Estimation of competitive adsorption isotherms based on nonlinear frequency response experiments using equimolar mixtures–numerical analysis for racemic mixtures

The nonlinear frequency response method for estimation of competitive adsorption isotherms, based on analysis of the response of a chromatographic column to sinusoidal perturbation of the inlet concentration, was modified in such a way to require experimentation with only 50:50 inlet mixtures, thus making it applicable for racemic mixtures of enantiomers. The applicability of the modified method was checked based on numerical experiments. The equilibrium dispersive model of the chromatographic column was used, with competitive Langmuir isotherm, and the frequency responses were simulated for 3 different steady-state points, 4 different input amplitudes and a number of input frequencies. It was proven that estimation of competitive adsorption isotherms from nonlinear frequency response experiments with equimolar inlet mixtures is feasible. ► A modification of the Nonlinear Frequency Response method for estimation of competitive adsorption isotherms is given. ► Only equimolar mixtures are needed for experimentation. ► Convenient for estimation of competitive isotherms of enantiomers, when only racemic mixtures are available for experimentation. ► The modified method was checked using numerical experiments. ► Very good agreement of the estimated isotherms with the original ones was obtained.