# Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 77

It is seen that the 1 micron column can provided an efficiency of over two hundred thousand plates whereas the column 100 micron column can provide an efficiency of over two billion theoretical plates (assuming an inlet pressure of 1000 p.s.i). However, it must be emphasized that the high efficiency column will be extremely long and have an inordenantly long analysis time. In addition, the practical limitations of present day chromatography equipment render the realization of even a modest performance from LC capillary columns extremely difficult to realize experimentally.

# Experimental Validation of the Van Deemter Equation

The different
equations were tested against an extensive set of accurately measured
experimental data reported by Katz *et al.* (24) and, in order to identify
the most pertinent equation, their data and some of their conclusions will be
considered in this chapter. The equations that were examined, are as follows,

The Van Deemter equation.

The Giddings equation.

The Huber equation.

The Knox equation.

The Horvath equation.

At first
sight, it might appear adequate to apply the above equations to a number of
experimental data sets of (H) and (u) and to identify that equation that
provides the best fit. Unfortunately, this is of little use as, due to their
nature, all five equations would provide an excellent fit to any given
experimentally derived data set, provided the data was obtained with sufficient
precision. However, all the individual terms in each equation *purport to
describe a specific dispersive effect*. That being so, if the dispersion
effect described is to be physically significant over the mobile phase velocity
range examined, all the constants for the above equations derived from a curve
fitting procedure *must be positive and real*. Any equation, that did not
consistently provide positive and real values for all the constants, would obviously
not be an appropriate and explicit equation to describe the dispersion effects
occurring over the range of velocities examined. However, any equation that *does
provide a good fit* to a series of experimentally determined data sets
and meet the requirement that all constants were positive and real *would still not uniquely identify* the correct equation
for column design.