ABSTRACT A kinetic study of the cobalt electrodeposition onto a carbon fiber ultramicroelectrode of 11 μm of diameter was conducted in overpotential conditions from an aqueous solution containing 0.01 M CoCl2 + 0.1 M NH4Cl. From the voltamperometric and chronoamperometric studies, it was found that the value of the diffusion coefficient is 1.2x10−5 cm2 s−1. The analysis of the current density transients suggests that cobalt electrodeposition onto a carbon fiber electrode follows an instantaneous nucleation process controlled by spherical diffusion mass transport. Also, the number of active nucleation sites increases as the applied potential decreases.

Ibuprofen is a widely used pharmaceutical because of its therapeutic properties; it is considered a safe medicament, thus it does not require medical prescription to be sold. However, in order to ensure consumer's health it is indispensable that the pharmaceutical industry relies on analytic methods for its quantification. Potentiometry has proven to be a successful technique using second type electrodes, which in agreement with Nernst's equation can detect anions activity. On consideration of this, this research work presents the development of a second type electrode based on the silver/silver ibuprofenate pair. This involved modifying a pure silver wire using a sodium ibuprofenate solution, to obtain the redox pair. The following analytic parameters were obtained with the aid of the modified electrode: a sensitivity of -0.049 V decade [ibuprofenate]-1, 8 µmol L-1 for the detection limit and a quantification limit of 1.2 µmol L-1. The repeatability value in terms of the relative standard deviation was 5.9%. After performing an interferences analysis using some ions and excipients, it was corroborated that there were none, thus allowing appropriate quantification on a real sample.

A modified screen printed electrode with [Fe(tris(3,5-dimethyl-1-pyrazolyl)borate)2]+[FeCl4]-, installed as part of a flow injection system, was used as an amperometric detector to determine hydrogen peroxide and glucose after on-line reaction with glucose oxidase. The influence of experimental variables on sensitivity, such as the flow rate, injection volume and reaction coil length, was evaluated using a two-level factorial experimental design. Under optimal conditions, detection limits of 15 μM and 0.5 mM for H2O2 and glucose, respectively, were obtained. A sampling rate of 60 determinations h-1 was achieved; the relative standard deviation of analytical measurements was <5.0%. The method was validated by comparing the obtained results with those provided by the enzymatic spectrophoto-metric method; no significant differences were observed (p < 0.05).

Un electrodo plano de carbono modificado con [Fe(tris(3,5-dimetil-1-pirazolil)borato)2]+[FeCl4]-, se integró en un sistema de inyección en flujo y se aplicó en la determinación amperométrica de peróxido de hidrógeno y glucosa mediante la incorporación de glucosa oxidasa. Se determinó la influencia de las variables experimentales como, caudal de trabajo, volumen de inyección y longitud del reactor sobre la sensibilidad mediante un diseño factorial completo a dos niveles. En condiciones óptimas se obtiene un límite de detección de 15 μM y 0.5 mM para H2O2 y glucosa, respectivamente, así como una velocidad de análisis de 60 determinaciones h-1, con una repetitividad expresada como desviación estándar relativa <5.0%. El método propuesto se validó comparando los resultados obtenidos con la metodología espectrofotométrica enzimática, no encontrándose diferencia significativa entre los resultados obtenidos por ambas metodologías (p < 0.05).