Determination of lead in the absence of supporting electrolyte using carbon fiber ultramicroelectrode without mercury film

The determination of lead ions directly in water, for application in analysis of samples of environmental interest, was studied by electroanalytical techniques. Linear sweep anodic stripping voltammetry with a carbon fiber disk ultramicroelectrode (7.0 mu m in diameter), without mercury film, has been used for lead determination, by standard addition, in purified water in the absence of supporting electrolyte. The response was linear in the range from 10.0 to 50.0 mu g L-1, with a detection limit of 0.8 mu g L-1, for 300 s preconcentration time, at -1.2 V and 1.0 V s(-1) scan rate. The reliability of the analytical procedure was evaluated by precision using relative standard deviations (5.6%, for three repetitive stripping current measurements of solution with 10.0 mu g L-1 lead ions) and by the accuracy with recovery experiments (mean of 110.8%) for the same concentration.

Serum electrolyte and total protein alterations in Pantaneiro horse during long distance exercise

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrical conductivity of silicate glasses with tetravalent cations substituting Si

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

Size distributions of fine silicate and other particles in Masaya's volcanic plume

Direct-sampling and remote-sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d <10 mu m) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d similar to 1.15 mu m. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as similar to 10(11) s(-1), equivalent to similar to 55 kg d(-1). Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(mu m) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d similar to 1 mu m. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as similar to 10(17) s(-1), equivalent to similar to 5.5 Mg d(-1) where d < 4 mu m.

Development and testing of anode-supported solid oxide fuel cells with slurry-coated electrolyte and cathode

A laboratory setup was designed and put into operation for the development of solid oxide fuel cells (SOFCs). The whole project consisted of the preparation of the component materials: anode, cathode and electrolyte, and the buildup of a hydrogen leaking-free sample chamber with platinum leads and current collectors for measuring the electrochemical properties of single SOFCs. Several anode-supported single SOFCs of the type (ZrO(2):Y(2)O(3)+NiO) thick anode/(ZrO(2):Y(2)O(3)) thin electrolyte/(La(0.65)Sr(0.35)MnO(3)+ZrO(2):Y(2)O(3)) thin cathode have been prepared and tested at 700 and 800 degrees C after in situ H(2) anode reduction. The main results show that the slurry-coating method resulted in single-cells with good reproducibility and reasonable performance, suggesting that this method can be considered for fabrication of SOFCs. (c) 2005 Elsevier B.V. All rights reserved.

Effects of different treatments on purity of silica from soluble sodium silicate

Noncrystalline silica was obtained with low iron, sodium, and nitrate ions concentrations from soluble sodium silicate (water glass) and nitric acid solution. Extractions with nitric acid solution and/or deionized water and/or dialysis were carried out to eliminate soluble metal ions. Products were dried in a microwave oven and characterized by chemical analysis, XRD, and IR. Dialysis seems to be the best treatment for the elimination of sodium and nitrate ions. Silica purified by nitric acid and water extractions followed by dialysis yields the purest silica sample.

Evaluation of glass ionomer cements properties obtained from niobium silicate glasses prepared by chemical process

Glass ionomer cements (GICs) are glass and polymer composite materials. These materials currently find use in the dental field. The purpose of this work is to obtain systems based on composition 4.5SiO(2)-3Al(2)O(3)-XNb2O5-2CaO to be used in Dentistry. The systems were prepared by chemical route at 700 degrees C. The results obtained by XRD and DTA showed that all systems prepared are glasses. The structures of the obtained glasses were compared to commercial material using Al-27 and Si-29 MAS NMR. The analysis of MAS NMR spectra indicated that the systems developed and commercial material are formed by SiO4 and AlO4 linked tetrahedra. The properties of glass ionomer cements based on the glasses prepared with several niobium contents were studied. Setting and working times of the cement pastes, microhardness and diametral tensile strength were evaluated for the experimental GICs and commercial luting cements. It was concluded that setting time of the cement pastes increased with increasing niobium content of the glasses (X). The properties to the GICs such as setting time and microhardness were influenced by niobium content. (c) 2005 Elsevier B.V. All rights reserved.

