title: Single-Particle Time-of-Flight Mass Spectrometry Utilizing a Femtosecond Desorption and Ionization Laser.
abstract: Single-particle time-of-flight mass spectrometry has now been used since the 1990s to determine particle-to-particle variability and internal mixing state. Instruments commonly use 193 nm excimer or 266 nm frequency-quadrupled Nd:YAG lasers to ablate and ionize particles in a single step. We describe the use of a femtosecond laser system (800 nm wavelength, 100 fs pulse duration) in combination with an existing single-particle time-of-flight mass spectrometer. The goal of this project was to determine the suitability of a femtosecond laser for single-particle studies via direct comparison to the excimer laser (193 nm wavelength, ∼10 ns pulse duration) usually used with the instrument. Laser power, frequency, and polarization were varied to determine the effect on mass spectra. Atmospherically relevant materials that are often used in laboratory studies, ammonium nitrate and sodium chloride, were used for the aerosol. Detection of trace amounts of a heavy metal, lead, in an ammonium nitrate matrix was also investigated. The femtosecond ionization had a large air background not present with the 193 nm excimer and produced more multiply charged ions. Overall, we find that femtosecond laser ablation and ionization of aerosol particles is not radically different than that provided by a 193 nm excimer.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Zawadowicz
authors.affiliation: Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology , Karlsruhe, Germany.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Abdelmonem
authors.affiliation: Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology , Karlsruhe, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Mohr
authors.affiliation: Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology , Karlsruhe, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Saathoff
authors.affiliation: Chemical Sciences Division, NOAA Earth System Research Laboratory , Boulder, Colorado 80305 United States.|Cooperative Institute for Research in Environmental Science, University of Colorado , Boulder, Colorado 80309 United States.
authors.forename: Karl D
authors.initials: KD
authors.lastname: Froyd
authors.affiliation: Chemical Sciences Division, NOAA Earth System Research Laboratory , Boulder, Colorado 80305 United States.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Murphy
authors.affiliation: Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology , Karlsruhe, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Leisner
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Cziczo