Adsorption of aqueous organic mixtures on a chiral stationary phase with bound antibiotic eremomycin

The adsorption of two typical hydro-organic mobile phases, with methanol and acetonitrile as the organic component, on an antibiotic based chiral stationary phase (CSP) Nautilus-E was studied by the minor perturbation method. In both cases, the excess adsorption of water was positive over a wide range of concentrations from 0 to ∼75 or 90 mol% for MeOH or MeCN containing mobile phases, respectively. Such hydrophilic properties of the CSP were attributed to multiple polar functional groups of the chiral ligand and to the residual silanol groups of the silica support. The adsorbed phase was found to be thinner for H2O-MeOH (∼1.1 Å) and thicker for H2O-MeCN (∼9.4 Å). The measurements of the column hold-up volume by different methods allowed us to suggest a model of the adsorbed phase consisting of the volume between bound chiral selectors inaccessible to large size molecules and of the stagnant layer of the mobile phase adsorbed on the external surface of the chiral selectors.