Preparation and characterization of a molecularly imprinted monolithic column for pressure‐assisted CEC separation of nitroimidazole drugs

A polymethacrylate‐based molecularly imprinted monolithic column bearing mixed functional monomers, using non‐covalent imprinting approach, was designed for the rapid separation of nitroimidazole compounds. The new monolithic column has been prepared via simple in situ polymerization of 2‐hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and ethylene dimethacrylate, using (S)‐ornidazole ((S)‐ONZ) as template in a binary porogenic mixture consisting of toluene and dodecanol. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of monomers as well as the composition of the porogenic solvent. The column performance was evaluated in pressure‐assisted CEC mode. Separation conditions such as pH, voltage, amount of organic modifier and salt concentration were studied. The optimized monolithic column resulted in excellent separation of a group of structurally related nitroimidazole drugs within 10 min in isocratic elution condition. Column efficiencies of 99 000, 80 000, 103 000, 60 000 and 99 000 plates/m were obtained for metronidazole, secnidazole, ronidazole, tinidazole and dimetridazole, respectively. Parallel experiments were carried out using molecularly imprinted and non‐imprinted capillary columns. The separation might be the result of combined effects including hydrophobic, hydrogen bonding and the imprinting cavities on the (S)‐ONZ‐imprinted monolithic column.     

Preparation and characterization of grafted imprinted monolith for capillary electrochromatography

In this paper, a molecularly imprinted polymer (MIP) coating grafted to a trimethylolpropane trimethacrylate (TRIM) core material for CEC was reported. The core monolith was prepared with a solution of 20% (w/w) TRIM in a mixture of porogen and a polymerization precursor, which can generate a stable electroosmotic flow due to the formation of ionizable groups after postpolymerization hydrolization. Graft polymerization took place on the resultant TRIM monolith with a mixture of template, methacrylic acid, and ethylene glycol dimethacrylate. Strong recognition ability (selectivity factor was 5.83) for S‐amlodipine and resolution of enatiomers separation (up to 7.99) were obtained on the resulting grafted imprinted monolith in CEC mode. The influence of CEC conditions on chiral separation, including the composition of mobile phase, pH value, and the operating voltages was studied. These results suggest that the method of grafted polymerization reported here allows a rapid development of MIP monolith once core materials with desired properties are available, and is a good alternative to prepare CEC‐based monolithic MIPs.     

Preparation and characterization of molecularly imprinted silica monolith for screening sulfamethazine

In this work, a novel approach of preparing molecularly imprinted film‐derivatized silica monolith materials was developed by a two‐step procedure. The silica monolithic support was first prepared by the sol–gel method with tetramethoxysilane as the precursor. Subsequently, vinyl groups were introduced onto the surface of silica monolith by immobilization of γ‐methacryloxypropyltrimethoxysilane. The prepolymerization mixtures, consisting of methacrylic acid as a functional monomer, ethylene dimethacrylate as a crosslinker, sulfamethazine as a template molecule and an ionic liquid as porogen, were injected into the silica monolith immobilized vinyl groups to form the molecularly imprinted films on the surface of the vinyl functionalized silica monolith. The monolithic materials were characterized by SEM, Fourier transform IR and solid‐state reflection UV spectra. The resulted imprinted materials were evaluated under CEC and HPLC mode. The results indicated that there were enough recognition sites on the surface of the imprinted film‐derivatized monolithic materials for selectively recognizing sulfamethazine from the sulfonamide mixture. Ionic liquids, which was utilized as the porogens, could improve the flow‐through property and the imprinting effect of the molecularly imprinted film‐functionalized silica monolithic materials.     

