Clean up of phenylurea herbicides in plant sample extracts using molecularly imprinted polymers

Two different molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using linuron or isoproturon (phenylurea herbicides) as templates and trifluormethacrylic acid as functional monomer. These materials were used as selective sorbents in the development of molecularly imprinted solid-phase extraction (MISPE) procedures for the determination of several phenylurea herbicides (fenuron, metoxuron, chlortoluron, isoproturon, metobromuron, and linuron) in plant samples extracts. The MISPE procedures were fully optimized and applied to the clean up of selected phenylurea herbicides in carrot, potato, corn, and pea sample extracts and finally determined by HPLC-UV at 244 nm. Although a high degree of clean up was obtained, a decrease of the MIP recognition capabilities was observed in subsequent runs. Thus, a previous clean up protocol based on the use of a non-imprinted polymer was used to prevent the loss of MIP performance and to ease the removal of interferences. Following this procedure, namely two-step MISPE, matrix compounds were almost completely removed by the non-imprinted polymer retaining the ability of MIPs to selectively rebind target analytes unaltered. The developed MISPE procedures allowed the screening of phenylurea herbicides in plant samples at concentration levels required by established European maximum residue limits.     

Development and characterisation of a molecularly imprinted polymer prepared by precipitation polymerisation for the determination of phenylurea herbicides

New materials based on molecularly imprinted polymers (MIPs) have been developed for use as sorbents in solid phase extraction to preconcentrate some urea herbicides. In the preconcentration step, different molecularly imprinted polymers were tested using methacrylic acid (MAA) and 2-(trifluoromethyl)acrylic acid (TFMAA) as functional monomers, and linuron and isoproturon as templates. The best results were obtained when the polymer was synthesised using MAA with isoproturon as template. Another parameter evaluated was the way in which the polymer was obtained. We observed that the imprinted polymers obtained by precipitation displayed a greater capacity to retain the phenylureas. Studies conducted using scanning electron microscopy (SEM) revealed that the bulk polymerisation method is far from ideal owing to the random shape and size distribution of the particles obtained, whereas when polymerisation was carried out in precipitation microspheres were obtained. In order to confirm the interaction between the functional monomer and the template, 1H NMR (CD2Cl2) analyses were conducted. The results obtained suggest that the hydrogen and/or nitrogen of the amino group of the template would be involved in the formation of hydrogen bonds with the functional monomer. The imprinted polymer obtained by precipitation polymerisation with MAA as functional monomer and isoproturon as template can be applied to preconcentrate phenylureas when the sample is dissolved in toluene. The proposed methodology was employed to evaluate polymer selectivity towards humic acids and towards other herbicides.     

Highly selective fenuron-imprinted polymer with a homogeneous binding site distribution prepared by precipitation polymerisation and its application to the clean-up of fenuron in plant samples

In the present study, two different imprinted polymers were synthesised by precipitation polymerisation using methacrylic acid (MAA) or 4-vinylpyridine (VP) as monomer and fenuron (FEN, a phenylurea herbicide) as template. After template removal, their ability to recognise fenuron was evaluated and the optimum loading, washing and elution conditions were established. From this study, it was concluded that imprinted binding sites were not formed in the vinylpyridine-based polymer. However, methacrylic acid-based polymer was able to recognise fenuron with high affinity and to selectively retain it from a mixture of several phenylurea herbicides. In addition, different rebinding experiments were carried out and the experimental binding isotherms were fitted to the Langmuir-Freundlich (LF) isotherm in order to assess the binding site distribution. It was concluded that the methacrylic acid-based polymer possesses a homogeneous binding site distribution and permits to achieve quantitative recoveries in a wide concentration range in molecularly imprinted solid-phase extraction (MISPE) processes. The developed MISPE procedure using methacrylic acid-based polymeric micro-spheres was evaluated for the trace-enrichment and clean-up of fenuron from plant sample extracts.     

