Adsorption equilibria of α- and δ-tocopherol from supercritical mixtures of carbon dioxide and 2-propanol onto silica by means of perturbation chromatography

For the determination of adsorption isotherms of dissolved components from supercritical fluids, an experimental equipment has been constructed. It consists of a fluid preparation and two chromatographic units with UV detector and pressure expansion. The equipment allows the performance of peak experiments (injecting samples onto an empty column) as well as perturbation experiments (perturbing the equilibrium in a saturated column). Adsorption isotherms of α- and δ-tocopherol on two unmodified silica gels were determined at a temperature of 313.15 K and pressures of 16.1, 20.0, and 26.1 MPa, respectively. Fluid phase was CO2 with 2-propanol (weight fraction 0.05) as modifier. Parameters of a cubic Hill isotherm were fitted to the data. Ideal adsorbed solution theory (IAST) was applied for prediction of mixture adsorption. Applicability of IAST was tested with perturbation chromatographic experiments using different mixtures. All isotherms show anti-Langmuir behaviour (concave shaped isotherms). These results agree with literature data. Competitive adsorption was successfully predicted by means of the IAS theory.