An ion guide array is disclosed comprising a first ion guide section and a second ion guide section. Each ion guide section may comprise a plurality of electrodes having an aperture through which ions are transmitted in use. A transfer section is arranged at the exit of the first ion guide section and ions are transmitted radially from the first ion guide section into the second ion guide section. Electrodes in the transfer section may have a radial aperture enabling ions to be transmitted radially from the first ion guide section to the second ion guide section.