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

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

Separation and determination of the antitumor drug piritrexim by molecularly imprinted microspheres in high-performance liquid chromatography

Molecularly imprinted microspheres were synthesised using the antitumor drug piritrexim (PTX) as a template molecule by aqueous microsuspension polymerisation and were used as a high-performance liquid chromatographic stationary phase. The molecularly imprinted column exhibited strong retention behaviour to the template molecule. The influences of pH of the buffer and the ratio of methanol to buffer on the retention behaviour were investigated in detail. Results indicated that the baseline separation of PTX, trimetrexate (TMX), trimethoprim (TMP) and sulfamethazine (SMZ) was achieved when the pH value of the acetate buffer was above pH 3.5 and the ratio of methanol to the buffer was 6:4 (v/v). A gradient elution programme was employed to enhance the separation, which led to an improvement in sensitivity and a reduction in determination errors. The method developed was used to analyse urine samples supplemented with PTX. The recoveries of 5 g mL^–1 PTX in the urine sample were 99.1±3.0% and 93.3±2.8% at the beginning and 24 h later, respectively.     

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

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

Preparation and characterization of monodisperse molecularly imprinted polymers for the recognition and enrichment of oleanolic acid

Monodisperse molecularly imprinted polymers for oleanolic acid were successfully prepared by a precipitation polymerization method using oleanolic acid as a template, methacrylic acid as a functional monomer, and divinylbenzene/ethylene glycol dimethacrylate as a crosslinker in a mixture of acetonitrile and ethanol (3:1, v/v). The imprinted polymers and nonimprinted polymers were characterized by using scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The resulting imprinted polymers had average diameters of 3.15 μm and monodispersity values of 1.024. The results clearly demonstrate that use of ethanol as a cosolvent is indeed exceedingly effective in promoting the dissolution of oleanolic acid and in obtaining uniform microspheres. Molecular recognition properties and binding capability to oleanolic acid were evaluated by adsorption testing, which indicated that the imprinted polymers displayed optimal binding performance with a maximum adsorption capacity of 17.3 mg/g and a binding saturation time of 80 min. Meanwhile, the produced imprinted polymers exhibited higher selectivity to oleanolic acid than that for ursolic acid and rhein. Herein, the studies can provide theoretical and experimental references for the oleanolic acid molecular imprinted system.     

Synthesis of molecularly imprinted polymer nanoparticles for the fast and highly selective adsorption of sunset yellow

Novel molecularly imprinted polymer nanoparticles were synthesized by precipitation polymerization with sunset yellow as the template and [2‐(methacryloyloxy)ethyl] trimethylammonium chloride as the functional monomer. The molecularly imprinted polymer nanoparticles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and their specific surface area and thermal stability were measured. The molecularly imprinted polymer nanoparticles had a high adsorption capacity in wide pH range (pH 1–8) for sunset yellow. The adsorption equilibrium only needed 5 min, and the quantitative desorption was very fast (1 min) by using 10.0 mol/L HCl as the eluant. The maximum adsorption capacity of the molecularly imprinted polymer nanoparticles for sunset yellow was 144.6 mg/g. The adsorption isotherm and kinetic were well consistent with Langmuir adsorption model and pseudo‐second‐order kinetic model, respectively. The relative selectivity coefficients of the molecularly imprinted polymer nanoparticles for tartrazine and carmine were 9.766 and 12.64, respectively. The prepared molecularly imprinted polymer nanoparticles were repeatedly used and regenerated ten times without significant absorption capacity decrease.     

Molecularly imprinted polymer microspheres for solid-phase extraction of protocatechuic acid in Rhizoma homalomenae

Molecularly imprinted polymers (MIPs) had been prepared by precipitation polymerization method using acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, acetonitrile as the porogen solvent and protocatechuic acid (PA), one of phenolic acids, as the template molecule. The MIPs were characterized by scanning electron microscopy and Fourier transform infrared, and their performance relative to non-imprinted polymers was assessed by equilibrium binding experiments. Six structurally similar phenolic acids, including p-hydroxybenzoic acid, gallic acid, salicylic acid, syringic acid, vanillic acid, ferulic acid were selected to assess the selectivity and recognition capability of the MIPs. The MIPs were applied to extract PA from the traditional Chinese medicines as a solid-phase extraction sorbent. The resultant cartridge showed that the MIPs have a good extraction performance and were able to selectively extract almost 82% of PA from the extract of Rhizoma homalomenae. Thus, the proposed molecularly imprinted-solid phase extraction-high performance liquid chromatography method can be successfully used to extract and analyse PA in traditional Chinese medicines.     

