Evaluation of deep eutectic solvents in the synthesis of molecularly imprinted fibers for the solid-phase microextraction of triazines in soil samples.

Nowadays, molecularly imprinted polymers (MIPs) are well established and are considered excellent materials for performing selective extractions. However, with the progressive implementation of the principles of green chemistry, it is necessary to find greener alternatives for both the synthesis and further use of MIPs in sample preparation. Accordingly, in the present work, different deep eutectic solvents (DES, both hydrophilic and hydrophobic), as an alternative to conventional organic solvents (i.e., toluene), were evaluated as porogens for the synthesis of imprinted fibers (monoliths), using fused silica capillaries as molds, for solid-phase microextraction (SPME). From this study, the polymer prepared with propazine (dummy template), methacrylic acid (monomer), ethylene glycol dimethacrylate (cross-linker), and a formic acid:L-menthol (1:1) DES (porogen) showed the best performance for selective rebinding of triazines. After optimization of the different variables involved in SPME, the new imprinted fibers were successfully applied to the extraction of target analytes (desisopropylatrazine, desethylatrazine, simazine, and atrazine) from soil sample extracts, providing relative recoveries ranging from 75.7 to 120.1%, reaching limits of detection within the range of 6.2-15.7 ng g-1, depending upon the analyte.

Recent advances and future trends in molecularly imprinted polymers-based sample preparation.

Molecular imprinting technology is a well-established technique for the obtainment of tailor-made polymers, so-called molecularly imprinted polymers, with a predetermined selectivity towards a target analyte or structurally related compounds. Accordingly, molecularly imprinted polymers are considered excellent materials for sample preparation providing unprecedented selectivity to analytical methods. However, the use of molecularly imprinted polymers in sample preparation still presents some shortcomings derived from the synthesis procedure itself limiting its general applicability. In this regard, molecularly imprinted polymers use to display binding sites heterogeneity and slow diffusion mass transfer of analytes to the imprinted sites affecting their overall performance. Besides, the performance of molecularly imprinted polymers in organic solvents is excellent, but their selective binding ability in aqueous media is considerably reduced. Accordingly, the present review pretends to provide an updated overview of the recent advances and trends of molecularly imprinted polymers-based extraction, focusing on those strategies proposed for the improvement of mass transfer and selective recognition in aqueous media. Besides, with the progressive implementation of Green Chemistry principles, the different steps and strategies for the preparation of molecularly imprinted polymers are reviewed from a green perspective.

Determination of polypeptide antibiotics in animal tissues using liquid chromatography tandem mass spectrometry based on in-line molecularly imprinted solid-phase extraction.

Effective purification and enrichment of polypeptide antibiotics in animal tissues is always a challenge, due to the co-extraction of other endogenous peptides which usually interfere their final determination. In this study, a molecularly imprinted column was prepared by packing polymyxin E-imprinted particles into a 100 mm × 4.6 mm i.d. HPLC column. The as-prepared imprinted columns were able to tolerate 100% aqueous phase and exhibited good stability and high column efficiency. Polypeptides antibiotics with similar molecular size or spatial structure to polymyxin E were well retained by the imprinted column, suggesting class selectivity. After optimization of mobile phase conditions of imprinted column, polypeptide antibiotics in animal tissue extracts were enriched and cleaned up by in-line molecularly imprinted solid-phase extraction, allowing the screening of target analytes in complex samples at low concentration levels by UV detection. Eluate fraction from the imprinted column was collected, and further dried and re-dissolved with methanol-0.5% formic acid aqueous solution (80:20, v/v) for final LC-MS/MS analysis. Analysis was accomplished using multiple reaction monitoring (MRM) in positive electrospray ionization mode and analytes quantified using the matrix-matched external calibration curves. The results showed high correlation coefficients for target analytes in the linear range of 2 ∼ 200 µg kg-1. At four different concentration levels (limit of quantification, 50, 100 and 200 µg kg-1), recoveries of four polypeptide antibiotics in swine, cattle and chicken muscles ranged from 66.7 to 94.5% with relative standard deviations lower than 16.0%. The limits of detection (LOD) were 2.0 ∼ 4.0 µg/kg, depending upon the analyte and sample. Compared with a conventional pretreatment method, the imprinted column was able to remove more impurities and to significantly reduce matrix effects, allowing the accurate analysis of polypeptide antibiotics.

