10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Two-Step Laser Desorption/Ionization Mass Spectrometry of Individual Microorganisms by Single Particle Aerosol Mass Spectrometry (SPAMS)
DAVID FERGENSON, Sean Kinahan, Joshua Santarpia, Livermore Instruments Inc.
Abstract Number: 1641 Working Group: Bioaerosols
Abstract A Single Particle Aerosol Mass Spectrometer (SPAMS) was used to generate real-time mass spectrometric data acquired from individual aerosolized non-pathogenic microorganism particles, analyzed by infrared desorption followed by ultraviolet ionization.
SPAMS is a technology whereby individual aerosol particles are analyzed in real-time, with a dual polarity mass spectrum acquired along with the aerodynamic diameter of each particle. This SPAMS is distinct from predecessor instruments in its simplicity, its ability to operate under high aerosol concentrations, and the number of aerosol particles that it can analyze per second. A SPAMS instrument is maintained under vacuum and aerosol particles are driven into its differentially pumped interface by atmospheric pressure. An aerodynamic focusing lens stack focuses the particles into a beam assuring that they arrive at the center of the source region of a dual polarity time-of-flight mass spectrometer. A single continuous-wave laser that is square in profile is oriented across the aerosol beam so that, when a particle crosses it, light scattered from that particle is detected by a photomultiplier tube. The duration of the light scattering indicates the velocity of the particle which is related to its aerodynamic diameter.
In a conventional SPAMS instrument, as the particle exits the laser, the cessation of detected scattered light is used to actuate a pulsed ultraviolet laser which is focused just below the scattering laser. The pulsed laser desorbs material from the particle and ionizes the material, with resulting ions analyzed by the mass spectrometers. Previous experiments involving the analysis of individual aerosolized microorganisms by SPAMS have demonstrated the technique’s ability to discern genera and, in some cases, species across different growth conditions. However, the information available in the mass spectra was limited by the fragmentation of the molecules by the harshness of the desorption process. Several predecessor instruments to the SPAMS were modified with an alternate desorption/ionization process whereby the individual particles were first desorbed into the vapor phase by a CO2 laser and then ionized using an ultraviolet laser in a second step, preserving molecular ion information intact. In this work, a SPAMS instrument was fitted with a 2-step desorption/ionization scheme and applied to the analysis of individual microorganisms.