Bromine, a less volatile compound than chlorine, is used as a sanitizing agent in drinking water systems, swimming pools, and spas. The DDPD Reagent, a methyl-substituted form of DPD is employed. Potassium iodide is added to the sample before analysis. Bromine reacts with the iodide to liberate iodine. The iodine reacts with the DDPD reagent to form a purple color. Results are expressed in ppm (mg/L) bromine as Br2.