Analytical procedures for determining Pb and Sr isotopic compositions in water samples by ID-TIMS

Few articles deal with lead and strontium isotopic analysis of water samples. The aim of this study was to define the chemical procedures for Pb and Sr isotopic analyses of groundwater samples from an urban sedimentary aquifer. Thirty lead and fourteen strontium isotopic analyses were performed to test different analytical procedures. Pb and Sr isotopic ratios as well as Sr concentration did not vary using different chemical procedures. However, the Pb concentrations were very dependent on the different procedures. Therefore, the choice of the best analytical procedure was based on the Pb results, which indicated a higher reproducibility from samples that had been filtered and acidified before the evaporation, had their residues totally dissolved, and were purified by ion chromatography using the Biorad® column. Our results showed no changes in Pb ratios with the storage time.

Óxidos do tipo perovskita para reação de redução de no com CO

In this work, the perovskite-type oxides LaNiO3, LaMnO3, La0,7Sr0,3NiO3 and La0,7Sr0,3MnO3 were prepared by co-precipitation and tested in the NO reduction with CO at 400 and 500 ºC for 10 h. The catalysts were characterized by X-ray diffraction, temperature programmed reduction with hydrogen, nitrogen adsorption and chemical analysis. The nonstoichiometric oxygen was quantified by temperature programmed reduction, and the catalytic tests showed that the La0,7Sr0,3MnO3 catalyst presented the higher performance for the reduction reaction of NO with CO. The partial substitution of lanthanum by strontium increased the NO conversion and the N2 yield.

The role of oxygen vacancy in the photoluminescence property at room temperature of the CaTiO(3)

In this paper, electron paramagnetic resonance, photoluminescence (PL) emission, and quantum mechanical calculations were used to observe and understand the structural order-disorder of CaTiO(3), paying special attention to the role of oxygen vacancy. The PL phenomenon at room temperature of CaTiO(3) is directly influenced by the presence of oxygen vacancies that yield structural order-disorder. These oxygen vacancies bonded at Ti and/or Ca induce new electronic states inside the band gap. Ordered and disordered CaTiO(3) was obtained by the polymeric precursor method. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3190524]

Nonlinear refraction and absorption through phase transition in a Nd:SBN laser crystal

Time-resolved Z-scan measurements were performed in a Nd(3+)-doped Sr(0.61)Ba(0.39)Nb(2)O(6) laser crystal through ferroelectric phase transition. Both the differences in electronic polarizability (Delta alpha(p)) and cross section (Delta sigma) of the neodymium ions have been found to be strongly modified in the surroundings of the transition temperature. This observed unusual behavior is concluded to be caused by the remarkable influence that the structural changes associated to the ferro-to-paraelectric phase transition has on the 4f -> 5d transition probabilities. The maximum polarizability change value Delta alpha(p)=1.2x10(-25) cm(3) obtained at room temperature is the largest ever measured for a Nd(3+)-doped transparent material.

Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths

1. Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil. 2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age - 25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected NO(3)(-)- (15)N, Rb(+) (analogue of K(+)) and Sr(2+) (analogue of Ca(2+)) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils. 3. Determination of foliar Rb and Sr concentrations and (15)N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer. 4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for NO(3)(-)- (15)N than for Rb(+) and Sr(2+) in the upper 50 cm of soil, the highest SRUP values for Sr(2+) and Rb(+) were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth. 5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

Sequential injections as an alternative to gradient exploitation for implementing differential kinetic analysis in a flow injection system

A novel flow-based strategy for implementing simultaneous determinations of different chemical species reacting with the same reagent(s) at different rates is proposed and applied to the spectrophotometric catalytic determination of iron and vanadium in Fe-V alloys. The method relies on the influence of Fe(II) and V(IV) on the rate of the iodide oxidation by Cr(VI) under acidic conditions, the Jones reducing agent is then needed Three different plugs of the sample are sequentially inserted into an acidic KI reagent carrier stream, and a confluent Cr(VI) solution is added downstream Overlap between the inserted plugs leads to a complex sample zone with several regions of maximal and minimal absorbance values. Measurements performed on these regions reveal the different degrees of reaction development and tend to be more precise Data are treated by multivariate calibration involving the PLS algorithm The proposed system is very simple and rugged Two latent variables carried out ca 95% of the analytical information and the results are in agreement with ICP-OES. (C) 2010 Elsevier B V. All rights reserved.

