Molecularly Imprinted Polymers for Solid Phase Extraction

The combination of molecularly imprinted polymers (MIPs) and solid phase extraction (SPE) is reviewed. MIPs, which have high selectivity and affinity for a predetermined molecule (template), have been used as sorbents for SPE to selectively isolate analytes from biological, pharmaceutical, and environmental samples. Solid phase extraction with molecularly imprinted polymers (MIP–SPE) is a promising technique which allows specific analytes to be selectively extracted from complex matrices. This survey summarizes the characteristics, development and application of MIP–SPE in recent years. Existed problems and the future direction of MIP–SPE are also discussed.     

Selective trace enrichment of acidic pharmaceuticals in real water and sediment samples based on solid-phase extraction using multi-templates molecularly imprinted polymers

A novel multi-templates molecularly imprinted polymer (MIP), using acidic pharmaceuticals mixture (ibuprofen (IBP), naproxen (NPX), ketoprofen (KEP), diclofenac (DFC), and clofibric acid (CA)) as the template, was prepared as solid-phase extraction (SPE) material for the quantitative enrichment of acidic pharmaceuticals in environmental samples and off-line coupled with liquid chromatography–mass spectrometry (LC/MS/MS). Washing solvent was optimized in terms of kind and volume for removing the matrix constituents nonspecifically adsorbed on the MIP. When 1 L of water sample spiked at 1 μg/L was loaded onto the cartridge, the binding capacity of the MIP cartridge were 48.7 μg/g for KEP, 60.7 μg/g for NPX, 52 μg/g for CA, 61.3 μg/g for DFC and 60.7 μg/g for IBP, respectively, which are higher than those of the commercial single template MIP in organic medium (e.g. toluene) reported in the literature. Recoveries of the five acidic pharmaceuticals extracted from 1 L of real water samples such as lake water and wastewater spiked at 1 μg/L were more than 95%. The recoveries of acidic pharmaceuticals extracted from 10-g sediment sample spiked at the 10 ng/g level were in the range of 77.4–90.6%. To demonstrate the potential of the MIP obtained, a comparison with commercial C18 SPE cartridge was performed. Molecularly imprinted solid-phase extraction (MISPE) cartridge showed higher recoveries than commercial C18 SPE cartridge for acidic pharmaceuticals. These results showed the suitability of the MISPE method for the selective extraction of a group of structurally related compounds such as acidic pharmaceuticals.     

Development of solid‐phase microextraction coupled with liquid chromatography for analysis of tramadol in brain tissue using its molecularly imprinted polymer

In this work, performance of a molecularly imprinted polymer (MIP) as a selective solid‐phase microextraction sorbent for the extraction and enrichment of tramadol in aqueous solution and rabbit brain tissue, is described. Binding properties of MIPs were studied in comparison with their nonimprinted polymer (NIP). Ten milligrams of the optimized MIP was then evaluated as a sorbent, for preconcentration, in molecularly imprinted solid‐phase microextraction (MISPME) of tramadol from aqueous solution and rabbit brain tissue. The analytical method was calibrated in the range of 0.004 ppm (4 ng mL⁻¹) and 10 ppm (10 μg mL⁻¹) in aqueous media and in the ranges of 0.01 and 10 ppm in rabbit brain tissue, respectively. The results indicated significantly higher binding affinity of MIPs to tramadol, in comparison with NIP. The MISPME procedure was developed and optimized with a recovery of 81.12–107.54% in aqueous solution and 76.16–91.20% in rabbit brain tissue. The inter‐ and intra‐day variation values were <8.24 and 5.06%, respectively. Finally the calibrated method was applied for determination of tramadol in real rabbit brain tissue samples after administration of a lethal dose. Our data demonstrated the potential of MISPME for rapid, sensitive and cost‐effective sample analysis.     

