title: Characterization of an Airborne Laser-Spark Ion Source for Ambient Mass Spectrometry.
abstract: An airborne laser plasma is suggested as an ambient ion source for mass spectrometry. Its fundamental physical properties, such as an excellent spatial and temporal definition, high electron and ion densities and a high effective cross section in maintaining the plasma, make it a promising candidate for future applications. For deeper insights into the plasma properties, the optical plasma emission is examined and compared to mass spectra. The results show a seemingly contradictory behavior, since the emitted light reports the plasma to almost entirely consist of hot elemental ions, while the corresponding mass spectra exhibit the formation of intact molecular species. Further experiments, including time-resolved shadowgraphy, spatially resolved mass spectrometry, as well as flow-dependent emission spectroscopy and mass spectrometry, suggest the analyte molecules to be formed in the cold plasma vicinity upon interaction with reactive species formed inside the hot plasma center. Spatial separation is maintained by concentrically expanding pressure waves, inducing a strong unidirectional diffusion. The accompanying rarefaction inside the plasma center can be compensated by a gas stream application. This replenishing results in a strong increase in emission brightness, in local reactive species concentration, and eventually in direct mass spectrometric sensitivity. To determine the analytical performance of the new technique, a comparison with an atmospheric pressure chemical ionization (APCI) source was conducted. Two kitchen herbs, namely, spearmint and basil, were analyzed without any sample pretreatment. The presented results demonstrate a considerably higher sensitivity of the presented laser-spark ionization technique.
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM) , Richard-Willstätter-Strasse 11, 12489 Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Bierstedt
authors.affiliation: University Wuppertal , Gaussstrasse 20, 42119 Wuppertal, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Kersten
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM) , Richard-Willstätter-Strasse 11, 12489 Berlin, Germany.
authors.forename: Reto
authors.identifier: 0000-0003-3528-4413
authors.initials: R
authors.lastname: Glaus
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM) , Richard-Willstätter-Strasse 11, 12489 Berlin, Germany.
authors.forename: Igor
authors.initials: I
authors.lastname: Gornushkin
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM) , Richard-Willstätter-Strasse 11, 12489 Berlin, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Panne
authors.affiliation: Bundesanstalt für Materialforschung und -prüfung (BAM) , Richard-Willstätter-Strasse 11, 12489 Berlin, Germany.
authors.forename: Jens
authors.identifier: 0000-0002-5273-6605
authors.initials: J
authors.lastname: Riedel