Analysis of sulfamerazine in pond water and several fishes by high-performance liquid chromatography using molecularly imprinted solid-phase extraction

The synthesis and evaluation of a molecularly imprinted polymer (MIP) used as a selective solid-phase extraction sorbent and coupled to high-performance liquid chromatography (HPLC) for the efficient determination of sulfamerazine (SMR) in pond water and three fishes are reported. The polymer was prepared using SMR as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the crosslinking monomer in the presence of tetrahydrofuran as the solvent. The SMR-imprinted polymers and nonimprinted polymers were characterized by FT-IR and static adsorption experiments. The prepared SMR-imprinted material showed a high adsorption capacity, significant selectivity and good site accessibility. The maximum static adsorption capacities of the SMR-imprinted and nonimprinted materials for SMR were 108.8 and 79.6 mg g⁻¹, respectively. The relative selectivity factor of this SMR-imprinted material was 1.6. Several parameters influencing the solid-phase extraction process were optimized. Finally, the SMR-imprinted polymers were used as the sorbent in solid-phase extraction to determine SMR in pond water and three fishes with satisfactory recovery. The average recoveries of the MIP-SPE method were 94.0% in ultrapure water and 95.8% in pond water. Relative standard deviations ranging from 0.3% to 5.2% in MIP were acquired. The results for the SMR concentrations in crucian, carp and wuchang fish were 66.0, 127.1 and 51.5 ng g⁻¹, respectively. The RSDs (n = 5) were 3.51%, 0.53% and 5.08%, respectively. The limit of detection (LOD) for SMR was 1 ng g⁻¹ and the limit of quantitation (LOQ) was 3.5 ng g⁻¹.     

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

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

Determination of multi-residue for malachite green,gentian violet and their metabolites in aquatic products by high-performance liquid chromatography coupled with molecularly imprinted solid-phase extraction

A sorbent was synthesized and investigated for molecularly imprinted solid-phase extraction (MISPE). Molecularly imprinted polymers (MIPs) were synthesized via precipitation polymerization procedure, where methacrylic acid (MAA) was used as functional monomer and ethylene glycol dimethacrylate (EDMA) as cross-linking agent. The imprinting effect and selectivity of the MISPE were evaluated by elution experiments. The resulting MISPE showed high extraction selectivity to malachite green, gentian violet and their metabolites, which may be caused by both the ion exchange and the hydrophobic interactions. The determination of multi-residue for malachite green, gentian violet and their metabolites in aquatic products by HPLC coupled with MISPE was also investigated. The mean recoveries calculated by solvent calibration curve for malachite green (MG), gentian violet (GV), leucomalachite green (LMG) and leucogentian violet (LGV) were from 89.8% to 99.1% for grass carp, 90.6% to 101.2% for shrimp and 91.3% to 96.3% for shellfish. The decision limit (CCα) and the detection capability (CCβ) obtained for MG, GV, LMG and LGV were in the range of 0.11–0.14 and 0.19–0.24 μg kg⁻¹ for grass carp, shrimp and shellfish. The MISPE was successfully used off-line for the determination of MG, GV and their metabolites in aquatic products.     

Binding capacity of molecularly imprinted polymers and their nonimprinted analogs

Molecularly imprinted polymers bind their target compounds at binding sites. The binding sites are typically based on some type of functional group, such as carboxyl group. The total amount of such functional groups and their distribution into available and unavailable groups is not well known. The total binding capacity is usually indirectly determined from adsorption isotherms, which are measured much below the theoretical binding capacity. This work shows that in a variety of differently prepared, methacrylic acid based molecularly imprinted and nonimprinted polymers, all carboxylic groups used for the polymer synthesis are retained in the polymer, 80–90% of them can be accessed by strong bases and essentially the same amount can be used for adsorption of weak bases. This high level of adsorption can only be achieved, however, if the adsorbed weak base is strong enough, if the polymer is sufficiently elastic and if the solvent does not compete too strongly for the binding sites. These results may explain why the maximum binding capacities obtained from isotherm measurements are usually not equal to the total amount of available binding sites. This study confirms the usefulness of nonimprinted polymers at high loadings.     