A (−)‐norephedrine‐based molecularly imprinted polymer for the solid‐phase extraction of psychoactive phenylpropylamino alkaloids from Khat (Catha edulis Vahl. Endl.) chewing leaves

A molecularly imprinted polymer (MIP) was prepared using (?)‐norephedrine as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker and chloroform as the porogen. The MIP was used as a selective sorbent in the molecularly imprinted solid‐phase extraction (MIP‐SPE) of the psychoactive phenylpropylamino alkaloids, norephedrine and its analogs, cathinone and cathine, from Khat (Catha edulis Vahl. Endl.) leaf extracts prior to HPLC‐DAD analysis. The MIP was able to selectively extract the alkaloids from the aqueous extracts of Khat. Loading, washing and elution of the alkaloids bound to the MIP were evaluated under different conditions. The clean baseline of the Khat extract obtained after MIP‐SPE confirmed that a selective and efficient sample clean‐up was achieved. Good recoveries (90.0–107%) and precision (RSDs 2.3–3.2%) were obtained in the validation of the MIP‐SPE‐HPLC procedure. The content of the three alkaloids in Khat samples determined after treatment with MIP‐SPE and a commercial Isolute C₁₈ (EC) SPE cartridge were in good agreement. These findings indicate that MIP‐SPE is a reliable method that can be used for sample pre‐treatment for the determination of Khat alkaloids in plant extracts or similar matrices and could be applicable in pharmaceutical, forensic and biomedical laboratories. Copyright © 2015 John Wiley & Sons, Ltd.     

Development of a Sensitive Method for the Determination of 4‐(Methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol in Human Urine Using Solid‐phase Extraction Combined with Ultrasound‐assisted Dispersive Liquid–liquid Microextraction and LC‐MS/MS Detection

An efficient and sensitive analytical method based on molecularly imprinted solid‐phase extraction (MISPE) and reverse‐phase ultrasound‐assisted dispersive liquid–liquid microextraction (USA‐DLLME) coupled with LC–MS/MS detection was developed and validated for the analysis of urinary 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL), a tobacco‐specific nitrosamine metabolite. The extraction performances of NNAL on three different solid‐phase extraction (SPE) sorbents including the hydrophilic‐lipophilic balanced sorbent HLB, the mixed mode cationic MCX sorbent and the molecularly imprinted polymers (MIP) sorbent were evaluated. Experimental results showed that the analyte was well retained with the highest extraction recovery and the optimum purification effect on MIP. Under the optimized conditions of MIP and USA‐DLLME, an enrichment factor of 23 was obtained. Good linearity relationship was obtained in the range of 5‐1200 pg/mL with a correlation coefficient of 0.9953. The limit of detection (LOD) was 0.35 pg/mL. The recoveries at three spiked levels ranged between 88.5% and 93.7%. Intra‐ and inter‐day relative standard deviations varied from 3.6% to 7.4% and from 5.4% to 9.7%, respectively. The developed method combing the advantages of MISPE and DLLME significantly improves the purification and enrichment of the analyte and can be used as an effective approach for the determination of ultra‐trace NNAL in complex biological matrices.     

粉煤灰基氧氟沙星分子印迹聚合物的制备及其应用

以工业废料粉煤灰微球为基质,氧氟沙星 (OFL) 为模板分子,采用表面印迹法制备印迹材料MIP。通过紫外光谱法结合理论分析选择实验条件,并对该印迹材料结构、吸附行为进行研究。结果表明,该印迹材料对氧氟沙星具有良好的特异识别性和优良的亲和性。与以硅胶为载体制备的印迹聚合物相比,该材料吸附容量更高和印迹效果更好。将其作为固相萃取填料对鸡产品进行分离富集,与C18柱相比,分离富集效果更好。结合UPLC,对实际样品中氧氟沙星进行分析,回收率为82.0%-96.7%,相对标准偏差低于5.5%,可用于鸡产品中氧氟沙星分离分析。     

Development and application of molecularly imprinted polymers as solid-phase sorbents for erythromycin extraction

Six molecularly imprinted polymers (MIPs) of erythromycin (ERY) were prepared by noncovalent bulk polymerization using methacrylic acid (MAA) as the functional monomer. On the basis of binding analysis, the MIPs with 1:2 optimum ratio of template to MAA were selected for subsequent scanning electron microscopy and Brunauer–Emmett–Teller analyses, which indicated that the MIPs had more convergent porous structures than the nonimprinted polymers. The equilibrium binding experiments showed that the binding sites of MIPs were heterogeneous, with two dissociation constants of 0.005 and 0.63 mg mL⁻¹, respectively. Furthermore, the performance of the MIPs as solid-phase extraction (SPE) sorbents was evaluated, and the selectivity analysis showed that the MIPs could recognize ERY with moderate cross-reactivity for other macrolides. The overall investigation of molecularly imprinted SPE for cleanup and enrichment of the ERY in pig muscle and tap water confirmed the feasibility of utilizing the MIPs obtained as specific SPE sorbents for ERY extraction in real samples. Figure Schematic diagram of the preparation and application of the erythromycin imprinted molecularly imprinted polymers Suquan Song and Aibo Wu contributed equally to this work.     

