Glass Membrane Electrodes:

The pH glass electrode while somewhat mechanically fragile resists a variety of sample media and along with the exception of hydroxide is hugely free from interferences. However, pH-sensitive glass electrodes form the basis of several successful sensors for environmentally sensitive gases. Therefore, glass membranes represent an important class of solid-membrane ion selective electrodes (ISEs).

The majority of pH electrodes available commercially are combination electrodes which have both glass H⁺ ion sensitive electrode and further reference electrode conveniently placed in one housing (see figure below). For a few specific applications separate pH electrodes and reference electrodes are still used - they permit higher precision required sometimes for research reasons. In most cases combination electrodes are precise sufficient and much more convenient to use.