Search

Membrane Inlet Mass Spectrometry (MIMS) was used to analyze monochloramine solutions (NH₂Cl) 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 NH₃ 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, NH₂Cl solutions, in addition to the NH₃Cl⁺ signal, presented a strong NH₄⁺ signal at m / z 18.034. Ammonia presence in the low-pressure zone before ionization is probable as NH₄⁺ was detected with all the precursors used, particularly CF₃⁺ and trimethylbenzene that presents a proton affinity higher than monochloramine. Ammonia may be formed inside the membrane due to the fact that NH₂Cl 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., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

In this paper, we present a compact Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) designed for real time analysis of volatile organic compounds (VOCs) in air or in water. The spectrometer is based on a structured permanent magnet made with NdFeB segments. Chemical ionization is implemented inside the ICR cell. The most widely used reaction is the proton transfer reaction using H₃O⁺ precursor ions, but other ionic precursors can be used to extend the range of species that can be detected. Complex mixtures are studied by switching automatically from one precursor to another. The accuracy obtained on the mass to charge ratio (Δ m / z 5 × 10 −3 ), allows a precise identification of the VOCs present and the limit of detection is 200 ppb without accumulation. The time resolution is a few seconds, mainly limited by the time necessary to come back to background pressure after the gas pulses. The real time measurement will be illustrated by the monitoring of VOCs produced during the thermal degradation of a polymer and by an example where three different precursor ions are used alternatively to monitor a gas sample.