Evaluation and application of bismuth as an internal standard for the determination of lead in wines by simultaneous electrothermal atomic absorption spectrometry

A method for the direct determination of Pb in wines by simultaneous multi-element atomic absorption spectrometry (SIMAAS) using a transversely heated graphite atomizer, Zeeman-effect background corrector and internal standardization is proposed. Bismuth was used as an internal standard and Pd(NO3)(2) plus Mg(NO3)(2) as chemical modifier,to stabilize both the analyte and the internal standard. The implementation of two pyrolysis steps avoided any build-up of carbonaceous residues on the graphite platform. All diluted samples (1 + 1 v/v) in 0.2% v/v HNO3 and reference solutions (5.0-50 mug l(-1) Ph in 0.2% v/v HNO3) were spiked with 25 mug l(-1) Bi. For a 20 mul aliquot dispensed into the graphite tube, a good correlation (r = 0.9997) was obtained between the ratio of the analyte signal to the internal standard signal and the analyte concentration of the reference solutions. The electrothermal behaviour of Pb and Bi in red, white and rose wines were compared. In addition, absorbance variations due to changes in experimental conditions, such as atomizer temperature, integration time, injected sample volume, radiation beam intensity, graphite tube surface, dilution and sample composition, were minimized by using Bi as internal standard. Relative standard deviations of measurements based on integrated absorbance varied from 0.1 to 3.4% and from 0.5 to 7.3% (n = 12) with and without internal standard correction, respectively. Good recoveries (91-104%) for Pb spikes were obtained. The characteristic mass was 45 pg Pb and the limit of detection based on integrated absorbance was 0.9 mug l(-1) Pb. Internal standardization increased the lifetime of the tube by 25%. Direct determinations of Pb in wines with and without internal standardization approaches were in agreement at the 95% confidence level. The repeatability and the tube lifetime were improved when using Bi as internal standard. The improvement in accuracy using an internal standard was only observed when the analytical results were affected by errors.

Purification, partial characterization and preliminary X-ray diffraction analysis of a mannose-specific lectin from Cymbosema roseum seeds

A lectin from Cymbosema roseum seeds (CRL) was purified, characterized and crystallized. The best crystals grew in a month and were obtained by the vapour-diffusion method using a precipitant solution consisting of 0.1 M Tris-HCl pH 7.8, 8% (w/v) PEG 3350 and 0.2 M proline at a constant temperature of 293 K. A data set was collected to 1.77 angstrom resolution at a synchrotron-radiation source. CRL crystals are orthorhombic, belonging to space group P2(1)2(1)2(1). Crystallographic refinement and full amino-acid sequence determination are in progress.

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.

Structural and vibrational analysis of nanocrystalline Ga1-xMnxN films deposited by reactive magnetron sputtering

The structural and vibrational properties of nanocrystalline Ga1-xMnxN films deposited by reactive magnetron sputtering were analyzed in a wide composition range (0 < x < 0.18). The films were structurally characterized using x-ray diffraction with Rietveld refinement. The corresponding vibrational properties were investigated using micro-Raman and Fourier transform infrared spectroscopies. The films present a high crystallized fraction, crystallites having wurtzite structure, and high orientation texture with the c axis oriented perpendicular to the substrate surface. Rietveld analysis indicates that Mn atoms are incorporated substitutionally into Ga positions and show that the ionic character of cation-N bonds along the c axis is favored by the Mn incorporation. No evidence for Mn segregation or Mn rich phases was found in the composition range analyzed. Micro-Raman scattering spectra and infrared absorption experiments showed progressive changes with the increase of x and monotonic shifts of the GaN TO and LO peaks to lower frequencies. The structural and vibrational analyses are compared and the influence of Mn on the static and dynamic properties of the lattice is analyzed. (C) 2007 American Institute of Physics.

Purification, crystallization and preliminary X-ray diffraction analysis of carboxyhaemoglobin-II from the fish Piaractus mesopotamicus (pacu)

Carboxyhaemoglobin-II isolated from the pacu (Piaractus mesopotamicus) has been crystallized and X-ray diffraction data were collected to 2.0 Angstrom resolution using synchrotron radiation. Crystals were characterized as belonging to the space group I23; preliminary structural analysis reveals the presence of one dimer in the asymmetric unit.

