Capillary Dielectric Barrier Discharge: Transition from Soft Ionization to Dissociative Plasma

• Published in: Analytical chemistry (Washington) 2016-05, Vol.88 (9), p.4701-4705
• Main Authors: Klute, Felix David, Michels, Antje, Schütz, Alexander, Vadla, Cedomil, Horvatic, Vlasta, Franzke, Joachim
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Capillarity; Dielectric barrier discharge; Dielectrics; Electric potential; Electrodes; Emission; Evolution; Ionization; Molecules; Plasma; Radiation; Voltage
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.5b04605

A capillary He dielectric barrier discharge was investigated with respect to its performance as a soft or dissociative ionization source. Spatiotemporal measurements of the plasma emission showed that in one voltage duty cycle the plasma evolved from a soft to dissociative ionization source. At the earliest time, the soft plasma was generated between the electrodes as well as outside the capillary forming the plasma jet. It was characterized by significant radiation arising only from He and N2 +, which are known to be important in the process of the soft ionization of the analyte. Later in time, the plasma capable of dissociating molecules develops. It is characterized by appreciable radiation from analyte dissociation products and is restricted to the interelectrode region in the capillary. Thus, for the soft ionization purposes, it is feasible to introduce the analyte exclusively in the plasma jet. For elemental analysis, the interelectrode plasma is appropriate.