Size-exclusion chromatography in 1,1,1,3,3,3-hexafluoro-2-propanol

Two molecularly imprinted polymers (MIPs) have been synthesised for the selective extraction of 4-nitrophenol (4-NP) from water samples. One polymer was synthesised via a non-covalent approach and the other via a semi-covalent approach. The selectivity of the polymers for 4-NP was evaluated when these polymers were applied in on-line solid-phase extraction (MISPE) coupled to reversed-phase HPLC. The MISPE conditions for both MIPs were optimised and a clean-up step was included to eliminate non-specific interactions. Differences between the two MIPs were observed with the non-covalent MIP being the more selective of the two, whereas the recoveries were slightly higher for the semi-covalent MIP. The performance of the imprinted polymers in the MISPE of real water samples was also evaluated.     

Development of a broad selective molecularly imprinted polymers-based solid phase extraction of contraceptive drug levonorgestrel from water samples

A broad selective molecularly imprinted polymers-based solid phase extraction (MISPE) for levonorgestrel (LNG) from water samples was developed. Using LNG as a template molecule, acrylamide (AA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as linking agent and bulk polymerisation as a synthetic method, the molecularly imprinted polymers (MIPs) were synthesised and characterised. The MIPs displayed a high specific rebinding for LNG with the imprinting factor of 3.71. The Scatchard analysis showed that there was at least one class of binding site for LNG formed in the MIPs with the dissociation constant of 8.046?µg?mL^?1. The results of selectivity testing indicated that the MIPs also exhibited high cross-reactivity with structurally related compounds (estrone, methylprednisolone and ethinyl estradiol), but no recognition with non-structurally related compound (indomethacin), suggesting that the MIPs could be used as a broad recognition absorbent. MISPE column was prepared by packing MIPs particles into a common SPE cartridge. The MISPE extraction conditions including loading, washing and eluting solutions were carefully optimised. Water samples spiked with LNG were extracted by MISPE column and detected by high-performance liquid chromatography. The recoveries were found to be 79.97?～?132.79% with relative standard deviations (RSD) of 1.92?～?10.43%, indicating the feasibility of the prepared MIPs for LNG extraction.     

Characterisation and application of molecularly imprinted polymers for group-selective recognition of antibiotics in food samples

Group-selective molecularly imprinted polymers (MIPs) for amphenicol antibiotics, including chloramphenicol (CAP), thiamphenicol (TAP), florfenicol (FF), and florfenicol amine (FFA), were developed for the first time using TAP as the template molecule. The characteristics of the obtained MIPs were systematically evaluated by chromatographic methods and frontal analysis, demonstrating that the MIPs had excellent chromatographic behaviors, good selectivity, and high-binding capability. A molecularly imprinted solid-phase extraction (MISPE) procedure was developed based on the chromatography results. The MIPs exhibited better group selectivity for CAP, TAP, FF, and FFA than non-imprinted polymers (NIPs) under the optimized washing conditions of 10% acetonitrile in PBS buffer (25 mmol L(-1), pH = 5). Compared with conventional solid-phase extraction, significant recoveries ranging from 92.4% to 98.8% with lower relative standard deviation values in the range of 3.2-7.3% for both intraday- and interday-assays were obtained. The limits of detection (LODs) of MISPE for CAP, TAP, FF, and FFA in shrimp were found to be 0.016, 0.093, 0.102, and 0.029 μg kg(-1), respectively. The results acquired in this study contribute to the strategic development of MIPs and MISPE methods for the multi-residual recognition of antibiotics from complex matrices.     

