A direct comparison of the performance of ground, beaded and silica-grafted MIPs in HPLC and turbulent flow chromatography applications

Exploring the potential of molecularly imprinted polymers and metal/metal oxide nanoparticles in sensors: recent advancements and prospects

Metal/metal oxide nanoparticles have gained increasing attention in recent years due to their outstanding features, including optical and catalytic properties, as well as their excellent conductivity. The implementation of metal/metal oxide nanoparticles, combined with molecularly imprinted polymers (MIPs) has paved the way for a new generation of building blocks to engineer and enhance the fascinating features of advanced sensors. This review critically evaluates the impact of combining metal/metal oxide nanoparticles with MIPs in sensors. It covers synthesis strategies, advantages of coupling these materials with MIPs, and addresses questions about the selectivity of these hybrid materials. In the end, the current challenges and future perspectives of this field are discussed, with a particular focus on the potential applications of these hybrid composites in the sensor field. This review highlights the exciting opportunities of using metal/metal oxide nanoparticles along with MIPs for the development of next-generation sensors.

An insight into chiral monolithic stationary phases for enantioselective high-performance liquid chromatography applications

In this review, three main classes of chiral monolithic stationary phases, namely silica-, organic polymer-, and hybrid-based monolithic stationary phases, are covered. Their preparations, applications, and advantages compared with the conventional-packed and open-tubular capillary columns are discussed. A detailed description of the different types and techniques used for the introduction of chiral selectors into the monolithic matrices such as immobilization, functionalization, coating, encapsulation, and bonding. Special emphasis is given to the recent developments of chiral selectors in HPLC monolithic stationary phases during the past 18 years.

Analytical applications of MIPs in diagnostic assays: future perspectives

Many efforts have been made to produce artificial materials with biomimetic properties for applications in binding assays. Among these efforts, the technique of molecular imprinting has received much attention because of the high selectivity obtainable for molecules of interest, robustness of the produced polymers, simple and short synthesis, and excellent cost efficiency. In this review, progress in the field of molecularly imprinted sorbent assays is discussed-with a focus on work conducted from 2005 to date.

Molecularly imprinted solid phase extraction coupled to high performance liquid chromatography for determination of aflatoxin M1 and B1 in foods and feeds

Molecularly imprinted solid phase extraction for determination of aflatoxin M₁ and B₁ in foods and feeds.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

Chromatographycally efficient microspherical composites of molecularly imprinted xerogels deposited inside mesoporous silica

A different approach to the preparation of microspheric particles of molecularly imprinted xerogels (MIX) is presented here. The technique consisted of filling up the pores of spherical, mesoporous, bare silica particles with a pregelification mixture by applying pressure. Upon gelification and drying, thin layers of MIX were deposited on the mesopores. Spherical composites of S-naproxen (S-NAP) imprints were produced by following this simple strategy. The performance of the imprints was quite satisfactory in terms of recognition ability (ascertained by selectivity against ibuprofen, α=4.9, and an imprinting factor of 13) whereas an outstanding improvement on dynamic features (expressed as column efficiency), as compared to the corresponding bulk format MIX (9 vs. 1.2 theoretical plates/cm), was reached.

Direct pharmacokinetic analysis of puqietinone by in vivo microdialysis sampling and turbulent-flow chromatography coupled with liquid chromatography-mass spectrometry

Sample pretreatment is a key step in bioanalytical process because of possible interference and matrix effects in mass spectrometry analysis. In this work, a novel strategy towards high speed and sensitivity was developed combining in vivo microdialysis (MD) sampling, turbulent-flow chromatography (TFC), and liquid chromatography-mass spectrometry (LC-MS). The procedures of cleanup, preconcentration, and separation were completed on-line in one step within 10min. During the MD optimization procedure, 1% hydroxypropyl-β-cyclodextrin (HP-β-CD) was used to improve the relative recovery of the analyte. Untreated MD samples were directly injected, and a TFC precolumn was flushed for 1min with aqueous phase of 4mL/min flow rate to desalt and concentrate biosamples. The retained analytes were then back-flushed by a switching valve onto a fast LC column (4.6mm×50mm, 1.8μm) for separation. Another diverter valve was employed to prevent the HP-β-CD that interferes with the ESI process from entering the MS. Puqietinone, a lipophilic alkaloid from Fritillaria puqiensis, was used as a case for validation. Results showed that the limit of quantification for puqietinone was 0.10ng/mL, and good linearity (R(2)=0.9993) was maintained over the range of 1.02-200.02ng/mL. Accuracy and precision were satisfactory within the range of the standard curve. This approach was able to effectively eliminate the influences of matrix effect and carry-over as the injection volume increased up to 20μL. The developed method was successfully applied to pharmacokinetic study of puqietinone after intravenous administration to rat. Results demonstrate the potential of using MD with TFC-LC/MS for in vivo monitoring experiments.

