title: Characterization of direct-current atmospheric-pressure discharges useful for ambient desorption/ionization mass spectrometry.
abstract: Two relatively new ambient ionization sources, direct analysis in real time (DART) and the flowing atmospheric-pressure afterglow (FAPA), use direct current, atmospheric-pressure discharges to produce reagent ions for the direct ionization of a sample. Although at a first glance these two sources appear similar, a fundamental study reveals otherwise. Specifically, DART was found to operate with a corona-to-glow transition (C-G) discharge whereas the FAPA was found to operate with a glow-to-arc transition (G-A) discharge. The characteristics of both discharges were evaluated on the basis of four factors: reagent-ion production, response to a model analyte (ferrocene), infrared (IR) thermography of the gas used for desorption and ionization, and spatial emission characteristics. The G-A discharge produced a greater abundance and a wider variety of reagent ions than the C-G discharge. In addition, the discharges yielded different adducts and signal strengths for ferrocene. It was also found that the gas exiting the discharge chamber reached a maximum of 235 degrees C and 55 degrees C for the G-A and C-G discharges, respectively. Finally, spatially resolved emission maps of both discharges showed clear differences for N(2)(+) and O(I). These findings demonstrate that the discharges used by FAPA and DART are fundamentally different and should have different optimal applications for ambient desorption/ionization mass spectrometry (ADI-MS).
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
authors.forename: Jacob T
authors.initials: JT
authors.lastname: Shelley
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Wiley
authors.forename: George C Y
authors.initials: GC
authors.lastname: Chan
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Schilling
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Ray
authors.forename: Gary M
authors.initials: GM
authors.lastname: Hieftje