Selective analysis of aristolochic acid I in herbal medicines by dummy molecularly imprinted solid‐phase extraction and HPLC

In this study, surface molecularly imprinted polymers were prepared as the selective sorbents for separation of aristolochic acid I in herbal medicine extracts by a facile approach. A less toxic dummy template, ofloxacin, was used to create specific molecule recognition sites for aristolochic acid I in the synthesized polymers. The polymers were characterized by Fourier‐transfer infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, elemental analysis, and nitrogen adsorption–desorption test. The adsorption capacity was calculated using adsorption kinetics, selectivity, and recycling experiments. The obtained polymers exhibited high thermostability, fast equilibrium time, and excellent binding ability. Subsequently, the polymers applied as the solid‐phase extraction absorbent was proposed and used for the enrichment and analysis of aristolochic acid I in herbal plants. The result showed that the aristolochic acid I was enriched up to 16 times after analysis by using high‐performance liquid chromatography. The good linearity for aristolochic acid I was obtained in the range of 0.1–200 μg/mL (R ² = 0.9987). The recovery and precision values were obtained (64.94–77.73%, RSDs% ≤ 0.8%, n  = 3) at three spiked concentration levels. This work provided a promising method for selective enrichment, extraction, and purification of aristolochic acid I from complex herbal plants.     

One‐step polymerization of hydrophilic ionic liquid imprinted polymer in water for selective separation and detection of levofloxacin from environmental matrices

A novel green hydrophilic levofloxacin imprinted polymer was presented via one‐step polymerization in water using ionic liquid 1,6‐hexa‐3,3′‐bis‐1‐vinylimidazolium bromine with multiple hydrophilic groups and 2‐hydroxyethyl methacrylate as a co‐functional monomer. Adsorption experiment revealed that the ionic liquid significantly improved the water compatible of imprinted polymer, and the excellent recognition of molecularly imprinted polymer for levofloxacin in water corresponds to the synergetic effect of H‐bonding and the electrostatic and π–π interactions between the levofloxacin and co‐functional monomer. Furthermore, the adsorption process of the imprinted material towards levofloxacin fitted the Langmuir model, and the maximum binding amount of levofloxacin onto the imprinted and corresponding non‐imprinted polymer were 16.45 and 6.82 mg/g at 25°C, respectively. After optimizing the parameters affecting solid phase extraction performance, an enrichment and determination system was achieved to separate and detect levofloxacin from water and sediment samples with recoveries that ranged from 83.67 to 101.33% and relative standard deviation of less than 5.59%.     

A new ionic liquid surface‐imprinted polymer for selective solid‐phase‐extraction and determination of sulfonamides in environmental samples

Toward improving the selective adsorption performance of molecularly imprinted polymers in strong polar solvents, in this work, a new ionic liquid functional monomer, 1‐butyl‐3‐vinylimidazolium bromide, was used to synthesize sulfamethoxazole imprinted polymer in methanol. The resulting molecularly imprinted polymer was characterized by Fourier transform infrared spectra and scanning electron microscopy, and the rebinding mechanism of the molecularly imprinted polymer for sulfonamides was studied. A static equilibrium experiment revealed that the as‐obtained molecularly imprinted polymer had higher molecular recognition for sulfonamides (e.g., sulfamethoxazole, sulfamonomethoxine, and sulfadiazine) in methanol; however, its adsorption of interferent (e.g., diphenylamine, metronidazole, 2,4‐dichlorophenol, and m‐dihydroxybenzene) was quite low. ¹H NMR spectroscopy indicated that the excellent recognition performance of the imprinted polymer was based primarily on hydrogen bond, electrostatic and π‐π interactions. Furthermore, the molecularly imprinted polymer can be employed as a solid phase extraction sorbent to effectively extract sulfamethoxazole from a mixed solution. Combined with high‐performance liquid chromatography analysis, a valid molecularly imprinted polymer‐solid phase extraction protocol was established for extraction and detection of trace sulfamethoxazole in spiked soil and sediment samples, and with a recovery that ranged from 93–107%, and a relative standard deviation of lower than 9.7%.     

