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Search Results: 1 - 10 of 249820 matches for " Antonio C. Spínola; "
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Determina??o espectrofotométrica simultanea de cobre e ferro em álcool etílico combustível com reagentes derivados da ferroína
Teixeira, Leonardo S. G.;Brasileiro, Jo?o F.;Borges Jr., Mário M.;Cordeiro, Paulo W. L.;Rocha, Sarah A. N.;Costa, Antonio C. Spínola;
Química Nova , 2006, DOI: 10.1590/S0100-40422006000400020
Abstract: in the present work three ferroin reagents were studied for the simultaneous spectrophotometric determination of iron and copper: 1,10-phenanthroline, 2,2'-bipyridine and 2,4,6-tri(2-pyridyl)-1,3,5-triazine. effect of ph, conditions, order reagent addition, interferences, amount of reagents, lineal range, sensitivity and stability of each system were compared. the 2,4,6-tri(2-pyridyl)-1,3,5-triazine can be used for determination of iron in the presence of copper with a detection limit of 5 μg l-1 and coefficient of variation of 2.0%; however it was not possible to determine directly copper in the presence of iron with this reagent. 1,10-phenanthroline can be used for simultaneous determination of the metallic ions with detection limits of 7 and 8 mg l-1 and coefficients of variation of 1.8 and 2.3% in the determination of iron and copper, respectively. the results showed also that 2,2'-bipyridine can be used for simultaneous determination of the metallic ions with detection limits of 11 and 32 μg l-1 and coefficients of variation of 1.9 and 2.5% in the determination of iron and copper, respectively. the reagents were used for spectrophotometric determination of iron and copper in ethanol fuel.
Separation and Pre-concentration of Cadmium, Copper, Lead, Nickel and Zinc by Solid-Liquid Extraction of their Cocrystallized Naphthalene Dithizone Chelate in Saline Matrices
Costa, Ant?nio C. Spínola;Lopes, Leila;Korn, Maria das Gra?as A.;Portela, Jicarla G.;
Journal of the Brazilian Chemical Society , 2002, DOI: 10.1590/S0103-50532002000500022
Abstract: a procedure for separation and pre-concentration of trace amounts of cadmium, copper, lead, nickel, and zinc in brine samples has been proposed. it is based on the adsorption of metal ions onto dithizone co-crystallized with microcrystalline naphthalene, in the ph range 8.5-9.1. nitric acid is used to back-extract the cations from the solid phase, which are measured by icp-oes. various parameters, such as the effect of ph, stirring time, and amounts of solid phase, have been studied in detail, to optimize the conditions for the determination of trace amounts of cd, cu, pb, ni and zn in synthetic brine samples. the limits of detection values expressed in μg l-1 are 44 (zn), 11 (ni), 30 (cd), 47 (pb) and 11 (cu). the precision of the procedure was determined by running 10 replicate samples, each one containing 250 μg l-1 of each element and the relative standard deviations were 2.71 % (cd), 2.15 % (cu), 1.53 % (pb), 2.47 % (ni), and 2.78 % (zn). the accuracy of the procedure was confirmed by applying the analyte additions method and the results indicated that quantitative recoveries (≥ 95 %) were obtained.
Separation and Pre-concentration of Cadmium, Copper, Lead, Nickel and Zinc by Solid-Liquid Extraction of their Cocrystallized Naphthalene Dithizone Chelate in Saline Matrices
Costa Ant?nio C. Spínola,Lopes Leila,Korn Maria das Gra?as A.,Portela Jicarla G.
Journal of the Brazilian Chemical Society , 2002,
Abstract:
Separation and Pre-concentration of Cadmium, Copper, Lead, Nickel and Zinc by Solid-Liquid Extraction of their Cocrystallized Naphthalene Dithizone Chelate in Saline Matrices
Costa Ant?nio C. Spínola,Lopes Leila,Korn Maria das Gra?as A.,Portela Jicarla G.