Molecularly imprinted polymer for solid-phase extraction of rutin in complicated traditional Chinese medicines

In the present work, an improved and direct approach for the preparation of molecularly imprinted polymers (MIPs) was proposed. The MIPs were prepared based on bulk polymerization by water-bath heating and ultrasonic elution of the template, using rutin as the template, acrylamide (AM) as the functional monomer and 2,2'-azobisisobutyronitrile (AIBN) as the cross linker. Molecularly imprinted polymers prepared by other elution methods, including microwave-assisted extraction and conventional Soxhlet extraction, were used for comparison and the results showed that the ultrasonic elution method is the best. The synthesized MIPs were characterized by Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). High performance liquid chromatography (HPLC) was used to evaluate the adsorption properties and recognition mechanism of the MIPs. Structurally similar compounds including quercetin and genistein were utilized for verifying the molecular selectivity and characterizing the recognition capability of the MIPs. The MIPs were used as a sorbent for the solid phase extraction of rutin, and the resultant cartridge showed a good extraction performance. Thus, a molecularly imprinted solid-phase extraction (MISPE) procedure for selective pre-concentration of rutin from complicated traditional Chinese medicine (TCM) samples was proposed. Various elution parameters that affect the adsorption capacity of the polymer were evaluated to optimize the selective pre-concentration of rutin. The characteristics of the MISPE method were validated by HPLC. The recoveries ranged from 85% to 91% for TCMs, which demonstrated that this MISPE-HPLC method could be applied to pre-concentrate and determinate rutin directly from complicated TCM samples in the presence of other interfering substances.     

Molecularly imprinted polymers for solid-phase extraction and solid-phase microextraction: recent developments and future trends

Molecularly imprinted polymers (MIPs) are synthetic polymers having a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials to be used in separation processes. In this sense, during past years a huge amount of papers have been published dealing with the use of MIPs as sorbents in solid-phase extraction, namely molecularly imprinted solid-phase extraction (MISPE). Although the majority of these papers were restricted to describe the use of different templates for different applications, several attempts proposing new alternatives to minimize the inherent drawbacks of the preparation and use of MIPs (i.e. template bleeding, tedious synthesis procedure, etc.) have been reported. Thus, this paper does not pretend to be a collection of MISPE-related papers but to give an overview on the significant attempts carried out during recent years to improve the performance of MIPs in solid-phase extraction. In addition, the use of MIPs packed in high performance liquid chromatography (HPLC) columns for the direct injection of crude sample extracts and the preparation of imprinted fibres for solid-phase microextraction will be also discussed.     

Molecularly imprinted solid-phase extraction of matrine from radix Sophorae tonkinensis

In the study, molecularly imprinted polymers (MIPs) with special molecular recognition properties of matrine (MAT) were prepared in our lab, using melamine-urea-formaldehyde (MUF) as the functional monomer and matrine as the template. An equilibrium binding experiment was performed to investigate the binding ability of the MIPs, and indicated that the MIPs had a high adsorption and good elution ability to the target molecule MAT, when the template/functional monomer ratio (T/M) was 5 mg g(-1). Scatchard analysis and isothermal equilibrium adsorption indicated that only one kind of binding site had existed in the MAT-imprinted polymers with its dissociation constants estimated to be 3.31 × 10(-4) mol L(-1) (200-400 mesh (inch(-1))) and 6.83 × 10(-4) mol L(-1) (over 400 mesh (inch(-1))) depending on the mesh of the MIPs. MAT purification and elution experiments were carried out using MIPs as the solid-phase extraction (MISPE) sorbent, and acetone, water, and chloroform as the elution solvents. The results demonstrated that MIPs achieved their highest adsorption capability after treatment with alkaline solution, while acetone was the most efficient elution solvent. Then, a crude extraction of matrine in radix Sophorae tonkinensis was performed using these MIPs as the separation medium. The results showed that MIPs had a high MAT selectivity, and the amount of matrine content obtained by MISPE was 1.4-fold to that obtained by liquid-liquid extraction.     

