Advanced Molecularly Imprinting Materials

By Ashutosh Tiwari and Lokman Uzun

Molecularly imprinted polymers (MIPs) are an important functional material because of their potential implications in diverse research fields. The materials have been developed for a range of uses including separation, environmental, biomedical and sensor applications. In this book, the chapters are clustered into two main sections: Strategies to be employed when using the affinity materials, and rational design of MIPs for advanced applications. In the first part, the book covers the recent advances in producing MIPs for sample design, preparation and characterizations. In the second part, the chapters demonstrate the importance and novelty of creation of recognition imprinted on the materials and surfaces for a range of microbial detection sensors in the biomedical, environmental and food safety fields as well as sensing human odor and virus monitoring systems.         

Part 1: Strategies of affinity materials

• Molecularly imprinted polymers
• MIP nanomaterials
• Micro- and nanotraps for solid phase extraction
• Carbonaceous affinity nanomaterials
• Fluorescent MIPs
• MIP-based fiber optic sensors

Part 2: Rational design of MIP for advanced applications

• MIP-based biomedical and environmental sensors
• Affinity adsorbents for environmental biotechnology
• MIP in food safety
• MIP-based virus monitoring
• MIP-based drug delivery and controlled release
• Biorecognition imprints on the biosensor surfaces
• MIP-based sensing of volatile organic compounds in human body odour
• MIP-based microcantilever sensor system

• Language: English
• Publisher: Wiley
• Release date: Nov 2, 2016
• ISBN: 9781119336167

Book preview

Preface

Molecularly imprinted polymers (MIPs) are a thoughtful, functional material due to their potential implications in diverse research fields. A range of affinity materials has been developed for separation, environmental, biomedical and sensor applications. In this book, the chapters are divided into two main sections: strategies for affinity materials and rational design of MIPs for advanced applications. In accordance with the main practice of MIPs, recent advances in producing MIPs for sample design, preparation and characterizations are covered in the first part of the book. In the second part, distinguished authors have summarized the importance and novelty of the creation of recognition imprinted on the materials and surfaces of sensors in biomedical, environmental and food safety applications; for example, microbial detection, drug delivery, cantilever sensor systems, chemical vapor sensing in human odor and virus monitoring.

In terms of advanced materials, molecularly imprinted polymers are a kind of applied material due to their potential uses. Therefore, the number of research and review articles, along with related books, has dramatically increased over the last decades. These materials are considered artificial recognition elements and are comprehensively evaluated as advanced smart materials for separation, environmental and biomedical sciences, and biosensor applications. Therefore, we could not ignore these materials when preparing the Advanced Materials Series and the editors are very proud to share this book with you. Included herein are milestone applications of affinity adsorbent for environmental biotechnology and solid-phase extraction, followed by a summary of two different perspectives on controlled drug release applications; enhancing the material properties and adjusting release kinetics.

As previously mentioned, the chapters of this book are divided into two main sections: MIPs as adsorbent and MIPs as recognition element. In accordance with the main practice with MIPs, recent advances in producing MIPs for sample preparation are presented in the first part of the book. Then, a smooth transition is made from separation science to the application of MIP sensors for food safety. In the second part of the book, the importance and novelty of creation of biorecognition imprinted on biosensor surfaces are summarized. Furthermore, MIP-based sensors for biomedical and environmental applications, fluorescent sensors, and fiber optic sensing platforms have also been compiled. Finally, the book ends with three interesting chapters on advanced imprinted materials for cantilever sensor systems, chemical vapor sensing in human odor, and virus monitoring.

The author of chapter 1 summarizes recent advances in molecularly imprinted materials for the purpose of sample preparation. In conjunction with this chapter, in chapter 2 compiles a genuine combination of solvent-free sample preparation techniques and molecularly imprinted nanomaterials. Recent progress in fluorescent molecularly imprinted materials is summarized in chapter 3; and chapter 4 includes some novel applications of imprinted materials as micro- and nanotraps for the purpose of solid phase extraction. A summary of carbonaceous imprinted materials with attractive applications for selective and specific analysis is presented in chapter 5. Chapter 6, which concludes the first part of the book, summarizes the use of imprinted materials as fiber optic sensor platform.

The second part of the book encompasses the rational design of imprinted materials for advanced applications. In chapter 7, the biomedical and environmental applications of imprinted materials-based sensors have been compiled. Moreover, chapter 8 summarizes the environmental biotechnology applications of imprinted materials. Molecular imprinting technology for sensing and separation in food safety is summarized in chapter 9. Advanced imprinted materials for virus monitoring are compiled in the pioneering work in chapter 10 which is the first comprehensive review of its kind in the related literature. In chapters 11 and 12, the authors summarize drug delivery and controlled release applications of imprinted materials while focusing on release kinetics and materials development strategies, respectively. Chapter 13 includes novel creation strategies for biorecognition imprints on biosensor surfaces. In chapter 14, the authors have figured out the recent application of imprinted materials for sensing of volatile organic compounds in human body odor. Finally, chapter 15 is a compilation of attractive applications of imprinted materials as recognition elements on the microcantilever sensor system.

This volume of the Advanced Materials Series includes 15 chapters in all showcasing the excellent efforts of prominent researchers from eleven different countries having more than twenty different academic and industrial affiliations. It is intended for a wide readership including university students and researchers from diverse backgrounds such as physics, chemistry and chemical engineering, materials science and nanotechnology engineering, electrical and computer engineering, biomedical engineering, environmental sciences, food sciences, life sciences, pharmacy, veterinary medicine, medicine, military science, and biotechnology. It can be used not only as a textbook for undergraduate and graduate students but also as a review and reference book for researchers in the materials science, bioengineering, medical, physics, forensics, agriculture, biotechnology, food safety, and nanotechnology arenas. We hope that the chapters of this book will provide the reader with valuable insight into molecularly imprinted polymers as advanced smart materials with respect to the different prominent features in novel designs and future applications.

Editors

Ashutosh Tiwari, PhD, DSc

Lokman Uzun, Doç. Dr.

September 2016, Linköping

Part 1

STRATEGIES OF AFFINITY MATERIALS

Chapter 1

Recent Molecularly Imprinted Polymer-based Methods for Sample Preparation

Antonio Martín-Esteban

Departamento de Medio Ambiente, INIA, Madrid, Spain

Corresponding author: [e-mail]

Abstract

In spite of the huge development in analytical instrumentation, sample preparation is still considered the bottleneck of the whole analytical process. Nowadays, several sample preparation techniques are available; however, all of them suffer from lack of selectivity making difficult in most cases the final determination of target analytes at the low concentration levels required. In this regard, molecularly imprinted polymers (MIPs) are considered excellent materials able to perform selective extractions. The incorporation of MIPs as sorbent in solid-phase extraction, so-called molecularly imprinted solid-phase extraction (MISPE), is already accepted in analytical laboratories, and some MIPs are commercially available. Besides, MIP incorporation to other sample preparation techniques, such as solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), or matrix solid-phase dispersion (MSPD), has been recently proposed and successfully applied to the extraction of different analytes from complex samples. Thus, the objective of this chapter is providing the reader an overview of the uses of MIPs in sample preparation including the most recent developments in this field.

Keywords: Molecularly imprinted polymers, sample preparation, solid-phase extraction, solid-phase microextraction, stir bar sorptive extraction

1.1 Introduction

The development of analytical instrumentation has been huge during past decades allowing eventually the determination of any compound in environmental, food, and biological samples. Typically, target analytes are determined by chromatographic techniques coupled to common detectors (UV, fluorescence) or, more recently, mass spectrometry (MS), or tandem MS. However, direct injections of crude sample extracts are not recommended even when the selective detection provided by MS is used since matrix components can inhibit or enhance the analyte ionization, hampering accurate quantification. Poorly treated sample may invalidate the whole analysis, and thus, a clean sample is generally convenient to improve separation and detection. Therefore, sample preparation is a key step of the whole analytical process, being critical for unequivocal identification, confirmation, and quantification of analytes.

