Preparation and selective recognition of a novel solid‐phase microextraction fiber combined with molecularly imprinted polymers for the extraction of parabens in soy sample

A prepared molecularly imprinted polymer with ethyl p‐hydroxybenzoate as template molecule was applied for the first time to a homemade solid‐phase microextraction fiber. The molecularly imprinted polymer‐coated solid‐phase microextraction fiber was characterized by scanning electron microscopy and thermogravimetric analysis. Various parameters were investigated, including extraction temperature, extraction time, and desorption time. Under the optimum extraction conditions, the molecularly imprinted polymer‐coated solid‐phase microextraction fiber exhibited higher selectivity with greater extraction capacity toward parabens compared with the nonimprinted polymer‐coated solid‐phase microextraction fiber and commercial fibers. The molecularly imprinted polymer‐coated solid‐phase microextraction fiber was tested using gas chromatography to determine parabens, including methyl p‐hydroxybenzoate, ethyl p‐hydroxybenzoate, and propyl p‐hydroxybenzoate. The linear ranges were 0.01–10 μg/mL with a correlation coefficient above 0.9943. The detection limits (under signal‐to‐noise ratio of 3) were below 0.30 μg/L. The fiber was successfully applied to the simultaneous analysis of three parabens in spiked soy samples with satisfactory recoveries of 95.48, 97.86, and 92.17%, respectively. The relative standard deviations (n=6) were within 2.83–3.91%. The proposed molecularly imprinted polymer‐coated solid‐phase microextraction method is suitable for selective extraction and determination of trace parabens in food samples.     

Preparation of hydrophilic molecularly imprinted solid‐phase microextraction fiber for the selective removal and extraction of trace tetracyclines residues in animal derived foods

The present work reported a novel hydrophilic and selective solid‐phase microextraction fiber by improved multiple co‐polymerization method immobilization of tetracycline molecularly imprinted polymer on a stainless steel wire and directly coupled with high‐performance liquid chromatography for sensitive determination of trace tetracyclines residues in animal derived foods. The developed molecularly imprinted polymer coated solid‐phase microextraction fibers were characterized through scanning electron microscopy, Fourier transfer infrared spectroscopy, thermogravimetric analysis, and adsorption experiments, the fiber with cross‐linked and porous structure was observed and high thermal and chemical stability. The maximum adsorption capacity of this fiber with good selectivity reached 2.35 µg/mg in aqueous matrices, and showed good repeatability (relative standard deviation ≤ 6.6%, n = 5) and satisfying reproducibility between fiber to fiber (relative standard deviation ≤ 7.8%, n = 5). Under the optimized solid‐phase microextraction conditions, satisfactory linearity (5–1000 µg/L) and detection limits (0.38–0.72 µg/kg, S/N = 3) for all the tetracyclines were obtained. The practicality of this method was proved by adding tetracycline, oxytetracycline at three levels to milk, chicken, and fish samples with good recoveries of 77.3–104.4%.     

Preparation and Characterization of Prometryn Molecularly Imprinted Solid‐Phase Microextraction Fibers

Abstract

A novel reproducible solid‐phase microextraction (SPME) coating was prepared on the surface of silanized silica fibers by molecularly imprinted polymerization using prometryn as template molecule. The structure and extraction performance of molecularly imprinted polymer (MIP) coating was studied with the scanning electron microscope and high performance liquid chromatography (HPLC). Specific selectivity was found with the prometryn MIP‐coated fiber to prometry and its structural analogues such as atrazine, simetryn, terbutylazin, ametryn, propazine and terbutryn. In contrast, these triazines could not be selectively extracted by the non‐imprinted polymer fiber or commercial polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), polyacrylate (PA) fibers.     

