# Plate Theory and Extensions - The Peak Capacity of a Chromatographic Column > Page 96

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The curves
show that the peak capacity increases with the column efficiency, as one would
expect, but the major factor that influences peak capacity is the capacity
ratio of the last peak. Thus, any aspect of the chromatographic system that
might limit the value of (k') for the last peak will also limit the peak
capacity. Davis and Giddings (28) have pointed out that the theoretical peak
capacity is an exaggerated value of the true peak capacity. The individual (k')
values for each solute in a realistic multi-component mixture will have a
statistically irregular distribution. They very adroitly point out, that the
solutes in real samples do not array themselves conveniently along the
chromatogram four standard deviations apart to provide the maximum peak
capacity. Nevertheless, the theoretical peak capacity values given by equation
(77) can be used as a reasonable practical guide for comparing *different*
columns although, in practice the theoretical values for peak capacity may
never be realized.

Courtesy of the Journal of Chromatographic Science

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**Figure 25.
Graph of Peak Capacity against Capacity Ratio**

It is clear from Figure 25 that any property of the chromatographic system that limits the magnitude of (k') must also limit the peak capacity. One such property, that limits the magnitude of (k') will be the detector sensitivity. The later the elution (the higher the (k') value), the greater the peak dispersion and the smaller the peak height. At some limiting (k') value, the peak will be so small that it will be indiscernible from the noise.