Multi-step Swelling Research Articles

Simultaneous determination of bisphenol A and its halogenated derivatives in river water by combination of isotope imprinting and liquid chromatography–mass spectrometry

A restricted access media-molecularly imprinted polymer (RAM-MIP) for [ 2H 16]bisphenol A (BPA-d 16) was prepared by a multi-step swelling and polymerization method using 4-vinylpyridine as a functional monomer and ethylene glycol dimethacrylate as a cross-linker, followed by hydrophilic surface modification using glycerol dimethacrylate and glycerol monomethacrylate as hydrophilic monomers. The obtained RAM-MIP showed excellent molecular recognition abilities for BPA and BPA-d 6 as well as BPA-d 16 used as the template molecule, and good ones for tetrachlorobisphenol A (Cl 4-BPA) and tetrabromobisphenol A (Br 4-BPA). Next, the RAM-MIP was utilized for selective on-line pretreatment and enrichment of BPA, Cl 4-BPA and Br 4-BPA in a river water sample, followed by their separation and determination by LC–MS. The calibration graphs of BPA, Cl 4-BPA and Br 4-BPA, constructed using BPA-d 6 as an internal standard, showed good linearity in the range of 12.5–200 pg/mL ( r > 0.999) with a 2-mL injection of a river water sample. The inter-day precision data for the assay of BPA, Cl 4-BPA and Br 4-BPA at 25 pg/mL were 1.08, 3.67 and 1.58%, respectively. Furthermore, this method was successfully applied for the simultaneous determination of BPA and its halogenated derivatives in river water.

Preparation and Characterization of Molecularly Imprinted Uniform-sized Poly(4VP-co-EGDMA) Microgels

Molecularly imprinted uniform-sized poly(4VP-co-EGDMA) microgels were prepared from 4-vinyl pyridine (4VP) monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent using monodisperse linear polystyrene seed particles by multi-step swelling polymerization method.The polymerization conditions were chosen in such a way that the formation of solution complexes between 4VP and the template (N-protected amino acid) prior to polymerization would be favored. The effects of polymerization parameters such as weight ratio of the monomer/seed and diluent/monomer, the concentration of crosslinking agent on the average particle size and pore size distribution were investigated.The molecularly imprinted polymer microgels were utilized as a stationary phase in HPLC. In the chromatographic mode, resolution of the enantiomers of Cbz-L,D-aspartic acid (Cbz: carbobenzoxy) were resolved with the imprinted polymer.

Retentivity and Enantioselectivity of Uniformly-sized Molecularly Imprinted Polymers for (S)-Nilvadipine in Aqueous and Non-Aqueous Mobile Phases

Uniformly-sized molecularly imprinted polymers (MIPs) for (S)-nilvadipine have been prepared by a multi-step swelling and polymerization method using methacrylic acid or 4-vinylpyridine (4-VPY) as a functional monomer, ethylene glycol dimethacrylate (EDMA) as a cross-linker, and toluene, chloroform, cyclohexanol or phenylacetonitrile as a porogen. The chiral recognition abilities of the MIPs for nilvadipine were evaluated using aqueous and non-aqueous mobile phases. Among the MIPs, the (S)-nilvadipine-imprinted 4-VPY-co-EDMA polymers prepared using toluene as a porogen showed the highest recognition ability for nilvadipine in both aqueous and non-aqueous mobile phases. In addition to molecular shape recognition, hydrogen-bonding interactions of the NH proton of nilvadipine with a pyridyl group of the (S)-nilvadipine-imprinted 4-VPY-co-EDMA polymers could play an important role in the retention and chiral recognition of nilvadipine in aqueous and non-aqueous mobile phases. Furthermore, the MIP for (S)-nilvadipine gave the highest molecular recognition ability when a porogenic solvent during polymerization was used as the mobile phase modifier.

