<P> Glass electrodes are commonly used for pH measurements . There are also specialized ion sensitive glass electrodes used for determination of concentration of lithium, sodium, ammonium, and other ions . Glass electrodes have been utilized in a wide range of applications--from pure research, control of industrial processes, to analyze foods, cosmetics and comparison of indicators of the environment and environmental regulations: a microelectrode measurements of membrane electrical potential of a biological cell, analysis of soil acidity, etc . </P> <P> Almost all commercial electrodes respond to single charged ions, like H, Na, Ag . The most common glass electrode is the pH - electrode . Only a few chalcogenide glass electrodes are sensitive to double - charged ions, like Pb, Cd and some others . </P> <P> There are two main glass - forming systems: </P> <Ul> <Li> silicate matrix based on molecular network of silicon dioxide (SiO) with additions of other metal oxides, such as Na, K, Li, Al, B, Ca, etc . </Li> <Li> chalcogenide matrix based on molecular network of AsS, AsSe, AsTe . </Li> </Ul>

Describe the source of ph dependence in a glass membrane electrode