Abstract
Membrane-introduction mass spectrometry (MIMS) has been presented as one of the promising approaches for online and real-time analysis of monochloramine (NH2Cl) in diverse matrices such as air, human breath, and aqueous matrices. Selective pervaporation of NH2Cl through the introduction membrane overcomes the need for sample preparation steps. However, both the selectivity and sensitivity of MIMS can be affected by isobaric interferences, as reported by several researchers. High-resolution mass spectrometry helps to overcome those interferences. Recent miniaturization of Fourier transform—ion cyclotron resonance—mass spectrometry (FT-ICR MS) technology coupled to the membrane-introduction system provides a potent tool for in field analysis of monochloramine in environmental matrices. Monochloramine analysis by MIMS based FT-ICR MS system demonstrated decomposition into ammonia. To further clarify the origin of this decomposition, headspace analyses after bypassing the membrane were undertaken and showed that monochloramine decomposition was not exclusively related to interactions within the membrane. Adsorption inside the MIMS device, followed by surface-catalyzed decomposition, was suggested as a plausible additional mechanism of monochloramine decomposition to ammonia.
Highlights
Monochloramine (NH2 Cl) has useful applications in many important industrial activities
Determining NH2 Cl concentrations in seawater contributes to the chemical speciation of chlorine-derived oxidants, which is helpful in understanding chlorine chemistry and to optimize treatment
(N,N-diethyl-p-phenylenediamine) kits for “free and total chlorine” analysis, from Hach (Lognes, France); and aqueous solutions were prepared with ultrapure water produced by a PURELAB Chorus 1 water purification system purchased from Veolia Water
Summary
Monochloramine (NH2 Cl) has useful applications in many important industrial activities. It is widely used as a disinfection and/or antifouling agent [1,2,3]. In seawater ammonia competes with bromide to react with chlorine. Several studies reported that formation of NH2 Cl dominates that of bromine (Br2 /HOBr/− OBr) in chlorinated seawater when ammonia concentration exceeds 0.4 ppm [5,6]. Compared to bromamines, which are very unstable and decompose rapidly, NH2 Cl can remain longer in chlorinated seawater [8]. Being a weaker oxidant than free bromine, monochloramine has a longer half-life and produces significantly less total organic halogen compounds such as trihalomethanes and haloacetic acid.
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