High mass ion detection system and method
AssigneePhrasor Scientific, Inc.
InventorsJohn F. Mahoney, Julius Perel
Life of this patent
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Abstract
An improved ion detection system and method for detection of low or high mass ions having high electron affinity constituent atoms or molecules. A target with a low work function target surface is employed to fragment the incident ions and produce secondary negative ions and electrons. A cesium or barium oxide source is employed to optimally provide a monolayer of cesium or barium oxide on the target surface of a molybdenum or tungsten target. The secondary ions and electrons are detected by a conventional electron multiplier detector. The potential difference between the target surface and electron multiplier detector is chosen to accelerate the secondary ions and electrons to the electron multiplier detector with an energy corresponding to high detection efficiency.
Claims20
An ion detection system, comprising:
- means for providing a beam of high mass organic ions having substantial percentages of carbon, hydrogen and oxygen atoms;
- target means for intercepting said molecular ions, dissociating said molecular ions into fragments having high electron affinities, and ejecting secondary negatively charged fragment ions and electrons, comprising:
- a target substrate having a first major surface oriented so as to intercept said ion beam, said target substrate having a temperature not greater than 400.degree. C;
- means, coupled to said target substrate, for maintaining said target substrate at a first bias potential;
- and
- means, coupled to said target substrate, for providing a low work function material having work function of less than 2.2 eV to said target substrate such that the first major surface of said target substrate is substantially coated with a layer of said low work function material;
- and
- detection means, configured with respect to said target so as to receive the secondary negatively charged fragment ions and electrons ejected from said target means, for detecting said secondary negatively charged fragment ions and electrons and for providing an electrical signal corresponding to said detected secondary particles.
An improved mass spectrometry system, comprising:
- means for providing a beam of high mass, ionized biomolecules;
- means for analyzing the beam of ionized biomolecules according to the mass-to-charge ratio of the ionized biomolecules and providing an output mass analyzed beam of biomolecular ions;
- and
- detector means for detecting said mass analyzed beam of biomolecules, comprising:
- means for shielding a portion of said detector means from said incident ion beam and for collimating said ion beam;
- a target positioned so as to intercept said incident beam of biomolecular ions, said target comprising a target substrate and a target surface, said target substrate having a temperature not greater than 400.degree. C.;
- a layer of low work function material on said target surface wherein said low work function material is selected from the group consisting of Cs, Cs.sub.2 O and Cs.sub.2 O.sub.2 ;
- means for biasing said target to a predetermined target bias potential;
- and
- means for detecting secondary ions and electrons emitted from said target surface.
A method for detecting positive or negative incident biomolecular ions, comprising the steps:
- accelerating said positive or negative incident ions of high mass toward a target, by means of a first bias potential applied to said target, said target having a target surface and a temperature not greater than 400.degree. C.;
- providing a layer of oxygenated cesium on said target surface;
- impacting said accelerated ions on said low work function target surface thereby causing secondary ions and electrons to be emitted from said target surface;
- accelerating said secondary ions and electrons away from said target surface toward a detector having an anode maintained at a second bias potential, said first and second bias potentials cooperatively accelerating said secondary ions above the threshold velocity of said detector;
- impacting said secondary ions and electrons on said detector anode thereby generating additional secondary electrons;
- and
- detecting said additional secondary electrons and providing a detection signal corresponding thereto.
Dependencies are inferred from the claim text.