Molecularly imprinted polymers as a tool for separation in CEC

Molecularly imprinted polymers (MIPs) are synthesized in the presence of a template which results in the formation of specific recognition cavities complementary to the template in shape and chemical functionality. One of the most successful application areas of MIPs is chromatographic sorbents, which are tailor-made synthetic polymers for a given analyte. However, low efficiency of MIP columns is often observed because of slow kinetics of the template. CEC-based MIPs are thought to improve efficiency of MIP-based separation due to the enhanced flow dynamics of CEC. Another attractive feature is the miniaturized format of CEC, so that fewer templates or monomers for the molecular imprinting are consumed, a characteristic desired for 'green chemistry'. The small dimensions of a capillary demand the development of novel polymer formats that can be applied to a miniaturized system. This review discusses the various formats, i.e., the micro- or nanoparticle, the coating and the monolith, for application in CEC as well as the use in MIP syntheses and characteristics.     

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

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

Molecularly imprinted polymers: a new tool for separation of steroid isomers

Molecularly imprinted polymers hold great promise for the separation of chiral compounds. A non-covalent approach to the synthesis of MIPs relies on the presence of specific and non-specific interactions, which lead to the formation of a molecular imprint. The structural differences between 17-alpha-estradiol and 17-beta-estradiol are too small to permit their efficient separation on a MIP prepared with beta-estradiol as a template. Molecular modeling revealed the presence of only one hydrogen bond that differentiates the two isomers.     

Molecularly imprinted polymers for chemical agent detection in multiple water matrices

In the past few years concerns over the possibility of terrorist actions against domestic and military water supplies has become paramount. Antibodies, peptides, and enzymes have been used as molecular recognition elements in chemical sensors; however, such devices often have storage and operational stability issues that limits their success. Molecularly imprinted polymers (MIPs), have been successfully demonstrated an alternative in pesticide applications [A.L. Jenkins, R. Yin, J.J. Jensen, Analyst 126 (2001) 798-802]. The MIP materials possess selective molecular recognition properties that are complementary to the analyte in the shape and positioning of functional groups. These polymers have high selectivity and affinity constants while maintaining excellent thermal and mechanical stability. In this study, direct imprinting of chemical agents EA2192, VX, sarin, and soman (the “G” agents), was performed and the limits of detection calculated. The ability of these sensors to work in various water matrices including tap, deionized and reverse osmosis water with residual chlorine was also evaluated. Typical detection limits for these MIP sensors are approximately 50 ppt with wide linear dynamic ranges (ppt-ppm). Sensor response time is approximately 15 min.     

Molecularly imprinted capillary electrochromatography for selective determination of thiabendazole in citrus samples

In this work, the suitability of the combination of molecular imprinting and capillary electrochromatography (MIP-CEC) to be used as powerful tool in environmental or food analysis has been for the first time studied and successfully demonstrated. A molecularly imprinted monolith (MIM) has been synthesised and evaluated as stationary phase for the selective determination of the fungicide thiabendazole (TBZ) in citrus samples by non-aqueous capillary electrochromatography. The influence of the mobile phase composition, the voltage of the power supply and the separation temperature on the recognition of TBZ by the imprinted polymer has been evaluated, and the imprint effect in the MIM was clearly demonstrated. Once optimum recognition conditions were established, other variables affecting mechanical properties and chromatographic performance of MIM were adjusted using computational approach. The high selectivity achieved by the MIP-CEC developed procedure allowed unambiguous detection and quantification of TBZ in citrus samples by direct injection of the crude sample extracts, without any previous clean-up, in less than 6 min. The developed method was properly validated and the calculated detection limits were below the established maximum residue limits (MRLs), clearly demonstrating the suitability of the method to be used for the control of the selected fungicide.     

Molecularly imprinted polymers for selective solid-phase extraction of phospholipids from human milk samples

Microchimica Acta - The authors describe a method for the extraction and determination of phospholipids (PLs) from human milk fat by using a molecularly imprinted polymer (MIP) as the sorbent...     

