Glass electrodes properties

O. Isatd, The dependence of glass-electrode properties on composition. 

The acid-base properties of a transient can be assessed directly by placing a glass electrode in a streaming fluid that is generating that transient a few ms after the mixer. The pH is measured after the electrode has equilibrated. A series of measurements of the extent of protonation vs pH yields a value in the usual way. The pJifa s of H3VO4 (and lower pro-tonated species) and Ni(H20)g could be determined, without interference by slightly slower polymerization. 

The glass electrode also belongs among homogeneous membranes. For the sake of completeness, its properties will be described in chapter 6, but for construction details the reader is referred to the literature ([48]). 

G. Eisenman, Particular properties of cation-selective glass electrodes containing AljO, Chapter 4 of Glass Electrodes for Hydrogen and Other Cations... 

Sodium ISEs (especially for biological applications) contain monensin XXVII (see [98, 99, 107,203]). Synthetic ligands for sodium ISEs were gradually developed the latest type, XXVIII [64] has properties sufficient for the ISE to be comparable to the sodium glass electrode (see [91 ] for determination of Na in urine). 

The main limitation of glass electrodes is the fact that they should always be in contact with an aqueous solution, e.g. 3moll 1KCl. If these electrodes become dry, their properties for pH measurement will drop. It is possible to recover pH electrodes after they have been dry for some time. However, it will be noted that these electrodes have longer reaction times, show a decrease of the slope of the A -pH calibration curve, and display increased impedance of the membrane and a shift of the zero point. 

Thermodynamic properties in dilute aqueous solutions are taken to be functions of ionic strength so that concentrations of reactants, rather than their activities can be used. This also means that pHc = — log[H+] has to be used in calculations, rather than pHa = — log a(H + ). When the ionic strength is different from zero, this means that pH values obtained in the laboratory using a glass electrode need to be adjusted for the ionic strength and temperature to obtain the pH that is used to discuss the thermodynamics of dilute aqueous solutions. Since pHa = — log-/(H + ) + pHc, the use of the extended Debye-Hiickel theory yields... 

The hydrophobias are a case where protein nanofibers can play a dual role in creating a biosensor. They can aid in the immobilization of bioactive components within a biosensor and also add further functionality to the transducing element of a biosensor device. Hydrophobins are self-assembling [3-sheet structures observed on the hyphae of filamentous fungi. They are surface active and aid the adhesion of hyphae to hydrophobic surfaces (Corvis et al., 2005). These properties can be used to create hydrophobia layers on glass electrodes. These layers can then facilitate the adsorption of two model enzymes glucose oxidase (GOX) and hydrogen peroxidase (HRP) to the electrode surface. The hydrophobin layer also enhances the electrochemical properties of the electrodes. 

Thin-film electrode — An electrode covered with a thin film of a given substance. The purpose of placing a thin film on the electrode surface is to obtain desired electrode properties. Many different substances have been used to prepare film electrodes they include among others mercury (see - thin mercury film electrodes) gold, boron-doped diamond (see - boron-doped diamond electrode), conductive polymers (see - polymer-modified electrode), and alkanethiols. The film thickness can vary from several micrometers (mercury) to monomolecular layers (thiols). In some cases (e.g., for - spectroelectrochemistry purposes) very thin layers of either gold or tin oxide are vapor-deposited onto glass plates. Thin film electrodes are often called - surface-modified electrodes. 

Experimental works which do not need expensive equipments could compete with works in the world rather early compared with other fields of solution chemistry. Complex formation studies by the pH-metry using glass electrodes, studies on weak ion-ion interactions by the conductometry, investigations of properties and structures of solutions by the UV-visible and IR spectrophotometry, and oxidation-reduction studies on ionic species by using polarography are typical examples in solution chemisny studies in Japan in the early stage after the second world war. 

An electrochemical cell can be used conveniently to study the properties of a solution quantitatively. For example, it is possible to determine Ag with an Ag electrode, with a Pt/H2(g) electrode or with a glass electrode,... 

Hygroscopic glass A glass that absorbs minute amounts of water on its surface hygroscopicity is an essential property in the membrane of a glass electrode. 

A typical approach, in which the ionic strength is established by a 1-1 salt, and the pH is adjusted by an acid or base that has an ion in common with the inert electrolyte and is measured by means of a glass electrode, was used to study the following systems by titration, electrophoresis, and electroacoustics. A purely aqueous system was usually studied as a reference. The physical properties of solvents relevant to the interpretation of electrokinetic data (viscosity and permittivity) may be very different from those of water, and they have to be taken into account in the interpretation of results. 

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