Potentiometry static

The diversity of interfacial electrochemical methods is evident from the partial family tree shown in Figure 11.1. At the first level, interfacial electrochemical methods are divided into static methods and dynamic methods. In static methods no current passes between the electrodes, and the concentrations of species in the electrochemical cell remain unchanged, or static. Potentiometry, in which the potential of an electrochemical cell is measured under static conditions, is one of the most important quantitative electrochemical methods, and is discussed in detail in Section IIB. 

In potentiometry the potential of an electrochemical cell is measured under static conditions. Because no current, or only a negligible current, flows while measuring a solution s potential, its composition remains unchanged. For this reason, potentiometry is a useful quantitative method. The first quantitative potentiometric applications appeared soon after the formulation, in 1889, of the Nernst equation relating an electrochemical cell s potential to the concentration of electroactive species in the cell. ... 

In potentiometry, the potential of an electrochemical cell under static conditions is used to determine an analyte s concentration. As seen in the preceding section, potentiometry is an important and frequently used quantitative method of analysis. Dynamic electrochemical methods, such as coulometry, voltammetry, and amper-ometry, in which current passes through the electrochemical cell, also are important analytical techniques. In this section we consider coulometric methods of analysis. Voltammetry and amperometry are covered in Section 1 ID. 

Potentiometry (discussed in Chapter 5), which is of great practical importance, is a static (zero current) technique in which the information about the sample composition is obtained from measurement of the potential established across a membrane. Different types of membrane materials, possessing different ion-recognition processes, have been developed to impart high selectivity. The resulting potentiometric probes have thus been widely used for several decades for direct monitoring of ionic species such as protons or calcium, fluoride, and potassium ions in complex samples. 

Potentiometry is a technique traditionally employed for the quantification of ions in a liquid solution. It is a static electroanalytical method, that is, there is no current flow inside the measurement cell (f = 0). The measurement cell is constituted by two electrodes which are immersed in the solution containing the analytes. A voltmeter measures the potential difference between the two electrodes, which is a fimction of the concentration (actually, the activity) of the analytes, as described by the well-known Nerst s equation (Kissinger and Heineman, 1996). 

In electrochemistry an electrode is an electronic conductor in contact with an ionic conductor. The electronic conductor can be a metal, or a semiconductor, or a mixed electronic and ionic conductor. The ionic conductor is usually an electrolyte solution however, solid electrolytes and ionic melts can be used as well. The term electrode is also used in a technical sense, meaning the electronic conductor only. If not specified otherwise, this meaning of the term electrode is the subject of the present chapter. In the simplest case the electrode is a metallic conductor immersed in an electrolyte solution. At the surface of the electrode, dissolved electroactive ions change their charges by exchanging one or more electrons with the conductor. In this electrochemical reaction both the reduced and oxidized ions remain in solution, while the conductor is chemically inert and serves only as a source and sink of electrons. The technical term electrode usually also includes all mechanical parts supporting the conductor (e.g., a rotating disk electrode or a static mercury drop electrode). Furthermore, it includes all chemical and physical modifications of the conductor, or its surface (e.g., a mercury film electrode, an enzyme electrode, and a carbon paste electrode). However, this term does not cover the electrolyte solution and the ionic part of a double layer at the electrode/solution interface. Ion-selective electrodes, which are used in potentiometry, will not be considered in this chapter. Theoretical and practical aspects of electrodes are covered in various books and reviews [1-9]. 

The electrochemical techniques can be divided into two major groups static (i = 0) and dynamic (i + 0) (6). Potentiometry is a static method, and it measures the rest potential vs. time the most common applications in potentiometry are the use of ion-selective electrodes and pH meters. The dynamic methods comprise mostly all the other electrochemical techniques (3). Table 1.1 lists the most commonly used methods among this group. 

Due to the high sensitivity of the scattering intensity to the presence of supermolecular structures in polymer solutions, static light scattering is a very helpful tool to study the course of PEC formation and to characterize the structure of the generated particles. Nevertheless, in comparison to such methods as potentiometry, conductometry, turbidity and viscometry, SLS studies of PEC formation are rather scarce. 

Different electrochemical techniques depend on whether they are bulk methods as in conductometry or interfacial methods. The latter may be static as in potentiometry or dynamic. Dynamic methods are classified on the basis of the current used. Conductometry uses a constant current but controlled current methods include voltametry, amperometry and coulometry. 

Indeed, while potentiometry refers to a static system, in which no reaction takes place, the current flow in controlled potential techniques is the cause of occurrence of a redox reactiOTi the electrode potential is imposed by an external source and eventually changes with time. Considering what happens at WE, reversibility... 

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