A Novel Electrochemical Sensor Based on Molecularly Imprinted Solid-Phase Extraction for Rapid Determination of Ractopamine in Pig Urine

A new absorbent (polymer) for solid-phase extraction of ractopamine (RAC) was synthesized on the multi-walled carbon nanotubes (MWCTs) using grafting technique and surface imprinting methods. The superficial characteristics of the polymer were studied by scanning electron microscopy (SEM) and UN spectrometry was applied to investigate the static and kinetic adsorption capacity of the new absorbent. After the experimental conditions for the solid-phase extraction of RAC were optimized, a sensing system for the determination of RAC was established by connecting the solid-phase extraction column with a portable amperometric sensing system. The SEM study showed that numbers of imprinted micro-pores were exhibited on the surface of the imprinted polymers, and the absorption experiments indicated that the molecularly imprinted absorbent possessed satisfactory kinetics for the adsorption of ractopamine. The current response of the amperometric sensor demonstrated a linear correlation to the concentration of RAC over the range of 50 to 450 nM (r = 0.998) and the detection limit was 15 nM. Satisfactory sensitivity and stability was also presented under the optimized experimental conditions. The recoveries of RAC samples reached 87.3–94.8% in urine sample.     

Synthesis and characterization of molecularly imprinted polymers for selective solid-phase extraction of pseudoephedrine

Molecular imprinted solid-phase extraction (MISPE) is a well known technique for the selective extraction and pre-concentration of analytes, are present at low levels in chemically complex materials. Herein, water-soluble, molecularly imprinted polymers (MIP) were prepared for solid-phase extraction of pseudoephedrine hydrochloride (PSE), which was monitored at 256 nm by the UV spectroscopy. MISPE conditions were optimized to allow the selective and determination of PSE in aqueous samples and composite materials, such as biological fluids and human urine. MIP was prepared by precipitation polymerization method, using methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross-linking agent in either acetonitrile or chloroform. The results suggest that the obtained MISPE exhibits high affinity for PSE, and the imprinted polymer demonstrates much higher efficiency than a non-imprinted polymer (NIP). The imprinting-induced extraction was confirmed by the determination of recovery values for NIP (4%) and MIP (80%) polymers, respectively. The binding capacity of the MIP for PSE was found of 47.6 mg g⁻¹.     

Molecularly imprinted solid-phase extraction for the selective determination of bromhexine in human serum and urine with high performance liquid chromatography

In this work, a novel method is described for the determination of bromhexine in biological fluids using molecularly imprinted solid-phase extraction as the sample cleanup technique combined with high performance liquid chromatography (HPLC). The water-compatible molecularly imprinted polymers (MIPs) were prepared using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker, chloroform as porogen and bromhexine as the template molecule. The novel imprinted polymer was used as a solid-phase extraction sorbent for the extraction of bromhexine from human serum and urine. Various parameters affecting the extraction efficiency of the polymer have been evaluated. The optimal conditions for molecularly imprinted solid-phase extraction (MISPE) consisted of conditioning 1 mL methanol and 1 mL of deionized water at neutral pH, loading of 5 mL of the water sample (25 μg L⁻¹) at pH 6.0, washing using 2 mL acetonitrile/acetone (1/4, v/v) and elution with 3× 1 mL methanol/acetic acid (10/1, v/v). The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of bromhexine. Results from the HPLC analyses showed that the calibration curve of bromhexine using MIP from human serum and urine is linear in the ranges of 0.5-100 and 1.5-100 μg L⁻¹ with good precisions (3.3% and 2.8% for 5.0 μg L⁻¹), respectively. The recoveries for serum and urine samples were higher than 92%.     

Ability of a salivary intrinsically unstructured protein to bind different tannin targets revealed by mass spectrometry

