Adsorption Isotherms and Sites Distribution of Caffeic Acid – Imprinted Polymer Monolith from Frontal Analysis

Abstract

The frontal analysis technique was successfully applied to the determination of the adsorption isotherms of the imprinted polymer monolith prepared by a in-situ synthesis method using caffeic acid as the template, and methacrylic acid, ethyl glycol dimethacrylate and2,2’-azobisisobutyronitrile as the functional monomer, cross-linker and initiator, respectively, with tetrahydrofuran-iso-octane (2:1, ν/ν) as a porogen. Adsorption isotherms of the monolith were measured at 25, 45 and 60°C using tetrahydrofuran containing 1, 3 and 5% acetic acid as mobile phase, respectively. The adsorption capacity of the monolith for the template was found to be much stronger than the other structurally related compounds. The column temperature significantly affected the adsorption capacity of the monolith. The acetic acid in the mobile phase showed some influence on the adsorption of the template on the stationary phase. The adsorption behavior of the template on the monolith is best described by the Freundlich isotherm. From the best coefficients of the Bi-Langmuir fit, the binding constant and saturation capacities of the molecularly imprinted polymer monolith were obtained.