Polydopamine‐coated magnetic molecularly imprinted polymer for the selective solid‐phase extraction of cinnamic acid,ferulic acid and caffeic acid from radix scrophulariae sample

We describe novel cinnamic acid polydopamine‐coated magnetic imprinted polymers for the simultaneous selective extraction of cinnamic acid, ferulic acid and caffeic acid from radix scrophulariae sample. The novel magnetic imprinted polymers were synthesized by surface imprinting polymerization using magnetic multi‐walled carbon nanotubes as the support material, cinnamic acid as the template and dopamine as the functional monomer. The magnetic imprinted polymers were characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometry. The results revealed that the magnetic imprinted polymers had outstanding magnetic properties, high adsorption capacity, selectivity and fast kinetic binding toward cinnamic acid, ferulic acid and caffeic acid. Coupled with high‐performance liquid chromatography, the extraction conditions of the magnetic imprinted polymers as a magnetic solid‐phase extraction sorbent were investigated in detail. The proposed imprinted magnetic solid phase extraction procedure has been used for the purification and enrichment of cinnamic acid, ferulic acid and caffeic acid successfully from radix scrophulariae extraction sample with recoveries of 92.4–115.0% for cinnamic acid, 89.4–103.0% for ferulic acid and 86.6–96.0% for caffeic acid.     

Isolation of sinapic acid from broccoli using molecularly imprinted polymers

A molecularly imprinted polymer was synthesized for the purpose of sinapic acid isolation from Egyptian nutraceutical Botrytis italica, L. (broccoli) due to its prominent medicinal and wide pharmacological activities. A computational study was first developed to determine the optimal template to functional monomer molar ratio. Based on the computational results, five polymers were synthesized using a bulk polymerization method with sinapic acid as the template molecule. Evaluation of the synthesized polymers binding performance was carried out using batch rebinding assay, which revealed that the molecularly imprinted polymer of molar ratio (1:4:20), template to functional monomer (4‐vinyl pyridine) to crosslinker (ethylene glycol dimethacrylate) was of optimum performance, thus, this polymer was applied for sinapic acid isolation from closely related analogues. This represents a more practical approach to isolate sinapic acid from different natural extracts selectively.     

Preparation of a multi‐hollow magnetic molecularly imprinted polymer for the selective enrichment of indolebutyric acid

A simple strategy was developed for the preparation of multi‐hollow magnetic molecularly imprinted polymers by incorporating 3‐indolebutyric acid and ferroferric oxide nanoparticles simultaneously into a poly(styrene‐co‐methacrylic acid) copolymer matrix. The as prepared absorbents were characterized using scanning electron microscopy, Fourier‐transform infrared spectroscopy and mercury porosimetry. The adsorption isotherms of indolebutyric acid revealed that there are two types of affinity binding sites in the absorbents. The apparent maximum binding capacity and dissociation constant were 17.88 mg/g and 158.7 μg/mL for high‐affinity binding sites and 9.310 mg/g and 35.04 μg/mL for low‐affinity binding sites, respectively. The results testified that multi‐hollow magnetic molecularly imprinted polymers possessed excellent recognition capacity and fast kinetic binding behavior to the objective molecules due to the high specific surface area as large as 511.3 m²/g. Recoveries of 75.5–86.8% were obtained for the indolebutyric acid spiked at three concentration levels in blank and pear samples.     