The main objectives of sample preparation are the removal of potential interferents, analyte preconcentration (especially in environmental water samples), converting (if needed) the analyte into a more suitable form for detection or separation, and providing a robust and reproducible method independent of variations in the sample matrix. More recently, new objectives have been set such as using smaller initial sample sizes, improvement of selectivity in extraction, facilitating the automation, and minimizing the amount of glassware and organic solvents to be used [1]. Traditional liquid–liquid extraction does not fulfill current requirements, and it has been displaced from laboratories by new extraction techniques such as solid-phase extraction (SPE), solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), and more recently by matrix solid-phase dispersion (MSPD), micro solid-phase extraction (MSPE), or liquid-phase microextraction (LPME), among others. All the mentioned techniques suffer from lack of selectivity making necessary an extensive optimization of the typical steps involved. However, even after careful optimization, some matrix components are co-eluted with target analytes making difficult to reach detection limits according to the nowadays stringent regulations. Some years ago, antibodies immobilized on an adequate support, called immunosorbents, were proposed as an alternative for use in SPE applications [2, 3] in order to overcome the aforementioned drawbacks associated with typical nonspecific sorbents. Different immunosorbents have been employed for the determination of pesticides, drugs, and polyaromatic hydrocarbons, among others, showing an excellent degree of cleanup owing to the inherent selectivity of the antibodies used. However, the obtainment of antibodies is difficult, time-consuming, and expensive, and in addition, it is difficult to guarantee its success. Also, it is important to point out that after the antibodies have been obtained they have to be immobilized on an adequate support, which may result in poor antibody orientation or even complete denaturation.

Molecularly imprinted polymers (MIPs) are synthetic materials able to specifically rebind a target molecule in preference to other closely related compounds. These materials are obtained by polymerizing functional and cross-linking monomers around a template molecule, leading to a highly cross-linked three-dimensional network polymer. The monomers are chosen considering their ability to interact with the functional groups of the template molecule. Once polymerization has taken place, template molecule is extracted and binding sites with shape, size, and functionalities complementary to the target analyte are established. The resulting imprinted polymers are stable, robust, and resistant to a wide range of pH, solvents, and temperature. Therefore, MIPs emulate natural receptors but without the associated stability limitations. In addition, MIPs synthesis is also relatively cheap and easy, making them a clear alternative to the use of natural receptors.

Three different approaches for the synthesis of MIPs have been reported: covalent, non-covalent, and semi-covalent approaches. Wulff and Sarhan [4] introduced the covalent approach, which involves the formation of reversible covalent bonds between the template and monomers before polymerization. Then, the template is removed from the polymer by cleavage of the corresponding covalent bonds, which are re-formed upon rebinding of the analyte. The high stability of template–monomer interaction leads to a rather homogenous population of binding sites, minimizing the existence of non-specific sites. However, the difficulty of designing an appropriate template–monomer complex in which covalent bond formation and cleavage are readily reversible under mild conditions makes this approach rather restrictive.

The non-covalent approach was introduced by Mosbach and Arshady [5], and nowadays it is by far the most used for the preparation of MIPs. The non-covalent approach is based on the formation of relatively weak non-covalent interactions (i.e. hydrogen bonding, ionic interactions) between template molecule and selected monomers before polymerization. The experimental procedure is rather simple and a wide variety of monomers able to interact with almost any kind of template are commercially available. However, it is not free of some drawbacks since template–monomer interactions are governed by an equilibrium process during the pre-polymerization step. Thus, in order to displace the equilibrium toward the formation of the template–monomer complex, a high amount of monomer is used. Consequently, the excess of free monomers is randomly incorporated to the polymeric matrix leading to the formation of non-selective binding sites. Figure 1.1 shows schematically the preparation of MIPs by the covalent and non-covalent approaches.

Figure 1.1 Preparation of MIPs.

An intermediate option is the semi-covalent approach [6, 7]. In this case, the template is also covalently bound to a functional monomer before polymerization, but the template rebinding is based only on non-covalent interactions.

The use of MIPs as selective sorbent materials allows performing a customized sample treatment step prior to the final determination. Thus, their use in SPE, so-called molecularly imprinted solid-phase extraction (MISPE), is by far the most advanced technical application of MIPs [8–13]. Besides, past recent years have seen a growing interest in the combination of MIPs with other sample preparation techniques. Thus, the present paper pretends to describe the most recent MIP-based sample preparation techniques, describing the most employed different approaches as well as highlighting selected applications.

1.2 Molecularly Imprinted Solid-phase Extraction

1.2.1 General Considerations

MISPE protocols do not differ from other SPE procedures. Typically, a small amount (15–500 mg) of imprinted polymer is packed into polyethylene (PE) cartridges. Then, after performing conditioning, loading, and washing steps, analytes are eluted, ideally free of co-extractives, and the elution extract is further analyzed by chromatography techniques. At present, MISPE can be considered the most advanced technical application of MIPs used for the selective extraction and/or clean-up of target analytes from different kind of samples. There are several research groups around the world active in this field, and there are a huge number of papers published describing the synthesis and the use of MIPs for SPE. Besides, some companies already commercialize cartridges packed with MIPs suitable for the determination of target analytes in different samples.

However, most MISPE-related papers just describe the use of different templates for different applications, and only few of them propose new ways to minimize the inherent drawbacks in preparing and using MIPs (e.g. template bleeding, tedious synthesis procedure, slow mass transfer, and poor performance in aqueous media). Originally, bulk polymerization, due to its simplicity, was the first strategy used to synthesize MIPs. Using this procedure, and after the unavoidable grinding and sieving steps, the particles obtained invariably possessed an heterogeneous particle size distribution with poor binding-site accessibility for the target analyte. Recent years have seen the development of new polymerization methodologies to obtain MIP beads with proper physical characteristics (i.e. size, porosity, pore volume, and surface area). Among these new alternatives, only multi-step swelling and polymerization [14] and precipitation polymerization [15] have been used for the preparation of MIPs for SPE of a wide variety of analytes in biological samples [16–18] and environmental samples [19–22]. More recently, microspheres were obtained by polymerizing monomers and template mixture into the pores of silica beads, being the latter dissolved with NH4HF2 after polymerization (Figure 1.2). The resulting MIP beads were successfully used in the MISPE of alternariol, a mycotoxin, in tomato sample extracts [23].

Figure 1.2 Scheme of the preparation of MIP microspheres with a silica mold and SEM images of the intermediate composite material (a) and the same beads after treatment with 3 M aqueous NH4HF2 (b). Reprinted from [23] with permission from Elsevier.

A new approach, proposed by Zhang et al. [24], has been the synthesis of single-hole hollow MIPs (SHH-MIPs for the MISPE of Sudan I in chili sauce). Firstly, carboxylated polystyrene particles are synthesized and then used in a multi-step swelling and polymerization process for swelling and pore-forming. The strong hydrogen-bond interactions between the carboxyl groups at the surface of the polystyrene seeds and the functional monomers will thus drive the selective polymerization at the surface of the polystyrene seeds, preventing secondary nucleation. A consecutive two-step procedure including swelling and polymerization was carried out followed by dissolving polystyrene seeds with dichloromethane to form a single hole in the highly cross-linked polymer shell. As a result, hollow MIPs with a single hole were obtained. Such particles exhibited larger specific surface area than irregular solid MIPs prepared by bulk polymerization and led to a much higher binding capacity. Besides, a large number of binding sites are located in the proximity of both interior and outer surfaces of the polymers, facilitating template removal and mass transfer. Accordingly, SHH-MIP was employed as SPE adsorbent for chili sauce analysis reaching limits of detection (LODs) of about 5 μg kg−1 by high-performance liquid chromatography with ultraviolet detection (HPLC–UV). In spite of the success, such an approach is not free of drawbacks. First, although the synthesis of monodisperse, imprinted beads with high yield is achieved, the experimental procedure is also laborious, and, second and more importantly, template–monomer interactions purely based on hydrogen bonding can be disrupted since the dispersion phase used during the synthesis is water saturated. Thus, its applicability is limited to templates able to interact with monomers through strong enough electrostatic and hydrophobic interactions.

