The evolution of arsenic excess induced by thermal annealing in arsenic-rich Ga1-xAsx films

The evolution of As excess in As-rich Ga1-xAsx films is analyzed for distinct As concentrations and different annealing temperatures. Initially the samples are amorphous and crystallize partially after thermal annealing. The formation of both amorphous and crystalline As clusters is examined by micro-Raman and X-ray diffraction analysis. When highly and moderately unbalanced materials are compared, differences are clearly observed concerning the crystallization temperature and the migration kinetics of the As excess. These differences are explained by the fort-nation of As precipitates around the GaAs crystallites in the moderately unbalanced material, contrasting with the migration of the As excess to the film surface in the highly unbalanced material.

Fetotoxicity caused by the interaction between zinc and arsenic in mice

Arsenic is an environmental pollutant that induces congenital malformations in experimental models and can contribute to human birth defects. The environmental exposure to arsenic is relatively small when compared with the doses required to cause teratogenicity in mice and other laboratory animals. In order to study the action of zinc in the arsenic-induced teratogenicity, in the present work mice were either pretreated with zinc and later with arsenic or were treated simultaneously with zinc and arsenic in vivo and in vitro. Following administration of arsenate on gestation day 8, pregnant females were killed on the 17th day of gestation; maternal and fetal data were collected by laparotomy and used to calculate reproductive parameters. Fetuses were analyzed for the presence of external malformation and, after the appropriate processing, visceral and skeletal analyses were accomplished. Conceptuses were exposed in whole embryo culture to arsenicals on gestation day 8 (3-6 somite stage). After a 26 h culture period, morphological development was assessed. Neither pretreatment with zinc nor simultaneous administration of zinc prevented arsenic teratogenicity in these experimental models. (C) 2002 Wiley-Liss, Inc.

Kinetics of Ag-rich precipitates formation in Cu-Al-Ag alloys

The kinetics of Ag-rich precipitates formation in the Cu-2 wt.% Al alloy with additions of 2, 4, 6, 8, 10 and 12 wt.% Ag was studied using microhardness changes with temperature and time, differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that an increase in the Ag content decreases the activation energy for Ag-rich precipitates formation, and that it is possible to estimate the values of the diffusion and nucleation activation energies for the Ag precipitates. (C) 2004 Elsevier B.V. All rights reserved.

Grain-boundary segregation and precipitates in La2O3 and Pr2O3 doped SnO2 center dot CoO-based varistors

Structural heterogeneities in SnO2.CoO-based varistors were analyzed by transmission electron microscopy. In SnO2.CoO-based system doped with La2O3 and Pr2O3 two kinds of precipitate phases at grain boundary region were found. Using energy dispersive spectrometry they were found to be Co2SnO4 and Pr2Sn2O7, presenting a defined crystalline structure. It was also identified that such precipitate phases are mainly located in triple-junctions of the microstructure. HRTEM analysis revealed the existence of other two types of junctions, one as being homo-junctions of SnO2 grains and other due to twin grain boundaries inside the SnO2.CoO grain. The role of these types of junction in the overall nonlinear electrical features is also discussed. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Direct determination of arsenic in sugar by GFAAS with transversely heated graphite atomizer and longitudinal Zeeman-effect background correction

A method has been developed for the direct determination of As in sugar by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer (end-capped THGA) and longitudinal Zeeman-effect background correction. The thermal behavior of As during the pyrolysis and atomization steps was investigated in sugar solutions containing 0.2% (v/v) HNO3 using Pd, Ni, and a mixture of Pd + Mg as the chemical modifiers. For a 60-muL sugar solution, an aliquot of 8% (m/v) in 0.2% (v/v)HNO3 was dispensed into a pre-heated graphite tube at 70 degreesC. Linear analytical curves were obtained in the 0.25 - 1.50-mug L-1 As range. Using 5 mug Pd and a first pyrolysis step at 600 degreesC assisted by air during 40 s, the formation of a large amount of carbonaceous residue inside the atomizer was avoided. The characteristic mass was calculated as 24 pg As and the lifetime of the graphite tube was around 280 firings. The limit of detection (L.O.D.) based on integrated absorbance was 0.08 mug L-1 (4.8 pg As) and the typical relative standard deviation (n = 12) was 7% for a sugar solution containing 0.5 mug L-1. Recoveries of As added to sugar samples varied from 86 to 98%. The accuracy was checked in the direct analysis of eight sugar samples. A paired t-test showed that the results were in agreement at the 95% confidence level with those obtained for acid-digested sugar samples by GFAAS.

