An Iodide-Adduct
High-Resolution Time-of-Flight Chemical-Ionization
Mass Spectrometer: Application to Atmospheric Inorganic and Organic
Compounds
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Abstract
A high-resolution
time-of-flight chemical-ionization mass spectrometer
(HR-ToF-CIMS) using Iodide-adducts has been characterized and deployed
in several laboratory and field studies to measure a suite of organic
and inorganic atmospheric species. The large negative mass defect
of Iodide, combined with soft ionization and the high mass-accuracy
(<20 ppm) and mass-resolving power (<i>R</i> > 5500)
of the time-of-flight mass spectrometer, provides an additional degree
of separation and allows for the determination of elemental compositions
for the vast majority of detected ions. Laboratory characterization
reveals Iodide-adduct ionization generally exhibits increasing sensitivity
toward more polar or acidic volatile organic compounds. Simultaneous
retrieval of a wide range of mass-to-charge ratios (m/Q from 25 to
625 Th) at a high frequency (>1 Hz) provides a comprehensive view
of atmospheric oxidative chemistry, particularly when sampling rapidly
evolving plumes from fast moving platforms like an aircraft. We present
the sampling protocol, detection limits and observations from the
first aircraft deployment for an instrument of this type, which took
place aboard the NOAA WP-3D aircraft during the Southeast Nexus (SENEX)
2013 field campaign