Potential of glass electrode

The immersion of glass electrodes in strongly dehydrating media should be avoided. If the electrode is used in solvents of low water activity, frequent conditioning in water is advisable, as dehydration of the gel layer of the surface causes a progressive alteration in the electrode potential with a consequent drift of the measured pH. Slow dissolution of the pH-sensitive membrane is unavoidable, and it eventually leads to mechanical failure. Standardization of the electrode with two buffer solutions is the best means of early detection of incipient electrode failure. 

M), and inserting a silver-silver chloride electrode. Provided that the internal hydrochloric acid solution is maintained at constant concentration, the potential of the silver-silver chloride electrode inserted into it will be constant, and so too will the potential between the hydrochloric acid solution and the inner surface of the glass bulb. Hence the only potential which can vary is that existing between the outer surface of the glass bulb and the test solution in which it is immersed, and so the overall potential of the electrode is governed by the hydrogen ion concentration of the test solution. 

R. H. Doremus, Diffusion potentials in glass. Chapter 4 of Glass Electrodes for... 

The electromotive force (emf) of liquid membrane electrodes depends on the activity of the ions in solution and their performance is similar in principle to that of the glass electrode. To characterize the behavior of liquid membrane electrodes, the linearity of the emf measurements vs. concentration of a certain ion in solution is checked. Additional performance data are the Nernstian slope of the linear range and the pH range over which the potential of the electrode is constant. 

Experimental measurements were made by immersing a pair of the electrodes in a 15-ml portion of purely aqueous solution A, B, C, or D and allowing the potentials to stabilize. When the potential became stable, a portion of the nonaqueous cosolvent was added to the solution in the cell and the potential was again recorded. This procedure was continued until 50 ml of the cosolvent had been added. The temperature of the cells was kept constant to within 0.05°C of the reported temperatures throughout the experiments. The potential measurement-cosolvent addition experiments were performed at least twice with each combination of glass electrodes and silver-silver chloride electrodes on at least two independently prepared solutions. 

In potentiometric colloid titration the amount of potential-determining ions in solution is measured by an appropriate electrode. For oxides, where mainly the pH determines the potential, a glass electrode is a suitable detector. For Agl we could use an Agl electrode etc. 

Variation of Reference Electrode Potentials with Temperature pH Values of Standard Solutions Used in the Calibration of Glass Electrodes Temperature vs. pH Correlation of Standard Solutions Used for the Calibration of Electrodes Solid Membrane Electrodes Liquid Membrane Electrodes... 

If both internal and external surfaces of the glass electrode were identical, it is obvious from equation (10) that the potential of the electrode system would be determined simply by the difference of pll of the solutions on the two sides of the glass membrane, apart from the potential of the inner electrode, e.g., Ag, AgCl. This expectation can be tested by measuring the e.m.p. of a cell in which the solution is the same inside and outside the glass bulb and the reference electrode is the same as the inner electrode thus... 

In the field of electroanalysis the problem of the operative mechanism of glass electrodes may be mentioned. Thin membranes of several types of glass act as perfect Nemst-type electrodes for protons or other ions over many decades of concentration. The basic question is whether a glass electrode reacts to an ion i because 1 is charge-determining or because a liquid junction potential is set up with the transport dominated by i. In the former case Nernst s law for the electrode potential, 11.5.5.1], applies, in the latter [1.6.7.8] is valid, with t = = 1... 

After it was recognized that pH glass electrodes were not permeable to hydrogen ions, the systematic development of new electrodes became more intellectually feasible. We have probably only begun to explore the potentialities of membrane electrodes. These electrodes should be thought of as ion-selective rather than ion-spedfic, since... 

The hydrogen electrode is not practical, and commercial pH meters are constructed with a glass electrode that has a sensing element made of a thin membrane of a special glass sensitive only to H ions (Figure 9.4a). The potential of the electrode is found to be proportional to the pH of the surrounding solution, and the response of this electrode is similar to that of a hydrogen electrode. 

---