Preparation and characterization of a novel molecularly imprinted polymer for the separation of glycyrrhizic acid

Theoretical and experimental proof for selective response of imprinted sorbent - analysis of hordenine in human urine

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 K_d (2.75 and 370 μmol L^-1) and two values of B_max (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 (ΔE_B1 = -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.

Ordered macroporous molecularly imprinted polymers prepared by a surface imprinting method and their applications to the direct extraction of flavonoids from Gingko leaves

In this work, to improve the availability of the recognition sites of molecularly imprinted polymers (MIPs), ordered macroporous molecularly imprinted polymers (OMMIPs) were facilely prepared by grafting a quercetin-MIPs layer on the pore walls of the ordered macroporous thiol group functionalized silica. The pore structures were characterized by FTIR, Raman, SEM, BET and TGA measurements. The results indicated that OMMIPs possessed a nanoscale polymer layer, a more regular macroporous structure and a greater porosity compared with the traditional bulk MIPs (TBMIPs). The polymer content of OMMIPs was about 49.7%. Kinetic and isothermal adsorption experiments indicated that OMMIPs exhibited higher affinity and selectivity towards quercetin than its structural analogues. Moreover, OMMIPs could improve the intra-particle adsorption and thus provide a significant improvement in recognition sites availability over TBMIPs. Using the quercetin-OMMIPs as SPE sorbent, quercetin was directly extracted from the crude Gingko leaves extract with a satisfying selectivity and elution recovery.

Design of selective molecularly imprinted sorbent for the optimized solid-phase extraction of S-pramipexole from the model multicomponent sample of human urine

The objective of this article was to design the selective molecularly imprinted sorbent dedicated to the solid-phase extraction of S-pramipexole from the complex matrix such as human urine. For that purpose, S-2,6-diamino-4,5,6,7-tetrahydrobenzothiazole was used as the template acting as the structural analog of S-pramipexole and five various monomers were employed in the presence of ethylene glycol dimethacrylate to produce molecularly imprinted polymers. The binding capabilities of resulted polymers revealed that the highest imprinting effect was noted for polymer prepared from the itaconic acid. The comprehensive analysis of morphology and the characterization of binding sites showed not only negligible differences in the extension of surfaces of imprinted and nonimprinted polymers but also higher heterogeneity of binding sites in the imprinted material. Comprehensive optimization of the molecularly imprinted solid-phase extraction allowed to select the most appropriate solvents for loading, washing, and elution steps. Subsequent optimization of mass of sorbent and volumes of solvents allowed to achieve satisfactory total recoveries of S-pramipexole from the model multicomponent real sample of human urine that equals to 91.8 ± 3.2% for imprinted sorbent with comparison to only 37.1 ± 1.1% for Oasis MCX.

Molecularly imprinted covalent organic polymers for the selective extraction of benzoxazole fluorescent whitening agents from food samples

Molecularly imprinted covalent organic polymers were constructed by an imine-linking reaction between 1,3,5-triformylphloroglucinol and 2,6-diaminopyridine and used for the selective solid-phase extraction of benzoxazole fluorescent whitening agents from food samples. Binding experiments showed that imprinting sites on molecularly imprinted polymers had higher selectivity for targets compared with those of the corresponding non-imprinted polymers. Parameters affecting the solid-phase extraction procedure were examined. Under optimal conditions, actual samples were treated and the eluent was analyzed with high-performance liquid chromatography with diode-array detection. The results showed that the established method has a wide linearity, satisfactory detection limits and quantification limits, and acceptable recoveries. Thus, this developed method possesses the practical potential for the selective determination of benzoxazole fluorescent whitening agents in complex food samples.

Preparation and evaluation of temperature and magnetic dual-responsive molecularly imprinted polymers for the specific enrichment of formononetin

Thermo-responsive magnetic molecularly imprinted polymers were prepared by simple surface molecular imprinting polymerization for the selective adsorption and enrichment of formononetin from Trifolium pretense by temperature regulation. Using formononetin as a template, N-isopropylacrylamide as the thermo-responsive functional monomer, and methacrylic acid as an assisting functional monomer, the polymers were synthesized on the surface of the magnetic substrate. The results show that imprinted polymers attained controlled adsorption of formononetin in response to the temperature change, with large adsorption capacity (16.43 mg/g), fast kinetics (60 min) and good selectivity at 35°C compared with that at 25 and 45°C. The selectivity experiment indicated that the materials had excellent recognition ability for formononetin and the selectivity factors were between 1.32 and 2.98 towards genistein and daidzein. The excellent linearity was attained in the range of 5-100 μg/mL, with low detection limits and low quantitation limits of 0.017 and 0.063 μg/mL, respectively. Furthermore, the thermo-responsive magnetic molecularly imprinted polymers were successfully utilized for enriching and purifying formononetin from Trifolium pretense. The analytical results indicate that the imprinted polymers are promising materials for selective identification and enrichment of formononetin in complicated herbal medicines by simple temperature-responsive regulation.