Gold nanoelectrode ensembles for direct trace electroanalysis of iodide

A procedure for the standardization of ensembles of gold nanodisk electrodes (NEE) of 30 nm diameter is presented, which is based on the analytical comparison between experimental cyclic voltammograms (CV) obtained at the NEEs in diluted solutions of redox probes and CV patterns obtained by digital simulation. Possible origins of defects sometimes found in NEEs are discussed. Selected NEEs are then employed for the study of the electrochemical oxidation of iodide in acidic solutions. CV patterns display typical quasi-reversible behavior which involves associated chemical reactions between adsorbed and solution species. The main CV characteristics at the NEE compare with those observed at millimeter sized gold disk electrodes (Au-macro), apart a slight shift in E1/2 values and slightly higher peak to peak separation at the NEE. The detection limit (DL) at NEEs is 0.3 M, which is more than one order of magnitude lower than DL at the Au-macro (4 M). The mechanism of the electrochemical oxidation of iodide at NEEs is discussed. Finally, NEEs are applied to the direct determination of iodide at micromolar concentration levels in real samples, namely in some ophthalmic drugs and iodized table salt

SURFACE-ENHANCED RAMAN SPECTROSCOPY OF TRANSITION-METAL COMPLEXES AT SILVER AND GOLD ELECTRODES

Surface-Enhanced Raman (SER) spectra have been obtained at the silver-aqueous interface for transition-metal ammine complexes containing bridging ligands. SERS bands due to metal-ammine, internal ammine, and ligand-surface vibrations were observed. The intensities and frequencies of most of these bands were mildly potential dependent. However, the peak frequency and bandshape of the thiocyanate C-N stretch mode were potential sensitive, this can be understood in terms of electron withdrawal by silver surfaces. SERS have been observed for transition-metal ammine cations which cannot bind to the silver surface and are separated from it by a monolayer of halide anions. Their SERS intensities were comparable to those seen for closely related surface bound complexes. The formal potential of the Ru(NH(,3))(,6)(\u273+/2+ )couple obtained from SERS and electrochemical data was consistent with the Raman scatterers being located at the outer Helmholtz plane. The intensities and frequencies of SERS bands for these cations were not potential dependent, provided the halide coverage remained a monolayer. SER spectra were also obtained for unadsorbed anions. The observation of SERS for unbound ions is understood in terms of their electrostatic attraction with counter ions on the surface.(\u27) Comparisons are made between the kinetic behaviors extracted from the SERS data and from faradaic measurements. For electrostatically attracted cations, the SERS and electrochemical rate behaviors are similar, while for directly bound cations, the reactivity at the SERS-active sites are higher than for those of prevalent adsorbates. Spectra have been obtained for cyanide and transition-metal complexes, at gold electrodes. The frequency and bandshape of the cyanide C-N stretching mode were sensitive to its surface concentration. The SERS frequencies of transition-metal complexes were indicative of their redox states. Observation of SERS for electrostatically bound reactants suggests their strong diffuse-layer adsorption, this enabled unimolecular rate constants, k(,et) (sec (\u27-1)) and transfer coefficients, (alpha)(,et), to be determined for Co(III) ammine cations on a halide coated silver electrode, using fast linear sweep voltammetry. Comparison with the corresponding values for the solution reactants at the mercury-aqueous interface enabled the influence of precursor stability upon the rate parameters to be assessed

An investigation on the relationship between risk factors and severity of Tardive Dyskinesia

Abstract: The focus of most previous research concerning tardive dyskinesia has been on the impact of risk factors on the development (Incidence) of this syndrome. In this paper, we report our results on the relationship between risk factors and the severity of tardive dyskinesia. A total of 33 patients diagnosed as tardive dyskinesia with no other medical illness were studied: 21 males and 12 females with a mean age of 50. Twenty four of them were diagnosed as schizophrenia and 9 as mood disorder. Assessment of severity of tardive dyskinesia was based on the AIMS score. Significant positive correlations were found between age, sex, primary mental illness and severity of tardive dyskinesia. Keywords: Tardive dyskinesia, Risk factor