Silica nanoparticle supported molecularly imprinted polymer layers with varied degrees of crosslinking for lysozyme recognition

Surface imprinting over nanosized support materials is particularly suitable for protein templates, considering the problems with mass transfer limitation and low binding capacity. Previously we have demonstrated a strategy for surface protein imprinting over vinyl-modified silica nanopartiles with lysozyme as a model template by polymerization in high-dilution monomer solution to prevent macrogelation. Herein, the synthesis process was further studied toward enhancement of the imprinting performance by examining the effect of several synthesis conditions. Interestingly, the feed crosslinking degree was found to have a great impact on the thickness of the formed imprinting polymer layers and the recognition properties of the resulting imprinted materials. The imprinted particles with a crosslinking degree up to 50% showed the best imprinting effect. The imprinting factor achieved 2.89 and the specific binding reached 23.3 mg g⁻¹, which are greatly increased compared to those of the lowly crosslinked imprinted materials reported previously. Moreover, the relatively high crosslinking degree led to no significant retarding of the binding kinetics to the imprinted particles, and the saturated adsorption was reached within 10 min. Therefore, this may be a promising method for protein imprinting.     

An optical sensor for the determination of digoxin in serum samples based on a molecularly imprinted polymer membrane

This paper reports the synthesis and testing of a molecularly imprinted polymer membrane for digoxin analysis. Digoxin-specific bulk polymer was obtained by the UV initiated co-polymerisation of methacrylic acid and ethylene glycol dimethacrylate in acetonitrile as porogen. After extracting the template analyte, the ground polymer particles were mixed with plasticizer polyvinyl chloride to form a MIP membrane. A reference polymer membrane was prepared from the same mixture of monomers but with no template. The resultant membrane morphologies were examined by scanning electron microscopy. The imprinted membrane was tested as the recognition element in a digoxin-sensitive fluorescence sensor; sensor response was measured using standard solutions of digoxin at concentrations of up to 4 × 10⁻³ mg L⁻¹. The detection limit was 3.17 × 10⁻⁵ mg L⁻¹. Within- and between-day relative standard deviations RSD (n = 5) were in the range 4.5-5.5% and 5.5-6.5% respectively for 0 and 1 × 10⁻³ mg L⁻¹ digoxin concentrations. A selectivity study showed that compounds of similar structure to digoxin did not significantly interfere with detection for interferent concentrations at 10, 30 and 100 times higher than the digoxin concentration. This simply manufactured MIP membrane showed good recognition characteristics, a high affinity for digoxin, and provided satisfactory results in analyses of this analyte in human serum.     

Chromatographic characterisation, under highly aqueous conditions, of a molecularly imprinted polymer binding the herbicide 2,4-dichlorophenoxyacetic acid

The affinity of a 2,4-dichlorophenoxyacetic acid (2,4-D) molecularly imprinted polymer (MIP), which was synthesised directly in an aqueous organic solvent, for its template (2,4-D) was studied and compared with the affinity exhibited by two other reference (control) polymers, NIPA and NIPB, for the same analyte. Zonal chromatography was performed to establish the optimal selectivity, expressed as imprinting factor (IF), under chromatographic conditions more aqueous than those described so far in the literature. Frontal analysis (FA) was performed on columns packed with these polymers, using an optimized mobile phase composed of methanol/phosphate buffer (50/50, v/v), to extract adsorption isotherm data and retrieve binding parameters from the best isotherm model. Surprisingly, the template had comparable and strong affinity for both MIP (K = 3.8 × 10⁴ M⁻¹) and NIPA (K = 1.9 × 10⁴ M⁻¹), although there was a marked difference in the saturation capacities of selective and non-selective sites, as one would expect for an imprinted polymer. NIPB acts as a true control polymer in the sense that it has relatively low affinity for the template (K = 8.0 × 10² M⁻¹). This work provides the first frontal chromatographic characterization of such a polymer in a water-rich environment over a wide concentration range. The significance of this work stems from the fact that the chromatographic approach used is generic and can be applied readily to other analytes, but also because there is an increasing demand for well-characterised imprinted materials that function effectively in aqueous media and are thus well-suited for analytical science applications involving, for example, biofluids and environmental water samples.     