Determination of selenium in nutritionally relevant foods by graphite furnace atomic absorption spectrometry using arsenic as internal standard

A method has been developed for the direct determination of Se in nutritionally relevant foods by graphite furnace atomic absorption spectrometry. Tungsten/rhodium carbide coating on the integrated platform of a transversely heated graphite atomizer or W coating with co-injection of Pd(NO3)(2) were used as a permanent modifiers. Samples and reference solutions were spiked with 500 mu g L-1 As and absorbance variations due to changes in experimental conditions were minimized. For 20 mu L aqueous analytical solutions delivered into the graphite tube, analytical curves in the 5.0-40 mu g L-1 with good linear correlation were established. Pyrolysis and atomization temperatures were evaluated using pyrolysis and atomization curves, respectively. The optimized heating program (temperature, ramp time, hold time) of the graphite tube of the Perkin-Elmer SIMAA 6000 atomic absorption spectrometer was: dry steps (110 degrees C, 5 s, 10 s; 130 degrees C, 15 s, 15 s); air-assisted pyrolysis step (600 degrees C, 20 s, 40 s; 20 degrees C, 1 s, 40 s); pyrolysis step (1300 degrees C, 10 s, 20 s); atomization step (2100 degrees C, 0 s, 4 s); clean step (2550 degrees C, 1 s, 5 s). The method was applied for Se determination in coconut water, coconut milk, soybean milk, cow milk, tomato juice, mango juice, grape juice and drinking water samples and four standard reference materials and results were in agreement at 95% confidence level. The lifetime of the tube was 500 firings and the relative standard deviations of measurements of typical samples containing 25 mu gL(-1) Se were 3.0% and 6.0% (n = 12) with and without internal standardization, respectively. The limits of detection were in the 0.35 mu g L-1-0.7 mu g Se L-1 range. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 98-109% range. (c) 2004 Elsevier Ltd. All rights reserved.

A hydride generation flow system for determination of arsenic and selenium by total reflection X-ray fluorescence spectrometry

In this work, a preconcentration and separation system based on continuous flow hydride generation is proposed to improve the determination of As and Se by total reflection X-ray fluorescence spectrometry. The generated hydrides are continuously separated from the liquid phase and collected in a chamber containing 250 mul of HCI/HNO3 1:1 (v/v) solution. Hydride generation conditions and collection of the hydrides were evaluated. Under optimised conditions, enrichment factors of 55 for As and 82 for Se were attained. Detection limits of 0.3 mug l(-1) for As and Se were obtained when 20 ml of sample was used. Analysis of a natural water standard reference material from National Institute of Standard and Technology (SRM-1640) was in agreement with the certified values at the 95% confidence level. (C) 2004 Elsevier B.V. All rights reserved.

Spectrophotometric detection of arsenic using flow-injection hydride generation following sorbent extraction preconcentration

An automated system with a C-18 bonded silica gel packed minicolumn is proposed for spectrophotometric detection of arsenic using flow-injection hydride generation following sorbent extraction preconcentration. Complexes formed between arsenic(III) and ammonium diethyl dithiophosphate (ADDP) are retained on a C-18 sorbent. The eluted As-DDP complexes are merged with a 1.5% (w/v) NaBH4 and the resulting solution is thereafter injected into the hydride generator/gas-liquid separator. The arsine generated is carried out by a stream of N-2 and trapped in an alkaline iodine solution in which the analyte is determined by the arsenomolybdenum blue method. With preconcentration time of 120 s, calibration in the 5.00-50.0 mu g As l(-1) range and sampling rate of about 20 samples h(-1) are achieved, corresponding to 36 mg ADDP plus 36 mg ammonium heptamolybdate plus 7 mg hydrazine sulfate plus 0.7 mg stannous chloride and about 7 mi sample consumed per determination. The detection limit is 0.06 mu g l(-1) and the relative standard deviation (n = 12) for a typical 17.0 mu g As l(-1) sample is ca. 6%. The accuracy was checked for arsenic determination in plant materials from the NIST (1572 citrus leaves; 1573 tomato leaves) and the results were in agreement with the certified values at 95% confidence level. Good recoveries (94-104%) of spiked tap waters, sugars and synthetic mixtures of trivalent and pentavalent arsenic were also found. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Arsenic as internal standard to correct for interferences in the determination of antimony by hydride generation in situ trapping graphite furnace atomic absorption spectrometry

The feasibility of using internal standardization (IS) to correct for interferences in hydride generation with in situ trapping in graphite furnace was evaluated. Arsenic was chosen as internal standard for Sb determination and Ir was used as permanent modifier. Fluctuations in the main parameters that affect the analytical results were minimized by IS and an effective contribution was verified in the studies of liquid phase interferences. Cobalt and Ni2+ were selected to illustrate the potential use of IS on the correction of interference by transition metals. The application of IS allows the Sb determination in samples containing up to 20-fold higher concentration of the Co2+ and Ni2+ when compared to the procedure without IS. The relative standard deviation of measurements varied from 0.3% to 0.7% and from 1.1% to 3.2% with and without IS, respectively. Recoveries within 92% and 107% of spiked aqueous solution containing Sb(III) and Sb(V) were found. (c) 2005 Elsevier B.V. All rights reserved.

