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Search Results: 1 - 10 of 495633 matches for " Arruda Marco A. Z. "
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Vermicompost as a natural adsorbent material: characterization and potentialities for cadmium adsorption
Pereira, Madson G.;Arruda, Marco A. Z.;
Journal of the Brazilian Chemical Society , 2003, DOI: 10.1590/S0103-50532003000100007
Abstract: vermicompost (humic material) samples were submitted to characterization by infrared spectroscopy, x-ray diffractometry, thermogravimetric analysis, electron microscopy etc. in addition, its cation exchange capacity (cec) was determined. factorial experiments were designed in order to elucidate the interaction mechanisms between cd2+ and the adsorptive sites of vermicompost. the maximum adsorptive capacity for cadmium was evaluated by a langmuir isotherm. the characterization revealed that vermicompost exhibits high cec values (ca. 72.9 meq per 100 g), high surface area (porous material), chelating groups and a maximum adsorptive capacity for cd (38.6 mg g-1) at ph 5.0. this potential application was exploited in the analysis of synthetic and real (mineral water) samples with cd concentrations of ca 5 mg l-1, requiring a preconcentration step. an enrichment factor of 100 was attained.
Vermicompost as a natural adsorbent material: characterization and potentialities for cadmium adsorption
Pereira Madson G.,Arruda Marco A. Z.
Journal of the Brazilian Chemical Society , 2003,
Abstract: Vermicompost (humic material) samples were submitted to characterization by infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, electron microscopy etc. In addition, its cation exchange capacity (CEC) was determined. Factorial experiments were designed in order to elucidate the interaction mechanisms between Cd2+ and the adsorptive sites of vermicompost. The maximum adsorptive capacity for cadmium was evaluated by a Langmuir isotherm. The characterization revealed that vermicompost exhibits high CEC values (ca. 72.9 meq per 100 g), high surface area (porous material), chelating groups and a maximum adsorptive capacity for Cd (38.6 mg g-1) at pH 5.0. This potential application was exploited in the analysis of synthetic and real (mineral water) samples with Cd concentrations of ca 5 mug L-1, requiring a preconcentration step. An enrichment factor of 100 was attained.
Experimentos didáticos em química analítica envolvendo separa??o de fases e pré-concentra??o
Nascentes, Clésia C.;Arruda, Marco A. Z.;Maniasso, Nelson;
Química Nova , 2002, DOI: 10.1590/S0100-40422002000300023
Abstract: the aim of this work was to propose two different didactic experiments, which can be used in practical classes of analytical chemistry courses. more flexible experiments related to the theme, giving some options to the instructor are proposed. in this way, the experiment 1 was divided in two parts. in the first one, the visualization of two distinct phases separation is emphasized: the rich and the poor phases in surfactant. in the second part, the metal pre-concentration (co as example) is emphasized. the experiment 2 has three different parts. in the first one, the complex formation is pointed out, in the second one, the ph influence is shown and in the last one, the influence of the complexation time is demonstrated.
Experimentos didáticos em química analítica envolvendo separa o de fases e pré-concentra o
Nascentes Clésia C.,Arruda Marco A. Z.,Maniasso Nelson
Química Nova , 2002,
Abstract: The aim of this work was to propose two different didactic experiments, which can be used in practical classes of analytical chemistry courses. More flexible experiments related to the theme, giving some options to the instructor are proposed. In this way, the Experiment 1 was divided in two parts. In the first one, the visualization of two distinct phases separation is emphasized: the rich and the poor phases in surfactant. In the second part, the metal pre-concentration (Co as example) is emphasized. The Experiment 2 has three different parts. In the first one, the complex formation is pointed out, in the second one, the pH influence is shown and in the last one, the influence of the complexation time is demonstrated.
Ultrasound-assisted extraction of Ca, K and Mg from in vitro citrus culture
Arruda, Sandra C. C.;Rodriguez, Adriana P. M.;Arruda, Marco A. Z.;
Journal of the Brazilian Chemical Society , 2003, DOI: 10.1590/S0103-50532003000300023
Abstract: an ultrasound extraction procedure for ca, k and mg from in vitro plant cultures is proposed, comparing cultures of different embryogenic levels of citrus sinensis and citrus limonia, employing ultrasound energy. parameters related to metals extraction, such as plant material sampling, acid concentration and sonication time were investigated. for accuracy check, the proposed ultrasound extraction procedure was compared with a microwave-assisted digestion procedure and no differences in the results were verified at 95% of the confidence level. with this simple and accurate extraction procedure, it was possible to determine differences in ca, k and mg concentrations during citrus embryo formation/development and between cultures (embryogenic and non-embryogenic). finally, the ultrasound extraction method demonstrated to be an excellent alternative for handless sampling and operational costs.
Ultrasound-assisted extraction of Ca, K and Mg from in vitro citrus culture
Arruda Sandra C. C.,Rodriguez Adriana P. M.,Arruda Marco A. Z.