Uniformly sized molecularly imprinted polymer for atropine and its application to the determination of atropine and scopolamine in pharmaceutical preparations containing Scopolia extract

A uniformly sized molecularly imprinted polymer (MIP) for atropine has been prepared. The MIP was prepared using 2-(trifluoromethyl) acrylic acid and ethylene glycol dimethacrylate as a functional monomer and cross-linker, respectively, by a multi-step swelling and thermal polymerization method. The selectivity factor, which is defined as the ratio of the retention factors ( k) on the molecularly imprinted and non-imprinted polymers, k imprinted/ k non-imprinted, was 2.2 for atropine on the MIP. The obtained MIP was applied for the determination of tropane alkaloids (atropine and scopolamine) in a commercial gastrointestinal drug by a column-switching HPLC system, consisting of an MIP material as a pre-column, and a conventional cation-exchange analytical column. An interference peak was observed at the retention time of atropine derived from pre-column. However, since the peak area was less than 0.5% the peak area of atropine of a standard solution under the analytical conditions of this study (0.2 μg of atropine was loaded), this interference was negligible in the determination of atropine. On the other hand, no interference peak was observed at the retention time of scopolamine. Calibration curves of atropine and scopolamine showed good linearity in the range of 0.02–0.9 μg/ml ( r = 0.9999) and 0.003–0.09 μg/ml ( r = 0.9998), respectively. The mean recoveries of atropine and scopolamine from a placebo pharmaceutical preparation sample were 98.9 and 99.9%, respectively. The intra-day precision (measured by relative standard deviation, R.S.D. (%)) of both ingredients was less than 2.0%. The optimized column-switching system was applied successfully to the determination of atropine and scopolamine in a commercial gastrointestinal drug.

Chromatographic molecular recognition for catechol-related compounds using thiacalix[4]arene as an effective selector.

Thiacalix[4]arene (5,11,17,23-tetra- tert-butyl-25,26,27,28-tetrahydroxy-2,8,14,20-tetrathiacalix[4]arene) is an amphiphilic molecule comprising four p-tert-butylphenol-like groups ortho-linked by single sulfur atoms. This molecule has a high electron density area owing to the close proximity of the hydroxyl groups and sulfur atoms. We studied the applicability of this interesting compound as a selector for high-performance liquid chromatography (HPLC) thereby presumably exploiting this feature. Firstly, uniformly sized polymer particles were prepared by using a multi-step swelling and polymerization method with ethylene glycol dimethacrylate (EDMA) as a cross-linker. Methacrylic acid (MAA) was introduced onto the surface of the resulting polymer particles through a new modification method. Thiacalix[4]arene was chemically bonded through the MAA group by using 1,4-dibromobutane as a spacer to reduce steric hindrance around the MAA and the polymer particle itself. The performance of the prepared polymer-based thiacalix[4]arene-modified stationary phase was evaluated with HPLC. Specific chromatographic retention behavior was observed for catechol relative to positional isomers of xylene, cresol, and benzene-diol. Catecholamine and catechol showed specific chromatographic retention behavior.

Retentivity and enantioselectivity of uniformly sized molecularly imprinted polymers for d-chlorpheniramine and -brompheniramine in hydro-organic mobile phases

Uniformly sized molecularly imprinted polymers (MIPs) for d-chlorpheniramine (CP) and -brompheniramine (BP) have been prepared by a multi-step swelling and polymerization method using methacrylic acid (MAA) or 2-(trifluoromethyl)acrylic acid (TFMAA) and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively. The retentive and enantioselective properties of CP, BP and their structurally related compounds on the MIPs were evaluated using hydro-organic mobile phases. CP and BP enantiomers were retained the most as a monovalent cation on MAA- co-EDMA polymers and a divalent cation on TFMAA- co-EDMA polymers. Ion exchange and hydrophobic interactions could mainly work for the retention and enantioseparation of CP and BP on both MAA- co-EDMA and TFMAA- co-EDMA polymers in hydro-organic mobile phases. Though the respective MIPs gave the highest enantioselectivity for the template molecule, cross-reactivity for CP and BP was observed with them.

Novel surface-modification techniques for polymer-based separation media: Stimulus-responsive phenomena based on double polymeric selectors

A pair of polymeric selectors potentially responding to stimulation was introduced onto monosized porous polymer particles to be evaluated as a packing material for HPLC. Possible complexes formed between polyacrylamide (PAAm) and poly(methacrylic acid) (PMAA) were utilized as stimulus responsive polymeric selectors. Uniformly sized base polymer particle was prepared by multi-step swelling and polymerization method, while the introduction of PAAm and PMAA was done by newly invented modification technique. In this technique, a solvent in which both acrylamide (AAm) and methacrylic acid (MAA) monomers are soluble, but PAAm and PMAA are insoluble, was utilized as a modification medium. The polymer particle doubly modified with PAAm and PMAA was utilized as packing material for HPLC and the stimulus responses were evaluated by changing temperature or pH to check change of the slope of a Van’t Hoff plot. By using water as a mobile phase, the expected inflection point of the Van’t Hoff plot was observed at upper critical solution temperature (UCST) of the polymer complexes and the temperature responsive ability was observed. Moreover, pH responsive ability was studied by using buffer of either pH 4 or 10 as mobile phase. Slope of the plot was changed in buffer of pH 4, but no change of slope was observed in the buffer of pH 10.

