The ideal chromatographic peak has a Gaussian profile, which occurs if the solute’s partition coefficient, KD, between the stationary phase and mobile phase
KD = [S]s/[S]m
is independent of the solute’s concentration. If this is not the case, then the chromatographic peak has an asymmetric peak shape similar to those shown in here.
The chromatographic peak in (a) is an example of tailing, which occurs when some sites on the stationary phase retain the solute more strongly than other sites. The peak in (b) is an example of fronting, which most often is the result of overloading the column with sample. For both (a) and (b) the green chromatogram is the asymmetric peak and the red dashed chromatogram shows the ideal, Gaussian peak shape. The insets show the relationship between the concentration of solute in the stationary phase, [S]s, and its concentration in the mobile phase, [S]m. The dashed red lines are for ideal behavior (KD is constant for all conditions) and the green lines show nonideal behavior (KD decreases or increases for higher total concentrations of solute). A quantitative measure of peak tailing, T, is shown in (a).