Preparation and evaluation of a monolithic molecularly imprinted polymer for the chiral separation of neurotransmitters and their analogues by capillary electrochromatography

A monolithic molecularly imprinted polymer (MIP) column was prepared as the stationary phase for the capillary electrochromatographic (CEC) separation of a group of structurally related compounds including dopamine (DA), (±)-epinephrine (EP), (-)-isoproterenol (ISO), (±)-norepinephrine (NE), (±)-octopamine (OCT), and (±)-synephrine (SYN). Here, (-)-NE was used as the template. Either methacrylic acid (MAA) or itaconic acid (IA) together with a mixture of ethylene glycol dimethacrylate (EDMA) and α,α'-azobis(isobutyronitrile) (AIBN) in N,N-dimethylformamide (DMF) was introduced into a pre-treated, silanised, fused-silica capillary by a thermal non-covalent polymerisation procedure. Optimised conditions for the polymerisation reaction were assessed by the separation efficiency of the template. Both the template/monomer/cross linker molar ratio and the compositions of the functional monomer, cross-linker, and porogen affected polymerisation. The optimum in situ polymerisation reaction was performed at 65 °C for 17 min. By varying CEC parameters like eluent composition and pH, we observed that the addition of SDS to the eluent clearly improved the CEC separations. With a mobile phase of citrate buffer (10 mM, pH 3)/SDS (40 mM)/acetonitrile (2/2/1, v/v/v) solution and an applied voltage of 10 kV, the six related structures of the template and their enantiomeric mixtures were satisfactorily separated at 30 °C.     

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%.     

Preparation of open tubular molecule imprinted polymer capillary columns with various templates by a generalized procedure and their chiral and non‐chiral separation performance in CEC

A generalized preparation procedure of open tubular (OT) molecule imprinted polymer (MIP) columns is proposed for a number of templates with acidic functionality such as profen drugs and others. The template (S‐enantiomer) was mixed with methacrylic acid, ethylene glycol dimethacrylate and 4‐styrenesulfonic acid, dissolved in a porogen mixture of ACN/2‐propanol (9/1), and incubated in a pretreated and silanized fused silica capillary by the thermal non‐covalent polymerization procedure. The whole preparation procedure was exactly the same for all the MIP capillaries except for the selection of template. Nevertheless, the morphologies of the MIP layers were markedly variant depending upon the choice of template. The separation efficiency of each OT‐MIP column for chiral separation of R‐ and S‐enantiomers was examined and tuned to obtain the best separation efficiency by changing the chromatographic parameters such as eluent composition and pH. Different optimized conditions were obtained for different OT‐MIP columns. Nevertheless, a unified eluent could be used to obtain still quite satisfactory results. Non‐chiral separation of the MIP columns were also examined in the unified eluent with two sets of test mixtures, that is, a mixture of alkylbenzenes and a mixture of small polar solutes. The chiral and non‐chiral separation of this study resulted in very good separation efficiencies. This work is the very first study for the generalization of preparation of OT‐MIP columns for a number of templates.     

分子印迹聚合物在毛细管电色谱拆分手性药物中的研究进展

手性药物通过与生物体内生物大分子之间的手性匹配与分子识别来发挥药理作用。两个对映体与体内手性环境相互作用的不同导致每个对映体表现出不同的药理活性、代谢过程、代谢速率及毒性等药代动力学特征。因此发展手性药物的拆分方法,对于手性药物的开发和生产过程的质量监控具有重要意义。分子印迹聚合物(MIPs)是以目标分子作为模板而制备的高分子聚合物,它具有特定的空间分子结构和官能团,对目标分子具有高度的特异性识别能力。基于该特点,MIPs非常适合于手性药物的拆分和纯化。毛细管电色谱(CEC)可同时基于毛细管电泳和液相色谱的分离机理对目标物进行分离,因此具有高分离效率和高选择性的特点。将MIPs材料作为CEC的固定相,可将这两种技术的优势结合,从而实现对手性药物的高效拆分。MIPs材料在1994年首次应用于CEC手性拆分,此后该研究领域开始获得关注和发展。MIPs材料主要通过4种模式在CEC中实现手性拆分,分别是作为开管柱、填充柱和整体柱的固定相以及分离介质中的准固定相。该综述以这4种模式作为分类基准,根据MIPs制备所需的材料和分离对象对其在CEC手性拆分中的应用进行了总结,揭示了MIPs在CEC手性...     

