Selective sample pretreatment by molecularly imprinted polymer monolith for the analysis of fluoroquinolones from milk samples

Water-compatible pefloxacin-imprinted monoliths synthesized in a water-containing system were used for the selective extraction of fluoroquinolones (FQs). The MIP monolith was synthesized by using methacrylic acid as the functional monomer, di(ethylene glycol) dimethacrylate as a cross-linker and methanol–water (10:3, v/v) as the porogenic solvent. The ability of the derivated MIP for selective recognition of FQs (ciprofloxacin, difloxacin, danofloxacin and enrofloxacin) and quinolones (flumequine, and oxolinic acid) was evaluated. The derivated monolith showed high selectivity and was able to distinguish between FQs and quinolones. A simple rapid and sensitive method using polymer monolith microextraction (PMME) based on the MIP monolith combined with HPLC with fluorescence detection was developed for the determination of four FQs from milk samples. Owing to the unique porous structure and flow-through channels in the network skeleton of the MIP monolith, phosphate buffer diluted milk samples were directly supplied to PMME; allowing non-specific bound proteins and other biological matrix to be washed out, and FQs to be selectively enriched. The limit of detection of the method was 0.4–1.6 ng/mL and recovery was 92.4–98.2% with relative standard deviations less than 5.9%.     

Selective determination of trace thiamphenicol in milk and honey by molecularly imprinted polymer monolith microextraction and high-performance liquid chromatography

A novel solid-phase microextraction (SPME) method based on molecularly imprinted polymer (MIP) monolith as the sorbent for the selective extraction of thiamphenicol (TAP) in milk and honey was developed. The newly developed MIP monolith was produced using TAP as the template molecule, 4-vinylpyridine (4-VP) as the functional monomer. The TAP-MIP monolith synthesized in a micropipette tip could be connected with syringes in different sizes simply to perform SPME process without any other treatment. The derivated MIP monolith showed high selectivity and enrichment ability for TAP. A simple, rapid and sensitive method for the determination of TAP in milk and honey using polymer monolith microextraction (PMME) based on the MIP monolith combined with high-performance liquid chromatography-photodiodes array detector was developed. Several parameters affecting MIP monolith microextraction were investigated, including the flow rate, volume, pH and salt concentration of sample, the type and volume of washing solution, the type and flow rate of eluent. The recovery of this method for TAP was investigated and high recoveries of 92.9-99.3% from milk and honey were obtained with relative standard deviations less than 4.9%.     

A selective molecularly imprinted polymer-solid phase extraction for the determination of fenitrothion in tomatoes

A new and selective sorbent for molecularly imprinted solid-phase extraction (MISPE) was developed and applied for the determination of residues of fenitrothion (FNT) in tomatoes, using HPLC coupled to photodiode array detection (HPLC-DAD). Using FNT as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene as the porogenic solvent, and bulk polymerization as the synthetic method, a molecularly imprinted polymer (MIP) was synthesized. In order to choose the medium which promotes the best molecular recognition of FNT by the MIP, the adsorption of FNT by the MIP was studied in different media containing acetonitrile and toluene. Besides FNT, three structurally related compounds were used to evaluate the selectivity of the FNT-molecularly imprinted polymer. The MIP exhibited the highest selective rebinding to FNT. The method developed was validated, using fortified blank tomato samples. The extraction efficiency was 96%. The limits of detection and quantitation were 0.050 and 0.130 μg g⁻¹, respectively. The intra-day precision was 5.9% and the inter-day precision 8.1%. The accuracy was higher than 89% for a concentration level around the maximum residue limit of 0.5 μg g⁻¹.     

