What are liquid junction potentials, and how do they affect measured potentials?
The salt solution required for a reference electrode must be separated from the analyte solution by a frit that allows ionic conduction between the two solutions, but does not allow appreciable contamination of the analyte solution by the reference electrode solution (or vice versa). This frit is usually made of either a ceramic material or of porous polymer membrane. Typically, the solutions separated by the frit do not contain the same ions, and the different rates of diffusion across the frit by the different ions gives rise to a potential across the frit – the junction potential. This is a further contribution to the potential between the working and reference electrodes. Since the junction potential is different for solutions of different ionic compositions, strictly speaking, redox potentials measured in different solutions (e.g., different organic solvents) cannot be compared directly, and an internal standard is required. See the page about reference electrodes.
