Method and device for in-phase excitation of ion ejection from ion trap mass spectrometers

A method for generating a mass spectrum of ions utilizing apparatus including a storage ion trap, a mechanism for introducing ions into the ion trap and a detector for detecting ions ejected from the trap, the ions being ejected from the trap in groups of ion pulses, all of the ion pulses in an ion pulse group comprising ions of substantially equal masses and being ejected during an ejection cycle corresponding to that group, each ejection cycle being of a finite time duration, the method comprising:

• applying to the storage ion trap with a storage signal generator an oscillating storage signal having an amplitude, a frequency and a phase;
• applying to the storage ion trap with an excitation signal generator an oscillating excitation signal having a frequency and a phase relative to the frequency and phase of the storage signal;
• setting the frequency and phase of the excitation signal relative to the frequency and phase of the storage signal to make the frequency of the excitation signal slightly smaller than a simple fraction of the frequency of the storage signal so that the phase of the excitation signal coincides with the phase of the storage signal periodically and the time period between successive phase coincidences is t;
• and
• varying the amplitude of the storage signal to consecutively eject ion pulse groups from the trap such that the time between the start of successive ejection cycles is constant and equal to t and the phase coincidences occur at a time during each ejection cycle at which a maximum ion output is expected.

Apparatus for recording a mass spectrum, the apparatus comprising:

• a quadrupole storage ion trap;
• a storage signal generator for applying to the storage ion trap an oscillating storage signal having an amplitude, a frequency and a phase;
• an excitation signal generator for applying to the storage ion trap an oscillating excitation signal having a frequency and a phase relative to the frequency and phase of the storage signal;
• an ion detection circuit for detecting ions ejected from the trap and generating an output signal, the ions being ejected from the trap in groups of ion pulses, all of the ion pulses in an ion pulse group comprising ions of substantially equal masses and being ejected during an ejection cycle corresponding to that group, each ejection cycle being of a finite time duration;
• a frequency control circuit which sets the frequency of the excitation signal relative to the frequency of the storage signal such that the phase of the excitation signal coincides with the phase of the storage signal periodically and the time period between said phase coincidences is t;
• and
• a scanning control circuit which varies the amplitude of the storage signal to consecutively eject ion pulse groups from the trap such that the time between the start of successive ejection cycles is constant and equal to t.

Apparatus for recording a mass spectrum, the apparatus comprising:

• a quadrupole ion trap;
• a storage signal generator for applying to the ion trap an oscillating storage signal having an amplitude, a frequency and a phase;
• an excitation signal generator for applying to the ion trap an oscillating excitation signal having a frequency and a phase relative to the frequency and phase of the storage signal;
• an ion detection circuit for detecting ions ejected from the trap and for generating an output signal, the ions being ejected from the trap in groups of ion pulses, all of the ion pulses in an ion pulse group comprising ions of substantially equal masses and being ejected during an ejection cycle corresponding to that group, each ejection cycle being of a finite time duration;
• a frequency control circuit for controlling the frequency and phase of the excitation signal relative to the frequency and phase of the storage signal such that the frequency of the excitation signal is slightly lower than a simple fraction of the storage frequency so that the phase of the excitation frequency coincides with the phase of the storage frequency periodically and the time period between successive phase coincidences is t;
• and
• a scanning control circuit for varying the amplitude of the storage signal to consecutively eject ion pulse groups from the trap such that the time between the start of successive ejection cycles is constant and equal to t and said phase coincidences occur at a time during each ejection cycle at which a maximum ion output is expected.