Evaluation of 2-hydroxyethyl methacrylate as comonomer in the preparation of water-compatible molecularly imprinted polymers for triazinic herbicides.

In this work, the preparation and evaluation of water-compatible molecularly imprinted polymers for triazines using 2-hydroxyethyl methacrylate and methacrylic acid as comonomers is described. Four sets of molecularly imprinted and non-imprinted polymers for propazine were prepared at varying monomer molar ratios (from 4:0 to 1:3), and evaluated for the recognition of several triazines directly in aqueous media. The evaluation was performed by loading 1 mL of an aqueous solution containing 500 ng of each selected triazine, washing with 500 µL of acetonitrile, and eluting with 500 µL of methanol followed by 2 × 500 µL of a solution of methanol containing 10% of acetic acid. Final determinations were performed by high-performance liquid chromatography-ultraviolet detection. Improvement in molecular recognition of triazines in water was obtained on those molecularly imprinted polymers incorporating 2-hydroxyethyl methacrylate in 3:1 or 2:2 molar ratios, being the former selected as optimum providing recoveries for propazine up to 80%. A molecularly imprinted solid-phase extraction protocol was developed to ensure that triazines-selective recognition takes place inside selective binding sites in pure water media. Finally, the developed method was successfully applied to the determination of the selected triazines in environmental waters providing limits of detection from 0.16 and the 0.5 µg/L concentration range.

Green molecularly imprinted polymers for sustainable sample preparation.

The use of molecularly imprinted polymers in sample preparation as selective sorbent materials has received great attention during the last years leading to analytical methods with unprecedented selectivity. However, with the progressive implementation of Green Analytical Chemistry principles, it is necessary to critically review the greenness of synthesis and further use of molecularly imprinted polymers in sample preparation. Accordingly, in the present review, the different steps and strategies for the preparation of molecularly imprinted polymers, the used reagents, as well as their incorporation to microextraction techniques are reviewed from a green perspective and recent alternatives to make the use of molecularly imprinted polymers more sustainable are provided.

Miniaturized analytical methods for determination of environmental contaminants of emerging concern - A review.

The determination of contaminants of emerging concern (CECs) in environmental samples has become a challenging and critical issue. The present work focuses on miniaturized analytical strategies reported in the literature for the determination of CECs. The first part of the review provides brief overview of CECs whose monitoring in environmental samples is of particular significance, namely personal care products, pharmaceuticals, endocrine disruptors, UV-filters, newly registered pesticides, illicit drugs, disinfection by-products, surfactants, high technology rare earth elements, and engineered nanomaterials. Besides, an overview of downsized sample preparation approaches reported in the literature for the determination of CECs in environmental samples is provided. Particularly, analytical methodologies involving microextraction approaches used for the enrichment of CECs are discussed. Both solid phase- and liquid phase-based microextraction techniques are highlighted devoting special attention to recently reported approaches. Special emphasis is placed on newly developed materials used for extraction purposes in microextraction techniques. In addition, recent contributions involving miniaturized analytical flow techniques for the determination of CECs are discussed. Besides, the strengths, weaknesses, opportunities and threats of point of need and portable devices have been identified and critically compared with chromatographic methods coupled to mass chromatography. Finally, challenging aspects regarding miniaturized analytical methods for determination of CECs are critically discussed.

Molecularly Imprinted Polymer-Quantum Dot Materials in Optical Sensors: An Overview of Their Synthesis and Applications.

