Experimental study of systm peaks and elution profiles for large concentration bands in the case of a binary eluent containing a strongly sorbed additive

Abstract

Band profiles of high-concentrations samples of single compounds eluted from a silica column by a binary mobile phase were recorded under various sets of experimental conditions. The mobile phase was a dilute solution 0.02–2%, v/v) of lights alkanols in dichloromethane or n-hexane. When the concentration of the strong solvent increases at a constant sample size, or the sample size increases at a constant strong solvent concentration, the elution profile, which is first of the type associated with a Langmuir adsorption isotherm with a sharp front and a slanted tail, changes the direction of its asymmetry and becomes similar in shape to the profiles associated with an anti-Langmuir isotherm, with a slanted front and a sharp tail. The shape of the profiles in the transition range is unusual and appears similar to the composite of two or three different bands. Finally, at large sample sizes and high strong solvent concentrations, the profile develops a hump on its front, which eventually may turn into a second peak. These experimental profiles are in excellent qualitative agreement with those predicted by theory and described in the accompanying paper. Their variations with the experimental parameters follow the trends predicted in that study. The competition between the molecules of the strong solvent (or modifier) and those of the samples is entirely responsible for these profiles.