Determination of methotrexate in human serum by high-performance liquid chromatography combined with pseudo template molecularly imprinted polymer

A pseudo template molecularly imprinted polymer (MIP) was prepared for methotrexate (MTX) and a RP-HPLC method combined with the MIP was developed for the determination of MTX in human serum. Because of the poor solubility of MTX in common MIP preparation solvents, trimethoprim (TMP), a molecule having the similar imprinting sites as MTX, is selected as the pseudo template. The MIP was prepared using methacrylic acid (MAA) and ethylene glycol dimethacrylate as functional monomer and cross-linker, respectively. ¹H NMR study showed highly strong interaction between TMP and MAA with hydrogen bonds. Chromatographic behaviors indicated that the TMP-MIP possessed excellent affinity and selectivity for MTX. And the imprinting factor for MTX was high up to 9.5 when 7:3 of acetonitrile:methanol (v/v) was used as mobile phase. Moreover, TMP-MIP was used as the solid-phase extraction (SPE) material to enrich the target compound MTX in human serum samples for HPLC analysis. The SPE process was carefully optimized and good recoveries of MTX were obtained as 81.6–86.2% with RSD of 0.22–1.84% when the spiked concentration of MTX was 2.0–10.0 μg mL⁻¹ in human serum samples. The results indicated that the pseudo template MIP can be applied to preconcentration, purification and analysis of MTX in clinic samples.     

Synthetic approaches to parabens molecularly imprinted polymers and their applications to the solid-phase extraction of river water samples

In this paper we describe the synthesis, characterisation and use of two distinct molecularly imprinted polymers (MIPs) prepared using esters of p-hydroxybenzoic acid (parabens) as templates: one MIP was synthesised by precipitation polymerisation using a semi-covalent molecularly imprinting strategy with methyl paraben as the template/target (MIP 1); the second MIP was prepared in monolithic form through a conventional non-covalent molecular imprinting strategy, with butyl paraben as the template (MIP 2). MIP 1 recognized methyl paraben, showed cross-selectivity for other parabens analytes used in the study and higher affinity towards these compounds than did a non-imprinted control polymer. Similarly, MIP 2 demonstrated higher affinity towards paraben analytes than a non-imprinted control polymer.For the analysis of environmental water samples, a solid-phase extraction (SPE) protocol was developed using MIP 2 as sorbent, and results were compared to a SPE using a commercial sorbent (Oasis HLB). With MIP 2 as sorbent and butyl paraben as target, when percolating 500 mL of river water spiked at 1 μg L⁻¹ through the SPE cartridge, and using 1 mL of isopropanol as cleaning solvent, a higher recovery of butyl 4-hydroxybenzoate (butyl paraben) and a cleaner chromatogram where achievable when using the MIP compared to the commercial sorbent.     

Synthesis and characterisation of molecularly imprinted catalytic microgels for carbonate hydrolysis

Novel molecularly imprinted microgels incorporating arginine and tyrosine side chains as functional monomers have been designed and synthesised with percentages of cross-linker ranging from 70 to 90%. Full chemico-physical characterisation including M_r, coil density and size particle determination concluded that all polymer preparations obtained can be classified as microgels. Molecular imprinting using a phosphate template was used to generate catalytic microgels for the hydrolysis of p-nitrophenyl carbonates. Kinetic characterisation of the catalytic activity of the different preparations indicated that values of critical monomer concentration (C_M) and percentage of cross-linker play an important role in determining the catalytic efficiency of the different preparations. Microgels containing 70% cross-linker were the only ones following the Michaelis-Menten saturation model and kinetic parameters were obtained using 4 mg/ml of M397: V_max = 1.34 × 10⁻⁶ M s⁻¹ (S.E. 1.28 × 10⁻⁷) and K_M = 2.38 × 10⁻³ M (S.E. 3.1 × 10⁻⁴).     

