Abstract: A mass spectrometer comprises an orifice plate having an orifice, a first multipole ion guide in a first chamber downstream of said orifice plate, said first multipole ion guide comprising a plurality of rods, and a second multipole ion guide in a second chamber downstream of said first chamber, said second multipole ion guide comprising a plurality of rods. A first ion lens is between the first and the second multipole ion guides. A third multipole ion guide is in a third chamber downstream of the second chamber, the third multipole ion guide comprises a plurality of rods. A second ion lens is between the second and third chambers. A tunable DC voltage source applies a tunable DC offset voltage to at least one of the above ion guide and ion lenses to increase an axial kinetic energy of the ions to cause at least one of declustering and/or fragmentation.