Synthesis by precipitation polymerisation of molecularly imprinted polymer microspheres for the selective extraction of carbamazepine and oxcarbazepine from human urine

Two molecularly imprinted polymers (MIPs), in the physical form of well-defined polymer microspheres, were synthesised via precipitation polymerisation (PP) using an antiepileptic drug, carbamazepine (CBZ), as template molecule, methacrylic acid as functional monomer and either divinylbenzene 80 (DVB-80) or a mixture of DVB-80 and ethylene glycol dimethacrylate (EGDMA) as crosslinking agents. The MIP obtained using DVB-80 alone as crosslinking agent (MIP A) had a narrow particle size distribution (9.5 ± 0.5 μm) and a well-developed permanent pore structure (specific surface area in the dry state = 758 m² g⁻¹), whereas when a mixture of DVB-80 and EGDMA (MIP B) were used as crosslinking agents, the polymer obtained had a broader particle size distribution (6.4 ± 1.8 μm) and a relatively low specific surface area (23 m² g⁻¹). The molecular recognition character of both polymers was evaluated by means of LC and then a molecularly imprinted solid-phase extraction (MISPE) protocol; CBZ was recognised by both polymers, and useful cross-selectivity for oxcarbazepine (OCBZ), which is the main metabolite of CBZ, also observed. In a detailed bioanalytical study, MIP A was selected in preference to MIP B since MIP A enabled a high volume of sample to be extracted such that lower limits of detection were achievable using this polymer. High recoveries of CBZ and OCBZ were obtained in a MISPE protocol when 50 mL of human urine spiked at 0.2 mg L⁻¹ were percolated through MIP A (90% and 83%, respectively).     

Preparation of high selective molecularly imprinted polymers for tetracycline by precipitation polymerization

High selective molecularly imprinted polymers(MIPs) for tetracycline have been prepared by precipitation polymerization. Effects of monomer and solvent,the ratio of monomer and template and the characterization of the polymer were investigated by frontal chromatography and selectivity experiment.The results clearly indicated that the polymer,which had the highest molecular recognition abilities for tetracycline antibiotics,had been received.     

Evaluation of 2-hydroxyethyl methacrylate as comonomer in the preparation of water-compatible molecularly imprinted polymers for triazinic herbicides

In this work, the preparation and evaluation of water-compatible molecularly imprinted polymers for triazines using 2-hydroxyethyl methacrylate and methacrylic acid as comonomers is described. Four sets of molecularly imprinted and non-imprinted polymers for propazine were prepared at varying monomer molar ratios (from 4:0 to 1:3), and evaluated for the recognition of several triazines directly in aqueous media. The evaluation was performed by loading 1 mL of an aqueous solution containing 500 ng of each selected triazine, washing with 500 μL of acetonitrile, and eluting with 500 μL of methanol followed by 2 × 500 μL of a solution of methanol containing 10% of acetic acid. Final determinations were performed by high-performance liquid chromatography-ultraviolet detection. Improvement in molecular recognition of triazines in water was obtained on those molecularly imprinted polymers incorporating 2-hydroxyethyl methacrylate in 3:1 or 2:2 molar ratios, being the former selected as optimum providing recoveries for propazine up to 80%. A molecularly imprinted solid-phase extraction protocol was developed to ensure that triazines-selective recognition takes place inside selective binding sites in pure water media. Finally, the developed method was successfully applied to the determination of the selected triazines in environmental waters providing limits of detection from 0.16 and the 0.5 μg/L concentration range.     

Solid-phase extraction using molecularly imprinted polymers for selective extraction of a mycotoxin in cereals

The aim of this work was to develop a method for the clean-up of a mycotoxin, i.e. Ochratoxin A (OTA), from cereal extracts employing a new molecularly imprinted polymer (MIP) as selective sorbent for solid-phase extraction (SPE) and to compare with an immunoaffinity column. A first series of experiments was carried out in pure solvents to estimate the potential of the imprinted sorbent in terms of selectivity studying the retention of OTA on the MIP and on a non-imprinted polymer using conventional crushed monolith. The selectivity of the MIP was also checked by its application to wheat extracts. Then, after this feasibility study, two different formats of MIP: crushed monolith and micro-beads were evaluated and compared. Therefore an optimization procedure was applied to the selective extraction from wheat using the MIP beads. The whole procedure was validated by applying it to wheat extract spiked by OTA at different concentration levels and then to a certified contaminated wheat sample. Recoveries close to 100% were obtained. The high selectivity brought by the MIP was compared to the selectivity by an immunoaffinity cartridge for the clean-up of the same wheat sample. The study of capacity of both showed a significant higher capacity of the MIP.     

