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Preparation and evaluation of a novel molecularly imprinted hybrid composite monolithic column for on-line solid-phase extraction coupled with HPLC to detect trace fluoroquinolone residues in milk
Abstract
A novel molecularly imprinted organic–inorganic hybrid composite monolithic column (MIP-HCMC) was prepared in a stainless-steel chromatographic column for the determination of fluoroquinolone residues in milk by on-line solid-phase extraction coupled with HPLC. The MIP-HCMC was prepared using enrofloxacin as the template, methacrylic acid and 2-hydroxyethyl methacrylate as functional monomers, tetraethoxysilane as inorganic precursor and methacryloxypropyltrimethoxysilane as coupling agent, toluene and polyethylene glycol as porogenic solvents, and ethylene glycol dimethacrylate as the cross-linking agent. The synthetic conditions were optimized. The chemical group, morphology, thermal stability, dynamic adsorption characteristic and swelling of the monolithic column were characterized by IR, SEM, TG, dynamic binding tests and swelling tests, respectively. An enrichment factor (EF) of 18.5 along with a good sample clean-up effect was obtained under the optimized conditions when the method was applied to milk sample analysis only after centrifugation. The average recoveries of four fluoroquinolones from milk spiked at 0.05, 0.1 and 0.25 mg kg−1 were in the range of 89.1–99.2% with the precision of 3.55–4.32%. The limits of detection and quantification of the proposed method were 1.69 and 5.63 μg kg−1 for ofloxacin, 1.63 and 5.43 μg kg−1 for lomefloxacin, 3.74 and 12.5 μg kg−1 for ciprofloxacin, 1.37 and 4.56 μg kg−1 for enrofloxacin, respectively. The proposed method was successfully applied to on-line extraction and determination of fluoroquinolone antibiotics in milk.
... In 1640 cm -1 , the residual C=C stretch of MAA and MPTS is observed. [29]. The peak at 2950 cm -1 is assigned to the asymmetric stretching of CH 2 groups present in the MPTS structure. ...
... During the next stage of heating (250 -420°C), the weight loss is probably due to the decomposition of the ester bond and the degradation of the 3-(trimethoxysilyl)propyl methacrylate) segment in MPTS, while in the temperature range 420 -800°C, poly(methacrylic acid) segmental cleavage takes place [31]. The residue weight at 800°C is probably due to the inorganic silica content of P(MAA-MPTS)/Sil, and the weight retention is about 64 %, indicating good heat resistance [29]. ...
In this study, a new organic-inorganic hybrid copolymer (P(MAA-MPTS)/Sil) was synthesized, characterized, and applied as a sorbent for s-triazines. The P(MAA-MPTS)/Sil was prepared by coupling free radical copolymerization of methacrylic acid and methacryloxypropyltrimethoxysilane and sol-gel processing, using tetramethoxysilane as a cross-linker. Scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption-desorption measurements were used for the characterization of the copolymer particles. The extraction efficiency of hybrid copolymer toward s-triazines was studied by batch procedure. High recoveries for all studied compounds (ametryne, atrazine, propazine, simazine, simetryn, and terbuthylazine) were achieved in the pH range 7 - 8 within 30 min. Quick quantitative desorption was achieved using a mixture of methanol and acetic acid. An analytical procedure based on solid-phase extraction of s-triazines on newly synthesized hybrid copolymer and HPLC measurements was developed for their quantification in surface waters. Experiments performed with different types of waters (tap, lake, river) and determination limits achieved demonstrated the successful applicability of P(MAA-MPTS)/Sil in monitoring programs for quality control of tap and surface waters.
... Monolithic MIPs were first prepared at conventional format in 4.6 mm i.d. stainless-steel columns as reported by Ou et al. [82,83] and more recently by other groups [84][85][86][87]. However, miniaturized formats, such as pipette tips or capillaries, represent today most of the developments. ...
... As for conventional SPE sorbents, MIPs have been mainly used off-line by packing MIPs particles into a cartridge between frits. For their online-coupling with conventional LC systems, some monolithic MIPs have been prepared in 4.6 mm internal diameter (i.d.) columns [86,87]. This approach was used to prepare a MIP column for HPLC separation [162,163] and did not require the covalent attachment of the MIP to the inner surface of the column since frits were used to maintain the sorbent in the column. ...
An important part in analytical chemistry is related to the miniaturization and integration of different analytical steps in a single device in order to meet portability and automation issues. However, solutions for the analysis of complex samples with limited volumes containing various analytes of interest that may be found at trace levels are still required. One approach consists in the in situ synthesis of imprinted monoliths within capillaries and their on-line coupling with a separation and/or detection step. After the study of the state-of-the-art concerning the integration of molecularly imprinted polymers in miniaturized extraction and separation devices, the development of miniaturized imprinted monolithic supports and their on-line coupling with a nano-liquid chromatography separation or directly with UV detection were performed for biological applications. Different synthesis pathways were screened. The characterization of the obtained supports was carried out in terms of morphology, permeability and synthesis repeatability. The selectivity of MIP monoliths was evaluated with nano-liquid chromatography by confronting their extraction potential with the one of non-imprinted monoliths synthesized in the same conditions but without the introduction of the template. The extraction protocols and coupling conditions were successfully optimized for the analysis of cocaine in saliva and plasma or the detection of benzoylecgonine in urine with detection thresholds in agreement with the legislation around tens of ng/mL. By exploiting the know-how acquired, other miniaturized imprinted supports were also produced to target neurotransmitters and structural analogues.
... Antibiotic pollution in agricultural crops is expected if the crops are irrigated with these water resources and fertilized with sewage sludge from water treatment plants or livestock manure. For environmental and public safety, several methods have been developed for high-performance liquid chromatography (HPLC) analysis and the recovery of these antibiotics from wastewater and soil using adsorbents [5][6][7][8][9][10][11][12][13][14][15][16][17]. The HPLC approach in these studies often involved gradient or isocratic elution combined with a C 18 stationary phase to resolve a limited number of antibiotics. ...
... The HPLC approach in these studies often involved gradient or isocratic elution combined with a C 18 stationary phase to resolve a limited number of antibiotics. However, an inconsistent elution order is often observed under the aqueous chromatographic condition [10,[15][16][17]. ...
This paper reports the isocratic resolution of 10 fluoroquinolone-based antibiotics and their precursors on the phenylethyl-bonded phase under the elution of the nonaqueous mobile phase composed of acetonitrile, methanol, acetic acid, and triethylamine. Most of the analytes were baseline resolved within 10 minutes. The interaction simulation and Fourier-transform infrared spectroscopy (FTIR) data indicated that the carbonyl-containing group, a secondary or tertiary amine of an analyte, was heavily involved in the retention, resulting in retention with residual silanol groups on the stationary phase. In some cases, the elution reversal or resolution enhancement of analytes was observed when the volume of acidic or basic additive in the mobile phase was dominant. However, the π - π complexation interaction between the fluorine-attached phenyl group of the analyte and the phenylethyl moiety on the stationary phase was not observed. Consequently, the resolution could not be reproduced either on the other stationary phase modified with C 18 , phenyl, or phenylhexyl moiety under the same chromatographic conditions or under the aqueous elution.
... On-line MISPE has the advantages of shortening pretreatment time, reducing the loss of samples, increasing repetition rate and sensitivity of detection [141]. The monolithic column has the advantages of being easy to prepare, quick mass transfer rate, good permeability and high repeatability [142]. Regarding MMISPE, magnetic MIPs have been used as the adsorbents for extraction and purification of samples by adding additional magnetic fields, which is less time consuming and more simple than DSPE [64]. ...
Molecularly imprinted polymers (MIPs) are well historically known class of material that have wide range of applications. Regarding chemical analysis, MIPs could replace biogenic materials, such as antibodies, to impart the required selectivity for analytical method. Apart from other purposes, preparing a MIP for analysis requires particular attention to certain aspects critically affecting the overall efficiency of the imprinting process. In this review we emphasized the critical steps during MIP preparation and characterization that would significantly affect the assessment of imprinting efficiency. MIP preparation starts with the selection of suitable monomers based on the nature of the used template. The template tends to form a stable complex with the used monomers. According to the type of bond formed between template and monomer molecules, three imprinting approaches are reported: covalent, non-covalent, and semi covalent. Then, polymerization of that complex takes place to produce MIP with template occupied binding sites or imprint cavities. So, for the completion of imprinting process and hence vacant cavity production, a suitable effective extraction technique is used. The assessment of template extraction process can be either direct, by template detection in the washing solution, or indirect, by measuring certain physical property of the polymer before and after template removal. Finally, the different parameters determined to assess the imprinting efficiency were summarized and the different sources of errors were addressed.
