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Abstract

A method of clean removal of ions from an ion trap mass spectrometer removes ions having a mass greater than a desired ion mass m using non-linear resonance. The ion trap mass spectrometer includes two end cap electrodes and an annular electrode. A high-frequency quadrupolar field with at least one superposed weak multipolar field is generated in the ion trap mass spectrometer. Higher mass ions are eliminated with minimal loss of ions having the desired mass m by adjusting the amplitude of a storage HF so that one of the physically determined non-linear resonance conditions of the multipolar field is satisfied for ions of mass m+1. The ions are weakly oscillated by applying an HF excitation voltage to the end caps of the ion trap mass spectrometer, such that ions of mass m+1 receive energy through non-linear resonance from the storage HF and leave an ion trap of the ion trap mass spectrometer. Ions having the desired mass m remain inside an ion cage.

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First Claim