Fragmentation of ions by resonant excitation in a high order multipole field, low pressure ion trap

A method of fragmenting ions, comprising:

• trapping ions in a linear ion trap by subjecting the ions to a substantially quadrupolar RF potential, the trap being disposed in an environment in which a background gas is present at a pressure of less than approximately 9×10−5 Torr;
• resonantly exciting trapped ions of a selected m/z value or values by applying to at least one set of poles straddling the trapped ions an auxiliary alternating excitation signal for a period exceeding approximately 25 milliseconds, to thereby promote collision-induced dissociation of the selected ions;
• and
• dampening the oscillatory motion of the resonantly excited selected ions approaching a radial periphery of the trap to thereby reduce the probability of radially ejecting the selected ions from the trap.

A method of mass analyzing a stream of ions, the method comprising:

• (a) subjecting a stream of ions to a first mass filter step, to select precursor ions having a mass-to-charge ratio in a first desired range;
• (b) trapping the precursor ions in a linear ion trap, the trap having a substantially quadrupolar RF trapping field superimposed with a higher order multipole field;
• (c) resonantly exciting selected trapped precursor ions in the quadrupolar field by subjecting the selected ions to an auxiliary alternating potential having a for an excitation period exceeding approximately 25 milliseconds under a background gas pressure of less than 9×10−5 Torr, to thereby generate fragment ions;
• and
• (d) mass analyzing the trapped ions to generate a mass spectrum.

A method of mass analyzing a stream of ions, the method comprising:

• (a) subjecting a stream of ions to a first mass filter step, to select precursor ions having a mass-to-charge ratio in a first desired range;
• (b) fragmenting the precursor ions in a collision cell, to thereby produce a first generation of fragment ions;
• (c) trapping any un-dissociated precursor ions and the first generation of fragment ions in a linear ion trap in which ions are trapped by a substantially quadrupolar RF field superimposed with a higher order multipole field, and:
• (i) subjecting the trapped ions to a second mass filter step, to thereby isolate ions having an m/z value(s) in a second desired range,
• (ii) resonantly exciting selected first generation ions in the quadrupolar field by subjecting the selected ions to an auxiliary alternating potential for an excitation period exceeding approximately 25 milliseconds under a background gas pressure of less than 9×10−5 Torr, to thereby generate a second generation of fragment ions, and
• (d) mass analyzing the trapped ions to generate a mass spectrum.

A method of mass analyzing a stream of ions, the method comprising:

• (a) subjecting a stream of ions to a first mass filter step, to select precursor ions having a mass-to-charge ratio in a first desired range;
• (b) fragmenting the precursor ions in a collision cell, to thereby produce a first generation of fragment ions;
• (c) trapping any un-dissociated precursor ions and the first generation of fragment ions in a linear ion trap in which ions are trapped by a substantially quadrupolar RF field superimposed with a higher order multipole field, and:
• (i) subjecting the trapped ions to a second mass filter step, to thereby isolate ions having an m/z value(s) in a second desired range,
• (ii) resonantly exciting trapped ions of a selected m/z value or values in the quadrupolar field by applying to at least one set of poles straddling the trapped ions an alternating excitation signal having an amplitude of less than approximately 1 V(0-pk) for a period exceeding approximately 25 milliseconds, to thereby promote collision-induced dissociation of the selected ions, and
• (d) mass analyzing the trapped ions to generate a mass spectrum.

A mass spectrometer, comprising:

• a linear ion trap having a quadrupolar rod set for generating a substantially quadrupole RF trapping field and a set of additional electrodes for superimposing a higher order multipole field to the trapping field;
• means for providing a background gas in said trap at a pressure of less than approximately 9×10−5Torr;
• means for introducing ions into said trap;
• means for applying a resonant excitation signal in order to promote collision-induced dissociation of selected ions;
• and
• means for mass analyzing the trapped ions to generate a mass spectrum.

A mass spectrometer, comprising:

• a linear ion trap including means for generating a substantially quadrupole RF trapping field and means for superimposing a higher order multipole field to the trapping field;
• means for providing a background gas in said trap at a pressure of less than approximately 9×10−5 Torr;
• means for introducing ions into said trap;
• means for applying a resonant excitation signal in order to promote collision-induced dissociation of selected ions;
• and
• means for mass analyzing the trapped ions to generate a mass spectrum.