In order to improve mass transfer, some in situ polymerization strategies have been proposed. At this regard, Du et al. [25] described the synthesis of kinetin molecularly imprinted monolith in a syringe by an in situ polymerization technique. The synthesis procedure is rather simple and easily performed in any laboratory equipped with basic instrumentation. However, in order to guarantee a proper porous morphological structure in MIP, thus providing flow paths through the monolithic column, an appropriate amount of a polar solvent (i.e. dodecanol) is included in the mixture of solvents used as porogen, which may disrupt the typical hydrogen-bonding interactions taking place between template and monomers during polymerization and thus its applicability is limited to certain templates.

The in situ synthesis of MIPs, into a cartridge, on the surface of microfiltration glass fiber membranes in multi-well filter plates has been proposed as an alternative [26–28]. Briefly, the synthesis procedure is as follows: first, membranes of a 24-well filter plate are washed with methanol and dried before use; then, 30–50 μL aliquots of polymerization mixture are transferred onto the filter plate membranes under oxygen-free argon atmosphere; the plate is covered with UV-transparent cling film and placed under a UV lamp for plate irradiation for 3 h. After polymerization, the template is removed by successive washing and ready for SPE experiments. The obtained MIP on the surface of the modified membranes forms a veil-like web between adjacent fibers, whereas, inside the membrane, the polymer is partly deposited in clusters on the glass fibers. Such a polymer structure permits fast filtration on the composite membrane. Such a synthesis procedure has been further improved by using high-viscosity solvents (i.e. paraffin oil, room temperature ionic liquids) as porogens. In this manner, with monomers:porogen ratios typical of bulk polymerization, it is possible to obtain regular shaped polymer micro (nano)spheres. The well-defined morphology and large surface area of the particles may increase the specific binding capacity of the membranes. Figure 1.3 shows, as an example, the SEM micrographs of the composite membranes prepared using different high-viscosity solvents, where the presence of polymer microspheres entrapped within the glass fiber network is clearly observed. This approach is a cost-effective, one-step procedure for preparing MIP-composite membranes and offers a viable alternative to existing MISPE cartridges. Other advantages such as a much easier and faster synthesis method, and high-throughput analysis should be also pointed out. However, its weakest point is the low breakthrough volumes observed (<1 mL), which exclude environmental samples from the possible applications, although it suits sample pretreatment of biological samples perfectly well.

Figure 1.3 SEM micrographs of MIP composite membranes prepared with different polymerization solvents: (a) caprylonitrile/paraffin oil, (b) toluene/paraffin oil, (c) trihexyl(tetradecyl)phosphoniumtris(pentafluoroethyl) trifluorophosphate (PH3 T FAP), (d) 1-butyl-3-methylimidazolium tetrafluoroborate, (e) cross-sectional view of a PH3 T FAP MIP, and (f) unmodified glass microfiber membrane. Reprinted from [28] {Renkecz, 2013, Molecularly Imprinted Polymer Microspheres Containing Photoswitchable Spiropyran-Based Binding Sites} with permission from John Wiley & Sons.

A similar approach was recently proposed for the synthesis of MIPs grafted onto porous PE frits [29, 30]. The synthesis procedure is based on the immersion of PE frits in a saturated solution of benzophenone (a photo-initiator capable of starting polymerization from the surface of the support material). Next, the frits, with the pores still wetted by this solution, were dipped in a vessel containing the polymerization mixture and the polymerization was carried out by UV irradiation. After irradiation, the template was removed from the imprinted frit by Soxhlet extraction and finally, the modified frits were placed inside SPE glass tubes. Under optimum polymerization conditions, polymer aggregates are spread throughout the PE frit surface without significantly affecting its macroporous structure. The obtained imprinted frits were applied to clean up spiked extracts of thiabendazole (a post-harvest systemic fungicide) from real citrus samples in the range of concentrations permitted in real samples according to the European legislation.

As mentioned above, another drawback typically attributed to MIPs is their poor performance in aqueous media, although aqueous samples can also be directly loaded onto MIP cartridges. However, in this case, MIPs behave like a reverse-phase sorbent and thus both target analytes and matrix components are retained trough non-specific interactions. Then, the washing solvent is the responsible of removing matrix components and, more important, of re-distributing nonspecifically bound analytes to the selective imprints. Unfortunately, the success of such procedure is not always achieved, and thus efforts have been directed toward the synthesis of water-compatible MIPs by incorporating hydrophilic surface properties to the polymer in order to reduce non-specific hydrophobic interactions. This goal can be mainly achieved by using polar porogens [31–33], hydrophilic comonomers (e.g. 2-hydroxyethyl methacrylate, acrylamide), or cross-linkers [e.g. pentaerythritoltriacrylate, methylenebis (acrylamide)] [34–36] and/or especially designed monomers capable of stoichiometrically interacting with the template functionalities [37, 38]. Such approaches have provided recognition of target analytes by MIPs in aqueous media to a certain extent, and thus, further research in this field is expected in the coming years.

Finally, template bleeding is considered one of the main drawbacks of MISPE in trace analysis. It is known that, even after exhaustive washing by different methodologies [39], traces of template remain in the polymer network and thus could affect the accurate determination of target analytes. The best manner of preventing the bleeding problem is the use of an analogue of the target analyte as template. Therefore, the bleeding of the template does not interfere in the quantification of the target analyte. This approach was originally proposed by Andersson et al. [40] for the selective extraction of sameridine on a MIP synthesized using a closely related compound to target analyte as template. Later, some other authors have followed this approach allowing the precise and accurate quantification of a great variety of analytes in different kind of samples. However, the main drawback of template-analogue imprinted polymers is the resulting inferior molecular recognition ability compared to those prepared using the analyte as template. In this sense, a very interesting alternative is the use of a stable isotope labeled compound as template molecule (isotope imprinting) [41, 42]. In this way, although template bleeding might did occur, target analyte can be accurately detected by selective ion monitoring. Obviously, although the potential of isotope imprinting to overcome the template bleeding problem is evident, its applicability is limited to the availability of the corresponding isotopic labeled compound analogue to the target analyte and the use of MS detection.

1.2.2 Online and Inline Protocols

In spite of the clear advantages of online and inline protocols, few papers have been published since the first works by Masqué et al. [43] (online) and Sellergren [44] (inline). Such low activity might be attributed to the usual lack of compatibility between the mobile-phase required to perform the separation on the analytical column and the elution solvent necessary to desorb analytes from the MIP precolumn in online systems. Besides, MIPs must provide a good permeability and fast mass transfer of analytes, which make necessary the synthesis of MIPs with improved properties.

At this regard, a novel sample preparation technique, termed dynamic liquid–liquid–solid microextraction (DLLSME), was developed and coupled online to HPLC for direct extraction, desorption, and analysis of trace estrogens in complex samples [45]. The DLLSME consists of an aqueous donor phase, an organic medium phase, and molecularly imprinted polymer filaments (MIPFs) as solid acceptor phase. The organic solvent with lesser density was directly added on top of the aqueous sample, and the dynamic extraction was performed by circulating the organic solvent through the MIPFs inserted into a polyether ether ketone (PEEK) tube, which served as an extraction and desorption chamber. Afterward, the extracted analytes on the MIPFs were online desorbed and then introduced into the HPLC for analysis. According to the authors, greater permeability was achieved, by compared with that of monolithic capillary or column packed with finely dispersed sorbents. Besides, the small i.d. tubing used could produce high linear flow rate on the surface of the coatings, resulting in a fast transfer of target analytes between the solid and liquid phases. It is evident that the use of MIPFs presents clear advantages compared to other online systems and likely new methodologies based on its use will be further developed in the near future.