Preparation and evaluation of molecularly imprinted microspheres for solid-phase extraction of 1,4-hydroxybenzoic acid esters in soy

Molecularly imprinted microspheres (MIMs) were prepared by precipitation polymerization for the binding and recognition of 1,4-hydroxybenzoic acid esters. Ethyl p-hydroxybenzoate (EtPHB) was used as the template molecule, methacrylic acid as the functional monomer, ethylene dimethacrylate as the linking agent. It was evaluated by solid-phase extraction column packed with MIMs combined with liquid chromatography to determine trace preservatives including benzoic acid, methyl p-hydroxybenzoate, EtPHB, propyl p-hydroxybenzoate in food products. A solid-phase extraction based on MIM procedure was used to isolate four additives from the food matrix before quantitative analysis. The Scatchard plot suggested that the template-polymer system had two-site binding behavior with the dissociation constants of 0.3577 and 3.952 mg/g, respectively. The rebinding test, based on the molecularly imprinted solid-phase extraction column technique, showed the recoveries of soy samples spiked with four additives within 88.4-110.6%, with the relative standard deviations of 1.97-3.82%. Finally, the method was successfully applied for the analysis of parabens in foodstuff without traditional pretreatment.     

Porous molecularly imprinted polymer membranes and polymeric particles

Porous free-standing molecularly imprinted polymer membranes were synthesised by the method of in situ polymerisation using the principle of synthesis of interpenetrating polymer networks and tested in solid-phase extraction of triazine herbicides from aqueous solutions. Atrazine-specific MIP membranes were obtained by the UV-initiated co-polymerisation of methacrylic acid, tri(ethylene glycol) dimethacrylate, and oligourethane acrylate in the presence of a template (atrazine). Addition of oligourethane acrylate provided formation of the highly cross-linked MIP in a form of a free-standing 60 μm thick flexible membrane. High water fluxes through the MIP membranes were achieved due to addition of linear polymers (polyethylene glycol M_w 20,000 and polyurethane M_w 40,000) to the initial mixture of monomers before the polymerization. As a result, typical semi-interpenetrating polymer networks (semi-IPNs) have been formed, where the cross-linked polymer was represented by the atrazine-specific molecularly imprinted polymer, while the linear one was represented by polyethylene glycol/polyurethane. Extraction of the linear polymers from the fully formed semi-IPNs resulted in formation of large pores in the membrane structure. At the same time, extraction of the template molecules lead to formation of the sites in the polymeric network, which in shape and arrangement of functional groups are complementary to atrazine. Reference polymeric membranes were prepared from the same mixture of monomers but in the absence of the template. Recognition properties of the MIP membranes were estimated in solid-phase extraction by their ability to selective re-adsorbtion of atrazine from 10⁻⁸ to 10⁻⁴ M aqueous solutions. The imprinting effect was demonstrated for both types of the MIP membranes and the influence of the type of the linear compound on their recognition properties was estimated. The recognition properties of the MIP membranes were compared to those of the MIP particles of the same composition. Morphology of the MIP membranes was investigated using the SEM microscopy. High fluxes of the developed membranes together with high affinity and adsorption capability make them an attractive alternative to MIP particles in separation processes.     

三氯生分子印迹传感器的制备及其性能研究

应用分子印迹技术, 以邻苯二胺为功能单体、三氯生为模板, 用循环伏安法在玻碳电极表面合成了性能稳定的三氯生分子印迹聚合膜, 并用方波伏安法对此印迹传感器进行了分析应用研究.     

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%.     

Catalytical oxidation of styrene by molecularly imprinted polymer with phenylacetic acid as template

This letter used the molecular imprinting technology to build up the microenvironment around co-monomer bemin to mimic the cytochrome P450 catalyzing the epoxidation of styrene. The results showed that the conversion rates of products were obviously enhanced by molecularly imprinted polymers, compared to free heroin solution, using three kinds of oxidants. The used axial ligand in polymers synthesis also improved the total conversion rates.     

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

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

Determination of donepezil in serum samples using molecularly imprinted polymer nanoparticles followed by high‐performance liquid chromatography with ultraviolet detection

A molecularly imprinted polymer designed for the selective extraction of donepezil from serum samples was synthesized using a noncovalent molecular imprinting approach. The molecularly imprinted polymer was evaluated chromatographically and then its affinity for donepezil was confirmed by solid‐phase extraction. The optimal conditions for solid‐phase extraction were provided by cartridge conditioning using acidified water purified from a Milli‐Q system, sample loading under basic aqueous conditions, clean‐up using acetonitrile, and elution with methanol/tetrahydrofuran. Desirable molecular recognition properties of the molecularly imprinted polymer led to good donepezil recoveries (90–102%). The data indicated that the imprinted polymer has a perfect selectivity and affinity for donepezil and could be used for selective extraction and analysis of donepezil in human serum.