Photometric determination of free chlorine, total chlorine and ozone with N,N-diethyl-1,4-phenylene diamine (DPD)/potassium iodide

Free chlorine, total chlorine and ozone react with DPD (N,N-diethyl-1,4-phenylene diamine) to form a red-violet dye. By defined addition of iodide ions one can differentiate between the individual components.