Journal of the Brazilian Chemical Society , 2003,
Abstract: An ultrasound extraction procedure for Ca, K and Mg from in vitro plant cultures is proposed, comparing cultures of different embryogenic levels of Citrus sinensis and Citrus limonia, employing ultrasound energy. Parameters related to metals extraction, such as plant material sampling, acid concentration and sonication time were investigated. For accuracy check, the proposed ultrasound extraction procedure was compared with a microwave-assisted digestion procedure and no differences in the results were verified at 95% of the confidence level. With this simple and accurate extraction procedure, it was possible to determine differences in Ca, K and Mg concentrations during Citrus embryo formation/development and between cultures (embryogenic and non-embryogenic). Finally, the ultrasound extraction method demonstrated to be an excellent alternative for handless sampling and operational costs.
Use of ultrasonic baths for analytical applications: a new approach for optimisation conditions
Nascentes, Clésia C.;Korn, Mauro;Sousa, Clarivaldo S.;Arruda, Marco A. Z.;
Journal of the Brazilian Chemical Society , 2001, DOI: 10.1590/S0103-50532001000100008
Abstract: optimisation conditions for obtaining maximum cavitation intensity in ultrasonic baths are proposed using a simple and fast method. parameters such as water volume, temperature, detergent concentration, horizontal and vertical positions, number of tubes in the bath, sonication time and bath water substitution were studied. the results obtained for both baths studied (neytech and cole-parmer) lead to the following conditions for maximum cavitation intensity: 1 l of water at room temperature, 0.2 % (v/v) of detergent, central position on the bottom of the tank. only one tube at a time should be used inside the bath during the ultrasound application. the cavitation intensity was linear with the sonication time up to 10 minutes and the water substitution during the sonication improved reproducibility. this system using continuous water change makes possible the sonication of 6 consecutive samples, without changes in the water volume.
On-line microwave-assisted sample decomposition for lead determination in fish slurry samples by electrothermal atomic absorption spectrometry
Arruda, Marco A.Z.;Fostier, Anne H.;Krug, Francisco J.;
Journal of the Brazilian Chemical Society , 1997, DOI: 10.1590/S0103-50531997000100008
Abstract: an on-line microwave-assisted decomposition procedure for the determination of lead in fish is proposed. 300 μl slurry and 400 μl of a 6 mol l-1 hno3 solution were simultaneously injected, and the mixture was positioned inside a microwave oven. the decomposed sample inside the flushing solution was collected in the autosampler cup of a graphite furnace. the proposed procedure covered the 2.5 to 25 μg l-1 pb range and presented a detection limit of 0.72 μg l-1 pb. precision expressed as rsd, was 10.5% (n = 20) for repeatability and 14.3% (n = 10) for reproducibility. accuracy was assessed using standard reference material, and also by comparing the results to a nitric-perchloric decomposition procedure.
River Sediment Analysis by Slurry Sampling FAAS: Determination of Copper, Zinc and Lead
Alves, Flávia L.;Cadore, Solange;Jardim, Wilson F.;Arruda, Marco A. Z.;
Journal of the Brazilian Chemical Society , 2001, DOI: 10.1590/S0103-50532001000600018
Abstract: an experimental procedure for direct sediment analysis was developed. using this procedure, copper, zinc and lead were determined and quantitative recoveries for these metals were accomplished at a low cost and with minimal sample manipulation. the influence of the nitric acid concentration on the slurry preparation, as well as the sediment particle size was investigated. sediment slurries were treated with 6.0 mol l-1 nitric acid and 2% (m/v) ammonium chloride, and sonicated for 15 minutes in an ultrasonic bath before quantification by flame atomic absorption spectrometry. using these conditions for a certified reference material, the percentage of recovery for copper, zinc and lead were 96.4 ± 4.9, 97.0 ± 4.0 and 99.7 ± 4.0, respectively.
Direct analysis of Antarctic krill by slurry sampling: determination of copper, iron, manganese and zinc by flame atomic absorption spectrometry
Alves, Flávia L.;Smichowski, Patricia;Farías, Silvia;Marrero, Julieta;Arruda, Marco A. Z.;
Journal of the Brazilian Chemical Society , 2000, DOI: 10.1590/S0103-50532000000400007
Abstract: slurry sampling in combination with flame atomic absorption spectrometry was employed for the direct determination of four essential trace elements, namely cu, fe, mn and zn in antarctic krill. the effect of instrumental operating conditions and slurry sampling preparation on the analytical signal was investigated. for the determination of cu, fe and zn, samples were suspended in a solution containing 2 mol l-1 hno3. in the case of mn, 4 mol l-1 hno3 was necessary for the preparation of the slurry. the precision between sample replicates was better than 5%. the method was applied to the direct determination of cu, fe, mn and zn in antarctic krill samples using aqueous reference solutions to prepare the calibration curves. the results obtained were in good agreement with those achieved by faas and icp-aes after microwave-assisted wet digestion of the krill samples. the detection limits were 4.5, 1.0, 4.9 and 8.4 mg l-1 for cu, zn, mn and fe, respectively.
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