The Experts below are selected from a list of 8295 Experts worldwide ranked by ideXlab platform

Jean M. J. Fréchet - One of the best experts on this subject based on the ideXlab platform.

Frantisek Svec - One of the best experts on this subject based on the ideXlab platform.

Harald D H Stover - One of the best experts on this subject based on the ideXlab platform.

  • monodisperse cross linked core shell polymer microspheres by precipitation polymerization
    Macromolecules, 2000
    Co-Authors: Harald D H Stover
    Abstract:

    Monodisperse cross-linked core−shell polymer microspheres having diameters in the micrometer-size range were prepared by semibatch and by two-step precipitation polymerization in the absence of any stabilizer. Commercial Divinylbenzenes, containing 55% or 80% Divinylbenzene, were used for the core, and several functional monomers including chloromethylstyrene, monovinyl, or divinyl methacrylic monomers were incorporated into the shell. Acetonitrile and toluene/acetonitrile mixtures were used as reaction media. Depending on the type of monomer and reaction medium used, the shell could be made nonporous or porous. The particle size distribution, surface morphology, internal texture, and porosity of the resulting core−shell particles were studied. The chromatographic properties of selected particles were evaluated.

  • growth mechanism of poly Divinylbenzene microspheres in precipitation polymerization
    Macromolecules, 1999
    Co-Authors: Jeffrey S Downey, Randy S Frank, Harald D H Stover
    Abstract:

    The residual surface vinyl groups in poly(Divinylbenzene) microspheres prepared by precipitation polymerization in acetonitrile were converted to hexyl groups by treatment with n-butyllithium and t...

  • porous monodisperse poly Divinylbenzene microspheres by precipitation polymerization
    Journal of Polymer Science Part A, 1998
    Co-Authors: Harald D H Stover
    Abstract:

    The precipitation polymerization of commercial Divinylbenzene in acetonitrile containing up to 40 vol. % toluene or other cosolvents is shown to produce novel porous monodisperse poly(Divinylbenzene) microspheres. These microspheres have diameters between 4 and 7 μm, total pore volumes of up to 0.52 cm3/g, and surface areas of up to 800 m2/g. As no surfactant nor stabilizer was used in the preparation of these particles, their surfaces are free of any such residues. The particles were slurry-packed into stainless steel columns for size exclusion chromatography evaluation, and the results show an exclusion limit at molecular weights of 500 g/mol. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1543–1551, 1998

  • synthesis of monodisperse poly Divinylbenzene microspheres
    Journal of Polymer Science Part A, 1993
    Co-Authors: Harald D H Stover
    Abstract:

    Highly crosslinked monodisperse poly(Divinylbenzene) microspheres were produced by precipitation polymerization with acetonitrile as solvent. The radical initiators AIBN, BPO, and ADVN were used. The process does not require stabilizers of any type, and produces monodisperse particles with diameters between 2 and 5 μm, depending on the conditions. These microspheres do not swell or dissolve in any common solvent, and have clean, stabilizer-free surfaces. The particle formation and growth mechanism is proposed to resemble that of dispersion polymerization, except that the particles are stabilized against coagulation by their rigid, crosslinked surfaces rather than by added stabilizers. Spherical particles were formed only at effective crosslinker/monomer or divinyl/monovinyl ratios larger than 1 : 2. © 1993 John Wiley & Sons, Inc.

Carmelo Garcia Barroso - One of the best experts on this subject based on the ideXlab platform.

  • optimisation of headspace solid phase microextraction for the analysis of volatile phenols in wine
    Journal of Chromatography A, 2003
    Co-Authors: Remedios Castro Mejias, Ramon Natera Marin, M V G Moreno, Carmelo Garcia Barroso
    Abstract:

    Headspace solid-phase microextraction has been applied to the analysis of volatile phenols in wine. Silica fibre coated with Carbowax-Divinylbenzene was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, polyacrylate, carboxen-polydimethylsiloxane, and polydimethylsiloxane-Divinylbenzene. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength and sample volume were optimised using a two-level factorial design expanded further to a central composite design, in order to evaluate several possibly influential and/or interacting factors. The headspace (HS)-SPME procedure developed shows adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds in wine. The recoveries obtained were close to 100%, with repeatability values lower than 16%. The method was applied to a variety of white and red wines.

  • optimisation of headspace solid phase microextraction for analysis of aromatic compounds in vinegar
    Journal of Chromatography A, 2002
    Co-Authors: Remedios Castro Mejias, Ramon Natera Marin, M V G Moreno, Carmelo Garcia Barroso
    Abstract:

    Abstract Headspace solid-phase microextraction has been applied to the analysis of aroma compounds in vinegar. Silica fibre coated with Carboxen–polydimethylsiloxane was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, Carbowax–Divinylbenzene, and polydimethylsiloxane–Divinylbenzene, but its repeatability was low. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength, and sample volume were optimised using a two-level factorial design expanded further to a central composite design. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. The extraction efficiency is inversely affected by the acetic acid content—an increase in the acetic acid concentration decreases the extraction efficiency. No interference is observed with the increase in content of polyphenols.

Christian G Huber - One of the best experts on this subject based on the ideXlab platform.

  • a decade of high resolution liquid chromatography of nucleic acids on styrene Divinylbenzene copolymers
    Journal of Chromatography B: Biomedical Sciences and Applications, 2002
    Co-Authors: Peter J Oefner, Christian G Huber
    Abstract:

    The introduction of alkylated, nonporous poly-(styrene-Divinylbenzene) microparticles in 1992 enabled the subsequent development of denaturing HPLC that has emerged as the most sensitive screening method for mutations to date. Denaturing HPLC has provided unprecedented insight into human origins and prehistoric migrations, accelerated the cloning of genes involved in mono- and polygenic traits, and facilitated the mutational analysis of more than a hundred candidate genes of human disease. A significant step toward increased sample-throughput and information content was accomplished by the recent introduction of monolithic poly(styrene-Divinylbenzene) capillary columns. They have enabled the construction of capillary arrays amenable to multiplex analysis of fluorescent dye-labeled nucleic acids by laser-induced fluorescence detection. Hyphenation of denaturing HPLC with electrospray ionization mass spectrometry, on the other hand, has allowed the direct elucidation of the chemical nature of DNA variation and determination of phase of multiple alleles on a chromosome.

  • high performance liquid chromatography electrospray ionization mass spectrometry of single and double stranded nucleic acids using monolithic capillary columns
    Analytical Chemistry, 2000
    Co-Authors: Andreas Premstaller, And Herbert Oberacher, Christian G Huber
    Abstract:

    Monolithic capillary columns were prepared by copolymerization of styrene and Divinylbenzene inside a 200-μm i.d. fused silica capillary using a mixture of tetrahydrofuran and decanol as porogen. With gradients of acetonitrile in 100 mM triethylammonium acetate, the synthesized columns allowed the rapid and highly efficient separation of single-stranded oligodeoxynucleotides and double-stranded DNA fragments by ion-pair reversed-phase high-performance liquid chromatography (IP-RP-HPLC). Compared with capillary columns packed with micropellicular, octadecylated poly-(styrene/Divinylbenzene) particles, an improvement in column performance of approximately 40% was obtained, enabling the analysis of an 18-mer oligodeoxynucleotide with a column efficiency of more than 190 000 plates per meter. The chromatographic separation system was on-line-coupled to electrospray ionization mass spectrometry (ESI-MS). To improve the mass spectrometric detectabilities, 25 mM triethylammonium bicarbonate was utilized as an io...