An Iodide-Adduct High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer: Application to Atmospheric Inorganic and Organic Compounds

TLDR

The iodide‑adduct HR‑ToF‑CIMS, with its large negative mass defect, soft ionization, and high mass accuracy (≤20 ppm) and resolving power (R > 5500), has been characterized and deployed to measure a wide range of organic and inorganic atmospheric species, enabling elemental composition determination for most detected ions. This study presents the sampling protocol, detection limits, and observations from the first aircraft deployment of the iodide‑adduct HR‑ToF‑CIMS aboard the NOAA WP‑3D during the 2013 Southeast Nexus field campaign. The instrument simultaneously records mass‑to‑charge ratios from 25 to 625 Th at >1 Hz, providing a comprehensive view of atmospheric oxidative chemistry and allowing rapid sampling of evolving plumes from fast‑moving platforms such as aircraft. Laboratory tests show that iodide‑adduct ionization exhibits increasing sensitivity toward more polar or acidic volatile organic compounds.

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 (R > 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.