Browsing by Subject "Square wave voltammetry"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Publication
    Open Access
    Application of voltammetric techniques at microelectrodes to the study of the chemical stability of highly reactive species
    (American Chemical Society (ACS), 2014-12-31) Laborda, Eduardo; Olmos, José Manuel; Torralba, Encarnación; Molina, Ángela; Química Analítica
    The application of voltammetric techniques to the study of chemical speciation and stability is addressed both theoretically and experimentally in this work. In such systems, electrode reactions are coupled to homogeneous chemical equilibria (complexations, protonations, ion associations,…) that can be studied in a simple, economical and accurate way by means of electrochemical methods. These are of particular interest when some of the participating species are unstable given that the generation and characterization of the species are performed in situ and in a short time scale. With the above aim, simple explicit solutions are presented in this paper for quantitative characterization with any voltammetric technique and with the most common electrode geometries. From the theoretical results obtained, it is pointed out that the use of square wave voltammetry in combination with microelectrodes is very suitable. Finally, the theory is applied to the investigation of the ion association between the anthraquinone radical monoanion and the tetrabutylammonium cation in acetonitrile medium.
  • Thumbnail Image
    Publication
    Open Access
    Effects of unequal diffusion coefficients and coupled chemical equilibria on square wave voltammetry at disc and hemispherical microelectrodes
    (Elsevier, 2015) Olmos Martínez, José Manuel; Molina Gómez, María de los Ángeles; Laborda Ochando, Eduardo; Martínez-Ortíz, Francisco Asís; Química Analítica
    Square wave voltammetry (SWV) at disc and hemispherical microelectrodes is studied when the electroactive species show different diffusivities and/or take part in chemical equilibria in solution, under both transient and steady state conditions. Despite the use of microelectrodes, experiments in pulse techniques such as SWV frequently correspond to transient conditions since the pulse duration are typically very short (<100ms, f>5Hz). As will be shown, under such conditions the case of unequal diffusion coefficients gives rise to a complex behaviour of the SWV peak, the features of which deviate from the theory and criteria already established under the assumption of equal diffusion coefficients. Also, the theoretical treatment is notably more difficult and no analytical solution has been deduced for multipulse techniques.The effects of coupled chemical equilibria and, particularly, of unequal diffusion coefficients on SWV will be described in depth as a function of the electrode size and shape and they will be compared with those observed in differential double pulse voltammetry (DDPV). The main discrepancies in the peak height, width and position with respect to the case of equal diffusion coefficients will be studied. Also, appropriate methodologies and experimental conditions will be discussed for the determination of, formal potentials and equilibrium constants.
  • Thumbnail Image
    Publication
    Open Access
    Sensing and characterization of neurotransmitter 2-phenylethylamine based on facilitated ion transfer at solvent polymeric membranes using different electrochemical techniques
    (Elsevier, 2016) Ortuño Sánchez-Pedreño, Joaquín Ángel; Olmos Martínez, José Manuel; Torralba Peñalver, Encarnación; Molina Gómez, María de los Ángeles; Química Analítica
    Square Wave Voltammetry (SWV), chronoamperometry and chronocoulometry are exploited to take advantage of their different performance characteristics in the determination, characterization and sensing of the neurotransmitter 2-phenylethylamine (PEA), based on the ion transfer of its protonated form at a solvent polymeric membrane facilitated by dibenzo-18-crown-6 (DB18C6). The general voltammetric features characterizing the PEA+ transfer are established by SWV and the standard ion transfer potential, diffusion coefficient and complexation constant value between PEA+ and DB18C6 are calculated from the SWV recordings. Next, the performance of double pulse chronoamperometry and double pulse chronocoulometry for the determination of PEA based on its facilitated ion transfer is studied. Limits of detection between 3.6 and 9.2 µM for chronoamperometry and 1.7 and 2.7 for chronocoulometry are obtained. The influence of common ions on both chronoamperometric and chronocoulometric determination is also considered. The sensitivity ratio values found between foreign cations and PEA+ are 0.05, 0.3 and 0.2 for Na+, K+ and H+, respectively, whereas no interference was observed for Li+. In addition, the electrode is tested as a sensor for monitoring PEA+ concentration using a pulsed-amperometric mode. Interestingly, a simple procedure to extend the range of linear response of quantitative electrochemical techniques significantly based on a previous analysis of chronoamperometric recordings is proposed and successfully tested.