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This article deals with electrochemical microscopy (SECM), a technique for the local analysis of surfaces based on the use of a mobile ultramicroelectrode (UME), making it possible to image and characterise the electrochemical reactivity of samples on a micrometric scale. Developed at the end of the 1980s, SECM offers a range of analysis modes (feedback, generation/collection, penetration) and can be applied to surface imaging, the study of reaction kinetics, corrosion, biological systems and microstructuring. It enables non-invasive and precise measurements, particularly useful in biology, corrosion and materials science in general, and nanotechnology.
There is currently an increasing need for fast and cost-effective analytical methods suitable for water pollutants monitoring and toxicological impact assessment. In this context, some techniques based on the specific properties of whole cells, enzymes, antibodies, DNA, biopolymers or materials of natural origin, appear as excellent alternatives or complementary techniques to classical chemical methods. This article will be more particularly focused on biosensors and biosorbents (principles, advantages and limitations, application to water quality assessment, new trends).
This paper describes voltamperometry on solid electrodes of various geometries, adapted to the study of insoluble, unstable or confined species. It covers: thin- voltamperometry (complete electrolysis of a confined species), the study of species adsorbed or confined in polymer films (closed systems voltamperometry on graphite paste electrodes (analysis of poorly soluble solids), rotating disc and voltamperometry (detection of reactive intermediates) and voltamperometry on ultramicroelectrodes, offering high spatial resolution, low ohmic drop and compatibility with poorly conducting media.
Differential or pulse techniques are variants of solid electrode voltammetry, in which the applied potential is modulated in a specific way to improve the detection of faradic current while reducing the signal component related to capacitive current. This article describes the main techniques (normal pulse voltammetry, constant or increasing amplitude superimposed pulse voltammetry, and square wave differential voltammetry) that offer a crucial improvement in measurement sensitivity, better resolution, and a better signal-to-noise ratio.
The aim of this article is to describe the evolution of voltammograms of electrochemical systems by the action of chemical reagents (electroactive or not) present in solution. Under certain conditions, this evolution can consist of a simple translation of the voltammograms along the potential axis and/or an amplification of the electrolysis intensity, depending on the chemical reactivity involved. These voltammogram modification characteristics can therefore be indicative of the presence of a non-electroactive reagent and enable its content to be determined indirectly. The study is limited to solid electrodes.
Chronopotentiometry is a measurement of potential, as a function of time, the excitation signal being constant or variable in time, but not zero, and the transfer of matter being ensured by diffusion. The article presents the theory and the different applications of chronoamperometry: - with monotonic imposed current, it is widely used for electrode characterization and study of reaction mechanisms - with cyclic or alternating current for the study of complex systems, - with pulse trains, for the determination of thermodynamic properties and interdiffusion coefficients of alloys.
This article deals with the theoretical basis of the current-potential characteristics at a solid electrode of simple redox couples (noted Red/Ox) in solution, by considering on the one hand the kinetics of electron transfer at the electrode/solution interface, and on the other hand the intervention of the transport of material in solution both in the stationary convective diffusion regime and in the pure natural diffusion regime. This article also presents the essential guidelines for the experimental implementation of the studied voltammetric techniques (electrode materials, equipment, domain of electroactivity, etc.).
Potentiometry is an easy-to-implement, fast, and accurate physicochemical analysis method and remains the most common electrochemical method (pH electrodes, selective electrodes, etc.). Advances in electronics, automation of measurements, and the development of liquid membrane electrodes and then solid-state electrodes have facilitated the development of this method. The general principles of this method, the concepts of activity and electrochemical potential, have been reviewed in this paper in order to introduce the basic laws of potentiometry. The operating principles of reference electrodes and indicator electrodes are detailed before presenting some specific electrodes.
Potentiometry allows two main types of measurement: pH and ion or molecule concentration. This article describes the electrodes that allow these measurements. The hydrogen electrode, quinhydrone electrode, antimony electrode, glass electrode, and pH ISFET are described for pH measurements. In the case of ion concentration measurement, the operation of ion indicator electrodes is based either on the exploitation of a redox potential or a membrane potential. The problem of selectivity and the impact on the measurement of the presence of other ions is also addressed. Dissolved gas indicator electrodes have also been described.
This paper contains selected applications to browse various fields of applications of GC. Examples involve different sample preparation techniques, injection methods, columns and hyphenation to various detectors to perform the best separations of complex mixtures as possible.
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