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Search Results: 1 - 10 of 199369 matches for " Wendy Rondón "
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Linde Type a Zeolite and Type Y Faujasite as a Solid-Phase for Lead, Cadmium, Nickel and Cobalt Preconcentration and Determination Using a Flow Injection System Coupled to Flame Atomic Absorption Spectrometry  [PDF]
Yaneira Petit de Pe?a, Wendy Rondón
American Journal of Analytical Chemistry (AJAC) , 2013, DOI: 10.4236/ajac.2013.48049
Abstract:

In this work, a flow injection analysis (FIA) method for the trace determination of lead, cadmium, nickel and cobalt in natural waters by formation of neutral chelates with ammonium pyrrolidine dithiocarbamate (APDC) was developed. The neutral chelates formed was retained in a mini-column packed with Linde type A zeolite (LTA) and type Y Faujasite zeolite (FAU) and then eluted with methyl isobutyl ketone (MIBK) to flame atomic absorption spectrometry (EAA) for its detection. Physicochemical characterization of this zeolite was carried out by Fourier Transform infrared spectroscopy and attenuated total reflectance (FTIR and IR-ATR), scanning electron microscopy and energy dispersive X-ray microanalysis (SEM-EDX) and X-ray power diffraction (XRD). Then, a FIA configuration was used with a column preconcentration system coupled to the detection system at room temperature (22?C). The detection limit and the relative standard deviation for 5 determinations of different solutions of Pb2+, Co2+, Ni2+ and Cd2+ for FAU and LTA zeolite were calculated. The sampling frequency ranged from 18-35 h-1 and preconcentration factors from 21-250 were achieved, for a sample volume of 6 mL using 20 mg of sorbents, indicating a high retention of the analytes on the zeolites material. The recoveries obtained in natural waters samples were close to 100% for all ions metal using synthetic zeolites, confirming the applicability of the method. The isotherm models of Langmuir, Scatchard, Freundlich and Dubinin-Radushkevich were used to study the equilibrium data, indicating that successfully followed the Freundlich and Dubinin

Application of 3A Zeolite Prepared from Venezuelan Kaolin for Removal of Pb (II) from Wastewater and Its Determination by Flame Atomic Absorption Spectrometry  [PDF]
Wendy Rondón, David Freire, Zully de Benzo, Angela B. Sifontes, Yorbin González, Maribel Valero, Joaquín L. Brito
American Journal of Analytical Chemistry (AJAC) , 2013, DOI: 10.4236/ajac.2013.410069
Abstract:

This work consists in the use of a 3A zeolite (K-LTA) obtained by a process of exchange of sodium for potassium (4A zeolite), synthesized from Venezuelan kaolin for the removal of Pb (II) ions from aqueous solutions by batch process mode in order to consider its application in treating industrial wastewaters. The 3A zeolite was characterized for X-ray powder diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscopy and energy dispersive X-ray microanalysis (SEM-EDX). The metal concentration in the equilibrium Ce (mg·L-1) after adsorption with 3A zeolite was analyzed using flame atomic absorption spectrometry (FAAS). The influences of the solution pH, contact time, metal initial concentration and adsorbent dosage have been studied. The retention of metal occurring at pH values around 6.5 and the adsorption equilibrium was obtained at 60 min. The equilibrium process was well described by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The Langmuir parameters qm (mg·g-1) and b (L·mg-1) (which are related to the sorption capacity and constant of sorption energy) obtained were 14.64 and 5.42 respectively. The Pb (II) experimental uptake was about 14.56 mg·g-1, a little smaller than the theoretical one given by Langmuir isotherm model. The

