Method for controlling the ion generation rate for mass selective loading of ions in ion traps

Method of m/z-selective loading of desired ion species in an ion trap, consisting of the following processes:

• (a) generating ions from administered substance vapors inside or outside the ion trap by known methods,
• (b) in case of external ion generation, transferring of the ions into the ion trap by known ion-optical means,
• (c) ejecting of all undesired ion species in a known manner by resonant excitation of their oscillations inside the ion trap, during ion generation and loading, by an electrical excitation AC field containing a mixture of discrete frequencies which match the oscillation frequencies of the undesired ion species,
• (d) controlling the ion generation rate of the ion generation process (a) or the ion transfer rate of the ion transfer process (b) in such a manner that the desired mass resolution of the ejection process (c) remains essentially undisturbed by the space charge of the ion population which is formed as equilibrium of ion generation rate and ion ejection rate.