Evidence of Reactivity in the Membrane for the Unstable Monochloramine during MIMS Analysis

Membrane Inlet Mass Spectrometry (MIMS) was used to analyze monochloramine solutions (NH(2)Cl) and ammonia solutions in a compact FTICR. Chemical ionization enables identification and quantification of the products present in the permeate. The responses of protonated monochloramine and ammonium increase linearly with the solution concentration. The enrichments were respectively 1.2 and 5.5. Pervaporation is dependent on pH and only the basic form of ammonia NH(3) pervaporates through the membrane. Unexpectedly, the small ammonia molecule permeated very slowly. It could be due to interactions with water molecules inside the membrane that create clusters. Moreover, NH(2)Cl solutions, in addition to the NH(3)Cl(+) signal, presented a strong NH(4)(+) signal at m/z 18.034. Ammonia presence in the low-pressure zone before ionization is probable as NH(4)(+) was detected with all the precursors used, particularly CF(3)(+) and trimethylbenzene that presents a proton affinity higher than monochloramine. Ammonia may be formed inside the membrane due to the fact that NH(2)Cl is unstable and may react with the water present in the membrane. Those results highlight the need for caution when dealing with chloramines in MIMS and more generally with unstable molecules.