Selective extraction of clonazepam from human plasma and urine samples by molecularly imprinted polymeric beads

A molecularly imprinted polymer (MIP) based on free‐radical polymerization was prepared with 1‐(N,N‐biscarboxymethyl)amino‐3‐allylglycerol and N,N‐dimethylacrylamide as functional monomers, N,N‐methylene diacrylamide as the cross‐linker, copper ion‐clonazepam as the template and 2,2‐azobis(2‐methylbutyronitrile) as the initiator. The imprinted polymer was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and SEM. The MIP of agglomerated microparticles with multipores was used for SPE. The imprinted polymer sorbent was selective for clonazepam. The optimum pH and sorption capacity were 5 and 0.18 mg/g at 20°C, respectively. The profile of the drug uptake by the sorbent reflects good accessibility of the active sites in the imprinted polymer sorbent. The MIP‐SPE was the most feasible technique for the extraction of clonazepam with a high recovery from human plasma and urine samples.     

Molecular imprinting of natural flavonoid antioxidants: application in solid-phase extraction for the sample pretreatment of natural products prior to HPLC analysis

As shown in the past years, SPE based on molecularly imprinted polymers (MIPs) may provide significant enhancement of selectivity in sample preparation and analyte preconcentration. The objective of this work was the fabrication of MIPs for the specific adsorption of rutin and quercetin. The two flavonoids were used as the template molecules for the preparation of MIP phases in a self-assembly (noncovalent) approach. The produced MIPs were validated with regard to the imprinting efficiency as media for LC and SPE. The retention behavior of several flavonoid compounds was studied using as stationary phases imprinted, control nonimprinted polymers, and commercial silica-based materials. MIPs were applied as materials for the selective SPE and preconcentration of the flavonoids from white and red wine, orange juice, and tea. The collected fractions were analyzed by high-pressure LC. MIP-SPE facilitated specific analyte isolation and effective sample clean-up. The results show that molecularly imprinted SPE can be a useful tool for the simple, selective, and cost-effective pretreatment of samples containing natural antioxidants.     

Solid-phase extraction using molecularly imprinted polymers for selective extraction of a mycotoxin in cereals

The aim of this work was to develop a method for the clean-up of a mycotoxin, i.e. Ochratoxin A (OTA), from cereal extracts employing a new molecularly imprinted polymer (MIP) as selective sorbent for solid-phase extraction (SPE) and to compare with an immunoaffinity column. A first series of experiments was carried out in pure solvents to estimate the potential of the imprinted sorbent in terms of selectivity studying the retention of OTA on the MIP and on a non-imprinted polymer using conventional crushed monolith. The selectivity of the MIP was also checked by its application to wheat extracts. Then, after this feasibility study, two different formats of MIP: crushed monolith and micro-beads were evaluated and compared. Therefore an optimization procedure was applied to the selective extraction from wheat using the MIP beads. The whole procedure was validated by applying it to wheat extract spiked by OTA at different concentration levels and then to a certified contaminated wheat sample. Recoveries close to 100% were obtained. The high selectivity brought by the MIP was compared to the selectivity by an immunoaffinity cartridge for the clean-up of the same wheat sample. The study of capacity of both showed a significant higher capacity of the MIP.     