Barium uptake by maize plants as affected by sewage sludge in a long-term field study

Along-term experiment was carried out under field conditions in Jaboticabal, SP, Brazil, with the objective of evaluating the concentration of Ba in soil and in maize plants grown in a soil treated with sewage sludge for nine consecutive years. During 2005/2006, maize was used as test plants and the experimental design was in randomized complete blocks with four treatments and five replicates. Treatments consisted of: 0.0, 45.0, 90.0 and 127.5 t ha(-1) sewage sludge (dry basis). Sewage sludge application increased soil Ba concentration. Barium accumulated in the parts of maize plants were generally affected by the successive applications of sewage sludge to the soil. However, the concentration of Ba in maize grain did not exceed the critical levels of Ba for human consumption. Sewage sludge applied to soil for a long time did not affect dry matter and grain production, nevertheless had the similar effect of mineral fertilization. Published by Elsevier B.V.

Elevated levels of selenium in the typical diet of Amazonian riverside populations

Selenium (Se) intake is generally from food, whose Se content depends on soil Se and plant accumulation. For humans, adequate Se intake is essential for several selenoenzymes. In the Lower Tapajos region of the Brazilian Amazon, Se status is elevated with large inter-community variability. Se intake in this region, where Hg exposure is among the highest in the world, may be important to counteract mercury (Hg) toxicity. The present study was conducted in 2006 with 155 persons from four communities of the Lower Tapajos. The objectives were: i) to evaluate Se content in their typical diet and drinking water; ii) to compare food Se concentrations with respect to geographic location; and iii) to examine the contribution of consumption of different food items to blood Se. More than 400 local foods and 40 drinking water samples were collected. Participants responded to an interview-administered food frequency questionnaire and provided blood samples. Food, water and blood Se levels were assessed by ICP-MS. Since Brazil nuts may also contain significant levels of barium (Ba) and strontium (Sr), these elements were likewise analyzed in nuts. The highest Se concentrations were found in Brazil nuts, but concentrations were highly variable (median: 13.9 mu g/g; range: 0.4-158.4 mu g/g). Chicken, game meat, eggs and beef also contained considerable levels of Se, with median concentrations from 0.3 to 1.4 mu g/g. There was no particular geographic distribution of food Se. Se concentration in drinking water was very low (<1.4 mu g/L). Blood Se covered a (103-1500 mu g/L), and was positively related to regular consumption of Brazil nuts, domestic chicken and game meat. Brazil nuts were found to contain highly variable and often very high concentrations of Ba (88.0 mu g/g, 1.9-1437 mu g/g) and Sr (38.7 mu g/g, 3.3-173 mu g/g). Further studies should address multiple nutrient/toxic interactions in the diet and related effects on health. (c) 2010 Elsevier B.V. All rights reserved.

Luminescent and morphological study of Sr(2)CeO(4) blue phosphor prepared from oxalate precursors

Luminescent and morphological studies of Sr(2)CeO(4) blue phosphor prepared from cerium-doped strontium oxalate precursor are reported Powder samples were prepared from 5 and 25 mol% Ce(3+)-doped strontium oxalate as well as from a mechanical mixture of strontium oxalate and cerium oxalate at a 4 1 ratio respectively All the samples were characterized by XRD IR PLS and SEM The luminescent and structural properties of the Sr(2)CeO(4) material are little affected by the SrCO(3) remaining from precursors The Sr(2)CeO(4) material consists in one-dimensional chains of edge-sharing CeO(6) octahedra that are linked together by Sr(2+) ions The carbonate ion might be associated with oxygen ions of the linear chain and also with the oxygen atoms located in the equatorial position which consequently affects the charge transfer bands between O(2-) and Ce(4+). As observed by SEM, the morphological changes are related to each kind of precursor and thermal treatment along with irregular powder particles within the size range 05-2 mu m (c) 2010 Elsevier B V All rights reserved

Neuromuscular activity of BaTX, a presynaptic basic PLA(2) isolated from Bothrops alternatus snake venom

