Thermal desorption characterisation of molecularly imprinted polymers. Part II: Use of direct probe GC–MS analysis to study crosslinking effects

A powerful method utilising direct probe thermal desorption GC–MS is presented for the study of molecularly imprinted polymers (MIPs). A series of 2-aminopyridine (2-apy)-imprinted methacrylic acid–ethyleneglycol dimethacrylate (MAA–EGDMA) copolymers were prepared under identical conditions but with varying amounts of EGDMA (crosslinking monomer). The use of appropriate temperature programmes permitted template removal, and the subsequent assessment of polymer affinity and specificity, all of which were found to be dependent on polymer composition and morphology. The system was sufficiently sensitive to identify a specific response of imprinted polymers over nonimprinted counterparts. Correlations were found to exist between thermal desorption analysis and solution phase binding, which was assessed by UV spectroscopy, where specificity was found to diminish with decreasing EGDMA concentration. This was attributed to the increased number of free carboxyl groups in those polymers containing a lower percentage of EGDMA. Thermal desorption profiles obtained for the analyte were found to be unaffected by the physical and chemical properties of the solvent used for analyte reloading. An erratum to this article can be found at     

The effect of molecular imprinting on the pore size distribution of polymers

Molecular imprinting techniques are becoming an increasingly important domain of porous polymers generally, to achieve molecule specific recognition through morphology or stereochemistry of cavities. Imprinting is sought to increase both selectivity and sensitivity where the polymer may be present as particulate, membrane or thin film forms. Here, we detail mechanisms involved in the formation, stability and adsorption of binding sites, through the influence of polymerisation conditions and templates on the porosity of highly crosslinked molecularly imprinted polymers (MIPs). Environmental control represents an important area for porous polymers, here we focus on two template fungicides, iprodione and pyrimethanil, for ethylene glycol dimethacrylate (EGDMA) based polymers. In general, control of the pre-polymerisation interactions were able to vary the surface areas of polymers from 40–60 m² g⁻¹ to 300–436 m² g⁻¹ while pore sizes fell into distributions (a) close to the micropore region at ∼3.8 nm, (b) in the 10 to 20 nm mesopore region and (c) in the 20 to 50 nm mesopore region. The importance of intermolecular interactions and aggregation in the pre-polymerisation solution to the Brunauer, Emmett, Teller (BET) surface areas and pore size distribution of final polymers has been demonstrated by systematic variation of chemical functionality. These effects confirm recent molecular dynamic simulation studies of MIP formation and cavity stability.     

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     

Water-compatible molecularly imprinted polymer for the selective recognition of fluoroquinolone antibiotics in biological samples

A novel water-compatible molecularly imprinted polymer (MIP), prepared with enrofloxacin (ENR) as the template, has been optimised for the selective extraction of fluoroquinolone antibiotics in aqueous media. The results of a morphological characterisation and selectivity tests of the polymer material for ENR and related derivatives are reported. High affinity for the piperazine-based fluoroquinolones marbofloxacin, ciprofloxacin, norfloxacin and ofloxacin was observed, whereas no retention was found for nonrelated antibiotics. Various parameters affecting the extraction efficiency of the polymer have been optimised to achieve selective extraction of the antibiotics from real samples and to reduce nonspecific interactions. These findings resulted in a MISPE/HPLC-FLD method allowing direct extraction of the analytes from aqueous samples with a selective wash using just 50% (v/v) organic solvent. The method showed excellent recoveries and precision when buffered urine samples fortified at five concentration levels (25–250 ng mL⁻¹ each) of marbofloxacin, ciprofloxacin, norfloxacin, enrofloxacin and sarafloxacin were tested (53–88%, RSD 1–10%, n = 3). Moreover, the biological matrix of the aqueous samples did not influence the preconcentration efficiency of the fluoroquinolones on the MIP cartridges; no significant differences were observed between the recovery rates of the antibiotics in buffer and urine samples. The detection limits of the whole process range between 1.9 and 34 ng mL^–1 when 5-mL urine samples are processed. The developed method has been successfully applied to preconcentration of norfloxacin in urine samples of a medicated patient, demonstrating the ability of the novel MIP for selective extraction of fluoroquinolones in urine samples.     

