Potentiometry with zero current

These methods are divided into potentiometry with zero current (classical potentiometry) and potentiometry with current flow. 

Enzymes, Antibodies, and Nucieic Acids with Zero-Current Potentiometry... 

With a low constant current -1 (see Fig. 3.71) one obtains the same type of curve but its position is slightly higher and the potential falls just beyond the equivalence point (see Fig. 3.72, anodic curve -1). In order to minimize the aforementioned deviations from the equivalence point, I should be taken as low as possible. Now, it will be clear that the zero current line (abscissa) in Fig. 3.71 yields the well known non-faradaic potentiometric titration curve (B B in Fig. 2.22) with the correct equivalence point at 1.107 V this means that, when two electroactive redox systems are involved, there is no real need for constant-current potentiometry, whereas this technique becomes of major advantage... 

Potentiometry deals with the electromotive force (EMF) generated in a galvanic cell where a spontaneous chemical reaction is taking place. In practice, potentiometry employs the EMF response of a galvanostatic cell that is based on the measurement of an electrochemical cell potential under zero-current conditions to determine the concentration of analytes in measuring samples. Because an electrode potential generated on the metal electrode surface,... 

In this present book, we will look at the analytical use of two fundamentally different types of electrochemical technique, namely potentiometry and amper-ometry. The distinctions between the two are outlined in some detail in Chapter 2. For now, we will anticipate and say that a potentiometric technique determines the potential of electrochemical cells - usually at zero current. The potential of the electrode of interest responds (with respect to a standard reference electrode) to changes in the concentration of the species under study. The most common potentiometric methods used by the analyst employ voltmeters, potentiometers or pH meters. Such measurements are generally relatively cheap to perform, but can be slow and tedious unless automated. 

In summary, then, the biggest difference between measurements of potential and current (potentiometry and amperometry, respectively) is that potentials are measured with a zero current wherever possible, implying that no compositional changes occur inside the cell during measurement, whereas compositional changes do occur during the measurement of current. 

The previous chapters dealt with ISE systems at zero current, i.e. at equilibrium or steady-state. The properties of the interface between two immiscible electrolyte solutions (ITIES), described in sections 2.4 and 2.5, will now be used to describe a dynamic method based on the passage of electrical current across ITIES. Voltammetry at ITIES (for a survey see [3, 8, 9, 10, 11, 12,18]) is an inverse analogue of potentiometry with liquid-membrane ISEs and thus forms a suitable conclusion to this book. 

Potentiometry is a method of obtaining chemical information by measuring the potential of an indicator electrode under zero current flow. It is based on the Nernst equation, which expresses the electrode potential as a function of the activity (or activities) of the chemical species in solution. The information obtained varies with indicator electrode, from the activity (concentration) of a chemical species to the redox potential in the solution. The potential of the indicator electrode is measured against a reference electrode using a high inptit-impedance mV/pH me-... 

Potentiometry is a method of electroanalytical measurement in which the equilibrium voltage of the cell consisting of an indicator electrode and a proper reference electrode is measured using a high-impedance voltmeter, i.e., effective at zero current. The potential of the indicator electrode is a function of particular species present in solutions and their concentration. By judicious choice of electrode material, the selectivity of the response to one of the species can be increased, and thus, interferences from other ions can be minimized. The method allows the determination of concentrations with detection limits of the order of 0.1 pmol per liter, although in some cases, as little as lOpmol differences in concentration can be measured. 

Electrochemical sensors can use amperometry, potentiometry, or conductometry as transduction principle [32], Potentiometric sensors make use of the development of an electrical potential at an electrode surface in contact with ions that exchange with the surface. The potential is measured under zero-current conditions against a reference electrode and is proportional to the logarithm of the analyte activity in the sample. Potentiometric sensors are limited to the measurement of charged species or of gases that dissociate to yield charged species in an electrolyte. Ion-selective electrodes are one example of this sensor type. 

With an external DC power supply connected to the electrolytic cell, the applied voltage that gives no DC current flow in the external circuit corresponds to the equilibrium potential of the half-cell (or actually the cell). It is the same voltage as read by a voltmeter with very high input resistance and virtually no current flow (pH meter). In electrochemistry, potentiometry is to measure the potential of an electrode at zero current flow, which is when the cell is not externally polarized. To understand the equilibrium potential with zero external current, we must introduce the concept of electrode reaction... 

Nonselective, metallic indicator electrodes have been used for potentiometric measurements in complex biological media, for example, Pt electrodes have been used to monitor the redox potential of fermentation broths as cultures grow [17]. However, zero-current potentiometry more often involves ISEs based on solid membranes, composed of a sparingly soluble salt of the ion of interest or liquid membranes, in which an ion-selective reagent is dissolved, with the membrane separating reference... 

In potentiometry the potential signal is measured at zero current intensity (Scholz, 2010). The typical potentiometric analytical cell has two electrodes immersed in a solution containing the analyte, whose concentration is to be measured (Fig. 13.1). The reference electrode (RE) has a constant contribution to the signal, independently of the solution matrix. Usually it contains a metal electrode in contact with an insoluble salt of the same metal (second type of electrode) and its potential depends only on the solubility of the salt. The most used RE is the silver/silver chloride (Ag/AgQ). The second electrode is the indicator electrode (IE) that contains a membrane sensitive to the... 

Potentiometry is the measurement of an electrical potential difference between two electrodes (half-ceUs) in an electrochemical cell (Figure 4-1) when the cell current is zero (galvanic cell). Such a cell consists of two electrodes (electron or metallic conductors) that are connected by an electrolyte solution (ion conductor). An electrode, or half-cell, consists of a single metallic conductor that is in contact with an electrolyte solution. The ion conductors can be composed of one or more phases that are either in direct contact with each other or separated by membranes permeable only to specific cations or anions (see Figure 4-1). One of the electrolyte solutions is the unknown or test solution this solution may be replaced by an appropriate reference solution for calibration purposes. By convention, the cell notation is shown so that the left electrode (Mi,) is the reference electrode the right electrode (Mr) is the indicator (measuring) electrode (see later equation 3). ... 

Potentiometry is a method in which the electrochemical cell potential is measured at equilibrium at which the current is zero. The properties of the interface region differ from the bulk properties. A potential is established at the phase boundaries, e.g., between the solution and the electrode surface. The potential of electrochemical cells is the sum of all interface potentials including electrode/electrolyte interface and liq-uid/Uquid interface (i.e., the two electrolyte solutions of different compositions that are in contact with each other). Ideally the measured potential should depend only on the potential between the interfaces of interest for analytical purpose. This is typically accomplished by keeping all other interfaces constant through a suitable electrode construction. Potentiometric sensors (e.g., ion selective electrodes) usually consist of a manbrane that contains ion exchangers, lipophilic salts, and plasticizers, and the transmembrane potential gives the activity of the analyte ion in solution. 

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