Chloronitramide Anion Quantitation in Tap Waters by Ion Chromatography with Electrical Conductivity and Ultraviolet Absorbance Detection

Chloronitramide anion (Cl-N-NO₂ ^-) is a recently discovered inorganic chloramine decomposition product, with prior quantitation by hydrophilic interaction liquid chromatography-ultrahigh-resolution mass spectrometry (HILIC-UHRMS). Here, Cl-N-NO₂ ^- quantitation was evaluated by ion chromatography (IC) separation with electrical conductivity (EC) and ultraviolet absorbance at 243 nm (UV₂₄₃) detection. Using a 5 mL injection loop and a 14.4 mM Na₂CO₃ eluent, the Cl-N-NO₂ ^- method detection limit was 9.3 μg L^-1 by IC-EC and 6.2 μg L^-1 by IC-UV₂₄₃. Matrix testing with Cl-N-NO₂ ^- spiked at 15, 25, 50, and 100 μg L^-1 into 12 waters in triplicate matched the expected Cl-N-NO₂ ^- for IC-EC (R² = 0.994) and IC-UV₂₄₃ (R² = 0.993). Cl-N-NO₂ ^- was found by HILIC-UHRMS in all tested tap waters disinfected with chloramines (n = 8) at 22-314 μg L^-1 and free chlorine (n = 3) at 2-7 μg L^-1, and strongly correlated with IC-EC (R² = 0.991; average residual, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mrow> <mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow> <mml:mrow><mml:mi>i</mml:mi></mml:mrow> </mml:msub> <mml:mspace></mml:mspace></mml:mrow> <mml:mrow><mml:mo>®</mml:mo></mml:mrow> </mml:mover> </mml:math> = +3.2 μg L^-1) and IC-UV₂₄₃ (R² = 0.997; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mrow> <mml:msub><mml:mrow><mml:mi>r</mml:mi></mml:mrow> <mml:mrow><mml:mi>i</mml:mi></mml:mrow> </mml:msub> <mml:mspace></mml:mspace></mml:mrow> <mml:mrow><mml:mo>®</mml:mo></mml:mrow> </mml:mover> </mml:math> = 0.0 μg L^-1). This is the first report of Cl-N-NO₂ ^- in free chlorine systems and concentrations ≳200 μg L^-1 in chloramine systems. These IC methods enable widescale collection of Cl-N-NO₂ ^- occurrence data, with IC-UV₂₄₃ subject to lesser measurement bias.