The Syntheses and Characterization of Molecularly Imprinted Polymers for the Controlled Release of Bromhexine

Imprinted polymers are now being increasingly considered for active biomedical uses such as drug delivery. In this work, the use of molecularly imprinted polymers (MIPs) in designing new drug delivery devices was studied. Imprinted polymers were prepared from methacrylic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker), and bromhexine (as a drug template) using bulk polymerization method. The influence of the template/functional monomer proportion and pH on the achievement of MIPs with pore cavities with a high enough affinity for the drug was investigated. The polymeric devices were further characterized by FT-IR, thermogravimetric analysis, scanning electron microscopy, and binding experiments. The imprinted polymers showed a higher affinity for bromhexine and a slower release rate than the non-imprinted polymers. The controlled release of bromhexine from the prepared imprinted polymers was investigated through in vitro dissolution tests by measuring absorbance at λ _max of 310 nm by HPLC-UV. The dissolution media employed were hydrochloric acid at the pH level of 3.0 and phosphate buffers, at pH levels of 6.0 and 8.0, maintained at 37.0 and 25.0 ± 0.5 °C. Results from the analyses showed the ability of MIP polymers to control the release of bromhexine In all cases The imprinted polymers showed a higher affinity for bromhexine and a slower release rate than the non-imprinted polymers. At the pH level of 3.0 and at the temperature of 25 °C, slower release of bromhexine imprinted polymer occurred.     

A catalytically active molecularly imprinted polymer that mimics peroxidase based on hemin: application to the determination of<Emphasis Type="Italic"> p</Emphasis>-aminophenol

Despite the increasing number of applications of molecularly imprinted polymers (MIP) in analytical chemistry, the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase remains as a challenge. In the current work, a new type of molecularly imprinted polymer (MIP) was synthesized with 4-aminophenol (4-APh) as the template and two monomers: hemin, which acts as the catalytic center, and methacrylic acid (MAA), which is used to build the active sites. This work shows that MIP successfully mimics peroxidase. For this purpose, a flow injection analysis system coupled to an amperometric detector was investigated through multivariate analysis. The determination of 4-APh was not affected by the equimolar presence of structurally similar phenol compounds, including catechol, 4-chloro-3-methylphenol, 2-aminophenol, guaiachol, chloroguaiachol and 2-cresol, thus highlighting the good performance of the imprinted polymer. Under the optimized experimental conditions, an analytical curve covering a wide linear response range from 0.8 up to 500 μmol L⁻¹ (r > 0.999) was obtained, and the method gave satisfactory precisions (n = 8), as evaluated via the relative standard deviation (RSD), of 4.1 and 3.2% for solutions of 4-APh of 50 and 500 μmol L⁻¹, respectively. Recoveries of 96–111% from water samples (tap water and river water) spiked with 4-APh were achieved, thus illustrating the accuracy of the proposed system. Figure Schematic presentation of the synthesis of the MIP     

Selective Solid-Phase Extraction of Trace Copper Ions in Aqueous Solution with a Cu(II)-Imprinted Interpenetrating Polymer Network Gel Prepared by Ionic Imprinted Polymer (IIP) Technique

An Cu(II)-imprinted interpenetrating polymer network (IPN) gel of epoxy-diethylenetriamine and methacrylic acid-acrylamide-N,N′-methylene-bis-(acrylamide) was synthesized by the ionic imprint polymer (IIP) technique. The first polymer network is formed by epoxy gelation with diethylenetriamine. The other is formed by copper methacrylate co- polymerization with acrylamide and cross-linker N,N′-methylene-bis-(acrylamide). The adsorption–desorption characteristics of the IPN gel as a highly selective solid-phase extraction (SPE) and preconcentration adsorbent for Cu²⁺ from aqueous solution were investigated. The experimental results show that trace Cu²⁺ ions can be quantitatively enriched at pH 5 with recovery >95%. The maximum static adsorption capacity of the ion-imprinted functionalized gel adsorbent was 76 mg g⁻¹. Comparing with non-imprinted IPN gel, the imprinted IPN gel has higher adsorption capacity and selectivity for Cu²⁺ by the static adsorption–desorption experiment. Simultaneously, the times of adsorption equilibration and complete desorption were remarkably short. The precision (RSD) for 11 replicate adsorbent extractions of 20 ng mL⁻¹ Cu²⁺ was 3.4%. The established procedure was applied to two real water samples with satisfactory results. The prepared ion-imprinted IPN gel adsorbent was shown to be promising for solid-phase extraction coupled with atomic absorption spectrometry (AAS) for the determination of trace copper in real samples. In addition, the coordination interaction of Cu²⁺ and functional groups of the IPN gel adsorbent was primarily discussed by FT-IR spectra.     

