Molecularly imprinted solid-phase extraction for the selective HPLC determination of ractopamine in pig urine

A method was developed for the determination of ractopamine in pig urine using molecularly imprinted solid-phase extraction (MISPE) as the sample clean-up technique combined with high-performance liquid chromatography. The molecularly imprinted polymer (MIP) was synthesized in acetonitrile-triethylamine system using ractopamine (RAC) as the template and acrylamide as the monomer. The binding capacity of the polymer toward RAC was found to be about 2.57 mg of ractopamine/g of polymer. The optimal procedures for MISPE consisted of conditioning with 3 mL methanol, equilibrating with 3 mL of water, loading volume of <10 mL of aqueous sample (pH 7), washing with 3 mL water and 3 mL methanol, and eluting with 5 mL of 5% ammonia in methanol. In the four spiked samples with the levels of 0.01, 0.1, 1.0 and 5.0 μg/mL, the mean recoveries of analyte on the MIP were higher than 90% with relative standard deviation <10%, and significant differences between imprinted and non-imprinted materials were observed. The MIP selectivity was evaluated by checking 11 drugs with similar and different molecular structures to that of RAC. The characteristics of three-dimensional cavities and hydrogen bond interaction were regarded as the main factors that dominated the retention of RAC on the MISPE cartridge.     

Extraction of Anthraquinones from Rhubarb by a Molecularly Imprinted–Matrix Solid-Phase Dispersion Method with HPLC Detection

A simple method based on matrix solid-phase dispersion for selective extraction of anthraquinones from rhubarb samples was developed using a molecularly imprinted polymer as sorbent. The molecularly imprinted polymer was prepared using emodin as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linking agent. The polymer was characterized by scanning electron microscopy and Fourier-transform infrared spectrometry. Isothermal adsorption and dynamic adsorption experiments were performed. The best extraction conditions for anthraquinones were obtained at a ratio of molecularly imprinted polymer to sample of 1:1, a dispersion time of 5 minutes, with 5% aqueous methanol as the washing solvent, and an elution solvent of methanol-acetic acid (99:1, v/v). Once the matrix solid-phase dispersion process was optimized, the extract was reacted with 8% hydrochloric acid for hydrolysis. The anthraquinones extracted from rhubarb were determined by liquid chromatography. The detection limits of chrysophanol, emodin, physcion, and aloe-emodin were 0.23, 0.24, 0.28, and 0.27 µg mL^?1, respectively. The proposed method was compared with the method in Chinese pharmacopoeia, and the results show that the extraction yield of anthraquinones obtained by molecularly imprinted polymer–matrix solid-phase dispersion method was higher. Moreover, the proposed method is faster and simpler and can achieve extraction and purification in the same system.     

Covalent imprinted polymer for selective and rapid enrichment of ractopamine by a noncovalent approach

A novel molecularly imprinted polymer (MIP) for the separation and concentration of ractopamine (RAC) was prepared by a covalent imprinting approach and the template was removed successfully by hydrolysis, so that four carboxylic acid groups were left in the cavities and could specifically rebind RAC through noncovalent interaction: hydrogen bonding. The conditions for synthesis of the MIP were optimized during the polymerization process, and a molar ratio of template–functional monomer complexes to cross-linker of 1:3 was confirmed. The adsorption capacity of the MIP was 4.1-fold that of the nonimprinted polymer, and the adsorption reaction reached equilibrium after 25 min at 50 mg L^-1 concentration. The results of the competitive adsorption test showed that the MIPs had specific recognition ability for the analyte RAC. In addition, the important factors affecting the efficiency of the method which was developed using the MIPs as a solid-phase sorbent for separation and determination of RAC combined with high-performance liquid chromatography with fluorescence detection were optimized. Under the optimum experimental conditions, the linear range of the calibration curve in the method was 0.05-5 μg L^-1 (R ² = 0.98) and the limit of detection (signal-to-noise ratio of 3) was 0.01 μg L^-1. The proposed method was applied to determination of RAC in spiked feedstuffs and urine samples, with recoveries ranging from 74.17 to 114.46% and relative standard deviation (n = 3) below 4.55 in all cases.     

