HANS D. BECKEY AND HIS CONTRIBUTION TO THE DEVELOPMENT OF MASS SPECTROMETRY

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EVIDENCE FOR IMAGING CONDUCTING POLYMER FOAMS IN NFIM WITH TETRACYANOETHYLENE AND DICHLORO-DICYANO-BENZOQUINONE

Unusual ion images of polymer layers formed by field polymerization of image gas molecules have been reported for tetracyanoethylene (TCNE) under conditions of negative field ion microscopy (NFIM). In these experiments the tip temperature was slightly lower than the ambient gas temperature. The present study shows that negative field ion images and dynamic phenomena obtained with 2,3-dichloro-5,6-dicyano-p-benzoquinone under similar experimental conditions closely resemble those observed with TCNE. Furthermore it is shown that the ion images of both image gases and the observed dynamic phenomena arise from an elastic foam structure of the polymer layer. The rings and ring structures are attributed to the ion emission from bubbles extending out of the surface with electrically conducting surface layers

ON THE SURFACE MORPHOLOGY UNDERLYING NFIM IMAGES OBTAINED WITH TETRACYANOETHYLENE

The ring structures and dynamic phenomena observed in field ion microscopy with negative ions (NFIM) of tetracyanoethylene (TCNE) are interpreted as ion images of a surface layer grown by field-induced polymerization of the image gas molecules. The ring structures are attributed to the formation of mobile surface elevations by the field stress on the polymer layer. These small surface elevations combined with larger surface deformations, generated by the field stress and resulting from elastic properties of the bulk of the layer, explain many features of NFIM such as the clustering of rings and compression of ring structures

DYNAMIC SIMS OF SUPERSATURATED SOLUTIONS

En SIMS liquide un échantillon est soumis au faisceau de particules (keV) et les ions moléculaires sont enregistrés pendant l'érosion de la couche. On s'est intéressé au mode de formation des ions moléculaires dans des conditions dynamiques de bombardement en fonction de divers paramètres de la solution. Les expériences ont été réalisées avec des peptides et sels organiques en utilisant la spectrométrie de masse et la microscopie optique.In liquid SIMS (or fast atom bombardment mass spectrometry) a liquid sample solution is exposed to an incident keV particle beam and molecular ions are recorded during continuous erosion of the layer. We have investigated this mode of molecular ion formation under dynamic bombarding conditions regarding the effect of concentration, solid particle formation by cristallization of solutes from supersaturated solutions and the formation of a closed solid surface layer prior to the onset of particle bombardment. The experiments were performed with peptides and organic salts applying mass spectrometry and optical microscopy. They showed that molecular ions and/or cluster ions are obtained under dynamic bombarding conditions without accumulation of radiation damage from supersaturated solutions, even in the presence of small precipitated particles and after erosion of thin solid surface layers from the remaining solution. Furthermore it was found that the incident particle beam hampers crystallization of the solute from a supersaturated solution

STUDIES OF NEGATIVE FIELD ION MICROSCOPY WITH TETRACYANOETHYLENE

Negative ion images generated by tetracyanoethylene (TCNE) under inverted field conditions in a field ion microscope have been investigated in more detail. The experiments confirm previous findings / l / and reveal further unique ionization phenomena such as the discontinuous development of ring structures in the ion image, the oscillation of rings in size and switching between different ion emitting surface structures. The observation of these phenomena critically depends on maintaining a tip temperature lower than the ambient gas temperature. The phenomena are attributed to the formation of an electrically conducting polymer layer of TCNE and to an elastic response of the layer surface to the field stress. Thus field enhancing and ion emitting protrusions are formed

FIELD EFFECTS IN MOLECULAR ION FORMATION BY THE THERMOSPRAY TECHNIQUE

Il semble que le champ électrique soit pour partie responsable de la formation des ions par la technique thermospray (TSP). Quelques phénomènes d'ionisation observés dans les spectres -TSP des saccharides et des sels d'ammonium diquaternaires sont rapportés et discutés. Seuls les signaux di-cationiques de ces spectres sont indicatifs de l'évaporation ionique de champ à partir de gouttelettes chargées.Field effects thought to be involved in the formation of ions by the thermospray (TSP) techniques are outlined. Some ionization phenomena observed in the TSP spectra of saccharides and diquaternary ammonium salts are reported and discussed. Only the dication signals in the spectra of the latter are indicative of field induced ion evaporation from charged droplets

FIELD ION EMISSION FROM LIQUID SOLUTIONS : ION EVAPORATION AGAINST ELECTROHYDRODYNAMIC DISINTEGRATION

In several ionization techniques currently applied in organic mass spectrometry a mechanism of field induced ion evaporation from charged droplets is assumed to play a dominant role in the desolvation of ions from liquids. This ion evaporation mechanism is briefly discussed regarding its competition with electrohydrodynamic disintegration of the surface of the liquid droplet under field stress. It is shown that ion evaporation is unlikely to occur for most solute/solvent systems and of no significance in the formation of gaseous ions. In contrast electro-hydrodynamic disintegration processes can contribute to the desolvation of ions from charged droplets

ENHANCED FORMATION OF MULTIPLY CHARGED IONS IN NEGATIVE ION FIELD DESORPTION MASS SPECTROMETRY OF ORGANIC COMPOUNDS

Enhanced formation of doubly and triply charged negative ions has been obtained in negative ion field desorption mass spectrometry (NFD MS) of acids and salts by applying a matrix mixture of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG). Abundant doubly charged ions of disaccharides could be obtained from a mixture with a quaternary ammonium salt and sodium chloride. The matrix properties leading to the formation of multiply charged ions are discussed

COMPARISON OF BARE WIRES AND ACTIVATED EMITTERS FOR FD MS OF OLIGOSACCHARIDES

Ion formation in field desorption (FD) from activated wire emitters covered with field enhancing microneedles has been compared with that from bare wires for some oligosaccharides doped with NaCl. The experiment revealed a close similarity between both types of emitters in the ion formation by electrohydrodynamic disintegration processes at temperatures near the onset of ion emission. In contrast, at higher temperatures above the melting point the sample layers are removed from smooth wires while on activated emitters they are retained in part between the microneedles. In this temperature range surface mobile molecules were found to be ionized not only by FI processes on microneedle tips but also by alkali ion attachment on charged alkali ion donating solid deposits. The latter mechanism has not been considered in FD mass spectrometry yet