title: Gas Flow Dynamics in Inlet Capillaries: Evidence for non Laminar Conditions.
abstract: In this work, the characteristics of gas flow in inlet capillaries are examined. Such inlet capillaries are widely used as a first flow restriction stage in commercial atmospheric pressure ionization mass spectrometers. Contrary to the common assumption, we consider the gas flow in typical glass inlet capillaries with 0.5 to 0.6 mm inner diameters and lengths about 20 cm as transitional or turbulent. The measured volume flow of the choked turbulent gas stream in such capillaries is 0.8 L·min(-1) to 1.6 L·min(-1) under typical operation conditions, which is in good agreement to theoretically calculated values. Likewise, the change of the volume flow in dependence of the pressure difference along the capillary agrees well with a theoretical model for turbulent conditions as well as with exemplary measurements of the static pressure inside the capillary channel. However, the results for the volume flow of heated glass and metal inlet capillaries are neither in agreement with turbulent nor with laminar models. The velocity profile of the neutral gas in a quartz capillary with an inner diameter similar to commercial inlet capillaries was experimentally determined with spatially resolved ion transfer time measurements. The determined gas velocity profiles do not contradict the turbulent character of the flow. Finally, inducing disturbances of the gas flow by placing obstacles in the capillary channel is found to not change the flow characteristics significantly. In combination the findings suggest that laminar conditions inside inlet capillaries are not a valid primary explanation for the observed high ion transparency of inlet capillaries under common operation conditions. Graphical Abstract ᅟ.
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany. wissdorf@uni-wuppertal.de.
authors.forename: Walter
authors.initials: W
authors.lastname: Wißdorf
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Müller
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Yessica
authors.initials: Y
authors.lastname: Brachthäuser
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Langner
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Valerie
authors.initials: V
authors.lastname: Derpmann
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Klopotowski
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Polaczek
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Kersten
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Brockmann
authors.affiliation: Bergische Universitat Wuppertal, Gaußstraße 20, 42119, Wuppertal, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Benter
keywords: Atmospheric pressure ionization; Capillary flow; Inlet capillary; Turbulence