... A careful selection of a suitable porogen for the synthesis of MIP is vital due to its important role in the final polymer morphology where it influences the surface morphology, surface area and pore diameter of the MIP [95,115]. Porogens reported in literature for the synthesis of MIPs for fluoroquinolones include toluene [115,116], dichloromethane [89], ionic liquids (1butyl-3-methylimidazolium tetrafluoroborate [117] and 1-butyl-3methylimidazolium tetrafluoroborate [118]), dimethyl sulfoxide [81], mixtures of acetonitrile and dimethyl sulfoxide (6:4; v/v) [ [80,124], toluene, dodecanol and methanol (1:2:2; v/v/v) [125], acetonitrile [59,84,87,90] and methanol [88,126]. Notably, various mixtures of methanol and water at different ratios have been reported as porogens. ...
In recent years, fluoroquinolones have been found present in important water resources and food sources which compromises the food quality and availability, thereby, causing risks to the consumer. Despite the recent advancement in the development of analytical instrumentation for routine monitoring of fluoroquinolones in water, food, and biological samples, sample pre-treatment is still a major bottleneck of the analytical methods. Therefore, fast, selective, sensitive, and cost-effective sample preparation methods prior to instrumental analysis for fluoroquinolones residues in environmental, food and biological samples are increasingly important. Solid-phase extraction using different adsorbents is one of the most widely used pre-concentration/clean-up techniques for analysis of fluoroquinolones. Molecularly imprinted polymers (MIPs) serve as excellent effective adsorbent materials for selective extraction, separation, clean-up and preconcentration of various pollutants in different complex matrices. Therefore, synthesis of MIPs remains crucial for their applications in sample preparation as this offers much-needed selectivity in the extraction of compounds in complex samples. In this study, the progress made in the synthesis of MIPs for fluoroquinolones and their applications in water, food and biological samples were reviewed. The present review discusses the selection of all the elements of molecular imprinting for fluoroquinolones, polymerization processes and molecular recognition mechanisms. In conclusion, the related challenges and gaps are given to offer ideas for future research focussing on MIPs for fluoroquinolones.
... They were first prepared at conventional format in in the whole section of 4.6 mm i.d. stainless-steel columns as reported by Ou et al. [67,68] and more recently by other groups [69][70][71][72]. However, their synthesis in capillaries or channels represents today most of the developments. ...
Molecularly imprinted polymers are highly selective and cost‐effective materials, which have attracted significant interest in various areas such as sample pretreatment and chromatographic and electrophoretic separations. This review aims to present the state of the art concerning the miniaturization of these materials in order to meet the societal demand for reliable, fast, cheap, and solvent/sample saving analyses. The polymerization route specificities for the production of miniaturized molecularly imprinted polymers in capillaries or chip channels such as open tubular, packed particles, magnetic nanoparticles, and in situ imprinted monoliths are investigated. Their performances as selective supports in solid phase extraction and as stationary phases in electrochromatography and liquid chromatography, as well as their possible perspectives are discussed.
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... For their on-line-coupling with conventional LC systems, some monolithic MIPs have been prepared in 4.6 mm internal diameter (i.d.) columns [10,11]. This approach was used to prepare a MIP column for HPLC separation [12,13] and did not require the covalent attachment of the MIP to the inner surface of the column since frits were used to maintain the sorbent in the column. ...
We report the on-line coupling of a monolithic molecularly imprinted polymer to nano-liquid chromatography for the selective analysis of cocaine and its main metabolite, benzoylecgonine, in complex biological samples. After the screening of different synthesis conditions, a monolithic molecularly imprinted polymer was in situ synthesized into a 100 µm internal diameter fused-silica capillary using cocaine as template, methacrylic acid as functional monomer, and trimethylolpropane trimethacrylate as cross-linker. Scanning electron microscopy was used to assess the homogeneous morphology of the molecularly imprinted polymer and its permeability was measured. Its selectivity was evaluated by nano-liquid chromatography-ultraviolet, leading to imprinting factors of 3.2 ± 0.5 and 2.2 ± 0.3 for cocaine and benzoylecgonine, respectively, on polymers resulting from three independent syntheses, showing the high selectivity and the repeatability of the synthesis. After optimizing the extraction protocol to promote selectivity, the monolithic molecularly imprinted polymer was successfully on-line coupled with nano-liquid chromatography-ultraviolet for the direct extraction and analysis of cocaine present in spiked human plasma and saliva samples. The repeatability of the obtained extraction recovery, between 85.4-98.7% for a plasma sample spiked at 100 ng.mL-1, was high with relative standard deviation values lower than 5.8% for triplicate analyses on each of the three independently synthesized molecularly imprinted polymers. A linear calibration range was achieved between 100 and 2000 ng mL-1 (R2 = 0.999). Limits of quantification of 14.5 ng mL-1 and 6.1 ng mL-1 were achieved in plasma and urine samples, respectively. The very clean-baseline of the resulting chromatogram illustrated the high selectivity brought by the monolithic molecularly imprinted polymer that allows the removal of a huge peak corresponding to the elution of interfering compounds and the easy determination of the target analyte in these complex biological samples.
... However, excessive use of AMP can result in varying levels of residues being present in animal-based foods, which can be detrimental to consumers [3]. Current methods of detecting AMP involve high-performance liquid chromatography (HPLC) [4][5][6], gas chromatography-mass spectrometry (GC-MS) [7,8], liquid chromatography-tandem mass spectrometry (LC-MS/MS) [9], and surface-enhanced Raman spectroscopy (SERS) [10][11][12]. However, the majority of these detection methods are used for qualitative analysis and there are few methods available for efficient quantitative analysis of trace residues [13]. ...
Surface-imprinted polymers (MIPs) microspheres with the ability to specifically recognize water-soluble molecules were prepared using self-made monodisperse porous poly(chloromethylstyrene-co-divinylbenzene) beads as the solid-phase matrix and ampicillin (AMP) as the template molecule. MIPs were synthesized using different template molecule: monomer: crosslinker ratios and the optimum preparation ratio were obtained by measuring adsorption. The maximum equilibrium amount of adsorption by the MIPs reached 115.62 mg/g. Scatchard analysis indicated that the MIPs contained two types of recognition sites: specific and nonspecific. Based on the adsorption kinetics, adsorption equilibrium was reached after 30 minutes. Penicillin G, amoxicillin, and sulbactam acid were used as competitive molecules to research the selective adsorption capacity of the MIPs. The imprinted material was found to have good selectivity with selectivity coefficients for penicillin G, amoxicillin, and sulbactam acid of 5.74, 6.83, and 7.25, respectively. The MIPs were used as solid-phase extraction filler, resulting in successful enrichment and separation of ampicillin residue from egg samples. Standard addition recovery experiments revealed that recovery was good with recoveries from the spiked samples ranging from 91.5 to 94.9% and relative standard deviations from 3.6 to 4.2%. The solid-phase extraction MIPs microcolumn was reused 10 times, where it maintained a recovery rate of over 80%. This work presents a sensitive, fast, and convenient method for the determination of trace ampicillin in food samples.
... The superiority of MIPs as selective SPE sorbents (MISPE) for the analysis of residues in food has been extensively demonstrated during the last decade; several studies have compared classical SPE sorbents and MISPE sorbents (Regal et al., 2012). Also, novel formats have emerged for multianalyte extraction in food, including for example molecularly imprinted stir-bars, monoliths and/or on-line clean-up columns, suggesting a clear tendency towards miniaturization in MIP technology (Lv et al., 2013;Xu et al., 2011;Zhang et al., 2014) Last but not least, any sample preparation protocol is usually started with homogenization or grinding of a considerable amount of sample. Hereafter, an aliquot of sample is taken for analysis, in most occasions transferring the desired analyte into a homogenous liquid medium or solvent. ...