Preparation of highly selective solid-phase extractants for Cibacron reactive dyes using molecularly imprinted polymers

Selective polymeric extractants were prepared for preconcentration of Cibacron reactive red dye, a dye that is often applied with Cibacron reactive blue and Cibacron reactive yellow for dyeing of fabrics. The best extractant was fabricated (in chloroform) using methacrylic acid (as monomer), ethylene glycol dimethacrylate (as crosslinker), AIBN (as initiator for polymerization), and red dye as template molecule, with a molar stoichiometric ratio of 8.0:40.0:2.5:0.63, respectively. The structure of the molecularly imprinted polymer (MIP) was robust, and resisted dissolution up to 260 °C. Compared with the un-imprinted polymer, the imprinted product has a large specific surface area which improved its adsorption capacity. The effect of imprinting was obvious from the adsorption capacity measured at pH 4 for red dye (the imprinted molecule), which was increased from 24.0 to 79.3 mg g⁻¹ after imprinting. Equilibrium adsorption studies revealed that the dye-imprinted-polymer enables efficient extraction of red dye even in the presence of blue and yellow dyes which have similar chemical natures to the red dye. The selectivity coefficients S _{red dye/dye}, were 13.9 and 17.1 relative to the yellow and blue dyes, respectively. The MIP was found to be effective for red dye preconcentration, with a preconcentration factor of 100, from tap water and treated textile wastewater. The factors affecting extraction of red dye by the MIP were studied and optimized. Under the optimized extraction conditions, red dye was selectively quantified in the presence of other competing dyes at a concentration of 20 μg L⁻¹ from different water systems with satisfactory recoveries (91–95%) and RSD values (∼5.0%).     

Development and application of molecularly imprinted polymers as solid-phase sorbents for erythromycin extraction

Six molecularly imprinted polymers (MIPs) of erythromycin (ERY) were prepared by noncovalent bulk polymerization using methacrylic acid (MAA) as the functional monomer. On the basis of binding analysis, the MIPs with 1:2 optimum ratio of template to MAA were selected for subsequent scanning electron microscopy and Brunauer–Emmett–Teller analyses, which indicated that the MIPs had more convergent porous structures than the nonimprinted polymers. The equilibrium binding experiments showed that the binding sites of MIPs were heterogeneous, with two dissociation constants of 0.005 and 0.63 mg mL⁻¹, respectively. Furthermore, the performance of the MIPs as solid-phase extraction (SPE) sorbents was evaluated, and the selectivity analysis showed that the MIPs could recognize ERY with moderate cross-reactivity for other macrolides. The overall investigation of molecularly imprinted SPE for cleanup and enrichment of the ERY in pig muscle and tap water confirmed the feasibility of utilizing the MIPs obtained as specific SPE sorbents for ERY extraction in real samples. Figure Schematic diagram of the preparation and application of the erythromycin imprinted molecularly imprinted polymers Suquan Song and Aibo Wu contributed equally to this work.     

On-line molecularly imprinted solid-phase extraction for the selective spectrophotometric determination of nicotine in the urine of smokers

This work describes an on-line molecularly imprinted solid-phase extraction (MISPE) method for spectrophotometric determination of nicotine in urine samples of smokers. This method is based on manganese (VII) to manganese (VI) reduction in an alkaline medium, promoted by nicotine. Two wash solutions (1:4 (v/v) acetonitrile:sodium hydroxide - pH 11.4, and nitric acid - pH 2.5) were employed to circumvent interferences. Aqueous solutions containing nicotine plus different possible concomitants (cotinine, anabasine, norcotinine and caffeine) were tested individually. The analytical calibration curve was prepared in urine samples collected from non-smokers and spiked with nicotine standard from 1.1 to 60 μmol L⁻¹ (r² > 0.998). The limit of quantification and the analytical frequency were 1.1 μmol L⁻¹ and 11 h⁻¹, respectively. The precision, evaluated using 3, 10 and 30 μmol L⁻¹ nicotine in urine, was 10, 10 and 4% (intra-day precision) and 12, 13 and 5% (inter-day precision), respectively. Accuracy was checked through high performance liquid chromatography and the results did not present significant differences at the 95% confidence level according to the Student's t-test.     

选择性提取单取代磺酰脲除草剂的印迹聚合物的合成及评价

以丙烯酰胺为功能单体合成了新型的单嘧磺隆印迹聚合物,用平衡吸附及液相色谱的方法研究了印迹聚合物对于印迹分子及其结构类似化合物NK#94827的识别特性及亲和能力.研究结果表明,以丙烯酰胺为功能单体得到的印迹聚合物对NK#94827具有较强的识别能力;为印迹聚合物应用于环境样品中NK#94827及其结构类似化合物的分析打下了基础.     