Preparation and characterization of a molecularly imprinted polymer by grafting on silica supports: a selective sorbent for patulin toxin

A new molecularly imprinted polymer (MIP) has been prepared on silica beads using the radical “grafting from” polymerization method for selective extraction of minor contaminant mycotoxin of patulin (PTL). After the introduction of amino groups onto the silica surface with 3-aminopropyltriethoxysilane, azo initiator onto the silica surface was achieved by the reaction of surface amino groups with 4,4′-azobis(4-cyanopentanoic acid). The scale-up synthesis of MIP was then carried out in the presence of 6-hydroxynicotinic acid as template substitute, functional, and cross-linking monomers. The prepared sorbent was characterized using FT-IR spectroscopy, scanning electron microscopy, elemental analysis, and the adsorption–desorption selectivity, and the capacity characteristic of the polymer was investigated by a conventional batch adsorption test and Scatchard plot analysis. The results indicated that coated polymers had specific adsorption to PTL as compared with its co-occurring 5-hydroxymethyl-2-furaldehyde (hydroxymethylfurfural (HMF)), at the same bulk concentration for solution of PTL and HMF, the maximum absorbance in the solid-phase extraction (SPE) method to PTL were 93.97% or 0.654 μg/mg while to HMF they were 76.89% or 0.496 μg/mg. Scatchard analysis revealed that two classes of binding sites were formed in PTL-MIP with dissociation constants of 3.2 × 10⁻² and 5.0 × 10⁻³ mg/mL and the affinity binding sites of 8.029 and 1.364 mg/g, respectively. The recoveries of PTL were more than 90% for the developed MISPE and around 75% for the traditional liquid–liquid extraction in spiked apple juice samples. It was concluded that the method is suitable for the scale-up synthesis of PTL-MIP grafted on silica, and the polymer can be effectively applied as SPE coupled with high-performance liquid chromatography (HPLC) for the determination of PTL in apple juice or other related products.     

Preparation of bovine hemoglobin-imprinted polymer beads via the photografting surface-modified method

Molecularly imprinted polymers (MIPs), based on photografting surface-modified polystyrene beads as matrices, were prepared with acrylamide as the functional monomer, bovine hemoglobin as the template molecule and N, N′-methylene bisacrylamide as the crosslinker in a phosphate buffer. The results of IR, scanning electron microscope (SEM) and elemental analyses demonstrated the formation of a grafting polymer layer on the polystyrene-bead surface. Subsequent removal of the template left behind cavities on the surface of the polymer matrix with a shape and an arrangement of functional groups having complementary binding sites with the original template molecule. The adsorption studies showed that the imprinted polymers have a good adsorption capacity and specific recognition for bovine hemoglobin as the template molecule. Our results demonstrated that the polymer prepared via the photografting surface-modified method exhibited better selectivity for the template. Attempts to employ the new method in molecular imprinting techniques may introduce new applications for MIPs and facilitate probable protein separation and purification. __________ Translated from Chemical Journal of Chinese Universities, 2008, 29(1): 64–70     

Chiral effects of alkyl-substituted derivatives of N,O-bismethacryloyl ethanolamine on the performance of one monomer molecularly imprinted polymers (OMNiMIPs)

