Quantification of gas phase hydrogen peroxide and methyl peroxide in ambient air: Using atmospheric pressure chemical ionization mass spectrometry with O2−, and O2−(CO2) reagent ions
Date of Original Version
Instrumentation and ion chemistry are described for the measurement of hydrogen peroxide (H2O2) and methyl peroxide (CH3OOH) in ambient air by chemical ionization mass spectrometry (CIMS). A CIMS, designed and certified for aircraft deployment, was used in this work. The reagent gas was ultrapure air containing 400 ppm CO2. The resultant reagent ions, O2− and O2−(CO2), form cluster ions with CH3OOH and H2O2, respectively, and are monitored at 80 m/z [O2−(CH3OOH)] and 110 m/z [O2− (CO2)(H2O2)]. The CIMS instrument was periodically calibrated using gas-phase standards generated from aqueous solutions. A Carulite-200® catalyst was used to remove peroxides from ambient air to blank the system to account for variations in the ambient air matrix. H2O2 also forms a stable cluster ion with O2− though its calibration behavior was more complex than that for O2−(CO2) in ambient air. The instrument was deployed on the National Center for Atmospheric Research Gulfstream-V aircraft. Representative measurements from the May-June 2012 Deep Convective Clouds and Chemistry experiment spanning altitudes between 0 and 13 km over the south-central midwest and southeastern United States are shown. Laboratory experiments, airborne experiments and theoretical molecular modeling approaches were utilized to identify and select reagent ions and to understand the ion-molecule reactions for the formation of peroxide-ion clusters in the ambient air matrix under tropospheric conditions. The analytical viability of a particular ion-molecule adduct was supported by ab-initio molecular orbital calculations.
Publication Title, e.g., Journal
International Journal of Mass Spectrometry
O'Sullivan, Danie W., Indira K. Silwal, Ashley S. McNeill, Victoria Treadaway, and Brian G. Heikes. "Quantification of gas phase hydrogen peroxide and methyl peroxide in ambient air: Using atmospheric pressure chemical ionization mass spectrometry with O2−, and O2−(CO2) reagent ions." International Journal of Mass Spectrometry 424, (2018). doi: 10.1016/j.ijms.2017.11.015.