Chapter: Modern Analytical Chemistry: Chromatographic and Electrophoretic Methods
Peak Capacity - Theory of Column Chromatography
Peak Capacity
Another important consideration is the number
of solutes that can be baseline re- solved on a given
column. An estimate of a column’s peak capacity, nc, is
where Vmin and Vmax are the smallest
and largest volumes
of mobile phase
in which a solute can be eluted and detected.
A column with 10,000 theoretical plates, for example, can resolve no more than
if the minimum and maximum volumes of mobile phase in which the solutes can elute are 1 mL and 30 mL. This estimate provides an upper bound on the number of solutes that might be separated and may help to exclude from con- sideration columns that do not have enough theoretical plates to separate a complex mixture. Just because a column’s theoretical peak capacity is larger than the number of solutes to be separated, however, does not mean that the separation will be feasible.
In most situations the peak capacity obtained is less than the estimated value because the retention characteristics of some solutes
are too similar to effect
their separation. Nevertheless, columns with more theo- retical
plates, or a greater range of possible
elution volumes, are
more likely to separate a complex mixture.
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