A PC compatible Brazilian software for obtaining thermal histories using apatite fission track analysis

In this work a software developed in the Instituto de Fisica Gleb Wataghin, IFGW, UNICAMP, Campinas, SP, Brazil for obtaining thermal histories using apatite fission track analysis is presented. This software works in Microsoft-Windows environment. It will be freely disposable in the web site of the Departamento de Raios Cosmicos, IFGW, UNICAMP. Thermal histories obtained through this software are compared with those deduced using Monte Trax the software compatible with Apple Macintosh developed by Gallagher. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Low power laser radiation at 685 nm stimulates stem-cell proliferation rate in Dugesia tigrina during regeneration

Today's scientific interest in tissue engineering for organ transplantations and regeneration from stem cells, allied with recent observations on biostimulation of tissues and cells by laser radiation, stands as a strong motivation for the present work, in which we examine the effects of the low power laser radiation onto planarians under regenerative process. To investigate those effects, a number of 60 amputated worms were divided in three study groups: a control group and two other groups submitted to daily 1 and 3 min long laser treatment sections at similar to 910 W/m(2) power density. A 685 nm diode laser with 35 mW optical power was used. Samples were sent to histological analysis at the 4th, the 7th and the 15th (lays after amputation. A remarkable increase in stem cells counts for the fourth day of regeneration was observed when the regenerating worms was stimulated by the laser radiation. Our findings encourage further research works on the influence of optical radiation onto stem cells and tissue regeneration. (c) 2005 Elsevier B.V. All rights reserved.

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.

Crystallization and preliminary X-ray diffraction analysis of prephenate dehydratase from Mycobacterium tuberculosis H37Rv

Tuberculosis remains the leading cause of mortality arising from a bacterial pathogen ( Mycobacterium tuberculosis). There is an urgent need for the development of new antimycobacterial agents. The aromatic amino-acid pathway is essential for the survival of this pathogen and represents a target for structure-based drug design. Accordingly, the M. tuberculosis prephenate dehydratase has been cloned, expressed, purified and crystallized by the hanging-drop vapour-diffusion method using PEG 400 as a precipitant. The crystal belongs to the orthorhombic space group I222 or I2(1)2(1)2(1), with unit-cell parameters a = 98.26, b = 133.22, c = 225.01 angstrom, and contains four molecules in the asymmetric unit. A complete data set was collected to 3.2 angstrom resolution using a synchrotron-radiation source.

Crystallization and preliminary X-ray diffraction analysis of XAC1151, a small heat-shock protein from Xanthomonas axonopodis pv. citri belonging to the alpha-crystallin family

The hspA gene (XAC1151) from Xanthomonas axonopodis pv. citri encodes a protein of 158 amino acids that belongs to the small heat-shock protein ( sHSP) family of proteins. These proteins function as molecular chaperones by preventing protein aggregation. The protein was crystallized using the sitting-drop vapour-diffusion method in the presence of ammonium phosphate. X-ray diffraction data were collected to 1.65 angstrom resolution using a synchrotron-radiation source. The crystal belongs to the rhombohedral space group R3, with unit-cell parameters a = b = 128.7, c = 55.3 angstrom. The crystal structure was solved by molecular-replacement methods. Structure refinement is in progress.

Structural and ultrastructural analysis of embryonic development of Prochilodus lineatus (Valenciennes, 1836) (Characiforme ; Prochilodontidae)

This survey was performed to characterize the embryogenesis of Prochilodus lineatus. Seven stages of embryo development were identified - zygote, cleavage, blastula, gastrula, segmentation, larval and hatching - after a period of incubation of 22h (24 degrees C) or 14h (28 degrees C). The following cleavage pattern was identified: the first plane was vertical (2 blastomeres); the second was vertical and perpendicular to the first (4 blastorneres); the third was vertical and parallel to the first (4 x 2); the fourth cleavage was vertical and parallel to the second (4 x 4); the fifth was vertical and parallel to the first (4 x 8); and the sixth cleavage was horizontal (64 blastomeres). At the blastula stage (3.0-4.0 h (24 degrees C); 1.66-2.0h (28 degrees C) irregular spaces were detected and periblast structuring was initiated. At the gastrula stage (4.0-8.0 h (24 degrees C); 3.0-6.0 h (28 degrees C) the epiboly, convergence and cell movements, as well as the formation of embryonic layers, had begun. The segmentation stage (10.0-15.0h (24 degrees C); 7.0-10.0h (28 degrees C)) was characterized by a rudimentary formation of organs and systems (somites, optic vesicle and intestinal delimitation). The embryo at the larval stage (16.0-21.0 h (24 degrees C); 11.0-13.0 h (28 degrees C)) showed a free tail, more than 25 somites, an optic vesicle and a ready-to-hatch larval shape. The blastomeres at cleavage stage had disorganized nuclei indicating high mitotic activity. At gastrula, the blastomeres and the periblast had euchromatic nuclei and a large number of mitochondria and vesicles. The yolk was organized into globose sacs, which were dispersed into small pieces prior to absorption.

