Fragmentation of ions by resonant excitation in a low pressure ion 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 by subjecting the ions to an RF alternating potential;
• c) resonantly exciting selected trapped precursor ions by subjecting them to an auxiliary alternating potential having a maximum amplitude of less than approximately 1V(0−pk) for an excitation period exceeding approximately 50 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 by subjecting the ions to an RF alternating potential, 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 by subjecting them to an auxiliary alternating potential for an excitation period exceeding approximately 25 milliseconds under a background gas pressure of less than about 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, 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 by applying to at least one set of poles straddling the trapped ions an alternating excitation signal 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, including at least one set of poles straddling at least a portion of trapped ions;
• 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;
• an alternating voltage source for applying to said at least one of set of poles a resonant excitation signal for a period exceeding approximately 25 milliseconds in order to promote collision-induced dissociation of selected ions;
• and
• means for mass analyzing the trapped ions to generate a mass spectrum.

A triple quadrupole mass spectrometer, comprising:

• first, second and third quadrupole rod sets arranged in sequence;
• said first quadrupole rod set being configured for isolating selected ions;
• said second quadrupole rod set being enclosed within a collision chamber having a background gas pressure significantly higher than the first and second rod sets;
• said third quadrupole rod set being configured as a linear ion trap, including at least one set of poles straddling at least a portion of trapped ions, the trap having a background gas pressure of less than approximately 9×10−5Torr;
• an alternating voltage source for applying to said at least one set of poles a resonant excitation signal having an amplitude of less than approximately 1V(0−pk) for a period exceeding approximately 25 milliseconds in order to promote collision-induced dissociation of selected ions;
• and
• means for mass analyzing the trapped ions to generate a mass spectrum.