Journal of the Brazilian Chemical Society , 2002,
Abstract: A procedure for separation and pre-concentration of trace amounts of cadmium, copper, lead, nickel, and zinc in brine samples has been proposed. It is based on the adsorption of metal ions onto dithizone co-crystallized with microcrystalline naphthalene, in the pH range 8.5-9.1. Nitric acid is used to back-extract the cations from the solid phase, which are measured by ICP-OES. Various parameters, such as the effect of pH, stirring time, and amounts of solid phase, have been studied in detail, to optimize the conditions for the determination of trace amounts of Cd, Cu, Pb, Ni and Zn in synthetic brine samples. The limits of detection values expressed in mug L-1 are 44 (Zn), 11 (Ni), 30 (Cd), 47 (Pb) and 11 (Cu). The precision of the procedure was determined by running 10 replicate samples, each one containing 250 mug L-1 of each element and the relative standard deviations were 2.71 % (Cd), 2.15 % (Cu), 1.53 % (Pb), 2.47 % (Ni), and 2.78 % (Zn). The accuracy of the procedure was confirmed by applying the analyte additions method and the results indicated that quantitative recoveries (superscript three 95 %) were obtained.
The role of fragmentation and landscape changes in the ecological release of common nest predators in the Neotropics
Michael V. Cove,R. Manuel Spínola,Victoria L. Jackson,Joel C. Saénz
PeerJ , 2015, DOI: 10.7717/peerj.464
Abstract: Loss of large mammalian carnivores may allow smaller mesopredators to become abundant and threaten other community members. There is considerable debate about mesopredator release and the role that other potential factors such as landscape variables and human alterations to land cover lead to increased mesopredator abundance. We used camera traps to detect four mesopredators (tayra, Eira barbara; white-nosed coati, Nasua narica; northern raccoon, Procyon lotor; and common opossum, Didelphis opossum) in a biological corridor in Costa Rica to estimate habitat covariates that influenced the species’ detection and occurrence. We selected these mesopredators because as semi-arboreal species they might be common nest predators, posing a serious threat to resident and migratory songbirds. Pineapple production had a pronounced positive effect on the detectability of tayras, while forest cover had a negative effect on the detection of coatis. This suggests that abundance might be elevated due to the availability of agricultural food resources and foraging activities are concentrated in forest fragments and pineapple edge habitats. Raccoon and opossum models exhibited little influence on detection from habitat covariates. Occurrence models did not suggest any significant factors influencing site use by nest predators, revealing that all four species are habitat generalists adapted to co-existing in human altered landscapes. Furthermore, fragmentation and land cover changes may predispose nesting birds, herpetofauna, and small mammals to heightened predation risk by mesopredators in the Neotropics.
Spectrophotometric Determination of Zinc Using 7-(4-Nitrophenylazo)-8-Hydroxyquinoline-5-Sulfonic Acid
Korn, Maria das Gra?as Andrade;Ferreira, Adriana Costa;Teixeira, Leonardo Sena Gomes;Costa, Antonio Celso Spínola;
Journal of the Brazilian Chemical Society , 1999, DOI: 10.1590/S0103-50531999000100008
Abstract: a sensitive and selective spectrophotometric method is proposed for the rapid determination of zinc(ii) using an 8-hydroxyquinoline derivative, 7-(4-nitrophenylazo)-8-hydroxyquinoline-5-sulfonic acid (p-niazoxs), as a new spectrophotometric reagent. the reaction between the p-niazoxs and zinc(ii) is instantaneous at ph 9.2 (borax buffer) and the absorbance remains stable for over 24 h. the method allows the determination of zinc over the range of 0.05-1.0 mg ml-1 with a molar absorptivity of 3.75x104 l mol-1 cm-1 and features a detection limit of 15 ng ml-1. the proposed method has been successfully applied to the determination of zinc in several pharmaceutical preparations and copper alloys. the precision (r.s.d. < 2%) and the accuracy obtained were satisfactory.
