Development of a new high-efficiency thermal ionization source for mass spectrometry

A thermal ionization source for mass spectrometry has been designed and tested. The ion source is based on a tungsten crucible with a deep cavity into which the sample is loaded. The crucible is heated by high energy electron bombardment from a tantalum filament surrounding the crucible. As the sample evaporates inside the crucible, gaseous analyte atoms are produced which interact with the inner surface of the crucible walls to produce positive ions through surface ionization. The ions are extracted from the cavity through a small opening at the end of the crucible. Regulation of the electron emission current makes it possible to control the energy and power applied to the crucible and, therefore, the crucible temperature. A number of elements have been tested in this source. The ionization efficiencies measured using a high transmission isotope separator spectrometer show 10 to 100 times higher efficiency than in conventional surface thermal ionization sources. (C) 1997 Elsevier Science B.V.