Superporous monolithic hydrogels (cryogel monoliths) are elastic, sponge-like materials that can be prepared in an aqueous medium through a cryotropic gelation technique. These monoliths show interesting properties for the development of high-throughput solid-phase extraction supports to treat large volumes of aqueous samples. In this work, a cryogel-supported molecularly imprinted solid-phase extraction approach for the endocrine disruptor bisphenol A (BPA) from river water and wine samples is presented. An imprinted polymer with molecular recognition properties for BPA was prepared in acetonitrile by thermal polymerization of a mixture of 4,4′-dihydroxy-2,2-diphenyl-1,1,1,3,3,3-trifluoropropane as a mimic template of BPA, 4-vinylpyridine and trimethylolpropane trimethacrylate in a molar ratio of 1 + 6 + 6. Fine imprinted particles (<10 μm) were embedded in a poly-acrylamide-co-N,N′-methylenbisacrylamide cryogel obtained by ammonium persulfate-induced cryopolymerization at −18 °C. The resulting monolithic gel was evaluated for its use as a sorbent support in an off-line solid-phase extraction approach to recover BPA from dilute aqueous samples with minimum pre-loading work-up. The optimized extraction protocol resulted in a reliable MISPE method suitable to selectively extract and preconcentrate BPA from river water and red wine samples, demonstrating the practical feasibility of cryogel-trapped imprinted polymers as solid-phase extraction materials     

In situ synthesis of molecularly imprinted polymers on glass microspheres in a column

A facile method to fabricate molecularly imprinted polymers (MIPs) on glass microspheres in a column was developed. The column was prepacked with glass microspheres, and then the prepolymerization mixture was injected into the interstitial volume of the column. The polymerization took place in situ and the column could be directly used for high-performance liquid chromatography after the template had been removed. The template consumption was reduced greatly because the prepolymerization mixture just filled the interstitial volume between the glass microspheres in the column. The MIPs obtained exhibited better kinetic properties, higher efficiency, and low back pressure of the column. Emodin imprinted polymers were prepared by this method and were used for solid-phase extraction.     

Molecularly imprinted polymer for the selective extraction of luteolin from Chrysanthemum morifolium Ramat

In this work, luteolin‐imprinted polymers were prepared by noncovalent precipitation polymerization for the first time. Their structural features and morphologies were analyzed by using Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The adsorption experiments revealed that the luteolin‐imprinted polymers presented high selective recognition property to luteolin. The selectivity experiment showed that the adsorption capacity and selectivity of polymers to luteolin was higher than that of three structural analogs, including quercetin, isorhamnetin, and ombuin. Furthermore, an efficient method based on luteolin‐imprinted polymers coupled with solid‐phase extraction was developed for the pretreatment of luteolin from Chrysanthemum morifolium Ramat. The results demonstrated that the luteolin‐imprinted polymers coupled with solid phase extraction method was proven to be a potentially competitive technique for the separation and enrichment of luteolin in complex samples such as Chinese patent medicines and biological samples.     

Solid-phase extraction using a molecularly imprinted polymer for the selective purification and preconcentration of norfloxacin from seawater

Abstract

A highly selective and effective method for the purification and preconcentration of norfloxacin (NFX) in seawater samples was developed based on molecularly imprinted solid-phase extraction (MISPE). The molecularly imprinted polymer was synthesized by precipitation polymerization. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were used as the functional monomer and crosslinker, respectively. The resulting molecularly imprinted polymer (MIP) showed high adsorption for NFX and was selective for its solid-phase extraction. An offline MISPE method followed by high performance liquid chromatography with diode array detection was established for the determination of NFX in seawater. The recoveries of spiked seawater samples using the MISPE columns were satisfactorily higher than 77.6%. The relative standard deviation was less than 5.60%, and the limit of detection was 0.027?μg L^?1. Four seawater samples obtained from the Bohai Sea were analyzed, and NFX was found only at one location at a concentration of 0.280?μg L^?1.     

Room temperature ionic liquid-mediated molecularly imprinted polymer monolith for the selective recognition of quinolones in pork samples

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.     

Selective Preconcentration of Mezlocillin from Eggs by Molecularly Imprinted Polymers on Silica

Surface molecularly imprinted polymers for mezlocillin were used for the selective solid-phase extraction of mezlocillin from eggs. The molecularly imprinted polymers were prepared using mezlocillin as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, silica particle as the support and were characterized by infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The adsorption properties of polymers were investigated in detail. The obtained polymers provided high imprinting efficiency to mezlocillin with an imprinting factor of 3.72 and were used as selective sorbents for mezlocillin. Molecularly imprinted solid-phase extraction followed by high-performance liquid chromatography was used for the determination of mezlocillin in eggs and the conditions were evaluated. The average recovery of mezlocillin in fortified eggs was between 69.8 and 82.3% with a relative standard deviation less than 6.9%. The results demonstrate the application of molecularly imprinted polymers for the extraction of mezlocillin from biological samples.     

