current dc and radio frequency rf potentials that makeup the low pressure components of atmospheric or near atmospheric pressure sources such as but not limited to electrospray atmospheric pressure chemical ionization photo ionization laser desorption including matrix desorption inductively coupled plasma and discharge ionization the inlet is comprised of an electrode or lens 10 and a set of four poles 30 a 30 b 30 c not shown 30 d not shown where the exits of the individual poles are adjacent to and symmetrically aligned with the corresponding poles 38 a 38 b 38 c not shown 38 d not shown of the quadrupole mass analyzer 36 the lens 10 may be formed from an aperture plate by adding a snout 12 for extending between the four poles 30 a 30 b 30 c not shown 30 d not shown of the lens along the central axis the snout 12 is tubular in nature but may be conical or have an irregular cylindrical shape the length of the snout depends on the length of the multi pole assembly and the spacing between the individual poles 30 of the multi pole assembly and the poles 38 of the mass analyzer 36 typically the individual poles 30 a 30 b 30 c not shown 30 d not shown of the lens are separated from the poles 38 a 38 b 38 c not shown 38 d not shown of the quadrupole analyzer 36 by an insulator or dielectric disk or rod not shown the snout 12 extends past the end of the multi pole assembly plus u00bd the distance separating the individual rods 30 a 30 b 30 c not shown 30 d not shown.