Molecularly imprinted polymer as a novel solid‐phase microextraction coating for the selective enrichment of trace imidazolinones in rice,peanut, and soil

The development and application of an imazethapyr molecularly imprinted polymer‐based solid‐phase microextraction coating were investigated. A novel molecularly imprinted polymer coating with imazethapyr as template was firstly prepared by a one‐step in situ polymerization method, and demonstrated specific selectivity to imidazolinone herbicides in complicated samples. The structural characteristics and extraction performance of the imazethapyr molecularly imprinted polymer coating were studied. The molecularly imprinted polymer coating was homogeneous, dense, and heat and solvent resistant. Adsorption capacity experiments showed that the molecularly imprinted polymer coating could selectively extract imazethapyr and its structural analogs, and the maximum adsorption capacity was 2.5 times as much as that of the nonimprinted polymer coating. A method for the determination of five imidazolinones by imazethapyr molecularly imprinted polymer solid‐phase microextraction coupled with high‐performance liquid chromatography was developed. The linear range was 0.50–50 μg/L for imazameth, imazamox, imazapyr acid, and imazethapyr, and 1.0–100 μg/L for imazaquin acid, and the detection limits were within the range of 0.070–0.29 μg/L. The method was applied to simultaneous and multiresidual determinations of trace imidazolinones in rice, peanut, and soil samples with satisfactory recoveries of 60.6–99.5, 79.1–123, and 61.3–116%, respectively, and relative standard deviations of 0.40–10%, which indicated that this method was suitable for the trace analysis of imidazolinones in complex food and environmental samples.     

Preparation of l‐phenylalanine‐imprinted solid‐phase extraction sorbent by Pickering emulsion polymerization and the selective enrichment of l‐phenylalanine from human urine

A novel l‐ phenylalanine molecularly imprinted solid‐phase extraction sorbent was synthesized by the combination of Pickering emulsion polymerization and ion‐pair dummy template imprinting. Compared to other polymerization methods, the molecularly imprinted polymers thus prepared exhibit a high specific surface, large pore diameter, and appropriate particle size. The key parameters for solid‐phase extraction were optimized, and the result indicated that the molecularly imprinted polymer thus prepared exhibits a good recovery of 98.9% for l‐ phenylalanine. Under the optimized conditions of the procedure, an analytical method for l‐ phenylalanine was well established. By comparing the performance of the molecularly imprinted polymer and a commercial reverse‐phase silica gel, the obtained molecularly imprinted polymer as an solid‐phase extraction sorbent is more suitable, exhibiting high precision (relative standard deviation 3.2%, n = 4) and a low limit of detection (60.0 ± 1.9 nmol·L^?1) for the isolation of l‐ phenylalanine. Based on these results, the combination of the Pickering emulsion polymerization and ion‐pair dummy template imprinting is effective for preparing selective solid‐phase extraction sorbents for the separation of amino acids and organic acids from complex biological samples.     

Magnetic molecularly imprinted composite for the selective solid‐phase extraction of p‐aminosalicylic acid followed by high‐performance liquid chromatography with ultraviolet detection

A new method for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples has been developed using magnetic molecularly imprinted polymer nanoparticles before determination by high‐performance liquid chromatography. The Fe₃O₄ nanoparticles were first prepared through the chemical coprecipitation of Fe²⁺ and Fe³⁺ and then coated with a vinyl shell. Subsequently, a layer of molecularly imprinted polymers was grafted onto the vinyl‐modified magnetic nanoparticles by precipitation polymerization. FTIR spectroscopy, scanning electron microscopy, vibrating sample magnetometry, and thermogravimetric analysis were applied to characterize the sorbent properties. Moreover, the predominant parameters affecting the magnetic solid phase extraction such as sample pH, sorption and elution times, the amount of sorbent, and composition and volume of eluent were investigated thoroughly. The maximum sorption capacity of the imprinted polymer toward p‐aminosalicylic acid was 70.9 mg/g, which is 4.5 times higher than that of the magnetic nonimprinted polymer. The magnetic molecularly imprinted polymer nanoparticles were applied for the selective extraction of p‐aminosalicylic acid from aqueous and urine samples and satisfactory results were achieved. The results illustrate that magnetic molecularly imprinted polymer nanoparticles have a great potential in the extraction of p‐aminosalicylic acid from environmental and biological matrices.     