Preparation of molecularly imprinted polymers based on magnetic nanoparticles for the selective extraction of protocatechuic acid from plant extracts

In this study, highly selective core–shell molecularly imprinted polymers on the surface of magnetic nanoparticles were prepared using protocatechuic acid as the template molecule. The resulting magnetic molecularly imprinted polymers were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and vibrating sample magnetometry. The binding performances of the prepared materials were evaluated by static and selective adsorption. The binding isotherms were obtained for protocatechuic acid and fitted by the Langmuir isotherm model and Freundlich isotherm model. Furthermore, the resulting materials were used as the solid‐phase extraction materials coupled to high‐performance liquid chromatography for the selective extraction and detection of protocatechuic acid from the extracts of Homalomena occulta and Cynomorium songaricum with the recoveries in the range 86.3–102.2%.     

Selective solid‐phase extraction using a molecularly imprinted polymer for the analysis of patulin in apple‐based foods

The aim of this work was to evaluate the use of a molecularly imprinted polymer as a selective solid‐phase extraction sorbent for the clean‐up and pre‐concentration of patulin from apple‐based food products. Ultra high pressure liquid chromatography coupled to ultraviolet absorbance detection was used for the analysis of patulin. The molecularly imprinted polymer was applied, for the first time, to the determination of patulin in apple juice, puree and jam samples spiked within the maximum levels specified by the European Commission No. 1881/2006. High recoveries (>77%) were obtained. The method was validated and found to be linear in the range 2–100 μg/kg with correlation coefficients greater than 0.965 and repeatability relative standard deviation below 11% in all cases. Compared with dispersive solid‐phase extraction (QuEChERS method) and octadecyl sorbent, the molecularly imprinted polymer showed higher recoveries and selectivity for patulin. The application of Affinisep molecularly imprinted polymer as a selective sorbent material for detection of patulin fulfilled the method performance criteria required by the Commission Regulation No. 401/2006, demonstrating the suitability of the technique for the control of patulin at low ppb levels in different apple‐based foods such as juice, puree and jam samples.     

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

Molecularly imprinted polymers of glycyrrhizic acid were prepared by solution polymerization using glycyrrhizic acid as the template molecule, N‐vinypyrrolidone as functional monomer, N ,N‐methylene bisacrylamide as cross‐linker and ascorbic acid and hydrogen peroxide as initiators. Focused on the adsorption capacity and separation degree of the polymer to glycyrrhizic acid, the effects of the monomers, crosslinker and initiators were investigated and optimized. Finally, the structure of the polymer was characterized by using Fourier transform infrared spectroscopy and scanning electron microscopy. To obtain objective results, non‐imprinted molecular polymers prepared under the same conditions were also characterized. The adsorption quantity of the polymer was measured by high‐performance liquid chromatography. Under the optimum conditions, the maximum adsorption capacity of glycyrrhizic acid approached 15 mg/g, and the separation degree was as high as 2.5. The adsorption kinetics could be well described by a pseudo‐first‐order model, while the thermodynamics of the adsorption process could be described by the Langmuir model.     

Surface molecularly imprinted polymers prepared by two‐step precipitation polymerization for the selective extraction of oleanolic acid from grape pomace extract

Surface molecularly imprinted polymers were successfully prepared by a novel two‐step precipitation polymerization method. The first‐step allowed the formation of 4‐vinylpyridine divinylbenzene and trimethylolpropane trimethacrylate copolymeric microspheres. In the second‐step precipitation polymerization, microspheres were modified with a molecularly imprinting layer of oleanolic acid as template, methacrylic acid as functional monomer, and divinylbenzene/ethylene glycol dimethacrylate as cross‐linker. The obtained polymers had an average diameter of 4.43 μm and a polydispersity index of 1.011; adsorption equilibrium was achieved within 40 min, with adsorption capacity reaching 27.4 mg/g. Subsequently, the polymers were successfully applied as the adsorbents of molecularly imprinted solid‐phase extraction to separate and purify the oleanolic acid from grape pomace. The content of oleanolic acid in the grape pomace extract was enhanced from 13.4 to 93.2% after using the molecularly imprinted solid‐phase extraction process. This work provides an efficient way for effective oleanolic acid separation and enrichment from complex matrices, which is especially valuable in industrial production.     

