AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Comprehensive Single Particle Analysis by Aerosol Mass Spectrometry with Different Desorption and Ionisation Techniques
MARKUS OSTER, Matthias Bente-von Frowein, Jürgen Schnelle-Kreis, Ralf Zimmermann, Helmholtz Zentrum München
Abstract Number: 62 Working Group: Instrumentation and Methods
Abstract Laser mass spectrometry is commonly used for on-line investigation aerosols on single particle basis (SP). Lasers are often applied for ionisation in several ways. A laser pulse with high power density (~10$^9W/cm$^2) generates ions via a one-step laser desorption/ionisation (LDI), that can be analysed and detected with a mass spectrometer. A reduced power density (~10$^7W/cm$^2) produces gas phase neutrals (laser desorption, LD). Another method is thermal desorption (TD), where particles impinge on a heated metal surface. Neutrals produced by LD or TD can be ionised by several techniques like single- or multiphoton-ionisation. The choice of desorption and ionisation method delivers different information of the particles. While LDI mainly provides information of inorganic compounds and carbon clusters, two-step desorption/ionisation allows the detection of fragile organic molecules.
A system is presented, that uses a differentially pumped inlet system to generate a particle beam from aerosols. Laser velocimetry provides information about the aerodynamic diameter and velocity of individual particles. A CO$_2-laser is used for LD, and a KrF-excimer laser for resonance-enhanced multiphoton-ionisation (REMPI), that selectively ionises polycyclic aromatic hydrocarbons (PAH) and alkylated PAH. Alternatively, LD can be replaced by TD, and instead of a two-step desorption/ionisation, the KrF-laser can also be used for a one-step LDI. The produced ions are subsequently analysed and detected by a reflectron time-of-flight mass spectrometer. By choosing adequate trigger settings for the lasers according to particle velocities, the LD-REMPI, TD-REMPI and LDI-mode can be performed with the same experimental setup.
With existing approaches, it is not possible to investigate inorganic and fragile organic components on single particle basis. To close this gap, in future work the LD-REMPI-mode will be combined with a subsequent LDI-process. By means of this method, besides collecting information of organic (specially PAH/alkylated PAH) components, inorganic compounds will be detected by recording a second mass spectrum of the same particle.