Purification and enrichment of chloronitramide anion in water

Chloronitramide anion (Cl–N–NO₂⁻) is a newly identified chloramine decomposition product with potential implications for human health. Although reported to be present widely, relatively pure and highly concentrated Cl–N–NO₂⁻ samples are currently unavailable, which hinders investigations into its toxicity, occurrence, and physicochemical characteristics. To address this limitation, an automated purification and enrichment strategy based on repeated valve-switching ion chromatography (IC) combined with vacuum concentration was developed to isolate Cl–N–NO₂⁻ from impurity-rich solutions. Using this approach, Cl–N–NO₂⁻ was successfully purified and enriched to obtain a highly concentrated (∼24 mM) and high-purity (>99%, except water) sample, representing the highest concentration and purity reported to date. The identity was systematically verified using multiple analytical techniques, including ultraviolet spectrum, mass spectrometry, and element ratio analysis. In addition, the thermal stability of Cl–N–NO₂⁻ was evaluated. Increasing water temperature (up to 95 °C) caused no significant loss of Cl–N–NO₂⁻, suggesting that it is neither volatile nor hydrolysable under the tested conditions. The developed strategy provides a novel practical tool to obtain highly pure and concentrated Cl–N–NO₂⁻, enabling future studies on its formation mechanisms, environmental fate, and potential health risks.