Glass Electrode

Definition - What does Glass Electrode mean?

A glass electrode is an electrode that consists typically of a glass tube, sealed at the bottom, with a thin-walled glass bulb containing a solution of constant pH (as a chloride buffer) and a silver-silver chloride reference electrode. This is immersed in an unknown solution, usually along with a calomel electrode, for determining the pH of this solution.

Corrosionpedia explains Glass Electrode

A glass electrode is a type of ion-selective electrode made of a doped glass membrane that is sensitive to a specific ion. It is an important part of the instrumentation for chemical analysis and physico-chemical studies. The electrode system has an electric potential when in a solution, and this allows it to be sensitive to any changes in the content of certain kinds of ions. This is normally represented by the dependence of an electromotive force. In other words, a glass electrode is devised to generate accurate electromotive force due to the difference in pH. And a reference electrode is devised not to cause electromotive force due to a difference in pH.

There are different types of pH glass electrodes. Some of them have improved characteristics for working in very alkaline or acidic medium. But almost all electrodes can operate in the 1 to 12 pH range.

The most common glass electrode is the pH electrode. There are also specialized ion-sensitive glass electrodes used for determination of concentration of lithium, sodium, ammonium, and other ions. It is simple to operate and can be used in portable instruments, and therefore extensively used in chemical, industrial, agricultural and biological laboratories.

The pH electrode is essentially a galvanic cell. The glass membranes in glass electrodes are designed to allow partial penetration by the analyte ion. They are most often used for pH measurements, where the hydrogen ion is the measured species. For example, a hydrogen electrode (or more commonly a glass electrode, which responds in the same way) together with a reference electrode, commonly the calomel electrode, serves to measure the actual hydrogen ion concentration, or the pH, of the solution.

Because of the ion-exchange nature of the glass membrane, it is possible for some other ions to concurrently interact with ion-exchange centers of the glass and to distort the linear dependence of the measured electrode potential on pH or other electrode function. In some cases it is possible to change the electrode function from one ion to another. For example, some silicate pNa electrodes can be changed to pAg function by soaking in a silver salt solution. In strongly acidic solutions of pH1, the salt effect due to anions is observed. It does not function properly in some organic solvents like pure alcohol.

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