Effect of polar interactions on the nonlinear behavior of phenol and aniline in reversed phase liquid chromatography

The effect of the coverage density and the activity of the unreacted silanol groups of the non-endcapped octadecyl bonded phase on the adsorption properties were investigated. The adsorption of two polar low molecular weight compounds with weak acidic (phenol) and with basic (aniline) character was measured. Adsorption data were acquired by frontal analysis from methanol-water and acetonitrile-water solutions to investigate the influence of the type of the organic modifier on the solute retention mechanism and adsorption under non-linear conditions. The adsorption behavior of phenol changes from Langmuir type (from aqueous mixture of methanol) to BET type (from aqueous mixture of acetonitrile). The adsorption of aniline becomes BET-type, regardless of the mobile phase composition in the tested range of the surface coverage of octadecyl ligands. The nature of the organic modifier significantly affects the retention mechanism and the shape of the overloaded elution bands of the studied compounds.