N-(1-naphthyl) ethylenediamine dihydrochloride is primarily used as a reagent in analytical chemistry, particularly in colorimetric assays. It is widely employed in the detection and quantification of nitrites and nitrates in various samples, such as water, food, and biological fluids. The compound reacts with nitrites under acidic conditions to form a diazo dye, which produces a distinct color that can be measured spectrophotometrically. This method is crucial for monitoring water quality and ensuring food safety. Additionally, it is used in biochemical research for studying nitrogen metabolism and related processes. Its stability and sensitivity make it a valuable tool in environmental and clinical laboratories.