Open circuit potentiometry

Potentiometry, which measures the open-circuit equilibrium potential of an indicator electrode, for which the substance being examined is potential determining... 

Open-circuit potential (OCP) — This is the - potential of the - working electrode relative to the - reference electrode when no potential or - current is being applied to the - cell [i]. In case of a reversible electrode system (- reversibility) the OCP is also referred to as the - equilibrium potential. Otherwise it is called the - rest potential, or the - corrosion potential, depending on the studied system. The OCP is measured using high-input - impedance voltmeters, or potentiometers, as in - potentiometry. OCP s of - electrodes of the first, the second, and the third kind, of - redox electrodes and of - ion-selective membrane electrodes are defined by the - Nernst equation. The - corrosion po-... 

One-electrode potentiometry involves the measurement of the potential of an indicator electrode with respect to a reference (nonpolarizable) electrode either at open circuit or with a small anodic or cathodic current applied to the indicator electrode. These three possibilities are shown in Figure 11.5.2 for the Fe -Ce titration, and the resulting titration curves are shown in Figure 11.5.3. The i = 0 curve, a), is the usual potentiometric titration curve, showing the equilibrium potential of the solution (F gq) as a function of/ When a small anodic current is impressed on the indicator electrode, the measured potential at a given/will be somewhat more positive than Fgq [curve (c)]. When a small cathodic cur-... 

When the solid electrolytes are used as membranes, there are three different operation modes, as shown in Fig. 3. Id. Mode 1 is under open circuit operation, in which no net current passes through the membrane. The reactor in this mode often serves as a sensor or an in situ characterization technique for catalytic gas-solid reactions under work conditions, named solid electrolyte potentiometry (SEP)... 

A Nernst equation may be written for every galvanic cell at equilibrium. Therefore the equation is the basis of all thermodynamic applications of potentiometry (i.e. measurement of open-circuit cell potentials by means of a potentiometer or other zero-current device). Cells may be constructed and appropriate Nernst equations written to find, for example, the dissociation constant of water, and many electrolyte activity coefficients and stability and solubilit,v constants. Potentiometric titration curves are also interpieted by means of the appropriate Nernst equation. 

As it is well known, potentiometry is the simplest and most often used electrometric measuring technique. In potentiometry the potential difference that is the electromotive force (often called open circuit potential) between the measuring and the reference electrodes is measured using a high resistance millivolt meter, like a pH meter. The concentration of the measured species is determined upon calibration. 

In environmental analysis, potentiometry is important for the detection of redox potential and as an analytical tool for the measurement of a variety of ionic and ionizable species. In both cases, the open circuit potential of a two-electrode cell is observed where an inert metal electrode or an ion-selective electrode (also called indicator electrode) is measured against a suitable reference electrode. 

Natural sweet waters, as samples with apparently the simplest matrix, can be analysed directly by stripping potentiometry, where solely appropriate buffering is needed (see references (37, 38, 48) and references therein). Compared to this, voltammetry usually requires mild digestion, such as UV irradiation however, this operation is not even needed if highly selective pre-cmicentrations are available (e.g. those utilising non-electrolytic principles, open circuit and/or medium exchange see Table 5.1 and reference (21)). 

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