Impact of homogeneous and filamentary discharge modes on the efficiency of dielectric barrier discharge ionization mass spectrometry.

The present study contributes to the evaluation of dielectric barrier discharge-based ambient ionization for mass spectrometric analysis (DBDI-MS) by providing a further step towards an understanding of underlying ionization processes. This examination highlights the effect of physical discharge modes on the ionization efficiency of the DBDI source. A distinction is made between the homogeneous and filamentary discharge mode due to different plasma gases in barrier configurations. Therefore, we first report on discharge modes of DBDI by demonstrating a universally applicable method to classify the predominant modes. Then, the ionization efficiency of these two modes is evaluated by a laser desorption-DBDI-MS with different molecular analytes. Here, the laser desorption is used to deliver neutral analytes which will be ionized by the plasma jet applied as dielectric barrier discharge ionization. With a clear increase of signal intensities in the homogeneous mode in contrast to the filamentary one, the present study indicates a pronounced dependence of the ionization efficiency on the discharge mode allowing further insight into the mechanisms of the ionization process.