| abstract |
A mass spectrometer is disclosed comprising a first ion trap or ion guide ( 2 ), a single ion mobility spectrometer or separator stage ( 3 ) and a second ion trap or ion guide ( 4 ) arranged downstream of the ion mobility spectrometer or separator ( 3 ). In a mode of operation ions from the second ion trap or ion guide ( 4 ) are passed from the second ion trap or ion guide back upstream to the ion mobility spectrometer or separator ( 3 ). |