A new molecularly imprinted polymer for selective extraction of cotinine from urine samples by solid-phase extraction

Cotinine, the main metabolite of nicotine in human body, is widely used as a biomarker for assessment of direct or passive exposure to tobacco smoke. A method for molecularly imprinted solid-phase extraction (MISPE) of cotinine from human urine has been investigated. The molecularly imprinted polymer (MIP) with good selectivity and affinity for cotinine was synthesized using cotinine as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linker. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with aqueous standards, by comparing recovery data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from the aqueous solutions resulted in more than 80% recovery. A range of linearity for cotinine between 0.05 and 5 μg mL⁻¹ was obtained by loading 1 mL blank urine samples spiked with cotinine at different concentrations in acetate buffer of pH 9.0, and by using double basic washing and acidic elution. The intra-day coefficient of variation (CV) was below 7% and inter-day CV was below 10%. This investigation has provided a reliable MISPE–HPLC method for determination of cotinine in human urine from both active smokers and passive smokers. Figure     

Preparation of a novel molecularly imprinted polymer for the highly selective extraction of baicalin

The selective extraction of baicalin is important to its quality control especially when the matrices are complicated. In this work, a novel molecularly imprinted polymer was prepared for the selective extraction of baicalin in herbs. The molecularly imprinted polymer was synthesized by the copolymerization of 4‐vinyl pyridine and ethylene glycol dimethacrylate in the presence of baicalin by a precipitation polymerization method. After the optimization of parameters for molecularly imprinted polymer preparation, including the functional monomer, porogen, sampling solvent, and washing solvent, good selectivity was obtained, with an imprinting factor of about 4, which is much better than that achieved by the bulk‐polymerization method. The performances of the prepared molecularly imprinted polymers were systematically investigated, including adsorption kinetics, isotherm experiment, and Scatchard analysis. On the basis of the good adsorptive capability of the prepared molecularly imprinted polymer, it was also applied for the pretreatment of baicalin in Scutellaria baicalensis Georgi. The result showed that most of the matrices were removed and baicalin was selectively enriched.     

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.     

The use of molecularly imprinted polymers for extraction of sulfonylurea herbicides

Molecularly imprinted polymers (MIPs) possessing a good binding ability for the family of sulfonylurea herbicides were prepared using 4- or 2-vinyl pyridine as functional monomers and ethylene glycol dimethylacrylate as a crosslinker. Metsulfuron methyl was used as a template. It was found that MIP prepared in a polar organic solvent (acetonitrile) showed good recognition of the template and five other sulfonylurea herbicides (thifensulfuron methyl, chlorsulfuron, prosulfuron, chlorimuron ethyl, triflusulfuron methyl). The binding capacity was 0.08-0.1 mg g⁻¹ of the polymer. It was found that the polymer could be used for quantitative enrichment (>75%) of five sulfonylurea herbicides from water.     

Rationally designed molecularly imprinted polymers for selective extraction of methocarbamol from human plasma

Molecularly imprinted polymers (MIPs) with high selectivity toward methocarbamol have been computationally designed and synthesized based on the general non-covalent molecular imprinting approach. A virtual library consisting of 18 functional monomers was built and possible interactions between the template and functional monomers were investigated using a semiempirical approach. The monomers with the highest binding scores were then considered for additional calculations using a more accurate quantum mechanical (QM) calculation exploiting the density functional theory (DFT) at B3LYP/6-31G(d,p) level. The cosmo polarizable continuum model (CPCM) was also used to simulate the polymerization solvent. On the basis of computational results, acrylic acid (AA) and tetrahydrofuran (THF) were found to be the best choices of functional monomer and polymerization solvent, respectively. MIPs were then synthesized by the precipitation polymerization method and used as selective adsorbents to develop a molecularly imprinted solid-phase extraction (MISPE) procedure before quantitative analysis. After MISPE the drug could be determined either by differential pulse voltammetry (DPV), on a glassy carbon electrode modified with multiwalled-carbon nanotubes (GC/MWNT), or high performance chromatography (HPLC) with UV detection. A comparative study between MISPE-DPV and MISPE-HPLC-UV was performed. The MISPE-DPV was more sensitive but both techniques showed similar accuracy and precision.     