分子印迹整体柱富集-高效液相色谱法测定植物中的痕量细胞分裂素

采用分子印迹整体柱富集-高效液相色谱法选择性分离分析了植物样品中痕量细胞分裂素的含量。结果表明,以激动素为模板分子,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,甲苯与十二醇为致孔剂,可在不锈钢柱管中原位聚合制备激动素分子印迹整体柱;与非分子印迹整体柱对比,该分子印迹整体柱能选择性富集4种细胞分裂素,具有较好的重复性和高的萃取效率;在优化的实验条件下,激动素(K)、激动素核苷(KR)、反式-玉米素(tZ)和meta-topolin(mT)的平均加标回收率分别为91.9%、80.0%、87.5%和50.2%,相对标准偏差均小于11.8%。本方法已成功地用于不同植物样品中4种细胞分裂素的分离和分析。     

苏丹红I分子印迹聚合物的制备及其性能评价

以苏丹红I为模板分子,通过沉淀聚合法制备了一种对苏丹红I具有特异性吸附的分子印迹聚合物。通过选择性评价和前沿色谱实验,评价了致孔剂的选择和用量、功能单体和模板分子的物质的量比对分子印迹聚合物识别性能的影响。实验结果表明: 当以甲醇和乙腈的混合液(体积比为30:10)为致孔剂,甲基丙烯酸(MAA)为功能单体,且功能单体和模板分子的物质的量比为8:1时,分子印迹聚合物的印迹因子为2.32,亲和位点总数(Bt)为0.50 μmol/g;将其作为固相萃取柱填料用于辣椒粉样品中痕量苏丹红I的净化和富集,结果表明: 苏丹红I浓度在10～500 μmol/L范围内时,呈现良好的线性关系(r=0.999);检出限为3.3 μmol/L,加标回收率为95.87%～98.41%,相对标准偏差低于3.1%。该方法有望用于辣椒粉样品中苏丹红I添加剂的常规检测。     

新型强阳离子交换聚合物整体柱的制备及其在奶制品中三聚氰胺测定中的应用

在内径为530 μm的石英毛细管中原位聚合得到一种新的强阳离子交换聚合物整体柱2-丙烯酰胺-2-甲基-1-丙磺酸-乙二醇二甲基丙烯酸酯聚合物(poly(AMPS-co-EDMA))整体柱,并将其作为聚合物整体柱微萃取(PMME)的萃取介质。优化N,N-二甲基甲酰胺(DMF)和聚乙二醇(PEG)致孔体系的比例,制备得到的poly(AMPS-co-EDMA)整体柱渗透性好、机械强度高且在水溶液中具有良好的稳定性。通过考察样品溶液的pH值、盐浓度和有机溶剂含量对萃取效率的影响,证明该整体柱主要通过强阳离子交换和疏水相互作用对三聚氰胺进行萃取富集。在PMME与高效液相色谱联用技术的基础上,建立了检测奶制品中三聚氰胺含量的分析方法。奶制品中三聚氰胺的检出限和定量限分别为0.09 mg/kg和0.3 mg/kg,在0.5~80 mg/kg的含量范围内具有良好的线性关系,日内、日间测定的相对标准偏差不高于7.5%。结果表明,该方法简便、快速、灵敏度高且成本低,适合于奶制品中微量三聚氰胺的检测。     

Synthesis and application of a molecularly imprinted polymer in the solid-phase extraction of ketoprofen from wastewater

Ketoprofen is a nonsteroidal anti-inflammatory drug widely consumed by humans as it possesses analgesic activities. A selective molecularly imprinted polymer (MIP) for ketoprofen was synthesized and applied as a solid-phase extraction sorbent. MIP was synthesized using 2-vinylpyridine, ethylene glycol dimethacrylate, 1,1′-azobis(cyclohexanecarbonitrile), toluene/acetonitrile (9:1, v/v), and ketoprofen as a functional monomer, cross-linker, initiator, porogenic mixture, and template, respectively. The polymerization was performed at 60 °C for 16 h, and thereafter the temperature was increased to 80 °C for 24 h to achieve a solid monolith polymer. Nonimprinted polymer was synthesized in a similar manner with the omission of ketoprofen. Characterization with thermogravimetric analysis and X-ray diffraction showed that the synthesized polymers were thermally stable and amorphous. Solid-phase extraction cartridges packed with MIP were used with high-performance liquid chromatography for quantitative analysis of ketoprofen in wastewater. The analytical method gave detection limits of 0.23, 0.17, and 0.09 μg/L in wastewater influent, effluent, and deionized water, respectively. The recovery for the wastewater influent and effluent spiked with 5 μg/L of ketoprofen was 68%, whereas 114% was obtained for deionized water. The concentrations of ketoprofen in the influent and effluent samples were in the ranges of 22.5–34.0 and 1.14–5.33 μg/L, respectively. Overall, the analytical method for the analysis of ketoprofen in wastewater was rapid, affordable, accurate, precise, sensitive, and selective.     