Selective adsorption of 2,4-dinitrophenol on molecularly imprinted nanocomposites of mesoporous silica SBA-15/polyaniline

Surface imprinting and adoption of a nano-sized physical form are two effective approaches to overcome the template transfer difficulty within molecularly imprinted polymers (MIPs). This work is an attempt to conquer the problem of template transfer difficulty within MIPs by using a nano-reactor as a substrate for the reaction between the monomer and the template. Negatively charged hexagonal nano-channels of SBA-15 can act as a support for attachment of positively charged aniline monomers and the 2,4-dinitrophenol (2,4-DNP) template. The imprinted and non-imprinted SBA-15/polyaniline nanocomposites were characterized by Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and nitrogen adsorption-desorption isotherms. The results showed that the synthesized polymer possessed a highly ordered mesoporous structure. The distribution coefficient values of 2,4-DNP, K(d (2,4-DNP)), were estimated as 301.4 ± 2.3 and 101.2 ± 1.0 mL g(-1) for imprinted and non-imprinted polymers (NIP), respectively. The MIP-solid-phase extraction (SPE) process was optimized by evaluating the type of washing solvent and the composition and volume of the eluting solvent. The prepared MIP was used as a selective sorbent for SPE of 2,4-DNP in the presence of phenolic compounds in tap and sea water. The experimental results indicated that the MIP-SPE and NIP-SPE column yielded recoveries higher than 96% and 38%, respectively. The R.S.D. values were also lower than 3.2% and 4.6% for MIP-SPE and NIP-SPE, respectively.     

Preparation and application of a molecularly imprinted polymer for the determination of trace metolcarb in food matrices by high performance liquid chromatography

In this article, for the first time, a molecularly imprinted polymer (MIP) for the metolcarb was prepared by bulk polymerization using metolcarb as the template, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross‐linker. The prepared polymer was characterized by FT‐IR, static and kinetic adsorption experiments, and the results showed that it has been successfully synthesized and had good selective ability for metolcarb. The MIP was applied as a sorbent in molecularly imprinted SPE coupled with HPLC‐UV for separation and determination of trace metolcarb in three kinds of food matrices at three concentration levels. Under the optimal conditions, the LODs (S/N=3) of cabbage, cucumber and pear were 7.622, 6.455 and 13.52 μg/kg, respectively, and recoveries were in the range of 68.80–101.31% with RSD (n=3) below 3.78% in all cases. To demonstrate further the selectivity of the MIP obtained, a comparison with commercially available C₁₈ SPE was performed. The results indicated that molecularly imprinted SPE showed better chromatography, better selectivity and higher recoveries for metolcarb than commercially available C₁₈ SPE.     

Determination of sulfamethoxazole in milk using molecularly imprinted polymer monolith microextraction coupled to HPLC

We report on a new method for the selective extraction of the antibiotic sulfamethoxazole (SMO) in milk that is making use of a molecularly imprinted polymer (MIP) monolith as the sorbent. The monolith was synthesized in the tip of a micropipette using SMO as the template and a combination of acrylamide and 4-vinylpyridine as the co-functional monomers. The monolith was connected to syringes in different sizes and used for microextraction without any other treatment and showed high selectivity and enrichment ability for SMO. It was applied to the selective extraction and sensitive determination of SMO in milk. The linear range is from 5–600?μg?L^?1, the correlation coefficient (r²) is 0.9984, and the detection limit (at S/N?=?3) is 1?μg?L^?1. Recoveries range from 93.6 to 101.7?%, with relative standard deviations of <6.1?%.

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.     

Glucuronide directed molecularly imprinted solid-phase extraction: isolation of testosterone glucuronide from its parent drug in urine

Two molecularly imprinted polymers (MIPs) that we recently described to be class-selective for glucuronides have been successfully exploited for the molecularly imprinted solid-phase extraction (MISPE) of testosterone glucuronide (TG) from its parent drug (T) in urine. Both sorbents targeted the glucuronate fragment but feature different functional groups for binding the carboxylate anion, MIP1, a neutral 1,3-diarylurea group, and MIP2, a cationic imidazolium functionality. MISPE-HPLC-UV methods developed using both sorbents allowed the extraction of TG from its parent compound in urine samples spiked at 150, 300 or 600 ng mL(-1) for TG and at 50 ng mL(-1) for T. By comparing the performance of the two sorbents it came out that MIP1 is a more suitable SPE packing than MIP2, since it isolated the glucuronide with a higher precision (RSD 2-5%, n = 3) and with an enhanced enrichment factor (EF = 4.2). On the basis of these results, the imprinted receptor MIP1 can be applied for the direct extraction of TG in doping and clinical analysis and to selectively capture any other relevant glucuronated metabolite avoiding tedious deconjugation steps prior to quantification.     

