A mass spectrometer comprising: an ion mobility spectrometer or separator having an axial length > 300 mm; a first ion guide comprising an ion funnel arranged downstream of said ion mobility separator or spectrometer, said first ion guide being arranged to receive ions from said ion mobility spectrometer or separator, and wherein said first ion guide comprises a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area; AC or RF voltage means arranged and adapted to apply an AC or RF voltage to at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of said plurality of electrodes of said first ion guide in order to confine ions radially within said first ion guide; an orthogonal acceleration Time of Flight mass analyser arranged downstream of said first ion guide; the mass spectrometer further comprising: a second ion guide comprising an ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area arranged upstream of said ion mobility spectrometer or separator, wherein in a mode of operation said second ion guide is arranged and adapted to trap, store or accumulate ions in an ion trapping region located towards, near or substantially at the exit of said second ion guide and wherein ions are periodically released from said ion trapping region of said second ion guide and are passed to said ion mobility spectrometer or separator; and a further ion guide upstream of said second ion guide, wherein said further ion guide comprises a further ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area. an ion mobility spectrometer or separator having an axial length > 300 mm; a first ion guide comprising an ion funnel arranged downstream of said ion mobility separator or spectrometer, said first ion guide being arranged to receive ions from said ion mobility spectrometer or separator, and wherein said first ion guide comprises a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area; AC or RF voltage means arranged and adapted to apply an AC or RF voltage to at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of said plurality of electrodes of said first ion guide in order to confine ions radially within said first ion guide; an orthogonal acceleration Time of Flight mass analyser arranged downstream of said first ion guide; the mass spectrometer further comprising: a second ion guide comprising an ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area arranged upstream of said ion mobility spectrometer or separator, wherein in a mode of operation said second ion guide is arranged and adapted to trap, store or accumulate ions in an ion trapping region located towards, near or substantially at the exit of said second ion guide and wherein ions are periodically released from said ion trapping region of said second ion guide and are passed to said ion mobility spectrometer or separator; and a further ion guide upstream of said second ion guide, wherein said further ion guide comprises a further ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area. a second ion guide comprising an ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area arranged upstream of said ion mobility spectrometer or separator, wherein in a mode of operation said second ion guide is arranged and adapted to trap, store or accumulate ions in an ion trapping region located towards, near or substantially at the exit of said second ion guide and wherein ions are periodically released from said ion trapping region of said second ion guide and are passed to said ion mobility spectrometer or separator; and a further ion guide upstream of said second ion guide, wherein said further ion guide comprises a further ion funnel comprising a plurality of electrodes having apertures through which ions are transmitted in use which become progressively smaller in size or in area.