Behavior of phenols and phenoxyacids on a bisphenol-A imprinted polymer. Application for selective solid-phase extraction from water and urine samples

A molecularly imprinted polymer (MIP), obtained by precipitation polymerisation with 4-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as cross-linker, and bisphenol-A (BPA) as template, was prepared. The binding site configuration of the BPA-MIP was examined using Scatchard analysis. Moreover, the behaviour of the BPA-MIP for the extraction of several phenolic compounds (bisphenol-A, bisphenol-F, 4-nitrophenol, 3-methyl-4-nitrophenol) and phenoxyacid herbicides such as 2,4-D, 2,4,5-T and 2,4,5-TP has been studied in organic and aqueous media in the presence of other pesticides in common use. It was possible to carry out the selective preconcentration of the target analytes from the organic medium with recoveries of higher than 70%. In an aqueous medium, hydrophobic interactions were found to exert a remarkably non-specific contribution to the overall binding process. Several parameters affecting the extraction efficiency of the BPA-MIP were evaluated to achieve the selective preconcentration of phenols and phenoxyacids from aqueous samples. The possibility of using the BPA-MIP as a selective sorbent to preconcentrate these compounds from other samples such as urine and river water was also explored.

Investigation of imprinting parameters and their recognition nature for quinine-molecularly imprinted polymers

A series of molecularly imprinted polymers (MIPs) was prepared using quinine as the template molecules by bulk polymerization. The presence of monomer-template solution complexes in non-covalent MIPs systems has been verified by both fluorescence and UV-vis spectrometric detection. The influence of different synthetic conditions (porogen, functional monomer, cross-linkers, initiation methods, monomer-template ratio, etc.) on recognition properties of the polymers was investigated. Scatchard analysis revealed that two classes of binding sites were formed in the imprinted polymer. The corresponding dissociation constants were estimated to be 45.00 micromol l(-1) and 1.42 mmol l(-1), respectively, by utilizing a multi-site recognition model. The binding characteristics of the imprinted polymers were explored in various solvents using equilibrium binding experiments. In the organic media, results suggested that polar interactions (hydrogen bonding, ionic interactions, etc.) between acidic monomer/polymer and template molecules were mainly responsible for the recognition, whereas in aqueous media, hydrophobic interactions had a remarkable non-specific contribution to the overall binding. The specificity of MIP was evaluated by rebinding the other structurally similar compounds. The results indicated that the imprinted polymers exhibited an excellent stereo-selectivity toward quinine.

Molecularly imprinted beads by surface imprinting

Molecular imprinting is a state-of-the-art technique for imparting molecular recognition properties to a synthetic polymeric matrix. Conventionally, the technique is easily carried out using bulk imprinting, where molecularly imprinted polymers (MIPs) are prepared in large chunks and post-treatment processes like grinding and sieving are then required. However, this strategy tends to produce sharp-edged, irregular MIP bits with a limited scope of direct application. In addition, due to the creation of binding sites within the polymeric bulk, the issue of the hindrance of adsorbate diffusion (especially in the case of macromolecules) during template rebinding makes the MIPs prepared through this approach unsuitable for practical applications. Thus over the years, many efforts to address the limitations of conventional molecular imprinting techniques have resulted in new imprinting methodologies. Systems like suspension and precipitation polymerization, where MIPs with tunable morphologies can be prepared, have been developed. Additionally, strategies like surface imprinting have also been employed. Ultimately, both of these approaches have been combined to prepare regularly shaped surface-imprinted MIP beads. Such an approach incorporates the advantages of both methodologies at the same time. Given their desirable physical morphologies and favorable adsorption kinetics, MIPs prepared in this manner show significant promise for industrial applications. Therefore, they will be the main focus of this review.

Evaluation of water-compatible molecularly imprinted polymers as solid-phase extraction sorbents for the selective extraction of sildenafil and its desmethyl metabolite from plasma samples

The evaluation of molecularly imprinted polymers (MIPs) as selective sorbents for the solid-phase extraction of sildenafil and its principal metabolite, desmethylsildenafil, was investigated. Two MIPs were synthesised using structural analogues of sildenafil as templates, and a comparison of the performance of the two MIP sorbents in organic and aqueous media was performed. Additionally, the feasibility of applying molecularly imprinted solid-phase extraction (MISPE) to the clean-up of plasma samples containing sildenafil and desmethylsildenafil was investigated. A preliminary, quantitative MISPE for the determination of both compounds in plasma was also performed. The results showed that the MIPs used for the selective extraction of sildenafil gave better compound recovery when aqueous samples were used in comparison to organic-based samples. A preliminary, quantitative MISPE of sildenafil and desmethylsildenafil indicated that the imprinted materials could be used successfully as SPE sorbents for sample pre-treatment for the determination of sildenafil, and related compounds, in plasma.