An electrochemical sensor for rapid determination of ractopamine based on a molecularly imprinted electrosynthesized o-aminothiophenol film

A simple electrochemical sensor based on a molecularly imprinted polymer film as the recognition element was developed for ractopamine (RAC) detection. This is the first report of a RAC-imprinted film on a gold electrode surface, synthesized through an electrochemical method using o-aminothiophenol as the functional monomer. The imprinting mechanism and experimental parameters affecting the capability of the imprinted film are discussed here. The sensor was successfully applied with constant potential amperometry for RAC detection in an indirect process with potassium ferricyanide as an electrochemical probe. The sensor had a rapid equilibrium time (120?s), high binding affinity and selectivity towards RAC, and with good reproducibility and stability. Under the experimental conditions applied, a linear relationship between the relative amperometric response and RAC ranged from 2.0?×?10(-7) to 1.4?×?10(-6)?mol?L(-1), with a lower limit of detection (LOD) of 2.38?×?10(-8)?mol?L(-1) (signal to noise ratio?=?3). The sensor was tested with feed samples spiked with trace amounts of RAC, with good recoveries between 87.4 and 90.5?%.     

Molecularly imprinted polymer for the determination of trace ractopamine in pork using SPE followed by HPLC with fluorescence detection

In this study, a molecularly imprinted functionalized polymer for the selective separation of ractopamine (RAC) was prepared by combining a surface molecular imprinting technique with a sol–gel method process. The polymer was evaluated by static, kinetic adsorption, and selective experiments. Results indicated that the molecularly imprinted polymer had high adsorption capacity, selective ability, and fast mass transfer rate. The polymer was applied for the determination of trace RAC through online SPE‐HPLC. With a sample loading flow rate of 2 mL/min, the enhancement factor of 516.26 and the LOD (S/N = 3) of 4.6 ng/L were achieved, respectively, and the linear range of the calibration curve was 0.04–18 μg/L with r² >0.99. The RAC in pork was determined at three spiked levels (0.5, 1, and 2 ng/g) with recoveries ranging from 55.86 to 67.28%.     

Quantification of Tricyclic and Nontricyclic Antidepressants in Spiked Plasma and Urine Samples Using Microextraction in Packed Syringe and Analysis by LC and GC-MS

In this paper, a highly selective Sudan IV molecularly imprinted polymer was synthesized by surface molecular imprinting technique in combination with a sol?Cgel process using ??-aminopropyl triethoxysilane as functional monomer, tetraethoxysilane as cross-linker and activated silica gel as support material. The imprinted polymer was characterized by FT-IR spectra, scanning electron micrograph and adsorption experiments and it was exhibited good recognition and selective ability, offered a faster rate for the adsorption of Sudan IV. Using the imprinted material as sorbent, a solid-phase extraction coupled with high-performance liquid chromatography method for determination of trace Sudan IV was presented. The detection limit (S/N = 3) was 25.2 ng L^?1, and the RSD for five replicate was 2.86%. With a loading flow rate of 2.5 mL min^?1 for loading 30 mL, an enrichment factor of 104 was achieved. This method was applied for extraction and determination of chilli powder and duck egg samples with good recoveries ranging from 85.3 to 98.1%.     

分子印迹固相萃取-高效液相色谱法测定饲料中莱克多巴胺

以莱克多巴胺为模板分子,丙烯酰胺为功能单体,乙二醇二甲基丙烯酸酯为交联剂,合成了对莱克多巴胺具有高选择性的分子印迹聚合物。考察了甲醇、乙腈、丙酮和氯仿-甲醇与三乙胺构成致孔剂合成的聚合物性能及其形貌特征。通过正交试验优化的聚合反应配方为: 1.0 mmol莱克多巴胺,4.0 mmol丙烯酰胺,20.0 mmol乙二醇二甲基丙烯酸酯,6.0 mL乙腈-三乙胺(30:1, v/v), 50.0 mg偶氮二异丁腈。建立的基于分子印迹固相萃取-高效液相色谱测定饲料试样中莱克多巴胺的方法,在0.50～100 mg/L质量浓度范围内有良好的线性关系(r=0.9994);饲料试样中1.0、10及100 mg/kg 3个添加水平的莱克多巴胺平均回收率大于80%;批内、批间测定的相对标准偏差小于10%;检出限(信噪比为3)达到0.1 mg/kg。该方法灵敏、可靠,用于饲料等复杂基质中莱克多巴胺检测的效果优于相关标准分析方法。     