Photocontrolled extraction of uric acid from biological samples based on photoresponsive surface molecularly imprinted polymer microspheres

We aim to develop novel photoresponsive surface molecularly imprinted polymer (SIMP) microspheres, an SiO₂‐SIMP, for the photocontrolled extraction of uric acid from biological samples. The SiO₂‐SMIP was prepared on silica microspheres by surface polymerization and characterized by using scanning electron microscopy, transmission electron microscopy, FTIR spectroscopy, thermogravimetric analysis, nitrogen adsorption–desorption analysis, and UV‐visible spectroscopy. The SiO₂‐SMIP microspheres showed a photocontrolled uptake and release of uric acid in NaH₂PO₄ buffer upon alternate irradiation at 365 and 440 nm. The SiO₂‐SMIP microspheres were able to photocontrollably extract uric acid from complicated biological samples for concentration analysis with no significant interference encountered and it exhibited very good recognition ability and fast binding kinetics toward uric acid.     

Synthesis of molecularly imprinted polymer adsorbents for solid‐phase extraction of strobilurin fungicides from agricultural products

Molecularly imprinted polymers for strobilurin fungicides were prepared by precipitation polymerization employing azoxystrobin as template molecular together with methacrylic acid monomer and trimethylolpropane triacrylate cross‐linker. Morphological characterization showed molecularly imprinted polymers were uniform spherical particles with about 0.2 μm in diameter, while the morphologies of nonimprinted polymers were irregular bulk. The equilibrium binding and selective experiments proved that molecularly imprinted polymers possessed a higher affinity toward four fungicides compared to nonimprinted polymers and heterogeneous binding sites were found in the molecularly imprinted polymers. Molecularly imprinted solid‐phase extraction conditions, including sample loading solvents, selective washing, and elution solvents, were carefully optimized. The developed method showed good recoveries (70.0–114.0%) with relative standard deviations in range of 1.0–9.8% (n  =  3) for samples (cucumber and peach) spiked at three different levels (10, 50, and 100 μg/ kg). The detection limit (signal/noise = 3) ranged from 0.01 to 0.08 μg/kg. The results demonstrated good potential use of this convenient and highly efficient method for determining trace strobilurin fungicides in agricultural products.     

Efficient discovery and capture of new neuronal nitric oxide synthase–postsynaptic density protein‐95 uncouplers from herbal medicines using magnetic molecularly imprinted polymers as artificial antibodies

In the scope of stroke treatment, new neuronal nitric oxide synthase–postsynaptic density protein‐95 uncouplers from herbal medicines were discovered and captured. To do so, highly selective magnetic molecularly imprinted polymers with a core–shell structure were prepared as artificial antibodies. According to the results of computational simulations, we designed and synthesized various polymers with varying amounts and types of template, functional monomer, cross‐linker, and solvent. Characterization and performance tests revealed that the most appropriate artificial antibodies showed uniform spherical morphologies, large adsorption capacities, fast‐binding kinetics, high selectivity, and quick separation. These artificial antibodies were then used as sorbents for dispersive magnetic solid‐phase extraction coupled with high‐performance liquid chromatography and mass spectrometry to capture and identify structural analogs to ZL006 from extracts of Scutellariae radix, Psoraleae fructus, and Trifolium pratense. Furthermore, according to the neuroprotective effect and coimmunoprecipitation test, Baicalein, Neobavaisoflavone, Corylifol A, and Biochanin A can be the potential uncouplers of neuronal nitric oxide synthase–postsynaptic density protein‐95. Therefore, this present study contributes valuable information for the discovery of neuronal nitric oxide synthase–postsynaptic density protein‐95 uncouplers from herbal medicines.     

