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キーワード:
Adsorption isotherms; Liquid chromatography; Nonlinear frequency response; Harmonic analysis; Higher-order frequency response functions; Parameter estimation
要旨:
The aim of this paper is to investigate the possibility of applying a nonlinear frequency response method described by Ilić et al. (2007b) to determine single solute adsorption isotherms. The method is based on the analysis of the nonlinear frequency response of a chromatographic column to a periodical change of the inlet concentration around several steady-state concentrations. The first, second and third local derivatives of single solute isotherms are estimated from the low frequency asymptotic behaviour of the corresponding frequency response functions. The adsorption of 4-tert-butylphenol and ethyl benzoate as single solutes is studied on octadecyl silica (C18) from methanol-water mixture (60:40). Experiments are performed using a standard gradient HPLC unit capable to realize inlet concentration changes in a nearly sine waveform. Small injections of compounds into the not preloaded column, as well as conventional frontal analysis experiments are performed for rough estimation of the adsorption isotherm coefficients and comparison with the results obtained using the nonlinear frequency response method.
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