Vacancy
chromatography can be considered theoretically using the equations derived from
the plate theory for the elution of positive concentration profiles. If a
mobile phase contains a solute at a concentration (Xo), then, after
equilibrium, the eluent from the column will also contain the solute at a
concentration (Xo). Let a sample containing the same solute
at a concentration (Xi) be injected onto the column under where
either (Xo<Xi) or (Xo>Xi),but
(Xo
Xi). Such an injection will
produce a transient change in the concentration (Xo) of solute in
the mobile phase. From the plate theory, this transient concentration change
will be eluted through the column as a concentration difference and will
be sensed as a negative or positive peak by the detector. The equation
describing the resulting concentration profile of the eluted peak, from the
plate theory will be,
| where X(n) | is the concentration of the solute in the mobile phase leaving the (n)th plate, |
| (v) | is the volume passed through the column in plate volumes, |
| and (n) | is the number of theoretical plates in the column. |
If the sample consisted of
pure mobile phase containing no solute, then Xi = 0 and
