# Dispersion in Chromatography Columns - Alternative Equations for Peak Dispersion > The Huber Equation > Page 66

However, on
consideration *there is a difference *between the Giddings equation and
that of Van Deemter as the C term in the Van Deemter equation would now only
describe the resistance to mass transfer in the *mobile phase contained in
the pores* of the particles, and thus, would constitute an additional *resistance to mass transfer in the stationary
(static mobile) phase*. This concept has some indirect experimental
support in the development of the form of f_{1}(k')
from experimental data which will be discussed later. The form of f_{1}(k') is shown to be closer to the
original form given by Van Deemter for f_{2}(k')
that is appropriate for the resistance to mass transfer in the stationary
phase. It is not known for certain, but it is possible and likely, that this
was the reason why Van Deemter *et al.* did not include a resistance to
mass transfer term for the mobile phase in their original form of the equation.

## The Huber Equation

The next HETP equation to be developed was that of Huber and Hulsman in 1967 (17). These authors introduced a modified multipath term somewhat similar in form to that of Giddings and a separate term describing the resistance to mass transfer in the mobile phase contained between the particles. The form of their equation was as follows:-

(47)

It is seen
that the first term differs from that in the Giddings equation, in that it now
contains the mobile phase velocity to the power of one half. Nevertheless,
again when u^{1/2 }>> E,
the first term reduces to a constant similar to the Van Deemter equation. The
additional term for the resistance to mass transfer in the mobile phase is an
attempt to take into account the 'turbulent mixing' that takes place between
the particles. Huber's equation implies (but, in fact, was not explicitly
stated by the authors) that the mixing effect between the particles (that
reduces the magnitude of the resistance to mass transfer in the mobile phase)
does not commence until the mobile phase velocity approaches the optimum
velocity (as defined by the Van Deemter equation). Furthermore, it is not
complete until the mobile phase velocity is well above the optimum velocity.
Thus, the shape of the HETP/u curve will be a little different from that
predicted by the Van Deemter equation.