Kinetic stationary phase particle diameter

At this point, the stationary phase particle diameter is extremely important for the kinetic optimization of separations. A smaller particle diameter reduces the distance for the necessary radial diffusion of analyte molecules on the one hand, but increases the geometrical radial concentration gradient that drives the diffusion. Both effects are synergistic for an efficient analyte transport and this is the physicochemical foundation for the decrease of the C-term with the squared particle diameter (dp ). This will be used effectively in the speed optimization strategy. 

Fortunately, the effects of most mobile-phase characteristics such as the nature and concentration of organic solvent or ionic additives the temperature, the pH, or the bioactivity and the relative retentiveness of a particular polypeptide or protein can be ascertained very readily from very small-scale batch test tube pilot experiments. Similarly, the influence of some sorbent variables, such as the effect of ligand composition, particle sizes, or pore diameter distribution can be ascertained from small-scale batch experiments. However, it is clear that the isothermal binding behavior of many polypeptides or proteins in static batch systems can vary significantly from what is observed in dynamic systems as usually practiced in a packed or expanded bed in column chromatographic systems. This behavior is not only related to issues of different accessibility of the polypeptides or proteins to the stationary phase surface area and hence different loading capacities, but also involves the complex relationships between diffusion kinetics and adsorption kinetics in the overall mass transport phenomenon. Thus, the more subtle effects associated with the influence of feedstock loading concentration on the... 

Nevertheless, the history of supports for HPLC does not stop at this point, and there are several further developments aimed at either a kinetic optimization of the materials (see Chapter 3), an extension of the usable pH range, or the pressure stability of the silicas. In the course of kinetic optimization of the materials, essentially the diffusion paths of the analytes interacting with the stationary phase are shortened. This is done primarily by reducing the particle diameter of the supports. 

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