Characterization of a capillary dielectric barrier plasma jet for use as a soft ionization source by optical emission and ion mobility spectrometry

This paper presents the characterization of a source for soft ionization of organic molecules. This source is based on a plasma jet established at the end of a capillary dielectric barrier discharge at atmospheric pressure. He, Ne and Ar as pure gas or with different concentrations of N2 are used as buffer gas for the plasma jet. Spectroscopic emission measurements are carried out along the plasma jet in and outside the capillary. The intensity variation of N2+ lines, for example emission at 391.4 and 427.8 nm, can be associated with the protonation process which is the basis for the soft ionization. The mechanism of the N2+ production outside the capillary, which is relevant for the protonation of molecules and sustains the production of primary ions, is investigated. The response signal of the ions in a nitrogen atmosphere was measured with an ion mobility spectrometer (IMS).