AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Detection of Light vs. Heavy Atoms with a Laser Induced Plasma Ionization Source for Single Particle Analysis
ANDREW J. HORAN, Justin Krasnomowitz, Murray Johnston, University of Delaware
Abstract Number: 571 Working Group: Instrumentation and Methods
Abstract On-line determination of the chemical composition of nanoparticles (<100nm dia.) in the atmosphere represents a significant analytical challenge. Laser induced plasma ionization in the Nano Aerosol Mass Spectrometer (NAMS) has proven effective for determining quantitative elemental composition of these particles containing low atomic number non-metals (C, O, N, S, Si). The ability to detect and quantify larger elements, both metals and non-metals, is desirable, but not fully tested. Here, the properties of this ionization are explored for a selection of elements which span the Periodic Table. Solutions of group I and VII salts, Cr(NO$_3)$_3, Fe(NO$_3)$_3, AgNO$_3, Al(NO$_3)$_3 TiO$_2, ZnO, poly(dimethylsiloxane), Pb(NO$_3)$_2 and silver nanoparticles are aerosolized (TOPAS ATM226 generator) to produce a flow of 80-100nm diameter particles. Additionally, mixtures of these solutions with organic molecules such as HEPES and sucrose are examined.
Particles are sampled through a flow limiting orifice and focused in an aerodynamic lens assembly for transmission into the ion source region. Positive ions produced by laser irradiation are analyzed with a reflecting time-of-flight mass spectrometer (R.M. Jordan Company). Charge states of atomic ions are used to assign the dominant type of ionization. Particles containing low atomic number nonmetals give multiply charged atomic ions indicative of plasma ionization. Few singly charged ions are observed (other than H+). In general, we have found that the relative mole fractions of C, O, N, S, Si are quantifiable to within +/- 10% of expected values. For elements in groups I, II, and VII, the mass spectra consist of both singly and multiply charged ions. Elemental compositions are generally quantifiable to within 20% of expected values. Metals toward the center of the Periodic Table give primarily singly charged ions indicative of desorption ionization. The metal ion signal is not quantitative, but the non-metal anion components are generally quantitative to each other.