Apart from the common drawbacks associated with the online and inline protocols, peak-broadening and peak-tailing phenomena are observed in the elution profiles of inline MISPE processes. These phenomena are attributed to a slow mass transfer and the existence of a heterogeneous binding-site distribution, even using imprinted beads obtained by precipitation polymerization or by polymerization within the pores of preformed spherical silica particles and subsequent dissolution of the silica matrix. These drawbacks typically lead to irreproducibility of peak-area measurements and long analysis times. Surface imprinting, which sets in place a thin film of imprinted polymer grafted onto the surfaces of preformed beads, may solve some of these drawbacks, thereby conferring better efficiency on the extraction process. In this regard, MIP microspheres with core–shell morphology and narrow particle-size distributions prepared by a two-step precipitation–polymerization procedure have been proposed for inline MISPE protocols [46, 47]. This synthetic procedure involves two steps: (1) polymer microspheres (the core particles) are obtained by precipitation polymerization of divinylbenzene-80 (DVB-80) in acetonitrile, and (2) the core particles are used as seed particles in the synthesis of molecularly imprinted core–shell particles with well-developed pore structures, by copolymerization of DVB-80 with methacrylic acid (MAA) in the presence of the template in a mixed solvent porogen (acetonitrile/toluene). Using such core–shell particles, a clear improvement in the chromatographic performance was achieved compared to that offered by imprinted polymer microspheres, where the imprinting is not confined to the outer surfaces. This result demonstrates that the slow mass-transfer kinetics associated with conventional MIP stationary phases can be dramatically improved by surface-imprinting techniques.

1.2.3 Improved Batch Protocols

At present, the use of magnetic nanoparticles as support of different stationary phases in batch SPE is one of the most active research area in sample preparation. Such modified magnetic particles, after extraction, can be separated from the media by a simple magnet, thereby avoiding tedious filtration and/or centrifugation steps. Properties of magnetic particles can be modified by the incorporation of MIPs providing selectivity to the extraction and a great variety of magnetic MIPs has been developed and used in batch MISPE [11, 48]. The synthesis of magnetic MIPs, although involving several steps, is rather simple: firstly, after obtaining Fe3O4 particles, they need to be treated with surface modifiers [e.g. ethylene glycol, oleic acid, and poly(vinyl alcohol)]; then, the polymerization solution, the modified Fe3O4 particles, and a dispersing medium are mixed and dispersed; and, finally the suspension is heated, allowing polymerization to take place on the surface of modified Fe3O4 particles. Once the magnetic MIP beads are obtained, they can be used in batch procedures. This procedure has been successfully used for the extraction of triazines from soil, soybean, lettuce, and millet [49], tetracycline antibiotics from egg and tissue [50], sulfonamides in poultry feed [51], and microcystins in environmental waters [52], among others.

Finally, a rather simple approach, so-called molecularly imprinted microSPE (MI-MSPE) has been proposed. As it shown in Figure 1.4, the MI-MSPE device comprises MIP particles enclosed within a porous polypropylene flat-sheet membrane envelope. Once the MI-MSPE device is obtained, it is conditioned and placed in the sample. The device tumbles freely within the sample solution during extraction for a certain period of time under stirring. After extraction, the device is manually removed with the help of tweezers and placed in a vial for elution of analytes. This approach has been successfully applied to the selective extraction of phenolic compounds from tap, river, and sewage waters [53], ochratoxin A from coffee, grape juice, and urine [54], and cocaine and its metabolites in human urine [55].

Figure 1.4 Schematic of preparation of molecularly imprinted microSPE device. Reprinted from [55] with permission from Elsevier.

1.3 Molecularly Imprinted Solid-phase Microextraction

Since its introduction by Arthur and Pawliszyn [56], SPME has become one of the most used techniques for sample preparation in analytical laboratories. SPME is based on the partitioning of target analytes between the sample and a stationary phase, typically coated to the surface of a fused silica fiber. After extraction, analytes are thermally desorbed directly onto the injection port of a gas chromatograph or eluted with a suitable solvent for further analysis by chromatographic techniques. Its simplicity of operation, solventless nature, and the availability of commercial fibers have made SPME to become a tool routinely used for certain applications. However, the variety of commercially available fibers is rather limited and just roughly covers the scale of polarity which leads to a lack of selectivity during the extraction process. In this sense, the combination of molecular imprinting and SPME would ideally provide a powerful analytical tool with the characteristics of both technologies (simplicity, flexibility, and selectivity).

1.3.1 MIP-coated Fibers

The preparation of the first MIP-coated silica fiber was proposed by Koster et al. [57] for the SPME of brombuterol from human urine. Silica fibers were activated by silylation and subsequently immersed in a polymerization solution composed by clenbuterol, MAA, EGDMA, and AIBN in acetonitrile to carry out polymerization during 12 h at 4 °C under irradiation at 350 nm. Fibers with a polymeric film thickness of ~75 μm were obtained in a reproducible manner.

Key factors influencing both the morphology and the width of the obtained MIP coating were systematically studied in a series of papers dealing with the preparation of different MIP-coated silica fibers [58–60]. In these works, silica fibers were activated by silylation prior immersion into polymerization solution (polymerization took place at 60 °C). Although the procedure and further pulling out of the fiber are tricky, the obtained coatings resulted to be homogenous and dense, and good reproducibility can be achieved by a strict control of polymerization conditions. The polymerization time is a key aspect of this procedure since it affects both coating thickness and fiber preparation reproducibility. In general, a polymerization time of 6 h was reported as optimum. Shorter time leads to bad uniformity and thin coating, and longer time produces a too solid polymer preventing the safe pulling out of the fiber. But also, a proper selection of the porogen is crucial, and it has been demonstrated that apolar solvents (i.e. toluene) lead to homogeneous MIP coating with thickness of 25.0 μm, whereas a thickness of 1.5 μm was achieved using acetone. This problem can be circumvented by immersing the obtained fibers again in fresh polymerization solutions, being fibers repeatedly coated by identical polymerization procedures until the desired thickness is reached. The scanning electron micrographics of a tetracycline MIP-coated fiber are shown in Figure 1.5, showing not only a homogeneous and dense morphological structure (Figure 1.5a) but also a highly cross-linked and porous structure (Figure 1.5b) [59].

Figure 1.5 Scanning electron micrographs of a tetracycline MIP-coated fiber at ×300 (a) and ×10,000 (b) magnification. Preparation conditions of MIP-coated fiber: solvent: acetone; monomer: acrylamide; cross-linker: trimethylolpropanetrimethacrylate; initiator: azo(bis)-isobutyronitrile; polymerization time: 6 h; coating times: 10. Reprinted from [59] with permission from Elsevier.

The preparation of MIP-coated silica fibers has been further improved by surface reversible addition–fragmentation chain transfer polymerization (RAFT), which permits a better control of the thickness of MIP coating [61]. Briefly, silylated silica fibers were further functionalized with phenyl magnesium bromide (a RAFT agent) in the presence of carbon disulfide. Finally, the RAFT-agent-functionalized fiber was immersed in the corresponding polymerization solution for 48 h at 60 °C and, thanks to the controllable radical growing and chain propagation in surface RAFT polymerization, MIP-coated fibers 0.55 μm thick can be obtained in a robust and reproducible manner. The ultra-thin thickness of the MIP coating guarantees sufficient accessibility to selective recognition sites and the porous morphological structure of MIP coating, enhancing the diffusion speed of analytes into the MIP coating.

The preparation of MIP-coated fibers by electropolymerization of suitable monomers (i.e. pyrrole) was recently explored [62, 63]. Using this approach, the MIP was synthesized and deposited directly onto a support (i.e. platinum or stainless steel) of any size and shape in a single step. The great advantage of this method is that the thickness of the polymer can be tuned and controlled by varying the polymerization conditions (e.g. circulated current). Although this methodology is at a very early stage, the results obtained are rather promising and further development is expected in the near future.

