The number of theoretical plates and H are related through the length of the column L . Note that as H decreases, the efficiency of the column increases, allowing more equilibrations to occur within a given length of column. As its number of theoretical plates increases, a chromatographic system can handle more difficult separations. Theoretically, the number of plates can be infinitely increased by lengthening the column. While the plate theory adequately describes the rate of solute migration and can approximate the width of eluted peaks, the theory fails to consider the effects of such experimental variables as particle size, molecular structure, and temperature on the shape of the eluted peak or on the parameters H and N .
Plate theory makes several assumptions that are proven incorrect by experimentation.
It assumes that the distribution coefficient of the solute is constant in all plates and independent of the solute concentration. In practice, however, the distribution coefficient is only independent of concentration over a very narrow range of concentrations. Another incorrect assumption is that the mobile phase is added in increments and moves in a discontinuous manner through the plates. Plate theory assumes that equilibration is rapid compared with mobile phase flow. Diffusion is never instantaneous, however, and a solute may be transferred from one plate to another before equilibrium is attained.