Evaluation of Ir and Pd(NO3)(2)/Mg(NO3)(2) as Modifiers for the Simultaneous Determination of Mn, Ni, Pb, and Sb in Fuel Ethanol by Graphite Furnace MS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Lability of Cd, Cr, Cu, Mn and Pb complexed by aquatic humic substances

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Exploring potentialities of the HR-CS FAAS technique in the determination of Ni and Pb in mineral waters

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Distribuição de Cr, Ni, Cu, Cd e Pb em frações húmicas de diferentes tamanhos moleculares extraídas de amostras de água e de sedimentos do reservatório de captação de água superficial Anhumas - Araraquara-SP

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

SEMICLASSICAL ESTIMATE OF THE COULOMB-EXCITATION OF THE GIANT-DIPOLE RESONANCE IN PB-208

A semiclassical approach to study pure Coulomb excitation of Pb-208 giant dipole isovector resonance is examined. We consider medium energy projectiles and assume the target excitation to be described by a simple Goldhaber-Teller model. It is shown that the main features concerning the angular distribution are obtained in the angular range described by the model and an estimate is made of the pure Coulomb dipole contribution to the measured cross sections.

Synthesis and sintering of PZT ceramics

Lead zirconate powder, with Zr/Ti ratio of 50/50 was prepared by polymeric precursor method and doped with 3, 5 and 7 mol% of Sr+2 Or Ba+2, as well as by 0.2 to 5 mol% of Nb+5. The powder was calcined at 750 degrees C by 4 hours and milled during 1.5 h in isopropilic alcohol. Powders were characterized by surface area measurements (BET method), by infrared spectroscopy and by X-ray diffraction to characterize the crystal structure. Isostatically pressed samples were sintered in a dilatometer furnace by using a constant heating rate of 10 degrees C/min from ambient to 1200 degrees C. Synthetic air and air with water vapor were used as atmospheres. Both Sr+2 and Ba+2 substitute Pb+2 and favor the formation of rhombohedral phase. Otherwise, Nb+5 substitute preferentially Zr+4 favoring tetragonal phase. The concentration of dopants and the atmosphere influence the densification and the microstructure of the PZT, which alters the dielectric and piezoelectric properties of the ceramics.

Silver as internal standard for simultaneous determination of Cd and Pb in whole blood by electrothermal atomic absorption spectrometry

The use of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for Cd and Pb determination in whole blood. The comparison of thermochemical and physicochemical parameters allowed the selection of Ag, Bi, and Tl as internal standard candidates. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte ( axis x), precision and accuracy were used to select Ag as the most appropriate internal standard. Blood samples were diluted (1 + 9) with 0.11% (m/v) Triton X-100 + 1.1% (v/v) HNO3 + 0.28% (m/v) NH4H2PO4 + 10 mug L-1 Ag+. Pyrolysis and atomization temperatures for the optimized heating program were 550 and 1700 degreesC, respectively. Characteristic masses based on integrated absorbance were 1.68 +/- 0.01 pg for Cd and 30.3 +/- 0.1 pg for Pb. The detection limits (DL) were 0.095 +/- 0.001 mug L-1 and 0.86 +/- 0.01 mug L-1 for Cd and Pb, respectively. The mean RSD for all determinations was the same for Cd (13 +/- 9%) with or without Ag as internal standard ( IS). on the other hand, the use of Ag as IS improved the RSD for Pb from 3.6 +/- 4.0% to 2.2 +/- 2.0%. An effective contribution of the internal standard Ag was verified in the recoveries of spiked samples (0.5 mug L-1 Cd2+ and 5.0 mug L-1 Pb2+). The mean recoveries were 81 +/- 8% and 91 +/- 4% for Cd, and 80 +/- 11% and 93 +/- 6% for Pb without and with IS correction, respectively. This is the first application of IS for a simultaneous determination by SIMAAS.

Tungsten permanent chemical modifier with co-injection of Pd(NO3)(2)+Mg(NO3)(2) for direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer (THGA((R))) used together with Pd(NO3)(2) + Mg(NO3)(2) as modifier is proposed for the direct determination of lead in vinegar by graphite furnace atomic absorption spectrometry. The optimized heating program (temperature, ramp time, hold time) of atomizer involved drying stage (110 degrees C, 5 s, 30 s; 130 degrees C, 5 s, 30 s), pyrolysis stage (1000 degrees C, 15 s, 30 s), atomization stage (1800 degrees C, 0 s, 5 s) and clean-out stage (2450 degrees C, I s, 3 s). For 10 mu L of vinegar delivered into the atomizer and calibration using working standard solutions (2.5-20.0 mu g L-1 Pb) in 0.2% (v/v) HNO3, analytical curve with good linear correlation (r = 0.9992) was established. The characteristic mass was 40 pg Pb and the lifetime of the tube was around 730 firings. The limit of detection (LOD) was 0.4 mu g L-1 and the relative standard deviations (n = 12) were typically <8% for a sample containing 25 pg L-1 Pb. Accuracy of the proposed method was checked after direct analysis of 23 vinegar samples. A paired t-test showed that results were in agreement at 95% confidence level with those obtained for acid-digested vinegar samples. The Pb levels varied from 2.8 to 32.4 pg L-1. Accuracy was also checked by means of addition/recovery tests and recovered values varied from 90% to 110%. Additionally, two certified reference materials were analyzed and results were in agreement with certified values at a 95% confidence level. (C) 2006 Elsevier Ltd. All rights reserved.