Spectrophotometric determination of uranium using 2-(2- Thiazolylazo)-p-Cresol (TAC) in the presence of surfactants
Teixeira Leonardo Sena Gomes,Costa Antonio Celso Spínola,Ferreira Sérgio Luís Costa,Freitas Maria de Lourdes
Journal of the Brazilian Chemical Society , 1999,
Abstract: A sensitive and selective spectrophotometric method is proposed for the rapid determination of uranium using 2-(2- Thiazolylazo)-p-Cresol (TAC). The reaction between TAC and uranium (VI) is instantaneous at pH 6.5 and the absorbance remains stable for over 3 h. N-cetyl-N,N,N-trimethylamonium bromide (CTAB) and triton X-100 are used for increasing the sensitivity and solubility of the system respectively. The method allows the determination of uranium in the range from 0.30 to 12.0 mug mL-1 with a molar absorptivity of 1.31 x 10(4) L mol-1 cm-1 and features a detection limit of 26 ng mL-1 at 588 nm. The selectivity of the reagent was improved by the use of (1,2-cyclohexylenedinitrilo) tetraacetic acid (CyDTA) as masking agent. The proposed method has been successfully applied to the determination of uranium in mine drainage waters. The precision (R.S.D. < 2%) and the accuracy obtained were satisfactory.
Spectrophotometric Determination of Zinc Using 7-(4-Nitrophenylazo)-8-Hydroxyquinoline-5-Sulfonic Acid
Korn Maria das Gra?as Andrade,Ferreira Adriana Costa,Teixeira Leonardo Sena Gomes,Costa Antonio Celso Spínola
Journal of the Brazilian Chemical Society , 1999,
Abstract: A sensitive and selective spectrophotometric method is proposed for the rapid determination of zinc(II) using an 8-hydroxyquinoline derivative, 7-(4-nitrophenylazo)-8-hydroxyquinoline-5-sulfonic acid (p-NIAZOXS), as a new spectrophotometric reagent. The reaction between the p-NIAZOXS and zinc(II) is instantaneous at pH 9.2 (borax buffer) and the absorbance remains stable for over 24 h. The method allows the determination of zinc over the range of 0.05-1.0 mug mL-1 with a molar absorptivity of 3.75x10(4) L mol-1 cm-1 and features a detection limit of 15 ng mL-1. The proposed method has been successfully applied to the determination of zinc in several pharmaceutical preparations and copper alloys. The precision (R.S.D. < 2%) and the accuracy obtained were satisfactory.
Nuevos documentos para el estudio de un convento de predicadores en la Oaxaca colonial: San Pedro Etla
Espinosa Spínola, Gloria
Anuario de Estudios Americanos , 2000,
Abstract: El presente artículo estudia el convento de Predicadores de San Pedro en la ciudad de Etla, estado de Oaxaca, como ejemplo de los conventos rurales o vicarías que los dominicos establecieron en Nueva Espa a. El trabajo, enfocado desde un punto de vista artístico, analiza las distintas etapas de construcción, la configuración arquitectónica final del edificio y las funciones de cada uno de los espacios arquitectónicos que lo forman. Con ello, se pretende ilustrar la política misional desarrollada por la orden dominica en el proceso de evangelización de la región oaxaque a.
Spectrophotometric determination of uranium using 2-(2- Thiazolylazo)-p-Cresol (TAC) in the presence of surfactants
Teixeira, Leonardo Sena Gomes;Costa, Antonio Celso Spínola;Ferreira, Sérgio Luís Costa;Freitas, Maria de Lourdes;Carvalho, Marcelo Souza de;
Journal of the Brazilian Chemical Society , 1999, DOI: 10.1590/S0103-50531999000600016
Abstract: a sensitive and selective spectrophotometric method is proposed for the rapid determination of uranium using 2-(2- thiazolylazo)-p-cresol (tac). the reaction between tac and uranium (vi) is instantaneous at ph 6.5 and the absorbance remains stable for over 3 h. n-cetyl-n,n,n-trimethylamonium bromide (ctab) and triton x-100 are used for increasing the sensitivity and solubility of the system respectively. the method allows the determination of uranium in the range from 0.30 to 12.0 mg ml-1 with a molar absorptivity of 1.31 x 104 l mol-1 cm-1 and features a detection limit of 26 ng ml-1 at 588 nm. the selectivity of the reagent was improved by the use of (1,2-cyclohexylenedinitrilo) tetraacetic acid (cydta) as masking agent. the proposed method has been successfully applied to the determination of uranium in mine drainage waters. the precision (r.s.d. < 2%) and the accuracy obtained were satisfactory.
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