Synthesis of isobutyl maleate–divinylbenzene microspheres by different techniques of heterogeneous polymerizations

AbstractCopolymers of isobutyl maleate–divinylbenzene in the form of microspheres were obtained. In their preparation, the following techniques of heterogeneous polymerization were used: emulsion, modified emulsion, precipitation, suspension, and multistep swelling polymerization. Among the obtained microspheres, those synthesized by modified emulsion and multistep swelling polymerizations have a size suitable for HPLC purposes, whereas the product of suspension polymerization can be used as packing material for gas chromatography. Their porous structure was studied in detail. The influence of the polymerization technique on the particle size and morphology is discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2008–2015, 2004

Development of trichloroacetic acid sensor based on molecularly imprinted polymer membrane for the screening of complex mixture of haloacetic acids in drinking water

This work shows developing conductometric sensor based on molecularly imprinted polymer (MIP) for the screening of complex mixture of haloacetic acids (HAAs) in drinking water. The recognition of the HAAs was achieved by trichloroacetic acid (TCAA)-imprinted polymers synthesised from the copolymerization of 4-vinylpyridine (4-VPD) and ethylene glycol dimethacrylate (EDMA) in the presence of the TCAA template in acetonitrile, either by bulk polymerization (BP) method or by a multi-step swelling polymerization (MSP) method. TCAA-imprinted polymer of both methods was tested for re-binding with the template and its analogs. It was found that these polymers could bind selectively to the template molecule and HAA derivatives. HAA measurements were carried out by the application of the polyvinyl chloride membrane fabricated with TCAA-imprinted polymer on conductometric sensors. The technological parameters (operating frequency, membrane composition, ionic strength and medium pH) for the sensors were identified and optimised in respect to the response to TCAA, using sensor fabricating with BP-based MIP as a model. The selectivity of the sensors constructed with MIPs made by either that of the two imprinting methods was also investigated, which the influence of the method of imprinting on the binding strength and selectivity of the recognition element embedded in sensor was observed. The sensors showed high sensitivity and selectivity for the response toward TCAA, the sensor modified with MSP-based MIP being better. In addition, the sensors, particularly when was constructed with MSP-based MIP exhibited good cross-reactivities with a wide range of HAAs, which is useful for the screening of the group of HAA usually present in chlorinated water in complex mixtures. Thus, the sensor modified with MSP-based MIP was chosen for analytical application. The calibration of this sensor was determined, showing the good linear graphs ( R 2>0.970) for HAAs over the concentration range of 25–1000 μg/l and the detection limit of each HAA in the range 0.2–5.0 μg/l. Moreover, the results in real analysis of the sensor indicate the simplicity and reliability of the method. The present work demonstrated that the sensor based on TCAA-imprinted polymer is a fast and sensitive screening method of HAAs in drinking water.

Preparation of uniformly sized molecularly imprinted polymers for phenolic compounds and their application to the assay of bisphenol A in river water.

Uniformly sized molecularly imprinted polymers, which can recognize bisphenol A (BPA), have been prepared by a multi-step swelling and polymerization method using BPA or a structurally related analogue of BPA [p-t-octylphenol (OP) or p-t-butylphenol (BP)] as the template molecule, 4-vinylpyridine as the functional monomer, and ethylene glycol dimethacrylate as the cross-linker. The BP-imprinted polymer showed higher molecular recognition ability for BPA than the OP-imprinted polymer. The BPA- and BP-imprinted polymers were applied for the assay of a trace amount of BPA in river water using column-switching HPLC with fluorescence detection: A BPA-imprinted polymer was used for removal of BPA from the pretreatment eluent as the trap column, and a BP-imprinted polymer was used for selective pretreatment and enrichment of BPA in river water as the pretreatment column. The calibration graph, constructed from peak area data plotted versus BPA concentration, was linear with a correlation coefficient of >0.999 in the concentration ranges of 25-1000 ppt. The limit of quantitation was 25 ppt with a 5-ml injection. The column-switching HPLC system was successfully applied for the assay of BPA in river water.

