Cold Cathode Quadrupole Mass Spectrometer

Abstract

A magnetron cold cathode ion source (CCIS) has been developed for ultrahigh vacuum residual gas analysis. The purpose is to eliminate the spurious spectra produced by the conventional hot filament source and to obtain greater sensitivity. A commercial quadrupole mass analyzer was used to evaluate source performance and potential. Resolution equaled that obtained with a hot filament source, giving mass invariant peak separations, with 10% valleys, of 1.0 amu below 150 amu and 0.7 amu below 50 amu. Sensitivities exceeded those obtained with a hot filament source, operated at a 3 mA emission current, by factors of 1.5 to 4.6, depending on pressure and mass. The corresponding CCIS sensitivities, at 1-amu peak separation, were 0.4 mA/Torr for mass 28 at 3×10−9 Torr and 1.2mA/Torr for mass 40 at 1×10−7 Torr. Experiments indicated a potential tenfold further sensitivity improvement if a quadrupole with a higher rf potential were used; by increasing quadrupole dimensions a still greater fraction of the source internal sensitivity, which is in the vicinity of 1 A/Torr, may be realized.

Gas analysis by modulated molecular beam mass spectrometry

“…To attain such a low background requires ultra high-vacuum techniques, a very clean system, and repeated bakeout of the entire system. Blum and Torney (2) have investigated the use of a cold cathode ionizer to reduce the substantial contribution of the hot filament and ionizer housing to the background.…”

“…For example, the Kf values for alkali metal ethylenediaminetetraacetate (EDTA) complexes are much smaller than those for alkaline earth-EDTA complexes. That is, for 1:1 NaT, Li+, Ba2+, Sr2+, and Ca2+ complexes of EDTA, the log Kf values are 1.66, 2.79, 7.76, 8.63, and 10.59, respectively (7,2). While it is known that alkaline earths form chelates involving both ends of the EDTA molecule, it is uncertain whether alkali metals form monodentate complexes or chelates of the alkaline earth variety.…”