Preparation of magnetic molecularly imprinted polymer for dispersive solid‐phase extraction of valsartan and its determination by high‐performance liquid chromatography: Box‐Behnken design

In this work, core/shell magnetic molecularly imprinted polymer nanoparticles were synthesized for extraction and pre‐concentration of valsartan from different samples and then it was measured with high‐performance liquid chromatography. For preparation of molecularly imprinted polymer nanoparticles, Fe₃O₄ nanoparticles were coated with tetraethyl orthosilicate and then functionalized with 3‐(trimethoxysilyl) propyl methacrylate. In the next step, molecularly imprinted polymer nanoparticles were synthesized under reflux and distillation conditions via polymerization of methacrylic acid, valsartan (as a template), azobisisobutyronitrile and ethylene glycol dimethacrylate as cross linking. The properties of molecularly imprinted polymer nanoparticle were investigated by FTIR spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Box‐Behnken design with the aid of desirability function was used for optimizing the effect of variables such as the amounts of molecularly imprinted polymer nanoparticles, time of sonication, pH, and volume of methanol on the extraction percentage of valsartan. According to the obtained results, the affecting variables extraction condition were set as 10 mg of adsorbent, 16 min for sonication, pH = 5.5 and 0.6 mL methanol. The obtained linear response (r² > 0.995) was in the range of 0.005–10 µg/mL with detection limit 0.0012 µg/mLand extraction recovery was in the range of 92–95% with standard deviation less than 6% (n = 3).     

Preparation of molecularly imprinted polymeric fibers using a single bifunctional monomer for the solid‐phase microextraction of parabens from environmental solid samples

In this study, molecularly imprinted polymer fibers for solid‐phase microextraction have been prepared with a single bifunctional monomer, N,O‐bismethacryloyl ethanolamine using the so‐called “one monomer molecularly imprinted polymers” method, replacing the conventional combination of functional monomer and cross‐linker to form high fidelity binding sites. For comparison, imprinted fibers were prepared following the conventional approach based on ethylene glycol dimethacrylate as cross‐linker and methacrylic acid as monomer. The recognition performance of the new fibers was evaluated in the solid‐phase microextraction of parabens, and from this study it was concluded that they provided superior performance over conventionally formulated fibers. Ultimately, real‐world environmental testing on spiked solid samples was successful by the molecularly imprinted solid‐phase microextraction of samples, and the relative recoveries obtained at enrichment levels of 10 ng/g of parabens were within 78–109% for soil and 83–109% for sediments with a relative standard deviation <15% (n = 3).     

Highly selective separation and detection of cyromazine from seawater using graphene oxide based molecularly imprinted solid‐phase extraction

A novel molecularly imprinted polymer based on graphene oxide was prepared as a solid‐phase extraction adsorbent for the selective adsorption and extraction of cyromazine from seawater samples. The obtained graphene oxide molecularly imprinted polymer and non‐imprinted polymer were nanoparticles and characterized by scanning electron microscopy. The imprinted polymer showed higher adsorption capacity and better selectivity than non‐imprinted polymer, and the maximum adsorption capacity was 14.5 mg/g. The optimal washing and elution solvents for molecularly imprinted solid phase extraction procedure were 2 mL of acetonitrile/water (80:20, v/v) and methanol/acetic acid (70:30, v/v), respectively. The recoveries of cyromazine in the spiked seawater samples were in the range of 90.3–104.1%, and the relative standard deviation was <5% (n = 3) under the optimal procedure and detection conditions. The limit of detection of the proposed method was 0.7 μg/L, and the limit of quantitation was 2.3 μg/L. Moreover, the imprinted polymer could keep high adsorption capacity for cyromazine after being reused six times at least. Finally, the synthesized graphene oxide molecularly imprinted polymer was successfully used as a satisfied sorbent for high selectivity separation and detection of cyromazine from seawater coupled with high‐performance liquid chromatography.     

