Nessler’s Reagent is a chemical solution used in analytical chemistry for the detection and quantification of ammonia (NH3) and other compounds that can be converted to ammonia. It is named after Julius Nessler, the German chemist who developed this reagent in the 19th century. Nessler’s Reagent consists primarily of a mixture of potassium iodide (KI), mercuric chloride (HgCl2), and potassium hydroxide (KOH) dissolved in water. When Nessler’s Reagent is added to a solution containing ammonia or ammonium ions, it forms a yellow to brownish precipitate of triiodide ions (I3-) due to the reaction between ammonia and mercuric chloride. The intensity of the color change is proportional to the concentration of ammonia in the sample, allowing for quantitative analysis.

This reagent is widely used in environmental and clinical laboratories for the determination of ammonia in water samples, wastewater analysis, and medical diagnostics. It provides a sensitive and reliable method for assessing the presence of ammonia and is particularly valuable in monitoring water quality and ensuring compliance with regulatory standards.