Patent ID: 6700120
Filing Date: 2004-03-02
Classification: H01J

Abstract:
A method of improving the ratio of precursor ions to unwanted ions in an ion beam, the method comprising:(1) subjecting the ion beam comprising both unwanted ions and precursor ions to a first mass resolving step, to select the precursor ions; (2) colliding the ion beam comprising the unwanted ions and the precursor ions with a gas signal brackets at a collision energy insufficient to cause substantial fragmentation of the precursor ions but sufficient to promote at least one of fragmentation and reaction of the unwanted ions, wherein the precursor ions remain substantially unfragmented after said colliding step, and whereby at least some of the unwanted ions generate secondary ions having a mass-to-charge ratio different from the mass-to-charge ratio of the precursor ions; and (3) subjecting the ion beam including the secondary ions and the substantially unfragmented precursor ions to a second mass resolving step, to reject at least some of the secondary ions with a mass-to-charge ratio different from the mass-to-charge ratio of the precursor ions, wherein the substantially unfragmented precursor ions remain in the ion beam for subsequent analysis, thereby increasing the ratio of precursor ions to unwanted ions in the ion beam.