1.3.2 MIP Fibers (Monoliths)

A completely different and much simpler approach for the preparation of MIP fibers using fused silica capillaries as molds has been proposed [64, 65]. In this method, silica capillaries are cut to approximately 30-cm-long pieces, and four windows of about 1.0 cm are prepared by burning the protecting polymer layer. Then, the capillary is filled with the polymerization mixture, and both capillary ends are closed with two small pieces of rubber. The filled capillaries are introduced in an oven, and polymerization takes place typically at temperatures higher than 60 °C for a certain period of time. Finally, capillaries are cut and immersed in an aqueous solution of NH4HF2 under agitation with silica walls being etched away. In this manner, MIP monoliths of 1 cm length are obtained, being its thickness dependent of the inner diameter of the silica capillary used. Moreover, as can be also observed in Figure 1.6a, the obtained fibers were flexible and it is possible to bend them to a certain extent preventing the easy breakage traditionally associated with the coated fused silica fibers. Similarly to MIP-coated fibers, solvent, cross-linker, and polymerization time have a direct influence on the porosity, and thus in the final analytical performance, of the obtained fibers. As an illustrative example, Figure 1.6b shows the chromatogram obtained after SPME of soil sample extracts using a propazine-imprinted monolith. The high selectivity provided by the propazine-imprinted fiber allows the detection of target analytes at very low concentration levels, which would be extremely difficult without performing any cleanup.

Figure 1.6 LC–UV chromatograms obtained at 220 nm for (A) a soil sample extract directly injected without any previous cleanup, (B) a soil sample extract enriched with triazines at 0.1 mg.L−1 concentration level after MI-SPME, (C) a 0.1 mg.L−1standard solution of triazines after MI-SPME, and (D) a nonspiked soil sample extract after MI-SPME. Peak numbers: (1) desisopropylatrazine, (2) desethylatrazine, (3) simazine, (4) cyanazine, (5) atrazine, (6) propazine, and (7) yerbutylazine. Reprinted from [64] with permission of American Chemical Society.

1.4 Molecularly Imprinted Stir Bar Sorptive Extraction

SBSE is based on the partitioning of target analytes between a liquid sample and a stationary phase-coated stir bar. Until now, only polydimethylsiloxane (PDMS)-coated stir bars are commercially available, restricting the range of applications to the extraction of hydrophobic compounds (organochlorine and organophosphorous pesticides) due to the apolar character of PDMS. It is obvious that the preparation and use of MIP-coated stir bars would extend the applicability of SBSE in sample preparation. In this regard, Zhu and colleagues developed stir bars coated with a MIP consisting of a film formed from a formic acid solution of nylon-6 polymer, imprinted with monocrotophos to extract successfully and selectively several organophosphorus pesticides from dichloromethane solution for the analysis of environmental soil samples [66]. Besides, the MIP-coated stir bars showed not only the expected high selectivity, but also rapid equilibrium adsorption thanks to the porous nature of the imprinted polymer obtained combined with a proper thickness of the coated polymer film (~160–180 mm).

More recently, the use of MIP-coated stir bars prepared by chemical bonding of the MIP to the stir bar through silylation of the substrate surface and followed by multiple co-polymerization reaction has been proposed. This procedure is similar to that described above for the preparation of MIP-coated fibers for SPME and has been applied for the determination of β2-agonists [67], triazole fungicides [68], sulfa drugs [69], thiabendazole [70], and environmental estrogens [71] in different samples. The MIP-coated stir bars synthesis procedure seems to be a more generally applicable procedure and easily performed in any laboratory. Figure 1.7 shows the chromatograms obtained after SBSE, using a dual-template MIP-coated stir bar, of several estrogens from lake and river water demonstrating clearly the suitability of the proposed imprinted stir bar for the selective extraction of environmental estrogens.

Figure 1.7 Chromatograms of 10 mg L−1 spiked water samples. (a) Directly injection of the spiked sample. (b) Spiked sample with NIP-coated SBSE. (c) Spiked sample with MIP-coated SBSE. (d) 1 mg L−1 estrogens mixed standard solution. Peak numbers: (1) bisphenol A, (2) estradiol, (3) bisphenol B, (4) estrone, and (5) diethylstilbestrol. Reprinted from [71] with permission from Elsevier.

1.5 Other Formats

1.5.1 Matrix Solid-phase Dispersion

MSPD is based on the complete disruption of the sample (liquid, viscous, semi-solid, or solid), allowing sample components to disperse into the solid sorbent. Experimentally, the sample is placed in a glass mortar and blended with the sorbent until complete disruption and dispersion of the sample in the sorbent is obtained. Then, the mixture is directly packed into an empty SPE cartridge, and analytes are eluted after a proper washing step to remove interfering compounds. Direct use of MIPs as dispersant sorbents is not straight forward, due to the high water content of the samples typically extracted by MSPD, as selective recognition by MIPs is not favored in aqueous samples, so the number of applications is rather scarce. However, use of water-compatible MIPs in MSPD has been demonstrated for the selective extraction and clean-up of fluoroquinolones from eggs and tissue [32], with average recoveries 72.2–114.1%, depending on the analyte and the sample, and relative standard deviations of less than 7.0%. The superior performance of MIPs compared to that achieved using conventional sorbents (C18 and Florisil), where recoveries were 24.9–84.6%, was clearly demonstrated. Recently, similar methodologies have been applied to the MSPD of steroids in goat milk [72, 73]. The simplicity of operation of MSPD guarantees to some degree further development in this area, although it will depend on obtaining MIPs with improved recognition capabilities in water-rich samples.

1.5.2 Liquid Membranes and MIPs Combination

The combination of liquid membranes and MIPs was reported for first time by Chimuka’s group for the extraction of 17β-estradiol from aqueous samples [74]. In this work, a specially designed stainless steel extraction device, composed of two compartments separated by a membrane, is used. Membranes are firstly equilibrated with a water-immiscible organic solvent, which acts as acceptor solution. Lower compartment is filled with the aqueous sample using the membrane as separation interface. The upper compartment is filled with the organic acceptor phase and with a small amount of MIP particles (30–50 mg). Then, target analytes are extracted, during a fixed extraction time (60–90 min), from the aqueous donor phase into the organic acceptor phase and from it to the binding sites of the MIP. Finally, MIP particles are separated from the organic phase by filtration through a syringe filter and specifically bound compounds released from the particles by passing a suitable elution solvent. Following this approach, enrichment factors ranging from 6 to 40 were achieved, depending on the analyte and the sample, with an impressive degree of selectivity even with complex samples such as wastewater.

In order to avoid filtration steps, a novel liquid–liquid–solid microextraction (LLSME) technique based on porous membrane-protected MIP-coated silica fiber was proposed [75]. A tercbutylazine-imprinted polymer-coated silica fiber was protected with a length of porous polypropylene hollow fiber membrane which was filled with water-immiscible organic phase. Subsequently, the whole device was immersed into aqueous sample for extraction of triazines as model compounds. The target analytes were firstly extracted from the aqueous sample through the membrane, and then finally extracted onto the MIP fiber. This procedure was successfully applied to the analysis of triazines in sludge water, watermelon, milk, and urine samples [75], and thiabendazole for citrus sample extracts [76]. However, it is important to point out that this procedure is a bit risky since the fibers are rather fragile, and it is necessary to handle them cautiously in order to prevent their breakage. As an alternative, a similar device for the extraction of sulphonamides [77] and triazines [78] in surface environmental waters was recently proposed. In this case, a small amount (few milligrams) of imprinted beads were packed into the lumen of a porous polypropylene capillary in order to protect and separate them from aqueous media. Then, the packed fiber was immersed in toluene filling the pores of the membrane and then, the target analytes were extracted from aqueous samples to the organic solvent where MIPs performed selective recognition. Finally, target analytes were easily eluted with methanol from polypropylene capillary and further analyzed by liquid chromatography. Figure 1.8 shows a comparison between the chromatograms after extraction of several triazines from lake water obtained using non-selective C18 SPE (Figure 1.8a) or following the proposed LLSME technique (Figure 1.8b). It is clear, according to Figure 1.8a, the presence in the chromatogram of a big hump corresponding to humic and fulvic acids, and a dirty and noisy baseline. Moreover, several interferent peaks appear in the chromatogram, one of them completely overlapping cyanizine and thus making impossible its determination. In contrast, the chromatogram obtained when samples were analyzed by LLSME technique shows a high degree of clean-up. As can be seen in Figure 1.8b, thanks to the high selectivity of the method developed, humic and fulvic acids were not co-extracted with the triazines of interest, neither other interferent compounds such that overlapping cyanizine, allowing determination and quantification of all the selected triazines at the required concentration level. Besides, it is important to point out that the proposed approach allows the selective recognition of target analytes in water samples, which open a new path to circumvent the frequent lack of selective recognition of MIPs in aqueous media.