Simultaneous determination of levofloxacin and ciprofloxacin in human urine by ionic‐liquid‐based,dual‐template molecularly imprinted coated graphene oxide monolithic solid‐phase extraction

A novel method was developed to simultaneously determine the ciprofloxacin and levofloxacin levels in human urine using an ionic‐liquid‐based, dual‐molecularly imprinted polymer‐coated graphene oxide solid‐phase extraction monolithic column coupled with high‐performance liquid chromatography. The molecularly imprinted monolithic column was prepared using ciprofloxacin and levofloxacin as templates, 1‐vinyl‐3‐ethylimidazolium bromide as the functional monomer, and graphene oxide as the core material. The resulting imprinted monoliths were characterized by scanning electron microscopy and fourier transform‐infrared spectroscopy. The efficiency and capacity of the ionic‐liquid‐based imprinted monolithic column were investigated by varying the synthesis conditions (ciprofloxacin/levofloxacin ratio and template/functional monomer/cross‐linker ratio). The solid‐phase extraction process was optimized by changing the washing and eluting conditions. The results suggested that the proposed ionic‐liquid‐based molecularly imprinted solid‐phase extraction monolithic‐high‐performance liquid chromatography method could separate ciprofloxacin and levofloxacin efficiently and simultaneously from human urine. The mean recoveries of ciprofloxacin and levofloxacin ranged from 89.2 to 93.8 and 86.7 to 94.6%, respectively. The intra‐ and interday relative standard deviation ranged from 0.9 to 3.2 and 0.8 to 2.9%, respectively. Under the optimized conditions, the recoveries of ciprofloxacin and levofloxacin were more than 93.8%.     

Molecularly imprinted polymer coating on metal‐organic frameworks for solid‐phase extraction of fluoroquinolones from water

In this work, a novel surface molecularly imprinted polymer with high adsorption capacity, high adsorption rate, and high selectivity for fluoroquinolones was prepared on the surface of UiO‐66‐NH₂, which is a kind of metal‐organic framework. The surface morphology and adsorption properties of this molecularly imprinted polymer were investigated. The maximum adsorption capacity was 99.19 mg/g, and adsorption equilibrium was achieved within 65 s. Combined with reversed‐phase high‐performance liquid chromatography, the molecularly imprinted polymer was used to selectively enrich, separate and analyze fluoroquinolones present in lake water. The results showed that the recoveries of the four fluoroquinolones were 92.6–100.5%, and the relative standard deviations were 2.9–6.4% (n = 3). The novel molecularly imprinted polymer is an excellent adsorbent and has broad application prospects in the enrichment and separation of trace analytes in complex samples.     

Preparation of bio‐based keratin‐derived magnetic molecularly imprinted polymer nanoparticles for the facile and selective separation of bisphenol A from water

In this study, new bio‐based magnetic molecularly imprinted polymer nanoparticles (∼23 nm) were synthesized from keratin extracted from chicken feathers and methacrylate‐functionalized Fe₃O₄ nanoparticles for its potential application in separation and removal of bisphenol A from water. The prepared magnetic molecularly imprinted polymer was characterized by Fourier‐transform infrared spectroscopy, field‐emission scanning electron microscopy, thermogravimetric analysis, alternative gradient field magnetometry, and energy‐dispersive X‐ray spectroscopy. The sorption of bisphenol A was investigated by changing the influencing factors such as pH, immersion time, Fe₃O₄ nanoparticles dosage, and the initial concentration of bisphenol A. Results illustrated that sorption was very fast and efficient (Q_m = 600 mg/g) having a removal efficiency of ∼98% in 40 min of immersion. The adsorption process showed better conformity with the Weber−Morris kinetics and the Freundlich isotherm model. The selectivity of bisphenol A by adsorbent was checked in the presence of hydroquinone, phenol, tetrabromobisphenol, and 4,4′‐biphenol as interferences.     