Innovative method for the enrichment of high‐polarity bioactive molecules present at low concentrations in complex matrices

Ginsenoside Rg1 is a valuable bioactive molecule but its high polarity and low concentration in complex mixtures makes it a challenge to separate Ginsenoside Rg1 from other saponins with similar structures, resulting in low extraction efficiency. The successful development of effective Rg1 molecularly imprinted polymers that exhibit high selectivity and adsorption may offer an improved method for the enrichment of active compounds. In this work, molecularly imprinted polymers were prepared with two different methods, precipitation polymerization or surface imprinted polymerization. Comparison of the adsorption abilities showed higher adsorption of the surface molecularly imprinted polymers prepared by surface imprinted polymerization, 46.80 mg/g, compared to the 27.74 mg/g observed for the molecularly imprinted polymers prepared by precipitation polymerization. Therefore, for higher adsorption of the highly polar Rg1, surface imprinted polymerization is a superior technique to make Rg1 molecularly imprinted polymers. The prepared surface molecularly imprinted polymers were tested as a solid‐phase extraction column to directionally enrich Rg1 and its analogues from ginseng tea and total ginseng extracts. The column with surface molecularly imprinted polymers showed higher enrichment efficiency and better selectivity than a C₁₈ solid‐phase extraction column. Overall, a new, innovative method was developed to efficiently enrich high‐polarity bioactive molecules present at low concentrations in complex matrices.     

Selective solid-phase extraction of dibutyl phthalate from soybean milk using molecular imprinted polymers

An analysis method is reported for dibutyl phthalate and related compounds with high selectivity and sensitivity by using the selective molecularly imprinted solid-phase extraction (MISPE) technique. In this report, dibutyl phthalate (DBP) is employed as the template molecule, and the molecularly imprinted polymers (MIPs) are synthesized through the bulk polymerization of methacrylic acid (MAA). The Scatchard plot suggests that the template-polymer system has two-site binding behavior with the dissociation constants of 0.5187 and 0.01898 mmol L⁻¹, respectively. The rebinding test, based on the MISPE column technique, shows the recoveries of soybean milk samples spiked with 5 phthalates are in the range of 75.8-107.5% with the relative standard deviations of 1.80-10.08%, indicating the feasibility of the prepared MIPs for phthalates extraction. Finally, the method is used to analyze the trace level of phthalates in commercial soybean milk.     

Preparation and evaluation of molecularly imprinted microspheres for solid-phase extraction of 1,4-hydroxybenzoic acid esters in soy

Molecularly imprinted microspheres (MIMs) were prepared by precipitation polymerization for the binding and recognition of 1,4-hydroxybenzoic acid esters. Ethyl p-hydroxybenzoate (EtPHB) was used as the template molecule, methacrylic acid as the functional monomer, ethylene dimethacrylate as the linking agent. It was evaluated by solid-phase extraction column packed with MIMs combined with liquid chromatography to determine trace preservatives including benzoic acid, methyl p-hydroxybenzoate, EtPHB, propyl p-hydroxybenzoate in food products. A solid-phase extraction based on MIM procedure was used to isolate four additives from the food matrix before quantitative analysis. The Scatchard plot suggested that the template-polymer system had two-site binding behavior with the dissociation constants of 0.3577 and 3.952 mg/g, respectively. The rebinding test, based on the molecularly imprinted solid-phase extraction column technique, showed the recoveries of soy samples spiked with four additives within 88.4-110.6%, with the relative standard deviations of 1.97-3.82%. Finally, the method was successfully applied for the analysis of parabens in foodstuff without traditional pretreatment.     

Supramolecular recognition of estrogens via molecularly imprinted polymers

The isolation and preconcentration of estrogens from new types of biological samples (acellular and protein-free simulated body fluid) by molecularly imprinted solid-phase extraction has been described. In this technique, supramolecular receptors, namely molecularly imprinted polymers (MIPs) are used as a sorbent material. The recognition sites of MIPs were prepared by non-covalent multiple interactions and formed with the target 17β-estradiol as a template molecule. High-performance liquid chromatography with spectroscopic UV, selective, and a sensitive electrochemical CoulArray detector was used for the determination of 17β-estradiol, estrone, and estriol in simulated body fluid which mimicked human plasma.     

