The Theoretical Plate as a Measure of Column Efficiency

In view of recent criticism, the role of the theoretical plate as a measure of column efficiency is examined. Plate height must, of course, be combined with other information to obtain resolution for a particular pair. However, it is shown that the plate height has a basic relationship to resolution, and gives a measure of the resolution per unit of relative (peak) velocity difference, or, stated in another way, it measures the resolution per unit or relative retention time difference. It is also shown that the effective plate height gives a measure of resolution per unit of relative selectivity. The resolution of any particular pair, therefore, can be gotten if, in addition to plate height, the relative velocity difference, etc., is known. Hence plate height should be considered as a significant but not complete expression of a column's power. It shares this limitation with other measures of column performance such as the effective plate number (EPN).