The desorption of surface-adsorbed molecules induced by cluster-surface collisions of neutral molecular clusters, in particular, SO2 clusters, was investigated by means of molecular dynamics simulations. The desorption efficiency was found to be in general much higher for clusters of polar molecules when compared to nonpolar cluster constituents, for both nonpolar and polar adsorbates. In all cases, desorption is shown to proceed via dissolvation of the analyte in the cluster. In systems with nonpolar cluster constituents, the process is mainly driven by the increase in the entropy of the dissolved analyte in a larger cluster fragment. The latter process is enhanced by polar cluster constituents since the respective clusters show lower fragmentation at comparable kinetic energy and thus provide in average larger cluster fragments for the analytes to be dissolved in. In systems with clusters of polar constituents and polar adsorbates, the process is most efficient due to the additional energetic stabilization of the desorbed molecule in the solvation shell formed in the cluster fragment.

Primary-ion-induced fragmentation in organic molecules can strongly influence the results in secondary-ion mass spectrometry (SIMS) of organic and biomolecular samples. In order to characterize this ion-induced fragmentation, oligopeptide samples irradiated in SIMS experiments were investigated by means of desorption/ ionization induced by neutral SO 2 clusters (DINeC). The latter is a nondestructive desorption method for mass spectrometry of biomolecules, which gives direct access to the fragments induced in the sample. Comparison of TOF-SIMS and DINeC mass spectra revealed qualitative differences between the fragments, which remain in the sample and the fragments sputtered during ion bombardment. The fragmentation strength and its spatial distribution were found to be quantitatively different for Bi 1 + , Bi 3 + , and Ar 1000 + primary ions, leading to different distributions of the degree of fragmentation in the samples as directly measured by means of DINeC depth profiles.

Desorption/ionization induced by neutral clusters (DINeC) is used as an ultrasoft desorption/ionization method for the analysis of fragile biomolecules by means of mass spectrometry (MS). As a test molecule, the glycopeptide vancomycin was measured with DINeC-MS, and resulting mass spectra were compared to the results obtained with electrospray ionization (ESI), matrix assisted laser desorption ionization, and time-of-flight secondary ion MS. Of the desorption-based techniques, DINeC spectra show the lowest abundance of fragments comparable to ESI spectra. The soft desorption nature of DINeC was further demonstrated when applied to MS analysis of teicoplanin.

Abstract. To elucidate the sources and chemical reaction pathways of organic vapors and particulate matter in the ambient atmosphere, real-time detection of both the gas and particle phase is needed. State-of-the-art techniques often suffer from thermal decomposition, ionization-induced fragmentation, high cut-off size of aerosols or low time resolution. In response to all these limitations, we developed a new technique that uses extractive electrospray ionization (EESI) for online gas and particle chemical speciation, namely the dual-phase extractive electrospray ionization time-of-flight mass spectrometer (Dual-Phase-EESI-TOF or Dual-EESI for short). The Dual-EESI was designed and optimized to measure gas- and particle-phase species with saturation vapor concentrations spanning more than 10 orders of magnitude with good linearity and a measurement cycle as fast as 3 min. The gas-phase selectivity of the Dual-EESI was compared with that of nitrate chemical ionization mass spectrometry. In addition, we performed organic aerosol uptake experiments to characterize the relative gas and particle response factors. In general, the Dual-EESI is more sensitive toward gas-phase analytes as compared to their particle-phase counterparts. The real-time measurement capability of the Dual-EESI for chemically speciated gas- and particle-phase measurements can provide new insights into aerosol sources or formation mechanisms, where gas-particle partitioning behavior can be determined after absolute parameterization of the gas / particle sensitivity.

Soft cluster-induced desorption/ionization of polystyrene oligomers was investigated with respect to application in mass spectrometry. Clear peak progressions corresponding to intact polystyrene molecules were observed in the mass spectra, and no fragmentation was detected; efficient desorption was deduced from quartz crystal microbalance measurements. Molecular dynamics (MD) simulations of the process revealed that even in the case of the nonpolar polystyrene molecules cluster-induced desorption proceeds via dissolvation in the polar clusters. Experimentally, a significantly lower desorption efficiency was observed for polystyrene molecules with larger chain length. Taking into account MD simulations and further experiments with mixed samples consisting of long- and short-chain polystyrene oligomers, the reduced desorption efficiency for longer chain polystyrene molecules was attributed to a stronger entanglement of the larger polystyrene molecules.