Characterization of molecularly imprinted polymers with the Langmuir-Freundlich isotherm

The majority of binding models that have been applied to molecularly imprin ted polymers (MIPs) have been homogeneous models. MIPs' on the other hand, are heterogeneous materials containing binding sites with a wide array of b inding affinities and selectivities. Demonstrated is that the binding behav ior of MIPs can be accurately modeled by the heterogeneous Langmuir-Freundl ich (LF) isotherm. The applicability of the LF isotherm to MIPs was demonst rated using five representative MIPs from the literature, including both ho mogeneous and heterogeneous MIPS. Previously, such comparisons required the use of several different binding models and analyses, including the Langmu ir model, the Freundlich model, and numerical approximation techniques. In contrast, the IF model enabled direct comparisons of the binding characteri stics of MIPs that have very different underlying distributions and were me asured under different conditions. The binding parameters can be calculated directly using the LF fitting coefficients that yield a measure of the tot al number of binding sites, mean binding affinity, and heterogeneity. Alter natively, solution of the Langmuir adsorption integral for the LF model ena bled direct calculation of the corresponding affinity spectrum from the IN fitting coefficients from a simple algebraic expression, yielding a measure of the number of binding sites with respect to association constant. Final ly, the ability of the LF isotherm to model MIPs suggests that a unimodal h eterogeneous distribution is an accurate approximation of the distribution found in homogeneous and heterogeneous MIPs.