Influence of polyvinylpyrrolidone on the hydrophobic properties of partially porous poly(styrene–divinylbenzene) particles for biological applications

AbstractFor the preparation of polymer particles by free radical, stabilizers are usually present in the reaction mixture to maintain the separation of particles from each other. Polyvinylpyrrolidone (PVP) is one the hydrophilic polymers that has been extensively used as the stabilizer in the polymerization system employing a polar solvent or solvent mixture as the continuous phase. As shown in the present study, the presence of PVP in the later steps could significantly influence the hydrophobic property of partially porous poly(styrene–divinylbenzene) (PS–DVB) particles, prepared by the method of multistep swelling and polymerization involving the use of polymeric porogens. The association of PVP molecules on the particle surface reduced the hydrophobicity and consequently the capability of particles for biological applications. For the reversed‐phase liquid chromatography of penicillin G and its enzymatic hydrolysis product, particles prepared without PVP led to an enhancement in both retention and resolution, compared with particles resulting from the use of PVP. Results from lipase immobilization on these particles also showed that the presence of PVP could shield the hydrophobic groups on the particle surface and then reduce the efficiency of enzyme immobilization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1818–1824, 2003

Restricted access media-molecularly imprinted polymer for propranolol and its application to direct injection analysis of beta-blockers in biological fluids.

A restricted access media-molecularly imprinted polymer (RAM-MIP) for propranolol (PRP) has been prepared for direct injection analysis of beta-blockers in biological fluids. First, the MIP for PRP was prepared using methacrylic acid and ethylene glycol dimethacrylate as the functional monomer and cross-linker, respectively, by a multi-step swelling and polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate and glycerol dimethacrylate was used for hydrophilic surface modification, and added directly to the MIP for PRP after 4 h from the start of polymerization. Then further polymerization was carried out for 20 h. The obtained RAM-MIP for PRP showed excellent molecular recognition ability for PRP, good ones for alprenolol (ALP) and pindolol, and fair ones for other beta-blockers. The RAM-MIP was applied for direct injection analysis of ALP enantiomers in a rat plasma sample by a column-switching HPLC system using a beta-cyclodextrin phenylcarbamate-bonded silica column as the analytical column. The calibration graph, constructed from peak area versus each ALP enantiomer concentration, was linear with a correlation coefficient of > 0.999 over the concentration ranges of 12.5-250 ng ml(-1). The limit of quantitation was 12.5 ng ml(-1) with a 50 microl injection. This method could be applicable for the assay of ALP enantiomers at the therapeutic plasma levels, and have wide applicability for the assay of beta-blockers in biological fluids.

Uniformly Sized Molecularly Imprinted Polymer for (S)-Nilvadipine. Comparison of Chiral Recognition Ability with HPLC Chiral Stationary Phases Based on a Protein

Uniformly sized molecularly imprinted polymers (MIPs) for (S)-nilvadipine have been prepared by a multistep swelling and polymerization method using methacrylic acid, 2-(trifluoromethyl)acrylic acid, 2-vinylpyridine, or 4-vinylpyridine (4-VPY) as a functional monomer and ethylene glycol dimethacrylate (EDMA) as a cross-linker. The chiral recognition abilities of the MIPs for nilvadipine and other dihydropyridine calcium antagonists were evaluated using a mixture of sodium phosphate buffer (or water) and acetonitrile or only acetonitrile as the mobile phase. The (S)-nilvadipine-imprinted 4-VPY-co-EDMA polymers gave the highest resolution for nilvadipine among the MIPs prepared. In addition, the enantioseparation of nilvadipine was attained using the (S)-nilvadipine-imprinted EDMA polymers, without use of a functional monomer. 1H NMR and molecular modeling studies suggested a one-to-one hydrogen-bonding-based complex formation of (S)-nilvadipine with 4-VPY in chloroform. These results reveal that the (S)-nilvadipine-imprinted EDMA polymers could recognize the template molecule by its molecular shape, and that in addition to this recognition, hydrophobic and hydrogen-bonding interactions seems to play important roles in the retention and chiral recognition of nilvadipine on the 4-VPY-co-EDMA polymers in hydroorganic mobile phases. By optimizing chromatographic conditions such as column temperature and flow rate, the baseline separation of nilvadipine enantiomers was attained with a short analysis time and with a column efficiency comparable to commercially available chiral stationary phases based on a protein, such as ovomucoid or alpha1-acid glycoprotein.

