Patent ID: 7989758

Claim:
A method for acquiring fragment ion spectra in a Kingdon ion trap mass spectrometer with a longitudinal potential well having a potential minimum inside the Kingdon ion trap in which ions can harmonically oscillate, comprising: (a) configuring the Kingdon ion trap so that ions can oscillate radially in a plane between two or more inner electrodes; (b) introducing metastable analyte ions into the Kingdon ion trap close to the potential minimum of the longitudinal potential well; (c) storing the metastable analyte ions in the minimum of the longitudinal potential well for a predetermined storage period so that the metastable ions oscillate and decompose to produce fragment ions; (d) exciting the analyte and fragment ions to execute harmonic oscillations in a longitudinal direction in the longitudinal potential well; and (e) measuring image currents of the ions oscillating in the longitudinal direction.