In the last decades analytical methods have focused on the determination of target analytes at very low concentration levels. This has been accomplished through the use of traditional analytical methods that usually require high reagent consumption, expensive equipment and long pretreatment steps. Thus, there is a demand for simple, rapid, highly selective and user-friendly detection procedures. Quantum dots (QDs) are semiconductor fluorescent nanomaterials with unique optoelectronic properties that have shown great potential for the development of fluorescence probes. Besides, the combination of QDs with molecularly imprinted polymer (MIPs), synthetic materials with selective recognition, have been proposed as useful materials in the development of optical sensors. The resulting MIP-QDs optical sensors integrate the advantages of both techniques: the high sensitivity of QDs-based fluorescence sensors and the high selectivity of MIPs. This review gives a brief overview of the strategies for the synthesis of MIPs-QDs based optical sensors, highlighting the modifications in the synthesis procedure that improve the sensor performance. Finally, a revision of recent applications in sensing and bioimaging is presented.

Fluorescent carbonaceous materials isolated from cigarette ashes for the determination of iron(iii) in water samples.

In the present work, ready-to-use fluorescent carbonaceous materials (CMs) were isolated from cigarette ashes by following a simple procedure based on the dispersion of ashes in water and subsequent filtration. The isolated raw material was characterized by fluorescence microscopy, Fourier transform infrared (FT-IR) spectroscopy, and dynamic light scattering (DLS) analysis. The isolated CMs displayed excitation-dependent fluorescence emission, which enables them to be used as a fluorescent probe. The developed fluorescent probe possesses high potential for sensitive and selective detection of Fe(iii) via a quenching mechanism. The decrease in fluorescence intensity was in linear relationship with the concentrations of Fe(iii) within the range of 0-89.6 µM. The fluorescent probe was successfully applied to the determination of Fe(iii) in tap and well waters with an average recovery of 87% with an excellent relative standard deviation (RSD) of 0.63%, regardless of the water sample analyzed. Besides, fluorescence variation in the presence of Fe(iii) was evaluated by analyzing red, green, and blue (RGB) channels of the fluorescence colors. Finally, the possibility of semi-quantitative determination of Fe(iii) in water by the naked eye using the proposed fluorescent probe was also evaluated.

Surface modified-magnetic nanoparticles by molecular imprinting for the dispersive solid-phase extraction of triazines from environmental waters.

Magnetic nanoparticles have been surface modified by molecular imprinting and evaluated as selective sorbents for the extraction of triazines from environmental waters. The use of propazine as template allowed us to synthesize a selective material able to simultaneously recognize and selective extract not only the template but also several other herbicides of the same family. A magnetic molecularly imprinted-based dispersive solid-phase extraction procedure was developed and fully optimized. Magnetic molecularly imprinted polymer particles can be easily collected and separated from liquid solvents and samples with the help of an external magnetic field, avoiding in that way any centrifugation or filtration steps, which represents a remarkable advantage over traditional procedures. Under optimum conditions, selective extraction of several triazines (cyanazine, simazine, atrazine, propazine, and terbutylazine) from environmental water samples was performed prior to final determination by high-performance liquid chromatography with diode-array detection. Recoveries for the studied triazines were within the range of 75.2-94.1%, with relative standard deviations lower than 11.3% (n = 3). The limits of detection were within 0.16-0.51 µg/L, depending upon the triazine and the type of sample analyzed.

Synthesis of Molecularly Imprinted Polymers for the Selective Extraction of Polymyxins from Environmental Water Samples.

The authors wish to make a change to the published paper [...].

Synthesis of Molecularly Imprinted Polymers for the Selective Extraction of Polymyxins from Environmental Water Samples.