A novel molecularly imprinted method with computational simulation for the affinity isolation and knockout of baicalein from Scutellaria baicalensis

A novel molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization with baicalein (BAI) as the template and used as solid‐phase extraction (SPE) adsorbent, aiming at the affinity isolation and selective knockout of BAI from Scutellaria baicalensis Georgi (SB). We used computational simulation to predict the optimal functional monomer, polymerization solvent and molar ratio of template to functional monomer. Characterization and performance tests revealed that MIP exhibited uniform spherical morphology, rapid binding kinetics, and higher adsorption capacity for BAI compared with nonimprinted polymer (NIP). The application of MIP in SPE coupled with high‐performance liquid chromatography to extract BAI from SB showed excellent recovery (94.3%) and purity (97.0%). Not only the single BAI compound, but also the BAI‐removed SB extract was obtained by one‐step process. This new method is useful for isolation and knockout of key bioactive compounds from herbal medicines. Copyright © 2015 John Wiley & Sons, Ltd.     

Computer aided-molecular design and synthesis of a high selective molecularly imprinted polymer for solid-phase extraction of furosemide from human plasma

Highly selective molecularly imprinted polymers (MIPs) for solid-phase extraction and determination of furosemide in human plasma have been designed and prepared. In order to study the intermolecular interactions in the pre-polymerization mixture and to find a suitable functional monomer in MIP preparation, a computational approach was developed. It was based on the comparison of the binding energy of the complexes between the template and functional monomers. Having confirmed the results of computational method, three MIPs were synthesized with different functional monomers, i.e. acrylamide (AAM), 4-vinylpiridine (4-VP) and acrylonitrile (ACN), and then evaluated using Langmuir-Freundlich (LF) isotherm. Using the MIP prepared by AAM as functional monomer, a molecularly imprinted solid-phase extraction procedure followed by high performance liquid chromatography with ultraviolet detector (MISPE-HPLC-UV) was developed for selective extraction and determination of furosemide in human plasma. For the proposed MISPE-HPLC-UV method, the linearity between responses (peak area) and concentration was found over the range of 75-3500 ng mL⁻¹ with a linear regression coefficient (R²) of 0.997. The limit of detection (LOD) and quantification (LOQ) in plasma were 12.9 and 43.3 ng mL⁻¹, respectively.     

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.     

Characterization of molecularly imprinted polymers for the extraction of tobacco alkaloids and their metabolites in human urine

Molecularly imprinted polymers (MIPs) are synthetic polymers designed to selectively extract target analytes from complex matrices (including biological matrices). The literature shows that MIPs have a degree of cross-selectivity from analytes within the same class of compounds. A commercially available MIP for tobacco-specific nitrosamines (TSNAs) is designed to be class selective for four TSNA compounds. This study sought to characterize the extent of cross-selectivity of the TSNA MIPs with other tobacco alkaloids. Cross-selectivity and recovery of the SupelMIP™ TSNA SPE cartridges was assessed with N-nitrosonornicotine (NNN), nicotine, cotinine and morphine. Their recoveries were compared with the recoveries of a nonimprinted polymer SPE cartridge, and two traditional SPE cartridges: a Waters mixed-mode cation exchange cartridge and a Waters hydrophilic–lipophilic balance cartridge. NNN and cotinine had the highest recoveries with the MIP cartridge, over 80%, and cotinine samples in urine had >80% recoveries. Nicotine had highly variable recoveries, possibly owing to differing chemical properties from the TSNAs. All three analytes had significantly different recoveries with the MIP cartridges compared with the traditional SPE cartridges. Morphine displayed nonspecific interactions with the MIP cartridges. Utilization of the TSNAs’ cross-selectivity allows for simultaneous extraction and identification of multiple tobacco biomarkers using one extraction technique.     

利用分子印迹技术预处理生物样品中头孢药物的研究

优化了头孢硫脒分子印迹聚合物的合成条件,探讨了分子印迹技术和固相萃取联用对血浆中头孢硫脒的分离富集,发现用4-乙烯基吡啶作功能单体合成的分子印迹聚合物作为固相萃取填充料,能定量吸附血浆中的头孢硫脒,并初步研究了其吸附机理。