Summary of Recent Progress with Diamond Electrodes in Electroanalysis, Spectroelectrochemistry and Electrocatalysis

Anodic Determination of Acetylsalicylic Acid at a Mildly Oxidized Boron-Doped Diamond Electrode in Sodium Sulphate Medium

Differential pulse voltammetry (DPV) and chronoamperometry (CA) were used to detect and determine acetylsalicylic acid (ASA) at a mildly oxidized boron-doped diamond (BDD) electrode in a neutral sodium sulphate solution as supporting electrolyte. ASA determination in unbuffered medium was achieved using neutralized standard and real samples. Over the concentration range of 0.01 mM–0.1 mM, linear calibration plots of anodic current peaks in DPV and anodic currents in CA experiments versus concentration were obtained with very high correlation coefficients and good sensitivity values. The limits of detection were situated around 1 μM. The association of DPV and CA techniques with standard addition method represented a suitable option for the determination of ASA in real samples such as pharmaceutical formulations.

Simultaneous Chronoamperometric Sensing of Ascorbic Acid and Acetaminophen at a Boron-Doped Diamond Electrode

Cyclic voltammetry (CV) and chronoamperometry (CA) have been used to sense and determine simultaneously L-ascorbic acid (AA) and acetaminophen (AC) at a boron-doped diamond electrode (BDDE) in a Britton-Robinson buffer solution. The calibration plots of anodic current peak versus concentration obtained from CV and CA data for both investigated compounds in single and di-component solutions over the concentration range 0.01 mM – 0.1 mM proved to be linear, with very good correlation parameters. Sensitivity values and RSD of 2-3% were obtained for various situations, involving both individual and simultaneous presence of AA and AC. The chronoamperometric technique associated with standard addition in sequential one step and/or two successive and continuous chronoamperograms at two characteristic potential levels represented a feasible option for the simultaneous determination of AA and AC in real sample systems such as pharmaceutical formulations. The average values indicated by the supplier were confirmed to a very close approximation from chronoamperomgrams by using several additions with the application of suitable current correction factors.

Fabrication of Optically Transparent Carbon Electrodes by the Pyrolysis of Photoresist Films: Approach to Single-Molecule Spectroelectrochemistry

This paper describes the preparation, physical and chemical characterization, and performance of carbon-based optically transparent electrodes (C-OTEs) fabricated by the pyrolysis of thin films of photoresist. The electrodes are prepared by spin coating dilute solutions of the positive photoresist AZ 4330 onto quartz substrates. Pyrolysis of these samples at 1000 degrees C in a reducing atmosphere yields optically transparent carbon films that have thicknesses ranging between 10 and 80 nm. Sheet resistance measurements, X-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy were used to determine the physical and chemical properties of the films, and cyclic voltammetry and chronoabsorptometry were employed to delineate the electrochemical and conventional spectroelectrochemical performance of the C-OTEs. These findings showed that the transparency of this material improves as film thickness decreases, but at the expense of an increase in film resistance. At a wavelength of 500 nm, for example, 13- and 79-nm-thick films have transparencies of 47 and 10% and sheet resistances of 1100 and 210 Omega/ square, respectively. Importantly, adjusting the dilution factor allows the facile and reproducible variation of thickness and transparency. Preliminary results using these C-OTEs for single-molecule spectroelectrochemistry, which represents a new development in the merger of optical and electrochemical techniques, by probing the potential dependence of the adsorption of individual YOYO-I-labeled lambda-DNA are also presented.

Interaction between co-deposited metals during stripping voltammetry at boron-doped diamond electrodes

Electrochemical processes, which underlie the use of conductive diamond electrodes for the simultaneous detection of two or more metal ions in solution by anodic stripping voltammetry (ASV), have been investigated. The model analyte system studied contains the two metal species, Ag+(aq) and Pb2+(aq), and the experimental techniques employed include cyclic and square wave voltammetries, along with X-ray photoelectron spectroscopy and secondary electron microscopy. Although the bulk metallic forms of Ag and Pb are immiscible, several interactions in the system between the two metal species present are observed, which significantly influence the electrodeposition and electrodissolution processes which underlie ASV. The subsequent nucleation and growth of a given metal on the electrode surface is enhanced by the presence of the second metal on the surface. The encapsulation of one metal by the other, within the metal particulates that form on the electrode surface, significantly reduces the stripping yield at the potentials characteristic of the individual metals. The stripping potentials are also influenced by bonding interactions between deposited Ag and Pb, which broaden the characteristic stripping peaks in cyclic voltammetry, as well as producing underpotential deposition and stripping. Given these interactions, the extent to which ASV at diamond electrodes can be used to determine the solution concentrations of Ag+(aq) and Pb2+(aq) is considered.