Synthesis and characterisation of molecularly imprinted catalytic microgels for carbonate hydrolysis

Novel molecularly imprinted microgels incorporating arginine and tyrosine side chains as functional monomers have been designed and synthesised with percentages of cross-linker ranging from 70 to 90%. Full chemico-physical characterisation including M_r, coil density and size particle determination concluded that all polymer preparations obtained can be classified as microgels. Molecular imprinting using a phosphate template was used to generate catalytic microgels for the hydrolysis of p-nitrophenyl carbonates. Kinetic characterisation of the catalytic activity of the different preparations indicated that values of critical monomer concentration (C_M) and percentage of cross-linker play an important role in determining the catalytic efficiency of the different preparations. Microgels containing 70% cross-linker were the only ones following the Michaelis-Menten saturation model and kinetic parameters were obtained using 4 mg/ml of M397: V_max = 1.34 × 10⁻⁶ M s⁻¹ (S.E. 1.28 × 10⁻⁷) and K_M = 2.38 × 10⁻³ M (S.E. 3.1 × 10⁻⁴).     

Enatioselective quantitative separation of d- and l-thyroxine by molecularly imprinted micro-solid phase extraction silver fiber coupled with complementary molecularly imprinted polymer-sensor

Thyroxine is a known disease biomarker which demands a highly sensitive and selective technique to measure ultratrace level with enantiodifferentiation of its optical isomers (d- and l-), in real samples. In this work, an approach of hyphenation between molecularly imprinted micro-solid phase extraction and a complementary molecularly imprinted polymer-sensor was adopted for enantioseparation, preconcentration, and analysis of d- and l-thyroxine. In both techniques, the same imprinted polymer, coated on a vinyl functionalized self-assembled monolayer modified silver wire, was used as the respective extraction fiber as well as sensor material. This combination enabled enhanced preconcentration of test analyte substantially so as to achieve the stringent limit [limit of detection: 0.0084 ng mL⁻¹, RSD = 0.81%, S/N = 3 (d-thyroxine); 0.0087 ng mL⁻¹, RSD = 0.63%, S/N = 3 (l-thyroxine)] of clinical detection of thyroid-related diseases, without any problems of non-specific false-positive contribution and cross-reactivity.     

Sacrificial spacer and non-covalent routes toward the molecular imprinting of “poorly-functionalized” N-heterocycles

A comparison of three different methods for the imprinting of small aromatic heterocycles containing only a single nitrogen atom, for the preparation of specific analytical phases, was carried out. A conventional non-covalent approach to the imprinting of pyridine using methacrylic acid as the functional monomer was compared with two sacrificial spacer methods, in which heterocycles were imprinted as covalent template analogues. The results of binding experiments showed that discrimination based on ligand size was possible when polymers were prepared using a silyl ester-based template. The most selective polymer was able to bind pyridine in preference to quinoline or acridine which is opposite to the trend predicted by the pK_HB values for the three ligands. Curve fitting of the isotherm for pyridine binding to this polymer to the Langmuir model gave an approximate K_d of 1.1±0.1 mM and a binding site concentration of 57±2 mmol g⁻¹. Acridine binding did not show saturation behaviour and was non-specific and cooperative in nature.     

