An on-line aerosol laser mass spectrometer with three, easily interchangeable laser based ionisation methods for characterisation of inorganic and aromatic compounds on particles

Abstract

An aerosol mass spectrometric set-up is presented comprising three different laser based techniques for on-line analysis of particles. The implemented methods are one-step laser desorption/ionisation (LDI), two-step laser desorption/photoionisation (LDPI) and thermal desorption/photoionisation (TDPI). Photoionisation processes for the latter two methods are based on resonance enhanced multiphoton ionisation (REMPI), which is highly selective and sensitive for polyaromatic hydrocarbons (PAH). LDI is especially suitable for the detection of inorganic compounds and the determination of sum values such as elemental carbon content. Investigated samples were particles from spruce wood ash generated by an oxygen-controlled residential heating system and exhaust gases from a gasoline driven passenger car. In the positive LDI mass spectra several metal cations such as potassium and iron are detectable, whereas carbon clusters can be observed with the negative mode. With LD-REMPI and TD-REMPI various PAH such as phenanthrene and derivatives, pyrene, etc., become visible. In the wood ash samples relatively high yields of retene were found, which could be used as tracer compound for coniferous wood combustion. All three modes can be applied with only slight modifications of the instrument. Thus, it allows characterising single particles on a real time basis and, depending on the application, the most convenient technique can be selected.