RESUMEN
A new device to perform spectroelectrochemical measurements in the UV/visible spectral region using screen-printed electrodes has been developed. Neurotransmitter dopamine has been selected as a proof of concept of the capabilities of the new device. The results obtained have allowed us both to study the oxidation mechanism of dopamine and to carry out the spectroelectrochemical detection of this neurotransmitter. Differences in dopamine oxidation mechanism have been observed depending on the initial concentration. Thus, dopamine concentrations lower than 10(-3) M led to a higher generation of dopaminochrome and its derivatives with a band centered at 305 nm, which was the best wavelength to determine dopamine spectrophotometrically at these concentrations. However, if dopamine concentration is higher than 10(-3) M, dopaminoquinone is stable enough to use its maximum of absorbance, 395 nm, to detect this neurotransmitter. Dopamine concentration can also be calculated from the electrochemical data in spectroelectrochemistry, the results being comparable to that obtained from spectroscopic data. Comparison between spectrophotometric and electrochemical determinations demonstrates that the two methods measure this analyte indistinctively, proving that spectroelectrochemistry represents an autovalidated technique. Partial least-squares regression has also been used, obtaining good results in the full dopamine concentration range. Finally, as spectroelectrochemistry is an intrinsically trilinear technique, PARAFAC has been used to study the effect of probable interfering species.
Asunto(s)
Dopamina/análisis , Electroquímica/instrumentación , Impresión , Dopamina/química , Electrodos , Oxidación-Reducción , Espectrofotometría Ultravioleta , Agua/químicaRESUMEN
Spatial scanning spectroelectrochemistry is a new analytical technique that provides spectral information at different distances from an electrified liquid/liquid interface where an electrochemical process takes place. As a proof of concept, we have studied two different electrochemical processes at the electrified liquid/liquid interface: (1) Ru(bpy)(3)(2+) transfer through the water/1,2-dichloroethane interface and (2) electrodeposition of Pd nanoparticles at the water/1,2-dichloroethane interface. The instrumental setup developed consists of a movable slit for the light beam to sample at well-defined positions on both sides of the interface, providing important information about the chemical process occurring. If the slit is scanned at different distances from the interface during an electrochemical experiment, a complete picture of the reactions and equilibria in the diffusion layer can be obtained. For example, in the case of the Ru(bpy)(3)(2+), the experiments show clearly how the complex is transferred from one phase to the other. In the case of electrosynthesis of Pd nanoparticles, it is demonstrated that nanoparticles are not only deposited at the interface but diffuse to the aqueous bulk solution. These in situ observations were confirmed by ex situ experiments using transmission electron microscopy.
RESUMEN
UV-vis reflection spectroelectrochemistry has proven to be a very useful multiresponse technique to evaluate the quality of bismuth films obtained by electrochemical deposition on glassy carbon electrodes (GCEs). Bismuth films have recently emerged as a promising and environmental friendly alternative to mercury electrodes for stripping analysis. Spectroelectrochemical measurements, carried out in a flow cell, allowed us to follow in situ the electrodeposition and stripping of bismuth and cadmium. Electrochemical and spectroscopic responses individually have led to successfully quantify the amount of cadmium in test solutions.
Asunto(s)
Bismuto/química , Galvanoplastia , Espectrofotometría/métodos , Cadmio/química , Electrodos , Factores de TiempoAsunto(s)
Electroquímica/métodos , Oro Coloide/química , Nanoestructuras/química , Nanoestructuras/ultraestructura , Nanotecnología/métodos , Semiconductores , Espectrofotometría Ultravioleta , Impedancia Eléctrica , Ensayo de Materiales , Membranas Artificiales , Teoría Cuántica , Electricidad Estática , Resonancia por Plasmón de SuperficieRESUMEN
A new spectroelectrochemical flow cell is presented and its capability to provide a better understanding of reaction mechanisms is illustrated with the study of the electrosynthesis and characterization of a conducting polymer, polyaniline (PANI). A spectroelectrochemical study of electropolymerization of aniline under flow conditions has been performed for the first time. The significant influence that the flow rate of feeding monomer solution has on the electropolymerization process and, consequently, on the electrochromic properties of the resulting polymer has been demonstrated.
RESUMEN
El estudio hace un análisis prospectivo del resultado obtenido en los primeros 10 casos tratados con la técnica de cirugía endoscópica de columna vertebral en diferentes patologías. El objetivo es analizar la factibilidad para realizar los procedimientos habituales en el campo quirúrgico a través del abordaje endoscópico. En 1995, se inició en el Centro de Atención de Lesionados Raquimedulares de la Ciudad de México DGSS del D.F., el protocolo de estudio de la técnica de cirugía endoscópica en tratamientos que requerían de abordaje anterior. Se trataron dos casos de enfermedad de Scheuermann, mediante discotomía y resección del ligamento vertebral común anterior en cinco niveles torácicos, T-VI a T-X y T-V a T-XI con aplicación intersomática de injertos óseos. Un caso de tuberculosis vertebral de los niveles T-IX a T-XI, con dos semanas de evolución de daño neurológico motor, se efectuó debridación del absceso descompresión del canal raquídeo y se colocó injerto óseo intersomático. Un caso de proceso tumoral localizado en el cuerpo de T-XI, con integridad neurológica, (diagnóstico preoperatorio de hemangioma), se realizó corpectomía y aplicación de injerto óseo. Seis casos de fracturas con invasión a canal raquídeo en los niveles: T-VI, T-VIII, T-IX, T-X y dos casos en el nivel T-XI; clasificados con la escala de Frankel: dos E, uno D, tres a: Se realizó en un caso descompresión del saco dural con sección parcial del cuerpo vertebral sin aplicación de injerto óseo, en cinco casos se colocó injerto óseo posterior a la descompresión y en un caso se realizó además fijación anterior con placa y dos tornillos del tipo HMA Hollw Screw, en nueve casos se practicó una segunda cirugía por vía posterior para la colocación de un sistema de fijación y artrodesis con injerto óseo. Los promedios de los parámetros evaluados fueron los siguientes: Tiempo de cirugía 4 h, con 24 min, sangrado transoperatoria 390 cc., tiempo de pleurostomía de 2.7 días con una colección de 300 cc., tiempo para efectuar la segunda cirugía en 9 casos 3.3 días, tiempo de estancia hospitalaria 19 días. No se presentaron complicaciones durante el acto quirúrgico relacionadas con el procedimiento endoscópico. La técnica de endoscopía para la cirugía de la columna vertebral en la región torácica reduce las complicaciones traumáticas de la toracotomía y permite una pronta recuperación del paciente