Synthesis and evaluation of new propazine-imprinted polymer formats for use as stationary phases in liquid chromatography

Silica particles have been used as supports for the preparation of three different propazine-imprinted polymer formats. First format refers to grafting of thin films of molecularly imprinted polymers (MIPs) using an immobilised iniferter-type initiator (inif-MIP). The other two new formats were obtained by complete filling of the silica pores with the appropriate polymerisation mixture leading to a silica-MIP composite material (c-MIP) followed by the dissolution of the silica matrix resulting in spherical MIP beads (dis-MIP). These techniques offer a mean of fine-tuning the particle morphology of the resulting MIP particles leading to enhanced capacity in chromatographic applications. Porous silica (specific surface area S = 380 m² g⁻¹, particle size p_s = 10 μm, pore volume V_p = 1.083 ml g⁻¹ and pore diameter d_p = 10.5 nm), methacrylic acid and ethylenglycol dimethacrylate were used for the preparation of the materials. All the MIP formats imprinted with propazine have been characterised by elemental analysis, FT-IR spectroscopy, nitrogen adsorption and scanning electron microscopy. Further, the materials were assessed as stationary phases in HPLC. Capacity factors, imprinting factors and theoretical plate numbers were calculated for propazine and other related triazines in order to compare the chromatographic properties of the three different stationary phases. For the inif-MIPs the column efficiency depended strongly on the amount of grafted polymer. Thus, only the polymers grafted as thin films of ca. 1.3 nm average thickness show imprinting effects and the highest column efficiency giving plate numbers (N) of 1600 m⁻¹ for the imprinted propazine. The performance of the c-MIP stationary phase decreases as result of the complete pore filling after polymerisation and increases again after the removal of the silica matrix due to a better mass transfer in the porous mirror-image resulting polymer. From this study can be concluded that the inif-MIP shows the best efficiency for use as stationary phase in HPLC for the separation of triazinic herbicides.     

Determination of molybdenum in environmental samples

Molecular imprinted membrane of indole-3-ethanol (IE) was prepared by hybridization of IE imprinted polymer powder and polysulfone (PSf) membrane. The IE imprinted polymer by covalent imprinting method was synthesized with copolymerization of indole-3-ethyl methacrylate (IEMA) and divinylbenzene (DVB). The cross-linked P(IEMA-co-DVB) was ground to be powders having less than 63 μm size and then hybridized within PSf membrane by using phase inversion process. The resultant imprinted powder showed binding capacities of 1.8, 7.2, 0 and 0 μmol g⁻¹ for IE, indole, 8-hydroxyquinoline and pyrrole in aqueous solution, respectively, and after hybridization with the PSf membrane, the value was 46, 26, 0 and 0 μmol g⁻¹. As a result, it was found that the IE imprinted powder alone showed non-selectively binding to the IE, but, the hybridized powder within the PSf membrane bound selectively the IE. Evidence was presented that hydrophobic interaction of the PSf matrix caused the selective and efficient binding. We also showed separation behavior of the hybrid membranes and discussed on the binding selectivity of the IE molecule. In view point of hybrid effect of the PSf membrane and the cross-linked imprinted powder, the results of the separation of these substrates were considered.     

A 3,3′-dichlorobenzidine-imprinted polymer gel surface plasmon resonance sensor based on template-responsive shrinkage

Molecularly imprinted polymer gel film on the gold substrate of a chip was prepared with minute amount of cross-linker for the fabrication of a surface plasmon resonance (SPR) sensor sensitive to 3,3′-dichlorobenzidine. The molecularly imprinted gel film was anchored on a gold chip by a surface-bound photo-radical initiator. The sensing of 3,3′-dichlorobenzidine is based on responsive shrinkage of the imprinted polymer gel film that is triggered by target binding. This change can improve the responsiveness of the imprinted SPR sensor to 3,3′-dichlorobenzidine. The molecularly imprinted polymer gel film was characterized with contact angle measurements, electrochemical impedance spectroscopy, cyclic voltammogram, swelling measurements and atomic force microscopy. The changes of SPR spectroscopy wavenumber shifts revealed that the imprinted gel sensing film can ‘memorize’ the binding of 3,3′-dichlorobenzidine compared to non-imprinted one. The imprinted gel-SPR sensor showed a linear response in the range of 9.0 × 10⁻¹² to 5.0 × 10⁻¹⁰ mol L⁻¹ (R² = 0.9998) for the detection of 3,3′-dichlorobenzidine, and it also exhibited high selectivity to 3,3′-dichlorobenzidine compared to its structurally related analogues. We calculated the detection limits to be 0.471 ng L⁻¹ for tap water and 0.772 ng kg⁻¹ for soil based on a signal to noise ratio of 3. The method showed good recoveries and precision for the samples spiked with 3,3′-dichlorobenzidine. This suggest that the imprinted gel-SPR sensing method can be used as a promising alternative for the detection of 3,3′-dichlorobenzidine.     