Evidence of hetero-epitaxial growth of Pb(Mg1/3Nb2/3)O-3 on the BaTiO3 seed particles of a citrate solution

Citrate solution was employed in preparing Pb(Mg1/3Nb1/3)O-3 (PMN) powder from polymeric precursors. BaTiO3 particles of 600 nm average size were used as seed for growing PMN. X-ray diffraction (XRD) indicated the presence of both, pyrochlore Pb6Nb6MgO22 (P6N) and perovskite phases. Transmission electron microscopy (TEM) observations indicated that only the PMN phase has hetero-epitaxially grown on the BaTiO3 seed particles. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Effects of the postannealing atmosphere on the dielectric properties of (Ba, Sr)TiO3 capacitors: Evidence of an interfacial space charge layer

The dielectric properties of (Ba, Sr)TiO3 films were found to be remarkably sensitive to the postannealing treatment atmosphere. This study demonstrates that postannealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that postannealing in a nitrogen atmosphere produces a slight dielectric relaxation. Such dependence of the dielectric relaxation was related both to oxygen vacancies and to the presence of negatively charged oxygen, trapped at the grain boundary and/or at the electrode/dielectric film interface. (C) 2000 American Institute of Physics. [S0003-6951(00)00817-2].

Distribution profile and availability of Cr, Ni, Cu, Cd and Pb in different sediments from anhumas surface water collection reservoir, Araraquara-São Paulo State, Brazil

In this work the influence of the anhtropogenic activities in the uptake of metals at a reservoir for public water supply in Araraquara City, São Paulo State, Brazil was studied. For this, the distribution of Cr, Ni, Cu, Cd and Pb in sediments collected from Anhumas reservoir, at seven sampling points and at three depths for each point was investigated. The pseudo-total and available metals contained in the different sediment samples were assessed using an ICP-AES technique. Among the five metals studied, cadmium possesses the largest relative potential availability, with percentages of 20 to 98% for the three different sediment types. In addition, the following decreasing availability order was characterized: Cd > Cu > Pb > Ni > Cr.

Distribution of Cr, Ni, Cu, Cd and Pb in different molecular size of humic fractions extracted from water and sediment samples collected at Anhumas reservoir - Araraquara/SP

In this work was studied the distribution of Cr, Ni, Cu, Cd and Pb in humic fractions with different molecular size. The HS were extracted from waters (AHS), surface sediments (HESS), interface water sediment (HSIS) and bottom sediment (HSBS) collected in the Anhumas surface water collection reservoir, located in the district of Araraquara - São Paulo State Brazil. The humic substances were extracted by procedures recommended by International Humic Substances Society (IHSS). After purification by dialysis, the humic substances were fractionated using a multistage tangential flow ultrafiltration system. The fractionation patterns of HS characterized a mass distribution relatively uniform among the fractions with different molecular sizes, with larger values in the fractions F-2 (20.8%) and F-4 (23.8%), Except for the ions Pb(II) and Cu(II), which presented relatively higher concentrations in the fractions F-2 and F-4, respectively. In general, chromium, nickel, cadmium and lead have similar distributions in the five fractions with larger and medium molecular sizes (F-1 to F-5). With relation to the mass distributions in the different humic substances fractions extracted from sediment samples collected at three depth, they presented 42-48% of HS in the fractions with larger molecular sizes (F-1 and F-2), 29-31% in the middle fractions (F-3 and F-4) and 13-20% in the fractions with smaller molecular sizes (F-5 and F-6). In general, the metallic ions presented distributions similar among the respective fractions F-1 to F-6, Exceptions for Pb(II) and M(II) in surface sediment with concentrations relatively smaller in the fractions F-2 and F-4, respectively,

Evaluation of Ir, Ru, and W as permanent modifiers for the simultaneous determination of As, Bi, Pb, Sb, and Se in natural water by electrothermal atomic absorption spectrometry

