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.