Figure 1.8 HPLC chromatograms obtained in the analysis of lake water sample (150 mL) enriched at the 0.5 ng mL−1 concentration level extracted onto C18 cartridge (a) and using the LLSME technique (b). Peak numbers: (1) simazine, (2) cianizyne, (3) atrazine, (4) propazine, and (5) tercbutylazine. Reprinted from [78] with permission from Elsevier.

1.6 Conclusions

MIPs, materials able to recognize a specific analyte or a group of analytes, are clearly compatible to current sample pretreatment procedures. Its excellent performance as selective sorbent in SPE has been demonstrated, making MISPE a powerful analytical tool. MIPs are capable of cleaning up complex samples leading to selective, sensitive, fast, and robust analytical methods without the need of using expensive detectors (i.e. MS detectors). Nevertheless, the development of new SPE formats improving mass diffusion as well as the use of new monomers favoring molecular recognition in aqueous media is expected in the near future.

Moreover, the recent developments achieved in the synthesis of imprinted fibers for SPME as well as the incorporation of MIPs to other extraction techniques such matrix-solid phase dispersion or SBSE also highlight the adaptability of MIPs to almost any extraction technique. At this regard, an improvement of its use in such techniques, its combination with others (i.e. liquid membranes), and the development of micro-MISPE devices will bring new selective and simple analytical methods.

References

1. Smith, R., Before the injection – modern methods of sample preparation for separation techniques, J. Chromatogr. A, 1000, 3, 2003.

2. Hennion, M., Pichon, V., Immuno-based sample preparation for trace analysis, J. Chromatogr. A, 1000, 29, 2003.

3. Martin-Esteban, A., Fernández, P., Stevenson, D., Cámara, C., Mixed immunosorbent for selective on-line trace enrichment and liquid chromatography of phenylurea herbicides in environmental waters., Analyst, 122, 1113, 1997.

4. Wulff, G., Sarhan, A., Über die Anwendung von enzymanalog gebauten Polymeren zur Racemattrennung, Angew. Chem., 84, 364, 1972.

5. Arshady, R., Mosbach, K., Synthesis of substrate-selective polymers by host-guest polymerization, Makromol. Chem., 182, 687, 1981.

6. Sellergren, B., Andersson, L., Molecular recognition in macroporous polymers prepared by a substrate-analog imprinting strategy, J. Org. Chem., 55, 3381, 1990.

7. Whitcombe, M., Rodriguez, M., Villar, P., Vulfson, E., A new method for the introduction of recognition site functionality into polymers prepared by molecular imprinting – synthesis and characterization of polymeric receptors for cholesterol, J. Am. Chem. Soc., 117, 7105, 1995.

8. Caro, E., Marce, R., Borrull, F., Cormack, P., Sherrington, D., Application of molecularly imprinted polymers to solid-phase extraction of compounds from environmental and biological samples, TrAC-Trends Anal. Chem., 25, 143, 2006.

9. Pichon, V., Haupt, K., Affinity separations on molecularly imprinted polymers with special emphasis on solid-phase extraction, J. Liq. Chromatogr. Related Technol., 29, 989, 2006.

10. Haginaka, J., Molecularly imprinted polymers as affinity-based separation media for sample preparation, J. Sep. Sci., 32, 1548, 2009.

11. Hu, Y., Pan, J., Zhang, K., Lian, H., Li, G., Novel applications of molecularly-imprinted polymers in sample preparation, TrAC-Trends Anal. Chem., 43, 37, 2013.

12. Martin-Esteban, A., Molecularly-imprinted polymers as a versatile, highly selective tool in sample preparation, TrAC-Trends Anal. Chem., 45, 169, 2013.

13. Bui, B., Haupt, K., Molecularly imprinted polymers: synthetic receptors in bioanalysis, Anal. Bioanal. Chem., 398, 2481, 2010.

14. Hosoya, K., Yoshizako, K., Shirasu, Y., Kimata, K., Araki, T., Tanaka, N., Haginaka, J., Molecularly imprinted uniform-size polymer-based stationary phase for high-performance liquid chromatography – Structural contribution of cross-linked polymer network on specific molecular recognition, J. Chromatogr. A, 728, 139, 1996.

15. Wang, J., Cormack, P., Sherrington, D., Khoshdel, E., Monodisperse, molecularly imprinted polymer microspheres prepared by precipitation polymerization for affinity separation applications, Angew. Chem.-Int. Ed., 42, 5336, 2003.

16. Haginaka, J., Takekira, H., Hosoya, K., Tanaka, N., Uniform-sized molecularly imprinted polymer for (S)-naproxen selectively modified with hydrophilic external layer, J. Chromatogr. A, 849, 331, 1999.

17. Haginaka, J., Sanbe, H., Uniform-sized molecularly imprinted polymers for 2-arylpropionic acid derivatives selectively modified with hydrophilic external layer and their applications to direct serum injection analysis, Anal. Chem., 72, 5206, 2000.

18. Sanbe, H., Haginaka, J., Restricted access media-molecularly imprinted polymer for propranolol and its application to direct injection analysis of beta-blockers in biological fluids, Analyst, 128, 593, 2003.

19. Tamayo, F.G., Casillas, J.L., Martin-Esteban, A., Highly selective fenuron-imprinted polymer with a homogeneous binding site distribution prepared by precipitation polymerisation and its application to the clean-up of fenuron in plant samples, Anal. Chim. Acta, 482, 165, 2003.

20. Cacho, C., Turiel, E., Martin-Esteban, A., Perez-Conde, C., Camara, C., Clean-up of triazines in vegetable extracts by molecularly-imprinted solid-phase extraction using a propazine-imprinted polymer, Anal. Bioanal. Chem., 376, 491, 2003.

21. Tamayo, F.G., Casillas, J.L., Martin-Esteban, A., Evaluation of new selective molecularly imprinted polymers prepared by precipitation polymerisation for the extraction of phenylurea herbicides, J. Chromatogr. A, 1069, 173, 2005.

22. Zhang, J., Jiang, M., Zou, L., Shi, D., Mei, S., Zhu, Y., Shi, Y., Dai, K., Lu, B., Selective solid-phase extraction of bisphenol A using molecularly imprinted polymers and its application to biological and environmental samples, Anal. Bioanal. Chem., 385, 780, 2006.

23. Abou-Hany, R., Urraca, J., Descalzo, A., Gomez-Arribas, L., Moreno-Bondi, M., Orellana, G., Tailoring molecularly imprinted polymer beads for alternariol recognition and analysis by a screening with mycotoxin surrogates, J. Chromatogr. A, 1425, 231, 2015.

24. Zhang, Z., Xu, S., Li, J., Xiong, H., Peng, H., Chen, L., Selective solid-phase extraction of Sudan I in chilli sauce by single-hole hollow molecularly imprinted polymers, J. Agric. Food. Chem., 60, 180, 2012.