... On the other hand, online techniques use automated systems that minimize sample manipulation. Flow techniques are commonly coupled to SPE [8,9] using solid phases composed of molecularly imprinted polymers (MIPs) [10][11][12], monolithic columns [13,14], and carbonaceous materials [15,16]. ...
Solid-phase extraction in combination with large-volume sample stacking-capillary electrophoresis (SPE-LVSS-CE) was applied to measure chlortetracycline, doxycycline, oxytetracycline, and tetracycline in milk samples. Under optimal conditions, the proposed method had a linear range of 29 to 200 µ g·L ⁻¹ , with limits of detection ranging from 18.6 to 23.8 µ g·L ⁻¹ with inter- and intraday repeatabilities < 10% (as a relative standard deviation) in all cases. The enrichment factors obtained were from 50.33 to 70.85 for all the TCs compared with a conventional capillary zone electrophoresis (CZE). This method is adequate to analyze tetracyclines below the most restrictive established maximum residue limits. The proposed method was employed in the analysis of 15 milk samples from different brands. Two of the tested samples were positive for the presence of oxytetracycline with concentrations of 95 and 126 µ g·L ⁻¹ . SPE-LVSS-CE is a robust, easy, and efficient strategy for online preconcentration of tetracycline residues in complex matrices.
... The MIP column preconditioned with water-acetonitrile (75:25, v/v; 2 mL) and water-acetonitrile (90:10, v/v; 2 mL), loaded with pretreated spiked milk extract, washed with methanol-water (7:93, v/v; 1.5 mL) and the analytes were eluted with mobile phase. MIP dynamic adsorption capacity was 4.08 mg/g for ENR, while NIP adsorption capacity was and 2.44 mg/g [67]. ...
Milk-producing animals are typically kept stationary in overcrowded large-scale farms and in most cases under unsanitary conditions, which promotes the development of infections. In order to maintain sufficient health status among the herd or promote growth and increase production, farmers administer preventative antibiotic doses to the animals through their feed. However, many antibiotics used in cattle farms are intended for the treatment of bacterial infections in humans. This results in the development of antibiotic-resistant bacteria which pose a great risk for public health. Additionally, antibiotic residues are found in milk and dairy products, with potential toxic effects for the consumers. Hence the need of antibiotic residues monitoring in milk arises. Analytical methods were developed for the determination of antibiotics in milk, with key priority given to the analyte extraction and preconcentration step. Extraction can benefit from the production of molecularly imprinted polymers (MIPs) that can be applied as sorbents for the extraction of specific antibiotics. This review focuses on the principals of molecular imprinting technology and synthesis methods of MIPs, as well as the application of MIPs and MIPs composites for the chromatographic determination of various antibiotic categories in milk found in the recent literature.
... This approach requires disintegrating the monolith [80]. Imprinting factor can also be determined from the ratio of breakthrough volumes or from ratios of retention factors (dynamic approaches), which in our opinion offer more realistic evaluations for monolithic columns since the original continuous structure of the monolith is not altered [143,155,156]. Standardization of the methodologies for determination of IF is needed to facilitate the assessment of the performance of MIPs that could then guide the most adequate synthesis route to optimized sorbent for the target analyte. ...
This review aims at presenting the state of the art concerning monolithic materials for on-line sample preparation emphasizing solid-phase extraction, matrix exchange, and analyte conversion. Emphasis was given to organic and silica-based, as well as hybrid monoliths reported in the literature mostly after 2010. The first part of this review presents materials and strategies for enrichment of inorganic species in environmental and biological samples using mostly ICP-MS detectors. In the second part we focus on organic analytes, discussing the role of surface area of the polymer monoliths and density of adsorption sites for specific interactions, including incorporation of nanoparticles, metal organic frameworks, as well as the preparation of hybrid organic-silica monoliths to increase the surface area. Incorporation of ionic liquids to increase the number of types of interaction mechanisms available for retention is also discussed. Monoliths affording molecular recognition properties achieved by including boronate moieties for cis-diol recognition, as well as antibodies and aptamers for specific molecular recognition are also reviewed. The largest number of applications of molecular recognition mechanisms was observed for molecularly imprinted polymer monoliths as a consequence of the simplicity of this approach when compared to the use of immunosorbents or aptamers. The final part examines the on-line applications of immobilized enzyme reactors used for protein digestion in proteomic analysis and for kinetic studies in drug discovery and clinical assays usually coupling the reactors to mass spectrometers.
... The traditional stainless steel monolithic column has the advantages of high hardness, strong toughness, large internal diameter, uniform structure, and large column capacity. Lv , s groups reported an internal surface reversed-phase monolithic column was prepared by in situ modification of hybrid monolithic columns (HMC) in a stainless steel column [6] . The HMC was synthesized via the cocondensation of methyltrimethoxysilane (MTMS) and tetraethoxysilane (TEOS). ...
... The fluoroquinolone residues were successfully determined in milk samples by on-line SPE coupled with organic-inorganic hybrid imprinted monolith in HPLC [68]. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were 1.69 and 5.63 mg kg À1 for ofloxacin, 1.63 and 5.43 mg kg À1 for lomefloxacin, 3.74 and 12.5 mg kg À1 for ciprofloxacin, 1.37 and 4.56 mg kg À1 for enrofloxacin, respectively. ...
Imprinted monoliths are highly selective and cost-effective materials, which have attracted significant interest in various areas, mostly as the stationary phase used in high performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). This review focuses on the recent significant progress of the imprinted monoliths in preparations and applications. Some thoughts on perspectives of imprinted monoliths are also expressed.
... MIP monoliths prepared inside stainless steel chromatographic columns appear as interesting pre-columns for on-line clean-up and the preconcentration of analytes. As an example, Lv et al. developed a method to extract fluoroquinolones (FQs) present in milk and honey using an on-line MIP-based monolithic precolumn [28,43]. By using this MIP monolith, FQs were selectively isolated from biological samples, and the impurities were eliminated simultaneously, showing high selectivity and sufficient accuracy to be used on trace levels of FQs analysis in biological samples. ...
Monolithic columns are gaining interest as excellent substitutes to conventional particle-packed columns. These columns show higher permeability and lower flow resistance than conventional liquid chromatography columns, providing high-throughput performance, resolution and separation in short run times. Monoliths possess also great potential for the clean-up and preparation of complex mixtures. In situ polymerization inside appropriate supports allows the development of several microextraction formats, such as in-tube solid-phase and pipette tip-based extractions. These techniques using porous monoliths offer several advantages, including miniaturization and on-line coupling with analytical instruments. Additionally, monoliths are ideal support media for imprinting template-specific sites, resulting in the so-called molecularly-imprinted monoliths, with ultra-high selectivity. In this review, time-saving LC columns and preparative applications applied to the analysis of residues and contaminants in food in 2010–2014 are described, focusing on recent improvements in design and with emphasis in automated on-line systems and innovative materials and formats.
... Molecular imprinting is a rapidly developing technique for preparation of polymers with excellent molecular recognition properties, which has been found effective in a variety of extraction techniques such as molecular imprinted solid-phase extraction (MI-SPE), molecular imprinted solid-phase microextraction (MI-SPME), molecular imprinted stir-bar sorptive extraction (MI-SBSE), molecular imprinted matrix solid-phase dispersion (MI-MSPD) [16] and so on. Fluoroquinolone-imprinted polymers have been applied for their enrichment and purification from complex samples such as milk [17], eggs [18], urine [19], fish [20], serum [21], water [22,23] and soil [24]. Good recoveries as well as high selectivity have been obtained due to the good molecular recognition properties of molecularly imprinted polymers (MIPs). ...
Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.
In food analysis, conventional one‐dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analyzed matrices. Therefore, the use of two‐dimensional liquid chromatography (2D‐LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D‐LC–MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimization of the different analytical aspects that will condition the 2D‐LC–MS performance. The presence of contaminants in food (food safety), the food quality, and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D‐LC–MS applications are mainly focused. Both heart‐cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D‐LC–MS for the analysis of such complex samples.
