An apparatus for filtering ions is disclosed comprising a separation device for separating ions temporally according to a first physico-chemical property and a first quadrupole rod set for filtering ions according to their mass to charge ratio, wherein the first quadrupole rod set comprises a plurality of rods and wherein the first quadrupole rod set is arranged downstream of the separation device. The apparatus further comprises a control system arranged and adapted during a single cycle of separation of the separation device: (i) to operate the first quadrupole rod set in a first resolving mode of operation wherein ions of interest are selected by the first quadrupole rod set; and (ii) to operate the first quadrupole rod set in a second non-resolving or transmission mode of operation at separation times when substantially no ions of interest are present so that substantially no ions impact upon the rods of the first quadrupole rod set.
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