Reversible intermittent flow-injection determination of mercury in sediments and vinasses by cold vapor atomic absorption spectrometry

A reversible intermittent pow-injection procedure is proposed for the automated determination of mercury in sediments and vinasses by cold vapor atomic absorption spectrometry, CVAAS. Solutions of sample and stannous chloride are carried by two air streams and sequentially injected into the generator/separator chamber in a segmented asynchronous merging zone configuration. The intermittent flow in the forward direction carries the mercury vapor through the flow cell, and in the backward direction, if aspirates the the remaining solution from the vessel to waste. We investigated composition and concentration of reagents, pow rates, commutation times, reactor configuration, and conditions for mercury release. The accuracy was checked by mercury determination in a certified sediment and spiked vinasses and river waters. The system handles about 100 samples per hour (0.50-5.00 mu g L-1), consuming ca. 2.5 mL of sample and 50 mg of SnCl2 per determination; Good recoveries (92-103%) were obtained with spiked samples. Results are precise (RSD <3% for 2.5 mu g Hg L-1, n = 12) and in agreement with values for certified reference material at 95% confidence level. (C) 1999 John Wiley & Sons, Inc.

Negative nonlinear absorption in Er3+-doped fluoroindate glass

We report the observation of negative nonlinear absorption in fluoroindate glasses doped with erbium ions. The pumping wavelength is 800 nm which is doubly resonant with Er3+ ions transitions. A large nonlinear intensity dependence of the optical transmittance and strong upconverted fluorescence are obtained. The dependence of the upconverted fluorescence intensity with the laser power is described by a system of coupled-rate equations for the energy levels' populations. (C) 1998 American Institute of Physics. [S0021-8979(98)07816-5].

Immobilized cells of Acidithiobacillus ferrooxidans in PVC strands and sultite removal in a pilot-scale bioreactor

The biooxidation of ferrous ion into ferric ion by Acidithiobacillus ferrooxidans can be potentially used for the removal of H2S from industrial gases. In this work, Fe3+ ions were obtained through the oxidation of Fe2+ using the LR strain of At. ferrooxidans immobilized in PVC stands in a pilot-scale bioreactor, while H2S was removed in an absorption tower equipped with Rasching rings. At. ferrooxidans LR strain cells were immobilized by inoculating the bacterium in a Fe2+-mineral medium and percolating it through the support. After complete Fe2+ oxidation, which took around 90 h, the reactor was washed several times with sulfuric acid (pH 1.7) before a new cycle was started. Four additional cycles using fresh Fe2+ mineral medium were then run. During these colonization cycles, the time required for complete iron oxidation decreased, dropping to about 60 h in the last cycle. The batch experiments in the H2S gas removal trials resulted in a gas removal rate of about 98-99% under the operational conditions employed. In the continuous experiments with the bioreactor coupled to the gas absorption column, a gas removal efficiency of almost 100% was reached after 500 min. Precipitate containing mainly sulfur formed during the experimental trial was identified by EDX. (c) 2005 Elsevier B.V. All rights reserved.

Electronic structure of Pb1-xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

The electronic structure of Pb1-xLaxTiO3 (PLT) compounds for x ranging from 0 to 30 at. % of La is investigated by means of soft x-ray absorption near edge structure (XANES) at the Ti L-3,L-2 and O K edges. The greatest modification in the structure of the Ti 2p XANES spectra of the PLT compounds is observed in the region of the high energy peak of the L-3 edge (e(g) states), which exhibits a splitting in the undoped sample. As the amount of lanthanum increases, this splitting becomes less pronounced. This modification is interpreted as a decrease in the degree of disorder of titanium atoms, which is correlated to the substitution of Pb by La atoms. The structural changes observed at the low energy peaks of the O K-edge XANES spectra of the PLT compounds may be interpreted in terms of hybridization between O 2p, Ti 3d, and Pb 6p orbitals. A decrease in the degree of hybridization observed as Pb atoms are replaced by La atoms may be related to the differences in the ferroelectric properties observed between x=0.0 and x=0.30 compounds. (c) 2006 American Institute of Physics.