The emergence of colistin resistance gen has aroused public concern. It is significant to assess the concentrations of polymyxins residues in aquatic environment since resistant bacteria carrying colistin resistance gen are frequently isolated from wastewater; surface water and ground water. However; no literature on the determination of polymyxins in water is available; probably due to the absence of an efficient extraction method. Accordingly; molecularly imprinted polymers were synthesized by precipitation polymerization with colistin as the template. The polymers were successfully used as sorbents for the determination of polymyxins from water based on molecularly imprinted solid-phase extraction and high-performance liquid chromatography-ultraviolet detection. The molecularly imprinted cartridge showed excellent affinity and cross-reactivity to analytes in aqueous media. Recoveries obtained from water samples were between 65.9% and 90.1%, with relative standard deviations lower than 10.2%. Limits of detection were between 1.0 and 2.0 µg L-1 concentration levels. Compared with C18 cartridge; the molecularly imprinted cartridge could remove more interference from co-extracted matrices. This method is practical for the routine monitoring of polymyxin residues in environmental water; which will benefit studies on drug-resistance and occurrence of polymyxins in the environment.

Analysis of Nosiheptide in Food Animal Tissues via Its Unique Degradation Product by Liquid Chromatography-Tandem Mass Spectrometry after Alkaline Hydrolysis.

Very weak signals of fragment ions of nosiheptide could be observed using liquid chromatography-tandem mass spectrometry. The preparation of 4-hydroxymethyl-3-methyl-1H-indole-2-carboxylic acid (HMIA), a specific fragment of nosiheptide, by alkaline hydrolysis is described. HMIA showed a good mass spectrometric signal in negative electrospray ionization mode. In the new method, the nosiheptide residue in muscle tissue was hydrolyzed with sodium hydroxide aqueous solution; this was followed by cleanup using mixed mode cartridges. Identification and quantification of nosiheptide were carried out by analyzing HMIA in hydrolysate of muscles. Nosiheptide showed a good linear relationship (r > 0.996) in the calibration range of 2-500 µg/kg, and a low limit of quantification of 2 µg/kg was obtained in swine, chicken, and fish muscles. Recoveries of nosiheptide from spiked muscle samples were 85-108% with relative standard deviations less than 10%. The proposed method was successfully applied for the detection of the nosiheptide residue in medicated animal tissues samples.

The application of the supported liquid membrane and molecularly imprinted polymers as solid acceptor phase for selective extraction of biochanin A from urine.

An efficient sample clean-up and preconcentration procedure for phytoestrogens analysis in urine has been developed. It was based on a combination of solid phase extraction with hollow-fiber supported liquid membrane and molecularly imprinted beads (MIPs-HF-SLM-SPE). The molecularly imprinted polymers (MIPs) were synthesized by precipitation polymerization technique with biochanin A (BCA) as a template, giving narrowly dispersed microspheres with a regular shape. As the functional monomer, (dimethylamino)ethyl methacrylate (-DEM) turned out to be better than methacrylic acid (MAA) to get the best-imprinted effects. The MIPs used as sorbents in the MIPs-HF-SLM-SPE extraction process exhibited excellent binding selectivity for BCA, in comparison to non-imprinted polymers as well as its structural analogs (genistein and daidzein). Finally, the developed method was used to detect BCA in urine. Under optimal extraction conditions, the recovery of BCA in urine samples (using 4.5 mL sample spiked with 10 µg L-1) was over 41%, with a coefficient of variation (CV) < 6.6% (n = 5). The detection limit (LOD) and quantification limit (LOQ) for BCA analysis in urine were 0.41 and 1.36 µg L-1, respectively.

Molecularly imprinted polymer monolith containing magnetic nanoparticles for the stir-bar sorptive extraction of thiabendazole and carbendazim from orange samples.

