Non-stationary electrochemical response of polycrystalline cadmium in sodium hydroxide solutions

The anodization of cadmium in NaOH solutions produces a hydrous cadmium hydroxide-cadmium oxide layer and soluble cadmium species in solution. These processes are investigated through conventional voltammetry, potentiostatic, rotating ring disc electrode and complex voltammetric techniques by using NaOH solutions in the 0.01-1 M range at 25°C. The threshold potential of the anodic reaction is very close to the reversible potential of the Cd/Cd(OH)2 electrode. The overall anodic and cathodic reactions can be interpreted through a complex reaction model comprising a number of parallel reactions following the initial formation of CdOHad species at the electrode surface level. The relative contribution of each parallel reaction is determined by the concentration of OH− ion at the interface. The reaction model implies a composite structure of layers starting from CdOHad at the electrode surface, and subsequent layers with an increase in the water content on approaching the outmost oxide layer. The water content of anodic layer should increase according to the pH and layer thickness and decrease on increasing the applied potential. Under certain conditions the electrochemical reactions become ohmic resistance controlled. This fact presumably involves the formation of aged species and the onset of passivity.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetics and mechanism of the electroreduction of anodic layers produced on cadmium in alkaline solution containing sodium sulphide

The kinetics of the potentiostatic electroreduction of different anodic layers produced on cadmium in Na₂S containing alkaline solutions has been studied at 25°C. Two types of anodic layer were used: (i) layers produced in the potential range of CdS and Cd(OH)₂ stability, and (ii) layers predominantly composed of CdS. The electroreduction kinetics for both layers can be explained reasonably well throughout the nucleation and growth processes under diffusion control.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Ellipsometric changes produced by oxidation—reduction potential cycles applied to cadmium in sodium hydroxide solutions

Ellipsometry data obtained for the Cd-NaOH solution interface under the influence of potential cycles in the potential window where the Cd(OH)2-CdO layer can be electroformed and electroreduced, are particularly sensitive to both the layer thickness and the upper electroformation potential limit. The best fitting of the experimental results is obtained for two limiting situations. For thin anodic layers (d ⩽ 6 nm) the ellipsometric data fit the equation ñ=1.55−i 0.005, whereas for relatively thicker anodic layers (d > 7 nm) data can be adjusted through the equation ñ=2.6−i 0.10. These equations are consistent with the electroformation of a hydrous cadmium oxide layer at low potentials, and a cadmium oxide layer with a lower water content which grows beneath the former one at high potentials. Otherwise, the electroreduction of the anodic oxide layer yields a cadmium overlayer which exhibits a shift of the corresponding ellipsometric data as compared to the starting cadmium surface. This shift is presumably related to the development of different metal surface textures resulting from the different electroreduction conditions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Ellipsometric data of cadmium oxide layers formed anodically in sodium hydroxide solutions

The voltammetric formation of cadmium oxide layers in alkaline solutions is related to the appearance of two peaks which were assigned to successive reactions occurring within well defined potential ranges. It is interesting to attempt to follow the electroformation and electroreduction of the cadmium oxide layers by means of ellipsometry and to combine the latter to voltammetry in order to provide throughout the correlation of data a way to achieve a better knowledge of the ellipsometric parameters of Cd(OH), and Cd0 layers in contact with the alkaline solution. [Extraído a modo de resumen]Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Kinetics of the electroreduction of anodically formed cadmium oxide layers in alkaline solutions

The kinetics of the potentiostatic electroreduction of cadmium oxide layers on polycrystalline cadmium electrodes have been investigated in 0.01–1.0m NaOH solutions. The study was undertaken to determine the influence of passive film formation conditions on the electroreduction process of the anodically produced hydrous cadmium hydroxide-oxide layers. By properly adjusting the electroreduction conditions the cathodic potentiostatic current transients can be satisfactorily described by a nucleation and growth mechanism involving the participation of soluble Cd(II) and passivating anodic species. Experimental data were analysed by the application of non linear least squares fit routines. From the parametric identification procedure coherent potential dependencies of the corresponding fitting parameters as well as reasonable values of the physicochemical constants included in the reaction model, have been obtained. In this way it is possible to correlate kinetic data of the electroreduction process of the anodic oxide layers to make a discrimination between the different mechanistic contributions to this complex reaction involving several steps.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Can modern infrared analyzers replace gas chromatography to measure anesthetic vapor concentrations?

<p>Abstract</p> <p>Background</p> <p>Gas chromatography (GC) has often been considered the most accurate method to measure the concentration of inhaled anesthetic vapors. However, infrared (IR) gas analysis has become the clinically preferred monitoring technique because it provides continuous data, is less expensive and more practical, and is readily available. We examined the accuracy of a modern IR analyzer (M-CAiOV compact gas IR analyzer (General Electric, Helsinki, Finland) by comparing its performance with GC.</p> <p>Methods</p> <p>To examine linearity, we analyzed 3 different concentrations of 3 different agents in O₂: 0.3, 0.7, and 1.2% isoflurane; 0.5, 1, and 2% sevoflurane; and 1, 3, and 6% desflurane. To examine the effect of carrier gas composition, we prepared mixtures of 1% isoflurane, 1 or 2% sevoflurane, or 6% desflurane in 100% O₂(= O₂group); 30%O₂+ 70%N₂O (= N₂O group), 28%O₂+ 66%N₂O + 5%CO₂(= CO₂group), or air. To examine consistency between analyzers, four different M-CAiOV analyzers were tested.</p> <p>Results</p> <p>The IR analyzer response in O₂is linear over the concentration range studied: IR isoflurane % = -0.0256 + (1.006 * GC %), R = 0.998; IR sevoflurane % = -0.008 + (0.946 * GC %), R = 0.993; and IR desflurane % = 0.256 + (0.919 * GC %), R = 0.998. The deviation from GC calculated as (100*(IR-GC)/GC), in %) ranged from -11 to 11% for the medium and higher concentrations, and from -20 to +20% for the lowest concentrations. No carrier gas effect could be detected. Individual modules differed in their accuracy (p = 0.004), with differences between analyzers mounting up to 12% of the medium and highest concentrations and up to 25% of the lowest agent concentrations.</p> <p>Conclusion</p> <p>M-CAiOV compact gas IR analyzers are well compensated for carrier gas cross-sensitivity and are linear over the range of concentrations studied. IR and GC cannot be used interchangeably, because the deviations between GC and IR mount up to ± 20%, and because individual analyzers differ unpredictably in their performance.</p

Isolation and primary cultures of human intrahepatic bile ductular epithelium

A technique for the isolation of human intrahepatic bile ductular epithelium, and the establishment of primary cultures using a serum- and growth-factor-supplemented medium combined with a connective tissue substrata is described. Initial cell isolates and monolayer cultures display phenotypic characteristics of biliary epithelial cells (low molecular weight prekeratin positive; albumin, alphafetoprotein, and Factor VIII-related antigen negative). Ultrastructural features of the cultured cells show cell polarization with surface microvilli, numerous interepithelial junctional complexes and cytoplasmic intermediate prekeratin filaments. © 1988 Tissue Culture Association, Inc