# Dispersion in Chromatography Columns - The Van Deemter Equation > Page 49

where, A=2ld_{p},
B=2gD_{m}
and _{}

Equation (33) is a hyperbolic function which has a minimum value of (H) for a particular value of (u). Thus, a maximum efficiency will obtained at a particular linear mobile phase velocity.

An example of an HETP curve obtained in practice showing this hyperbolic relationship is given in figure 11.

**Figure 11.
HETP Curve for Hexamethylbenzene**