In food analysis, conventional one‐dimensional liquid chromatography methods sometimes lack sufficient separation power due to the complexity and heterogeneity of the analysed matrices. Therefore, the use of two‐dimensional liquid chromatography (2D‐LC) turns out to be a powerful tool to consider, especially when coupled to mass spectrometry (MS). This review presents the most remarkable 2D‐LC‐MS food applications reported in the last 10 years, including a critical discussion of the multiple approaches, modulation strategies as well as the importance of the optimisation of the different analytical aspects that will condition the 2D‐LC‐MS performance. The presence of contaminants in food (food safety), the food quality and authenticity or the relationship between the beneficial effects of food and human health are some of the fields in which most of the 2D‐LC‐MS applications are mainly focused. Both heart‐cutting and comprehensive applications are described and discussed in this review, highlighting the potential of 2D‐LC‐MS for the analysis of such complex samples.
For thousands of year dairy products have been the major parts of human diet because fermented milk products like
curd, cheese, and butter could be better preserved than the fresh raw milk from which they were made (Kok & Hutkins,
2018). Most fermented dairy products naturally contain organic acids, ethanol, or other microbial compounds that
inhibit the growth of the spoilage organisms and food borne pathogens (Ross & Hill, 2002). In our daily life, fermented
dairy products play an important role. These products contain a diverse microbiota (Fernandez et al., 2015) apart their
preservation qualities. Fermented foods have other attributes like flavor, texture, and appearance, and also add functional and economic value. Fermented foods are the most important sources of nutrients in many parts of the world
(Marsh et al., 2014). Bread and sausage are the cultured dairy products, they are very rich in protein, vitamins, and
minerals. Fermentation processes also reduce the amount of lactose and fermentable sugars and increase phenolic compounds which provide antioxidant activity (Shah, 2006).
Solid phase extraction (SPE) plays an important role in chemical and biological analysis. Compared with liquid–liquid extraction, SPE has the advantages of low solvent consumption, high efficiency, low cost, convenient operation and short time-consuming. However, the adsorbent used in SPE usually shows poor selectivity. The molecularly imprinted polymers (MIPs), which is similar to the binding of antigen and antibody, has specific adsorption capability to the specific molecules. Using MIP as the adsorbent of SPE prepared molecularly imprinted solid phase extraction (MISPE), can significantly improve the selectivity of SPE. MISPE has been widely used in separation, enrichment, pretreatment and detection. In this review, various modes of MISPE are systematically introduced, including off-line MISPE, on-line MISPE, molecularly imprinted-dispersive SPE, molecularly imprinted-matrix solid phase dispersion and magnetic MISPE. In addition, the applications of MISPE in food safety, environmental monitoring, drug and biological samples analysis are also reviewed.
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Enrofloxacin (ENR) is a broad-spectrum fluoroquinolone antibiotic widely used in both human medicine and veterinary medicine. In this study, the milk-excretion patterns of ENR and its metabolite ciprofloxacin (CIP) were determined up to the 10th milking following the intramuscular administration of ENR (2.5mg/kg of body weight) to lactating dairy buffaloes. The milk of each animal was collected and the concentrations of ENR and CIP were detected in milk by LC-MS/MS. The detection limits of the method were determined for ENR and CIP as 0.35 µg/kg and 0.12 µg/kg, respectively. The highest total mean concentrations of ENR and its metabolite CIP was determined in the second milking after injection as 603 µg/kg. The residue level in all buffalo milk samples was found to be lower than the maximum residue limit (100 µg/kg) at the fifth milking. In addition, the employed method is successfully applied to evaluate the presence of ENR and CIP residue in 50 marketed buffalo milk samples and none of the samples contained these antibiotics. Consequently, the present study provided information on the milk excretion levels of ENR and CIP in Anatolian buffalo milks by an LC-MS/MS method. © 2021, Chartered Inst. of Building Services Engineers. All rights reserved.
We prepared ofloxacin restricted access media‐molecularly imprinted polymers using surface‐initiated atom transfer radical polymerization on the surface of brominated silica gel using ofloxacin as a template molecule, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinking agent. We then characterized and studied the surface morphology and adsorption properties of the polymer. Experimental results show that saturation is reached within 25 min, and that the saturated adsorption capacity was 80.67 mg/g and the imprinting factor was 1.94. Our findings also showed that the polymer surface had good hydrophilicity and an excellent protein exclusion rate, which was 98.49%. The restricted access media‐molecularly imprinted polymers were then successfully applied to the enrichment and separation of ofloxacin in bovine serum. When combined with HPLC, the average recovery of ofloxacin was 95.6%, and the RSD was 2.47‐3.38%. In a word, the restricted access media‐molecularly imprinted polymers are a method that involves a simple preparation procedure that results in excellent performance, which is a great improvement in the speed of detection of antibiotics. These qualities are what bestow upon this method its great potential for broad application.
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Graphene oxide (GO) was introduced in the process of systematic evolution of ligands by exponential enrichment (SELEX) to screen ofloxacin-specific single-stranded DNA aptamers. Four sequences with high homology, ap1, ap3, ap4 and ap5 were picked out. Their secondary structures were simulated, and the dissociation constants (Kd) were measured, which were 251.3, 130.1, 159.1 and 304.4 nM, respectively. The specificity of the aptamers was also evaluated.
This review will concentrate on recent progress (since 2013) towards preparation of organic-silica hybrid monoliths and their latest applications as extraction and separation media largely focusing on capillary liquid chromatography and capillary electrochromatography. Main emphasis will be given to advancement of approaches relying on the sol-gel chemistry of tetra- and tri-alkoxysilanes, sol-gel chemistry of alkoxysilanes and free-radical copolymerization with organic monomers, and free radical and ring-opening copolymerization of polyhedral oligomeric silsesquioxanes with organic monomers. Hybrid molecularly-imprinted polymer monoliths and hybrid monoliths made with non-silica-based precursors or in combination with metal alkoxides will be included as well. This article is protected by copyright. All rights reserved.
Food safety is a priority public health concern that demands analytical methods capable to detected low concentrations level of contaminants (e.g. pesticides and antibiotics) in different food matrices. Due to the high complexity of these matrices a sample preparation step is in most cases mandatory to achieve satisfactory results being usually tedious, lengthy and prone to the introduction of errors. For this reasons many research groups has focused efforts in the development of online systems capable to do the cleanup, concentration and separation steps at once through multidimensional separation techniques (MDS). Among several possible setups, the most popular are the multidimensional chromatographic techniques (MDC) that consist in combining more than one mobile or/and stationary phase to provide a satisfactory separation. In the present review we selected a variety of multidimensional separation systems used for food contaminant analysis in order to discuss the instrumentation aspects, the concept of orthogonality, column approaches used in these systems and new materials that can be used in these columns. Selected classes of contaminants present in food matrices are introduced and discussed as example of the potential applications of multidimensional liquid phase separation techniques in food safety. This article is protected by copyright. All rights reserved.
Molecular imprinting technology (MIT), often described as a method of making a molecular lock to match a molecular key, is a technique for the creation of molecularly imprinted polymers (MIPs) with tailor-made binding sites complementary to the template molecules in shape, size and functional groups. Owing to their unique features of structure predictability, recognition specificity and application universality, MIPs have found a wide range of applications in various fields. Herein, we propose to comprehensively review the recent advances in molecular imprinting including versatile perspectives and applications, concerning novel preparation technologies and strategies of MIT, and highlight the applications of MIPs. The fundamentals of MIPs involving essential elements, preparation procedures and characterization methods are briefly outlined. Smart MIT for MIPs is especially highlighted including ingenious MIT (surface imprinting, nanoimprinting, etc.), special strategies of MIT (dummy imprinting, segment imprinting, etc.) and stimuli-responsive MIT (single/dual/multi-responsive technology). By virtue of smart MIT, new formatted MIPs gain popularity for versatile applications, including sample pretreatment/chromatographic separation (solid phase extraction, monolithic column chromatography, etc.) and chemical/biological sensing (electrochemical sensing, fluorescence sensing, etc.). Finally, we propose the remaining challenges and future perspectives to accelerate the development of MIT, and to utilize it for further developing versatile MIPs with a wide range of applications (650 references). Total 75pages.
