An Iodide-Adduct High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer: Application to Atmospheric Inorganic and Organic Compounds
Online chemical ionization mass spectrometry is uniquely capable of measuring many chemical species and rapid processes relevant to air quality. The development of iodide CI-TOFMS described by Lee et al. in Environmental Science and Technology (2014) significantly advanced the measurement of inorganic gases, oxygenated volatile organic compounds (VOC), and low-volatility VOCs.
The authors coupled a medium-pressure ion-molecule reactor (IMR) to the API-TOF platform provided by TOFWERK and Aerodyne Research, Inc. Iodide ions were created by flowing methyl iodide source gas through a 210Po ion source, and operational parameters of the IMR were optimized to enhance iodide-molecule adduct formation. Thorough instrument characterization was undertaken, including interpretation of the mass spectrum, response to changing ambient humidity, comparison of ion-molecule binding energies with the measured chemical space, and determination of detection limits and their relationship to functional group.
The instrument was deployed on a government research aircraft and in chamber experiments, and demonstrated measurement of a number of photochemical oxidation products difficult to measure with conventional analytical techniques. Iodide chemical ionization mass spectrometry has now been widely adopted, and is used extensively in atmospheric chemistry research.