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l(-1) HNO3 and in 1 + 1 v/v diluted wine using mixtures of Pd(NO3)(2) + Mg(NO3)(2) and NH4H2PO4 + Mg(NO3)(2) as chemical modifiers. With 5 mug Pd + 3 mug Mg as the modifiers and a two-step pyrolysis (10 s at 400 degreesC and 10 s at 600 degreesC), the formation of carbonaceous residues inside the atomizer was avoided. For 20 mul of sample (wine + 0.056 mol l(-1) HNO3, 1 + 1, v/v) dispensed into the graphite tube, analytical curves in the 0.10-1.0 mug l(-1) Cd and 5.0-50 mug l(-1) Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 mug l(-1) for Cd, 0.8 mug l(-1) for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 mug l(-1) and for Pb at 500 mug l(-1). The relative standard deviations (n = 12) were typically < 8% for Cd and < 6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Ph was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level. (C) 2001 Elsevier B.V. B.V. All rights reserved.

High current-density anodic electro-dissolution in flow-injection systems for the determination of aluminium, copper and zinc in non-ferroalloys by flame atomic absorption spectrometry

An automatic Procedure with a high current-density anodic electrodissolution unit (HDAE) is proposed for the determination of aluminium, copper and zinc in non-ferroalloys by flame atonic absorption spectrometry, based on the direct solid analysis. It consists of solenoid valve-based commutation in a flow-injection system for on-line sample electro-dissolution and calibration with one multi-element standard, an electrolytic cell equipped with two electrodes (a silver needle acts as cathode, and sample as anode), and an intelligent unit. The latter is assembled in a PC-compatible microcomputer for instrument control, and far data acquisition and processing. General management of the process is achieved by use of software written in Pascal. Electrolyte compositions, flow rates, commutation times, applied current and electrolysis time mere investigated. A 0.5 mol l(-1) HNO3 solution was elected as electrolyte and 300 A/cm(2) as the continuous current pulse. The performance of the proposed system was evaluated by analysing aluminium in Al-allay samples, and copper/zinc in brass and bronze samples, respectively. The system handles about 50 samples per hour. Results are precise (R.S.D < 2%) and in agreement with those obtained by ICP-AES and spectrophotometry at a 95% confidence level.

Color and structural analysis of CoxZn7-xSb2O12 pigments

The polymeric precursor method was successfully used to synthesize CoxZn7-xSbO12 (x = 0-7) powders. Pigments were evaluated using colorimetry, X-ray diffraction, UV-vis and infrared spectroscopy. The optical band gap values vary with the Co2+ substitution. These results suggest that the concomitant presence of Co and Zn in the spinel lattice leads to the rupture of the Vegard law, as well as other properties of the studied system, such as unit cell volume. The Co-richer samples display a higher absorbance than the Co-lean samples. The high absorption of the Co7Sb2O12 sample at most of the visible region makes this compound a candidate for a black pigment. It was shown that color depends on the site where the chromophore ion is located, in agreement with the ligand field theory. (c) 2006 Elsevier Ltd. All rights reserved.

Crystallization and preliminary X-ray diffraction analysis of a novel Arg49 phospholipase A(2) homologue from Zhaoermia mangshanensis venom

Zhaoermiatoxin, an Arg49 phospholipase A(2) homologue from Zhaoermia mangshanensis (formerly Trimeresurus mangshanensis, Ermia mangshanensis) venom is a novel member of the PLA(2)-homologue family that possesses an arginine residue at position 49, probably arising from a secondary Lys49 -> Arg substitution that does not alter the catalytic inactivity towards phospholipids. Like other Lys49 PLA(2) homologues, zhaoermiatoxin induces oedema and strong myonecrosis without detectable PLA(2) catalytic activity. A single crystal with maximum dimensions of 0.2 x 0.2 x 0.5 mm was used for X-ray diffraction data collection to a resolution of 2.05 angstrom using synchrotron radiation and the diffraction pattern was indexed in the hexagonal space group P6(4), with unit-cell parameters a = 72.9, b = 72.9, c = 93.9 angstrom.