Preparation and application of a coated‐fiber needle extraction device

In this study, a needle‐trap device with fibers coated with a molecularly imprinted polymer was developed for separation. A number of heat‐resistant Zylon filaments were longitudinally packed into a glass capillary, followed by coating with a molecularly imprinted polymer. Then, the molecularly imprinted polymer coating was copolymerized and anchored onto the surface of the fibers. The bundle of synthetic fibers coated with the molecularly imprinted polymer was packed into a 21G stainless‐steel needle and served as an extraction medium. The coated‐fiber needle extraction device was used to extract volatile organic compounds from paints and gasoline effectively. Subsequently, the extracted volatile organic compounds were analyzed by gas chromatography. Calibration curves of gaseous benzene, toluene, ethylbenzene, and o‐xylene in the concentration range of 1–250 μg/L were obtained to evaluate the method, acceptable linearity was attended with correlation coefficients above 0.998. The limit of detection of benzene, toluene, ethylbenzene, and o‐xylene was 11–20 ng/L using the coated‐fiber needle‐trap device. The relative standard deviation of needle‐to‐needle repeatability was less than 8% with an extraction time of 20 min. The loss rates after storage for 3 and 7 days at room temperature were less than 30%.     

Novel metal‐ion‐mediated,complex‐imprinted solid‐phase microextraction fiber for the selective recognition of thiabendazole in citrus and soil samples

A novel metal‐ion‐mediated complex‐imprinted‐polymer‐coated solid‐phase microextraction (SPME) fiber used to specifically recognize thiabendazole (TBZ) in citrus and soil samples was developed. The complex‐imprinted polymer was introduced as a novel SPME coating using a “complex template” constructed with Cu(II) ions and TBZ. The recognition and enrichment properties of the coating in water were significantly improved based on the metal ion coordination interaction rather than relying on hydrogen bonding interactions that are commonly applied for the molecularly imprinting technique. Several parameters controlling the extraction performance of the complex‐imprinted‐polymer‐coated fiber were investigated including extraction solvent, pH value, extraction time, metal ion species, etc. Furthermore, SPME coupled with HPLC was developed for detection of TBZ, and the methods resulted in good linearity in the range of 10.0–150.0 ng/mL with a detection limit of 2.4 ng/mL. The proposed method was applied to the analysis of TBZ in spiked soil, orange, and lemon with recoveries of 80.0–86.9% and RSDs of 2.0–8.1%. This research provides an example to prepare a desirable water‐compatible and specifically selective SPME coating to extract target molecules from aqueous samples by introducing metal ions as the mediator.     

Molecularly imprinted polymeric stir bar: Preparation and application for the determination of naftopidil in plasma and urine samples

In this study, molecularly imprinting technology and stir bar absorption technology were combined to develop a microextraction approach based on a molecularly imprinted polymeric stir bar. The molecularly imprinted polymer stir bar has a high performance, is specific, economical, and simple to prepare. The obtained naftopidil‐imprinted polymer‐coated bars could simultaneously agitate and adsorb naftopidil in the sample solution. The ratio of template/monomer/cross‐linker and conditions of template removal were optimized to prepare a stir bar with highly efficient adsorption. Fourier transform infrared spectroscopy, scanning electron microscopy, selectivity, and extraction capacity experiments showed that the molecularly imprinted polymer stir bar was prepared successfully. To utilize the molecularly imprinted polymer stir bar for the determination of naftopidil in complex body fluid matrices, the extraction time, stirring speed, eluent, and elution time were optimized. The limits of detection of naftopidil in plasma and urine sample were 7.5 and 4.0 ng/mL, respectively, and the recoveries were in the range of 90–112%. The within‐run precision and between‐run precision were acceptable (relative standard deviation <7%). These data demonstrated that the molecularly imprinted polymeric stir bar based microextraction with high‐performance liquid chromatography was a convenient, rapid, efficient, and specific method for the precise determination of trace naftopidil in clinical analysis.     

