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Characterization of rhodamine 6G release in electrospray ionization by means of spatially resolved fluorescence spectroscopy

  • In the present work, the density distribution of rhodamine 6G ions (R6G) in the gas phase and the droplets of an electrospray plume was studied by spatial and spectral imaging. The intention is to contribute to the fundamental understanding of the release mechanism of gaseous R6G in the electrospray ionization (ESI) process. Furthermore, the influence of ESI-parameters on the release efficiency of R6G, e. g. solvent flow, R6G and salt concentration were examined via direct fluorescence imaging of R6G. A solvent-shift of the fluorescence maximum,lambda(max) = 555 nm in methanolic solution and lambda(max) = 505 nm in gas phase, allows the discrimination between solvated and gaseous R6G. Two experimental setups were used for our measurements. In the first experiment, the R6G fluorescence and the light scattered from the spray plume were imaged in two spatial dimensions using a tunable wavelength filter. The second experiment was designed for obtaining 1-dimensional spatially resolved emission spectra of the spray. Here, the intensityIn the present work, the density distribution of rhodamine 6G ions (R6G) in the gas phase and the droplets of an electrospray plume was studied by spatial and spectral imaging. The intention is to contribute to the fundamental understanding of the release mechanism of gaseous R6G in the electrospray ionization (ESI) process. Furthermore, the influence of ESI-parameters on the release efficiency of R6G, e. g. solvent flow, R6G and salt concentration were examined via direct fluorescence imaging of R6G. A solvent-shift of the fluorescence maximum,lambda(max) = 555 nm in methanolic solution and lambda(max) = 505 nm in gas phase, allows the discrimination between solvated and gaseous R6G. Two experimental setups were used for our measurements. In the first experiment, the R6G fluorescence and the light scattered from the spray plume were imaged in two spatial dimensions using a tunable wavelength filter. The second experiment was designed for obtaining 1-dimensional spatially resolved emission spectra of the spray. Here, the intensity distribution of solvated and gaseous R6G as well as scattered light (lambda = 355 nm) were measured simultaneously. The results show the distribution of gaseous R6G in the plane, orthogonal to the ESI capillary, decreasing slightly towards the spray center and showing maxima at the cone margins. The distribution of gaseous R6G confirms the preferred release of gaseous ions from nano-droplets, indicating the ion evaporation model (IEM) to be the dominating release mechanism. Up to now, only a few fluorescence spectra of ionic compounds in the gas phase were published because the measurement of emission spectra of mass-selected ions in an ion trap is experimentally challenging. The fluorescence spectrum of gaseous lucigenin at atmospheric pressure is reported for the first time. This spectrum of lucigenin in the gas phase exhibits a blue shift of about Delta lambda = 10 nm in comparison to the corresponding spectrum in methanol.show moreshow less

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Metadaten
Author:Daniel Riebe, Martin ZühlkeGND, Karl Zenichowski, Toralf BeitzORCiD, Carsten DoscheGND, Hans-Gerd LöhmannsröbenORCiDGND
DOI:https://doi.org/10.1524/zpch.2011.0149
ISSN:0942-9352
Parent Title (English):Zeitschrift für physikalische Chemie : international journal of research in physical chemistry and chemical physics
Publisher:De Gruyter Oldenbourg
Place of publication:München
Document Type:Article
Language:English
Year of first Publication:2011
Year of Completion:2011
Release Date:2017/03/26
Tag:Electrospray Ionization; Fluorescence; Gaseous Ions; Lucigenin; Rhodamine 6G
Volume:225
Issue:9-10
Page Number:18
First Page:1055
Last Page:1072
Funder:German Federal Ministry of Education and Research (BMBF); PT Julich [FKZ: 03FO1042]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert