A multipole ion guide comprises rods disposed about an axis, each of the rods having a first end and a second end remote from the first end. Each of the rods is disposed at a respective greater distance from the axis at the first end than at the second end. The multipole ion guide comprises means for applying a radio frequency (RF) voltage between adjacent pairs of rods, wherein the RF voltage creates a multipole field in a region between the rods; and means for applying a direct current (DC) voltage drop along a length of each of the rods. A mass spectroscopy system is also disclosed.