Plate Theory and Extensions - Vacancy Chromatography > Page 71
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 (X_{o}), then, after equilibrium, the eluent from the column will also contain the solute at a concentration (X_{o}). Let a sample containing the same solute at a concentration (X_{i}) be injected onto the column under where either (X_{o}<X_{i}) or (X_{o}>X_{i}),but (X_{o}X_{i}). Such an injection will produce a transient change in the concentration (X_{o}) 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 X_{i }= 0 and