In an electrolytic cell, a supporting electrolyte is an inert or relatively unreactive ionic substance that is added to the solution to increase its electrical conductivity and control the electrochemical conditions of the cell. It is particularly important in electroanalytical methods such as polarography, voltammetry, amperometry and certain forms of electrolysis. The supporting electrolyte generally does not participate directly in the electrode reaction being studied. Instead, it provides a suitable ionic environment in which the movement of the electroactive species can be controlled and the measured current can be related more accurately to the analytical concentration of the substance. One of the main purposes of adding a supporting electrolyte is to increase the electrical conductivity of the solution. A solution containing only a small concentration of the analyte may have relatively low conductivity. When a potential is applied between the electrodes, the resistance of such a solution can cause a significant potential drop within the solution. This phenomenon is known as the iR drop, where *i* represents the current and *R* represents the resistance of the solution. The actual potential at the electrode may therefore differ from the potential applied by the instrument. Addition of a sufficiently concentrated supporting electrolyte reduces the resistance of the solution and consequently minimizes the iR drop. This allows the applied potential to be controlled more accurately. Supporting electrolytes also help to maintain a relatively constant ionic strength of the solution. Ionic strength affects the activities of ions and therefore influences electrochemical reactions. In analytical measurements, it is desirable that changes in the observed current or electrode potential should mainly result from changes in the concentration of the analyte rather than changes in the ionic environment. By using an excess of supporting electrolyte, the ionic strength remains approximately constant even when the concentration of the analyte changes. This improves the reproducibility and reliability of analytical measurements. Another important purpose is to reduce the migration of the electroactive species. In an electric field, charged analyte particles can move toward the electrode not only because of diffusion but also because of ionic migration. In electroanalytical measurements, the current produced by an analyte should ideally be controlled by diffusion or another well-defined mass-transfer process. If migration makes a significant contribution, the measured current may not be directly proportional to the concentration of the analyte. A high concentration of supporting electrolyte supplies a large number of ions that carry most of the electrical current. As a result, the relative contribution of analyte migration becomes very small. The transport of the analyte to the electrode is then governed predominantly by diffusion. This is particularly important in polarographic and voltammetric methods. Supporting electrolytes can also help to maintain a stable potential distribution near the electrode surface. In the absence of sufficient electrolyte, the movement of charged species can produce significant changes in the concentration of ions near the electrode. These