25. Du, F., Ruan, G., Liang, S., Xie, F., Liu, H., Monolithic molecularly imprinted solid-phase extraction for the selective determination of trace cytokinins in plant samples with liquid chromatography-electrospray tandem mass spectrometry, Anal. Bioanal. Chem., 404, 489, 2012.

26. Ceolin, G., Navarro-Villoslada, F., Moreno-Bondi, M., Horvai, G., Horvath, V., Accelerated development procedure for molecularly imprinted polymers using membrane filterplates, J. Comb. Chem., 11, 645, 2009.

27. Renkecz, T., Ceolin, G., Horvath, V., Selective solid phase extraction of propranolol on multiwell membrane filter plates modified with molecularly imprinted polymer, Analyst, 136, 2175, 2011.

28. Renkecz, T., Laszlo, K., Horvath, V., In situ synthesis of molecularly imprinted nanoparticles in porous support membranes using high-viscosity polymerization solvents, J. Mol. Recognit., 25, 320, 2012.

29. Barahona, F., Turiel, E., Martin-Esteban, A., Molecularly imprinted polymer grafted to porous polyethylene frits: a new selective solid-phase extraction format, J. Chromatogr. A, 1218, 7065, 2011.

30. Díaz-Álvarez, M., Turiel, E., Improved molecularly imprinted polymer grafted to porous polyethylene frits for the solid-phase extraction of thiabendazole from citrus sample extracts, Mol. Impr., 2, 30, 2015.

31. Sellergren, B., Wieschemeyer, J., Boos, K., Seidel, D., Imprinted polymers for selective adsorption of cholesterol from gastrointestinal fluids, Chem. Mater., 10, 4037, 1998.

32. Yan, H., Qiao, F., Row, K., Molecularly imprinted-matrix solid-phase dispersion for selective extraction of five fluoroquinolones in eggs and tissue, Anal. Chem., 79, 8242, 2007.

33. Sun, H., Qiao, F., Liu, G., Liang, S., Simultaneous isolation of six fluoroquinolones in serum samples by selective molecularly imprinted matrix solid-phase dispersion, Anal. Chim. Acta, 625, 154, 2008.

34. Dirion, B., Cobb, Z., Schillinger, E., Andersson, L., Sellergren, B., Water-compatible molecularly imprinted polymers obtained via high-throughput synthesis and experimental design, J. Am. Chem. Soc., 125, 15101, 2003.

35. Benito-Pena, E., Martins, S., Orellana, G., Moreno-Bondi, M., Water-compatible molecularly imprinted polymer for the selective recognition of fluoroquinolone antibiotics in biological samples, Anal. Bioanal. Chem., 393, 235, 2009.

36. Lv, T., Yan, H., Cao, J., Liang, S., Hydrophilic molecularly imprinted resorcinol-formaldehyde-melamine resin prepared in water with excellent molecular recognition in aqueous matrices, Anal. Chem., 87, 11084, 2015.

37. Urraca, J., Hall, A., Moreno-Bondi, M., Sellergren, B., A stoichiometric molecularly imprinted polymer for the class-selective recognition of antibiotics in aqueous media, Angew. Chem. Int. Ed., 45, 5158, 2006.

38. Urraca, J., Moreno-Bondi, M., Hall, A., Sellergren, B., Direct extraction of penicillin g and derivatives from aqueous samples using a stoichiometrically imprinted polymer, Anal. Chem., 79, 695, 2007.

39. Ellwanger, A., Berggren, C., Bayoudh, S., Crecenzi, C., Karlsson, L., Owens, P., Ensing, K., Cormack, P., Sherrington, D., Sellergren, B., Evaluation of methods aimed at complete removal of template from molecularly imprinted polymers, Analyst, 126, 784, 2001.

40. Andersson, L., Paprica, A., Arvidsson, T., A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting, Chromatographia, 46, 57, 1997.

41. Kawaguchi, M., Hayatsu, Y., Nakata, H., Ishii, Y., Ito, R., Saito, K., Nakazawa, H., Molecularly imprinted solid phase extraction using stable isotope labeled compounds as template and liquid chromatography-mass spectrometry for trace analysis of bisphenol A in water sample, Anal. Chim. Acta, 539, 83, 2005.

42. Sambe, H., Hoshina, K., Hosoya, K., Haginaka, J., Simultaneous determination of bisphenol A and its halogenated derivatives in river water by combination of isotope imprinting and liquid chromatography-mass spectrometry, J. Chromatogr. A, 1134, 16, 2006.

43. Masque, N., Marce, R., Borrull, F., Cormack, P., Sherrington, D., Synthesis and evaluation of a molecularly imprinted polymer for selective on-line solid-phase extraction of 4-nitrophenol from environmental water, Anal. Chem., 72, 4122, 2000.

44. Sellergren, B., Direct drug determination by selective sample enrichment on an imprinted polymer, Anal. Chem., 66, 1578, 1994.

45. Zhong, Q., Hu, Y., Hu, Y., Li, G., Dynamic liquid-liquid-solid microextraction based on molecularly imprinted polymer filaments on-line coupling to high performance liquid chromatography for direct analysis of estrogens in complex samples, J. Chromatogr. A, 1241, 13, 2012.

46. Barahona, F., Turiel, E., Cormack, P.A.G., Martin-Esteban, A., Synthesis of core-shell molecularly imprinted polymer microspheres by precipitation polymerization for the inline molecularly imprinted solid-phase extraction of thiabendazole from citrus fruits and orange juice samples, J. Sep. Sci., 34, 217, 2011.

47. Barahona, F., Turiel, E., Cormack, P.A.G., Martin-Esteban, A., Chromatographic performance of molecularly imprinted polymers: core-shell microspheres by precipitation polymerization and grafted MIP films via iniferter-modified silica beads, J. Polym. Sci., Part A: Polym. Chem., 48, 1058, 2010.

48. Chen, L., Li, B., Application of magnetic molecularly imprinted polymers in analytical chemistry, Anal. Methods, 4, 2631, 2012.

49. Zhang, Y., Liu, R., Hu, Y., Li, G., Microwave heating in preparation of magnetic molecularly imprinted polymer beads for trace triazines analysis in complicated samples, Anal. Chem., 81, 967, 2009.

50. Chen, L., Liu, J., Zeng, Q., Wang, H., Yu, A., Zhang, H., Ding, L., Preparation of magnetic molecularly imprinted polymer for the separation of tetracycline antibiotics from egg and tissue samples, J. Chromatogr. A, 1216, 3710, 2009.

51. Kong, X., Gao, R., He, X., Chen, L., Zhang, Y., Synthesis and characterization of the core-shell magnetic molecularly imprinted polymers (Fe3O4@MIPs) adsorbents for effective extraction and determination of sulfonamides in the poultry feed, J. Chromatogr. A, 1245, 8, 2012.

52. Pan, S., Chen, X., Li, X., Cai, M., Shen, H., Zhao, Y., Jin, M., Double-sided magnetic molecularly imprinted polymer modified graphene oxide for highly efficient enrichment and fast detection of trace-level microcystins from large-volume water samples combined with liquid chromatography-tandem mass spectrometry, J. Chromatogr. A, 1422, 1, 2015.

53. Feng, Q., Zhao, L., Lin, J., Molecularly imprinted polymer as micro-solid phase extraction combined with high performance liquid chromatography to determine phenolic compounds in environmental water samples, Anal. Chim. Acta, 650, 70, 2009.

54. Lee, T., Saad, B., Khayoon, W., Salleh, B., Molecularly imprinted polymer as sorbent in micro-solid phase extraction of ochratoxin A in coffee, grape juice and urine, Talanta, 88, 129, 2012.

55. Sanchez-Gonzalez, J., Tabernero, M., Bermejo, A., Bermejo-Barrera, P., Moreda-Pineiro, A., Porous membrane-protected molecularly imprinted polymer micro-solid-phase extraction for analysis of urinary cocaine and its metabolites using liquid chromatography – Tandem mass spectrometry, Anal. Chim. Acta, 898, 50, 2015.

