A new method for determination of adsorption isotherms based on nonlinear frequency response : Experimental identification

A concept of higher-order frequency response functions (FRFs) based on Volterra series and generalized Fourier transform is used for the analysis of the nonlinear frequency response functions of a chromatographic column [1,2]. The derivatives of the adsorption isotherm can be estimated from the low frequency asymptotes of corresponding FRFs. The adsorption of ethyl benzoate and 4-tert-butylphenol as single solutes was studied on Octadecyl Silica (C18) using methanol and water (60:40, v/v) as the solvent. Simulations of the response of a chromatographic column were performed for inlet concentration changes in sine wave form. In the experiments, sine wave form was approximated with stair case function. The experiments were performed using a standard HPLC system, which enables periodic changes of the feed concentration at the inlet of a column filled with the C18 durig the experiment. The amplitude that gives the best agreement between the reference [3] and the estimated coefficients is selected based on simulations. Simulated and experimental results will be presented, as well as the explanation of the experimental procedure. References: [1] Petkovska M. and Seidel-Morgenstern A., Nonlinear frequency response of a chromatographic column. Part I: Application to estimation of adsorption isotherms with inflection point, Chemical Engineering Communications (2005), in print [2] Petkovska M., Zivkovic V., Kaufmann J. and Seidel-Morgenstern A., Estimation of Adsorption Isotherms Using Nonlinear Frequency Response of a Chromatographic Column - Experimental Study, 2003 AIChE Annual Meeting, San Francisco, CA, 16-21 Nov. 2003, Paper 329h, Proceedings on CD [3] Gritti F. and Guiochon G., Band splitting in overloaded isocratic elution chromatography II. New competitive adsorption isotherms, Journal of Chromatography A, 1008 (2003) 23-4