Reagent ions created during use in a discharge region move from the discharge region into a reaction region. Analytical molecules/ions move into a reaction region, where they are partly screened by an electric field generated by a discharge device (DD) in a discharge region that has a discharge chamber. The DD has a corona discharge device with a corona needle. - Independent claims are also included for the following: - (a) A mass spectrometer with a source of ions; - (b) and for an electro-spray ionization (ESI)/atmosphere pressure chemical ionization (APCI) source of ions for carrying out electro-spray ionization (ESI)/atmosphere pressure chemical ionization (APCI); - (c) and for a source of ions with a reaction chamber for retaining analytical molecules/ions.
