4. Reference electrodes

These are half-cells corresponding to reversible electrochemical systems, whose potential remains invariable whatever the solute composition of the solution in which they are immersed. They include an ion junction which acts as an interface between the internal filling solution and the solution to be analyzed in which they are immersed. The use of a reference electrode makes it possible to compare the potentials of different indicator electrodes immersed in the same solution, or that of the same indicator electrode immersed in different solutions. By convention, in water, the scale of potentials is referred to the normal hydrogen electrode taken as the origin. However, as this type of electrode presents a number of difficulties, other so-called comparison electrodes (and, by extension, reference electrodes) are commonly used