56. Arthur, C., Pawliszyn, J., Solid-phase microextraction with thermal-desorption using fused-silica optical fibers, Anal. Chem., 62, 2145, 1990.

57. Koster, E., Crescenzi, C., den Hoedt, W., Ensing, K., de Jong, G., Fibers coated with molecularly imprinted polymers for solid-phase microextraction, Anal. Chem., 73, 3140, 2001.

58. Hu, X., Hu, Y., Li, G., Development of novel molecularly imprinted solid-phase microextraction fiber and its application for the determination of triazines in complicated samples coupled with high-performance liquid chromatography, J. Chromatogr. A, 1147, 1, 2007.

59. Hu, X., Pan, J., Hu, Y., Huo, Y., Li, G., Preparation and evaluation of solidphase microextraction fiber based on molecularly imprinted polymers for trace analysis of tetracyclines in complicated samples, J. Chromatogr. A, 1188, 97, 2008.

60. Hu, X., Pan, J., Hu, Y., Li, G., Preparation and evaluation of propranolol molecularly imprinted solid-phase microextraction fiber for trace analysis of beta-blockers in urine and plasma samples, J. Chromatogr. A, 1216, 190, 2009.

61. Hu, X., Fan, Y., Zhang, Y., Dai, G., Cai, Q., Cao, Y., Guo, C., Molecularly imprinted polymer coated solid-phase microextraction fiber prepared by surface reversible addition-fragmentation chain transfer polymerization for monitoring of Sudan dyes in chilli tomato sauce and chilli pepper samples, Anal. Chim. Acta, 731, 40, 2012.

62. Mazzotta, E., Malitesta, C., Diaz-Alvarez, M., Martin-Esteban, A., Electrosynthesis of molecularly imprinted polypyrrole for the antibiotic levofloxacin, Thin Solid Films, 520, 1938, 2012.

63. Diaz-Alvarez, M., Mazzotta, E., Malitesta, C., Martin-Esteban, A., Evaluation of electrochemically synthesized sulfadimethoxine-imprinted polymer for solid phase microextraction of sulfonamides, J. Mol. Recognit., 27, 415, 2014.

64. Turiel, E., Tadeo, J.L., Martin-Esteban, A., Molecularly imprinted polymeric fibers for solid-phase microextraction, Anal. Chem., 79, 3099, 2007.

65. Djozan, D., Baheri, T., Preparation and evaluation of solid-phase microextraction fibers based on monolithic molecularly imprinted polymers for selective extraction of diacetylmorphine and analogous compounds, J. Chromatogr. A, 1166, 16, 2007.

66. Zhu, X., Cai, J., Yang, J., Su, Q., Gao, Y., Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos, J. Chromatogr. A, 1131, 37, 2006.

67. Xu, Z., Hu, Y., Hu, Y., Li, G., Investigation of ractopamine molecularly imprinted stir bar sorptive extraction and its application for trace analysis of β2-agonists in complex samples, J. Chromatogr. A, 1217, 3612, 2010.

68. Hu, Y., Li, J., Li, G., Synthesis and application of a novel molecularly imprinted polymer-coated stir bar for microextraction of triazole fungicides in soil, J. Sep. Sci., 34, 1190, 2011.

69. Xu, Z., Song, C., Hu, Y., Li, G., Molecularly imprinted stir bar sorptive extraction coupled with high performance liquid chromatography for trace analysis of sulfa drugs in complex samples, Talanta, 85, 97, 2011.

70. Turiel, E., Martin-Esteban, A., Molecularly imprinted stir bars for selective extraction of thiabendazole in citrus samples, J. Sep. Sci., 35, 2962, 2012.

71. Xu, Z., Yang, Z., Liu, Z., Development of dual-templates molecularly imprinted stir bar sorptive extraction and its application for the analysis of environmental estrogens in water and plastic samples, J. Chromatogr. A, 1358, 52, 2014.

72. Ganan, J., Gallego-Pico, A., Garcinuño, R., Fernandez-Hernando, P., Morante, S., Sierra, I., Durand, J., Development of a molecularly imprinted polymermatrix solid-phase dispersion method for selective determination of beta-estradiol as anabolic growth promoter in goat milk, Anal. Bioanal. Chem., 403, 3025, 2012.

73. Ganan, J., Morante-Zarcero, S., Gallego-Pico, A., Garcinuño, R., Fernandez-Hernando, P., Sierra, I., Evaluation of a molecularly imprinted polymer for determination of steroids in goat milk by matrix solid phase dispersion, Talanta, 126, 157, 2014.

74. Nemulenzi, O., Mhaka, B., Cukrowska, E., Ramstrom, O., Tutu, H., Chimuka, L., Potential of combining of liquid membranes and molecularly imprinted polymers in extraction of 17-β-estradiol from aqueous samples, J. Sep. Sci., 32, 1941, 2009.

75. Hu, Y.L., Wang, Y.Y., Hu, Y.F., Li, G.K., Liquid-liquid-solid microextraction based on membrane-protected molecularly imprinted polymer fiber for trace analysis of triazines in complex aqueous samples, J. Chromatogr. A, 1216, 8304, 2009.

76. Barahona, F., Turiel, E., Martin-Esteban, A., Supported liquid membrane-protected molecularly imprinted fibre for solid-phase microextraction of thiabendazole, Anal. Chim. Acta, 694, 83, 2011.

77. Diaz-Alvarez, M., Barahona, F., Turiel, E., Martin-Esteban, A., Supported liquid membrane-protected molecularly imprinted beads for micro-solid phase extraction of sulfonamides in environmental waters, J. Chromatogr. A, 1357, 158, 2014.

78. Turiel, E., Diaz-Alvarez, M., Martin-Esteban, A., Supported liquid membrane-protected molecularly imprinted beads for the solid phase micro-extraction of triazines from environmental waters., J. Chromatogr. A, 1432, 1, 2016.

Chapter 2

A Genuine Combination of Solvent-free Sample Preparation Technique and Molecularly Imprinted Nanomaterials

Santanu Patra1, Ekta Roy1, Rashmi Madhuri1* and Prashant K. Sharma2

1Department of Applied Chemistry, Indian School of Mines, Dhanbad, Jharkhand, India

2Functional Nanomaterials Research Laboratory, Department of Applied Physics, Indian School of Mines, Dhanbad, Jharkhand, India

*Corresponding author: [e-mail]

Abstract

Even though we have reached the 21st century, the sample preparation prior to the trace-level analysis or specific separation is still considered the bottleneck of the whole analytical process. Sometimes, we have a very small sample volume to be extracted or detected from large and contaminated samples; at that time, we always think about a setup, which could be easily and effectively applied and provide us the solution. From day one, the introduction of solid-phase microextraction (SPME) has shown their tremendous role in improving the extraction efficiency and detection limit. SPME is a solvent-free extraction technique, widely accepted and applied as a sample preparation for the analysis of environmental, biological, and food samples. Although SPME is a successful and popular technique in the field of extraction/separation, they suffer from the problem of target selectivity during the extraction process. To resolve this, one of the most popular and versatile options is hyphenation of SPME and molecular imprinting technology. In this chapter we have tried to incorporate all the aspects (the past, present, and future) of this hyphenated technique. This chapter reviews and focuses about the advancement have been made in the field of molecularly imprinted solid-phase microextraction (MISPME) by classifying them with respect to the coating materials, solid supports, monolithic fibers, and the role of nanomaterials. Our main goal for this chapter is to explore full view of MISPME, starting from their basic principle to the recent advancement, after incorporation of nanotechnology.

Keywords: Solid-phase microextraction, molecularly imprinted polymer, nanomaterials

2.1 Introduction

2.1.1 The Overview

From a very ancient age, we are familiar with the separation or sample preparation process which means separating one useful thing from a complex matrix or separating more than one from a mixture of several. In nature also, we always get the