Used as a key reagent in water quality testing, particularly for the determination of free and total chlorine in drinking water, swimming pools, and wastewater. When exposed to chlorine, it reacts to form a pink-colored compound, the intensity of which is proportional to the chlorine concentration, allowing for colorimetric measurement. Also employed in detecting oxidants such as bromine, iodine, and chlorine dioxide in various environmental and industrial samples. Its high sensitivity and rapid reaction make it ideal for field test kits and laboratory analysis. Additionally, it serves as an indicator in titrations involving oxidizing agents.