System (100) and method of automatically controlling an active oxidant concentration (e.g. sodium hypochlorite) for a process of producing monochloramine comprising applying metered amounts of an oxidant solution and an amine solution to a defined area (114). An electrochemical measurement device is provided in association with the oxidant solution and prior to the defined area, N comprising at least first and second electrodes and an output terminal. A predetermined voltage potential is applied across the first and second electrodes, wherein an obtained amperometric measurement corresponds to a real-time concentration of the active oxidant in the oxidant solution. A feedback signal is generated based on the obtained measurement via the output terminal to a controller (108), which automatically regulates, in real-time and based at least in part on the control signal, the metered amount of oxidant solution provided to the defined area.