The objective of this paper was to extend comprehensive theoretical and experimental investigations at the molecular level to identify factors responsible for the high selectivity of imprinted sorbents. This knowledge was utilized in a new analytical strategy devoted to the analysis of hordenine in human urine after beer consumption. Among the various polymeric compositions tested, the most effective material was built up from methacrylic acid and ethylene glycol dimethacrylate (MIP1), showing a satisfactory binding capacity (4.44 ± 0.15 µmol g-1) and high specificity towards hordenine (AF = 5.90). The comprehensive analyses of porosity data and surface measurements revealed differences between imprinted polymers. The characterization of binding sites of MIP1 revealed a heterogeneous population with two values of Kd (2.75 and 370 μmol L-1) and two values of Bmax (1.82 and 99 μmol g-1) for higher and lower affinity respectively. The extensive theoretical analyses of interactions between various analytes and the MIP model cavity showed the highest binding energy for hordenine (ΔEB1 = -175.17 kcal mol-1). The method was validated for selectivity, lowest limit of quantification, calibration curve performance, precision, accuracy, matrix effect, carry-over and stability in urine. Extracts were prepared according to guidelines of the European Medicines Agency. The validation criteria were fulfilled, and the method was satisfactorily applied to urine samples collected prior to, and 2 h after, consumption of 2 L of beer, revealing the presence of hordenine at the mean level of 129 ± 27 ng mL-1. Additionally, ability of the sorbent to purify the urine sample was assessed using flow injection analysis tandem mass spectrometry, for comparison with other extraction techniques.
Keywords: Beer marker; Hordenine; Human urine; Molecular modelling; Molecularly imprinted polymers; Solid phase extraction.
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