Iridium-, Ru-, and W-coated platforms were prepared by thermal treatment of the transversely heated graphite atomizer and investigated for the simultaneous determination of As, Bi, Pb, Sb, and Se in tap water by electrothermal atomic absorption spectrometry. The maximum pyrolysis temperature for As and Bi increased in a modifier sequence W < Ru < Ir. For Pb, Sb, and Se, this sequence was W < Ru, It. Calculated characteristic masses in the presence of It, Ru, and W were 35, 33, and 35 pg for As; 63, 51, and 52 pg for Bi; 50, 32, and 34 pg for Pb; 40, 35, and 31 pg for Sb; and 39, 39, and 93 pg for Se, respectively. Ruthenium was elected as the optimum modifier.Repeatability of the measurements was typically < 6%. Recoveries of As, Bi, Pb, Sb, and Se added to tap water samples varied from 79 to 109%. Accuracy was also checked by analysis of five certified reference materials (CRMs) from the National Institute of Standards and Technology (NIST1640 - Trace Elements in Natural Water; NIST 1643d Trace Elements in Water) and High Purity Standards (Trace Metals in Drinking Water Standards, lots #812708, #591107, and #710710). A paired t-test showed that the results for the CRMs were in agreement at the 95% confidence level with the certified values. The graphite tube lifetime was about 650 firings. multi-element determination is particularly challenging due to the necessity of carefully optimizing compromise conditions.Based on the considerations listed above, the aim of this paper was to evaluate the behavior of Ir, Ru, and W as permanent modifiers for the simultaneous determination of As, Bi, Pb, Sb, and Se. The performance of the proposed procedure was also verified after the ETAAS analysis of tap waters and reference materials.

Microstructure and dielectric properties of (Ba,Sr)TiO3 thin film produced by the polymeric precursor method

BaxSr1-xTiO3 (x = 0.6) (BST) thin films were successfully prepared on a Pt(111)/TiO2/SiO2/Si(100) substrate by spin coating, using the polymeric precursor method. BST films with a perovskite single phase were obtained after heat treatment at 700 degrees C. The multilayer BST thin films had a granular structure will a grain size of approximately 60 nm. A 480-nm-thick film was obtained by carrying out five cycles of the spin-coating/heating process. Scanning electron microscopy and atomic force microscopy analyses showed that the thin films had a smooth, dense, crack-free surface with low surface roughness (3.6 nm). At room temperature and at a frequency of 100 kHz, the dielectric constant and the dissipation factor were, respectively, 748 and 0.042. The high dielectric constant value was due to the high microstructural quality and chemical homogeneity of the thin films obtained by the polymeric precursor method.

Terrane transfer during the Grenville orogeny: tracing the Amazonian ancestry of southern Appalachian basement through Pb and Nd isotopes

Whole rock Pb isotope data can be used to determine the provenance of different blocks within the Rodinia supercontinent, providing a test for paleogeographic reconstructions. Calculated isotopic values for the source region of the Grenville-deformed SW Amazon craton (Rondonia, Brazil), anchored by published U-Pb zircon ages, are compared to those from the Grenville belt of North America and Grenvillian basement inliers in the southern Appalachians. Both the SW Amazon craton and the allochthonous Blue Ridge/Mars Hill terrane are defined by a similar Pb isotopic signature, indicating derivation from an ancient source region with an elevated U/Pb ratio. In contrast, the Grenville Province of Laurentia (extending from Labrador to the Llano Uplift of Texas) is characterized by a source region with a distinctly lower, time-integrated U/Pb ratio. Published U-Pb zircon ages (ca. 1.8 Ga) and Nd model ages (1.4-2.2 Ga) for the Blue Ridge/Mars Hill terrane also suggest an ancient provenance very different from the rest of the adjacent Grenville belt, which is dominated by juvenile 1.3-1.5 Ga rocks. The presence of mature continental material in rocks older than 1.15 Ga in the Blue Ridge/ Mars Hill terrane is consistent with characteristics of basement rocks from the SW Amazon craton. High-grade metamorphism of the Blue Ridge/Mars Hill basement resulted in purging of U, consistent with observations of the rest of the North American Grenville province. In contrast, the Grenvillian metamorphic history of the Amazon appears to have been much more heterogeneous, with both U enrichment and U depletion recorded locally. We propose that the Blue Ridge/ Mars Hill portion of the Appalachian basement is of Amazonian provenance and was transferred to Laurentia during Grenvillian orogenesis after similar to1.15 Ga. The presence of these Amazonian rocks in southeastern Laurentia records the northward passage of the Amazon craton along the Laurentian margin, following the original collision with southernmost Laurentia at ca. 1.2 Ga. (C) 2004 Elsevier B.V. All rights reserved.