We have previously isolated a Lys49 phospholipase A(2) homolog (BaTX) from Bothrops alternatus snake venom using a combination of molecular exclusion chromatography and reverse phase HPLC and shown its ability to cause neuromuscular blockade. In this work, we describe a one-step procedure for the purification of this toxin and provide further details of its neuromuscular activity. The toxin was purified by reverse phase HPLC and its purity and molecular mass were confirmed by SIDS-PAGE, MALDI-TOF mass spectrometry, amino acid analysis and N-terminal sequencing. BaTX (0.007-1.4 mu M) produced time-dependent, irreversible neuromuscular blockade in isolated mouse phrenic nerve-diaphragm and chick biventer cervicis preparations (time to 50% blockade with 0.35 mu M toxin: 58 +/- 4 and 24 +/- 1 min, respectively; n = 3-8; mean +/- S.E.) without significantly affecting the response to direct muscle stimulation. In chick preparations, contractures to exogenous acetylcholine (55 and 110 mu M) or KCl (13.4 mM) were unaltered after complete blockade by all toxin concentrations. These results, which strongly suggested a presynaptic mechanism of action for this toxin, were reinforced by (1) the inability of BaTX to interfere with the carbachol-induced depolarization of the resting membrane, (2) a significant decrease in the frequency and amplitude of miniature end-plate potentials, and (3) a significant reduction (59 +/- 4%, n=12) in the quantal content of the end-plate potentials after a 60 min incubation with the toxin (1.4 mu M). In addition, a decrease in the organ bath temperature from 37 degrees C to 24 degrees C and/or the replacement of calcium with strontium prevented the neuromuscular blockade, indicating a temperature-dependent effect possibly mediated by enzymatic activity. (C) 2009 Elsevier Inc. All rights reserved.

Preventive Effect of Commercial Desensitizing Toothpastes on Bovine Enamel Erosion in vitro

This study evaluated in vitro commercial desensitizing toothpastes with respect to the prevention of erosion and explored the effect of their agents alone or in combination with fluoride. Bovine enamel blocks were randomly allocated to five groups of 20 and exposed to: Sensodyne ProNamel (1,425 ppm F as NaF, 5% KNO(3)), Sensodyne Original (no fluoride, 10% SrCl(2)), Colgate Sensitive (1,450 ppm F as sodium monofluorophosphate, 5% K citrate), Crest (fluoride-only toothpaste, 1,100 ppm F as NaF) and water (negative control). A second experiment was conducted with experimental dentifrices containing fluoride (NaF, 1,100 ppm F), 10% SrCl(2), 5% KNO(3) or 5% K citrate alone or the latter three combined with F. The samples were submitted to four cycles, alternating demineralization (cola, 10 min) and remineralization (artificial saliva, 1 h). Before and between cyclic de- and remineralization, blocks were treated with slurries of the respective toothpastes or water (1 min). Erosive tissue loss was analyzed by profilometry. Data were analyzed by Kruskal-Wallis and Dunn`s tests (p < 0.05). The mean erosion depth (+/- SE, mu m) was significantly less for Colgate Sensitive (0.04 +/- 0.00), Sensodyne Original (0.06 +/- 0.01) and Crest (0.07 +/- 0.01) than for Sensodyne ProNamel (2.36 +/- 0.25) or water (2.92 +/- 0.24), which did not significantly differ from each other. Both F and the desensitizing agents alone reduced erosion, but no additive effect was found. In addition, the combination of F and KNO(3) did not reduce erosion. These in vitro results suggest that the presence of fluoride or desensitizing substances in toothpastes, alone or in combination, can reduce erosion of enamel, but this is not valid for all the formulations. Copyright (C) 2010 S. Karger AG, Basel

Near-infrared integral field spectroscopy of the Homunculus nebula around eta Carinae using Gemini/CIRPASS

