An ionization device includes: a plasma generating device for generating metastable particles and/or ions of an ionization gas in a primary plasma region; a field generating device for generating a glow discharge in a secondary plasma region; an inlet for supplying a gas to be ionized into the secondary plasma region; and a further inlet for supplying the metastable particles and/or the ions of the ionization gas into the secondary plasma region. A mass spectrometer includes such an ionization device and a detector downstream of the outlet of the ionization device for the mass-spectrometric analysis of the ionized gas.