Molecularly imprinted polymers: synthetic receptors in bioanalysis

Molecularly imprinted polymers (MIPs) are tailor-made synthetic materials possessing specific cavities designed for a target molecule. Since they recognise their target analyte with affinities and selectivities comparable to those of antibody–antigen, enzyme–substrate and ligand–receptor interactions, they are often referred to as synthetic receptors or plastic antibodies. In this review, we describe the great potential and recent developments of MIPs in affinity separations, with emphasis on their application to the solid-phase extraction (SPE) of analytes from complex matrices. Research efforts made in this field to obtain water-compatible polymers for their applicability in aqueous environments are described. We particularly discuss problems encountered in the use of MIPs in SPE and the attempts carried out to improve their efficiency.     

Molecularly imprinted polymers for sample preparation: A review

In spite of the huge development of analytical instrumentation during last two decades, sample preparation is still nowadays considered the bottleneck of the whole analytical process. In this regard, efforts have been conducted towards the improvement of the selectivity during extraction and/or subsequent clean-up of sample extracts. Molecularly imprinted polymers (MIPs) are stable polymers with molecular recognition abilities, provided by the presence of a template during their synthesis and thus are excellent materials to provide selectivity to sample preparation. In the present review, the use of MIPs in solid-phase extraction and solid-phase microextraction as well as its recent incorporation to other extraction techniques such as matrix-solid phase dispersion and stir bar sorptive extraction, among others, is described. The advantages and drawbacks of each methodology as well as the future expected trends are discussed.     

Molecularly imprinted polymers for the clean-up of a basic drug from environmental and biological samples

A molecularly imprinted polymer (MIP) was synthesized and evaluated to selectively extract an alpha-blocker, i.e. alfuzosin, from human plasma. The synthesis of the MIP was performed in dichloromethane with methacrylic acid as monomer and the target drug as template. A first series of experiments was carried out in dichloromethane to estimate the potential of the MIP in its specific recognition medium, i.e. dichloromethane, by developing a selective procedure and by measuring the capacity of the sorbent. An optimized procedure was developed for the selective extraction of alfuzosin with a recovery close to 100% in this medium and a specific capacity of 1.3 micromol g(-1) of MIP was measured. A study in aqueous media was also carried out by a comprehensive approach of the retention mechanism in order to build a selective procedure of extraction. The effects of the amount and of the charge of cations were studied and an optimal pH value was defined to limit matrix effects. Then, the alfuzosin MIP was then directly used to selectively extract the target drug from human plasma with an extraction recovery of 60%. Lastly, a soil was extracted by a pressurized solvent and the resulting extract was cleaned up on the MIP, showing the possibility to use this selective sorbent for the sample treatment of various complex matrices.     

Molecularly imprinted sol gel for ibuprofen: An analytical study of the factors influencing selectivity

This paper describes the preparation and testing of a sol gel specific for the non-steroidal anti-inflammatory drug ibuprofen. Ibuprofen was selected as a model compound due to the fact that it contains a number of structural and functional analogues, in this case ketoprofen and naproxen. In order to study the specific criteria affecting selectivity in sol gels, three sol gels were prepared for ibuprofen utilising two and three functional silane systems. The relative rebinding of each of the three compounds to the sol gels was assessed by % recovery in solid phase extraction. The results of the experiments indicate that along with the functionality imparted to the sol gel by the development of template-monomer complexes a major determinant of selectivity is shape selective memory. The utilisation of a three monomer system affords the cavity recognition based on the formation of π-π stacking interactions, hydrogen bonding, van der Waals forces, electrostatic interactions and shape complementarity and minimises cross reactivity. In addition real sample analysis has been performed on urine samples containing ibuprofen and metabolites showing specific preconcentration.     

