An ion guide, comprising: an entrance end; an exit end at a distance from the entrance end along a guide axis; a plurality of electrodes surrounding a guide volume and axially spaced from each other along the guide axis from the entrance end to the exit end; and RF electronics configured for applying an RF drive signal to the electrodes effective for generating an RF field in the guide volume comprising a plurality of potential wells distributed along the guide axis, wherein the RF field comprises a waveform effective for moving the potential wells in at least one set of the electrodes in an axial direction toward the exit end, wherein: the plurality of electrodes comprises a plurality of electrode sets repeated in sequence along the guide axis; each electrode set comprises N electrodes where N = 3 or greater; the RF drive signal comprises N different RF drive signals respectively comprising N different waveforms, each of the N different waveforms having a parameter whose value differs from the value of the parameter of the other waveforms; the RF electronics is configured for applying the N different RF drive signals to the respective N electrodes of each electrode set, wherein the sequence in which the N different RF drive signals are applied is repeated from one electrode set to the next electrode set; the N different RF waveforms have the form V i F(ω m t - φ i) exp (jωt), where V i is a zero-to-peak amplitude, F is a complex function of its argument and is periodic with period 2π, ω and ω m are scalars representing a main angular frequency and a modulating angular frequency, t is time, φ i is a phase, and i is an integer from 1 to N, and wherein the phase φ i differs for each of the N different RF waveforms; characterized in that a speed at which the potential wells move in the axial direction is set such that an effective potential of the RF field is time averaged to a non-zero magnitude of the effective potential on the guide axis for singly-ionized Lithium ions. an entrance end; an exit end at a distance from the entrance end along a guide axis; a plurality of electrodes surrounding a guide volume and axially spaced from each other along the guide axis from the entrance end to the exit end; and RF electronics configured for applying an RF drive signal to the electrodes effective for generating an RF field in the guide volume comprising a plurality of potential wells distributed along the guide axis, wherein the RF field comprises a waveform effective for moving the potential wells in at least one set of the electrodes in an axial direction toward the exit end, wherein: the plurality of electrodes comprises a plurality of electrode sets repeated in sequence along the guide axis; each electrode set comprises N electrodes where N = 3 or greater; the RF drive signal comprises N different RF drive signals respectively comprising N different waveforms, each of the N different waveforms having a parameter whose value differs from the value of the parameter of the other waveforms; the RF electronics is configured for applying the N different RF drive signals to the respective N electrodes of each electrode set, wherein the sequence in which the N different RF drive signals are applied is repeated from one electrode set to the next electrode set; the N different RF waveforms have the form V i F(ω m t - φ i) exp (jωt), where V i is a zero-to-peak amplitude, F is a complex function of its argument and is periodic with period 2π, ω and ω m are scalars representing a main angular frequency and a modulating angular frequency, t is time, φ i is a phase, and i is an integer from 1 to N, and wherein the phase φ i differs for each of the N different RF waveforms; characterized in that a speed at which the potential wells move in the axial direction is set such that an effective potential of the RF field is time averaged to a non-zero magnitude of the effective potential on the guide axis for singly-ionized Lithium ions. the plurality of electrodes comprises a plurality of electrode sets repeated in sequence along the guide axis; each electrode set comprises N electrodes where N = 3 or greater; the RF drive signal comprises N different RF drive signals respectively comprising N different waveforms, each of the N different waveforms having a parameter whose value differs from the value of the parameter of the other waveforms; the RF electronics is configured for applying the N different RF drive signals to the respective N electrodes of each electrode set, wherein the sequence in which the N different RF drive signals are applied is repeated from one electrode set to the next electrode set; the N different RF waveforms have the form V i F(ω m t - φ i) exp (jωt), where V i is a zero-to-peak amplitude, F is a complex function of its argument and is periodic with period 2π, ω and ω m are scalars representing a main angular frequency and a modulating angular frequency, t is time, φ i is a phase, and i is an integer from 1 to N, and wherein the phase φ i differs for each of the N different RF waveforms; characterized in that a speed at which the potential wells move in the axial direction is set such that an effective potential of the RF field is time averaged to a non-zero magnitude of the effective potential on the guide axis for singly-ionized Lithium ions.