Où achat cialis sans ordonnance et acheter viagra en France.


Influence of the Glycidyl Methacrylate Content on the
Properties of Porous Copolymers
L. de Lucca Freitas,*, S. F. de Moura, R. Pedroso, T. M. Pizzolato and M. A. de Luca Chemistry Institute, Federal University of Rio Grande do Sul, 91501 970, Porto Alegre, Brazil Solid-phase extraction (SPE) is one of the most important techniques for sample enrichment in water analysis. Typical applications include the pre-concentration of trace amounts of pesticides, organic contaminants, and pharmaceuticals in water1. The use of porous styrene-divinylbenzene copolymer particles as adsorbent in SPE has significantly increased in the last decade. Sometimes specific functional groups were introduced by Friedel Krafts reactions in order to increase retention of polar analytes1. Other properties like particle size, specific surface area and pore size play also an important role in the performance of the phases2. In order to increase the efficiency of the adsorbents in the pre-concentration of polar analytes by SPE, copolymers of styrene, divinylbenzene and different amounts of glycidyl methacrylate were synthesised by suspension radical polymerization. A mixture of heptane and toluene (70/30 v/v) was used as porogenic agent. The initiator was 2,2’-azobisbutyronitrile (AIBN). The organic phase was dispersed in the aqueous phase, a solution of hydroxymethylcellulose and sodium chloride. The reaction was carried out at 75 oC for 10 hours under nitrogen atmosphere. In all reactions 50 mol-% of divinylbenzene was used. The styrene and glycidyl methacrylate quantities were varied between 0 and 50 mol-%. The microspheres obtained were washed with water, acetone and methanol and dried at 60 °C. The specific surface area was measured by nitrogen adsorption using the BET-method. The microspheres were observed by scanning electron microscopy and the images were analysed with the Quantikov-program3, developed for microstructural quantification.The efficiency of the copolymers as adsorbents for SPE was evaluated against tetracycline, a wide used antibiotic. For these tests SPE cartridges were packed with 150 mg of the microspheres (adsorbent). The adsorbent was conditioned with methanol prior to use. An aqueous solution (100 ml) of tetracycline (50 µg l-1) was percolated through the cartridge. The elution was carried out with 5 ml of a mixture of ammonium oxalate aqueous solution (0.1mol l-1) and N,N-dimethylformamide. Thereafter the solution was concentrated to 1 ml and analyzed by HPLC (C-8 column, UV detector, 280 nm) using as mobile phase a mixture of an aqueous solution of ammonium oxalate (0.1 mol l-1), N,N-dimethylformamide and an aqueous solution of ammonium hydrogen phosphate (0.2 mol l-1). The results obtained are summarized in table 1. All microspheres are opaque, due to light diffraction caused by their heterogeneous structure. The heterogeneous structure results from the phase separation during polymerization in the presence of porogenic agents with poor solvating capacity. In the scanning electron micrographies it can be observed that the microspheres have a rough surface with irregular channel distribution. The specific surface area of the microspheres decreases with increasing amounts of glycidyl methacrylate in the copolymers, due probably to the decrease in the difference between the solubility parameter of the copolymer and that of the porogenic agent (δ=16.0 MPa1/2). The recovery of tetracycline after percolation of its aqueous solution through the different adsorbents is higher for the copolymers containing glycidyl methacrylate than for the commercial phase (EnviChromPTM), indicating that these copolymers can be used with great advantage for the pre-concentration of this kind of analyte by solid-phase extraction. Table 1. Characterization of the microspheres and recovery of tetracycline using the different adsorbents.

1Huck, C.W.; Bonn, G.K. J. Chromatogr. A 2000, 885, 51-72.
2Neves, M.S.; Coutinho, F.M.B.; Dias, M.L.; Simão, R.A.; Achete, C.A. J. Appl. Polym. Sci. 2002, 84, 541-551.
3Pinto, L.C.M. PhD Thesis, USP/IPEN, 1996.
* Presenting author: lfreitas@iq.ufrgs.br

Source: http://www.qmc.ufsc.br/fbpol2005/docs/posters/posters_a_abstracts_pdf/liane_de_lucca_freitas.pdf


ASSESSING THE FUNCTION OFGENETIC VARIANTS IN CANDIDATEGENE ASSOCIATION STUDIES Timothy R. Rebbeck*, Margaret Spitz ‡ and Xifeng Wu‡ Knowledge of inherited genetic variation has a fundamental impact on understanding humandisease. Unfortunately, our understanding of the functional significance of many inherited geneticvariants is limited. New approaches to assessing functional significance o

Microsoft word - caulking 06f

CAULKING AND WEATHERIZATION Autumn may be a confusing time of year if you need to seal up your house for the coming winter. Where do you use caulking? Weatherstripping? Glazing? How are they different? Don't feel alone in your confusion. There are a lot of products available, and the differences among them, where you use them, and how you use them would likely confuse many home buil

Copyright © 2010-2014 Pdf Medic Finder