吲哚美辛纳米胶体金分子印迹聚合物的制备及其在固相萃取中的应用

以吲哚美辛(IDM)为模板分子,丙烯酰胺(AA)为功能单体,乙二醇二甲基丙烯酸酯(EGDMA)为交联剂,本体聚合法制备过程中加入纳米胶体金,合成了吲哚美辛胶体金分子印迹聚合物(MIPs/Au),利用MIPs/Au表面胶体金对蛋白吸附作用,将抗吲哚美辛的多克隆抗体固定在MIPs/Au上,得到表面固定有抗体的新型聚合物(MIPs/Au-Ab)并对其进行了表征。制备了填充材料为MIPs/Au-Ab的固相萃取柱并对其上样、淋洗和洗脱条件进行了优化,并将所制备的新型萃取柱用于水样中IDM的分离富集。抗吲哚美辛抗体交联在聚合物表面,不仅增加了萃取柱的特异性吸附容量,而且有效地降低了MIP的非特异性吸附。     

Synthesis of molecularly imprinted polymers via ring-opening metathesis polymerization for solid-phase extraction of bisphenol A

The use of molecularly imprinted polymers (MIPs) prepared by ring-opening metathesis polymerization (ROMP) for bisphenol A (BPA) was reported in this article. The resulting MIPs have high imprinting and adsorption capacities, and can be used for separation and determination of BPA in environmental water samples. The successful application of ROMP in the molecular imprinting field is described here. For the first time, two cross-linkers (dicyclopentadiene and 2,5-norbornadiene) and two Grubbs catalysts (first and second generation) were investigated to compare their effects on the binding performance of MIPs. The ROMP technique is able to create the imprinted polymers within 1 h under mild conditions. Furthermore, it can provide MIPs with obvious imprinting effects towards the template, very fast template rebinding kinetics, high binding capacity and appreciable selectivity over structurally related compounds. The adsorption process for MIPs in this study can be completed within 45 min, which is much faster than that of bulk MIPs synthesized by traditional free-radical polymerization. The resulting imprinting polymer was evaluated for its use as a sorbent support in an off-line solid-phase extraction approach to recover BPA from diluted aqueous samples. The optimized extraction protocol resulted in a reliable MISPE method suitable for selective extraction and preconcentration of BPA from tap water, human urine and liquid milk samples. This article demonstrates the practical feasibility of the MIPs prepared via ROMP as solid-phase extraction materials.     

Molecularly imprinted polymers for bisphenol A for HPLC and SPE from water and milk

Molecularly imprinted polymers (MIPs) for bisphenol A (BPA) were prepared by two synthetic routes: semi-covalent and noncovalent methodology. The molecular imprinting effect was evaluated using the polymers in HPLC and SPE. Polymers prepared with noncovalent mode were proven more effective. These polymers were applied in SPE facilitating selective retention of BPA from bottled water and milk. The developed sample preparation was simple and efficient comprising only dilution of milk and MISPE prior to LC-MS analysis. Overall MISPE enhanced sample clean-up. Compared with control nonimprinted polymers and conventional C18 SPE cartridges, the MIPs exhibited selective analyte recognition. The method provided quantitative BPA recoveries, very good reproducibility (% RSDs lower than 7%), and low LOD (0.2 ng/g). MIP interacts similarly with deuterated BPA allowing its use as internal standard in LC-MS. The most critical parameters of MISPE were the organic content in loading-washing medium and the washing volume. Low flow rates in the elution step enhanced extraction recovery. Important advantages of the MIP were: the high breakthrough volumes (> 500 mL of water), high mass capacity (> 10 ng/mg of MIP sorbent), good linearity, and good stability in performance for over 35 cycles of use.     

水相识别分子印迹技术

在各种基于超分子方法的仿生识别体系中,分子印迹聚合物已经证明是一种有潜力的合成受体,受到了广泛的关注。传统的分子印迹技术通常是在有机溶剂中制备对小分子具有选择性的印迹聚合物,而在水相中制备及识别生物大分子的研究仍具有相当的挑战性。从小分子到生物大分子、从有机相到水相,反映了分子印迹技术的发展趋势。本文对最近几年分子印迹在水相制备与识别方面的最新进展进行了总结与评述,探讨了水相识别印迹聚合物的设计策略与制备方法;着重介绍了水相识别技术在固相萃取、色谱固定相、药物控释、中药有效成份提取以及生物分子识别等方面的应用;指出了提高水相识别选择性的途径并对其将来的发展进行了建议与展望。     