Enantioselective Release of Controlled Delivery Granules Based on Molecularly Imprinted Polymers

The objectives of our study were two fold: to examine enantioselective release of controlled delivery granules based on molecularly imprinted polymers (MIPs) for various racemic drugs, including ibuprofen and ketoprofen (NSAIDs) and propranolol (β-blockers); to evaluate the use of controlled delivery granules containing a combination of different MIPs for the multiple simultaneous enantioselective-controlled delivery of mixed racemic drugs. In this work, the MIP beads selective to S-Ibuprofen, S-ketoprofen, and R-propranolol were prepared using multistep swelling and thermal polymerization method. Afterward, the MIP beads were formulated with racemate of the chiral drugs and a binder and followed by granulation. Then, the enantioselective release of racemic drugs from the prepared MIP granules was investigated by an in vitro dissolution test using a chiral HPLC for assays of enantiomers. The influence of drug/polymer ratio and medium pH on the selective enantiomeric release of MIP granules was explored. Further, the release of the enantiomers of racemic ibuprofen and racemic ketoprofen from the granule containing two MIPs - S-ibuprofen MIP and S-ketoprofen MIP - was examined. The release profiles of both S-ibuprofen MIP granule and R-propranolol MIP granule exhibited differential release of enantiomers. Also, the findings indicated the stereoselective retardation of those controlled delivery granules as well as the influence of MIP formulation on enantioselective release mechanism. The enantioselective release of S-ibuprofen MIP granule and R-propranolol MIP granule appeared to depend on polymer loading and medium pH. In this case, the drug/polymer ratio of 1:25 showed the best enantioselective release with initial enantiomeric excess of 100%. On the other hand, the enantioselectivity of both granules was the greatest in buffer pH 7.4. Furthermore, the efficiency in enantioselective release of the combined MIP granule was higher than its relative single MIP granules, as a result of the cross-reactivities of the MIPs. In our study, controlled delivery granules based on MIPs demonstrated significant enantioselective release for several chiral drugs, and thus it may be developed as a tool to administer chiral pharmaceutical as a single enantiomer.

Preparation strategy for uniformly sized, polymer-based HPLC packing materials having practically acceptable column efficiency. 1. Copolymerization technique.

Uniformly sized, polymer-based packing materials affording excellent chromatographic performance in semimicro HPLC were prepared from mixtures of alkyl methacrylate and glycerol dimethacrylate by a copolymerization technique using a multistep swelling and polymerization method. A column efficiency of up to 13000 plates was obtained for a 2-mm-i.d. x 150-mm column with beads prepared from a 1:1 (v:v) mixture of an alkyl methacrylate and glycerol dimethacrylate. The packing materials exhibit a considerable improvement in column efficiency, as demonstrated on the separation of polyaromatic hydrocarbons (PAHs) having a relatively long retention time, which thus far has been a serious problem of polymer-based packing materials. Detailed studies suggested a rather limited optimum pore size, and its distribution was depicted to get the excellent column efficiency on polymer-based packing materials.

Uniformly sized molecularly imprinted polymer for d-chlorpheniramine : Evaluation of retention and molecular recognition properties in an aqueous mobile phase

A uniformly sized molecularly imprinted polymer (MIP) for d-chlorpheniramine has been prepared by a multi-step swelling and polymerization method using methacrylic acid and ethylene glycol dimethacrylate as a functional monomer and cross-linker, respectively. The retentive and enantioselective properties of chlorpheniramine and its structurally related compounds on the MIP were evaluated using an aqueous mobile phase. Electrostatic and hydrophobic interactions could mainly work for the retention and enantioseparation of chlorpheniramine in aqueous mobile phase. Further, the MIP showed the highest recognition for chlorpheniramine and slight recognition for its structurally related compounds, and enantioseparation of pheniramine was attained.