Tailor‐made ion‐imprinted polymer based on functionalized graphene oxide for the preconcentration and determination of trace copper in food samples

A tailor‐made Cu(II) ion‐imprinted polymer based on large‐surface‐area graphene oxide sheets has been synthesized for the preconcentration and determination of trace copper from food samples by solid‐phase extraction. Attributed to the ultrahigh surface area and hydrophilicity of graphene oxide, the Cu(II) ion‐imprinted polymer prepared by the surface ion‐imprinting technique exhibited a high binding capacity and a fast adsorption rate under the optimized experimental conditions. In the static adsorption experiments, the maximum adsorption capacity of Cu(II) ion‐imprinted polymer is 109.38 mg/g at 25°C, which is much higher than that of the nonimprinted polymer (32.12 mg/g). Meanwhile, the adsorption is very rapid and equilibrium is reached after approximately 30 min. The adsorption mechanism is found to follow Langmuir adsorption model and the pseudo‐second‐order adsorption process. The Cu(II) ion‐imprinted polymer was used for extracting and detecting Cu(II) in food samples combined with graphite flame atomic adsorption spectrometry with high recoveries in the range of 97.6–103.3%. The relative standard deviation and limit of detection of the method were evaluated as 1.2% and 0.37 μg/L, respectively. The results showed that the novel absorbent can be utilized as an effective material for the selective enrichment and determination of Cu(II) from food samples.     

An aptamer based assay for the β-adrenergic agonist ractopamine based on aggregation of gold nanoparticles in combination with a molecularly imprinted polymer

A sensitive visual aptamer-based assay is presented for the determination of ractopamine (RAC) in animal feed beef. In the absence of RAC, the aptamer binds to gold nanoparticles (AuNPs) and this prevents the AuNPs to undergo salt-induced aggregation which usually is accompanied by a color change from red to blue. If however, RAC is present, it will bind to the aptamer while the AuNPs remain uncoated so that aggregation and a color change will occur due to salt-induced aggregation. This can be monitored by spectrophotometer or even with bare eyes. Under optimal conditions, the aptasensor exhibits a linear range that covers the 10 to 400 ng.mL￣¹ RAC concentration range. The limit of detection is as low as 10 ng.mL￣¹. In order to further improve selectivity, a RAC-selective molecularly imprinted membrane was prepared and used to pre-extract RAC from complex samples. The combined method (molecularly imprinted membrane and aptasensor) was applied to the determination of RAC in spiked animal feed and beef and gave recoveries that ranged from 72.7 % to 87.3 % for complete feed and from 78.2 % to 86.5 % for beef, respectively.

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Graphical abstract A sensitive visual aptamer-based assay based on aggregation of gold nanoparticles in combination with a molecularly imprinted polymer was developed for the determination of ractopamine (RAC) in animal feed and beef.

     

Synthesis and Characterization of a Molecularly Imprinted Polymer for Preconcentration of Clothianidin in Environmental Samples

A molecularly imprinted polymer for the selective solid-phase extraction of clothianidin was prepared using the analyte as a template, methacrylic acid and styrene as functional monomers, ethylene glycol dimethacrylate as the cross-linker, acetonitrile as a porogen, and 2,2-azobisisobutyronitrile as an initiator. The polymer was characterized by scanning electron microscopy and infrared spectroscopy. Adsorption measurements indicated that the molecularly imprinted polymers exhibited good recognition ability and fast dynamics toward clothianidin. Using this imprinted polymer as a sorbent, a new method of molecularly imprinted solid phase extraction coupled to high performance liquid chromatography for the determination of clothianidin residues was developed. The molecularly imprinted solid phase extraction procedure was optimized to purify and enrich clothianidin residues in river water, soil, tomatoes, grapes, and Chinese cabbage. The average recoveries of clothianidin spiked at 0.005 to 0.05 mg/L were 84.32 to 89.49% in river water with a relative standard deviation 2.22 to 4.79% (n = 3). The average recoveries of clothianidin spiked at 0.05 to 0.5 mg/kg were 85.49 to 96.36% in soil, grapes, Chinese cabbage, and tomatoes, with a relative standard deviation of 2.40 to 6.02% (n = 3). Overall, this study provides a sensitive and effective method for the accurate determination of clothianidin residues in environmental samples.     

