Nessler

Nessler is a German surname. It may refer to individuals such as Julius Nessler, a chemist after whom Nessler's reagent is named.

Nessler's reagent, or Nessler's solution, is a chemical reagent used for the qualitative and quantitative detection of ammonia in aqueous samples. It is typically prepared by forming potassium tetraiodomercurate(II) in a strongly alkaline medium, usually with potassium hydroxide. When ammonia or ammonium ions are present, the reagent develops a yellow to brown color, the intensity of which correlates with ammonia concentration. The method of analysis is known as Nesslerization.

Common applications include testing drinking water, wastewater, and certain clinical or industrial samples. The reagent is sensitive to primary and secondary amines and can be affected by matrix interferences. Because it contains mercury compounds, Nessler's reagent is hazardous and requires careful handling, appropriate containment, and proper disposal in accordance with hazardous waste regulations. Stability is enhanced by storage in dark glass and protection from light; containers are typically amber to minimize degradation.

Historically important in analytical chemistry, Nessler's method provided a practical means to measure ammonia levels before the advent of many modern instrumental techniques. In contemporary practice, Nessler's method is sometimes complemented or replaced by less hazardous colorimetric methods or by instrumental ammonia determination techniques that avoid mercury-containing reagents.