Patent ID: 6949743
Filing Date: 2005-09-27
Classification: H01J

Abstract:
1. A method of fragmenting ions in an ion trap of a mass spectrometer, comprising the steps of: selecting for fragmentation a set of ions having a mass-to-charge ratio of interest; applying an RF trapping voltage sufficient to bring the Q of the selected set of ions to a first value; applying a resonance excitation voltage pulse for a pulse duration to cause at least a portion of the set of ions to undergo collisions and break into ion fragments, the ion fragments including low-mass ion fragments, the resonance excitation voltage pulse having at least one frequency corresponding to a resonant frequency of the selected set of ions; and after a predetermined delay time following termination of the resonance excitation voltage pulse, reducing the RF trapping voltage to lower the Q of the selected set of ions to a second value less than the first value, the delay time and pulse duration being sufficiently brief to prevent expulsion of low-mass ion fragments from the ion trap.