A highly selective method for the analysis of triazine herbicides in corn samples based on molecularly imprinted solid phase extraction (MISPE) has been developed. Molecularly imprinted polymers (MIPs) were synthesized by precipitation polymerization using atrazine as a template, methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinker, and 2,2′-azobis-isobutrynitrile as an initiator. MISPE was developed for the on-line and automated enrichment of atrazine, simazine, terbutryn, simetryn and ametryn from corn sample extracts. High-performance liquid chromatography and time-of-flight mass spectrometry were used for the separation and confident determination of the herbicides. The limits of detection and quantitation of the proposed method were set to be 1.6–3.3 μg kg−1 and 5.0–10.0 μg kg−1. The method was successfully applied for the analysis of five types of corns and the recoveries of the triazines from the spiked samples ranged from 80.2 to 119.1%.
Th e polymerization of monomers in the presence of a target molecule that imprints structural
information into resulting network polymers, called molecularly imprinted polymer (MIP), is a
scientifi c fi eld that is rapidly gaining signifi cance for a wide range of applications in chemistry,
biotechnology and pharmaceutical research. Due to their analytically useful properties, such
as selectivity, shelf stability, robustness and reusability, MIP off ers potential for the synthesis of
artifi cial recognition material and they are being proposed for the development of novel biorecognition
techniques for human health and bioterrorism protection technologies. MIPs are
successfully applied for developing and applying the analytical protocol/technology for selective
and specifi c determination of a wide range of pharmaceutics in various matrices. Th e proposed
chapter deals with all aspects of application of this technology (MIP) for analytical determination
of pharmaceutical samples.
Molecularly imprinted polymers are artificial synthetic materials with high selectivity and affinity to template molecule and its structural analogues. They are prepared through molecular imprinting technique. This current review surveys molecularly imprinted polymers ranging from preparation to application in solid phase extraction, and recent application in the analysis of chemical hazards in foods.
TLC-densitometric method was developed for the identification and quantitative determination of selected fluoroquinolones. Silica gel TLC 60 F254 plates were used as the stationary phase. For the separation of examined compounds the suitability of the following four mobile phases with different dynamic viscosity was checked: (I) methanol:ammonia:ethyl acetate:acetonitrile 1:1:2:1 v/v/v/v (1.70 mPa · s), (II) dichloromethane:methanol:isopropanol:ammonia 4:4:5:2 v/v/v/v (2.08 mPa · s), (III) dichloromethane:ethanol:toluene:ammonia:n-butanol:water 6:6:2:1.8:3:0.3 v/v/v/v/v/v (2.27 mPa · s), (IV) 1,4- dioxane:ammonia:tetrahydrofuran 6:3:2 v/v/v (3.24 mPa · s). The calculated values of retardation factors RF, capacity factors k, selectivity factors α, resolution factors Rs, and also asymmetry factors As for the evaluation of separation conditions were used. The obtained results confirmed that dynamic viscosity of the mobile phases is essential and influences the retention parameters of the studied fluoroquinolone chemotherapeutics. The validation results for the mobile phase IV indicate its suitability for the identification and also quantitative analysis of selected drugs in pharmaceutical analysis.
A molecularly imprinted polymer (MIP) monolith was initially prepared in a silica capillary mold by microwave irradiation. After the silica wall was etched away after polymerization, the resulting monolithic bar was embedded in a porous hollow fiber membrane tube (HFMT), in which a thin supported liquid membrane (SLM) was formed in the pores and an acceptor solution was filled in its lumen. It can be used to overcome the common water-compatibility problem in the MIP application by the developed hollow fiber-liquid-solid microextraction (HFLSME) system. The main factors affecting the selective extraction including extraction and desorption time, extraction solvent in the hollow fiber (HF) lumen, off-line desorption solvent, stirring rate and pH of the sample solution were investigated for HFLSME procedures in detail. Selectivity was also evaluated using the atrazine template molecule, its analogues and non-analogue. The extraction amount for each structurally-related pesticide including atrazine, 2-amino-4-methoxy-6-methyl-1,3,5-triazine, terbutylazine and ametryn was obtained about 10 times using atrazine-imprinted hollow fiber than that using non-imprinted hollow fiber, whilst no obvious difference was found for its non-analogues of metribuzin. The resulted hollow fibers were successfully applied to detect atrazine and its analogues in lake water coupled to high performance liquid chromatography (HPLC) and resulted in recoveries in the range of 72.8-113.2%, respectively.
A novel restricted access material - hybrid monolithic column (RAM-HMC) was prepared by in situ modification method in a stainless-steel column for on-line solid-phase extraction of sulfonamide residues from honey. The hydrophobic HMC was prepared by sol-gel process using acid-catalytic reaction of methyltrimethoxysilane and tetraethoxysilane. The hydrophilic structures were formed on the through hole surface of the HMC by grafting 3-(2, 3-epoxypropoxy) propytrimethoxysilane. The synthetic conditions were optimized for obtaining the uniform microchannel and the stable skeleton structure. The chemical group, morphology, dynamic adsorption capacity, swelling, hydrophilic and hydrophobic characteristic of the monolithic column were characterized by IR, SEM, dynamic binding, solvent adsorption, chromatographic analysis of serum proteins and benzene series, respectively. When the RAM-HMC was applied to on-line extraction of sulfonamides residue from the honey samples, an enrichment factor of 16.9 and a better sample clean-up effect were obtained under the optimized conditions. The average recoveries of three sulfonamides antibiotics spiked honey at 0.05, 0.1 and 0.2 mg kg-1 were in the range of 73.50-105.80% with the precision of 2.25-5.32%. The limits of detection and quantitation of the proposed method were in a range of 6.9-14.6 μg kg-1 and 23.0-48.2 μg kg-1, respectively. The proposed method was successfully applied to on-line extraction and determination of sulfonamides antibiotics in the honey sample.
A rapid, specific, and sensitive method was developed for determination of tetracyclines (TCs) in egg, milk, and milk powder samples by online molecularly imprinted solid-phase extraction (MISPE) coupled to a reversed-phase high-performance liquid chromatography (HPLC). A molecularly imprinted polymer hybrid composite material (MIP-HCM) was prepared using TC as the template, methacrylic acid as the functional monomer, tetraethoxysilane as inorganic precursor, and methacryloxypropyltrimethoxysilane as the coupling agent. A new technique of online solid-phase extraction (SPE) coupled with HPLC was established. The conditions of online SPE were optimized. Under the optimal conditions, three TCs residues in egg, milk, and milk powder were separated and detected by the proposed method with better clean-up and recoveries. The recoveries of TCs ranged from 85.3% to 98.3%. The limits of detection and quantitation of the proposed method were in the range of 0.76–1.13 µg/kg and 2.53–3.77 µg/kg, respectively. The MIP-HCM was first used as online SPE packing and the hyphenated technique is promising as a general strategy for direct determination of veterinary drug residues in milk and other biological samples.
An organic–inorganic hybrid molecular imprinting monolith (HMIM) has been prepared, characterized and applied for the determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in rice with high-performance liquid chromatography-photodiodes array detector (HPLC–PAD). By optimizing the polymerization conditions, such as the volume ratio of the inorganic alcoholysate and organic part, the 2,4-D-HMIM was synthesized in a micro pipette tip using acrylamide as the functional monomer, ethylene dimethacrylate as the cross-linker and methanol as the porogenic solvent. The morphology of the monolith was studied by scanning electronmicroscopy and Fourier transform infrared spectra. The imprinted factor of the monolith for 2,4-D reached 3.29. A simple, rapid and sensitive method for the determination of 2,4-D in rice using the HMIM microextraction combined with high-performance liquid chromatography-photodiodes array detector was developed. Some parameters affecting the sample pretreatment were investigated, including the type and volume of eluent, the flow rate and volume of sample solution. The assay exhibited a linear dynamic range of 167–4167 μg/kg with the correlation coefficient above 0.9972. The detection limit (at S/N = 3) was 50 μg/kg. The proposed method was successfully applied for the selective determination of 2,4-D in rice.
A novel molecularly imprinted organic-inorganic hybrid composite material (MIP-HCM) was developed based on molecular imprinting technique in combination with hybrid composite synthesis and sol-gel technology for selective solid-phase extraction (SPE) of tetracyclines residues in milk. The MIP-HCM was prepared using oxytetracycline as the template, methacrylic acid as organic functional monomer, tetraethoxysilane as inorganic precursor and methacryloxypropyltrimethoxysilane as the coupling agent. Synthesis conditions are optimized by changing some factors to obtain sorbent with the controllable adsorption capacity, selectivity, hardness and toughness. Binding study demonstrated that the imprinted hybrid composites showed excellent affinity and high selectivity to oxytetracycline. An enrichment factor of 18.8 along with a good sample clean-up was obtained under the optimized SPE conditions. The average recoveries of three tetracyclines antibiotics spiked milk at 0.1, 0.2 and 0.5 mg kg⁻¹ were in the range of 80.9-104.3% with the precision of 1.5-5.0%. The limits of detection and quantitation of the proposed method were in a range of 4.8-12.7 μg kg⁻¹ and 16.0-42.3 μg kg⁻¹, respectively.
