Dimensional effects, structural, material

All of the currently used porous packing materials have a three-dimensional network structure, effectively giving rise to a pore size distribution. In these separating media, the dependence of 7 on A will be less sharp compared with the one in Fig. 3. It is desired by chromatographers that the retention time is a linear function of log M. Because the retention time is a linear function of K, the plot of K needs to be a linear function of log M in as broad a range of MWs as possible. A naturally occurring pore size distribution is not sufficient to cause the desired linearity. Therefore, mixed-bed columns, packed with porous materials of different pore-size-distribution ranges, have been developed and used broadly as linear columns. 

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