Influence of binary/ternary complex of imprint ion on the preconcentration of uranium(VI) using ion imprinted polymer materials

Ion imprinted polymer (IIP) materials were prepared for uranyl ion (imprint ion) by forming binary (5,7-dichloroquinoline-8-ol (DCQ) or 4-vinylpyridine (VP)) or ternary (5,7-dichloroquinoline-8-ol and 4-vinylpyridine) complexes in 2-methoxy ethanol (porogen) and copolymerizing in the presence of styrene and divinyl benzene as functional and crosslinking monomers, respectively and 2,2′-azobisisobutyronitrile as initiator. IIP particles were obtained by leaching the imprint ion in these polymer materials with 50% (v/v) hydrochloric acid, filtering, drying in an oven at 50 °C and grinding. Control polymer particles were also prepared under identical conditions. The above synthesized polymer particles were characterized by IR, CHN, X-ray diffraction, and pore size analyses. These leached polymer particles can now pick up uranyl ions from dilute aqueous solutions. The IIP particles obtained with ternary complex of uranyl ion alone gave quantitative enrichment of traces of uranyl ions from dilute aqueous solutions. The optimal pH for quantitative enrichment is 4.5-7.5 and eluted completely with 10 ml of 1.0 M HCl. The retention capacity of uranyl IIP particles was found to be 34.05 mg of uranyl ion per gram of polymer. Further, the percent extraction, distribution ratio, and selectivity coefficients of uranium and other selected inorganic ions were also evaluated. Five replicate determinations of 25 μg of uranium present in 1.0 l of aqueous solution gave a mean absorbance of 0.036 with a relative standard deviation of 2.50%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5 μg l⁻¹.     

Porous molecularly imprinted polymer membranes and polymeric particles

Porous free-standing molecularly imprinted polymer membranes were synthesised by the method of in situ polymerisation using the principle of synthesis of interpenetrating polymer networks and tested in solid-phase extraction of triazine herbicides from aqueous solutions. Atrazine-specific MIP membranes were obtained by the UV-initiated co-polymerisation of methacrylic acid, tri(ethylene glycol) dimethacrylate, and oligourethane acrylate in the presence of a template (atrazine). Addition of oligourethane acrylate provided formation of the highly cross-linked MIP in a form of a free-standing 60 μm thick flexible membrane. High water fluxes through the MIP membranes were achieved due to addition of linear polymers (polyethylene glycol M_w 20,000 and polyurethane M_w 40,000) to the initial mixture of monomers before the polymerization. As a result, typical semi-interpenetrating polymer networks (semi-IPNs) have been formed, where the cross-linked polymer was represented by the atrazine-specific molecularly imprinted polymer, while the linear one was represented by polyethylene glycol/polyurethane. Extraction of the linear polymers from the fully formed semi-IPNs resulted in formation of large pores in the membrane structure. At the same time, extraction of the template molecules lead to formation of the sites in the polymeric network, which in shape and arrangement of functional groups are complementary to atrazine. Reference polymeric membranes were prepared from the same mixture of monomers but in the absence of the template. Recognition properties of the MIP membranes were estimated in solid-phase extraction by their ability to selective re-adsorbtion of atrazine from 10⁻⁸ to 10⁻⁴ M aqueous solutions. The imprinting effect was demonstrated for both types of the MIP membranes and the influence of the type of the linear compound on their recognition properties was estimated. The recognition properties of the MIP membranes were compared to those of the MIP particles of the same composition. Morphology of the MIP membranes was investigated using the SEM microscopy. High fluxes of the developed membranes together with high affinity and adsorption capability make them an attractive alternative to MIP particles in separation processes.     