Design of an imprinted clean-up method for mycophenolic acid in maize

In the present work, the development of imprinted polymers selective towards mycophenolic acid and their application in food analysis are reported for the first time. To synthesize the molecularly imprinted polymer (MIP) 4-vinylpyridine and ethyleneglycol dimethacrylate were applied as functional monomer and cross-linker, respectively. Besides the toxin itself, the implementation of structural analogues as templates was evaluated. A molecularly imprinted solid-phase extraction (MISPE) procedure was designed for the selective clean-up of maize extracts. Binding experiments and Scatchard analysis indicated the presence of specific binding sites in the imprinted polymers. The imprinting effect varied along with the selected template. The dissociation constant (K(D)) of the higher affinity binding sites ranged from 0.8 μmol/l to 15.6 μmol/l, while the K(D) of the lower affinity binding sites was in the range of 138.5-519.3 μmol/l. The performance of the MIPs throughout the clean-up of spiked maize sample extracts was evaluated and compared with the results obtained when applying a non-imprinted polymer. Depending on the polymers and the spiked concentration, recoveries after MISPE and non-imprinted solid-phase extraction varied respectively from 49% to 84% and from 28% to 31%. The imprinted polymers were superior regarding matrix effect, limit of detection (LOD) and limit of quantification (LOQ). LOD ranged from 0.17 μg/kg to 0.25 μg/kg and LOQ varied from 0.57 μg/kg to 0.82 μg/kg. Analysis of 15 maize samples by liquid chromatography tandem mass spectrometry revealed that the MIPs could be excellent sorbents for clean-up of contaminated food samples.     

Role of molecularly imprinted polymers for selective determination of environmental pollutants--a review

The molecularly imprinted polymers (MIPs) are synthetic polymers possessing specific cavities designed for a target molecule. By a mechanism of molecular recognition, the MIPs are used as selective tools for the development of various analytical techniques such as liquid chromatography, capillary electrochromatography, solid-phase extraction (SPE), binding assays and biosensors. This review describes the application of MIPs to the determination of environmental pollutants in these different analytical approaches with a special emphasis on their potential as selective SPE sorbent for the selective extraction of target analytes from complex matrices.     

Molecularly imprinted polymer for selective extraction of endocrine disrupters nonylphenol and its ethoxylated derivates from environmental solids

Nonylphenol isomers (NP), linear nonylphenol (4-n-NP) and NP short chain ethoxylated derivates (NPEO1 and NPEO2) are degradation products of nonylphenol polyethoxylates, a worldwide used group of surfactants. All of them are considered endocrine disrupters due to their ability to mimic natural estrogens. In this paper, the preparation and evaluation of several 4-n-NP molecularly imprinted polymers (MIPs) for the selective extraction and clean-up of 4-n-NP, NP, NPEO1 and NPEO2 from complex environmental solid samples is described. Among the different combinations tested, a methacrylic acid-based imprinted polymer prepared in toluene provided the better performance for molecularly imprinted SPE (MISPE). Under optimum MISPE conditions, the polymer was able to selectively retain not only linear NP but also the endocrine disruptors NPEO1, NPEO2 and NP with recoveries ranging from 60 to 100%, depending upon the analyte. The developed MISPE procedure was successfully used for the determination of 4-n-NP, NP, NPEO1 and NPEO2 in sediments and sludge samples at concentration levels according to data reported in the literature for incurred samples. Finally, various sludge samples collected at five different sewage treatment plants from Madrid and commercial sludge for agriculture purposes were analysed. The measured concentrations of the different compounds varied from 3.7 to 107.5 mg/kg depending upon the analyte and the sample.     

Clozapine imprinted polymers: synthesis, characterization and application for drug assay in human serum

A variety of molecularly imprinted polymers (MIPs) against clozapine (CLZ) were synthesized and their recognition properties were compared with blank non-imprinted polymers. Methacrylic acid (MAA) was used as a functional monomer and Chloroform or tetrahydrofuran (THF) were applied as polymerization solvents. Chloroform as the solvent and MAA/CLZ ratio of 5 was selected as optimized polymerization condition. In Scatchard analysis of MIP-CLZ interactions, two classes of binding sites were found in MIP—high affinity (KD = 14.5 μM) and low affinity (KD = 322.5 μM) binding sites. The polymer was evaluated as a selective sorbent in molecularly imprinted solid-phase extraction (MISPE) of CLZ from human serum. The MISPE procedure was developed and optimized with a recovery of 88-102%. The intra- and inter-day precision values were less than 1.36% and 2.5%, respectively. The selectivity of MISPE for CLZ was studied in comparison with some drugs. These drugs could be present with CLZ, simultaneously in serum of patients. The data indicated that the imprinted polymer had a good selectivity and affinity for CLZ and could be used for selective extraction and analysis of CLZ in human serum.     