CEC separation of ofloxacin enantiomers using imprinted microparticles prepared in molecular crowding conditions

Molecular crowding is a new concept to obtain molecularly imprinted polymers (MIPs) with greater capacity and selectivity, which could shift the equilibrium of a print molecule reacting with functional monomers in the direction of complex formation side. In this work, molecular crowding agent was first applied to the preparation of MIPs microparticles by precipitation polymerization. A new system of molecular crowding surrounding was developed, composed of polystyrene and tetrahydrofuran, in the presence of the template (S)-ofloxacin. Partial filling capillary electrochromatography (CEC) was utilized to evaluate imprinting effect of the resulting microparticles by chiral separations of ofloxacin. Some important parameters in the preparation, i.e. template to monomer ratio, influence of cross-linking monomers and functional monomer composition on the CEC separation of MIP microparticles were investigated. Baseline separation of ofloxacin (R(s) =1.53) was obtained under optimized conditions and the highest theory plate of the later eluent (S)-ofloxacin was 5400. The textural and morphological parameters for imprinted particles, such as Brunauer-Emmett-Teller surface areas, pore volumes and pore size distributions have also been determined. Compared to the MIP microparticle prepared by conventional precipitation polymerization, the (S)-ofloxacin-imprinted particles formed under molecular crowding conditions showed higher selectivity (α=1.09) and separation efficiency (<25 min) in the CEC mode.     

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%.     

Coatings of one monomer molecularly imprinted polymers for open tubular capillary electrochromatography

One monomer molecularly imprinted polymer coatings were first synthesized in fused silica capillary columns with 2-methacrylamidopropyl methacrylate (MAM) as single functional monomer in addition to a cross-linking monomer. Since MAM may generate no or little EOF, a strategy of precursor of polymerization, which does not interfere with the formation of defined imprints, was used to introduce an ionizable functional monomer to generate a stable electroosmotic flow for electrochromatography (CEC) by post-polymerization hydrolization. The resulting MAM-based open-tubular imprinted capillary was able to separate enantiomers by means of CEC. The resolution of enantiomers separation achieved on S-amlodipine-imprinted capillary was up to 16.1. The strong recognition ability (selectivity factor was 3.23) and high column performance (theory plates was 26,053 plates m(-1)) of template were obtained. The MIP coatings were also prepared using either S-naproxen or S-ketoprofen as template molecule. The resolutions of enantiomers separation were 2.20 and 4.56, respectively. The results illustrate that the synthesis of MIP using one monomer is not only an experimental-simplified process, but also an approach to producing chiral stationary phase with high efficiency and selectivity.     

Preparation, evaluation and application of molecularly imprinted solid-phase microextraction monolith for selective extraction of pirimicarb in tomato and pear

A simple, rapid and sensitive method for the determination of pirimicarb in tomato and pear using polymer monolith microextraction (PMME) based on the molecularly imprinted polymer (MIP) monolith combined with high-performance liquid chromatography-photodiodes array detector (HPLC-PAD) was developed. By optimizing the polymerization conditions, such as the nature of porogenic solvent and functional monomer, the molar ratio of the monomer and cross-linker, an pirimicarb MIP monolith was synthesized in a micropipette tip using methacrylic acid (MAA) as the functional monomer, ethylene dimethacrylate (EGDMA) as the cross-linker and the mixture of toluene-dodecanol as the porogenic solvent. The MIP monolith showed highly specific recognition for the template pirimicarb. The monolith was applied for the selective extraction of pirimicarb in tomato and pear. Several parameters affecting MIP-PMME were investigated, including the nature and volume of extraction solvent, sample volume, flow rate and sample pH. Under the optimum PMME and HPLC conditions, the linear ranges were 2.0-1400 μg/kg for pirimicarb in tomato and pear with the correlation coefficient of above 0.999. The detection limits (s/n=3) were both 0.6 μg/kg. The proposed method was successfully applied for the selective extraction and determination of pirimicarb in tomato and pear.     