A Simple Method Based on ICP-MS for Estimation of Background Levels of Arsenic, Cadmium, Copper, Manganese, Nickel, Lead, and Selenium in Blood of the Brazilian Population

Throughout the world, biomonitoring has become the standard for assessing exposure of individuals to toxic elements as well as for responding to serious environmental public health problems. However, extensive biomonitoring surveys require rapid and simple analytical methods. Thus, a simple and high-throughput method is proposed for the determination of arsenic (As), cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and selenium (Se) in blood samples by using inductively coupled plasma-mass spectrometry (ICP-MS). Prior to analysis, 200 l of blood samples was mixed with 500 l of 10% v/v tetramethylammonium hydroxide (TMAH) solution, incubated for 10 min, and subsequently diluted to 10 ml with a solution containing 0.05% w/v ethylenediamine tetraacetic acid (EDTA) + 0.005% v/v Triton X-100. After that, samples were directly analyzed by ICP-MS (ELAN DRC II). Rhodium was selected as an internal standard with matrix-matching calibration. Method detection limits were 0.08, 0.04, 0.5, 0.09, 0.12, 0.04, and 0.1 g//L for As, Cd, Cu, Mn, Ni, Pb, and Se, respectively. Validation data are provided based on the analysis of blood samples from the trace elements inter-\comparison program operated by the Institut National de Sante Publique du Quebec, Canada. Additional validation was provided by the analysis of human blood samples by the proposed method and by using electrothermal atomic absorption spectrometry (ETAAS). The method was subsequently applied for the estimation of background metal blood values in the Brazilian population. In general, the mean concentrations of As, Cd, Cu, Mn, Ni, Pb, and Se in blood were 1.1, 0.4, 890, 9.6, 2.1, 65.4, and 89.3 g/L, respectively, and are in agreement with other global populations. Influences of age, gender, smoking habits, alcohol consumption, and geographical variation on the values were also considered. Smoking habits influenced the levels of Cd in blood. The levels of Cu, Mn, and Pb were significantly correlated with gender, whereas Cu and Pb were significantly correlated with age. There were also interesting differences in Mn and Se levels in the population living in the north of Brazil compared to the south.

Precipitates segmentation from scanning electron microscope images through machine learning techniques

The presence of precipitates in metallic materials affects its durability, resistance and mechanical properties. Hence, its automatic identification by image processing and machine learning techniques may lead to reliable and efficient assessments on the materials. In this paper, we introduce four widely used supervised pattern recognition techniques to accomplish metallic precipitates segmentation in scanning electron microscope images from dissimilar welding on a Hastelloy C-276 alloy: Support Vector Machines, Optimum-Path Forest, Self Organizing Maps and a Bayesian classifier. Experimental results demonstrated that all classifiers achieved similar recognition rates with good results validated by an expert in metallographic image analysis. © 2011 Springer-Verlag Berlin Heidelberg.

Automatic segmentation of the secondary austenite-phase island precipitates in a superduplex stainless steel weld metal

Duplex and superduplex stainless steels are class of materials of a high importance for engineering purposes, since they have good mechanical properties combination and also are very resistant to corrosion. It is known as well that the chemical composition of such steels is very important to maintain some desired properties. In the past years, some works have reported that γ 2 precipitation improves the toughness of such steels, and its quantification may reveals some important information about steel quality. Thus, we propose in this work the automatic segmentation of γ 2 precipitation using two pattern recognition techniques: Optimum-Path Forest (OPF) and a Bayesian classifier. To the best of our knowledge, this if the first time that machine learning techniques are applied into this area. The experimental results showed that both techniques achieved similar and good recognition rates. © 2012 Taylor & Francis Group.

Evaluation of sample preparation procedures and krypton as an interference standard probe for arsenic speciation by HPLC-ICP-QMS

Different conditions of extraction using water, a methanol-water mixture and nitric acid solutions were evaluated for speciation of As(iii), As(v), DMA and MMA in plant samples that previously received As(v) after being sown and emergence was investigated. Microwave-assisted extraction (MAE) using diluted nitric acid solutions was also performed for arsenic extraction from chicken feed samples. The separation and determination of arsenic species were performed using HPLC-ICP-MS. The interference standard method (IFS) using 83Kr+ as the IFS probe was employed to minimize spectral interferences caused by polyatomic species, such as 40Ar 35Cl+. The extraction procedures tested presented adequate extraction efficiencies (90%), and the four arsenic species evaluated were found in plant samples. Extractions with diluted nitric acid solution at 90 °C were the most efficient strategy, with quantitative recoveries for all four As species in plant tissues. On the other hand, the methanol-water mixture was the solvent with the lowest extraction efficiency (50-60%). For chicken feed samples, MAE at 100 °C for 30 min resulted in an extraction efficiency of 97% and only As(v) was found, without any species interconversion. The IFS method contributed to improving precision and limits of detection and quantification for all tested extraction procedures. Significant improvements on accuracy were obtained by applying the IFS method and recoveries between 77 and 94%, and 82 and 93% were obtained for plant extracts and chicken feed samples, respectively. This journal is © 2013 The Royal Society of Chemistry.

Ag-rich precipitates formation in the Cu-11%Al-10%Mn-3%Ag alloy

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

Speciation analysis of inorganic arsenic in river water by Amberlite IRA 910 resin immobilized in a polyacrylamide gel as a selective binding agent for As(v) in diffusive gradient thin film technique

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