The main goal of this work was determination of residues of the antibiotics ofloxacin (OFLO), norfloxacin (NOR), ciprofloxacin (CIPRO), and enrofloxacin (ENRO) in wastewater samples. The samples, after acidification to pH 4.5 and addition of EDTA, were extracted on an anion-exchange cartridge in tandem with an Oasis HLB cartridge. The LC-FD method, developed in previous studies, was based on application of a monolithic C(18) column. The limit of quantification (LOQ) of the method was 250 ng L(-1) for OFLO, 25 ng L(-1) for NOR and CIPRO, and 50 ng L(-1) for ENRO. Mean recovery ranged between 75 and 121% for OFLO, NOR, CIPRO, and ENRO. A total of 14 wastewater samples were analyzed; these were collected from four hospitals and from influent and effluent from a wastewater-treatment plant in Coimbra, Portugal, during spring and autumn. CIPRO was present in all the samples, NOR was detected second most often, followed by OFLO. ENRO was found at concentrations under the LOQ in five hospital samples, and the highest level was found in influent from the WWTP.
On-line solid-phase extraction method was developed by enrofloxacin- imprinted monolithic column (monolithic MIP) coupling with reversed-phase high-performance liquid chromatography for preconcentration and separation of fluoroquinolone residues in milk. The monolithic MIP was prepared by in situ polymerization in a stainless-steel chromatographic column. An enrichment factor of 6.70 along with a good sample clean-up effect was obtained. High recoveries for three fluoroquinolones such as enrofloxacin, ciprofloxacin and norfloxacin were achieved, which was in the range of 82.0-94.0 % with precision lower than 5.6 %. The limit of detection and limit of quantitation of the proposed method were in a range of 4.31-7.62 μg/kg and 14.37-25.40 μg/kg, respectively. The proposed method was successfully applied to on-line preconcentration, separation and determination of the fluoroquinolones in the milk sample.
A monolithic molecularly imprinted polymer for enrofloxacin was synthesized by in situ copolymerization of methylacrylic acid and methyl methacrylate in a traditional stainless-steel chromatographic column for the rapid separation and determination of enrofloxacin and ciprofloxacin in eggs. By optimizing the polymerization condition, the monolithic MIP showed highly specific recognition for enrofloxacin over its active metabolite ciprofloxacin. The influence of components of monomers on hydrophobicity, contractibility, selectivity, and binding capacity of polymer were investigated. As shown by SEM, the mesopores and macropores were formed in the monolith column; this allowed the mobile phase to flow through the column with low backpressure. Furthermore, some chromatographic conditions such as mobile phase composition and flow rate on the retention times were investigated. The binding capacity was evaluated by static adsorption and Scatchard analysis, which showed that the dissociation constant and the maximum binding capacity were 117.7 mg/L and 27.27 mg/g for high affinity binding site, and 297 mg/L and 187.4 mg/g for lower affinity binding site, respectively. The mean recoveries of enrofloxacin and ciprofloxacin from egg samples were 103.3–115% and 89.3–95.1%, respectively. The research has shown that copolymerization provides more adjustable conditions for making molecularly imprinted monolithic columns with different morphologies and higher selectivity.
As new separation media, continuous rods of molecularly imprinted polymers were prepared by an in situ method. The preparation procedure was simple and easy to perform: a template compound, a functional monomer which interacts with the template molecules, and a cross-linker were placed in a stainless steel column and heated for polymerization. In this study, diaminonaphthalene and phenylalanine anilide were used as model template molecules. The molecular recognition capabilities of the prepared molecular-imprinted polymer rods were evaluated by separating positional isomers of diaminonaphthalene and resolving enantiomers of phenylalanine anilide. The results showed that the original- template compounds were more strongly retained than their isomers. It is suggested that the templates were successfully imprinted in the prepared polymer rods by the employed in situ method.
Silica-based hybrid molecularly imprinted polymer (MIP) monoliths with good chiral recognition ability are synthesized (see figure) using a novel method, a room temperature ionic liquid (RTIL)-mediated, non-hydrolytic sol-gel technique. The approach avoids the cracking and shrinking of the bed during drying, which is commonly associated with conventional sol-gel processing, overcomes the shortcomings associated with conventional organicpolymer-based MIP matrices, and offers improved selectivity.
A simple on-line molecularly imprinted solid-phase extraction coupled with liquid chromatographic separation was developed
for the simultaneous determination of enrofloxacin and its active metabolite ciprofloxacin from urine samples. The molecularly
imprinted monolithic columns were synthesized in water-containing systems using norflorxacin as dummy template and methanol–water
(5:1, v/v) as porogenic solvent, which reveal high affinity to enrofloxacin and ciprofloxacin in the aqueous environment. Due to the
unique porous structure and flow-through channels existing in the network skeleton of the imprinted monolith, urine samples
could be injected directly into the imprinted column, proteins and other biological matrix were quickly washed out and the
analytes were selectively retained and enriched. Good linearity was obtained from 0.05 to 200mgL−1 with relative standard deviations less than 3.1%. The recoveries were higher than 87% at three different concentrations and
the limit of detection of the method was 0.01mgL−1. Moreover, by increasing the injection volume, the sensitivity of the method could be further improved.
A molecularly imprinted polymer as a selective solid-phase extraction adsorbent for efficient preconcentration and analysis
of metribuzin residues in corn fields has been synthesised and evaluated. Results showed that molecular imprinting of the
polymer was highly effective and the polymer had high affinity and selectivity for metribuzin in water-containing systems.
A monolithic column containing molecularly imprinted polymer was prepared and used for on-line preconcentration, separation,
and detection of metribuzin residues in soil sampled during investigation of the degradation of the herbicide metribuzin in
corn fields. The detection limit of the method was 8.3×10−4mgkg−1, recovery was between 94.9% and 103%, and RSD in analysis of soil samples was less than 3.2%.
Molecular imprint polymers recognize specific compounds and show promise as separation media, especially for chiral molecules.
A preliminary study of the chromatographic performance and permeability of a continuous silica xerogel column under reversed-phase HPLC conditions was performed. A porous chromatographic support was synthesized inside a 0.32 mm i.d. × 13 cm fused silica tube from potassium silicate solution and derivatized with dimethyloctadecylchlorosilane. The plate height at 0.01 cm/s (0.5 μL/min), near the apparent optimum linear velocity, was about 65 μm. The column efficiencies in terms of numbers of plates per meter were 5000 and 13 000 for ethyl benzoate (k = 0.8) and naphthalene (k = 2.0), respectively, at 0.5 μL/min. The major parameter affecting column efficiency was the heterogeneous morphology of the xerogel, modifications to which are expected to improve chromatographic performance. The column provided efficiencies comparable to those reported for continuous polymeric columns but less than that previously reported for a continuous silica column. Gradient elution mode was demonstrated with a mixture of polycyclic aromatic hydrocarbons. The column was highly permeable, exhibiting a linear dependence of pressure to flow rate and a back pressure of only 632 psi at 10 μL/min when a 95% aqueous mobile phase was used.
As a new generation of stationary phases, monolithic supports have attracted significant interest in high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) because of their ease of preparation, high reproducibility, versatile surface chemistry and rapid mass transport. Molecularly imprinted polymers (MIPs) are synthetic materials with high specific recognition ability to template molecule. The combination of monolithic column and MIPs integrates the high efficiency of modern chromatography and the high selectivity provided by MIPs. This review focuses on the recent developments and applications of all kinds of monolithic matrix, i.e. organic polymer-based and silica-based MIP monolith in HPLC and CEC mode.
