Electrochemical sensor types potentiometric

In the early part of this century, many types of solid electrolyte had already been reported. High conductivity was found in a number of metal halides. One of the first applications of solid electrolytes was to measure the thermodynamic properties of solid compounds at high temperatures. Katayama (1908) and Kiukkola and Wagner (1957) made extensive measurements of free enthalpy changes of chemical reactions at higher temperatures. Similar potentiometric measurements of solid electrolyte cells are still made in the context of electrochemical sensors which are one of the most important technical applications for solid electrolytes. 

The idea of separating the gas sample by a gas-permeable membrane from the actual internal sensing element is common to several types of electrochemical and some optical sensors. The potentiometric Severinghaus electrode and the amperometric oxygen Clark electrode have already been discussed. Actually, most types of sensors can be used in this configuration and the conductometric sensor is not an exception (Bruckenstein and Symanski, 1986). 

An electrochemical sensor is generally an electrochemical cell containing two electrodes, an anode and a cathode, and an electrolyte. Electrochemical sensors in general are classified, based on the mode of its operation, and they are conductivity sensors potentiometric sensors, and voltammetric sensors. Amperometric sensors can be considered as a special type of voltammetric sensors. The fundamentals of these sensors operational principles are described exceptionally well in several excellent electro-analytical books. In this entry, only the essential features are included. 

There are three types of electrochemical sensors potentiometric, amperometric, and potentiodynamic sensors. 

Clearly, electrochemical indication prevails over all other methods of transduction. Potentiometric and amperometric enzyme electrodes are at the leading edge of biosensor technology with respect to the body of scientific literature as well as to commercially available devices (Schindler and Schindler, 1983). Only a few conductometric biosensors have been described, but the relevance of this sensor type may increase because of the relative ease of their preparation and use. Furthermore, the development of biochemically sensitized field effect transistors, being at present only at an initial stage, offers new prospects (Pinkerton and Lawson, 1982). 

Electrochemical sensors can be classified according to their mode of operation, e.g. conductivity/capacitance sensors, potentiometric sensors, and voltammetric sensors. Amperometric sensors can be considered a specific type of voltammetric sensor. The general principles of electrochemical sensors have been extensively described in other chapters of this volume or elsewhere. This chapter will focus on the fabrication of electrochemical sensors of micro or miniature size. 

Amperometric electrodes are a type of electrochemical sensor, as are potentiometric electrodes discussed in Chapter 13. In recent years there has been a great deal of interest in the developmenfoTv ious types of electrochemical sensors that exhibit increased selectivity or sensitivity. These enhanced measurement capabilities of amperometric sensors are achieved by chemical modification of the electrode surface to produce chemically modified electrodes (CMEs). 

Different electrochemical sensors have been developed for cell concentration measurement. The most promising of these sensors are based on impedimetric measurements. A commercial version of a sensor that measures the frequency-dependent i)ermittivity is available from Aber Instruments Ltd [137-139]. Another type of electrochemical probe measures the potential changes in the cell suspension caused by the production of electroactive substances during cell growth [140-143]. To date, no on-line applications of these potentiometric sensors under real cultivation conditions have been reported. Other types of probes, such as amperometric and fuel-cell sensors, measure the current produced during the oxidation of certain compounds in the cell membrane. Mediators are often used to increase the sensitivity of the technique [143-145]. 

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. 

Electrochemical Sensor of Gaseous Contaminants, Fig. 3 Typical structure of (a) Type I, (b) Type II and (c) Type ni potentiometric gas sensors... 

Naturally, in other areas with different technical requirements for the measuring system, preference will be given to other gas sensors with other sets of advantages, which depend not only on the sensor type but also on its version. This facet can be well illustrated using the example of electrochemical sensors, which can be realized either as conductometric, potentiometric, or amperometric (voltammetric) sensors (Brett and Brett 1998 Brett 2001). 

