Resolving Power in Two-Dimensional Separations

To better understand the heightened resolving power of 2D systems, we need some measure by which 2D and ID separations can be compared. Not all criteria of separation power lend themselves to ready comparison. The resolution of a specific pair is not a suitable criterion because this resolution varies widely for different separation mechanisms irrespective of ID or 2D configurations. Plate height and plate number are not directly comparable because these are defined only for a single dimension. While H or N values can be found for each axis, it is not immediately obvious how to combine them for both axes in order to compare the overall separation effectiveness with that of a ID system. 

For steady-state zones, where H and N also lack definition, we turned to the peak capacity as a common denominator for different methods. We have learned how to estimate peak capacity for ID separations we now extend this concept to incorporate two axes. For this we must reconsider the matter of spot dimensions when migration occurs along both axes rather than just one. 

As far as zone and spot dimensions for sequential two-dimensional separations are concerned, the equations of Section 6.3 are applicable if we use the two equations above to obtain crx and cry, respectively. 

The peak capacity nc, as usual, is the number of zones that can be crowded into the available separation space. However, in two dimensions space is measured by area, not length. We can thus estimate ne as bed area L,L2 over spot area A 

We now note that the peak capacity for a separation along the x coordinate alone is of the order of 

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