The effects of molecular weight and thermal decomposition on the sensitivity of a thermal desorption aerosol mass spectrometer. Issue 2 (1st February 2016)

• Record Type: Journal Article
• Authors: Murphy, D. M.
• Is Part Of: Aerosol science and technology. Volume 50:Issue 2(2016)
• Page Start: 118
• Page End: 125
• Publication Date: 2016-02-01
• Subjects: Paul J. Ziemann; Aerosols -- Periodicals; Aerosol Propellants -- Periodicals; Aerosols -- Periodicals; 660.294515
• DOI: 10.1080/02786826.2015.1136403
• Languages: English
• ISSNs: 0278-6826

Abstract

ABSTRACT: In free molecular flow the slower speed of heavier molecules means that they spend more time in the ion source of a mass spectrometer. Hence the sensitivity of the thermal desorption mass spectrometers such as the Aerodyne Aerosol Mass Spectrometer (AMS) should include a term that scales as the square root of the molecular weight. Thermal decomposition on the vaporizer reduces the molecular weight prior to ionization and changes electron impact cross-sections. Thermal decomposition therefore has the potential to change the sensitivity, in some cases by more than a factor of three. Current AMS calibrations that rely upon an ammonium nitrate calibration and scaling for other components with a relative ionization efficiency may overestimate the concentration of large, thermally stable molecules and underestimate small or thermally unstable molecules. The overall sensitivity of the AMS to organics includes a partial cancellation of these effects. There is an incomplete understanding of the vaporization process, including that of ammonium nitrate.