Determination of trichloramine in drinking water using headspace gas chromatography/mass spectrometry

Trichloramine (NCl₃) is one of the major causes of the chlorine odor in drinking water. In the present study, a method was developed for analysis of NCl₃ concentration in water using headspace gas chromatography/mass spectrometry (HS–GC/MS). For quantification of NCl₃, m/z of 51 was selected because other major m/z of NCl₃ were also observed as fragments of trichloromethane (CHCl₃) and the peaks of NCl₃ and CHCl₃ overlapped on the chromatogram. The limit of quantification for NCl₃ was set to 15 μg-Cl₂/L. The calibration curve of NCl₃ was expressed as a quadratic curve because of the partial NCl₃ decomposition. NCl₃ concentrations in chlorinated ammonium solution were determined by HS–GC/MS and titration using N,N-diethyl-p-phenylenediamine and ferrous ammonium sulfate (DPD/FAS), and the results using the two methods were similar at pH 6 and 7. However, at pH 8, NCl₃ was detected using HS–GC/MS, but not using DPD/FAS titration. NCl₃ concentrations in nine tap water samples were determined using HS–GC/MS and ranged from < 15 to 46 μg-Cl₂/L. The results of the present study indicated that HS–GC/MS is applicable to determination of NCl₃ in drinking water.