Chloronitramide anion
The chloronitramide anion, also known as chloroazanide, is a chemical byproduct of the disinfectant chloramine first identified in 2024. It is present in the tap water of about 113 million people in the United States in varying concentrations. Its toxicity has not yet been determined, although it may be removable by an activated carbon filter. Although its molecular formula and structure were unknown, it was first recorded as a byproduct of chloramine in the early 1980s.
Chloramine is often used as an alternative to chlorine for water disinfection because of chlorine's harmful byproducts, and on the basis that clean water improves health much more than small concentrations of byproducts harm it. Other methods of disinfection exist, including ozone and UV light, but these cannot currently be used in the US because the law requires water to have small residual amounts of disinfectant to prevent re-infection.
One study of 40 locations in the US found a median chloronitramide anion concentration of 23 micrograms per liter in drinking water, with a first quartile of 1.3 and a third quartile of 92.
Research
Early research
The chloronitramide anion was first detected as a UV absorbance interference during monitoring of chloramine and dichloramine in 1981. It was then shown to form during the decomposition of both chemicals. It was shown to likely be an anion in 1990. In the 1980s and 1990s methods of producing it in high concentrations were identified, and the molecule was shown through destruction to contain both nitrogen and chlorine. According to Julian Fairey, research on the compound slowed down in the mid-1990s after attempts to identify it were unsuccessful.Identification of structure
The structure of the molecule was finally identified in 2024 using a combination of techniques, first identifying the molecular formula, then creating a candidate structure, then confirming it.Ion chromatography, a method of separating ions and ionizable polar molecules, was used to separate the chloronitramide anion from the many salts present in water samples containing it, which otherwise made it difficult to use mass spectrometry; the water salinity was higher than that of saltwater.
Mass spectrometry was sufficient to determine the molecular mass of the ion, but it was too small for structure determination from the fragmentation pattern. The ion was found to have the molecular formula ClN2O2−1 by electrospray ionisation mass spectrometry. A candidate structure was confirmed by 15N NMR spectroscopy and infrared spectroscopy.