Method of clean removal of ions

A method of well-defined ejection of ions of mass m+1, with minimal loss of ions of mass m from an ion trap of an ion trap mass spectrometer, said ion trap mass spectrometer having two end cap electrodes and on annular electrode, in which a high-frequency quadrupolar storage field with at least one superposed weak multipolar field is generated, comprising the steps of:

• adjusting the amplitude of a high-frequency storage field to satisfy a non-linear resonance condition of said at least one superposed weak multipolar field for ions of mass m+1;
• and
• applying a high-frequency excitation voltage to said two end caps of said ion trap mass spectrometer to weakly oscillate all ions, said ions of mass m+1 receiving energy through non-linear resonance from said high-frequency storage field and leaving said ion trap, whereas ions of mass m remain inside said ion trap.

A method of well-defined ejection of undesired ions of mass m+n, with n.gtoreq.1, while keeping desired ions of mass m in an ion trap of an ion trap mass spectrometer, comprising the steps of:

• adjusting the amplitude of high-frequency storage field to satisfy a non-linear resonance condition of a multipolar field generated in said ion trap mass spectrometer, for ions of mass m+n;
• and
• removing said ions of mass m+n from said ion trap by non-linear resonance, said non-linear resonance ejecting said ions when their secular frequency reaches the frequency of the non-linear resonance and ions of mass m+1 being ejected from the ion trap without being resonantly excited.