Optical sensor materials for the detection of amines in organic solvents

A new optical polymer-based sensor was developed, which is able to recognize amines in organic solvents with high sensitivity. Thin polymer membranes were prepared and investigated, which contain a chromogenic functional dye (reactand) that shows a significant colour change during a reversible chemical reaction with the analyte. For that purpose the azo dye 4-trifluoroacetyl-4′-[N-(methacryloxyethyl)-N-(ethyl)amino]-azobenzene (CR-465) was synthesized, which contains a trifluoroacetyl moiety (receptor for interaction with amines) and in addition, a polymerizable methacrylate group. The methacrylate group links the dye covalently to the polymer matrix and the receptor recognizes the analyte via covalent binding. For immobilisation of the dye cross-linked methacrylate polymers with different composition were used. The highly cross-linked polymer network was stable against most organic solvents and exhibited enhanced stability against mechanical strain compared to plasticized PVC. The sensitivity of the reaction between the analyte and the dye was tailored by the choice of the solvent in which the analysis of the sensor layer was performed, with equilibrium constants for 1-butylamine ranging from 80 to 2000 M⁻¹ in chloroform and DMSO, respectively. In toluene as the solvent, sensor layers typically exhibited equilibrium constants of 100 M⁻¹ for 1-butylamine, 1300 M⁻¹ for 1,4-diaminobutane and 20,000 M⁻¹ for tris-(2-aminoethyl)amine. We have also investigated the cross-linked sensor layers with respect to molecular imprinting and did not find any enhancement in selectivity through imprinting in the presence of different analyte molecules.     

Comparison of pyrimethanil-imprinted beads and bulk polymer as stationary phase by non-linear chromatography

A pyrimethanil-imprinted polymer (P1) was prepared by iniferter-mediated photografting a mixture of methacrylic acid and ethylene dimethacrylate onto homemade near-monodispersed chloromethylated polydivinylbenzene beads. The chromatographic behaviour of a column packed with these imprinted beads was compared with another column packed with irregular particles obtained by grinding a bulk pyrimethanil-imprinted polymer (P2). The comparison was made using the kinetic model of non-linear chromatography, studying the elution of the template and of two related substances, cyprodinil and mepanipyrim. Extension of the region of linearity, capacity factors for the template and the related substances, column selectivity, binding site heterogeneity, apparent affinity constant (K) and lumped kinetic association (k_a) and dissociation rate constant (k_d) were studied during a large interval of solute concentration, ranging between 1 and 2000 μg/ml. From the experimental results obtained, in the linearity region of solute concentration column selectivity and binding site heterogeneity remained essentially the same for the two columns, while column capacity (at 20 μg/ml, P1 = 23.1, P2 = 11.5), K (at 20 μg/ml, P1 = 8.3 × 10⁶ M⁻¹, P2 = 2.5 × 10⁶ M⁻¹) and k_a (at 20 μg/ml, P1 = 3.5 μM⁻¹ s⁻¹, P2 = 0.47 μM⁻¹ s⁻¹) significantly increased and k_d (at 20 μg/ml, P1 = 0.42 s⁻¹, P2 = 0.67 s⁻¹) decreased for the column packed with the imprinted beads. These results are consistent with an influence of the polymerisation method on the morphology of the resulting polymer and not on the molecular recognition properties due to the molecular imprinting process.     

Molecularly imprinted solid phase extraction for the selective HPLC determination of alpha-tocopherol in bay leaves