Molecularly imprinted polymers for on-line preconcentration by solid phase extraction of pirimicarb in water samples

The synthesis and performance of a molecularly imprinted polymers (MIPs) as a selective solid phase extraction sorbent for the preconcentration of the carbamate pirimicarb from water samples is described. The MIP was prepared using pirimicarb as the template, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer, and using chloroform as the solvent. The detection of pirimicarb was carried out by differential pulse voltammetry (DPV) at a hanging mercury drop electrode (HMDE) in 0.1 mol l⁻¹ HCl. Solvents of different polarities were checked for the polymer synthesis, and different experimental variables (sample pH, selection of the eluent used, eluent volume, analyte and eluent flow rates and sample volume) associated with the rebinding/extraction process were optimised. For a 25 ml sample, the process took about 13 min and resulted in a nominal enrichment factor of 50 (eluent MeOH:H₂O:HAc, 7:2:1; 0.5 ml) for pirimicarb. A limit of detection of 4.1 μg l⁻¹ was obtained, and a good reproducibility of the measurements using different MIP microcolumns was found. Furthermore, the MIP selectivity was evaluated by checking several substances with similar and different molecular structures to that of pirimicarb. As an application, pirimicarb was determined in water samples of diverse origin which were spiked at a concentration level of 71.5 μg l⁻¹.     

Molecularly imprinted solid-phase extraction for the determination of fenitrothion in tomatoes

Organophosphorus insecticides are widely employed in agriculture, and residues of them can remain after harvesting or storage. Pesticide residue control is an important task for ensuring food safety. Common chromatographic methods used in the determination of pesticide residues in food require clean-up and concentration steps prior to quantitation. While solid-phase extraction has been widely employed for this purpose, there is a need to improve selectivity. Due to their inherent biomimetic recognition systems, molecularly imprinted polymers (MIP) allow selectivity to be enhanced while keeping the costs of analysis low. In this work, a MIP that was designed to enable the selective extraction of fenitrothion (FNT) from tomatoes was synthesized using a noncovalent imprinting approach. The polymer was prepared using methacrylic acid as functional monomer and ethyleneglycol dimethacrylate as crosslinking monomer in dichloromethane (a porogenic solvent). The polymer was characterized by Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and nitrogen sorption porosimetry. The pore structure and the surface area were evaluated using the BET adsorption method. To characterize the batch rebinding behavior of the MIP, the adsorption isotherm was measured, allowing the total number of binding sites, the average binding affinity and the heterogeneity index to be established. A voltammetric method of quantifying FNT during the molecularly imprinted solid-phase extraction (MISPE) studies was developed. The polymer was placed in extraction cartridges which were then used to clean up and concentrate FNT in tomato samples prior to high-performance liquid chromatographic quantitation. The material presented a medium extraction efficiency of 59% (for analyses performed with three different cartridges on three days and a fortification level of 5.0 μg g⁻¹) and selectivity when used in the preparation of tomato samples, and presented the advantage that the polymer could be reused several times after regeneration. Figure       

Selective solid-phase extraction of a triterpene acid from a plant extract by molecularly imprinted polymer

A molecularly imprinted polymer (MIP) has been prepared by a thermal polymerisation method using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linking agent, chloroform as porogenic solvent and an oleanane triterpene compound (18-beta-glycyrrhetinic acid) as imprinted molecule (template). Equilibrium ligand binding experiments were done to assess the performance of the MIP relative to non-imprinted polymer (NIP). After optimisation of SPE protocol (CHCl3 as washing solvent and MeOH as elution solvent), successful imprinting was confirmed by comparison of the recoveries between NIP (5%) and MIP (97%) cartridges. The binding capacity of the MIP for 18-beta-glycyrrhetinic acid was determined to be 0.94 mg g(-1). Four structurally related oleanane triterpenes (18-alpha-glycyrrhetinic acid, oleanolic acid, echinocystic acid, erythrodiol) were selected to assess the MIP selectivity. Experimental data illustrated the influence of functional groups on the triterpene skeleton. The MIP was applied to the solid-phase extraction of triterpenoids from a plant extract prior HPLC analysis. However, CHCl3 was replaced by ACN during the washing step in order to suppress non-specific interactions due to polar matrix components. A selective extraction of 18-beta-glycyrrhetinic acid from hydrolyzed extract of liquorice roots was achieved with a good extraction yield (98%).     