Preparation and application of partially porous poly(styrene‐divinylbenzene) particles for lipase immobilization

Partially porous poly(styrene-divinylbenzene) (PS-DVB) particles in the micron size range were prepared by the method of multistep swelling and polymerization involving the use of polymeric porogens. Polystyrene (PS) seeds prepared by dispersion polymerization were expanded in particle size by absorbing styrene and initiator, and then polymerized to form polymeric porogen particles. The newly synthesized PS chains served as the porogens of the PS-DVB particles, resulting from the copolymerization of styrene and divinylbenzene in the swollen polymeric porogen particles. PS-DVB particles with a specific surface area of up to 34 m2/g and a pore volume of up to 0.15 cm3/g were obtained. The average pore diameter of PS-DVB particles was in the range of 15–24 nm. An increasing amount of toluene used in the copolymerization step increased the pore volume and specific surface area. Lipase from Candida rugosa was immobilized on the prepared PS-DVB by physical adsorption. The optimum temperature for enzymatic activity was increased and the thermal deactivation of enzyme in organic solvent was slowed down by the immobilization. However, compared with soluble enzyme, the immobilized lipase on PS-DVB retained a less activity after the first stage deactivation, suggesting a possible change in the conformation of enzyme molecule by immobilization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 39–46, 2001

Uniformly sized molecularly imprinted polymer for ( S)-naproxen : Retention and molecular recognition properties in aqueous mobile phase

A uniformly sized molecularly imprinted polymer (MIP) for ( S)-naproxen has been prepared by a multi-step swelling and polymerization method using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively. We optimized the preparation method of the MIP by changing the molar amounts of the template molecule and functional monomer. Further, we examined the effects of organic modifier type, column temperature and flow-rate on the retentivity and enantioselectivity for naproxen using a mixture of phosphate buffer and organic modifier (acetonitrile, ethanol and 2-propanol) as an eluent. When the amounts of ( S)-naproxen, 4-VPY and EDMA used were 4, 6 and 25 mmol, respectively, the enantioselectivity and resolution for naproxen were good despite the shorter retention. When acetonitrile was used as an organic modifier, the highest column efficiency was obtained for the separation of naproxen enantiomers. With regard to the effects of column temperature and flow-rate, the column performance was improved by elevating a column temperature and decreasing a flow-rate.

Preparation and application of partially porous poly(styrene‐divinylbenzene) particles for lipase immobilization

Partially porous poly(styrene-divinylbenzene) (PS-DVB) particles in the micron size range were prepared by the method of multistep swelling and polymerization involving the use of polymeric porogens. Polystyrene (PS) seeds prepared by dispersion polymerization were expanded in particle size by absorbing styrene and initiator, and then polymerized to form polymeric porogen particles. The newly synthesized PS chains served as the porogens of the PS-DVB particles, resulting from the copolymerization of styrene and divinylbenzene in the swollen polymeric porogen particles. PS-DVB particles with a specific surface area of up to 34 m 2 /g and a pore volume of up to 0.15 cm 3 /g were obtained. The average pore diameter of PS-DVB particles was in the range of 15-24 nm. An increasing amount of toluene used in the copolymerization step increased the pore volume and specific surface area. Lipase from Candida rugosa was immobilized on the prepared PS-DVB by physical adsorption. The optimum temperature for enzymatic activity was increased and the thermal deactivation of enzyme in organic solvent was slowed down by the immobilization. However, compared with soluble enzyme, the immobilized lipase on PS-DVB retained a less activity after the first stage deactivation, suggesting a possible change in the conformation of enzyme molecule by immobilization.

Uniform-sized molecularly imprinted polymers for 2-arylpropionic acid derivatives selectively modified with hydrophilic external layer and their applications to direct serum injection analysis.

Uniform-sized molecularly imprinted polymers (MIPs) for (S)-naproxen and -ibuprofen selectively modified with hydrophilic external layer, restricted access media (RAM)-MIPs, have been prepared. First, the MIP for (S)-naproxen or -ibuprofen was prepared using 4-vinylpyridine and ethylene glycol dimethacrylate as a functional monomer and cross-linker, respectively, by a multistep swelling and thermal polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate and glycerol dimethacrylate was used for hydrophilic surface modification, and it was added directly to the MIP for (S)-naproxen or -ibuprofen 4 h after the start of molecular imprinting. The obtained RAM-MIP material for (S)-naproxen or -ibuprofen was applied for direct serum injection assays of the drug by a column-switching system, consisting of a RAM-MIP material and conventional C18-silica column. However, leakage of the imprint molecule prevented accurate and precise assays of the drug. This problem has been overcome by using the RAM-MIP for (S)-naproxen for the assays of ibuprofen in rat plasma. The optimized column-switching system was applied successfully to the assay of ibuprofen in rat plasma after oral administration.