title: Microplasma-based flowing atmospheric-pressure afterglow (FAPA) source for ambient desorption-ionization mass spectrometry.
abstract: A new direct-current microplasma-based flowing atmospheric pressure afterglow (FAPA) source was developed for use in ambient desorption-ionization mass spectrometry. The annular-shaped microplasma is formed in helium between two concentric stainless-steel capillaries that are separated by an alumina tube. Current-voltage characterization of the source shows that this version of the FAPA operates in the normal glow-discharge regime. A glass surface placed in the path of the helium afterglow reaches temperatures of up to approximately 400 °C; the temperature varies with distance from the source and helium flow rate through the source. Solid, liquid, and vapor samples were examined by means of a time-of-flight mass spectrometer. Results suggest that ionization occurs mainly through protonation, with only a small amount of fragmentation and adduct formation. The mass range of the source was shown to extend up to at least m/z 2722 for singly charged species. Limits of detection for several small organic molecules were in the sub-picomole range. Examination of competitive ionization revealed that signal suppression occurs only at high (mM) concentrations of competing substances.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Offer M
authors.initials: OM
authors.lastname: Zeiri
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Storey
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN 47405, USA. Electronic address: sjray2@buffalo.edu.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Ray
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Hieftje
keywords: Ambient desorption-ionization; Ion source; Mass spectrometry; Microplasma