This work presents the first integral field spectroscopy of the Homunculus nebula around eta Carinae in the near-infrared spectral region (J band). We confirmed the presence of a hole on the polar region of each lobe, as indicated by previous near-IR long-slit spectra and mid-IR images. The holes can be described as a cylinder of height (i.e. the thickness of the lobe) and diameter of 6.5 and 6.0 x 10(16) cm, respectively. We also mapped the blue-shifted component of He I lambda 10830 seen towards the NW lobe. Contrary to previous works, we suggested that this blue-shifted component is not related to the Paddle but it is indeed in the equatorial disc. We confirmed the claim of N. Smith and showed that the spatial extent of the Little Homunculus matches remarkably well the radio continuum emission at 3 cm, indicating that the Little Homunculus can be regarded as a small H II region. Therefore, we used the optically thin 1.3 mm radio flux to derive a lower limit for the number of Lyman-continuum photons of the central source in eta Car. In the context of a binary system, and assuming that the ionizing flux comes entirely from the hot companion star, the lower limit for its spectral type and luminosity class ranges from O5.5 III to O7 I. Moreover, we showed that the radio peak at 1.7 arcsec NW from the central star is in the same line-of-sight of the `Sr-filament` but they are obviously spatially separated, while the blue-shifted component of He I lambda 10830 may be related to the radio peak and can be explained by the ultraviolet radiation from the companion star.

Searching for s-Process-Enhanced Metal-Poor Stars

We present preliminary results for the estimation of barium [Ba/Fe], and strontium [Sr/Fe], abundances ratios using medium-resolution spectra (1-2 angstrom). We established a calibration between the abundance ratios and line indices for Ba and Sr, using multiple regression and artificial neural network techniques. A comparison between the two techniques (showing the advantage of the latter), as well as a discussion of future work, is presented.

Immobilization of glucose oxidase enzyme (GOD) in large pore ordered mesoporous cage-like FDU-1 silica

Large pore ordered mesoporous silica FDU-1 with three-dimensional (3D) face-centered cubic, Fm3m arrangement of rnesopores, was synthesized under strong acid media using B-50-6600 poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer (EO(39)BO(47)EO(39)), tetraethyl orthosilicate (TEOS) and trimethyl-benzene (TMB). Large pore FDU-1 silica was obtained by using the following gel composition 1TEOS:0.00735B50-6600:0.00735TMB:6HCl:155H(2)O. The pristine material exhibited a BET specific surface area of 684 m(2) g(-1), total pore volume of 0.89 cm(3) g(-1), external surface area of 49 m(2) g(-1) and microporous volume of 0.09 cm(3) g(-1). The enzyme activity was determined by the Flow Injection Analysis-Chemiluminescence (FIA-CL) method. For GOD immobilized on the FDU-1 silica, GOD supernatant and GOD solution, the FIA-CL results were 9.0, 18.6 and 34.0 U, respectively. The value obtained for the activity of the GOD solution with FIA-CL method is in agreement with the 35 U, obtained by spectrophotometry. (C) 2011 Elsevier B.V. All rights reserved.

Adsorption of Pb(2+), Cu(2+) and Cd(2+) in FDU-1 silica and FDU-1 silica modified with humic acid

Ordered mesoporous silica with cubic structure, type FDU-1, was synthesized under strong acid media using B-50-6600 poly(ethylene oxide)-poly(butilene oxide)-poly(ethylene oxide) triblock copolymer (EO(39)BO(47)EO(39)) and tetraethyl orthosilicate (TEOS). Humic acid (HA) was modified to the synthesis process at a concentration of 1.5 mmol per gram of SiO(2). Thermogravimetry, small angle X-ray diffraction, nitrogen adsorption and high resolution transmission electron microscopy were used to characterize the samples. The pristine FDU-1 and FDU-1 with incorporated 1.5 mmol of HA were tested for adsorption of Pb(2+), Cu(2+) and Cd(2+) in aqueous solution. Incorporation of humic acid into the FDU-1 silica afforded an adsorbent with strong affinity for Cd(2+), Cu(2+) and Pb(2+) from single ion solutions. Adsorption of Cu(2+) was significantly enhanced after incorporation of humic acid, a fact that can be explained by the formation of complexes with carboxylic and phenolic groups at low concentrations of the metal cation. The results demonstrated the potential applicability of FDU-1 with incorporated HA in the removal of low concentrations of heavy metal cations from aqueous solution, such as wastewaters, after usual precipitation of metal hydroxides in alkaline medium and proper pH conditioning in the range between 6 and 7. (C) 2007 Elsevier Inc. All rights reserved.