Abstract: A electrochemical sensor comprising a mounting having screen printed array of electrodes located thereon, the array comprising a reference electrode, a counter electrode and a plurality of working electrodes, wherein the working electrodes are each overlaid with an insulating layer of insulating material, the insulating layer having an array of apertures, exposing a respective array of working regions of the working electrodes, and a method of making same by applying screen printing technic, and a method of using same for chlorine determination.