylor dispersion of a tracer in packed beds, mass transfer Peclet numbers based on interpellet axial dispersion coefQcients, and the resolution of a chromatograph to explain how the performance of a chromatographic separation device depends on the length of the packed column if all other design parameters, particularly the size of the packing material, remain constant. 

This treatment is based on the two differential material balance equations on a fixed-bed and packed particles. Although these equations, together with an adsorption isotherm and suitable boundary and initial conditions, describe precisely the performance of chromatography, the complexity of their mathematical treatment sometimes makes them insolvable. If the distribution coefficient K given by Equation 11.1 is constant, then Hs can be correlated to several parameters by use of the first absolute moment and the second central moment, as given by Equation 11.20 [3]. 

---