Determination of enrofloxacin and ciprofloxacin in milk using molecularly imprinted solid-phase extraction

A molecularly imprinted solid-phase extraction procedure was developed for the simultaneous identification of enrofloxacin and its active metabolite, ciprofloxacin, in milk samples. Water-compatible molecularly imprinted polymers synthesized in a water-methanol system show a high degree of cross-reactivity for enrofloxacin and ciprofloxacin in aqueous environments. The imprinted particles were applied as selective sorbents in a solid-phase extraction process focusing upon complex milk matrices, which allowed the matrix compounds present in milk samples to be removed effectively. The extracts were sufficiently clean for further chromatographic analysis, and no interference originating from the biological matrix was observed. The mean recoveries of enrofloxacin and ciprofloxacin from milk sample were 82.6-93.5% and 81.2-94.8%, respectively, with the RSD less than 7.5%. This method is simple and sensitive, and is therefore an alternative tool to the existing HPLC methods for analyzing residual enrofloxacin and ciprofloxacin in biological samples.     

Determination of Chlorogenic Acid and Rutinum in Herba Artemisiae Scopariae with Multitemplate Molecularly Imprinted Polymers for Solid-phase Extraction with High-performance Liquid Chromatography

Novel multitemplate molecularly imprinted polymers were prepared using mixtures of chlorogenic acid and rutinum as molecular templates, acrylamide as a functional monomer, divinylbenzene as the cross-linker, and 20:80 methanol:acetone as the porogen. The polymers were assessed for solid-phase extraction (SPE) for the purification of two compounds from Herba Artemisiae Scopariae. The synthesized molecularly imprinted polymers were identified by infrared spectroscopy and scanning electron microscopy. Systematic characterization of the functional monomer and porogens on the recognition properties of the molecularly imprinted polymers were carried out. Comparison with single-template molecularly imprinted polymers showed that the multitemplate molecular polymers exhibited higher selectivity and adsorption capacity for multiple analytes. The optimization of washing solvent as 1:9 acetone:water and the elution solvent as 9:1 acetonitrile:acetic acid provided a reliable analytical method with strong recognition toward multiple analytes in Herba Artemisiae Scopariae extracts with satisfactory recoveries of 89.6% for chlorogenic acid and 93.8% for rutinum. These results demonstrate that the multitemplate molecularly imprinted polymers coupled with SPE are effective for the selective purification of bioactive compounds in complex samples.     

Development of a selective molecularly imprinted polymer-based solid-phase extraction for indomethacin from water samples

A selective molecularly imprinted solid-phase extraction (MISPE) for indomethacin (IDM) from water samples was developed. Using IDM as template molecule, acrylamide (AM) or methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and bulk or suspension polymerization as the synthetic method, three molecularly imprinted polymers (MIPs) were synthesized and characterized with a rebinding experiment. It was found that the MIP of AM-EDMA produced by bulk polymerization showed the highest binding capacity for IDM, and so it was chosen for subsequent experiments, such as those testing the selectivity and recognition binding sites. Scatchard analysis revealed that at least two kinds of binding sites formed in the MIP, with the dissociation constants of 7.8 μmol L⁻¹ and 127.2 μmol L⁻¹, respectively. Besides IDM, three structurally related compounds — acemetacin, oxaprozin and ibuprofen — were employed for selectivity tests. It was observed that the MIP exhibited the highest selective rebinding to IDM. Accordingly, the MIP was used as a solid-phase extraction sorbent for the extraction and enrichment of IDM in water samples. The extraction conditions of the MISPE column for IDM were optimized to be: chloroform or water as loading solvent, chloroform with 20% acetonitrile as washing solution, and methanol as eluting solvent. Water samples with or without spiking were extracted by the MISPE column and analyzed by HPLC. No detectable IDM was observed in tap water and the content of IDM in a river water sample was found to be 1.8 ng mL⁻¹. The extraction efficiencies of the MISPE column for IDM in spiked tap and river water were acceptable (87.2% and 83.5%, respectively), demonstrating the feasibility of the prepared MIP for IDM extraction. Figure Molecularly imprinted polymer-based solid-phase extraction for indomethacin     

Water-compatible molecularly imprinted polymers for efficient direct injection on-line solid-phase extraction of ropivacaine and bupivacaine from human plasma

