Patent ID: 8283628

Claim:
A method of mass spectrometry comprising: passing a first group of ions through an ion mobility spectrometer or separator in order to separate temporally at least some of said ions; operating an ion gate so that ions having drift times within a time window T 1 are transmitted by said ion gate but ions having drift times outside of said time window T 1 are not transmitted by said ion gate; passing at least some of said ions having drift times within said time window T 1 through said ion mobility spectrometer or separator again in order to separate temporally at least some of said ions; and passing at least some or substantially all of said ions having drift times outside of said time window T 1 back through said ion mobility spectrometer or separator and storing said ions in a first upstream ion trap; wherein prior to passing at least some of said ions having drift times within said time window T 1 through said ion mobility spectrometer or separator again said method further comprises the steps of: trapping said ions having drift times within said time window T 1 in a downstream ion trap, passing said ions back upstream through said ion mobility spectrometer or separator, storing said ions in a second upstream ion trap and ejecting said ions from said second upstream ion trap into said ion mobility spectrometer or separator.