Influence of nutrition on the glucose absorption and tolerance test in horses submitted to different fasting periods

Four groups of horses of Brasileiro de Hipismo bred were submitted to fasting for 24 and 48 hours in order to study the absorption capacity of the small intestine. Two groups were fed with coast cross grass (Cynodon dactylon) and the other two groups with coast cross pasture and grains. At the end of the fasting periods, the groups received 1g of glucose/kg of body weight in a 20% solution through a nasogastric tube. Blood samples were collected immediately before and 70, 60, 120, 180, 240, 300, and 360 minutes after glucose administration. Glycemia was determined by the orthotoluidine method and insulin by radioimmunoassay. The animals which received grains showed larger increase in glycemia and insulinemia than those maintained on pasture regimen alone. The 48-hour fasting period induced higher glycemia and insulinemia levels than those observed after 24-hour fasting.

Low-temperature synthesis of single-phase Co7Sb2O12

Polycrystalline Co7Sb2O12 compounds have been synthesized by a chemical route, which is based on a modified polymeric precursor method. In order to study the physical properties of the samples, X-ray diffraction (XRD), thermal analyses (TG and DSC), infrared spectroscopy (IR), specific surface area (BET), and magnetization measurements were performed on these materials. Characterization through XRD revealed that the samples are single-phase after a heat-treatment at 1100degreesC for 2h, while the X-ray patterns of the samples heat-treated at lower temperatures revealed the presence of additional Bragg reflections belonging to the Co6Sb2O6 phase. These data were analyzed by means of Rietveld refinement and further analyze showed that Co7Sb2O12 displays an inverse spinel crystalline structure. In this structure, the Co2+ ions occupy the eight tetrahedral positions, and the sixteen octahedral positions are randomly occupied by the Sb5+ and Co2+ ions. IR studies disclosed two strong absorption bands, v(1) and v(2), in the expected spectral range for a spinel-type binary oxide with space group Fd3m. Exploratory studies concerning the magnetic properties indicated that this sample presents a spin-glass transition at T-f similar to 64 K. (C) 2004 Elsevier B.V. All rights reserved.

Structural study of tungstate fluorophosphate glasses by Raman and X-ray absorption spectroscopy

Transparent glasses were synthesized in the NaPO3-BaF2 WO3 tertiary system and several structural characterizations were performed by X-ray absorption spectroscopy (XANES) at the tungsten L-I and L-III absorption edges and by Raman spectroscopy. Special attention was paid to the coordination state of tungsten atoms in the vitreous network.XANES investigations showed that tungsten atoms are only six-fold coordinated (octahedra WO6) and that these glasses are free of tungstate tetrahedra (WO4).In addition, Raman spectroscopy allowed to identify a break in the linear phosphate chains as the amount of WO3 increases and the formation of P-O-W bonds in the vitreous network indicating the modifier behavior of WO6 octahedra in the glass network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed to identify the presence of W-O- and W=O terminal bonds and a progressive apparition of W-O-W bridging bonds for the most WO3 concentrated samples (&GE; 30% molar) due to the formation of WO6 clusters. © 2004 Elsevier B.V. All rights reserved.

INVITRO ACTION OF VASOPRESSIN ON WATER-ABSORPTION BY RAT COLON

The action of vasopressin on water absorption was studied in vitro in the colon of rats, weighing approximately 250 g. Everted sacs of intestinal segments (ascending and descending colons) prepared with mucosa only were used. Vasopressin (10 mM) significantly stimulated water absorption in both the proximal (4.85 +/- 3.78 vs 1.51 +/- 1.16 ml/mg) and distal (10.39 +/- 3.52 vs 7.22 +/- 3.58 ml/mg) colon, which corresponds to an increase of 220% and 50%,respectively. The results indicate the need for a study of the possible physiological function of vasopressin in enhancing intestinal water absorption, when it is released in response to plasma hyperosmolarity.