New monomers were synthesized and evaluated for their molecular imprinting performance by a recently discovered methodology referred to as one monomer molecularly imprinted polymers (OMNiMIPs). The structural design of the new monomers was based on a lead compound methacrylamidoethyl methacrylate (1) used for the synthesis of OMNiMIP1, and introduced alkyl groups of various sizes at the α-amino position of the lead compound. Enantioselectivity, determined by liquid chromatography, was used to compare the performance of the imprinted polymers. Methyl substitution provided crosslinker 5 (2-methacrylamidopropyl methacrylate), which upon imprint polymerization afforded OMNiMIP5 with approximately the same enantioselectivity (α = 3.8) as OMNiMP1 (α = 3.7) made with the lead compound (1). The other two monomers (6 and 7) with larger alkyl substitutions (isopropyl and sec-butyl respectively) resulted in OMNiMIPs with low selectivity values (α = 1.0 and 1.2 respectively). Last, a strong influence of diastereomeric complexes on OMNiMIP5 selectivity was determined, with L/L and D/D monomer/template pairs giving α values of 3.6–3.8, while L/D and D/L monomer/template pairs had α values of 2.3–2.4. There is no intrinsic enantioselectivity seen for the OMNiMIP5 control polymer made without template at all, giving an α value of 1.03. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Chromatographic evaluation of polymers imprinted with analogs of chloramphenicol and application to selective solid-phase extraction

To obtain a highly selective material for the antibiotic chloramphenicol, which has several harmful side effects in humans, different molecularly imprinted polymers (MIPs) were prepared. In order to avoid a major traditional drawback associated with MIPs of residual template bleeding, molecules that are structurally related to chloramphenicol were used as templates for polymer synthesis. Chromatographic evaluation indicated that the employed template imparted a significant influence on the recognition properties of the corresponding polymer. A strong retention of chloramphenicol under nonpolar elution conditions (k = 68.03, IF = 17.72) and under aqueous elution conditions (k = 92.44, IF = 1.35) was achieved. After chromatographic evaluation, the MIP was utilized as the recognition sorbent in a solid-phase extraction to determine chloramphenicol using either an organic or aqueous washing solvent. Recoveries of nearly 100% from the chloramphenicol standard solution and nearly 90% from honey samples spiked with chloramphenicol were attained. Furthermore, the applicability of the MIP for sample cleanup was demonstrated.     

On-line ionic imprinted polymer selective solid-phase extraction of nickel and lead from seawater and their determination by inductively coupled plasma-optical emission spectrometry

Nickel(II) and lead(II) ionic imprinted 8-hydroxyquinoline polymers were synthesized by a precipitation polymerization technique and were used as selective solid phase extraction supports for the determination of nickel and lead in seawater by flow injection solid phase extraction on-line inductively coupled plasma-optical emission spectrometry. An optimum loading flow rate of 2.25 mL min⁻¹ for 2 min and an elution flow rate of 2.25 mL min⁻¹ for 1 min gave an enrichment factor of 15 for nickel. However, a low dynamic capacity and/or rate for adsorption and desorption was found for lead ionic imprinted polymer and a flow rate of 3.00 mL min⁻¹ for 4-min loading and a flow rate of 2.25 mL min⁻¹ for 1-min elution gave a enrichment factor of 5. The limit of detection was 0.33 μg L⁻¹ for nickel and 1.88 μg L⁻¹ for lead, with a precision (n = 11) of 8% (2.37 μg Ni L⁻¹) for nickel and 11% (8.38 μg Pb L⁻¹) for lead. Accuracy was also assessed by analyzing SLEW-3 (estuarine water) and TM-24 (lake water) certified reference materials, and the values determined were in good agreement with the certified concentrations.     

Covalent imprinted polymer for selective and rapid enrichment of ractopamine by a noncovalent approach

A novel molecularly imprinted polymer (MIP) for the separation and concentration of ractopamine (RAC) was prepared by a covalent imprinting approach and the template was removed successfully by hydrolysis, so that four carboxylic acid groups were left in the cavities and could specifically rebind RAC through noncovalent interaction: hydrogen bonding. The conditions for synthesis of the MIP were optimized during the polymerization process, and a molar ratio of template–functional monomer complexes to cross-linker of 1:3 was confirmed. The adsorption capacity of the MIP was 4.1-fold that of the nonimprinted polymer, and the adsorption reaction reached equilibrium after 25 min at 50 mg L^-1 concentration. The results of the competitive adsorption test showed that the MIPs had specific recognition ability for the analyte RAC. In addition, the important factors affecting the efficiency of the method which was developed using the MIPs as a solid-phase sorbent for separation and determination of RAC combined with high-performance liquid chromatography with fluorescence detection were optimized. Under the optimum experimental conditions, the linear range of the calibration curve in the method was 0.05-5 μg L^-1 (R ² = 0.98) and the limit of detection (signal-to-noise ratio of 3) was 0.01 μg L^-1. The proposed method was applied to determination of RAC in spiked feedstuffs and urine samples, with recoveries ranging from 74.17 to 114.46% and relative standard deviation (n = 3) below 4.55 in all cases.     