Rapid determination of Δ-Tetrahydrocannabinol in saliva by polymer monolith microextraction combined with gas chromatography-mass spectrometry

A method was developed for the determination of Δ⁹-Tetrahydrocannabinol (THC) in saliva by polymer monolith microextraction (PMME) combined with gas chromatography-mass spectrometry. The poly(methacrylic acid-co-ethylene glycol dimethacrylate) (p(MAA-co-EGDMA)) monolithic capillary column was selected as the extraction medium of PMME, which showed high extraction capacity towards THC in saliva. To reach optimum PMME extraction performance, several PMME parameters were investigated, including matrix pH, flow rate for extraction, sampling volume and elution solvent. Under the optimal conditions, good extraction efficiency was obtained with no matrix interference in the process of extraction and the subsequent GC-MS analysis. In the selected-ion monitoring (SIM) mode, the limit of detection (LOD) for THC was 0.68 ng/mL. The linearity range of the method was 3-300 ng/mL. Excellent reproducibility of the method was exhibited by intra- and inter-day precisions, yielding the relative standard deviations (R.S.D.s) less than 12%; recoveries higher than 89%. The proposed method was proved to be rapid, sensitive, and competently applied to the determination of THC in saliva samples.     

Application of multivariate analysis to the screening of molecularly imprinted polymers (MIPs) for ametryn

Among the solid-phase extraction (SPE) techniques, a novel system for a triazine herbicide named ametryn, has been developed based on a molecular imprinted polymer (MIP) phase. Through this method, the synthesis of the complementary to ametryn MIP was accomplished and the factors influencing its efficiency have been optimized. Through the optimization process, the type and the amounts of functional monomer and solvents, template amount, cross-linker, initiator as well as the polymerization temperature were considered to be evaluated. Based on the obtained results, the optimum conditions for the efficient polymerized sorbent, considering the recovery efficiency were solvent: acetonitrile, 6.41 mL; monomer: methacrylic acid, 5.41 mmol; template: 1.204 mmol; cross-linker: 27.070 mmol; initiator: 2.03 mmol; temperature: 40.86 degrees C. The optimum molar ratio among the template, monomer and cross-linker for ametryn was 1:4.49:22.48. The reversed-phase HPLC-UV was used for the ametryn determination, using an isocratic solvent delivery system (acetonitrile: H(2)O, 60:40), flow-rate of 0.8 mL min(-1) and a UV wavelength of 220 nm. In line with the obtained results, using central composite design (CCD) can increase the precision and accuracy of synthesis and optimization of MIP to ametryn and possibly other similar analogues.     

Capillary electrochromatography with monolithic stationary phases. II. Preparation of cationic stearyl-acrylate monoliths and their electrochromatographic characterization

