title: Thermal desorption-multiphoton ionization time-of-flight mass spectrometry of individual aerosol particles: a simplified approach for online single-particle analysis of polycyclic aromatic hydrocarbons and their derivatives.
abstract: Online single-particle (SP) laser mass spectrometry (MS) is an important tool for fundamental and applied aerosol research. Usually laser desorption/ionization (LDI) is applied for ablation and ionization of atoms and molecular fragments from the nanometer- or micrometer-sized air-borne particles and time-of-flight analysers (TOFMS) are used for mass-selective detection of mainly inorganic analytes. The detection of molecular organic compounds is solely possible under very special experimental conditions and extremely dependent on the particle matrix and thus limited to special applications. Very recently it was shown that by implementation of a two-step laser desorption (LD) resonance-enhanced multiphoton ionization (REMPI) postionization approach the single-particulate molecular signature of polycyclic aromatic hydrocarbons (PAH) and their derivatives can be recorded (LD-REMPI-SP-TOFMS). By this, particles from different sources could be differentiated via the patterns of specific molecular source tracers such as retene for soft wood combustion or larger PAH as indicator for gasoline car emissions. One drawback of the LD-REMPI-SP-TOFMS method in particular for field applications is, however, the necessity of operation and adjustment of two lasers. In this paper the successful implementation of a thermal desorption step in single-particle mass spectrometry is described (TD-REMPI-SP-TOFMS). After size determination by particle velocimetry, individual particles are thermally desorbed on a heated surface in the ion source of the TOFMS. Desorbed molecules are ionized subsequently by REMPI, which addresses selectively PAH and molecular trace indicators. The TD-REMPI-SP-TOFMS concept was tested with reference particles and applied for automotive exhaust and ambient monitoring. The comparison of the results with the ones obtained by the two-laser approach (LD-REMPI-SP-TOFMS) indicates that the patented TD-REMPI-SP-TOFMS technology presented here is nearly equally well suited for studying organic source tracers in ambient aerosols and aerosol emissions. The increased ruggedness and simplicity of the new approach, however, may favor its application for field measurements in aerosol science and technology.
authors.affiliation: Institut für Okologische Chemie, Helmholtz Zentrum München, 85764 Neuherberg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Bente
authors.forename: Martin
authors.initials: M
authors.lastname: Sklorz
authors.forename: Thorsten
authors.initials: T
authors.lastname: Streibel
authors.forename: Ralf
authors.initials: R
authors.lastname: Zimmermann
mesh_terms: D000336:Aerosols; D005742:Gasoline; D006361:Heating; D007834:Lasers; D013058:Mass Spectrometry / Q000379:methods*; D009862:Online Systems; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis* / Q000737:chemistry*; D011522:Protons; D013696:Temperature; D013997:Time Factors; D001335:Vehicle Emissions / Q000032:analysis; D014835:Volatilization
chemical_list: D000336:Aerosols; D005742:Gasoline; D011084:Polycyclic Aromatic Hydrocarbons; D011522:Protons; D001335:Vehicle Emissions