| CPC H01J 49/063 (2013.01) [H01J 49/0045 (2013.01); H01J 49/022 (2013.01); H01J 49/065 (2013.01); H01J 49/067 (2013.01); H01J 49/24 (2013.01)] | 12 Claims |

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1. A mass spectrometer, comprising:
an orifice plate having an orifice for receiving a plurality of ions,
a first multipole ion guide disposed in a first chamber positioned downstream of said orifice plate,
a second multipole ion guide disposed in a second chamber positioned downstream of said first chamber,
a first ion lens disposed between said first and second multipole ion guides,
a third multipole ion guide disposed in a third chamber positioned downstream of said second chamber, said third multipole ion guide comprising a plurality of rods arranged to allow passage of said plurality of ions therebetween,
a second ion lens disposed between said second and third chambers, and
a mass filter disposed in a fourth chamber downstream of the third chamber, and
at least one tunable DC voltage source configured to apply a tunable DC offset voltage between said second multipole ion guide and said second ion lens or between said second ion lens and said third multipole ion guide, so as to increase an axial kinetic energy of said plurality of ions to cause at least one of declustering and fragmentation of at least a portion of said plurality of ions in said third chamber,
wherein said first chamber is maintained at a pressure in a range of about 5 Torr to about 15 Torr, said second chamber is maintained at a pressure in a range of about 1 Torr to about 5 Torr, and said third chamber is maintained at a pressure in a range of about 3 mTorr to about 12 mTorr.
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