A novel cationic monolithic stationary phase based on the co-polymerization of pentaerythritol diacrylate monostearate (PEDAS) with a selected quaternary amine acrylic monomer was designed for performing capillary electrochromatography at high flow velocity. While PEDAS functioned as both the ligand provider and the cross-linker, the quaternary amine acrylic monomer was introduced to control the magnitude of the electroosmotic flow (EOF). The fabrication of the cationic stearyl-acrylate monolith (designated as cationic C17 monolith) with controlled porosity was achieved by free radical polymerization using the initiator 2,2'-azobisisobutyronitrile in the presence of a ternary porogenic solvent composed of cyclohexanol, ethylene glycol and water. Four different quaternary amine acrylic monomers were investigated in order to find the optimum monomer for achieving maximum electroosmotic flow (EOF) velocity. Both photo- and thermally-initiated polymerization proved effective in producing the cationic C17 monolith, and the best monolith was achieved when [2-(acryloyloxy)ethyl]trimethyl ammonium methyl sulfate (AETA) was used as the quaternary amine acrylic monomer. Although the zeta potential of the resulting cationic C17 monolith is positive with respect to water, the magnitude and direction of the EOF was markedly affected by the nature of the electrolyte in the mobile phase. Consequently, anodal, zero or cathodal EOF was observed depending on the nature of the electrolyte, and this was attributed to the adsorption of the ionic components of the electrolyte on to the solid stationary phase, which is characterized by its amphiphilic nature consisting of C17 chains, ester functions, hydroxyl groups and quaternary amine moieties. Optimized PEDAS-AETA monoliths yielded columns with high separation efficiency and allowed rapid separations on the time scale of seconds to be achieved with short capillaries.     

聚合物整体柱固相微萃取-高效液相色谱法测定中成药和保健食品中枸橼酸西地那非

采用聚(甲基丙烯酸-乙二醇二甲基丙烯酸酯)聚合物整体柱固相微萃取(PMME),并与高效液相色谱联用,建立了中成药中枸橼酸西地那非的检测方法。实验优化了影响萃取效率的因素,包括萃取流速、萃取体积、样品基质pH值等参数。中成药样品经溶解和过滤后可直接进行分离分析。结果表明,枸橼酸西地那非在0.5～50μg/mL的浓度范围内具有良好的线性关系,检出限为0.05μg/mL,日内、日间测定的相对标准偏差不高于9.7%。方法已成功地应用到实际样品检测中,其加标回收率大于83.40%。该方法简单、快速、灵敏度高,适用于中成药及保健品中西地那非的分析检测。     

Preparation and Adsorption Ability of Molecularly Imprinted Polymer Microspheres for Malachite Green

Molecularly imprinted polymer (MIP) microspheres were synthesized through precipitation polymerization using malachite green (MG) as template, methacrylic acid (MAA) as monomer, and trimethylolpropane trimethacrylate (TRIM) as cross-linker. The microsphere structure of MIP was characterized by IR spectroscopy and SEM. The influence of preparation conditions such as monomer and cross-linker dosages on the polymer absorption of MG in acetonitrile solution was also explored. Under the optimum synthesis conditions (0.25 mmol MG, 1.5 mmol MAA, 2.5 mmol TRIM, 40 mL acetonitrile), the prepared MIP microspheres have a binding capacity as high as 2000 µg g^?1 of MG with an imprinting factor of above 4.0. The result suggests that the prepared MIP microspheres are promising material for the selective extraction of MG in complicated matrix solutions.     

邻苯二甲酸二（2-丙基庚）酯分子印迹固相萃取剂的制备及其应用

以邻苯二甲酸二辛酯（DOP）为虚拟模板分子,α-甲基丙烯酸（MAA）为功能单体,乙二醇二甲基丙烯酸酯（EDMA）为交联剂,采用沉淀聚合法制备了对邻苯二甲酸二（2-丙基庚）酯（DPHP）具有高选择性的分子印迹聚合物（MIP）。用紫外分光光度法探索了不同功能单体与模板分子的结合能力,与功能单体丙烯酸（AA）相比,MAA与DOP的结合能力更强,其最佳结合的物质的量比为6：1。考察MIP对DOP、DPHP、邻苯二甲酸二甲酯（DMP）、邻苯二甲酸二丁酯（DBP）的选择吸附性能,发现该聚合物对DPHP具有更高的选择吸附性。以制备的聚合物为固相萃取填料,结合HPLC分析,考察了淋洗剂与洗脱剂的种类和用量对DPHP回收率的影响。将DPHP甲醇溶液加载至萃取柱后用1 mL甲醇-水（1：9,v/v）淋洗,5 mL甲醇-乙酸（9：1,v/v）洗脱,DPHP在分子印迹固相萃取（MISPE）柱上的回收率达到96.8%,而在非印迹固相萃取（NISPE）柱上的回收率仅为52.9%。将建立的MISPE-HPLC方法应用于测定兔口服DPHP后不同时间点兔血清中DPHP的浓度,发现其血药浓度的最大值为5.88 μg/mL,达峰值时间为4 h,DPHP加标回收率为90.0%~92.0%,相对标准偏差小于5%。     

