The membrane process, the best available technology in chlor-alkali electrolysis, requires highly purified sodium chloride brine electrolytes. One of the most important parameters to be monitored is the concentration of iodide. In the electrolysis cell, iodide is oxidized to iodate, which precipitates in the ion-exchange membrane and decreases the membranes useful lifetime. The described voltammetric method is straightforward and sensitive for the trace determination of iodide in brine. The method involves the oxidation of iodide to iodate and the subsequent determination of the iodate by differential pulse voltammetry. The limit of detection is approximately 2.5 μg/L iodide.