Selective solid-phase extraction of tebuconazole in biological and environmental samples using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using tebuconazole (TBZ) as a template. Frontal chromatography and selectivity experiments were used to determine the binding capabilities and binding specificities of different MIPs. The polymer that had the highest binding selectivity and capability was used as the solid-phase extraction (SPE) sorbent for the direct extraction of TBZ from different biological and environmental samples (cabbage, pannage, shrimp, orange juice and tap water). The extraction protocol was optimized and the optimum conditions were: conditioning with 5 mL methanol:acetic acid (9:1), 5 mL methanol and 5 mL water respectively, loading with 5 mL aqueous samples, washing with 1.2 mL acetonitrile (ACN):phosphate buffer (5:5, pH3), and eluting with 3 mL methanol. The MIPs were able to selectively recognize, effectively trap and preconcentrate TBZ over a concentration range of 0.5–15 μmol/L. The intraday and interday RSDs were less than 9.7% and 8.6%, respectively. The limit of quantification was 0.1 μmol/L. Under optimum conditions, the MISPE recoveries of spiked cabbage, pannage, shrimp, orange juice and tap water were 62.3%, 75.8%, 71.6%, 89% and 93.9%, respectively. MISPE gave better HPLC separation efficiencies and higher recoveries than C18 SPE and strong cation exchange (SCX) SPE. Figure HPLC analysis of spiked pannage after MISPE (A) and after C18 SPE (B). HQ (1), E3 (2), p-NP (3), FTF (4), TBZ (5), PNZ (6), HXZ (7) Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Rational design and synthesis of water-compatible molecularly imprinted polymers for selective solid phase extraction of amiodarone

Novel water-compatible molecularly imprinted polymers (MIPs) selective for amiodarone (AD) were designed via a new methodology which relies on screening library of non-imprinted polymers (NIPs). The NIP library consisted of eighteen cross-linked co-polymers synthesized from monomers commonly used in molecular imprinting. The binding capacity of each polymer in the library was analyzed in two different solvents. Binding in water was used to assess non-specific (hydrophobic) interactions and binding in an appropriate organic solvent was used to assess specific interactions. A good correlation was found between the screening tests and modeling of monomer–template interactions performed using computational approach. Additionally, analysis of template–monomer interactions was performed using UV–vis spectroscopy. As the result, 4-vinylpyridine (4-VP) was selected as the best monomer for developing MIP for AD. The 4-VP-based polymers demonstrated imprinting factor equal 3.9. The polymers performance in SPE was evaluated using AD and its structural analogues. The recovery of AD was as high as 96% when extracted from spiked phosphate buffer (pH 4.5) solution and 82.1% from spiked serum samples. The developed MIP shown as a material with specific binding to AD, comparing to its structural analogues, 1-(2-diethylaminoethoxy)-2,6-diiodo-4-nitrobenzene and lidocaine, which shown 9.9% and 25.4% of recovery from the buffer solution, correspondingly. We believe that the screening of NIP library could be proposed as an alternative to commonly used computational and combinatorial approaches.     

Quercetin molecularly imprinted polymers: Preparation, recognition characteristics and properties as sorbent for solid-phase extraction

Molecular imprinted polymers (MIPs) were prepared through thermal polymerization by using quercetin as the template molecule, acrylamide (AA) as the functional monomer and ethylene glycol dimethacrylate (EDMA) as the cross-linker in the porogen of tetrahydrofuran (THF). The synthesized MIPs were identified by both Fourier transform infrared (FTIR) and scanning electron microscope (SEM). Systematic investigations of the influences of key synthetic conditions, including functional monomers, porogens and cross-linkers, on the recognition properties of the MIPs were conducted. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. Besides quercetin, two structurally similar compounds of rutin and catechol were employed for molecular recognition specificity tests of MIPs. It was observed that the MIPs exhibited the highest selective rebinding to quercetin. Accordingly, the MIPs were used as a solid-phase extraction (SPE) sorbent for the extraction and enrichment of quercetin in cacumen platycladi samples, followed by HPLC-UV analysis. The application of MIPs with high affinity and excellent stereo-selectivity toward quercetin in SPE might offer a novel method for the enrichment and determination of flavonoid compounds in the natural products.