In this work, a novel molecularly imprinted stir-bar was developed for the stir-bar sorptive extraction (SBSE) of thiabendazole (TBZ) and carbendazim (CBZ) from orange samples. Magnetic nanoparticles were surface modified with oleic acid and then encapsulated by a silica shell using a conventional sol-gel procedure. Subsequently, nanoparticles were functionalized with methacrylate functionalities by grafting onto the particles surface. Finally, the modified magnetic nanoparticles were entrapped in a polymer monolith synthetized by copolymerization with the imprinting polymerization mixture using a glass vial insert as a mold. Variables affecting the polymerization and rebinding conditions of target analytes were optimized. The uptake capacity for the template (TBZ) was evaluated as well as the cross-reactivity for the related compound CBZ by rebinding experiments. Finally, the proposed magnetic imprinted monolith was applied to the SBSE of TBZ and CBZ from orange sample extracts providing a remarkable clean-up ability. The calculated detection limit were 0.13 and 0.10 mg kg-1 for CBZ and TBZ respectively, low enough to satisfactory analysis of both compounds in orange samples according to current European Union regulations.

Molecularly imprinted polymer-hollow fiber microextraction of hydrophilic fluoroquinolone antibiotics in environmental waters and urine samples.

In the present work, the preparation of a new selective molecularly imprinted polymer (MIP) for the family of fluoroquinolones (FQs) in the pores of polypropylene hollow fibers (HFs) is proposed. The resulting MIP-HFs, which combine solid-phase microextraction (SPME) and molecular imprinting technologies, were used to develop a selective microextraction methodology (MIP-HFM) to determine selected FQs danofloxacin, norfloxacin, enrofloxacin and ciprofloxacin in real samples of environmental and biological interest. Measurements during the optimization of the MIP-HFM and its application to the analyses of real samples were performed by HPLC-UV and HPLC-MS/MS. In order to establish optimum rebinding conditions, the effect of key experimental parameters such as loading media, extraction time and stirring-rate were studied. The developed MIP composites exhibited recognition properties towards the selected hydrophilic antibiotics in non-polar media (toluene) and in polar protic systems such as methanol and methanol/water solutions, up to 20% water content. Recoveries by the developed method for all FQs tested in surface water, groundwater and urine spiked with the analytes of interest at two different concentration levels were within 9.4-24.5 %, with a relative standard deviation, generally <20% (n = 3). The detection limits were within 0.1-10 µg L-1, depending upon the antibiotic and the type of sample.

Hollow fiber membrane-protected molecularly imprinted microspheres for micro solid-phase extraction and clean-up of thiabendazole in citrus samples.

In the present work, molecularly imprinted polymer (MIP) microspheres were packed in polypropylene hollow fiber (HF) segments for the micro solid-phase extraction and clean-up of thiabendazole (TBZ) in citrus samples. Experimental parameters affecting TBZ extraction were carefully optimized. Hollow fiber membrane was able to protect MIP beads from solid matrix allowing the extraction and clean-up without the inclusion of further filtration and/or centrifugation steps. Under optimum experimental conditions, recoveries for TBZ at 0.83 mg kg-1 concentration level ranged from 5.1 to 6.1%, depending upon the sample analyzed (orange or lemon peel samples), with relative standard deviations (RSDs) lower than 4%. The limits of detection were 0.004 mg kg-1 in orange and 0.009 mg kg-1 in lemon, low enough for the determination of TBZ according to European Union legislation.

Molecularly imprinted magnetic nanoparticles for the micro solid-phase extraction of thiabendazole from citrus samples.

The preparation of molecularly imprinted core-shell magnetic nanoparticles and their subsequent use in the solid-phase extraction of thiabendazole from citrus sample extracts is described. Molecularly imprinted core-shell magnetic nanoparticles were prepared by the precipitation copolymerization of the imprinting polymerization mixture on the surface of vinyl-modified silica magnetic nanoparticles and were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The obtained molecularly imprinted core-shell magnetic nanoparticles exhibited a high selectivity for thiabendazole and were easily collected and separated by an external magnetic field without additional centrifugation or filtration steps. Under optimum conditions, a magnetic molecularly imprinted solid-phase extraction method was developed allowing the extraction of thiabendazole from citrus sample extracts and final determination by high-performance liquid chromatography with fluorescence detection. The detection limit was 0.2 mg/kg, far lower than the maximum residue limit established within the European Union for thiabendazole in citrus samples.