Determinación de níquel en cereales y derivados mediante extracción y preconcentración en línea con detección por EAA
Yaneira Petit de Pe?a,Wendy Rondón,Pablo Carrero
Avances en Química , 2010,
Abstract: Determination of nickel in cereals and derivates by on line extraction and preconcentration with AAS detection. An analytical methodology for the determination of nickel traces in commercial solid samples of cereals and corn flour was developed. Nickel was on-line extracted from solid samples in a lab-made cell incorporated to a flow injection system (FIA). After the extraction, a neutral chelate between nickel and ammonium pyrrolidinedithiocarbamate (APDC) was adsorbed on a minicolumn packed with zeolite type YNa. Finally, the chelate was eluted with methyl isobutyl ketone (MIBK) for nickel detection in a flame atomic absorption spectrometer. Under the optical conditions a preconcentration factor of 85 was readily achieved related to the direct introduction of aqueous solutions into an atomic absorption spectrometer. The detection limit (3σ), RSD% and linear calibration graphs were 0.72, 0.22 and (30-70) μg.l-1, respectively, for a sample volume of 6 ml.
Biological Template Based on ent-Kaurane Diterpenoid Glycosides for the Synthesis of Inorganic Porous Materials  [PDF]
ángela B. Sifontes, Mirla Rodriguez, David Freire, Wendy Rondón, Ligia Llovera, Edgar Ca?izales, Franklin J. Méndez, Andrea Monaco, Yraida Díaz
Advances in Chemical Engineering and Science (ACES) , 2013, DOI: 10.4236/aces.2013.34035
Abstract: Recent studies on the preparation of porous nano-materials revealed that the use of kaurane diterpenoids molecules from steviol as biological template favors the obtaining of metallic oxides with tubular morphology as nanorods or nanofibers. In this sense, the present contribution shows an analysis in order to understand how these glycosides of kaurane diterpenoids control the nucleation and growth of inorganic materials favoring the obtaining of these morphologies. For this purpose, it was necessary to carry out studies of the leaf aqueous extract of Stevia rebaudiana by HRTEM, FTIR and 1H-NMR.
Revisión taxonómica del género de Melochia L. (sterculiaceae) en Venezuela
Baudilio Rondón,José;
Acta Botánica Venezuelica , 2009,
Abstract: this critical research based on the analysis of collected samples and of preserved ma-terial in the most important herbaria of venezuela represents the first revision of the genus melochia for the country. seventeen species of this genus, generally located in deciduous forests, were clearly recognized. melochia lanceolata is reported for the first time to venezuela. melochia caracasana, m. nodiflora, m. parvifolia, m. pyramidata and m. to-mentosa are the species with widest distribution, being located from the center-western to the eastern states of venezuela. the sections accompanied by keys, descriptions and illustra-tions are indicated with details of flowers, fruits, seeds and information of use, habit and phenology of the species. the form of the fruit, type of inflorescence, calyx lobe sinuses type, form and pubescence of the petal, presence of staminodia, and floral morphology are characters used to distinguish species.
La Osteopetrosis y el Tratamiento Ortodoncico.: Reporte de un Caso.
Rondón Pacero,Sandra;
Acta Odontológica Venezolana , 2000,
Abstract: we present a clinic case of osteopetrosis which was diagnosticated during the orthodontic treatment. this rare bone entity, as we describe in the review of the literature, is for the firt time associated with the orthodontic movement. we believe it?s very important to the orthodontist, specially during the planification and prognosis of the cases.
Revisión taxonómica del género Waltheria L. (Sterculiaceae) en Venezuela
Baudilio Rondón,José;
Ernstia , 2008,
Abstract: through the critical revision of collected samples, and material genus preserved in the more important herbaria of venezuela, ten species of the waltheria l. were identified, which are located predominantly in the warm zones of the entire national territory. waltheria indica l. is the most widely distributed in venezuela. in the taxonomic treatment the sections are indicated to which the species belong. keys, descriptions and illustrations of each species with details of the leaves, flower, fruit and seed are presented.
Gestión de la movilidad mediante tarifas
Salas Rondón,Miller;
Revista de Ingeniería , 2009,
Abstract: abstract the introduction of a fee to manage mobility is widely used by many governments to mitigate the social costs. these costs occur when the demand exceed the road capacity. moreover, in order to reduce congestion, the fee can generate revenues for strengthening public transport, create infrastructure and implement innovations that improve the mobility of the inhabitants. this article aims to identify the different theoretical, technological and practical aspects also including the opponents of this policy that implies the adoption of this type of solutions to manage the mobility problems in congested urban roads.
DIARREA VIRAL BOVINA: PATOGéNESIS E INMUNOPATOLOGíA
Rondón,Iang;
Revista MVZ Córdoba , 2006,
Abstract: bovine viral diarrhea (bvd) represents a problem of worldwide causing considerable losses so much in meat livestock as in dairy herds, affecting it in diverse ways, which are subordinated to the age of the animal, immunologic state and moment of gestation, in which the infection takes place. bvd is caused by rna virus, gender pestivirus, family flaviviridae, which has been classified in 2 biotypes (cytopathic and non cytopathic) according to its behavior in cultivation cells and in 2 genotypes (i and ii) based on its genetic sequence. depending on the infectious strains a square clinical matter is presented, varying in severity from a subclinic form, going by the clinical form and even producing the fatal disease of the mucous ones (md) or causing deleterious effects on the fetus. although studies already exist in our environment on this entity, the implementation of diagnostic methodologies constitutes an obstacle for the handling of the same one. this review is focused on pathogenyty and inmunopathology of the bvd.
Revisión taxonómica del género de Melochia L. (sterculiaceae) en Venezuela Taxonomic revision of the genus Melochia L. (Sterculiaceae) in Venezuela
José Baudilio Rondón
Acta Botánica Venezuelica , 2009,
Abstract: Esta investigación crítica basada en el análisis de muestras colectadas y de material preservado en los herbarios más importantes del país representa la primera revisión del gé-nero Melochia L. para Venezuela. Se reconocieron diecisiete especies de este género locali-zadas generalmente en bosques deciduos, de las cuales Melochia lanceolata se reporta por primera vez para Venezuela. Melochiacaracasana, M.nodiflora, M.parvifolia, M.pyramidata y M.tomentosa son las especies con mayor distribución, ubicándose desde los estados centro-occidentales hasta el oriente del país. Se indican las secciones acompa adas de cla-ves, descripciones e ilustraciones con detalles de flores, frutos y semillas, e información del uso, hábitat y fenología de las especies. La forma del fruto, tipo de inflorescencia, senos que separan los lóbulos del cáliz, forma y pubescencia del pétalo, presencia de estaminodios y hábitat, son caracteres determinantes para identificar las especies. This critical research based on the analysis of collected samples and of preserved ma-terial in the most important herbaria of Venezuela represents the first revision of the genus Melochia for the country. Seventeen species of this genus, generally located in deciduous forests, were clearly recognized. Melochia lanceolata is reported for the first time to Venezuela. Melochia caracasana, M. nodiflora, M. parvifolia, M. pyramidata and M. to-mentosa are the species with widest distribution, being located from the center-western to the eastern states of Venezuela. The sections accompanied by keys, descriptions and illustra-tions are indicated with details of flowers, fruits, seeds and information of use, habit and phenology of the species. The form of the fruit, type of inflorescence, calyx lobe sinuses type, form and pubescence of the petal, presence of staminodia, and floral morphology are characters used to distinguish species.
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