Synthesis of molecular imprinted polymer nanoparticles followed by application of response surface methodology for optimization of metribuzin extraction from urine samples

A molecular imprinted polymer was prepared with precipitation polymerization technique and applied as a sorbent for selective extraction and enrichment of metribuzin herbicide prior to high performance liquid chromatography. Optimization of critical variables affecting the efficiency of molecularly imprinted solid-phase extraction (MISPE), such as sorbent mass, sample pH and flow rate of sample, volume, concentration, and flow rate of elution solvent was done by employing central composite design (CCD) of the response surface methodology. Two separate models were developed for the adsorption and recycling steps. The analysis of variance (ANOVA) demonstrated that, experimental data were excellently fitted to the proposed response models. The optimum operating conditions were: a sorbent mass of 25 mg, sample pH 6.19, sample flow rate of 2.15 mL/min, and a 5 mL portion of methanol/acetic acid with 92.7:7.3 (v/v) ratio and flow rate of 2.1 mL/min for the extraction process. Under the optimized conditions, the linear range was obtained from 20 to 120 µg/L (R²?=?0.999) and the lowest detectable concentration (LOD) and the lowest quantitative concentration (LOQ) were calculated as 5.75 and 19.86 µg/L, respectively. Finally, the designed MISPE method was successfully applied to determine trace amount of metribuzin in real samples. The diluted urine samples were spiked with metribuzin at 4 levels and extracted with recoveries ranging from 93.82 to 97.84% and the relative standard deviation (RSD) less than 4.8%.     

Determination of Tetracyclines by Solid-Phase Extraction with a Molecularly Imprinted Polymer and High-Performance Liquid Chromatography

Tetracyclines are widely used antibiotics classified as emerging pollutants and may lead to an increase in bacterial resistance in the environment. In order to determine these compounds at low concentrations, a water-compatible molecularly imprinted polymer was developed for solid-phase extraction followed by high-performance liquid chromatography analysis. The monomers 2-hydroxyethyl methacrylate and glycerol dimethacrylate were added 1 h after the start of the synthesis to provide hydroxyl groups on the polymer surface. This hydrophilic layer established hydrogen bonds with water, minimizing interferences of this solvent in the analyte-polymer complex, increasing analyte adsorption. The polymer was then used for solid-phase extraction to preconcentrate the tetracyclines. The method provided low limits of quantification (5 µg L^?1), good linearity, precision, and accuracy for tetracyclines, with preconcentration factors of 14, 19, 29, and 41 for oxytetracycline, tetracycline, chlortetracycline, and doxycycline, respectively.     

Synthesis of a novel molecularly imprinted polymer based on functionalized multi-walled carbon nanotubes for selective extraction of sulfadiazine prior to spectrophotometric determination

A novel and efficient sulfadiazine imprinted polymer was synthesized via co-precipitation method and successfully grafted on magnetic multi-walled carbon nanotubes. The synthesized magnetic imprinted polymer was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction analysis, thermal analysis and applied as a sorbent for selective magnetic solid-phase extraction of sulfadiazine. The retained sulfadiazine was eluted by 150.0 µL methanol/acetic acid (6:4) solution and quantified by fiber optic linear array spectrophotometry via formation of a detectable azo dye. All parameters affecting the extraction of sulfadiazine were investigated and optimized. Under the optimized conditions, the method exhibited a linear dynamic range of 2.0–50.0 µg L^?1 with a detection limit of 0.56 µg L^?1 and enrichment factor of 300.0. The relative standard deviation at 30.0 µg L^?1 of sulfadiazine (N = 6) was 2.8 and 4.6% for intra-day and inter-day, respectively. The method was successfully applied to determine sulfadiazine in human urine, honey, milk and environmental water samples.     