Molecularly imprinted polymers for the selective solid-phase extraction of chloramphenicol

A variety of bulk polymers for the selective separation of chloramphenicol were synthesised from 2-vinylpyridine, diethylaminoethyl methacrylate or methacrylic acid monomers. Chromatographic evaluation indicated that chloramphenicol was retained under nonpolar elution conditions (k = 58.65) through selective hydrogen bonding and ionic interactions. The retention of chloramphenicol under aqueous elution conditions (k > 100) results from nonselective hydrophobic interactions. Under nonpolar elution conditions, the functional monomer employed imparted a significant influence on the recognition properties of the corresponding polymer. After solid-phase extraction using a molecularly imprinted polymer as sorbent and either an organic or aqueous washing solvent, nearly 100% recovery from the chloramphenicol standard solution was achieved, and nearly 90% recovery could be attained from spiked honey samples. The molecularly imprinted polymer was well suited to suppress matrix effects, and provided optimal preconcentration of the target molecule (chloramphenicol) prior to chromatographic analysis.     

Molecularly imprinted polymers labeled with amino-functionalized carbon dots for fluorescent determination of 2,4-dinitrotoluene

The authors have prepared amino-functionalized carbon dots (AC-dots) and applied them to fluorescently label a molecularly imprinted polymer (MIP) prepared by using 2,4-dinitrotoluene (DNT) as a template. Since DNT can retard vinyl polymerization, poly(methyl acrylate-co-acrylic acid) was used as a monomer. Non-imprinted polymers (NIPs) were also synthesized in order to compare data. As expected, MIPs exhibit higher adsorption than NIPs, with imprinting efficiencies ranging from 2 to 2.5. DNT is specifically captured by the cavities in the MIP and interact with AC-dots on the surface, resulting in quenching of the fluorescence of the AC-dots. Response to DNT reaches equilibrium within ~30 min. The method has a dynamic range that extends from 1 to 15 ppm, and allows for quantitation of DNT in aqueous solutions, with a detection limit of 0.28 ppm. Selectivity tests conducted in presence of DNT analogs demonstrated the selective recognition of DNT.

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Graphical Abstract Schematic of the preparation of molecularly imprinted polymers labeled with amino-functionalized carbon dots (AC-dots) for the quenchometric determination of 2,4-dinitrotoluene (DNT).

     

Molecularly imprinted polymers for 5-fluorouracil release in biological fluids

The aim of this work was to investigate the possibility of employing Molecularly Imprinted Polymers (MIPs) as a controlled release device for 5-fluorouracil (5-FU) in biological fluids, especially gastrointestinal ones, compared to Non Imprinted Polymers (NIPs). MIPs were synthesized using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent. The capacity of the polymer to recognize and to bind the template selectively in both organic and aqueous media was evaluated. An in vitro release study was performed both in gastrointestinal and in plasma simulating fluids. The imprinted polymers bound much more 5-Fu than the corresponding non-imprinted ones and showed a controlled/sustained drug release, with MIPs release rate being indeed much more sustained than that obtained from NIPs. These polymers represent a potential valid system for drug delivery and this study indicates that the selective binding characteristic of molecularly imprinted polymers is promising for the preparation of novel controlled release drug dosage form.     

Molecularly imprinted polymers as synthetic receptors for the QCM-D-based detection of l-nicotine in diluted saliva and urine samples

Molecularly imprinted polymers (MIPs) are synthetic receptors that are able to specifically bind their target molecules in complex samples, making them a versatile tool in biosensor technology. The combination of MIPs as a recognition element with quartz crystal microbalances (QCM-D with dissipation monitoring) gives a straightforward and sensitive device, which can simultaneously measure frequency and dissipation changes. In this work, bulk-polymerized l-nicotine MIPs were used to test the feasibility of l-nicotine detection in saliva and urine samples. First, l-nicotine-spiked saliva and urine were measured after dilution in demineralized water and 0.1× phosphate-buffered saline solution for proof-of-concept purposes. l-nicotine could indeed be detected specifically in the biologically relevant micromolar concentration range. After successfully testing on spiked samples, saliva was analyzed, which was collected during chewing of either nicotine tablets with different concentrations or of smokeless tobacco. The MIPs in combination with QCM-D were able to distinguish clearly between these samples: This proves the functioning of the concept with saliva, which mediates the oral uptake of nicotine as an alternative to the consumption of cigarettes.