Molecular imprinting polymerization by Fenton reaction

The aim of this study is the preparation of molecularly imprinted polymers by employing a redox pair as initiator system. Bulk molecularly imprinted polymers were synthesized by using Fenton reagents as initiator system. Theophylline, methacrylic acid, and ethylene glycol dimethacrylate were employed as model template, functional monomer, and crosslinking agent, respectively. Conventional imprinted polymers were also prepared by using 2,2′-azoisobutyronitrile in order to evaluate the efficiency of the proposed initiator system. Redox molecularly imprinted polymers and conventional molecularly imprinted polymers were characterized by water uptake measurement, while the imprinting effect of synthesized polymers were evaluated by performing binding experiments in organic (acetonitrile) and in water (buffered water solution at pH = 7.4) media.     

Competitive capacitive biosensing technique (CCBT): A novel technique for monitoring low molecular mass analytes using glucose assay as a model study

A novel technique for monitoring of low molecular mass analytes using a flow-injection capacitive biosensor is presented. The method is based on the ability of a small molecular mass analyte to displace a large analyte–carrier conjugate from the binding sites of an immobilized biorecognition element with weak affinity to both compounds. A model study was performed on glucose as the small molecular mass analyte. In the absence of glucose, binding of a glucose polymer or a glycoconjugate to concanavalin A results in a capacitance decrease. Upon introduction of glucose, it displaces a part of the bound glucose polymer or glycoconjugate leading to a partial restoration of capacitance. Experimental results show that the change in capacitance depends linearly on glucose concentration within the range from 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, corresponding to 1.8 μg ml⁻¹ to 18 mg ml⁻¹ in a logarithmic plot, with a detection limit of 1.0 × 10⁻⁶ (0.18 μg ml⁻¹) under optimized conditions. In addition, by modifying the molecular mass of the glucose polymer, amount of biorecognition element, and buffer composition, we were able to tune the analyte-sensing range. The developed technique has the benefits of expanded dynamic range, high sensitivity, and excellent reusability.     

Synthesis and characterization of molecularly imprinted polymers for recognition of ciprofloxacin

A molecularly imprinted polymer (MIP), with special molecule recognition properties of ciprofloxacin (CIP), was prepared by thermal polymerization in which ciprofloxacin acted as template molecule, α-methacrylic acid (MAA) acted as functional monomer and trimethylolpropane trimethylacrylate (TRIM) acted as crosslinker. The optimized ratio was determined to be n(CIP): n (MMA):n(TRIM)51:6:16 by investigation of the effects of different concentrations of functional monomer and the crosslinker on the MIP’s recognition properties. Equilibrium binding experiment was used to investigate the adsorption dynamics, the binding ability to template molecule and the substrate selectivity. Scatchard analysis was used to study the MIP’s binding characteristic to template molecule. The results indicated that MIP has higher adsorption ability and selectivity. The equilibrium distribution coefficient K _D was 41.64 and the separation factor α was 1.62. Scatchard analysis showed that two different kinds of binding sites were produced in the polymer matrix and their dissociation constants were calculated to be K _d1 = 5.249 × 10⁻⁵ mol·L⁻¹, K _d2 = 2.237 × 10⁻³ mol·L⁻¹. __________ Translated from Chemistry, 2008, 71(2): 132–137     

Impedance studies on the 5-V cathode material,LiCoPO<Subscript>4</Subscript>

Olivine-structured LiCoPO₄ is synthesized by a Pechini-type polymer precursor method. The structure and the morphology of the compounds are studied by the Rietveld-refined X-ray diffraction, scanning electron microscopy, Brunauer, Emmett, and Teller surface area technique, infrared spectroscopy, and Raman spectroscopy techniques, respectively. The ionic conductivity (σ ionic), dielectric, and electric modulus properties of LiCoPO₄ are investigated on sintered pellets by impedance spectroscopy in the temperature range, 27–50 °C. The σ (ionic) values at 27 and 50 °C are 8.8 × 10⁻⁸ and 49 × 10⁻⁸ S cm⁻¹, respectively with an energy of activation (E _a) = 0.43 eV. The electric modulus studies suggest the presence of non-Debye type of relaxation. Preliminary charge–discharge cycling data are presented.     