Chiral separation by （S）-naproxen imprinted monolithic column with mixed functional monomers

Molecularly imprinted polymers (MIPs), using (S)-naproxen as template and the combination of butyl methacrylate (BMA) and MAA (1:1 molar ratio) as functional monomers were synthesized by an in situ polymerization reaction. The rendered monolithic column was evaluated in HPLC mode. The result showed that the monolithic MIPs with the combination of two monomers produced better chiral resolution of rac-naproxen (Rs=1.55) and column efficiencies of imprinted molecules (N=2860 plates/m)than that with pure MAA.     

Monodispersed, molecularly imprinted polymers for cinchonidine by precipitation polymerization

Three monodispersed, molecularly imprinted polymers (MIPs) for cinchonidine (CD) have been synthesized by precipitation polymerization. MIP1 was prepared using methacrylic acid (MAA) as a functional monomer and divinylbenzene (DVB) as a cross-linker and MIP2 was prepared with further addition of 2-hydroxyethyl methacrylate (HEMA) as a co-monomer. For the preparation of MIP3, core-shell type MIP, monodispersed DVB homopolymers, which are prepared by precipitation polymerization, were used as a core and CD-imprinted MAA-DVB copolymer phases were coated onto the core. Three MIPs synthesized gave monodispersed, spherical beads in micrometer sizes. The binding characteristics and molecular recognition properties of MIP1-3 were examined by Scatchard analysis and chromatographic studies. The association constant of CD with MIP1 was the highest among MIPs prepared, while that with MIP3 was the lowest. The template molecule, CD, was more retained than its stereoisomer, cinchonine, on the three MIPs, and the stereoseparation factor of 38 was obtained with MIP3.     

Selective separation of magnolol using molecularly imprinted membranes

Molecularly imprinted membranes (MIMs) for selective separation of magnolol were prepared by thermal polymerization using magnolol as the template, ethylene glycol dimethacrylate (EGDMA) as the cross‐linker, 2,2‐azobisisobutyronitrile (AIBN) as the initiator, organic solvent as the porogen, methacrylamide (MAM) and acrylic acid (AA) as the functional monomers and cellulose acetate as the agglutinant. Commercial filter paper was used as the supporting material. The effects of different porogens and the ratio of functional monomers on the binding and recognition capacity of MIMs were investigated, and the morphology of the membranes was examined by scanning electron microscopy (SEM). The results showed that the MIMs have the highest selectivity to magnolol when the ratio of MAM/AA was 1:4 and tetrahydrofuran (THF) with dimethyl sulfoxide (DMSO) was used as the porogen. The morphology of the imprinted membranes after template extracting is much rougher with big cavities than that of the non‐imprinted membranes (NIMs) and the imprinted membranes before template extracting. The MIMs can selectively separate the magnolol.     

Open tubular layer of S‐ofloxacin imprinted polymer fabricated in silica capillary for chiral CEC separation

An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin.     

A novel sensor based on multi-walled carbon nanotubes and boron-doped double-layer molecularly imprinted membrane for the analysis of SCZ in pharmaceutical and biological samples

ABSTRACT

A molecularly imprinted electrochemical sensor for the rapid detection of the anti-parasitic drug Secnidazole (SCZ) is reported. In this work, the build electrochemical sensor was based on a carbon paste electrode (CPE) modified with multi-wall carbon nanotubes (MWCNTs) and boron-embedded duplex molecularly imprinted composite membranes (B-DMICMs), that significantly increased the efficiency of the sensor for the detection of template molecule SCZ. Density functional theory (DFT) was employed to study the interactions between the template and monomers to select appropriate functional monomers for rational design of the B-DMICMs.The optimal experimental conditions were optimised for the factors affecting the performance of the sensor. Under the optimal conditions, the reduction peak currents of SCZ by differential pulse voltammetry increased linearly with SCZ concentration in the range from 3.0 × 10^?4 to 1.0 × 1.0^?6 mol L^?1 and 1.0 × 1.0^?6 to 1.91 × 10^?8 mol L^?1 with a detection limit of 1.72 × 10^?8 mol L^?1 for secnidazole, which is significantly lower than those in the currently used methods and in previous reports. This method offers low cost, sensitive and effective determination of SCZ and can potentially be used for detection of SCZ in pharmaceutical and biological samples with good precision and accuracy.     