Selective solid-phase extraction of dibutyl phthalate from soybean milk using molecular imprinted polymers

An analysis method is reported for dibutyl phthalate and related compounds with high selectivity and sensitivity by using the selective molecularly imprinted solid-phase extraction (MISPE) technique. In this report, dibutyl phthalate (DBP) is employed as the template molecule, and the molecularly imprinted polymers (MIPs) are synthesized through the bulk polymerization of methacrylic acid (MAA). The Scatchard plot suggests that the template-polymer system has two-site binding behavior with the dissociation constants of 0.5187 and 0.01898 mmol L⁻¹, respectively. The rebinding test, based on the MISPE column technique, shows the recoveries of soybean milk samples spiked with 5 phthalates are in the range of 75.8-107.5% with the relative standard deviations of 1.80-10.08%, indicating the feasibility of the prepared MIPs for phthalates extraction. Finally, the method is used to analyze the trace level of phthalates in commercial soybean milk.     

Clean up of phenylurea herbicides in plant sample extracts using molecularly imprinted polymers

Two different molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using linuron or isoproturon (phenylurea herbicides) as templates and trifluormethacrylic acid as functional monomer. These materials were used as selective sorbents in the development of molecularly imprinted solid-phase extraction (MISPE) procedures for the determination of several phenylurea herbicides (fenuron, metoxuron, chlortoluron, isoproturon, metobromuron, and linuron) in plant samples extracts. The MISPE procedures were fully optimized and applied to the clean up of selected phenylurea herbicides in carrot, potato, corn, and pea sample extracts and finally determined by HPLC-UV at 244 nm. Although a high degree of clean up was obtained, a decrease of the MIP recognition capabilities was observed in subsequent runs. Thus, a previous clean up protocol based on the use of a non-imprinted polymer was used to prevent the loss of MIP performance and to ease the removal of interferences. Following this procedure, namely two-step MISPE, matrix compounds were almost completely removed by the non-imprinted polymer retaining the ability of MIPs to selectively rebind target analytes unaltered. The developed MISPE procedures allowed the screening of phenylurea herbicides in plant samples at concentration levels required by established European maximum residue limits.     

Development of a group selective molecularly imprinted polymers based solid phase extraction of malachite green from fish water and fish feed samples

A group selective molecularly imprinted solid phase extraction (MISPE) for malachite green (MG) from fish water and fish feed samples was developed. Using MG as template molecule, methacrylic acid as functional monomer, ethylene glycoldimethacrylate as linking agent and bulk polymerization as synthetic method, the molecularly imprinted polymers (MIPs) were synthesized and characterized with rebinding experiment. The Scatchard polt's analysis revealed that the template-polymer system showed the two-site binding behavior with dissociation constants of 0.3194 μmol L⁻¹ and 15.70 μmol L⁻¹, respectively. MG and two structurally related compounds, leucomalachite green (LMG) and crystal violet (CV) were employed for selectivity test. The MIPs exhibited the highest selective rebinding to MG, but also displayed 83.0% and 87.5% of cross-reactivity with LMG and CV, demonstrating that MIPs could be used as group recognition sorbents in solid phase extraction. The extraction conditions of MISPE column for MG were optimized. Tap water samples spiked with MG at concentration of 0.5-10 ng mL⁻¹ were extracted by MISPE column and analyzed by high performance liquid chromatography. The recoveries of MISPE column for MG extraction were found to be 76.8-93.7% with the relative standard deviations of 2.12-10.09%, indicating the feasibility of the prepared MIPs for MG extraction. No detectable MG was observed in one fish farming water sample and two fish feed samples; while the MG concentrations in two pet fishpond water samples were found at 1.50 ng mL⁻¹ and 0.67 ng mL⁻¹, respectively.     