Rapid measurements of curcumin from complex samples coupled with magnetic biocompatibility molecularly imprinted polymer using electrochemical detection

Curcumin widely exists in food, and rapid selective and accurate detection of curcumin have great significance in chemical industry. In this experiment, a new magnetic biocompatibility molecularly imprinted polymer was prepared with nontoxic and biocompatible Zein to adsorb curcumin selectively. The polymer has high biocompatibility, good adsorption capacity, and specific adsorption for curcumin. Combined with portable electrochemical workstations, the polymer can be used to detect curcumin rapidly and cost‐effectively. Using curcumin as a template and Zein as the crosslinking agent, the polymers were synthesized on the surface of Fe₃O₄ particles for solid phase extraction. The experimental results showed that the polymer reached large adsorption capacity (32.12 mg/g) with fast kinetics (20 min). The adsorption characteristic of the polymer followed the Langmuir isotherm and pseudo‐second‐order kinetic models. Hexacyanoferrate was used as electrochemical probe to generate signals, and the linear range was 5–200 µg/mL for measuring curcumin. The experimental analysis showed that the polymer was an ideal material for selective accumulation of curcumin from complex samples. This approach has been successfully applied to the determination of curcumin in food samples with electrochemical detection, indicating that this is a feasible and practical technique.     

Molecularly imprinted polymer solid‐phase microextraction coupled with ultra high performance liquid chromatography and tandem mass spectrometry for rapid analysis of pyrrolizidine alkaloids in herbal medicine

Pyrrolizidine alkaloids are the most widely distributed natural toxins, and pyrrolizidine alkaloid‐containing herbal medicines are probably the most common poisonous plants affecting humans. We reported pyrrolizidine alkaloid‐molecularly imprinted polymer solid‐phase microextraction for the selective adsorption of toxic pyrrolizidine alkaloids from herbal medicine. A sulfonic compound, sodium allylsulfonate, was chosen as the functional monomer to interact with pyrrolizidine alkaloids through strong ionic interaction. To avoid template leakage and for the aim of cost saving, a relatively cheap dummy template was used for the fabrication of molecularly imprinted polymer‐solid‐phase microextraction fibers. The obtained fibers showed selective adsorption ability for four pyrrolizidine alkaloids, including europine, echimidine, lasiocarpine, and heliotrine. The extraction parameters, such as extraction time, extraction temperature, shaking speed, elution solvent and elution time, were optimized. Then ultra high performance liquid chromatography with mass spectrometry coupled with molecularly imprinted polymer‐solid‐phase microextraction method was developed for the fast and efficient analysis of four pyrrolizidine alkaloids from the model herbal plant Farfarae Flos. The established method was validated and exhibited satisfactory accuracy and precision. The present method provides an innovative and fast analytical strategy for the determination of trace toxic pyrrolizidine alkaloids in complicated samples.     

Ultratrace analysis of uracil and 5‐fluorouracil by molecularly imprinted polymer brushes grafted to silylated solid‐phase microextraction fiber in combination with complementary molecularly imprinted polymer‐based sensor

Main inborn errors of metabolism diagnosable through uracil (Ura) analysis and the therapeutic monitoring of toxic 5‐fluorouracil (5FU) in dihydro pyrimidine dehydrogenase (DPD) deficient patients require a sensitive, reproducible, selective and accurate method. In this work, an artificial receptor in the format of molecularly imprinted polymer (MIP) brush ‘grafted to’ the surface of sol–gel immobilized on cost‐effective homemade solid‐phase microextraction (SPME) fibers, individually imprinted with either of Ura and 5FU, was used in combination with a voltammetric sensor duly modified with the same MIP. This combination provided up to 10‐ and 8.4‐fold preconcentrations of Ura and 5FU, respectively, which was more than sufficient for achieving stringent detection limits in the primitive diagnosis of uracil disorders and fluoropyrimidine toxicity in DPD‐deficient patients. The proposed method permits the assessment of Ura and 5FU plasma concentrations with detection limits pf 0.0245 and 0.0484 ng mL^?1 (RSD = 1.0–2.5%, S/N = 3), respectively, without any problems of non‐specific false‐positives and cross‐reactivities in complicated matrices of biological samples. Copyright © 2008 John Wiley & Sons, Ltd.