A Thermal Desorption Chemical Ionization Ion Trap Mass Spectrometer for the Chemical Characterization of Ultrafine Aerosol Particles

Abstract

The development of a thermal desorption chemical ionization ion trap mass spectrometer for the chemical characterization of ultrafine aerosol particles is reported and first experimental results are presented. Atmospheric particles are size-classified and collected using a unipolar charger, a radial differential mobility analyzer and an electrostatic precipitator, and analyzed after thermal desorption and chemical ionization using an ion trap mass spectrometer. Integration of an ion trap mass spectrometer allows for fast scans of the entire mass spectrum every 0.5 s and bears the potential to identify unknown particulate compounds by tandem mass spectrometry. Particle collection efficiencies range from 90–100% for 25 nm particles to about 50% for 40 nm particles. In the current configuration, the absolute sensitivity of the instrument with regard to ammonium is in the range of 10–100 pg NH + 4 . In ambient samples collected in the Colorado Front Range, NH + 4 was the major signal peak in the positive ion spectrum, and additional minor signals and peak patterns of organic compounds including methylamine were found.