Preparation and evaluation of a phenylboronate affinity monolith for selective capture of glycoproteins by capillary liquid chromatography

A phenylboronate affinity monolith was prepared and applied to the selective capture of glycoproteins from unfractionated protein mixtures. The monolith was synthesized in a 100 μm i.d capillary by an in situ polymerization procedure using a pre-polymerization mixture consisting of 4-vinylphenylboronic acid (VPBA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, diethylene glycol and ethylene glycol as binary porogenic solvents, and azobisisobutyronitrile (AIBN) as initiator. The prepared monolith was characterized in terms of the morphology, pore property, and recognition property. The selectivity and dynamic binding capacity were evaluated by using standard glycoproteins and nonglycoproteins as model proteins. The chromatographic results demonstrated that the phenylboronate affinity monolith had higher selectivity and binding capacity for glycoprotein than nonglycoprotein. The resulting phenylboronate affinity monolith was used as the sorbent for in-tube solid phase microextraction (in-tube SPME), and the extraction performance of the monolith was assessed by capture of ovalbumin from egg white sample.     

Preparation of a mixed-mode hydrophilic interaction/anion-exchange polymeric monolithic stationary phase for capillary liquid chromatography of polar analytes

A novel cationic hydrophilic interaction monolithic stationary phase based on the copolymerization of 2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate (META) and pentaerythritol triacrylate (PETA) in a binary porogenic solvent consisting of cyclohexanol/ethylene glycol was designed for performing capillary liquid chromatography. While META functioned as both the ion-exchange sites and polar ligand provider, the PETA, a trivinyl monomer, was introduced as cross-linker. The monolithic stationary phases with different properties were easily prepared by adjusting the amount of META in the polymerization solution as well as the composition of the porogenic solvent. The hydrophilicity of the monolith increased with increasing content of META in the polymerization mixture. A typical hydrophilic interaction chromatography mechanism was observed when the content of acetonitrile in the mobile phase was higher than 20%. The poly(META-co-PETA) monolith showed very good selectivity for neutral, basic and acidic polar analytes. For polar-charged analytes, both hydrophilic interaction and electrostatic interaction contributed to their retention. Peak tailing of basic compounds was avoided and the efficient separation of benzoic acid derivatives was obtained.     

Molecularly imprinted solid-phase extraction for the selective determination of 17β-estradiol in fishery samples with high performance liquid chromatography

A molecularly imprinted polymer (MIP) has been synthesized by a thermo-polymerization method using methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, acetonitrile as porogenic solvent, and 17β-estradiol as template. The MIP showed obvious affinity for 17β-estradiol in acetonitrile solution, which was confirmed by absorption experiments. After optimization of molecularly imprinted solid-phase extraction (MISPE) conditions, three structurally related estrogenic compounds (17β-estradiol, estriol, and diethylstilbestrol) were used to evaluate the selectivity of the MIP cartridges. The MIP cartridges exhibited highly selectivity for E₂, the recoveries were 84.8 ± 6.53% for MIPs and 19.1 ± 1.93% for non-imprinted polymer (NIP) cartridges. The detection and quantification limits correspond to 0.023 and 0.076 mg L⁻¹. Furthermore, the MISPE methods were used to selectively extract E₂ from fish and prawn tissue prior to HPLC analysis. This MISPE-HPLC procedure could eliminate all matrix interference simultaneously and had good recoveries (78.3-84.5%).     

反乌头酸分子印迹聚合物微球的制备及其分子识别功能

以乙腈为分散剂,采用沉淀聚合法合成了反乌头酸分子印迹聚合物微球。研究了合成反应条件对聚合物形貌的影响,发现聚合前主客体氢键络合物和功能单体氢键低聚体是控制微球形成及其粒径大小的关键因素。通过振荡吸附法对聚合物的结合特性进行了评价,发现印迹聚合物微球对模板分子的识别选择性优于块状印迹聚合物和非印迹聚合物。