A salt bridge is an important component of an electrochemical cell, particularly in a galvanic or voltaic cell, because it completes the electrical circuit and maintains electrical neutrality in the two half-cells. In electroanalytical chemistry, salt bridges are especially significant because the potential measured in an electrochemical system depends on the proper functioning of the cell. A salt bridge generally consists of a U-shaped tube containing a concentrated solution of an inert electrolyte, such as potassium chloride (KCl), potassium nitrate (KNO₃), or ammonium nitrate (NH₄NO₃), often incorporated into an agar or gelatin gel to prevent rapid mixing of the solutions. Its principal function is to allow the controlled movement of ions between the half-cells while preventing direct mixing of the electrolytes. An electrochemical cell normally consists of two half-cells. Each half-cell contains an electrode immersed in an electrolyte solution. For example, in a Daniell cell, zinc is immersed in zinc sulfate solution and copper is immersed in copper sulfate solution. When the cell operates, oxidation takes place at the zinc electrode, which acts as the anode, while reduction occurs at the copper electrode, which acts as the cathode. Electrons flow through the external circuit from zinc to copper. However, electron flow alone cannot sustain the reaction because the solutions in the half-cells would rapidly develop an excess of electrical charge. The salt bridge prevents this charge accumulation by allowing ions to migrate between the two solutions. At the anode, oxidation of zinc occurs according to the reaction: Zn → Zn²⁺ + 2e⁻ As zinc atoms are oxidized, Zn²⁺ ions accumulate in the anodic solution. Consequently, the solution tends to become positively charged. If this positive charge were allowed to build up, it would oppose further oxidation of zinc and eventually stop the flow of electrons. The salt bridge supplies anions, such as Cl⁻ or NO₃⁻, toward the anode compartment. These anions compensate for the increasing positive charge and maintain electrical neutrality. At the cathode, the reduction reaction is: Cu²⁺ + 2e⁻ → Cu The Cu²⁺ ions are removed from the cathodic solution as copper is deposited on the electrode. Therefore, the solution tends to develop an excess of negative charge. Cations from the salt bridge migrate toward the cathode compartment to compensate for this negative charge. Thus, ion migration through the salt bridge permits the electrode reactions to continue for a considerable period. Another important role of the salt bridge is to complete the internal electrical circuit. Electrons cannot pass through the salt bridge; instead, ions carry charge through the internal part of the electrochemical cell. Electrons move through the external metallic conductor, whereas