Dummy Fragment Template Molecularly Imprinted Polymers for the Selective Solid-phase Extraction of Gonyautoxins from Seawater

A multitemplate molecularly imprinted polymer was synthesized using fragments similar to gonyautoxins 1 and 4 including 2,4,6-triaminopyrimidine, 4-hydroxy-2-butanone, and imidazole as dummy templates by bulk polymerization. Scanning electron microscopy and infrared spectroscopy showed a porous structure and the formation of organic groups in the imprinting process of the polymer. One millilitre of 0.1?mol?L^?1 acetic acid and 1?mL of 95% methanol were the optimized washing and eluting solutions during the molecularly imprinted solid-phase extraction. The adsorption capacity of the multitemplate molecularly imprinted polymer was lower than for the monotemplate molecularly imprinted polymer prepared in a previous study in seawater in which Alexandrium tamarense and Alexandrium minutum were cultivated. This result may due to the inappropriate combination of the dummy template fragments in the synthesis resulting in the unfitness of the imprinting sites for gonyautoxins 1 and 4. In general, it is inappropriate to use fragments with the similar parts to the analyte as the dummy templates. However, this work indicated the optimal molecularly imprinted polymer for the selective extraction of gonyautoxins 1 and 4.     

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.     

Zwitterionic molecularly imprinted polymer‐based solid‐phase micro‐extraction coupled with molecularly imprinted polymer sensor for ultra‐trace sensing of L‐histidine

The proposed L ‐histidine sensing system composed of a molecularly imprinted solid‐phase microextraction component combined with a molecularly imprinted polymer sensor was used to determine critical levels of test analyte in a complex matrix of highly diluted human blood serum without any non‐specific sorption and false‐positive contributions. The molecularly imprinted polymer was a zwitterionic polymer brush derived from the disodium salt of EDTA and chloranil, grafted to solid‐phase microextraction material. The hyphenated approach was able to detect L ‐histidine quantitatively with a limit of detection as low as 0.0435 ng/mL (RSD = 0.2%, S/N = 3).     

A novel method to prepare monolithic molecular imprinted polymer fiber for solid‐phase microextraction by microwave irradiation†

In this paper, a new approach to prepare monolithic molecularly imprinted polymer (MIP) fibers for solid‐phase microextraction is proposed with the help of microwave irradiation. Imprinting polymerization was carried out within silica capillaries in 4.5 min, using dimethyl phthalate (DMP) as a template molecular, α‐methacrylic acid as a functional monomer and ethylene dimethacrylate as a crosslinker, acetonitrile as the porogenic solvent. The synthesis was optimized by varying the ratio of template/monomer and different volume of porogen. The resulted MIP fibers were obtained after silica being etched away with a controlled length of 1 cm, and subsequently characterized by SEM. In order to increase the selective extraction of DMP, factors affecting the extraction including extraction time, salt concentration, desorption time, and desorption solvents were investigated for solid‐phase microextraction procedures in detail. The selectivity coefficients, defined as the extraction amount ratio of MIP to its nonimprinting fiber, were 5.6, 2.6, and 1.4 for DMP and its counterpart including dibutyl phthalate and di‐n‐octylo‐phthalate, respectively. The resulted fibers were also applied to detect DMP, dibutyl phthalate, and di‐n‐octylo‐phthalate in bottled beverage samples coupled to HPLC and resulted in relative recoveries of up to 73.8–98.5%, respectively.     