Experimental and computational studies on molecularly imprinted solid-phase extraction for gonyautoxins 2,3 from dinoflagellate <Emphasis Type="Italic">Alexandrium minutum</Emphasis>

An innovative and effective extraction procedure based on molecularly imprinted solid-phase extraction (MISPE) was developed for the isolation of gonyautoxins 2,3 (GTX2,3) from Alexandrium minutum sample. Molecularly imprinted polymer microspheres were prepared by suspension polymerization and and were employed as sorbents for the solid-phase extraction of GTX2,3. An off-line MISPE protocol was optimized. Subsequently, the extract samples from A. minutum were analyzed. The results showed that the interference matrices in the extract were obviously cleaned up by MISPE procedures. This outcome enabled the direct extraction of GTX2,3 in A. minutum samples with extraction efficiency as high as 83 %, rather significantly, without any need for a cleanup step prior to the extraction. Furthermore, computational approach also provided direct evidences of the high selective isolation of GTX2,3 from the microalgal extracts.     

A novel dual-function molecularly imprinted polymer on CdTe/ZnS quantum dots for highly selective and sensitive determination of ractopamine

A novel dual-function material was synthesized by anchoring a molecularly imprinted polymer (MIP) layer on CdTe/ZnS quantum dots (QDs) using a sol–gel with surface imprinting. The material exhibited highly selective and sensitive determination of ractopamine (RAC) through spectrofluorometry and solid-phase extraction (SPE) coupled with high performance liquid chromatography (HPLC). A series of adsorption experiments revealed that the material showed high selectivity, good adsorption capacity and a fast mass transfer rate. Fluorescence from the MIP-coated QDs was more strongly quenched by RAC than that of the non-imprinted polymer, which indicated that the MIP-coated QDs acted as a fluorescence sensing material could recognize RAC. In addition, the MIP-coated QDs as a sorbent was also shown to be promising for SPE coupled with HPLC for the determination of trace RAC in feeding stuffs and pork samples. Under optimal conditions, the spectrofluorometry and SPE-HPLC methods using the MIP-coated QDs had linear ranges of 5.00 × 10⁻¹⁰–3.55 × 10⁻⁷ and 1.50 × 10⁻¹⁰–8.90 × 10⁻⁸ mol L⁻¹, respectively, with limits of detection of 1.47 × 10⁻¹⁰ and 8.30 × 10⁻¹¹ mol L⁻¹, the relative standard deviations for six repeat experiments of RAC (2.90 × 10⁻⁹ mol L⁻¹) were below 2.83% and 7.11%.     

A molecularly imprinted polymer for solid phase extraction of allantoin

We describe a molecularly imprinted polymer (MIP) for the solid-phase extraction of the skin protectant allantoin. The MIP was deposited on the surface of monodisperse silica microspheres possessing acroyl groups on the surface (MH-SiO₂). The resulting MIP microspheres (MH-SiO₂@MIP) showed a 3.4-fold higher adsorption capacity and a 1.9-fold better selectivity for allantoin than the respective non-imprinted polymer (MH-SiO₂@NIP). The monolayer adsorption capacities of the MH-SiO₂@MIP and the MH-SiO₂@NIP were calculated with the help of the Langmuir model and found to be 6.8 and 1.9 mg?g^?1, respectively. Adsorption kinetics fit a pseudo-second order rate mechanism, with an initial adsorption rate of 1.44 for the MH-SiO₂@MIP, and of 0.07 mg?g^?1?min^?1 for the MH-SiO₂@NIP. The material can be regenerated, and its adsorption capacity for allantoin remains stable for at least five regeneration cycles. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.

