# Plate Theory and Extensions - Vacancy Chromatography > Page 75

The curves in
Figure 19 show that as the injection volume is increased, so the retention
volume of the peak also increases. The retention volume of the small negative
peak produced by the smallest charge will be the same as that for a sample where
X_{i}>X_{0} and the same as that for a solute
chromatographed in the normal way with the column carrying pure mobile phase
only. The significant dispersion that occurs with larger charges is clearly
demonstrated.

Courtesy of th Journal of Chromatography (ref. 21)

**Figure 19.
Vacancy Elution Curves from Different Injection Volumes on a Column of 500
Theoretical Plates**

This
theoretical treatment assumes that the presence of a relatively low
concentration of solute in the mobile phase does not influence the retentive
characteristics of the stationary phase. The concentration of solute in the *eluted*
peak does not fall to zero until the sample volume is in excess of 100 plate
volumes and, at this sample volume, the peak width has become about five times
the standard deviation of the normally loaded peak.

Equation (63)
can be extended to provide a general equation for a column equilibrated with
(q) solutes at concentrations X_{1},
X_{2}, X_{3},...X_{q}. For any particular
solute (S), if its normal retention volume is V_{r}_{(S)} on a column containing (n) plates,
then from the plate theory, the plate volume of the column for the solute (S), *i.e*.,
(v_{S}) is given by