Investigation of the nature of MIP recognition: The development and characterisation of a MIP for Ibuprofen

This paper describes the rational design, generation and testing of a molecularly imprinted polymer specific for Ibuprofen. Ibuprofen is a member of the class of drugs termed non-steroidal anti-inflammatory drugs (NSAIDS). In the present study, Ibuprofen was used as a template molecule for the preparation of molecularly imprinted polymers. A MIP has been produced which is capable of recognising Ibuprofen in aqueous media. Furthermore, Ibuprofen can be selectively extracted from aqueous conditions by molecularly imprinted solid phase extraction (MISPE). Recoveries were typically high (>80%) and good selectivity for Ibuprofen over structurally related analogues was seen. Moreover, the nature of the recognition between MIP and template has been investigated by NMR and molecular modelling to analyse whether or not it is possible to predict how well a given MIP will perform under set conditions. In addition, the physical characteristics of the MIP have been investigated including the particle size distribution on exposure of the MIP to different solvents. This has been related to the ability of the MIP to rebind Ibuprofen under the same conditions. The data from the characterisation of the MIP has been used to further enhance the understanding of the nature of MIP recognition.

Column-switching high-performance liquid chromatographic analysis of fluvastatin in rat plasma by direct injection

A column-switching high-performance liquid chromatographic (HPLC) method has been developed and validated for quantification of fluvastatin in rat plasma. Plasma samples were diluted with an equal volume of mobile phase, i.e. acetonitrile-5 mM potassium phosphate buffer (pH 6.8) (15:85, v/v), and the mixture was directly injected onto the HPLC system. The analyte was enriched in a pre-treatment column, while endogenous components were eluted to waste. The analyte was then back-flushed onto an analytical column and quantified with fluorescence detection (lambdaex=305 nm; lambdaem=390 nm). The standard curve for the drug was linear in the range 0.5-100 ng mL(-1) in rat plasma. The limit of quantitation for plasma was found to be 0.5 ng mL(-1). This method has been fully validated and shown to be specific, accurate and precise. The method is simple and rapid because of a minimized sample preparation and appears to be useful for the pharmacokinetic study of fluvastatin.

Determination of dl-tetrahydropalmatine in Corydalis yanhusuo by l-tetrahydropalmatine imprinted monolithic column coupling with reversed-phase high performance liquid chromatography

A method for direct determination of DL-tetrahydropalmatine (DL-THP) in Corydalis yanhusuo, a traditional Chinese herb, by L-THP imprinted monolithic precolumn on-line/off-line coupling with reversed-phase high performance liquid chromatography (RP-HPLC) was developed. The L-THP imprinted monolithic column has been prepared by in situ polymerization using methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. With the optimization of chromatographic conditions, such as mobile phase composition, flow rate, column temperature and sample loading, for the separation of enantiomer, DL-THP was base-line separated on the MIP. The imprinted monolithic column was used as a precolumn for fractionation of the C. yanhusuo extract. Both the non-retained and retained fractions were separated by RP-HPLC. Meanwhile, the D-THP and L-THP can be detected in the non-retained and retained fractions, respectively. Additionally, direct determination of L-THP using molecularly imprinted monolith on-line coupling with a reversed-phase column was acquired.

Direct rapid synthesis of MIP beads in SPE cartridges

Selecting optimal compositions for non-covalent molecularly imprinted polymers (MIPs) and screening for appropriate rebinding conditions necessitates synthesising a large number of polymers. This is extremely labour-intensive and usually results in very limited "optimisation" in studies of MIPs. Here, a new method is proposed for rapid synthesis of MIPs in a beaded form that can be used directly in many different performance evaluation studies. The method is based on synthesis of spherical particles by suspension polymerisation in liquid fluorocarbon [Mayes, A., Mosbach, K., 1996. Molecularly imprinted polymer beads: suspension polymerisation using a liquid perfluorocarbon as the dispersing phase. Anal. Chem. 68, 3769-3774]. The polymers were directly polymerised under UV light in solid phase extraction (SPE) cartridges, then washed and extracted in the same cartridges where they had been synthesised, resulting in a rapid and automatable process that requires no transfer or manipulation of the polymer particles. The particles were similar in terms of size, morphology and functional performance to particles obtained by suspension polymerisation in fluorocarbon solvent using a conventional reactor. In this initial study, 36 polymers were synthesised to study the effect of a variation in the type and amount of four different functional monomers, methacrylic acid (MAA), acrylic acid (AA), hydroxyethyl methacrylate (HEMA) and 2-vinylpyridine (2-VPy), for the imprinting of propranolol and morphine. The performance of polymers synthesised using MAA was as expected, but those synthesised with AA as functional monomer showed more surprising rebinding properties as a function of monomer to cross-linker ratios, demonstrating the potential value of pragmatic synthesis and screening approaches to polymer optimisation.