Internal standardization in graphite furnace atomic absorption spectrometry: Comparative use of As and Ge to minimize matrix effects on Se determination in milk

Arsenic and germanium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium in milk by graphite furnace atomic absorption spectrometry (GFAAS) using tubes with integrated platform, pre-treated with W together with I'd as chemical modifier. The efficiency of As and Ge as internal standards for 25 mu g L-1 Se plus 500 mu g (L)-1 As or Ge in diluted (1 + 9 v/v) milk plus 1.0% (v/v) HNO3 was evaluated by means of correlation graphs plotted from the normalized absorbance signals (n = 20) of internal standard (axis gamma) versus analyte (axis x). The equations that describe the linear regression were: A(As)= - 0.004 +/- 0.019 +/- 1.02 + 0.019 A(Se) (r=0.9967 +/- 0.005); A(Ge)= - 0.0 17 +/- 0.015 + 1.01 +/- 0.015 A(Se) (r = 0.9978 +/- 0.004). Samples and reference solutions were automatically spiked with 500 mu g L-1 Ge or As and 1.0% (v/v) HNO3 by the autosampler. For 20 mu L of aqueous standard solutions, analytical curves in the 5.00-40.0 mu g L-1 Se range were established using the ratio of Se absorbance to internal standard absorbance (A(Se)A(IS)) versus analyte concentration, and good linear correlations were obtained. The characteristic mass was 40 pg Se. Limits of detection were 0.55 and 0.40 mu g L-1 with As and Ge as the internal standard, respectively. Relative standard deviations (RSD) for a sample containing 25 mu g L-1 Se were 1.2% and 1.0% (n = 12) using As and Ge, respectively. The RSD without internal standardization was about 6%. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 99-105% range with IS and in the 70-80% range without IS. Using Ge as the internal standard, results of analysis of standard reference materials were in agreement with certified values at a 95% confidence level. The selenium concentration for 10 analyzed milk samples varied from 5.0 to 20 mu g L-1. (c) 2005 Elsevier 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.

Energy States of Phosphorous Donor in Silicon in Fields up to 18 T

The evolution of the energy states of the phosphorous donor in silicon with magnetic field has been the subject of previous experimental and theoretical studies to fields of 10 T. We now present experimental optical absorption data to 18 T in combination with theoretical data to the same field. We observe features that are not revealed in the earlier work, including additional interactions and anti-crossings between the different final states. For example, according to the theory, for the "1s -> 2p (+)" transition, there are anti-crossings at about 5, 10, 14, 16, and 18 T. In the experiments, we resolve at least the 5, 10, and 14 T anti-crossings, and our data at 16 and 18 T are consistent with the calculations.

Changes on iron electrode surface during hydrogen permeation in borate buffer solution

Hydrogen interaction with oxide films grown on iron electrodes at open circuit potential (E-oc) and in the passive region (+0.30 V-ECS) was studied by chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy techniques. The results were obtained in deaerated 0.3 mol L-1 H3BO3 + 0.075 mol L-1 Na2B4O7 (BB, pH 8.4) solution before, during and after hydrogen permeation. The iron oxide film modification was also investigated by means of in situ X-ray absorption near-edge spectroscopy (XANES) and scanning electrochemical microscopy (SECM) before and during hydrogen permeation. The main conclusion was that the passive film is reduced during the hydrogen diffusion. The hydrogen permeation stabilizes the iron surface at a potential close to the thermodynamic water stability line where hydrogen evolution can occur. The stationary condition required for the determination of the permeation parameters cannot be easily attained on iron surface during hydrogen permeation. Moreover, additional attention must be paid when obtaining the transport parameters using the classical permeation cell. (c) 2007 Elsevier Ltd. All rights reserved.

Evaluation by Free Vibration Method of Moisture Absorption Effects in Polyamide/Carbon Fiber Laminates

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

Determination of Total Sulfur in Agricultural Samples by High-Resolution Continuum Source Flame Molecular Absorption Spectrometry

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