Differentiation and quantification of free chlorine and inorganic chloramines in aqueous solution by MIMS

A membrane introduction mass spectrometric (MIMS) method for differentiation and quantification of free chlorine and inorganic chloramines in aqueous solution was developed based on a low-cost mass spectrometer. Several factors were examined for system optimization. Only membrane temperature and liquid flow rate exerted substantial influences on the performance of MIMS. Essentially linear response curves over several orders of magnitude of concentrations were observed, and limits of detection for free chlorine and mono-, di-, and trichloramine at 0.1, 0.1,0.02, and 0.06 mg/L as Cl₂, respectively, were demonstrated. System performance was evaluated with chlorination of ammoniacal water. Similar results were obtained by the MIMS method, conventional DPD/FAS titration, and UV-visible spectroscopy. Identification and quantification of inorganic chloramines by the MIMS method and DPD/FAS titration were also compared for chlorination of an aqueous solution containing glycine as the nitrogen source as well as samples of potable water and wastewater. These experiments demonstrated an advantage of MIMS relative to titration in that MIMS was able to unambiguously quantify and characterize the inorganic chlorine residual.