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 Xi>X0 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 X1, X2, X3,...Xq. For any particular solute (S), if its normal retention volume is Vr(S) on a column containing (n) plates, then from the plate theory, the plate volume of the column for the solute (S), i.e., (vS) is given by