A new sorbent for molecularly imprinted solid phase extraction (MISPE) was synthesized to extract and purify α-tocopherol (α-TP) from vegetable sources. Molecularly imprinted polymers (MIP) were synthesized using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent using a photo-polymerization procedure. A thermo-polymerization was also performed but no imprinting effect in the resulting materials was raised.The proposed MISPE protocol could overcome the drawback of traditional detection methods, which require pre-treatments of the samples. The possibility to obtain the selective recognition of α-TP from natural samples in aqueous mixtures represents one of the main advantages of our materials. Our procedure involves the direct HPLC injection of eluate without any treatment and above all the use of no toxic and biocompatible organic solvents.After the evaluation of the selectivity of the α-TP imprinted polymers, the performance of these materials as solid phase extraction (SPE) sorbents was investigated. Our MISPE-HPLC procedure has a high sensitivity, LOD and LOQ were 3.49 × 10⁻⁷ and 1.16 × 10⁻⁶ mol L⁻¹, respectively, as well as good precision (intraday precision below 3.3% and interday precisions below 6.5%) and recovery (60%). Thus, it can be successfully used for the purification of α-TP from bay leaves.     

Piezoelectric quartz crystal sensor for rapid analysis of pirimicarb residues using molecularly imprinted polymers as recognition elements

A new piezoelectric quartz crystal (PQC) sensor using molecularly imprinted polymer (MIP) as sensing material has been developed for fast and onsite determination of pirimicarb in contaminated vegetables. Three MIPs particles have been prepared by conventional bulk polymerization (MIP-B) and precipitation polymerization in either acetonitrile (MIP-P1) or chloroform (MIP-P2). MIP-P2, with uniform spherical shape and mean diameter at about 50 nm, has shown the best performance as the sensing material for PQC sensor. The sensor fabricated with MIP-P2 can achieve a steady-state response within 5 min, a very short response time as compared to MIPs-coated PQC sensor reported in the literature. The sensor developed exhibits good selectivity (low response to those pesticides with similar structures to pirimicarb, such as atrazine, carbaryl, carbofuran and aldicarb) and high sensitivity to pirimicarb with a linear working range from 5.0 × 10⁻⁶ to 4.7 × 10⁻³ mol L⁻¹ (following a regression equation (r = 0.9988) of −ΔF = 0.552 + 1.79 × 10⁶ C), a repeatability (R.S.D., n = 5) of 4.3% and a detection limit (S/N = 3, n = 5) of 5 × 10⁻⁷ mol L⁻¹. The MIP-coated PQC sensor developed is shown to provide a sensitive and fast method for onsite determination of pirimicarb in aqueous extract from contaminated vegetables with satisfactory recoveries from 96 to 103% and repeatability (R.S.D., n = 5) from 4.6 to 7.1% at pirimicarb concentrations ranging from 8.0 × 10⁻⁶ to 2.0 × 10⁻⁴ mol L⁻¹.     

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10⁻⁹ mol L⁻¹ to 1.5 × 10⁻² mol L⁻¹ in atrazine) and low detection threshold (10⁻⁷ mol L⁻¹).     

Ternary ion-association complex based ion imprinted polymers (IIPs) for trace determination of palladium(II) in environmental samples

A new ion imprinted polymer (IIP) material was synthesized by co-polymerization of palladium-iodide-vinyl pyridinium/palladium-thiocyanate-vinyl pyridinium ion ternary ion-association complex taken in methanol/DMSO with 2-hydroxyethyl methacrylate (functional monomer) and ethylene glycol dimethacrylate (crosslinking monomer) in the presence of 2,2′-azobisisobutryonitrile (initiator). The imprinted anionic species [PdI₄]²⁻ or [Pd(SCN)₄]²⁻ were removed by leaching the dried and powdered materials particles for 18 h with 6 M HCl to obtain leached IIP particles. Non-imprinted/control polymers were also prepared in a similar fashion without the template. Various parameters that influence the percent extraction of palladium, viz. concentration of KI or KSCN, pH, weight of polymer particles, preconcentration and elution times, aqueous phase volume, etc., were systematically studied for both the systems, i.e., in batch as well as flow injection modes. As the on-line flow injection-flame atomic absorption spectrometric (FI-FAAS) allow offer higher enrichment factor, better precision and can analyze more samples for a given time, compared to batch method, this procedure is preferred for the analysis of palladium present in the street/fan blade dust samples collected from busy cities of India and the values obtained were compared with the standard ICPMS values.     