A novel hybrid organic-inorganic monolith for high performance liquid chromatography (HPLC) was firstly developed by atom transfer radical polymerization (ATRP) by a simple and rapid method, in which vinyl ester resin was used as the monomer, natrium bisulfurosum was used both as organic adjunct and coadunate initiator to alter the activity of the free radical in the process of polymerization and then to control the molecular mass. The conditions of polymerization were optimized. The chemical group of the monolith was assayed by infrared spectra method, the morphology of monolithic material was studied by scanning electron microscopy (SEM) and the pore size distribution was determined by a mercury porosimeter. Finally, the monolith was used to separate lysozyme (Lys) from chicken egg white with good resolution and reproducibility that were obtained in a short time (10 min) by HPLC. In addition, the influences of buffer concentration and pH value on elution have been investigated and the hybrid monolith was used to separate benzene and its homologs from the mixture.
A novel molecularly imprinted polymer monolith was prepared by the room temperature ionic liquid-mediated in situ molecular imprinting technique, using norfloxacin (NOR) as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker. The optimal synthesis conditions and recognition properties of NOR-imprinted monolithic column were investigated. The results indicated that the imprinted monoliths exhibited good ability of selective recognition against the template and its structural analog. Using the fabricated material as solid-phase extraction sorbent, a sample pre-treatment procedure of molecularly imprinted solid-phase extraction coupling with HPLC was developed for determination of trace quinolone residues in animal tissues samples. The recoveries ranging from 78.16 to 93.50% for eight quinolones antibiotics such as marbofloxacin, NOR, ciprofloxacin, danofloxacin, difloxacin, oxolinic acid, flumequine and enrofloxacin were obtained.
Water-compatible pefloxacin-imprinted monoliths synthesized in a water-containing system were used for the selective extraction of fluoroquinolones (FQs). The MIP monolith was synthesized by using methacrylic acid as the functional monomer, di(ethylene glycol) dimethacrylate as a cross-linker and methanol-water (10:3, v/v) as the porogenic solvent. The ability of the derivated MIP for selective recognition of FQs (ciprofloxacin, difloxacin, danofloxacin and enrofloxacin) and quinolones (flumequine, and oxolinic acid) was evaluated. The derivated monolith showed high selectivity and was able to distinguish between FQs and quinolones. A simple rapid and sensitive method using polymer monolith microextraction (PMME) based on the MIP monolith combined with HPLC with fluorescence detection was developed for the determination of four FQs from milk samples. Owing to the unique porous structure and flow-through channels in the network skeleton of the MIP monolith, phosphate buffer diluted milk samples were directly supplied to PMME; allowing non-specific bound proteins and other biological matrix to be washed out, and FQs to be selectively enriched. The limit of detection of the method was 0.4-1.6ng/mL and recovery was 92.4-98.2% with relative standard deviations less than 5.9%.
A novel solid phase extraction (SPE) method for determination of tetracyclines (TCs) in milk and honey samples by molecularly imprinted monolithic column was developed. Using tetracycline (TC) as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, methanol as the solvent, cyclohexanol and dodecanol as the mixed porogenic solvents, a TC imprinted monolithic column was prepared by in situ molecular imprinting technique for the first time, and the optimal synthesis conditions and the selectivity of TC imprinted monolithic column were investigated. The interfering substances in food samples and TCs can be separated successfully on imprinted column. Molecularly imprinted solid phase extraction (MISPE) coupling with C18 column was used to determinate the TCs in milk and honey. The recoveries of this method for six tetracyclines antibiotics such as tetracycline (TC), oxytetracycline (OTC), minocycline (MINO), chlortetracycline (CTC), metacycline (MTC) and doxycycline (DTC) were investigated, and high recoveries of 73.3-90.6% from milk samples and 62.6-82.3% from honey samples were obtained. A method for determination of TCs at low concentration level in milk and honey samples was successfully developed by using the monolithic column as the precolumn for solid phase extraction of six TCs compounds.
A "one-pot" process for the preparation of organic-silica hybrid capillary monolithic columns by concurrently using organic monomers and alkoxysilanes was described. In this process, the hydrolyzed alkoxysilanes of tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as precursors for the synthesis of a silica-based monolith using the sol-gel method and the organic monomer (allyldimethyldodecylammonium bromide (ADDAB) or acrylamide (AA)) with vinyl groups for free radical polymerization along with the initiator of azobisisobutyronitrile (AIBN) were concurrently introduced into a pretreated capillary; after that, the polycondensation of alkoxysilanes and the copolymerization of organic monomers and as-precondensed siloxanes were subsequently carried out within the confines of a capillary at the proper reaction conditions. Two types of organic-silica hybrid capillary monolithic columns with hydrophobic and hydrophilic properties have been fabricated, respectively, by this "one-pot" process using two different organic monomers of ADDAB and AA. The morphologies of the synthesized organic-silica hybrid monolithic columns were characterized by scanning electron microscopy (SEM). The performances of these organic-silica monolithic columns were investigated by capillary electrochromatography (CEC). The retention behaviors of the neutral and polar compounds on the resulting hydrophobic and hydrophilic organic-silica hybrid monolithic columns confirmed the successful incorporation of organic monomers in the silica monolithic matrix. In addition, the ADDA-silica hybrid capillary monolithic column was also applied in the analysis of tryptic digests of bovine serum albumin (BSA) and mouse liver extract by microliquid chromatography-tandem mass spectrometry (microLC-MS/MS) for demonstrating its potential in proteome analysis.
A rapid, specific, and sensitive method has been developed using molecularly imprinted polymers (MIPs) as solid-phase extraction sorbents for extraction of trace tetracycline antibiotics (TCs) in foodstuffs. MIPs were prepared by precipitation polymerization using tetracycline as the template. Under the optimal condition, the imprinting factors for MIPs were 4.1 (oxytetracycline), 7.0 (tetracycline), 7.4 (chlortetracycline), 7.7 (doxycycline), respectively. Furthermore, the performance of MIPs as solid-phase extraction sorbents was evaluated and high extraction efficiency of molecularly imprinted solid-phase extraction (MISPE) procedure was demonstrated. Compared with commercial sorbents, MISPE gave a better cleanup efficiency than C18 cartridge and a higher recovery than Oasis HLB cartridge. Finally, the method of liquid chromatography–tandem mass spectrometry coupled with molecular-imprinted solid-phase extraction was validated in real samples including lobster, duck, honey, and egg. The spiked recoveries of TCs ranged from 94.51% to 103.0%. The limits of detection were in the range of 0.1–0.3 μg kg−1.
Chromatograms obtained by direct injection of the spiked egg extracts (5 × 10-3 mmol L−1) and purification with MISPE
The bisphenol A (BPA) imprinted monolithic precolumn has been prepared by in situ polymerization using 4-vinylpyridine (4-VP) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. The column with good flow-through property was obtained by changing the molar ratio of the porogens (toluene and dodecanol). The selectivity and retention properties of the monolith for the BPA and other phenolic compounds were evaluated. The results show that the hydrophobic and hydrogen-bonding interaction plays important roles in the recognition process. The determination of BPA and other phenolic compounds with on-line solid-phase extraction (SPE) by monolithic precolumn coupled with conventional particulates packed and monolithic reversed-phase columns, respectively, was performed. The method was successfully applied to the analysis of phenolic compounds in river water.
A simple, cost-effective, and high throughput method using on-line column-switching liquid chromatography fluorescence detection was developed and validated for analysing five (fluoro)quinolones (FQs)--enrofloxacin (ENRO), ciprofloxacin (CIPR), sarafloxacin (SARA), oxolinic acid (OXOL), and flumequine (FLUM) in bovine milk. Norfloxacin (NORF) and nalixidic acid (NALI) were used as internal standards. After simple deproteination of milk sample with 5% (w/v) metaphosphoric acid, the supernatant was subject to on-line column clean-up and direct analysis by LC-FLD. The extraction cartridge was prepared in-house by slurry packing with hydrophilic-lipophilic polymer sorbent. The accuracy of measurement for each (fluoro)quinolone at different maximum residue limits (MRL) was 101-103% (ENRO), 92.8-97.4% (CIPR), 89.8-92.8% (SARA), 116-121% (OXOL), and 81.3-85.5% (FLUM), whilst the precision was 2.9-6.1% (ENRO), 2.5-5.1% (CIPR), 2.3-5.0% (SARA), 3.1-5.9% (OXOL), and 5.6-6.5% (FLUM). The decision limits, detection capabilities, specificity and analytes stability during storage were also investigated.
