The present disclosure relates generally to a method of separating ions according to their ion mobility, comprising (i) accumulating a first population of ions in a first region of an ion mobility separator, (ii) separating said first population of ions according to their ion mobility in said first region of said ion mobility separator, and (iii) accumulating a second population of ions in said first region of said ion mobility separator while said first population of ions are being separated according to their ion mobility in said ion mobility separator.