Tracking Monochloramine Decomposition in MIMS Analysis

Area of Science:

• Analytical Chemistry
• Environmental Science

Background:

• Membrane-introduction mass spectrometry (MIMS) enables online, real-time analysis of monochloramine (NH2Cl).
• Isobaric interferences can impact MIMS selectivity and sensitivity.
• High-resolution mass spectrometry, particularly miniaturized Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR MS), can mitigate these interferences.

Purpose of the Study:

• To investigate the decomposition of monochloramine (NH2Cl) during MIMS analysis.
• To elucidate the mechanisms contributing to NH2Cl decomposition into ammonia.
• To assess the suitability of MIMS-FT-ICR MS for in-field environmental monitoring.

Main Methods:

• Utilized membrane-introduction mass spectrometry (MIMS) coupled with Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR MS).
• Performed headspace analyses bypassing the membrane to isolate decomposition origins.
• Investigated potential adsorption and surface-catalyzed decomposition within the MIMS device.

Main Results:

• Monochloramine (NH2Cl) analysis via MIMS-FT-ICR MS showed decomposition into ammonia.
• Decomposition was not solely due to membrane interactions.
• Adsorption within the MIMS device followed by surface-catalyzed decomposition was identified as a significant factor.

Conclusions:

• MIMS-FT-ICR MS is a potent tool for in-field monochloramine analysis.
• Monochloramine decomposition in MIMS involves both membrane and device-related processes.
• Surface adsorption and catalysis within the MIMS system contribute to monochloramine degradation to ammonia.