Dopamine sensor based on molecularly imprinted electrosynthesized polymers

Molecularly imprinted polymers (MIPs) have been applied as molecular recognition elements to chemical sensors. In this paper, we combined the use of MIPs and electropolymerization to produce a sensor which was capable of detecting dopamine (DA). The MIP electrode was obtained by electrocopolymerization of o-phenylenediamine and resorcinol in the presence of the template molecular DA. The MIP electrode exhibited a much higher current response compared with the non-imprinted electrode. The response of the imprinted sensor to DA was linearly proportional to its concentration over the range 5.0 × 10⁻⁷-4.0 × 10⁻⁵ M. The detection limit of DA is 0.13 μM (S/N = 3). Moreover, the proposed method could discriminate between DA and its analogs, such as ascorbic acid and uric acid. This method was successfully applied to the determination of DA in dopamine hydrochloride injection and healthy human blood serum. These results revealed that such a sensor fulfilled the selectivity, sensitivity, sped, and simplicity requirements for DA detection and provided possibilities of clinical application in physiological fields.     

Preparation of ultramicro-, micro-, and supermicroporous carbon adsorbents by template procedure

The new template procedure for preparing ultramicro-, micro-, and supermicroporous carbon adsorbents is proposed on the basis of the use of two polymers with different thermal stabilities as a template matrix and a carbonizable carbon source. The polymeric template matrix is removed by thermal decomposition in the low-temperature pyrolysis of the polymer mixture, whereas the second polymer component of a mixture is transformed into a carbonizate. The resultant monolithic carbonizate is the polymeric matrix replica and represents a molecular-sieve ultramicroporous carbon adsorbent, which adsorbs water vapor at 293 K and does not adsorb nitrogen vapor at 77 K. The activation of this carbonizate with water vapor leads to a series of micro-and supermicroporous carbon adsorbents with a broad range of the parameters of a pore structure: BET specific surface area S _BET is 610–2130 m²/g, micropore volume W ₀ is 0.20–0.69 cm³/g, micropore half-width x ₀ (slit model) is 0.20–0.70 nm, mesopore specific area S _me is 20–1000 m²/g, and characteristic adsorption energy E ₀ is 15.6–27.4 kJ/mol. Original Russian Text ? O.K. Krasil’nikova, A.M. Voloshchuk, A.E. Evsyukhin, N.Y. Lomovsakaya, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 207–213.     

Study on an on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography for separation and determination of trace estrone in environment

Estrone is one of the important potential endocrine-disrupting compounds, and the sensitive and reliable analytical methods for the determination of estrone are required for the assurance of human health. In this paper, using estrone as template molecule, 3-aminopropyltriethoxysilane as function monomer, and tetraethoxysilicane as cross-linker, a highly selective molecularly imprinted microsphere was synthesized by surface molecular imprinting technique combined with a sol–gel process. The imprinted material was characterized by the Fourier transform infrared and static adsorption experiments, and the results showed that it exhibited good recognition and selective ability for estrone. A novel method for separation and determination of trace estrone in environmental sample was developed using on-line molecularly imprinted solid-phase extraction coupled to high-performance liquid chromatography. With a sample loading flow rate of 2.6 mL min⁻¹ for a 9.6-min extraction, the enrichment factor obtained by the slopes of the linear portion in comparison with the direct injection of 10 μL standard sample solution was 1,045. The detection limit (S/N = 3) was 5.7 ng L⁻¹, and the relative standard deviations for nine replicate extractions of 5.0 μg L⁻¹ estrone was less than 10.0%. This method was evaluated for quantitative determination of estrone in well and lake water samples spiked at two levels (0.5 and 1.0 μg L⁻¹) with recoveries ranging from 86% to 95%.