A novel hybrid organic-inorganic silica-based monolithic column possessing phenyl ligands for reversed-phase (RP) capillary electrochromatography (CEC) is described. The monolithic stationary phase was prepared by in situ co-condensation of tetraethoxysilane (TEOS) with phenyltriethoxysilane (PTES) via a two-step catalytic sol-gel procedure to introduce phenyl groups distributed throughout the silica matrix for chromatographic interaction. The hydrolysis and condensation reactions of precursors were chemically controlled through pH variation by adding hydrochloric acid and dodecylamine, respectively. The structural property of the monolithic column can be easily tailored through adjusting the composition of starting sol solution. The effect of PTES/TEOS ratios on the morphology of the created stationary phases was investigated. A variety of neutral and basic analytes were used to evaluate the column performance. The CEC columns exhibited typical RP chromatographic retention mechanism for neutral compounds and had improved peak shape for basic solutes.
Separation and purification of chlorogenic acid by removal of the impurities compounds co-existed in the product using molecular imprinting technique was firstly reported. In this work, an in situ synthesis method was utilized for the preparation of molecularly imprinted polymer monolithic stationary phase using the impurity molecule (caffeic acid) as template, the mixture of tetrahydrofuran and isooctane as solvent, and methacrylic acid and ethyl glycol dimethacrylate as functional monomer and cross-linker, respectively. The retention behavior of the monolithic polymer to chlorogenic acid molecule, the template and several main impurities compounds in the product was studied and the adsorption capacity of compounds on the stationary phase determined by frontal chromatographic technique. A relatively weak retention of the target product molecule (chlorogenic acid) on the polymer and a strong adsorption capability of the monolith to the template and several main impurities were observed. This might mainly result from the 'shape' difference of chlorogenic acid molecule with the impurities compounds molecules. This approach was shown to be successful for the separation and purification of chlorogenic acid from the extract of Eucommia ulmodies leaves.
A method for direct determination of DL-tetrahydropalmatine (DL-THP) in Corydalis yanhusuo, a traditional Chinese herb, by L-THP imprinted monolithic precolumn on-line/off-line coupling with reversed-phase high performance liquid chromatography (RP-HPLC) was developed. The L-THP imprinted monolithic column has been prepared by in situ polymerization using methacrylic acid (MAA) and ethylene dimethacrylate (EDMA) as functional monomer and cross-linker, respectively. With the optimization of chromatographic conditions, such as mobile phase composition, flow rate, column temperature and sample loading, for the separation of enantiomer, DL-THP was base-line separated on the MIP. The imprinted monolithic column was used as a precolumn for fractionation of the C. yanhusuo extract. Both the non-retained and retained fractions were separated by RP-HPLC. Meanwhile, the D-THP and L-THP can be detected in the non-retained and retained fractions, respectively. Additionally, direct determination of L-THP using molecularly imprinted monolith on-line coupling with a reversed-phase column was acquired.
A monolithic ODS-silica gel column modified by saturating it with lithium dodecylsulfate (Li-DS) was used to demonstrate the high-speed separation of H+ from other mono- and divalent cations, such as Na+, NH4+, K+, Mg2+ and Ca2+ using ion chromatography (IC). Using a 5 mM EDTA-2K solution containing 0.10 mM Li-DS (pH 4.80) as eluent, H+ was eluted with a sharp and symmetrical peak within 1.0 min before other cations at a flow-rate of 1.5 ml min(-1). The rapid elution of H+ and its conductimetric detection could be attributed to the presence of EDTA (HY2-), which can convert H+ ions as anions. i.e. H(+) + H2Y(2-) --> H3Y(-). The acidity of rainwater and deionized water samples was determined using this IC system with satisfactory results.
A monolithic molecularly imprinted polymer (monolithic MIP) for sulfamethoxazole (SMO) was prepared by in situ polymerization method as the HPLC stationary phase. By optimizing the polymerization conditions, the monolithic MIP showed highly specific recognition for the template SMO over its three structurally related analogs. As shown by SEM and the pore size distribution profile, the resultant MIP monolith showed a main pore diameter of 594 nm and a large specific surface area of 124 m2 g(-1), this allowed the mobile phase to flow through the column with low backpressure. Furthermore, the recognition abilities of the monolithic MIP in aqueous and organic media were studied. The results exhibited that the monolithic MIP possessed excellent recognition ability in aqueous media. Hydrophobic interactions, in addition to shape recognition, were the dominant effect for recognition in the mobile phase with high water content. Moreover, the binding sites and the dissociation constant were also determined by frontal chromatography as 122 micromol g(-1) and 1.88 x 10(-5)mol L(-1), respectively, which demonstrated that the obtained SMO-MIP monolith had a high binding capacity and strong affinity ability to the template molecule. Furthermore, the resultant SMO-MIP monolith was used as HPLC column directly to determine the SMO contents in three kinds of pharmaceutical tablets with the optimized aqueous mobile phase.
A room temperature ionic liquid (RTIL)-mediated nonhydrolytic sol-gel (NHSG) protocol was explored for the fabrication of new molecularly imprinted silica-based hybrid monoliths for chiral separation of a basic template zolmitriptan by CEC. The RTIL-mediated NHSG protocol involved free-radical copolymerization and NHSG process. Three carboxylic acids (trifluoromethyl acrylic acid, cinnamic acid, and methacrylic acid (MAA)) were examined as both the functional monomers and the catalysts for the NHSG condensation of methacryloxypropyltrimethoxysilane (MPTMS) to form silica-based framework. RTIL was incorporated to reduce gel shrinkage and also to act as the pore template. The effects of carboxylic acids and RTIL on the performance of the silica-based hybrid molecularly imprinted polymer (MIP) monoliths were investigated in detail to realize excellent chiral recognition and to give new insights into the mechanism of the RTIL-mediated NHSG strategy. Excellent chiral separation of (R)/(S)-zolmitriptan was achieved when the molar ratio of MAA to MPTMS was 1:4 and 1:2 with RTIL involved. The synergism of the free-radical copolymerization of the C=C bond of carboxylic acids and MPTMS with the NHSG condensation of MPTMS catalyzed by the carboxylic acids was demonstrated. The incorporation of RTIL increased porosity, and hence improved selectivity of the prepared hybrid monoliths.
A novel kind of immobilized trypsin reactor based on organic-inorganic hybrid silica monoliths has been developed. With the presence of cetyltrimethyl ammonium bromide (CTAB) in the polymerization mixture, the hybrid silica monolithic support was prepared in a 100 microm i.d. capillary by the sol-gel method with tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) as precursors. Subsequently, the monolith was activated by glutaraldehyde, and trypsin was covalently immobilized. By monitoring the reaction of a decapeptide, C-myc (EQKLISEEDL), the enzymatic activity of the immobilized trypsin was calculated, and the results showed that the digestion speed was about 6600 times faster than that performed in free solution. The performance of such a microreactor was further demonstrated by digesting myoglobin, with the digested products analyzed by microflow reversed-phase liquid chromatography coupled with tandem mass spectrometry (microRPLC-MS/MS). With a stringent threshold for the unambiguous identification of the digests, the yielding sequence coverage for on-column digestion was 92%, the same as that obtained by in-solution digestion, whereas the residence time of myoglobin in the former case was only 30 s, about 1/1440 of that performed in the latter case (12 h). Moreover, such an immobilized trypsin reactor was also successfully applied to the digestion of a mixture of model proteins and proteins extracted from E. coli.
An HPLC-DAD method for determining corticoids in calf feed and in animal feeding water samples using a monolithic column has been developed and validated. The method optimization included the study of binary mobile phases of water and acetonitrile. The optimum separation was achieved at 40 degrees C, with acetonitrile:H(2)O 29:71 v/v used as mobile phase and a 3 ml/min flow-rate, which resulted in their separation in about 5 min. Two reported sample procedures were applied to feed and for animal feeding water samples prior to HPLC. Method validation was carried out according to the EU criteria established for quantitative screening methods. The results indicate that this method is highly specific, reproducible and accurate. The proposed method was found to be robust and unaffected by small variations in the extraction procedure and in HPLC conditions. The developed method for the determination of corticoids in feed and water samples was also found to be suitable for different kinds of feeds and waters.
- Takeuchi