Studies of ion-imprinted polymers for solid-phase extraction of ruthenium from environmental samples before its determination by electrothermal atomic absorption spectrometry

The examination of the effect of interfering ions on the analytical signal of ruthenium measured by electrothermal atomic absorption spectrometry was initially performed in this work. The complexes of ruthenium(III) with thiosemicarbazide (TSd) and acetaldehyde thiosemicarbazone (AcTSn) were prepared and imprinted in polymeric network. The ion-imprinted polymers were synthesized by copolymerization of methacrylic acid, as functional monomer and ethylene glycol dimethacrylate, as crosslinking agent in the presence of 2,2-azobisisobutyronitrile as initiator. The effects of sample volume, pH, and flow rate on the extraction of analyte were studied in dynamic mode. The optimum pH for quantitative retention of ruthenium on each of the studied sorbents was 7.5 ± 0.5. The elution of analyte was completed with 0.2 mol L⁻¹ thiourea in 0.2 mol L⁻¹ HCl. The effect of matrix ions on ruthenium(III) separation process was studied. The analytical performance of the Ru-TSd polymer in the presence of competing ions was better than Ru-AcTSn polymer, considering recovery of analyte, reproducibility of results, selectivity coefficients, and sorbent capacity. The detection limit of the proposed method (0.16 ng mL⁻¹ on Ru-TSd and 0.25 ng mL⁻¹ on Ru-AcTSn) is lower in comparison with the previously published methods. The developed separation method was successfully applied to the determination of trace amounts of ruthenium in spiked water samples, sludge, grass, and human hair.     

Molecularly imprinted polymer for selective extraction of domoic acid from seafood coupled with high-performance liquid chromatographic determination

In this work, a highly selective sample cleanup procedure that combining molecular imprinting technique (MIT) and solid phase extraction (SPE) was developed for the isolation of domoic acid (a fascinating marine toxin) from seafood samples. The molecular imprinting polymer (MIP) for domoic acid was prepared using 1,3,5-pentanetricarboxylic acid as the template molecule instead of domoic acid. 4-Vinyl pyridine was used as the functional monomer and ethylene glycol dimethacrylate was used as the cross-linking monomer. The obtained imprinted polymer showed high affinity to domoic acid and was used as selective sorbent for the SPE of domoic acid from seafood samples. An off-line molecularly imprinted solid phase extraction (MISPE) method followed by high-performance liquid chromatography (HPLC) with diode-array detection for the detection of domoic acid was also established. Good linearity was obtained from 0.5 mg L⁻¹ to 25 mg L⁻¹ (R² > 0.99) with a quantitation limit of 0.1 mg L⁻¹, which was sufficient to determine domoic acid at the maximum level permitted by several authorities. The mean recoveries of domoic acid from mussel extracts were 93.4-96.7%. It was demonstrated that the proposed MISPE-HPLC method could be applied to direct determination of domoic acid from seafood samples.     

Bisphenol A-recognition polymers prepared by covalent molecular imprinting

A specific recognition material for bisphenol A (BPA) was prepared by using a covalent imprinting technique. A chloroform solution containing bisphenol A dimethacrylate as a template, ethylene glycol dimethacrylate as a cross-linking agent and 2,2′-azobis(isobutyronitrile) as an initiator was polymerized by UV initiation. When BPA was removed from the resulting polymer by hydrolysis of the ester bonds with aqueous sodium hydroxide, carboxylic acid residues were generated in the polymer. After the polymer was packed into a stainless steel column, retention factors of BPA and related compounds were measured. The imprinted polymer adsorbed BPA and structurally related compounds such as 4,4′-dihydroxybenzophenone, bis(4-hydroxyphenyl)sulfone and 4,4′-dihydroxybiphenyl. A typical association constant (K_a) was calculated to be 1.72×10⁵ M⁻¹ by Scatchard analysis. Interestingly, 17α- and 17β-estradiol were also bound to the imprinted polymer (K_a=1.68×10⁵ M⁻¹), indicating that the polymer could be used as artificial receptors for screening the compounds having estrogenic action.