The present invention relates to an ionization source having a chamber for ionizing a sample. The ionization chamber has surfaces to reduce the overall interaction with reactive samples. The inner surface walls of the ionization chamber or the ionization chamber may be formed from an inert super alloy. For instance, Inconel.TM. 625, Inconel.TM. 601 or Hastelloy.RTM. may comprise the ionization chamber or the surface walls of the ionization chamber. The invention also includes a method for reducing the interaction of a reactive analyte with an ion source.