Molecularly Imprinted Polymers with Enhanced Selectivity Based on 4-(Aminomethyl)pyridine-Functionalized Poly(2-oxazoline)s for Detecting Hazardous Herbicide Contaminants

Abstract

The detection of hazardous compounds is of importance to control (drinking) water quality. Here, we report the development of poly(2-oxazoline)-based molecularly imprinted polymers (MIPs) for the detection of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). In view of enhanced selectivity of the MIPs, it was hypothesized that incorporation of pyridine groups would lead to stronger interactions with 2,4,5-T. The synthesis of 4-(aminomethyl)pyridine (4-AMP)-functionalized poly(2-methoxycarbonylpropyl-2-oxazoline)s with various degrees of modification was, therefore, investigated via stoichiometric and kinetic control over the functionalization degree. The molecular imprinting of 2,4,5-T is performed by direct amidation of the methyl ester side chains with diethylenetriamine. The experimental data of 2,4,5-T adsorption were interpreted with various models to quantify the adsorption thermodynamics and kinetics. The best fit was obtained for a single-site Langmuir model, indicating uniform binding site energies. A further investigation shows that the maximum adsorption capacity is reached at low 4-AMP modification degrees, whereas greater adsorption energies and higher selectivities are observed for higher 4-AMP modification degrees. Finally, the developed 4-AMP-modified MIP adsorbents were successfully used for quantification of 2,4,5-T by direct analysis with ambient mass spectrometry. In comparison with the pure analyte solution, the detection limits decreased by three orders of magnitude.