Glass electrode composition

All of these requirements limit the glass electrode composition and configuration and make glass electrode manufacturing an art. 

Specific-Ion Electrodes In addition to the pH glass electrode specific for hydrogen ions, a number of electrodes that are selective for the measurement of other ions have been developed. This selectivity is obtained through the composition of the electrode membrane (glass, polymer, or liquid-liquid) and the composition of the elec trode. Tbese electrodes are subject to interference from other ions, and the response is a function of the total ionic strength of the solution. However, electrodes have been designed to be highly selective for specific ions, and when properly used, these provide valuable process measurements. 

Table 15.2 Composition of glasses for cation-sensitive glass electrodes...

Glass electrodes are responsive to univalent cations. The selectivity for these cations is achieved by varying the composition of a thin ion-sensitive glass membrane. 

For a review of compositional and constructional aspects of glass electrodes (especially the pH electrode), see Mattock43. 

G.G. Guilbault, G.J. Lubrano, and D.N. Gray, Glass-metal composite electrodes. Anal. Chem. 45, 2255-2259 (1973). 

The membrane of the glass electrode used for pH measurements is selectively permeable to hydrogen ions and from this basic concept a whole range of ion-selective electrodes have been developed. Varying the composition of the glass membrane can change the permeability of the glass and several cation-sensitive... 

SO Electrode. A gas-sensing SO2 electrode marketed by Ionics, Inc. was used to provide additional VLE data at 25°C as a function of composition. Aqueous SO2 equilibrates across a polymeric membrane with a filling solution containing about 0.1 M NaHSO-j. Ionic species do not diffuse across the membrane. A small combination glass electrode measures the pH of the filling solution. The SO2 activity (Pso ) is proportional to the activity of H+ (10"PH), because the bisulfite activity is constant ... 

Table 6.1. Gto composition for glass electrodes suitable for determining Li, Na, K and Ag [319].

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

This pH definition for non-aqueous and mixed solvent systems is practically the same as that for aqueous solutions (Section 6.2.1). Thus, if a pH standard is available for the solvent or mixed solvent under study, the glass electrode is calibrated with it and then the pH of the sample solution is measured. The pHRVs values for 0.05 mol kg-1 KHPh have been assigned to aqueous mixtures of eight organic solvents (see 5 for pHRVs at 25 °C). Although they are for discrete solvent compositions, the pHRVs in between those compositions can be obtained by use of a multilinear regression equation [14b],... 

A potentiometric method for determination of ionization constants for weak acids and bases in mixed solvents and for determination of solubility product constants in mixed solvents is described. The method utilizes glass electrodes, is rapid and convenient, and gives results in agreement with corresponding values from the literature. After describing the experimental details of the method, we present results of its application to three types of ionization equilibria. These results include a study of the thermodynamics of ionization of acetic acid, benzoic acid, phenol, water, and silver chloride in aqueous mixtures of acetone, tetrahydrofuran, and ethanol. The solvent compositions in these studies were varied from 0 to ca. 70 mass % nonaqueous component, and measurements were made at several temperatures between 10° and 40°C. 

Chemical sensing is part of an information-acquisition process in which an insight is obtained about the chemical composition of the system in real-time. In this process, an amplified electrical signal results from the interaction between some chemical species and the sensor. Generally, the interaction consists of two steps recognition and amplification. One common example is the measurement of pH with a glass electrode (Fig. 1.1). 

The dissociation of acetic acid in aqueous solution is an example of the simplest type of protolytic process. The dissociation constant was one of the first chemical parameters to be studied as a function of isotopic composition of the solvent (La Mer and Chittum, 1936 Homel and Butler, 1936), and the determinations have been repeated by several groups of workers. Conductivity measurements (La Mer and Chittum, 1936), potentiometry using the quinhydrone electrode (Korman and La Mer, 1936) or glass electrodes (Salomaa et al., 1964a Gold and Lowe, 1968), and measurements of the rate of a hydrogen-ion... 

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