1. PrinciplesElectrochemistry implies the transfer of charge from an electrode to another phase, which can be a solid or a liquid sample. During this process chemical changes take selleck screening library place at the electrodes and the charge is conducted through the bulk of the Tubacin HDAC inhibitor sample phase. Both the electrode reactions and/or the charge transport can be modulated chemically and serve as the basis of the sensing process [9].Electrochemical sensors are based upon potentiometric, amperometric, or conductivity measurements. The different Inhibitors,Modulators,Libraries principles always require a specific design of the electrochemical cell. The structure of electrochemical sensors is shown in Figure 1. Their operating and measurement Inhibitors,Modulators,Libraries principles will be summarized in the next sections according to the types listed above.
Figure 1.
Clinical analysis procedures based on electrochemical sensors.2.1.1. Potentiometric sensorsIn potentiometric Inhibitors,Modulators,Libraries sensors, the potential difference between the reference electrode and the Inhibitors,Modulators,Libraries indicator electrode is measured without polarizing the electrochemical cell, that is, very small current is allowed.The reference electrode is required to provide a constant half-cell potential. The indicator Inhibitors,Modulators,Libraries electrode develops a variable potential depending on the activity or concentration of a specific analyte in solution. Inhibitors,Modulators,Libraries The change in potential is related to concentration in a logarithmic manner.
The Nernst equation relates the potential difference Inhibitors,Modulators,Libraries at the interface to the activities of species i in sample phases (s) and in the electrode phase (��):E=E0+RTZiFlnaisai��,where E0 is the standard electrode potential of the sensor electrode; ai is the activity of the ion, R is the universal gas constant; Inhibitors,Modulators,Libraries T is the absolute temperature; F is the Faraday constant; Zi Drug_discovery is the valency of the ion.
The ion-selective electrode (ISE) for the measurement of electrolytes is a common potentiometric sensor. In many cases, the potentiometric sensor comprises a membrane with a unique composition, noting that the membrane can be either a solid (i.e., glass, inorganic crystal) or a plasticized polymer, and the ISE composition is Dacomitinib chosen in order to impart a potential that is primarily associated with the ion of interest via a selective binding process at the membrane-electrolyte interface.
Figure 2 (a) show the cell configuration of a conventional liquid junction ISE.
selleck Afatinib selleck chem inhibitor A reversible ion or electron transport mechanism is present at the membrane-analyte solution interface. Another type of ion sensor was developed in which ion-selective polymeric membranes are deposited directly onto solid electrode surfaces with no internal electrolyte solution. Figure 2 (b) illustrates the cell configuration for this kind of sensors, called solid-contact ISEs.Figure 2.The schematic of: (a) liquid junction ISE, (b) solid-contact ISE.2.1.2. Amperometric sensorsAmperometry is a method of electrochemical analysis in which the signal of interest is a current that is linearly dependent upon the concentration of the analyte.