Ion entry/exit device

An ion guide comprising:

• a plurality of electrodes;
• and
• at least one voltage supply configured to:
• supply voltages to electrodes of the plurality of electrodes to generate a travelling DC potential to guide ions in a first direction;
• and
• supply voltages to electrodes of the plurality of electrodes to generate a travelling DC potential to guide ions in a second direction;
• wherein the plurality of electrodes forms a closed-loop in the first direction, wherein the at least one voltage supply is configured to generate a travelling DC potential to guide ions around the closed-loop in the first direction, and wherein the at least one voltage supply is configured to generate a travelling DC potential to guide ions into or out of the closed-loop in the second direction.

An ion mobility separator comprising an ion guide, the ion guide comprising:

• a plurality of electrodes;
• and
• at least one voltage supply configured to:
• supply voltages to electrodes of the plurality of electrodes to generate a travelling DC potential to guide ions in a first direction;
• and
• supply voltages to electrodes of the plurality of electrodes to generate a travelling DC potential to guide ions in a second direction;
• wherein the at least one voltage supply is configured to generate a travelling DC potential to cause ions to separate according to their ion mobility in the first direction, and wherein the at least one voltage supply is configured to generate a travelling DC potential to guide ions into or out of the ion mobility separator in the second direction.