Simultaneous Mobility-Mass Evaluation of charged Clusters

Nano-particles in the size range below 3nm (ultra fine particles), consisting of few agglomerated molecules or even large single molecules, have been of special interest for some time. Biological macromolecules and molecular groups (proteins, viruses) also belong to this size range. For studies performed under laboratory conditions, the characterization as well as the generation of well defined nano-aerosols with sizes down to single molecules is of crucial importance. The Electro Mobility Spectrometry is a widely recognized method to determine the size and concentration of ultra fine particles. The classification of aerosols according to their electrical mobility in a Differential Mobility Analyzer (DMA) in combination with an appropriate aerosol generator provides an excellent source of highly monodisperse particles with well-defined properties for laboratory experiments. However, in the size range of molecular clusters, the behaviour of the classified particles cannot be sufficiently described unless additional information (e.g. particle mass) is simultaneously obtained. Singly charged particles with a well-defined mobility exiting a DMA can be efficiently transferred into a Mass Spectrometer (MS). To provide an adequate resolution power and minimize diffusion losses, high flow DMAs as well as an optimized setup (DMA-MS) have to be considered. An improved high flow DMA operating in closed loop arrangement with well controlled carrier gas properties was investigated in a preliminary study and found suitable for the purpose of classifying and analyzing molecular clusters. This device will be combined with a standard Quadrupole Mass Spectrometer to provide simultaneous information of electrical mobility and mass of molecular clusters in the size range below 1.7 nm mobility equivalent diameter. Experiments in cooperation with Prof. Curtius (Univ. Frankfurt) will focus on the mobility and mass determination of ionic clusters produced by ionizing processes (bipolar charging and corona discharge), widely used to provide a defined charging state of the particles prior to mobility classification. The influence of different carrier gases and spurious gases will be studied. Different aerosol generators (electrospray, wire generator, spark generator) will be evaluated for potential cluster sources. Further experiments, in cooperation with Prof. Wagner (Univ. Wien) and Prof. Kulmala (Univ. of Helsinki), on ion induced nucleation on highly monodisperse and well defined molecular cluster species are in preparation. The proposed project will contribute significantly to the understanding of the fundamental properties of charged molecular clusters.

Nano-particles in the size range below 3nm (ultra fine particles), consisting of few agglomerated molecules or even large single molecules, have been of special interest for some time. Biological macromolecules and molecular groups (proteins, viruses) also belong to this size range. For studies performed under laboratory conditions, the characterization as well as the generation of well defined nano-aerosols with sizes down to single molecules is of crucial importance. The Electro Mobility Spectrometry is a widely recognized method to determine the size and concentration of ultra fine particles. The classification of aerosols according to their electrical mobility in a Differential Mobility Analyzer (DMA) in combination with an appropriate aerosol generator provides an excellent source of highly monodisperse particles with well-defined properties for laboratory experiments. However, in the size range of molecular clusters, the behaviour of the classified particles cannot be sufficiently described unless additional information (e.g. particle mass) is simultaneously obtained. Singly charged particles with a well-defined mobility exiting a DMA can be efficiently transferred into a Mass Spectrometer (MS). To provide an adequate resolution power and minimize diffusion losses, high flow DMAs as well as an optimized setup (DMA-MS) have to be considered. An improved high flow DMA operating in closed loop arrangement with well controlled carrier gas properties was investigated in a preliminary study and found suitable for the purpose of classifying and analyzing molecular clusters. This device will be combined with a standard Quadrupole Mass Spectrometer to provide simultaneous information of electrical mobility and mass of molecular clusters in the size range below 1.7 nm mobility equivalent diameter. Experiments in cooperation with Prof. Curtius (Univ. Frankfurt) will focus on the mobility and mass determination of ionic clusters produced by ionizing processes (bipolar charging and corona discharge), widely used to provide a defined charging state of the particles prior to mobility classification. The influence of different carrier gases and spurious gases will be studied. Different aerosol generators (electrospray, wire generator, spark generator) will be evaluated for potential cluster sources. Further experiments, in cooperation with Prof. Wagner (Univ. Wien) and Prof. Kulmala (Univ. of Helsinki), on ion induced nucleation on highly monodisperse and well defined molecular cluster species are in preparation. The proposed project will contribute significantly to the understanding of the fundamental properties of charged molecular clusters.