Method and apparatus for injection of ions into an electrostatic ion trap

A method of injecting ions into an electrostatic trap, comprising:

• generating ions in an ion source;
• transporting the ions from the ion source to an ion store downstream of the ion source;
• releasing the ions from the ion store to a non-trapping ion guide downstream of the ion store;
• and
• accelerating the ions from the ion guide as a pulse into an orbital electrostatic trap for mass analysis, wherein the average velocity of the ions as the ions exit from the ion guide is substantially higher than the average velocity of the ions as they exit from the ion store, wherein there is a delay between releasing the ions from the ion store and accelerating the ions from the ion guide such that for ions of the same m/z forming an ion packet, the duration of the ion packet as it enters the electrostatic trap is substantially shorter than when the ion packet enters the ion guide from the ion store.