Factors affecting metabolic and electrolyte changes after reperfusion in liver transplantation

Background. The metabolic and electrolyte changes were evaluated after various durations of cold and warm ischemia times to correlate ASA status with hemodynamic changes that may affect the severity of the reperfusion syndrome.Patients and methods. Sixty-one patients who underwent liver transplantation (OLT) were monitored by arterial pH, PaO2, PaCO2, HCO3, BE, K+, Ca2+, Na+, GL, and serial Ht at three specific times: after the skin incision (baseline), 10 minutes before reperfusion (T-2), and 10 minutes after reperfusion (T-3). Changes in metabolic parameters were correlated with ASA status, hemodynamic changes, time of OLT, as well as cold and warm ischemia times.Results. The pH in ASA IV patients was significantly lower at T-1 and T-3, and PCO2 higher in ASA V at T-1. A significant correlation was observed between pH, PaCO2, HCO3 BE, Na+, Ca2+, and glucose with the phase of the procedure. The pH and HCO3 decreased significantly from T-1 and T-2, increasing during T-3. Ca2+ fell from T-1 to T-2 increasing in T-3. Mean glucose and sodium levels increase from T-1 to T-3. Mean BE dropped from T-1 to T-2 and increased at T-3 without a significant correlation between the metabolic parameters in any phase of the study and the cold or warm ischemia times. Patients with a high ASA status showed an increased risk for cardiovascular collapse after reperfusion.Conclusions. Patients with advanced ASA status are more prone to metabolic and acid-base disturbances during reperfusion, without any relation to the cold or warm ischemia times. High ASA status shows an increased risk for cardiovascular collapse after reperfusion.

Physical properties of silicate glasses doped with SnO2

The presence of tin in the network of silicate glasses produces changes in several of their physico-chemical properties. Glasses with the composition (mol%) 22Na(2)O (.) 8CaO (.) 70SiO(2) containing up to 5 wt% of SnO2 were analyzed under several experimental techniques. Dilatometric measurements showed an increase of the glass transition temperature with increasing tin content, while the average thermal expansion coefficient is reduced. Vickers microhardness, density, and refractive index also increase with the tin content. Diffuse reflectance spectra in the infrared (DRIFT) showed that the presence of tin, even at low concentrations, is responsible for some structural changes since there is an increase of the bridging oxygen concentration. The doped glasses present a brown color and optical absorption spectra measurements are interpreted as being due to precipitation of tin in the form of colloidal particles during cooling of the melted glass. In the Na+ <-> K+ ion exchange process the presence of tin in the glass network hinders the diffusion of these ions. The diffusion coefficients of those ions were calculated by the Boltzmann-Matano technique, after concentration profiles obtained by EDS measurements. All results obtained present evidences that Sn4+ cation acts as a glass network former. (c) 2005 Elsevier B.V. All rights reserved.

ROLE OF LATERAL HYPOTHALAMUS ON FLUID, ELECTROLYTE, AND CARDIOVASCULAR-RESPONSES TO ACTIVATION OF THE MSA

In this study we investigated the influence of electrolytic lesion or of opioid agonist injections into the lateral hypothalamus (LH) on the dipsogenic, natriuretic, kaliuretic, antidiuretic, presser, and bradycardic effects of cholinergic stimulation of the medial septal area (MSA) in rats. Sham- and LH-lesioned male Holtzman rats received a stainless steel cannula implanted into the LH. Other groups of rats had cannulas implanted simultaneously into the MSA and LH. Carbachol (2 nmol) injection into the MSA induced water intake, presser, and bradycardic responses. LH lesion reduced all of these effects (1-3 and 15-18 days). Previous injection of synthetic opiate agonist, FK-33824 (100 ng), into the LH reduced the water intake, natriuresis, kaliuresis, and presser responses induced by carbachol injected into the MSA. These data show that both electrolytic lesion or injection of an opiate agonist in the LH reduces the fluid-electrolyte and cardiovascular responses to cholinergic activation of the MSA. The involvement of LH with central excitatory and inhibitory mechanisms related to fluid-electrolytic and cardiovascular control is suggested.