Two novel molecularly imprinted polymers (MIPs) selected from a combinatorial library of bupivacaine imprinted polymers were used for selective on-line solid-phase extraction of bupivacaine and ropivacaine from human plasma. The MIPs were prepared using methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linking monomer and in addition hydroxyethylmethacrylate to render the polymer surface hydrophilic. The novel MIPs showed high selectivity for the analytes and required fewer and lower concentrations of additives to suppress non-specific adsorption compared with a conventional MIP. This enabled the development of an on-line system for direct extraction of buffered plasma. Selective extraction was achieved without the use of time-consuming solvent switch steps, and transfer of the analytes from the MIP column to the analytical column was carried out under aqueous conditions fully compatible with reversed-phase LC gradient separation of analyte and internal standard. The MIPs showed excellent aqueous compatibility and yielded extractions with acceptable recovery and high selectivity.     

Rapid and selective determination of urinary lysozyme based on magnetic molecularly imprinted polymers extraction followed by chemiluminescence detection

A rapid, low cost and selective chemiluminescence method coupled with magnetic molecularly imprinted polymers extraction was developed to detect lysozyme in human urine samples. Compared with traditional solid-phase extraction, this method could achieve selective extraction for the lysozyme, avoid the time consuming elution from a column or centrifugation steps, and then showed great potential in the high-throughput screening of clinical samples. The parameters affecting the performance of extraction and chemiluminescence were investigated. Under optimal conditions, the whole analytical procedure was completed within 12 min and spiked recovery ranged from 90.1% to 103.7% (R.S.D.≤6.7%). The limit of quantitation was 5 ng mL(-1). Furthermore, the results obtained by the proposed method were linearly correlated to those by commercial lysozyme detection kit (r=0.9595). Finally, the validated method was used to measure the urinary lysozyme of renal disease patients and healthy controls. The results confirmed the reliability and practicality of the protocol and revealed a good perspective of this method for biological sample analysis.     

Novel enrofloxacin imprinted polymer applied to the solid-phase extraction of fluorinated quinolones from urine and tissue samples

A new molecularly imprinted polymer, prepared following a non-covalent approach, was synthesised using enrofloxacin as a template molecule. The imprinting effect of the polymer was verified by chromatographic evaluation and, interestingly, this evaluation also revealed that the imprinted polymer showed a high degree of cross-reactivity for ciprofloxacin, the major metabolite of enrofloxacin. The molecularly imprinted polymer was then applied as a selective sorbent in a two-step solid-phase extraction method focussing upon complex biological matrices, specifically human urine and pig liver. This two-step solid-phase extraction protocol, in which a commercial Oasis HLB cartridge and a molecularly imprinted solid-phase extraction cartridge were combined, allowed enrofloxacin and ciprofloxacin to be determined by liquid chromatography coupled to a UV detector at levels below the maximum residue limits established by the European Union. The quantification and detection limits in tissue samples of enrofloxacin and ciprofloxacin were established at 50 μg kg⁻¹ and 30 μg kg⁻¹, respectively.     

A novel sol-gel-material prepared by a surface imprinting technique for the selective solid-phase extraction of bisphenol A

A novel and simple imprinted amino-functionalized silica gel material was synthesized by combining a surface molecular imprinting technique with a sol-gel process on the supporter of activated silica gel for solid-phase extraction-high performance liquid chromatography (SPE-HPLC) determination of bisphenol A (BPA). Non-imprinted silica sorbent was synthesized without the addition of BPA using the same procedure as that of BPA-imprinted silica sorbent. The BPA-imprinted silica sorbent and non-imprinted silica sorbent were characterized by FT-IR and the static adsorption experiments. The prepared BPA-imprinted silica sorbent showed high adsorption capacity, significant selectivity and good site accessibility for BPA. The maximum static adsorption capacity of the BPA-imprinted and non-imprinted silica sorbent for BPA was 68.9 and 34.0 mg g⁻¹, respectively. The relatively selective factor value of this BPA-imprinted silica sorbent was 4.5. Furthermore, the difference of the retention characteristics of BPA on the C₈ SPE column and BPA-imprinted silica SPE (MIP-SPE) was compared. The MIP-SPE-HPLC method showed higher selectivity to BPA than the traditional SPE-HPLC method. At last, the BPA-imprinted polymers were used as the sorbent in solid-phase extraction to determine BPA in water samples with satisfactory recovery higher than 99% (R.S.D. 3.7%).