Rapid Preparation of Monolithic Molecular Imprinted Polymer Fiber for Solid Phase Microextraction by Microwave Irradiation

In this paper, a simple, fast and in situ polymerization strategy to prepare monolithic molecularly imprinted polymer (MIP) fibers for solid phase microextraction (SPME) is developed using silica capillaries as molds. With the help of microwave irradiation, polymerization was carried out in 5.5 min using olivetol as a template molecular, α‐methacrylic acid (MAA) as a functional monomer and ethylene dimethacrylate (EDMA) as a crosslinker, toluene and dodecanol as the binary porgens. The resulted MIP fibers were finally obtained after silica being etched away with a controlled length, and subsequently characterized by scanning electron microscope (SEM) and Fourier transform infrared absorption spectroscopy (FT‐IR). Under the optimal extraction conditions, a simple method based on the coupling of MIP SPME with high performance liquid chromatography (HPLC) was used for the selective determination of the model mixtures of olivetol, phenol and m‐toluidine in lake water and wheat bran samples. The recoveries of olivetol, phenol and m‐toluidine for both samples were in the range of 87.3‐93.6%, 21.4‐27.2%, 18.9‐24.8% at three spiked levels, respectively, demonstrating that higher extraction and the specific absorption occurred between the template molecule and the prepared MIP fiber.     

Multifiber solid‐phase microextraction using different molecularly imprinted coatings for simultaneous selective extraction and sensitive determination of organophosphorus pesticides

Three types of molecularly imprinted solid‐phase microextraction fibers were fabricated through sol‐gel method using diazinon, parathion‐methyl, and isocarbophos as templates, respectively, and assembled together to construct a multifiber for analysis of organophosphorus pesticides in complex matrices. The multifiber provided large extraction capacity and high imprinting factor up to 3.89. In contrast, the imprinting factor of a single fiber was around 1.6, and the multi‐template imprinted coating showed no selectivity. The multifiber was applied to analyze pesticides in fruits and vegetables. The limits of detection, which ranged from 0.0052 to 0.23 µg/kg, were lower than those obtained by a single molecularly imprinted fiber, and much lower than those reported by other methods. The recoveries of five analytes in spiked apple, cucumber, Chinese cabbage, and cherry tomato samples were 75.1–123.2%. The study shows that the molecularly imprinted multifiber could achieve simultaneous selective extraction and sensitive determination of multiple targets in complex matrices for high‐throughput analysis.     

Magnetic molecularly imprinted polymer for the efficient and selective preconcentration of diazinon before its determination by high‐performance liquid chromatography

A molecularly imprinted polymer was selectively applied for solid‐phase extraction and diazinon residues enrichment before high‐performance liquid chromatography. Diazinon was thermally copolymerized with Fe₃O₄@polyethyleneglycol nanoparticles, methacrylic acid (functional monomer), 2‐hydroxyethyl methacrylate (co‐monomer), and ethylene glycol dimethacrylate (cross‐linking monomer) in the presence of acetonitrile (porogen) and 2,2‐azobisisobutyronitrile (initiator). Then, the imprinted diazinon was reproducibly eluted with methanol/acetic acid (9:1, v/v). The sorbent particles were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The comprehensive study of variables through experimental design showed that the maximum performance was achieved under these conditions: pH 7, 10 mL sample volume, 15 mg sorbent, 10 min vortex time, 5 min ultrasonic time, 200 μL methanol/acetic acid (9:1, v/v) as eluent, and 5 min desorption time. Under optimized conditions, the molecularly imprinted polymer solid‐phase extraction method demonstrated a linear range (0.02–5 g/mL), a correlation coefficient of 0.997, and 0.005 g/mL detection limit.     

替代模板分子印迹技术在样品前处理中的应用

分子印迹聚合物具有抗恶劣环境、选择性高、稳定性好等特点,广泛应用于复杂样品的前处理。采用结构类似物作为替代模板分子,可以解决分子印迹聚合物制备时目标物溶解性差的问题,替代模板分子印迹聚合物不仅对目标分析物具有选择性识别能力,还可以避免模板泄露对痕量分析造成的影响。本文综述了替代模板分子印迹技术在样品前处理中的应用进展,包括替代模板分子印迹技术在固相萃取、固相微萃取、色谱固定相、基质固相分散萃取中的应用,最后对替代模板分子印迹技术在未来的样品前处理中的研究进行了展望。