NOVEL EVIDENCE THAT BETA-ADRENOCEPTORS OF THE MEDIAL SEPTAL AREA REGULATE BLOOD-PRESSURE AND ELECTROLYTE BALANCE

We investigated the participation of the beta-adrenoceptors of the septal area (SA) in sodium and potassium excretion and urine flow. The alterations in arterial pressure and some renal functions were also investigated. The injection of 2.10(-9) to 16.10(-9)M of isoproterenol, through a cannula permanently implanted into the SA produced a significant dose-dependent decrease in urinary Na+ and K+ excretion and urinary flow. Pretreatment with 16.10(-9) M butoxamine antagonized the effect of 4.10(-9) M isoproterenol but pretreatment with 16.10(-9) M practolol did not abolish the effect of isoproterenol. The beta 2-agonist terbutaline and salbutamol (4.10(-9) M when injected intraseptally also caused a decrease in urine flow and in renal Na+ and K+ excretion. After injection of isoproterenol or salbutamol (4.10(-9) M) into the SA, the arterial pressure, glomerular, filtration rate (GFR) and filtered Nd were reduced while Na+ fractional reabsorption was increased. The results indicate that the beta 2-adrenoceptors of the SA play a role in the decrease of Na+, K+ and urine flow and this effect may be due to a drop in GFR and filtered Na+ and to the rise in tubular Na+ reabsorption.

Red and blue emissions of europium doped gadolinium silicate from porous silica matrix and hydroxide carbonate with spherical shaped particles

In this work, Eu(III) and Eu(II) doped gadolinium silicates has been obtained as compact tubes starting from spherical gadolinium hydroxide carbonate using the pores of silica matrix as support and its surface as reagent. Eu(III) doped gadolinium silicate with hexagonal phase shows an interesting visible shifted charge transfer band when compared to disilicate with orthorhombic phase that was also obtained. Eu(II) gadolinium silicate has been prepared using CO atmosphere presenting an intense blue emission. The divalent europium system shows a potential application as an UV-blue converter. The samples were characterized by scanning electron microscopy (SEM), X-ray powder diffractometry (XRD) and photoluminescence spectroscopy. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Procedure optimization of silicate rocks dissolution in open vessels for ICP-AES analysis.

The main variables found on procedure of the dissolution silicate rocks using acid dissolution in teflon open vessel for analysis of micro elements by ICP-AES has been determined. The results obtained for some samples showed strong dependence of the rock mineralogical composition, then it was recommended an alkaline fusion step after acid dissolution. The decomposition procedure use 20 mi of an acid mixture of HF:HNO3 in the proportion 3:1 for a fraction of 250 mg pulverized sample. The recommended temperatures were 60 degrees C for attack and 90 degrees C for acid volatilization. The fusion step with 50 mg LiBO2 at 1000 degrees C may be used if non-attacked residue is observed in the solution. The whole time was 6 h per sample. Nine types os silicate rocks that show mineralogical and chemical different compositions were chosen for obtaining the optimization of the variables. The elements used were Ce, Y, Yb and Zr. In addition, ultrassonic nebulization has been used. The percentual standard deviations obtained for five determinations were 0.7 and 1.4 for triplicate samples. The mineralogical and textural information from the petrographical analysis of the samples indicated the need of increasing the fusion step on the optimized procedure.

Vascular effects and electrolyte homeostasis of the natriuretic peptide isolated from Crotalus oreganus abyssus (North American Grand Canyon rattlesnake) venom

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)