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In this paper, the possibility of analyzing levodopa and carbidopa by differential pulse voltammetry (DPV) utilizing a glassy carbon electrode in 0.1 mol L À1 HClO 4 is reported. Cyclic voltammograms of levodopa show a redox couple with anodic and cathodic peak potentials at 0.58 V and 0.52 V (vs. Ag/AgCl), respectively. For carbidopa, there are two oxidation waves with maximum currents at 0.53 V and 1.02 V, without any cathodic counterpart at slow enough scan rate. Since in such conditions, the oxidation product of carbidopa does not undergo reduction, it is possible to analyze levodopa without interference. On the other hand, carbidopa can be determined between 0.85 V and 1.1 V in the presence of levodopa, coating the electrode with a Nafion film, which is selective for carbidopa. The developed methodology was applied to two different commercial samples of pharmaceutical products. The obtained data were compared with the results of the analysis by high performance liquid chromatography (HPLC) with UV detection, showing good correlation (relative errors changing between 0.4% and 3.5%) and absence of interference of the other components that accompanied the pharmaceuticals.

It can be concluded that the use of the four priming agents, which are based on organic sulfur compounds, effectively enhanced bonding to the Ag-Pd-Cu-Au alloy and the component metals, although the bonding performance varied among the priming agents and metal elements. The priming agents appeared to have more of an effect on the alloy, silver and gold than on the palladium and copper.

, mas em sistemas tampões e especialmente em fosfato foram verificadas velocidades satisfatórias de transferência de elétrons. As diferenças observadas no comportamento eletroquímico e espectro de absorção UV-visível entre as flavinas imobilizadas foram discutidas em termos de diferentes tipos de interação. , but in buffer systems and especially in phosphate a good rate of electron transfer was observed. The differences verified in the electrochemical behavior and UV-visible absorption spectra among the immobilized flavins are discussed in terms of different kinds of interaction.

Abstract. This paper is concerned with the characterization of thin film electrodes by electrochemical impedance. The main problem addressed is the quantitative description of microscopic processes giving rise to frequency dispersion. Models are suggested for the identification and analysis of transport and capacitive processes occurring either at the bulk of the diffusion layer, or at its boundaries. Suitable representations in terms of transmission lines with generalized and distributed elements are provided. The main result is the possibility of the models to provide hints on the origin of the frequency dispersion and therefore correlating the response to structural elements. An application of the method is examined by analysis of impedance measurements of a WO3 electrochromic layer and a conducting polymer electrode.

This study examined the effect of alumina air-abrasion with different pressure on bonding between an acrylic resin and casting alloys. Disk specimens (8 and 10 mm in diameter) were cast from a silver-palladium-copper-gold (Ag-Pd-Cu-Au, Castwell M.C.12) alloy and a titanium-aluminum-niobium alloy (Ti-6Al-7Nb, T-Alloy Tough). The disks were air-abraded with alumina particles (50-70 microm) under different air-pressures (0 unabraded, 0.1, and 0.6 MPa). The disk pairs were bonded together with a tri-n-butylborane (TBB)-initiated acrylic resin, and shear bond strengths were determined both before and after thermocycling. Bond strength varied from a maximum of 37.1 MPa to a minimum of 3.6 MPa for the Ag-Pd-Cu-Au alloy, whereas bond strength to Ti-6Al-7Nb alloy ranged from 34.7 MPa to 0.1 MPa. Specimens abraded with 0.6 MPa pressure recorded the greatest post-thermocycling bond strength (21.7 MPa and 17.9 MPa), and unabraded specimens showed the lowest strength (3.6 MPa and 0.1 MPa) for both alloys. Post-thermocycling bond strength to the Ag-Pd-Cu-Au alloy was higher than that to the Ti-6Al-7Nb alloy under identical air-abrading conditions. It can be concluded that alumina air-abrasion with an air-pressure of 0.6 MPa is effective in enhancing retentive characteristics of the TBB-initiated resin joined to the alloys.

Prodigiosin is a red pigment characterizing S. marcescens and produced in abundance by the bacterium on peptone-glycerol (PG) agar plates incubated at 30°C. In a PG liquid culture, however, S. marcescens was unable to produce prodigiosin. On addition of silica gel (8.0 mg/ml) to the liquid medium, S. marcescens became able to proliferate better and produced prodigiosin and serrawettins (biosurfactant) profusely. The effect of the silica gel on the production of exolipids was dependent on source (manufacturers). By microscopic examination, sessile bacterial populations were recognized on the silica particles active in the promotion of prodigiosin production, but not on the particles unable to promote the production. Prodigiosin and serrawettins are structurally unrelated but seem to have the same production control systems responding to temperature (T. Matsuyama, et al., J. Gen. Microbiol., 132, 865-875, 1986) and silica gel.