Experimental studies have also shown that selective detection is an important advantage of an electrochemical sensor, but sometimes their responses are affected by the presence of other gases (Park et al. 2003). As established in numerous experiments, cross-sensitivity is often observed when lype II or Type III potentiometric sensors are exposed to gas species that form thermodynamically more stable compounds or kinetically more favorable compounds in spite of lower thermodynamic stability (Weppner 1992). 

L. Liu, X.C. Tan, X.X. Fang, Y.X. Sun, F.H. Lei and Z.Y. Huang, Electrochemical sensor based on molecularly imprinted polymer film prepared with functional abietic-type acids as cross-linker for the determination of quinine. Electroanalysis, 24 (7) 1647-1654,2012. R.N. Liang, Q. Gao and W. Qin, Potentiometric sensor based on molecularly imprinted polymers for rapid determination of clenbuterol in pig urine, Chinese J. Anal. Chem., 40 (3) 354-358, 2012. 

In this chapter, types of electrochemical sensor or biosensor which are based on electrical properties and which cannot be grouped into normal voltammetric or potentiometric sensors will be addressed, giving the fimdamental principles and selected examples to show how they are implemented for characterisation and for analysis. This will concern sensors based on impedance, solid-state miniaturised sensors and piezoelectric transducer-based sensors. 

Potentiometric measurements are done under the condition of zero current. Therefore, the domain of this group of sensors lies at the zero-current axis (see Fig. 5.1). From the viewpoint of charge transfer, there are two types of electrochemical interfaces ideally polarized (purely capacitive) and nonpolarized. As the name implies, the ideally polarized interface is only hypothetical. Although possible in principle, there are no chemical sensors based on a polarized interface at present and we consider only the nonpolarized interface at which at least one charged species partitions between the two phases. The Thought Experiments constructed in Chapter 5, around Fig. 5.1, involved a redox couple, for the sake of simplicity. Thus, an electron was the charged species that communicated between the two phases. In this section and in the area of potentiometric sensors, we consider any charged species electrons, ions, or both. 

Electrode modification by the attachment of various types of biocomponents holds considerable promise as a novel approach for electrochemical (potentiometric, conductometric, and amperometric) biosensors. Potentiometric sensors based on coupled biochemical processes have already demonstrated considerable analytical success [26,27]. More recently, amperometric biosensors have received increasing attention [27,28] partially as a result of advances made in the chemical modification of electrode surfaces. Systems based on... 

Studies on ethanol trace detection in aqueous solutions were carried out in an electrochemical cell of peroxidase-mimetic sensor of the potentiometric type, consisting of a reference electrode (Ag/AgCl) and a biomimetic electrode. Redistilled water was used for the background solution. The biomimetic electrode was prepared by adhering hematin-containing meroxidase mimetic to aluminum foil with Pattex adhesive [7, 8],... 

Polarized Electrochemical Vapor Deposition to Deposit Auxiliary Phases at the Working Electrode of Type III Potentiometric CO Sensors... 

This anodic reaction provides sodium ions and electrons to the solid electrolyte and the inert Pt counter electrode, respectively, at the source side. Both the sodium ions and electrons will then travel through the solid electrochemical cell along previously-mentioned ionic and electronic paths to sustain the PEVD cathodic reaction for Na COj product formation at the sink side. Eurthermore, based on anodic reaction 60, the chemical potential of sodium is fixed by the vapor phase at the source side. Under open circuit conditions, this type of source can also serve as the reference electrode for a CO potentiometric sensor. 

The PEVD system for Na CO auxiliary phase formation at the working electrode of a type III potentiometric CO sensor is schematically shown in Eigure 10. The electrochemical cell for this PEVD process can be illustrated as ... 

Abstract Brief historic introduction precedes presentation of main types of transducers used in sensors including electrochemical, optical, mass sensitive, and thermal devices. Review of chemical sensors includes various types of gas sensitive devices, potentiometric and amperometric sensors, and quartz microbalance applications. Mechanisms of biorecognition employed in biosensors are reviewed with the method of immobilization used. Some examples of biomimetic sensors are also presented. 

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