Investigation of ractopamine‐imprinted polymer for dispersive solid‐phase extraction of trace β‐agonists in pig tissues

Ractopamine, as an alternative β‐agonist to clenbuterol, is more and more used as leanness‐enhancing agent in the swine industry. This work presents a new molecularly imprinted polymer (MIP) using ractopamine as template for dispersive solid‐phase extraction of trace ractopamine and the structural related β‐agonists in animal tissues. The binding properties and selectivity of MIP were investigated. High selectivity in polar environment was found, since the extraction capacity of ractopamine with the MIP was 4.5‐fold as much as that with the non‐imprinted polymer in acetonitrile. Cross‐selectivity investigation indicates that the MIP preferentially binds the template and then the structural analogues according to their molecular similarity. Thermodynamic and kinetic investigation was performed to interpret the specific adsorption and molecular recognition of the MIP for ractopamine. Standard free energy, standard enthalpy, and standard entropy were determined. Related information suggested that adsorption of ractopamine onto MIP was an exothermic, spontaneous process. The MIP can be applied as dispersive solid‐phase extraction material for enrichment of ractopamine, isoxsuprine, fenoterol and clenbuterol in complex samples before HPLC analysis. The method revealed detection limits of 0.20–0.90 μg/L, recoveries of 83.8–115.2 and 85.2–110.2% for the spiked pig muscle and pig liver, respectively, with the RSD from 2.5 to 8.8%.     

安定分子印迹聚合物的制备及应用

以安定为模板分子,通过本体聚合和沉淀聚合的方法合成了分子印迹聚合物材料,考察了交联剂、致孔剂及温度等条件对聚合物材料性能的影响。电镜扫描图片显示本体聚合得到的聚合物呈不规则形状,而沉淀聚合得到的则是微球颗粒,形状规则。吸附实验表明,聚合物微球对安定的最大吸附量约为130μg/g,对奥沙西泮和硝西泮的吸附量约为110μg/g,对安定类化合物具有较高的吸附性能和选择性。通过对比合成现象和聚合物性能,最终选用以DVB为交联剂、乙腈为致孔剂合成的聚合物微球为固相萃取材料填充固相萃取小柱,从饲料及猪尿样品中选择性地分离、富集痕量安定类药物。结合高效液相色谱法检测,奥沙西泮、硝西泮和安定3种药物在0.1～20 mg/L范围内线性良好,相关系数为0.999 6～0.999 9,检出限(S/N=3)为0.03～0.08 mg/L,加标回收率为66%～79%。该方法为安定类药物的检测提供了一种新途径。     

多壁碳纳米管表面熊果酸印迹聚合物的制备及固相萃取

以聚乙烯醇修饰的多壁碳纳米管(MWCNTs)为基材,熊果酸(UA)为模板分子,甲基丙烯酸(MAA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,采用表面印迹技术在碳纳米管表面合成对熊果酸具有良好选择性的分子印迹聚合物( MWCNTs-MIPs).讨论了不同摩尔比例的功能单体与模板分子合成印迹聚合物的效果,得出...     

The application of pseudo template molecularly imprinted polymer to the solid-phase extraction of cyromazine and its metabolic melamine from egg and milk

The combination of molecularly imprinted polymer with high performance liquid chromatography has been developed to determine cyromazine and its metabolic melamine in some samples. However, the potential risk of template leakage used in molecularly imprinted polymer is a major disadvantage. To solve this problem, 2-(4,6-diamino-1,3,5-triazin-2-ylamino) ethanethiol disulfide, a molecule that shares the similar imprinting sites with cyromazine and melamine, was selected as pseudo template to prepare molecularly imprinted polymer. Methacrylic acid, ethylene glycol dimethyl acrylate and toluene were selected as functional monomer, crosslinker and porogen, respectively. The molecular recognition property and binding capability of cyromazine and melamine were evaluated by adsorption test and Scatchard analysis. The results showed that the molecularly imprinted polymer based on pseudo template had more excellent affinity and selectivity for cyromazine and melamine. The resulting molecularly imprinted polymer was used as a solid-phase extraction material to enrich cyromazine and melamine in egg and milk samples for high performance liquid chromatography analysis. The solid-phase extraction process was carefully optimized. It was found that when different concentration of cyromazine and melamine standards were spiked into samples, satisfactory recovery rate of cyromazine and melamine were obtained as 85.6-98.8% with relative standard deviation <5.5%.