Chiral resolution of derivatized amino acids using uniformly sized molecularly imprinted polymers in hydro-organic mobile phases

Uniformly sized molecularly imprinted polymers (MIPs) for Boc-l-Trp were prepared using ethylene glycol dimethacrylate (EDMA) as the cross-linker, and methacylic acid (MAA) and/or 4-vinylpyridine (4-VPY) as the functional monomers or without use of a functional monomer. The MIPs prepared were evaluated using acetonitrile or a mixture of phosphate buffer and acetonitrile as the mobile phase. The Boc-l-Trp-imprinted EDMA polymers can recognize Boc-l-Trp by its molecular shape, and can thus afford the enantioseparation of Boc-Trp. Besides the molecular shape recognition, the hydrophobic interactions with the polymer backbones as well as the hydrogen-bonding interactions of Boc-l-Trp with carboxyl and pyridyl groups in the polymers should work for the retention and recognition of Boc-l-Trp on the imprinted MAA-co-EDMA and 4-VPY-co-EDMA polymers, respectively, in the hydro-organic mobile phase. The hydrogen-bonding interactions seem to become dominant when only acetonitrile is used as the mobile phase. The Boc-l-Trp-imprinted 4-VPY-co-EDMA polymers gave the highest retentivity and enantioselectivity for Boc-Trp among the MIPs prepared. However, the simultaneous use of MAA and 4-VPY was not effective for the enantioseparation of Boc-Trp in a hydro-organic mobile phase. Furthermore, the baseline separation of Boc-Trp enantiomers was attained within 10 min on the Boc-l-Trp-imprinted 4-VPY-co-EDMA polymers under the optimized HPLC conditions.     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.     

Molecularly imprinted polymers as tools for the screening of felodipine from dihydropyridine calcium antagonists by pressurized capillary electrochromatography

A group of structurally similar dihydropyridine calcium antagonists (DHPs) and related compounds were used to simulate a combinatorial library. A molecularly imprinted polymer (MIP) comprising felodipine (FLD) was synthesized in situ inside the capillary for use in the separation of FLD from other DHPs by pressurized electrochromatography (pCEC). To evaluate the feasibility of using the MIP columns for the separation of FLD, parameters including pH, the applied voltages, and the effect of organic modifier were studied. The results indicated that the MIP columns demonstrated better recognition properties over a pH range of 4–6. The efficiency (plates/m) at pH 5.0 for the non-imprinted analytes was 117,000 for thiourea, 18,700 for nicarpidine, 17,300 for nisoldipine, and 14,600 for nifedipine; however, the efficiency for the imprinted analyte FLD was low, as evidenced by the broad peak, yielding only 5,100 plates/m. The column efficiency was also investigated under both micro-HPLC and pCEC conditions.     

Electroosmotic pump‐supported molecularly imprinted monolithic column for capillary chromatographic separation of nitrophenol isomers

In this work, a novel molecularly imprinted polymer (MIP) monolithic column with integrated in‐column electroosmotic pump (EOP) was designed and successfully prepared to facilitate the capillary chromatography with MIP column. A silica‐based EOP was synthesized at the detection end of the MIP monolithic capillary column by so‐gel to provide the hydrodynamic driven force for the capillary chromatography. Because of large surface area and low fluidic resistance of the silica monolith,a strong and steady EOF was generated by silica‐based EOP, indicating that the EOP was quite compatible with MIP capillary column. With the sufficient EOF provided by EOP, the electro‐driven based capillary chromatographic separation of nitrophenol isomers was achieved in 4‐vinylpyridine‐based MIP monolithic capillary, which was originally proved infeasible because of the EOF shortage. No significant influence upon the specific recognition of the MIP was found due to the setting of EOP after the detection window of the column. The influence of experimental parameters on the EOF such as voltage and pH value of running buffer was investigated. The column was also evaluated by capillary liquid chromatographic mode to compare with EOP‐driven capillary chromatography. Higher column efficiency was obtained by EOP‐driven separation with improved peak shape. The results suggested that EOP‐supported technique would be a good way to solve the problem of weak EOF generation in electro‐driven capillary chromatography.