The invention provides a multipole ion trap. The trap has a longitudinal axis. An oscillating on-axis potential is set up along the longitudinal axis, providing a potential well in which ions are trapped. In some embodiments, rods forming the poles are symmetrically and equidistantly positioned about the longitudinal axis and RF signal with different magnitudes are applied to the poles. In other embodiments, the rods are not positioned symmetrically about the longitudinal axis and the RF signals applied to the poles may have the same or different magnitudes. Poles used in the invention may include two or more rods. An ion trap according to the invention may include more than two poles, and in some embodiments, a third or additional pole may be added to provide the oscillating on-axis potential. The ion trap may be used mass selectively scan ions, fragment ions and to trap and separate differently charged ions, among other uses.