Molecularly imprinted core-shell magnetic nanoparticles for selective extraction of triazines in soils.

In this work, a propazine-imprinted polymer was synthesized on the surface of modified magnetic nanoparticles to be used in the solid-phase extraction of triazines in soil samples. The effect of different solvents on the selective extraction of target analytes was assessed to establish the optimum rebinding conditions. The obtained magnetic molecularly imprinted particles exhibited high selectivity for triazines and were easily collected and separated by an external magnetic field without additional centrifugation or filtration steps. Under optimum conditions, a magnetic molecularly imprinted solid-phase extraction method was developed allowing the extraction of several triazines (desisopropylatrazine, desethylatrazine, simazine, atrazine, and propazine) from soil samples and their subsequent final determination by high-performance liquid chromatography with diode-array detection. Recoveries for the triazines studied were within the range 5.4% to 40.6%, with relative standard deviations lower than 7.0% (n = 3). The detection limits were within 0.1 to 3 ng g-1 , depending upon the triazine and the type of soil used.

Molecularly imprinted polymer monolith containing magnetic nanoparticles for the stir-bar sorptive extraction of triazines from environmental soil samples.

In this work, novel molecularly imprinted stir-bars based upon the entrapment of modified magnetic nanoparticles within an imprinted polymer monolith is developed for stir-bar sorptive extraction (SBSE). Firstly, magnetic nanoparticles were surface modified with oleic acid followed by encapsulation inside a silica network. Then, vinyl-groups were grafted onto the particles surface for the subsequent copolymerization with the imprinting polymerization mixture using a glass vial insert as a mold. As a result, the obtained imprinted monolith presented magnetic properties allowing its use as magnetic stir-bar. Variables affecting both polymer morphology (i.e., amount of magnetic nanoparticles, polymerization time) and binding-elution conditions of target analytes (i.e., solvents, time) was carefully optimized. Optimum imprinted stir-bars were evaluated for the SBSE of triazines in soil sample extracts. Recoveries, at 16ngg-1 concentration level, ranged from 2.4 to 8.7% with relative standard deviations lower than 15% (n=3). Although low recoveries were obtained, the high selectivity provided by the new molecularly imprinted stir-bars allowed reaching detection limits below 7.5ngg-1 by liquid chromatography coupled to UV detection.

Molecularly imprinted polymer-coated hollow fiber membrane for the microextraction of triazines directly from environmental waters.

In this work, novel molecularly imprinted polymer-coated hollow fibers (MIP-HFs) have been prepared and evaluated for the development of a micro-solid phase extraction method for the analysis of triazines in aqueous samples using high performance liquid chromatography and UV detection. The proposed extraction method combines liquid-liquid microextraction and molecular imprinting technology. In brief, a thin film of toluene is immobilised in the pores of the obtained MIP-HF. Afterwards, the conditioned MIP-HF is immersed in the water sample. Under stirring for a certain time, the target analytes are liquid-liquid extracted from the sample to the immobilised toluene and then these diffuse to the specific binding sites of the MIP. The effect of various experimental parameters as time and stirring-rate and salting-out effect among others, were studied for the establishment of optimum rebinding conditions. Recoveries for seven triazines tested in 100mL pure water samples spiked with 15 µg L(-1) of each triazine were within 0.8-6.9%, with a relative standard deviation (RSD)<10% (n=3). The detection limits (LODs) were within 0.05-0.1 µg L(-1), depending upon the triazine. The proposed methodology was successfully applied to extract the triazines from spiked tap and river water samples at µg L(-1) concentration level. The mircroextraction procedure with the developed MIP-HFs overcomes the typical low performance and lack of selective recognition of MIPs in aqueous media, allowing the determination of triazines in environmental waters at expected real concentration levels.