Molecularly imprinted polymers: An analytical tool for the determination of benzimidazole compounds in water samples

Molecularly imprinted polymers (MIPs) for benzimidazole compounds have been synthesized by precipitation polymerization using thiabendazole (TBZ) as template, methacrylic acid as functional monomer, ethyleneglycol dimethacrylate (EDMA) and divinylbenzene (DVB) as cross-linkers and a mixture of acetonitrile and toluene as porogen. The experiments carried out by molecularly imprinted solid phase extraction (MISPE) in cartridges demonstrated the imprint effect in both imprinted polymers. MIP–DVB enabled a much higher breakthrough volume than MIP–EDMA, and thus was selected for further experiments. The ability of this MIP for the selective recognition of other benzimidazole compounds (albendazole, benomyl, carbendazim, fenbendazole, flubendazole and fuberidazole) was evaluated. The obtained results revealed the high selectivity of the imprinted polymer towards all the selected benzimidazole compounds.An off-line analytical methodology based on a MISPE procedure has been developed for the determination of benzimidazole compounds in tap, river and well water samples at concentration levels below the legislated maximum concentration levels (MCLs) with quantitative recoveries. Additionally, an on-line preconcentration procedure based on the use of a molecularly imprinted polymer as selective stationary phase in HPLC is proposed as a fast screening method for the evaluation of the presence of benzimidazole compounds in water samples.     

Quercetin molecularly imprinted polymers: Preparation, recognition characteristics and properties as sorbent for solid-phase extraction

Molecular imprinted polymers (MIPs) were prepared through thermal polymerization by using quercetin as the template molecule, acrylamide (AA) as the functional monomer and ethylene glycol dimethacrylate (EDMA) as the cross-linker in the porogen of tetrahydrofuran (THF). The synthesized MIPs were identified by both Fourier transform infrared (FTIR) and scanning electron microscope (SEM). Systematic investigations of the influences of key synthetic conditions, including functional monomers, porogens and cross-linkers, on the recognition properties of the MIPs were conducted. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. Besides quercetin, two structurally similar compounds of rutin and catechol were employed for molecular recognition specificity tests of MIPs. It was observed that the MIPs exhibited the highest selective rebinding to quercetin. Accordingly, the MIPs were used as a solid-phase extraction (SPE) sorbent for the extraction and enrichment of quercetin in cacumen platycladi samples, followed by HPLC-UV analysis. The application of MIPs with high affinity and excellent stereo-selectivity toward quercetin in SPE might offer a novel method for the enrichment and determination of flavonoid compounds in the natural products.     

Forensic analysis of dyed textile fibers

A rapid, specific, and sensitive method has been developed using molecularly imprinted polymers (MIPs) as solid-phase extraction sorbents for extraction of trace tetracycline antibiotics (TCs) in foodstuffs. MIPs were prepared by precipitation polymerization using tetracycline as the template. Under the optimal condition, the imprinting factors for MIPs were 4.1 (oxytetracycline), 7.0 (tetracycline), 7.4 (chlortetracycline), 7.7 (doxycycline), respectively. Furthermore, the performance of MIPs as solid-phase extraction sorbents was evaluated and high extraction efficiency of molecularly imprinted solid-phase extraction (MISPE) procedure was demonstrated. Compared with commercial sorbents, MISPE gave a better cleanup efficiency than C18 cartridge and a higher recovery than Oasis HLB cartridge. Finally, the method of liquid chromatography–tandem mass spectrometry coupled with molecular-imprinted solid-phase extraction was validated in real samples including lobster, duck, honey, and egg. The spiked recoveries of TCs ranged from 94.51% to 103.0%. The limits of detection were in the range of 0.1–0.3 μg kg⁻¹. Chromatograms obtained by direct injection of the spiked egg extracts (5 × 10^-3 mmol L⁻¹) and purification with MISPE