Characterization of an improved thermal ionization cavity source for mass spectrometry

A new thermal ionization source for use with a quadrupole mass spectrometer has been designed and characterized. The new source provides significant a dvantages over the previously reported prototype source and traditional fil ament-type thermal ionization sources. The operational interface between th e source and the quadrupole mass spectrometer has been redesigned. A vacuum interlock, a translational stage, and an adjustable insertion probe are ad ded to improve the source performance. With these modifications, the source is easier to operate while maximizing sample throughput. In this work, the performance of the newly developed source is examined. The ionization effi ciencies are measured with a quadrupole mass spectrometer. The efficiency v alues obtained with this system are comparable to those obtained from a lar ge scale isotope separator. The relationships among the ionization potentia l, vapor pressure, and measured ionization efficiency results are discussed . The crucible lifetime has been quantitatively estimated by measuring the crucible sputtering rate. Diagnostic studies of the new source show that th e crucible position is a crucial parameter for sensitivity and performance. Stability tests demonstrate that the source can be run several weeks at a fixed emission current without significant degradation. (J Am Soc Mass Spec trom 1999, 10, 1008-1015) (C) 1999 American Society for Mass Spectrometry.